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Why do humans have digestive system present at front and kidneys back?

Why do humans have digestive system present at front and kidneys back?


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Outlet of digestive system is present at back of the body but its digestive system at front.

Outlet of urinary system is present at front of the body but its system present at back.

Why do humans have digestive system present at front and kidneys back?


I don't claim to have the full answer to why these organs are located in the way they are, but I think these factors have an influence on the anatomy:

1- The urinary system's link with the reproductive system in male mammals: The male reproductive system outlet needs to be located as far to the front as possible in a 4 legged mammal to facilitate sexual function, forcing the urinary system to follow

2- The kidneys are very fragile and need to be protected by the thick back muscles and partly under the rib cage. They would be too vulnerable at the front

3- The urinary system is generally sterile of bacteria, and so is the reproductive system in males, and partially in females. The digestive system isn't sterile in both. The outlet of the digestive system can't be in the front of the genitals in a male as this will increase the risk of urinary infections overall and also genital infections after mating. It can't be in between the urinary and reproductive outlets for the same reason, so it has to be located behind both to cause the least interference with their functions


A Look Inside Your Digestive System

Priyanka Chugh, MD, is board-certified gastroenterologist with a background in internal medicine. She practices with Trinity Health of New England​ in Waterbury, Connecticut.

The digestive system consists of several organs that function together to break down the foods you eat into molecules your body can use for energy and nutrients. The digestive tract includes the mouth, esophagus, stomach, intestines, and anus. So-called "accessory" organs include the liver, pancreas, and gallbladder food doesn't move through these organs, but they secrete hormones and chemicals that are essential to digestion. Here's what to know about your digestive system organs and functions.


Structure of the Liver

The liver is a reddish brown, wedge-shaped structure. In adults, the liver normally weighs about 1.5 kg (about 3.3 lb). It is both the heaviest internal organ and the largest gland in the human body. The liver is divided into four lobes of unequal size and shape. Each lobe, in turn, is made up of lobules, which are the functional units of the liver. Each lobule consists of millions of liver cells, called hepatic cells (or hepatocytes). They are the basic metabolic cells that carry out the various functions of the liver.

As shown in Figure 15.6.3, the liver is connected to two large blood vessels: the hepatic artery and the portal vein. The hepatic artery carries oxygen-rich blood from the aorta, whereas the portal vein carries blood that is rich in digested nutrients from the GI tract and wastes filtered from the blood by the spleen. The blood vessels subdivide into smaller arteries and capillaries, which lead into the liver lobules. The nutrients from the GI tract are used to build many vital biochemical compounds, and the wastes from the spleen are degraded and excreted.

Figure 15.6.3 The portal vein supplies the liver with wastes filtered out of the blood in the spleen, as well as nutrients from the gastrointestinal tract. Oxygen-rich blood enters the liver via the hepatic artery.


Chronic Lower Abdominal Symptoms

As with upper abdominal symptoms, pain in the lower abdomen does not necessarily mean that the problem lies in the intestines, as pain can radiate. However, there are several digestive disorders that can contribute to intestinal symptoms, including lower abdominal pain, cramping, and bowel movement problems.

Here are some of the more common ones:

    : People who have celiac disease can't eat gluten since it damages the small intestine. This is a condition you would need to have diagnosed by a healthcare provider, and it's often mistaken for other gastrointestinal disorders before being recognized. : Diverticulitis is the inflammation of diverticula, which are protrusions in the walls of the intestines. Symptoms include sharp pains in the lower left abdomen, usually accompanied by a fever.   If left untreated, diverticulitis can cause life-threatening complications. : This is an umbrella term for two separate conditions: Crohn's disease and ulcerative colitis. Both are chronic conditions that require lifelong monitoring and treatment. : People dealing with this very common digestive disorder have recurring abdominal pain, and either diarrhea, constipation, or both.

The role of the small intestine in the absorption of liquids

Fortunately for us, the small intestine is more than up to the task. It&rsquos quite an extensive organ, boasting a length of around 20 feet (6 meters). It also has a huge inner surface area of roughly 250 square meters &ndash the size of a tennis court! (Source) This large surface area helps to absorb water and other liquids quickly and efficiently.

Of the almost 10 liters of water that enters our stomach every day, 80-90% is absorbed by the small intestine. The remaining 10% (amounting to 1 liter of water) is passed on to the large intestine, which absorbs as much water as possible from the waste substances ready to be excreted from the body as feces.


16 Comments

I have sand-like gallstones.
I have sand-like gallstones. A surgeon told me that the worst thing I could do is a liver/gallbladder flush as this could cause the small stones to enter the pancreatic duct and cause pancreatitus. I have done numerous flushes over the years, but after hearing this I got fearful. Is there any truth to this, and because I have sand-like stones is it better to have the gallbladder removed? Mark

Ask your surgeon if he&rsquos saying that liver/gallbladder flushes really work, that they really do flush gallstones from your gallbladder, and that they are beneficial for most people, just not you. That would be remarkable for a surgeon to acknowledge the efficacy of the liver/gallbladder flush. If however, he tells you that they don&rsquot work and can&rsquot flush anything from your gallbladder, then the question becomes: how can they then be dangerous to your pancreas and why would he have said that? You need to clarify whether your doctor is actually making an informed statement, or merely trying to scare you. Once you know that, you will be better placed to make an informed decision yourself.

The surgeon said nobody can
The surgeon said nobody can be helped. Please..let’s forget about him. I KNOW THE FLUSH IS GOOD. WHAT I AM ASKING AND NEED TO KNOW IS….DO YOU HAVE ANY HARD EVIDENCE AND HARD EXPLANATION OF ….IF AND HOW MY GALLSTONES COULD GET CAUGHT IN THE PANCREATIC DUCT. I AM DESPARATE FOR AN HONEST EDUCATED ANSWER FROM A NATURAL DOCTOR. Thank you in advance for your reply.

I do not care what any
I do not care what any surgeon says. I want to know how I can avoid getting stones stuck in the my pancreatic duct. Anything natural I can do?

For obvious legal reasons, we cannot diagnose or prescribe for specific illnesses. Merely, provide information. For that reason, our site contains a great deal of information on natural methods for both softening stones and expelling them from the body. You need to read over that information and then make your own decisions.

I have suggested ascorbic
I have suggested ascorbic acid for stones to a friend in the past kidney stones in this case.

Shortly after he tried the C, he had a very painful episode of passing kidney stones.

At first he was upset and blamed the C for the stones. However he quickly changed his mind and attributed only the passing of the stones to the C.

Ascorbic acid is a very aggressive acid, so aggressive that it will dull glass. It should never be used as a mouthwash, however against stones it might offer some relief. I use ascorbic acid C in the day and at night switch to calcium ascorbate C, as I attempt to raise my body pH at night. After taking ascorbic acid powder, I use some baking soda mouthwash to neutralize the ascorbic acid remaining in the mouth. Baking soda mouthwash could also neutralize the acid produced by staph in the mouth.

Mark,
This article has helped

Mark,

This article has helped me tremendously. Thank you for providing a well written, easy to understand and comprehensive explanation of pancreatic health. I’ll definitely be subscribing to your newsletter!

