Respiration And Digestion In Human Physiology Biology Essay

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The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood. Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the respiratory system through the mouth and the nose. The oxygen then passes through the larynx where speech sounds are produced) and the trachea which is a tube that enters the chest cavity. In the chest cavity, the trachea splits into two smaller tubes called the bronchi. Each bronchus then divides again forming the bronchial tubes. The bronchial tubes lead directly into the lungs where they divide into many smaller tubes which connect to tiny sacs called alveoli. The average adult's lungs contain about 600 million of these spongy, air-filled sacs that are surrounded by capillaries. The inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale.The diaphragm's job is to help pump the carbon dioxide out of the lungs and pull the oxygen into the lungs. The diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. As the diaphragm contracts and relaxes, breathing takes place. When the diaphragm contracts, oxygen is pulled into the lungs. When the diaphragm relaxes, carbon dioxide is pumped out of the lungs. The purpose of this lab is to observe the respiratory system, its mechanics, and how it works in the human body.

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- The respiratory tract (or system) is a complex arrangement of organs and tissues. Its main functions are taking in oxygen and getting rid of carbon dioxide. The respiratory tract can be separated into two parts: (a) The proximal-conducting, nonrespiratory airways that include the nose, pharynx, larynx, trachea, bronchi, and nonalveolar bronchioles. (b) The distal respiratory region Gas exchange between air and blood occurs in the respiratory region. The geometry of the respiratory tract differs among different individuals. This contributes to differences in the amount of airborne material each person would deposit in his/her respiratory tract for a given exposure scenario. The structural features of the respiratory tract (nose, pharynx, larynx, trachea, bronchi and bronchioles, gas exchange airways, and lymphatic system) are summarized below.

- Nose. The nose is the first potential target for inhaled substances except when one breathes through the mouth. The nose is important in odor detection. The interior parts of the nose warm, moisten, and filter air. This helps to protect the lungs from harm. Some inhaled material can be trapped in the nasal cavity. After inhaled air goes through the nasal vestibule, the air then passes through the narrowest part of the upper airway, the nasal valve, into the main chamber.

- The lumen of the main chamber is lined with mucous membranes that are covered by a layer of mucus and are associated with numerous nerves and blood vessels. The mucous layer, which contains entrapped material, is moved by underlying cilia to the pharynx where it is swallowed. Again, this is one way in which trapped substances are transported from the nasal region.

-Turbinates (bony structures) project into the airway lumen from the lateral walls. The nasal turbinates are of three types: superior, middle, and inferior. They increase the inner surface area of the nose, which is important in filtering, humidifying, and warming the inhaled air. Pharynx: Inhaled substances that do not deposit in the nose or mouth could deposit in the pharynx. The pharynx connects the nasal and/or oral airway with the laryngeal airway during breathing. The pharynx is shaped somewhat like a funnel. It can be anatomically divided into nasal, oral, and laryngeal regions. The pharynx lies just behind the nasal and oral cavities and extends partway down the neck. The wall of the pharynx consists of striated muscle lined with a mucous membrane. The pharynx allows passage of air and food and provides a resonating chamber for speech sounds.

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- The lowest portion is called the laryngopharynx, which extends downward and becomes continuous with the esophagus and larynx. Both the pharynx and laryngopharynx are digestive and respiratory pathways. The larynx is a short cavity that has a slit-like narrowing in its central portion. The narrowing is caused by two pairs of folds in the larynx walls. The lower folds are called vocal chords and the upper folds the false vocal chords. The larynx connects the pharynx with the trachea and has three functions:  A pathway for inhaled and exhaled air during breathing;

- A valve in conjunction with the epiglottis (a muscular flap) to prevent swallowed food from entering the lower respiratory tract during eating and drinking; and A tone-producing structure.

-Trachea: Inhaled substances that pass through the larynx with the inhaled air could deposit in the trachea. The trachea is continuous with the larynx in the neck and extends into the thoracic cavity where it branches to form the left and right main bronchi. The structure of the trachea airway is maintained during breathing because of many rings made of cartilage found within its wall.

-Bronchi and Bronchioles. Inhaled substances that pass through the trachea with the inhaled air could deposit in the bronchi or bronchioles.

-The main bronchi branch into the lobar bronchi, then into segmental and sub segmental bronchi, and the conducting airways and eventually end at the smallest of the conducting airways, the terminal bronchioles. Gas Exchange Airways. Inhaled substances that do not deposit in other parts of the respiratory tract could deposit in gas-exchange airways. The conducting airways terminate in gas-exchange airways, which are made up of respiratory bronchioles and alveolar ducts.

-The Lymphatic System: The lymphatic system of the lungs plays an important supportive role in maintaining liquids, respiratory defenses, and in removal of inhaled material deposited in the lungs. The large flow of lymph from the lung tissue spaces toward the blood helps in removing excess fluid.