I have had chronic
I have had chronic pancreatitis since July of 2005. Prior to understanding everything that I’d been missing upon birth, a surgeon performed a biductor sphincterotomy on me. I have congenital absence of the gall bladder and cystic duct and the ventral duct in my pancreas. The dorsal duct is also dysfunctional, so even though I have a diagnosis of pancreatic divism with chronic pancreatitis, I have only been basically functioning through the minor papillary duct in the pancreas for drainage. I am in tremendous pain…constantly, and have been on narcotics for years along with many pancreatic enzymes and other meds to enhance the digestive process. I have severe gastritis due to the over accumulating acid in my system which has rendered me basically raw from mouth to anus. I have gone through many doctors, a lot of symptoms, and I am so tired of being so ill. Any suggestions? It’s hard for me to afford to see the local naturopath regularly due to the cost, but if you could guide me in a direction of enzymes and nutrition it would be greatly appreciated. I am cuurently trying to wean down my meds, have a spinal stimulator or pump placed and trying to do what I can naturally to halt the progression of this illness. My pancreas has already been seen to have the entire pancreas affected with lobular tissue due to the fact that it is digesting itself due to the enzymes being pre-released into my pancreas. Much more to say, but don’t want to overload you. Thank you.

hey, i mad a blood test IgG 4
hey, i mad a blood test IgG 4 and it was more than the normal woth one star *. my doctor asked me to do a scan and i did but nthng dangerous was seen !! so he told me i have imflamations in the pancreas !! what doctor should i see ?? any help ?? i have digestive problems

For obvious legal reasons, we
For obvious legal reasons, we cannot diagnose or prescribe for specific medical conditions &ndash merely provide information. With that said&hellip

Yes, higher than normal levels of IgG 4 are an indicator of autoimmune pancreatitis &ndash among other things. Combine that with your digestive problems, and you might want to have your doctor check for blockage in the bile duct. You also might want to check out this report, which contains information on how to flush out your liver, gallbladder, and bile duct. https://www.jonbarron.org/detox/program-phase-three-liver-blood-cleansing. Keep in mind that before doing a liver detox, you will want to do an intestinal cleanse and a kidney flush in preparation.

I had a whipple done 5 years
I had a whipple done 5 years ago due to IPMT in the head, 3 cm. I am now on enzymes but also suffer from fibromyalgia with IBS symptoms. What I would like to know is this as good as I am going to get? I have constant pain and swelling especially at end of day. I try and eat veg and fruits with some meat, gluten free products and low in sodium and sugar.

Hi,
Hi,
This is a highly interesting article and it explained the pancreatic functions simple enough , yet informative for a lay person like me to understand. I shall follow up more on how to take Tender Loving Care of my pancreas, liver and gall bladder , the 3 often neglected organs.

God Bless and keep up the good work.

Hi I have this typical high
Hi I have this typical high triglycerid levels. Tried exercising diet control but still its nt controlled. Some dr suggested it may be due to improper function of pancreas

We’re sorry to hear that you

We’re sorry to hear that you have high triglycerid levels. However, understand that the Foundation receives thousands of emails and comments per month and we do not have the staff to answer questions personally. We are a non-profit, Free — online health information resource only. We provide thousands of pages of information on a variety of subjects for you to use as a resource. If you have not already done so, use the SEARCH function built in at the top left of every page in the website. There is a good chance that Jon has already addressed your issue. For example, did you read the above article till the end?

Hi Mark,
Hi Mark,
I really enjoyed reading this article as I am looking for information about the Pancreas and have found it really difficult to find much…
I have been diagnosed with a severely atrophic pancreas with fatty infiltration…I did some blood tests and it seems my lipase levels are a little low.
The doctors so far are all stumped regarding my case. I have done an endoscopy, I think they were looking to see if I had pancreatitis which I don’t.
What can be the cause of a “shrinking” pancreas?
I typically drink 1 cocktail or glass of wine about 5 days a week. I quit smoking about 7 years ago. I don’t eat processed foods or fatty foods. I cook fresh meals every day, eat a lot of fruits and vegetable.
I am a 47 year old female btw.
There is a family history of problems with the pancreas in my family. My mother had problems, my grandmother on my mothers side also had and now I seem to be starting to have problems and my older brother has a fatty pancreas.
Any clues?
I’m worried that I will eventually end up with a “non-functioning” pancreas…
Thank you
Luiza

You should not be drinking at
You should not be drinking at all with Chronic Pancreatitis. It will cause pain and inflammation of the Pancreas.

Very informative,
Very informative, comprehensive article, thanks!


Excretion in Animals, Humans and Plants (with diagram)

Chemical reactions occur in the cells of living organisms all the time to carry out the life processes.

The sum of these reactions is called metabolism. Metabolism produces useful products as well as toxic (poisonous) by-products.

These toxic substances have to be removed as they are harmful if allowed to accumulate. The removal of metabolic waste products from the body of an organism is known as excretion.

The major excretory products are carbon dioxide, excess water, and nitrogenous compounds like ammonia, urea, uric acid, etc. Carbon dioxide and water are produced in the process of tissue respiration. Nitrogenous compounds are formed from the breakdown of proteins and amino acids. Water and salts in excess of the body’s needs are also excreted.

We acquire most of the water with our food and drink and some by metabolism, e.g., the water produced during cellular respiration. Other excretory products include chemicals from medicines, toxic substances, and circulating hormones that have already served their purpose. We will learn how metabolic wastes get eliminated.

Excretion in animals:

Many unicellular organisms like Amoeba throw out their wastes by diffusion from their body surface. Protozoan’s have no organs for excretion. As they live in an aquatic habitat, their wastes are eliminated by diffusion through the plasma membrane.

Simple multicellular organisms like Hydra throw out solid waste matter through their mouth. Higher multicellular organisms have well-defined specialized excretory organs. These organs could be simple tubular structures as in flatworms and leech.

The excretory organs of insects (e.g., grasshopper, cockroach and housefly) are also tubular. They remove nitrogenous wastes from the body fluid and help in maintaining the water balance in the body.

In vertebrates, the main organs of excretion and maintenance of water balance are the kidneys.

Excretion in human beings:

Although the kidneys are the main organs of excretion, the skin, lungs and liver also help in excretion.

Our skin has sweat glands, through which we excrete small amounts of water, urea and salts.

The liver excretes bile, which contains bile pigments. These are produced by the breakdown of old RBCs in the liver. As hemoglobin breaks down, its iron is retained, while the pigment (haem) is excreted with the bile. The liver also excretes cholesterol.

The lungs help in getting rid of carbon dioxide, formed as a result of cellular respiration, through exhalation.

Excretory System in Man:

Our excretory system consists of kidneys, blood vessels that join them, ureters, urinary bladder and urethra. They help produce and excrete urine.

There are two bean-shaped kidneys that lie in the abdominal cavity, one on either side of the vertebral column. The kidneys are reddish brown. Each of them is about 10 cm long and weighs about 150 g. Although they weigh less, they receive a lot of blood for filtration.

A volume of blood nearly equivalent to that in the whole body passes through the kidneys every four or five minutes. The kidneys produce urine to filter out the waste products, like urea and uric acid, from the blood.

Urine leaves each kidney through a tube called ureters. The ureters from both the kidneys are corrected to the urinary bladder that collects and stores urine. Ureters carry urine from the kidneys into the urinary bladder. The urethra is a canal that carries urine from the bladder and expels it outside the body.

Internal Structure of a Kidney:

Each kidney is enclosed in a thin, fibrous covering called the capsule. A renal artery brings blood into the kidney, along with nitrogenous waste materials. After filtration in the kidney, the purified blood leaves the kidney through a renal vein.

Two distinct regions can be seen in the section of a kidney:

(1) An outer, dark, granular cortex and (2) an inner, lighter medulla. The hollow space from where the ureter leaves the kidney is called the pelvis. Each kidney is made up of numerous (about one million) coiled excretory tubules, known as nephrons, and collecting ducts associated with tiny blood vessels. A nephron is the structural and functional unit of a kidney, having three functions— filtration, reabsorption and secretion.

A cluster of thin-walled blood capillaries remains associated with the cup-shaped end of each nephron tubule. These capillaries bring blood from the body to the nephron for filtration. The network of capillaries spreads over the nephron tubules also. These capillaries finally carry purified blood to the body.

Structure and Function of a Nephron:

A nephron consists of a long coiled tubule and the Malpighian corpuscle. The tubule of the nephron is differentiated into the proximal convoluted tubule, Henle’s loop and the distal convoluted tubule. The distal tubule opens into the collecting duct.

At the proximal end of the nephron is the Malpighian corpuscle, which consists of Bowman’s capsule and the glomerulus. Bowman’s capsule is a double-walled cuplike structure which surrounds the dense network of blood capillaries called the glomerulus.

The process of excretion in nephron:

The process of excretion may be divided into three stages- tubular secretion.

Filtration of blood occurs under high pressure in the nephrons of the kidney. Blood enters the glomerulus through the afferent arteriole (with a wider lumen) and leaves through the efferent arteriole (with a narrow lumen). Therefore, blood passes through the glomerulus under pressure. This results in filtration of blood.

Water and small molecules are forced out of the walls of the capillaries of the glomerulus and Bowman’s capsule and enter the tubule of the nephron. Large molecules remain in the blood of the glomerulus. The filtrate contains water, glucose, salts, urea, vitamins, etc. It is called the glomerular filtrate.

Selective reabsorption:

Some molecules of the glomerular filtrate are selectively reabsorbed into the blood. The glomerular filtrate flows through the proximal convoluted tubule, the U-shaped Henle’s loop and the distal convoluted tubule. It contains many useful substances such as glucose, amino acids and salts.

These are reabsorbed by a process, which requires energy. Without reabsorption, these nutrients could have been lost with the urine. The filtrate now contains urea, some salts and water. Reabsorption of solutes into the blood increases the water concentration of the filtrate.

Then water is reabsorbed into the blood by the process of osmosis, and the osmotic balance is restored. The amount of water reabsorbed depends on the amount of excess water in the body and that of the dissolved waste to be excreted.

This reabsorption of water from the filtrate to maintain the water balance of the body fluid is known as osmoregulation. In this way the kidneys serve as water-conserving organs. After reabsorption from 180 L of filtrate in the kidney, only 1-2 L of urine is produced.

Some nitrogenous waste products like creatinin and some other substances like potassium ions are removed from the blood by the distal convoluted tubule, and are then added to the urine. This is called tubular secretion.

The urine that is formed continually collects in the urinary bladder. As the bladder expands, its pressure creates an urge to pass urine through the urethra. As the bladder is muscular, the urge to urinate is under voluntary nervous control.

Kidney Failure and the Survival Kit—Haemodialysis:

The kidneys may be damaged due to infection, injury, diabetes, and extremes of blood pressure. A damaged kidney cannot function efficiently to remove urea, ions, water, etc., from the blood. This malfunctioning results in the accumulation of toxic wastes like urea (uremia), which can lead to death.

One of the ways to treat kidney failure is to use a ‘dialysis machine’ that acts as an artificial kidney. It has a long tube like structure made of Cellophane suspended in a tank (dialyser) of a fresh dialysis fluid (dialysis). The Cellophane tube is partially permeable and therefore allows solutes to diffuse through. The dialysis fluid has the same concentration as normal tissue fluid, but nitrogenous wastes and excess salts are absent.

During dialysis, the blood of the patient is withdrawn from an artery and cooled at 0°C. It is maintained in a liquid state by adding an anticoagulant and by other special treatments. It is pumped through the dialysis machine. Here, the nitrogenous waste products from the blood diffuse into the dialysis fluid. The purified blood is then warmed to the body temperature and pumped back into the patient’s body through a vein.

The dialyser is specific for each patient to avoid infections. Dialysis through an artificial kidney has to be carried out at frequent intervals. This process of purification of blood is called haemodialysis.

A dialysis machine works like a kidney except that no selective reabsorption takes place in the former.

(1) Helps remove harmful wastes, extra salts and water

(2) Controls blood pressure and

(3) Maintains the balance of sodium and potassium salts in a patient whose kidneys have failed.

Excretion in plants:

Compared to animals, plants do not have a well-developed excretory system to throw out nitrogenous waste materials. This is because of the differences in their physiology. Therefore, plants use different strategies for excretion.

The gaseous waste materials produced during respiration (carbon dioxide) and photosynthesis (oxygen) diffuse out through stomata in the leaves and through lenticels in other parts of the plant. Excess water evaporates mostly from stomata and also from the outer surface of the stem, fruits, etc., throughout the day. This process of getting rid of excess water is called transpiration.

The waste products, like oxygen, carbon dioxide and water, are the raw materials for other cellular reactions. The excess of carbon dioxide and water are used up in this way. The only major gaseous excretory product of plants is oxygen!

Many plants store organic waste products in their permanent tissues that have dead cells, e.g., in heartwood. Plants also store waste within their leaves or barks. These wastes are periodically removed as the leaves and barks fall off.

Some of the waste products are stored in special cells or cellular vacuoles. Various waste products such as tannins, essential oils, gums, resins, etc., are produced during catabolic processes. Tea leaves, amla and betel nuts (supari) contain tannin. Tannins are found also in the barks of trees.

The leaves of many plants, like Eucalyptus, lemon, sacred basil (tulsi), etc., contain essential oils. The rind of oranges and lemons and the petals of flowers like rose and jasmine also contain oils. Some plant wastes are stored as a thick, white fluid. You may have seen white fluid ooze out when you pluck a papaya or a fig or the leaves of yellow oleander (pila kaner). This white fluid is called latex.

Gums are a group of sticky, water- soluble wastes found in the common gum tree (babul). Resins are another group of wastes found commonly in the stems of conifers (e.g., pine, fir).

Alkaloids are a group of toxic waste products. But some of these are useful to us. Quinine and morphine are medicines derived from alkaloids stored in Cinchona bark and opium poppy flowers respectively. Caffeine found in coffee seeds and nicotine in tobacco leaves is also alkaloids.

Organic acids, which might prove harmful to plants, often combine with excess cations and precipitate out as insoluble crystals that can be safely stored in plant cells. Calcium oxalate crystals accumulate in some tubers like yam (zamikand).

Aquatic plants lose most of their metabolic wastes by direct diffusion into the water surrounding them. Terrestrial plants excrete some waste into the soil around them.


Main Parts of Human Digestive System (With Diagram)

The vestibule is a slit-like space bounded externally by lips and cheeks and internally by the gums and teeth.

(b) Oral Cavity (Buccal Cavity):

It is inner portion of the mouth which has the following parts.

The roof of the oral cavity (buccal cavity) is called palate. Anterior part of the palate is known as hard palate which bears transverse ridges, the rugae. The posterior part of the palate is smooth and is termed the soft palate. The hinder free part of the soft palate freely hangs down as a small flap, the uvula.

(ii) Tongue. The tongue is attached to the floor of the mouth by a fold called the lingual frenulum. An inverted V-shaped furrow termed the sulcus terminalis divides the upper surface of the tongue into anterior oral part and posterior pharyngeal part. The apex of the sulcus terminalis projects backward and is marked by a small median pit, named the foramen caecum.

The upper surface of the tongue has four types of papillae (little projections).

(a) Vallate papillae or Circumvallate papillae are usually about 8 to 12 in number. Each vallate papilla contains up to 100 taste buds. These papillae are the largest of the four types of papillae.

(b) Filiform papillae are the smallest and most numerous of the four types. They are conical. They are found mainly near the centre and most of the upper surface of the tongue. These papillae contain tactile (touch) receptors but not taste buds.

(c) Fungiform papillae are much less numerous than the filiform papillae. They are rounded but smaller than vallate but larger than filiform papillae. They are most numerous near the tip of the tongue. Each fungiform papilla contains about five taste buds.

(d) Foliate papillae are not developed in human tongue. These are leaf-like and are situated at the sides of the base of the tongue. On each border there are four or five vertical folds. Their taste buds degenerate in early childhood.

Human tongue has four taste areas (sweet, salt, sour and bitter). Areas of sweet and salt can overlap.

Functions of the Tongue:

The tongue acts as an accessory digestive organ.

(i) It helps in chewing the food.

(ii) It aids in swallowing the food,

(iii) It acts as a brush to clean the teeth,

(iv) It plays a role in speech,

(v) It is an organ of taste.

Men have diphyodont (two sets of teeth— milk or de­ciduous and permanent), thecodont (teeth are embedded in the sockets of the jaw bones) and heterodont teeth (different types of teeth). There are present four kinds of teeth— incisors, canines, premolars and molars.

They are usually specialized for cutting.

They lie immediately behind the incisors. They are also used for cutting the food.

These are called cheek teeth which are broad, strong crush­ing teeth. Third molars in human being are called wisdom teeth. The latter are vesti­gial in human beings.

The milk or deciduous or temporary teeth are 20 in number 10 each in the upper jaw and in the lower jaw. The milk teeth begin to erupt when the child is about 6 months old and should all be present by the end of 24 months. The permanent teeth begin to replace the milk teeth in the 6th year of age. These teeth are 32 and usu­ally complete by 18-25 years.

Milk teeth of man include 8 incisors, 4 canines and 8 molars (premolars are absent). Molars of milk teeth are shed off and premolars of permanent teeth take their place. The permanent teeth are 8 incisors, 4 canines, 8 premolars and 12 molars. Thus 12 teeth (8 premolars and 4 molars) are monophyodont (teeth which grow only once in life). Dental Formulae of milk teeth and permanent teeth of human are given below.

Milk teeth Permanent Teeth:

The dental formula gives half of the total number of teeth. This is doubled to determine the full number.

A typical tooth consists of three regions crown— the part which projects above the gums, the neck— the part which is surrounded by gum and the root— the part which is embedded in the bone.

The incisors and canines have one root, the upper first premolars have two roots and the upper second premolars and lower premolars usually have only one root. The upper molars have three roots and the lower molars have two roots.

A human tooth consists of the following parts:

It is the hardest substance of the human body. It covers the dentin in the crown.

It has numerous fine canaliculi that pass radially from the pulp cavity towards the enamel.

It covers the root of the tooth.

It is made up of collagen fibres and covers the cement. It fixes the tooth in its socket.

Dentin encloses the pulp cavity that contains a mass of cells, blood vessels and nerves which constitute the pulp. Narrow extensions of the pulp cavity called root canals, run through the root of the tooth.

Apart from the connective tissue cells of the pulp and of the periodontal membrane and the cementocytes in cement, there are two main types of cells. These are dentine forming odon­toblasts and enamel forming ameloblasts.

II. Pharynx (Throat):

It is divided for descriptive purposes into three parts the nasopharynx, oropharynx and laryngopharynx.

(i) The nasopharynx (nasal part of the pharynx) lies behind the nasal cavities, above the soft palate. The Eustachian tube (also called auditory tube) connects nasopharynx with the middle ear.

(ii) The oropharynx (oral part of the pharynx) lies behind the oral cavity (buccal cavity). The nasopharynx and oral cavity open into the oropharynx which is a com­mon passage for both food and air.

(iii) The laryngopharynx (laryngeal part of the pharynx), is the most inferior portion of the pharynx. It leads into the oesophagus behind and into the larynx in front.

The pharynx is a common passage for food and air.

The lymphatic tissues of the pharynx and oral cavity are arranged in a ring like manner, which are collectively called Waldeyer’s ring (- Waldeyer’s lymphatic ring).

The ring mainly consists of the following:

(i) Pharyngeal Tonsil is attached to pharynx. In children pharyngeal tonsil may become enlarged and is then referred to as the adenoids. The resulting swelling may be a cause of obstruction to normal breathing.

(ii) Tubal Tonsils are situated around the Eustachian tube.

(iii) Palatine Tonsils are attached to the palate. The palatine tonsils are often in­fected (tonsillitis) leading to sore throat. Such enlarged tonsils may become a focus of infection and their surgical removal (ton­sillectomy) becomes necessary.

(iv) Lingual Tonsil is attached to pharyngeal part of the tongue.

All these lymphoid tissues are active in production of immunoglobin. A which forms an important part of our immune system.

III. Oesophagus:

The human oesophagus or food pipe is about 25 cm long. It lies behind the trachea and the heart. It comprises three parts: cervical part in the neck, thoracic part in the thorax and abdominal part in the abdomen. The oesophagus passes through the diaphragm and opens into the stomach.

The oesophagus transfers food from the pharynx to the stomach.

IV. Stomach (= Gaster):

It is the wid­est organ of the alimentary canal. The stomach is J-shaped organ. The lesser cur­vature lies on the posterior surface of the stomach. The greater curvature is on the anterior surface of the stomach.

The fold of peritoneum which attaches the stomach to the posterior abdominal wall extends be­yond the greater curvature. This is called the greater omentum which stores fat. The stomach has four parts: cardiac part, fundus, body and pyloric part.

(i) Cardiac Part (= cardia):

It is so called because it is present near the heart. The gastro esophageal sphincter (= car­diac sphincter) lies in the opening between oesophagus and stomach. It is not a true valve. It is a functional sphincter.

It is commonly filled with air or gas.

It is the main part of the stomach.

(iv) Pyloric Part (Pylorus):

It is the posterior part of the stomach.

The pyloric part is divided into the pyloric antrum and the pyloric canal. The latter opens into the duodenum. The pyloric sphincter guards the opening between the stomach and the duodenum and periodically permits partially digested food to leave the stomach and enter the duodenum.

Functions of the Stomach:

It stores food for some time. It churns and breaks up food and mixes the pieces with gastric juice. Partial digestion of food (proteins and fats) takes place here. It produces Castle’s intrinsic factor (a glycoprotein) which is necessary for the absorption of vitamin B12 to be absorbed in the intestine.

It secretes pro-enzymes— pepsi­nogen and pro-rennin and enzymes gastric lipase and gastric amylase. It also secretes gastrin (hormone). Alcohol, aspirin, some lipid-soluble drags, moderate amounts of sugar and water are absorbed by the stomach wall.

V. Small Intestine:

It is so named because it has small diameter. Length is correlated with the height of the individual but not with weight. It is the longest part of the alimentary canal. It is about 6.25 metres long. It comprises three parts duodenum, jejunum and ileum.

It is so called because it is about as long as the breadth of 12 fingers. It is about 25 cm long and is the shortest, widest part of the small intestine. It is somewhat С-shaped. The hepatopancreatic ampulla (ampulla of Vater) opens into the duodenum. This ampulla receives both bile duct from the liver and main pancreatic duct from the pancreas. Iron is mainly absorbed in the duodenum.

It has a diameter of about 4 cm. Its wall is thick. It is redder and more vascular. It is the middle part of the small intestine and is about 2.5 metres long.

It has a diameter of 3.5 cm. Its wall is thinner than that of the jejunum. It is the longest part of small intestine and is about 3.5 metres long. Both the jejunum and ileum are greatly coiled. They are suspended by mesentery.

Small nodules of lymphatic tissue can be seen along the entire length of the small intestine. In some places, particularly along the ileum, these nodules are clustered together in groups called Peyer’s patches or lymph nodules.

Peyer’s patches are a distinguishing characteristic of the ileum, which produce lymphocytes (type of WBCs). Finger-like projec­tions of the mucosa, the villi are present in the small intestine. Villi are absent over the Peyer’s patches.

The villi increase the surface of the small intestine. Each villus is covered with epithelium and contains a lymph capillary (lacteal) and blood capillaries. The entire small intestine has circular folds of the mucous membrane, the plicae circulares (‘Valves’ of Kerkring). These folds are more prominent in the jejunum. They further increase the absorptive surface considerably.

Functions of the small intestine:

The small intestine completes digestion of proteins, carbohydrates, fats and nucleic acids. It absorbs nutrients into the blood and lymph. It secretes certain hormones such as cholecystokinin, secretin, enterogastrone, duocrinin, enterocrinin and villikinin. It also secretes digestive enzymes.

VI. Large Intestine:

Its diameter is larger than that of the small intestine. Hence it is so named. It is about 1.5 metres long and is divisible into three parts caecum, colon and rectum.

(i) Caecum and vermiform appendix:

The caecum is a pouch-like structure which is about 6 centimetres. The vermiform appendix (commonly called the appendix) is an outgrowth of the caecum.

It is a slightly coiled blind tube of about 8 centimetres long. Its wall contains prominent lymphoid tissue. Appendix is thought to be vestigial. The inflam­mation of vermiform appendix is called appendicitis. The caecum and appendix are well developed in herbivorous mammals like rabbits.

The caecum leads into the colon, which is divided into four regions the ascending, transverse, descending and sigmoid colon (pelvic colon is its former name). Ascending colon is the shortest part of the colon. The colon has three longitudinal bands called taeniae coli and small pouches called haustra (sing, haustrum).

The sigmoid colon opens into the rectum. The rectum comprises the last 20 centimetres of the digestive tract and terminates in the 2-centimetre long anal canal. The opening of the anal canal is called anus.

The anus has an internal anal sphincter composed of smooth muscle fibres and an external anal sphincter comprised of striped (voluntary) muscle fibres. Structures formed due to enlargements of veins of anal columns in anal canal as well as anus are called haemorrhoids or piles.

Functions of the large intestine:

The chief functions of the large intestine are the absorption of water and the elimination of solid wastes. However, moderate quantities of vitamin К and vitamin В complex are manufactured by bacteria in the large intestine.

Histology of Human Gut (Alimentary Canal):

The wall of alimentary canal consists of four basic layers.

From the outer surface inward to the lumen (cavity) the layers are as follows:

1. Visceral peritoneum (= Serosa):

It is made up of squamous epithelium and areolar connective tissue. It is continuous with the mesentery. Since the oesophagus lies outside the coelom, its outer wall is not covered by peritoneum (serosa) but by an irregular coat of dense elastic fibrous connective tissue called adventitia external ( = external adventitia).

2. Muscularis (Muscular coat):

It is composed of outer longitudinal and inner cir­cular muscle fibres. In the stomach an additional layer of oblique muscle layer is found inner to the circular muscle fibres.

These muscle fibres are un-striped (smooth). In between the longitudinal and circular muscle fibres there is a network of nerve cells and parasym­pathetic nerve fibres, called the Auerbach’s plexus (= myenteric plexus). The Auerback s plexus controls peristalsis.

It consists of loose connective tissue richly supplied with blood and lymphatic vessels and in some areas with glands. Another network of nerve cells and sympathetic nerve fibres, called Meissner’s plexus (= sub-mucosal plexus) is present be­tween the muscular coat and the mucosa. This plexus controls the secretion of intestinal juice.

4. Mucosa (= Mucous membrane):

It is the innermost layer lining the lumen of the alimentary canal. It is so named because it secretes mucus to lubricate the inner lining of the gut. This layer forms irregular folds (rugae) in the stomach.

Mucosa is composed of three layers:

(i) The muscular is mucosa consists of outer longitudinal and inner circular muscle fibres, both are un-striped.

(ii) The lamina propria consists of loose connective tissue, blood vessels, glands and some lymphoid tissue.

(iii) The epithelium forms gastric glands in stomach, and villi and intestinal glands in small intestine.

In upper one third of the oesophagus both Auerbach and Meissner’s plexuses are absent.

Part # 2. Digestive Glands

I. Salivary Glands (Fig. 16.10):

Salivary glands discharge their secretion into the oral cavity. In man, the salivary glands are three pairs— parotid, sublingual and submandibulor glands,

(i) Parotid glands. These are the largest salivary glands which are situated near the ears. Their ducts open into the oral cavity near the upper second molars. The duct of parotid gland is called Stenson’s duct,

(ii) Sublingual glands. These are smallest salivary glands which are located beneath the tongue and their ducts called sublingual ducts or ducts of Rivinus which open into the floor of the oral cavity,

(iii) Submandibular (also called sub maxillary) glands.

These are me­dium sized salivary glands which are located at the angles of the lower jaw. Their ducts open into the oral cavity near the lower central incisors.

The duct of submandibular gland is called Wharton’s duct. The parotid salivary glands secrete much of salivary amylase or a-amylase (= ptyalin). Sub-lingual and sub-mandibular salivary glands secrete salivary amylase and mucus. Salivary amylase is absent in herbivores.

The disease mumps is a viral infection that may involve one or both parotid salivary glands. The fluids secreted by the salivary glands constitute saliva. Saliva is slightly acidic (pH 6.8). About 1,000-1500 ml of saliva is secreted per day.

Saliva is a mixture of water and electrolytes (Na + , K + , CI – , HC03 – ), derived from blood plasma, mucus and serous fluids (watery constituent of saliva), and salivary amylase or ptyalin (enzyme) and lysozyme (antibacterial agent). Ions of thyocyanate are also present in the saliva.

II. Gastric Glands (Fig. 16.11):

These are numerous microscopic, tubular glands formed by the epithelium of the stom­ach. Gastric glands have three major types of cells.

(i) Chief cells or Peptic cells (= Zymogenic cells) are usually basal in location and secrete gastric digestive enzymes as pro-enzymes or zymogens pepsinogen and pro-rennin.

The chief cells also produce small amount of gastric amylase and gastric lipase. Gastric amylase action is inhibited by the highly acid condition. Gastric lipase con­tributes little to digestion of fat. Pro-rennin is secreted in young mammals. It is not secreted in adult mammals.

(ii) Oxyntic cells (= Parietal cells) are large and are most numerous on the side walls of the gastric glands. They are called oxyntic cells because they stain strongly with eosin. They are called parietal cells as they lie against the basement membrane. They secrete hydrochloric acid and Castle intrinsic factor.

(iii) Mucous cells (= Goblet cells) are present throughout the epithelium and secrete mucus.

The secretions of these cells form gastric juice with pH 1.5-2.5 (very acidic). Infant’s gastric juice pH is 5.0. About 2,000-3,000 ml of gastric juice is secreted per day. The gastric juice contains two pro-enzymes— pepsinogen (pro-pepsin) and pro-rennin, and enzymes gastric lipase and gastric amylase, and mucus and hydrochloric acid.

The epithelium of gastric glands also has the following two types of cells:

(i) Endocrine cells are usually present in the basal parts of the gastric glands. These are argentaffin cells and Gastrin cells (= G-cells). Argentaffin cells produce serotonin (its precursor is 5-hydroxytryptamine, 5-HT), somatostatin and histamine. Gastrin Cells (= G-cells) are present in the pyloric region and secrete and store the hormone gastrin.

Serotonin is a vasoconstrictor and stimulates the smooth muscles. Somatostatin suppresses the release of hormones from the digestive tract. Histamine dilates the walls of blood vessels. Gastrin stimulates the gastric glands to release the gastric juice.

(ii) Stem cells are undifferentiated cells that are also present in the epithelium of the gastric glands. They multiply and replace other cells. They increase in number when the gastric epithelium is damaged (e.g., when there is a gastric ulcer) and play an important role in healing.

III. Liver (= Hepar):

It is the largest gland of the body. The liver lies in the upper right side of the abdominal cavity just below the diaphragm. It is heavier in males than females. In males it generally weighs 1.4-1.8 Kg and in females 1.2-1.5 Kg.

The liver is divided into two main lobes— right and left lobes separated by the falciform ligament. The latter is a membrane that is continuous with the peritoneum. The right lobe of the liver is further differentiated into right lobe proper, a quadrate lobe and a caudate lobe on the posterior surface.

Internally, the structural and functional units of liver are the hepatic lobules containing hepatic cells arranged in the form of cords. Each lobule is covered by a thin connective tissue sheath called the Glisson’s capsule. Glisson’s capsule is the characteristic feature of mammalian liver. The mammalian liver also contains Kupffer cells that are phagocytic cells and eat worn out WBCs, RBCs and bacteria.

Fat storage cells are also present. The plates of liver cells are separated from the endothelial lining of the sinusoid by a narrow perisinusoidal space of Disse. Some fat cells may also be seen in the space of Disse. Blood vessels and bile ductules present in the portal canals are surrounded by a narrow space of Mall.

Bile is secreted by the liver cells (hepatocytes). Bile enters bile canaliculi or bile capillaries (a net work of tubular spaces between the liver cells). The bile canaliculi empty into small Hering’s canals walled by cuboidal epithelium. These canals pour bile into interlobular bile duct (=bile ductule) walled by columnar epithelium.

A pear shaped sac like structure is attached to the posterior surface of the liver by connective tissue. It stores bile secreted by the liver. Rat and horse do not have gall bladder.

The right and left hepatic ducts join to form the common hepatic duct. The latter joins the cystic duct which arises from the gall bladder. The cystic duct and common hepatic duct join to form bile duct which passes downwards posteriorly to join the main pancreatic duct to form the hepatopancreatic ampulla (= ampulla of Vater).

The ampulla opens into the duodenum. The opening is guarded by the sphincter of Oddi. The sphincter of Boyden surrounds the opening of the bile duct before it is joined with the pancreatic duct.

Blood Supply (Fig. 16.15):

Blood enters the liver from two sources. From the hepatic artery it gets oxygenated blood and from the hepatic portal vein it receives deoxygenated blood. Blood in the hepatic artery comes from the aorta. Blood in the hepatic portal vein comes directly from the intestine containing newly absorbed nutrients. The hepatic portal vein also brings blood from the spleen to the liver. Liver has high power of regeneration.

Bile is a watery greenish fluid mixture containing bile pigments, bile salts, cholesterol and phospholipids.

Bile serves the following functions:

(i) Neutralization of HCI:

Its sodium bicarbonate neutralizes HC1 of chyme (semi-fluid food that comes from the stomach).

Sodium glycocholate and sodium taurocholate break the large fat droplets into the smaller ones. This process is called emulsification.

(iii) Absorption of fat and fat-soluble vitamins:

Its salts help in the absorption of fat (fatty acids and glycerol) and fat-soluble vitamins (A, D, E and K) in the small intestine.

Bile pigments (bilirubin and biliverdin) are excretory products.

(v) Prevention of Decomposition:

Bile is alkaline hence it prevents the decomposition of food by preventing the growth of bacteria on it.

(vi) Stimulation of Peristalsis:

Bile increases peristalsis of the intestine.

(vii) Activation of Lipase:

Bile contains no enzyme but activates the enzyme lipase.

Obstruction of the hepatic or bile duct by gall stones or due to other causes is common. Jaundice occurring as a result of such obstruction is called obstructive jaundice. In this disease the bile is absorbed into the blood instead of going to the duodenum and cause yellowing of eyes and skin.

IV. Pancreas (Fig. 16.12 & 16.16):

The pancreas is soft, lobulated, greyish- pink gland which weighs about 60 grams. It is about 2.5 centimetres wide and 12 to 15 centimetres long, located posterior to the stomach in the abdominal cavity.

External Structure of Pancreas:

The Pancreas comprises the head, neck, body and tail. The head lies in the curve of the duodenum, the neck follows the head, the body behind the stomach and the tail reaches the spleen lying in front of the left kidney.

The main pancreatic duct (= duct of Wirsung) is formed from smaller ducts within the pancreas. The main pancreatic duct opens into the hepatopancreatic ampulla (= ampulla of Yater). An accessory pancreatic duct (= duct of Santorini) is also present in the pancreas and opens directly into the duodenum.

Internal Structure of Pancreas:

It consists of two parts: exocrine part and endocrine part.

The exocrine part of the pancreas consists of rounded lobules (acini) that secrete an alkaline pancreatic juice with pH 8.4. About 500-800 ml of pancre­atic juice is secreted per day. The pancreatic juice is carried by the main pancreatic duct into the duodenum through the hepatopancreatic ampulla.

The accessory pancreatic duct di­rectly pours the pancreatic juice into the duodenum. The pancreatic juice contains sodium bicarbonate, three pro-enzymes trypsinogen, chymotrypsinogen and procarboxypeptidase and some enzymes such as elastase, pancreatic a-amylase, DNase, RNase and pancre­atic lipase. The pancreatic juice helps in the digestion of starch, proteins, fats and nucleic acids.

The endocrine part of the pancreas consists of groups of islets of Langerhans. The human pancreas has about one million islets. They are most numerous in the tail of the pancreas. Each islet of Langerhans consists of the following types of cells which secrete hormones to be passed into the circulating blood.

(a) Alpha cells (= α-cells):

These cells are more numerous towards the periphery of the islet and constitute 15% of the islet of Langerhans. They produce glucagon hormone which converts glycogen into glucose in the liver. Thus glucagon is diabetogenic hormone.

These cells are more numerous towards the middle of the islet and constitute 65% of the islet of Langerhans. They produce insulin hormone which converts glucose into glycogen in the liver and muscles. Deficiency of insulin causes dia­betes mellitus.

(c) Delta cells (= δ-cells):

These cells are also found towards the periphery of the islet of Langerhans and constitute 5% of the islet of Langerhans. They secrete somatostatin (SS) hormone which inhibits the secretion of glucagon by alpha cells and secretion of insulin by beta cells. This hormone also slows absorption of nutrients from the gasrointestinal tract.

Somatostatin secreted by argentaffin cells of gastric and intestinal glands suppresses the release of hormones from the digestive tract. Somatostatin is also secreted by the hypo­thalamus of the brain where it inhibits the release of growth hormone (somatotropin) by the ante­rior lobe of pituitary gland. That is why it is also called growth inhibitory hormone.

(d) Pancreatic polypeptide cells (= PP cells or F-cells):

Apart from the three main types of cells described above, the PP cells are also present in the pancreas, which constitute 15% of the Islet of Langerhans. These cells secrete pancre­atic polypeptide (PP) which inhibits the release of pancreatic juice. Thus the pancreas performs two main func­tions i.e., secretion of pancreatic juice which contains digestive enzymes and production of hor­mones.

V. Intestinal Glands (Fig. 16.17):

These are formed by the surface epithelium of the small intestine. These are of two types: crypts of Lieberkuhn and Brunner’s glands.

(i) The crypts of Lieberkuhn are simple, tubular structures which occur through­out the small intestine between the villi. They secrete digestive enzymes and mucus. The mucus is secreted by the goblet cells (= mucous cells) whereas water and electrolytes are secreted by enterocytes present on the intestinal crypts. These crypts have at the base paneth cells and argentaffin cells.

(a) Paneth cells are found particularly in the duodenum. These cells are present in the bottom of crypts of Lieberkuhn. These cells are rich in zinc and contain acidophilic granules. The function of these cells is not certain but there is evidence that they secrete lysozyme (antibacterial substance). Paneth cells are also capable of phagocytosis.

(b) Argentaffin cells synthesize secretin hormone and 5-hydroxytryptamine (5-HT).

(ii) The Brunner’s glands are found only in the duodenum and are located in the submucosa. They secrete a little enzyme and mucus. The mucus protects the duodenal wall from getting digested. Digestion of most of nutrients takes place in the duodenum under the action of various enzymes. The Brunner’s glands open into the crypts of Lieberkuhn.

The secretion of intestinal glands is called intestinal juice or succus entericus with pH 7.8. About 2,000-3,000 ml of intestinal juice is secreted per day. The intestinal juice contains many enzymes— maltase, isomaltase, sucrase, lactase, α- dextrinase, enterokinase, aminopeptidases, dipeptidases, nucleotidases, nucleosidases and intestinal lipase.

In addition to the glands mentioned above the entire alimentary canal has mucous glands that produce mucus. The mucus lubricates the digestive tract and food. Human digestive system has many accessory organs. Tongue, salivary glands, liver, gall bladder and pancreas are some important human accessory digestive organs.

Swallowing or Deglutition (Fig. 16.18):

The food is tasted in the oral cavity and mixed with saliva. Tongue manipulates food during chewing and mixing with saliva. This collection of food, the bolus (mass of food) is then pushed inward through the pharynx into the oesophagus.

This process is called swallowing or deglutition. Swallowing involves coordinated activity of tongue, soft palate, pharynx and oesophagus.

Swallowing is conveniently divided into three stages:

(i) The Voluntary stage:

The tongue blocks the mouth. The bolus is forced to move from the oral cavity into the pharynx (oropharynx). This represents the volun­tary stage of swallowing.

(ii) The Pharyngeal stage:

With the passage of the bolus into the pharynx, the invol­untary pharyngeal stage of swallowing begins. The palate closes off the nose and the epiglottis seals off the glottis of larynx. Thus breathing is temporarily interrupted. The bolus is passed from the pharynx into the oesophagus.

(iii) The Oesophageal stage:

This also represents the involuntary stage of swallowing. The bolus passes through the laryngopharynx and enters the oesophagus in 1 to 2 seconds. The respiratory passage then reopens and breathing resumes. Swallowing is controlled by a swallowing centre located in the medulla oblongata and lower pons varolii of the brain.

During the oesophageal phase of swallowing, food is pushed through the oesophagus by involuntary muscular movements called peristalsis.

Peristalsis is produced by involuntary contraction of circular muscles in the oesophagus lying just above and around the top of the bolus and simultaneous contraction of the longitudinal muscles lying around the bottom of and just below the bolus.

Contraction of the longitudinal muscles shortens the lower part of the oesophagus, pushing its walls out­ward so that it can receive the bolus. After this circular muscles of the oesophagus relax. The contractions are repeated in a wave that moves down the oesophagus, pushing the food towards the stomach. There is least peristaltic movement in the rectum of human being.


Common COVID-19 Vaccine Myths Explained

Even if you understand the scientific process, trust medical experts and know how important vaccines are for fighting infectious diseases, you might still have some questions or concerns about the new COVID-19 vaccines – especially with so many rumors floating around online.

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It’s normal and healthy to have questions, says Thaddeus Stappenbeck, MD, PhD, Chairman of the Department of Inflammation and Immunity at Cleveland Clinic’s Lerner Research Institute.

“These are new therapeutics and it’s totally reasonable to be asking constructive questions with an open mind,” he reassures.

That said, it’s also important to seek out trusted sources of information. Here, Dr. Stappenbeck helps set the record straight on some common questions, concerns and myths that have emerged about COVID-19 vaccines.

Myth 1: We can’t trust COVID-19 vaccines because they were rushed.

The first vaccines for COVID-19 do involve new technology, and they were developed in record time. But it’s not because there were shortcuts in the process.

The new technology at the center of Pfizer’s and Moderna’s COVID-19 vaccines is called messenger RNA, or mRNA. While this is the first time it’s being widely used in a vaccine for the public, researchers have actually been working on this vaccine strategy for more than three decades.

“It was a lucky thing that the technology has been robustly developed quite well over the last few years and tested in several animal models of infection, so we knew that it was safe and worked quite well in these animal models,” Dr. Stappenbeck says.

“When COVID-19 came around, this was an obvious opportunity to use this novel technology, and vaccine developers were poised to do it.”

The companies put their vaccines through rigorous clinical trials involving tens of thousands of volunteers. In the U.S., the Food and Drug Administration requires them to follow up with volunteers for up to two years after receiving the vaccines to make sure they are safe and effective. Because of how prevalent COVID-19 is, it only took a few months for the clinical trials to collect enough data to make an initial evaluation. The FDA, as well as an independent panel of vaccine experts, closely scrutinized the data from those trials and deemed Pfizer’s and Moderna’s vaccines safe and effective for emergency use. Similar independent panels in several other countries are in agreement.

Myth 2: The vaccine will give me COVID-19.

Vaccines prime your immune system to recognize and fight off a disease, but they don’t actually cause an infection.

The first two COVID-19 vaccines that are available in the U.S. contain a strand of genetic material called mRNA. When the mRNA enters your cells, it instructs them to make a piece of the “spike” protein that’s present on the coronavirus that causes COVID-19. Those protein pieces don’t actually harm your body, but they do trigger your immune system to mount a response to fight them off.

You might have some fatigue, muscle aches, a headache or a fever after you get the vaccine. That’s normal with any vaccine – it’s a sign that your immune system is responding.

Myth 3: We don’t know what’s in these vaccines.

Both Pfizer and Moderna have published the ingredient lists for their vaccines. In addition to the star ingredient, the COVID-19 mRNA for the spike protein, both vaccines contain lipids (fats) that help deliver the mRNA into your cells and a few other common ingredients that help maintain the pH and stability of the vaccine. Despite theories circulated on social media, they do not contain microchips or any form of tracking device.

Myth 4: These vaccines will alter my DNA.

The vaccines use mRNA to instruct our cells to make a piece of the coronavirus’s hallmark spike protein in order to spark an immune system response. Once the mRNA does that, our cells break it down and get rid of it.

“Messenger RNA is something that’s made from DNA, but it’s not designed to integrate with our DNA, and it doesn’t permanently change our genome and who we are in any way,” Dr. Stappenbeck says.

Myth 5: I already had COVID-19, so I won’t benefit from the vaccine.

We don’t yet know how long natural immunity to COVID-19 lasts, Dr. Stappenbeck says. Right now, it seems that getting COVID-19 more than once is not common, but there are still many questions that remain unanswered. Experts say that, even if you’ve had COVID-19, it would still be appropriate for you to get the vaccine to make sure you’re protected.

Myth 6: Since COVID-19’s survival rate is so high, I don’t need a vaccine.

It’s true that most people who get COVID-19 are able to recover. But it’s also true that some people develop severe complications. So far, more than 1.7 million people around the world have died from COVID-19 – and that doesn’t account for people who survived but needed to be hospitalized. Because the disease can damage the lungs, heart and brain, it may also cause long-term health problems that experts are still working to understand.

There’s another reason to consider getting the vaccine: It protects those around you. Even if COVID-19 doesn’t make you very sick, you could pass it on to someone else who might be more severely affected. Widespread vaccination protects populations, including those who are most at risk and those who can’t be vaccinated. It will be important for ending the pandemic.

Myth 7: Once I get the vaccine, I won’t have to wear a mask or worry about social distancing.

Even if you get the vaccine, you should continue to wear a mask around others, wash your hands and practice physical distancing. There are a few reasons for this. The first is that both of the authorized vaccines require two doses given three to four weeks apart to achieve the best possible immunity.

When you get your first shot, you don’t become immediately immune. “It takes at least a week to 10 days for your body to begin to develop antibodies, and then those antibodies continue to increase over the next several weeks,” Dr. Stappenbeck says.

The second is that these vaccines were developed and tested for their ability to prevent severe illness and death from COVID-19. It’s not clear whether they also protect against asymptomatic infection and spread.

“There will be ongoing studies to evaluate this question, but it will be some time before we actually know,” Dr. Stappenbeck says. “So after you get the vaccine, you should still take steps to protect other people who haven’t been vaccinated yet.”

Myth 8: Now that we have vaccines, the pandemic will be over very soon.

“I would love to say that we’re going to flip a switch and everything’s going to be back to normal, but it’s actually going to take a long time for us to be able to vaccinate an adequate number of people to where we’ll start to see the cases really dropping,” Dr. Stappenbeck explains.

In order to achieve what’s called herd immunity – the point at which the disease is no longer likely to spread – about 70% of the population will need to have been vaccinated or infected, he says. But the companies that make these vaccines can only make so many at a time. So the vaccines will be distributed in phases, with priority given to people with greatest need. They may not be widely available to the general public until several months into 2021.

For now, we should all continue to do our part to help slow the spread of the virus, including wearing a mask, washing our hands and physical distancing.

If you have more questions about the vaccine, talk with your trusted healthcare provider or look to reliable sources like the Centers for Disease Control and Prevention or the World Health Organization.

Myth 9: The vaccine will cause infertility.

Because the COVID-19 vaccines do not contain the live virus (remember, it’s an mRNA vaccine), they are not thought to cause increased risk of infertility, first or second trimester loss, still birth or congenital anomalies. Additionally, there is no evidence to suggest that the vaccine is a risk to a breastfeeding baby.

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What is the difference between a rat and a human digestive system?

There are several similarities between the digestive system of a rat and a human as far as location and function are concerned. Both mammals possess the three main areas of the digestive system: salivary glands, the oral cavity, and the abdominal cavity. Each of these is subdivided into specific organs.

Digestion, by definition, is the process by which food substances are chemically altered into forms of energy where they can be absorbed through cell membranes.

Because a rat's digestive tract is so similar to that of a human, it is fair to say that they function in similar ways.

An animal's diet is revealed by its dentition pattern. This refers to the types of teeth the animal has, the number of teeth, and how they are arranged. There are three main types of dentition patterns: herbivourous, carnivorous, and omniverous. Rats and humans are both omnivores, meaning they eat meat and vegetation. Rats, however, need to chew more rough food, like tree bark, and in domestic rats, chew toys. This is because their front incisor teeth would, if left to grow freely with nothing to wear it down, would grow through the rodents jaw. This of course, would never happen with humans. Human teeth stop growing after they reach a certain point.

Another major difference between the rat and human digestive tract, aka the alimentary canal, is the fact that while we as humans have gall bladders, rats do not. Instead of a gall bladder, rats have a bile duct (ductus choledochus) which is formed from several tubes from the liver. the various lobes of the liver unite to form this tube (the bile duct) and this allows the transport of bile into the duodenum.

Also, because rats do not have gall bladders, they are more apt to graze constantly throughout the day, which is why (if you have a pet rat--though i doubt this..) you are not supposed to just continually feed them throughout the day. Because they do not have a gene to trigger a feeling of fullness, rats would (along with other rodents, such as guinea pigs, hamsters and mice) literally eat themselves to death.

And finally, because i have to finish a lab report (on a rat dissection no doubt)..when the food enters the caecum (latin spelling of the word..it can also be spelled cecum!) the nutrients is then absorbed. Many anumanls, including man, have a short veriform appendix at the end of the cecum, this is absent in the rat. Oh and rats do not have uvula (i do not know if i said that already) but its true (haha i are dork!)