 

 

3. What are the factors which may cause the lungs to collapse?

- A variety of factors can lead to a collapsed lung, including a plug of mucus, a tumor or something breathed into the lungs. Pressure on an airway from outside can also cause a lung to collapse. When the airway is blocked, the blood absorbs the air inside the air sacs.. Without more air, the sac shrinks. The space where the ling was before the collapse fills up with blood cells, fluids and mucus, It ma then become infected. Abdominal swelling can also lead to collapsed lungs. This can happen in premature babies or in adults who have had too much oxygen therapy or mechanical ventilation. Large doses of opinoids or sedatives. Lying immobilized in bed.

4. Explain hyperventilation, Tidal volume, vital capacity, residual volume.

- Hyperventilation is breathing in excess of what the body needs. This is sometimes called over breathing. Rapid or deep breathing is sometimes seen in very serious conditions such as infection, bleeding, or heart attack. The tidal volume is the volume of air inspired or expired in a single breath during regular breathing. Vital capacity is the amount of air that can be forced out of the lungs after a maximal inspiration, the emphasis on completeness of expiration also the maximum volume of air that can be voluntarily moved in and out of the respiratory system. The residual volume is the air remaining in the lungs after the most complete expiration possible; it is elevated in diffuse obstructive emphysema and during an attack of asthma.

5. A patient is asthmatic. Any allergies taken into the respiratory system may trigger asthmatic symptoms. Explain what happens in this process.

- An acute exacerbation of asthma is commonly referred to as an asthma attack. The cardinal symptoms of an attack are shortness of breath, wheezing, and chest tightness. Although the former is often regarded as the primary symptom of asthma, some people present primarily with coughing, and in the late stages of an attack, air motion may be so impaired that no wheezing is heard. When present the cough may sometimes produce clear septum. The onset may be sudden, with a sense of constriction in the chest, as breathing becomes difficult and wheezing occurs. It is important to note inspiratory strider without expiratory wheeze however, as an upper airway obstruction may manifest with symptoms similar to an acute exacerbation of asthma, with strider instead of wheezing, and will remain unresponsive to bronchodilators.

6. Define: Histamines, Diaphragm, Surfactant, Pneumothorax, antihistamines.

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- Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter.[1] Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and other proteins, in order to allow them to engage foreign invaders in the infected tissues.[2] It is found in virtually all animal body cells. The diaphragm is the primary muscle of inspiration. It is a thin, dome-shaped sheet of muscle that inserts into the lower ribs. When it contracts, it pushes downward and spreads out, increasing the vertical dimension of the chest cavity and driving up abdominal pressure. This increase in pressure drives the abdominal contents down and out, which in turn increases the transverse size of the chest cavity. Surfactants are compounds that lower the surface tension of a liquid, allowing easier spreading, and lowering of the interfacial tension between two liquids, or between a liquid and a solid. Surfactants may act as: detergents, wetting agents, emulsifiers, foaming agents, and dispersants. Pneumothorax (plural pneumothoraces) is a collection of air or gas in the pleural cavity of the chest between the lung and the chest wall. It may occur spontaneously in people without chronic lung conditions ("primary") as well as in those with lung disease ("secondary"), and many pneumothoraces occur after physical trauma to the chest, blast injury, or as a complication of medical treatment. Antihistamines are medicines that help stop allergy symptoms, such as itchy eyes, sneezing and a runny nose. Sometimes, an antihistamine can also help itchy rashes (especially hives).

7. Lung Cancer:

The lung cancer is cancer that begins in the lungs, the two organs found in the chest that help you breathe. The lungs are made up of areas called lobes. The right lung has three lobes; the left lung has two, so there's room for the heart. When you breathe, air goes through your nose, down your windpipe (trachea), and into the lungs where it spreads through tubes called bronchi. Most lung cancer begins in the cells that line these tubes.There are two main types of lung cancer:Non-small cell lung cancer (NSCLC) is the most common type of lung cancer. Small cell lung cancer makes up about 20% of all lung cancer cases.If the lung cancer is made up of both types, it is called mixed small cell/large cell cancer. If the cancer started somewhere else in the body and spread to the lungs, it is called metastatic cancer to the lung. The causes of lung cancer are following: The lung cancer occurs when a lung cell's gene mutation makes the cell unable to correct DNA damage and unable to commit suicide. Mutations can occur for a variety of reasons. Most lung cancers are the result of inhaling carcinogenic substances.Carcinogens are a class of substances that are directly responsible for damaging DNA, promoting or aiding cancer. Tobacco, asbestos, arsenic, radiation such as gamma and x-rays, the sun, and compounds in car exhaust fumes are all examples of carcinogens. When our bodies are exposed to carcinogens, free radicals are formed that try to steal electrons from other molecules in the body. These free radicals damage cells and affect their ability to function and divide normally. About 87% of lung cancers are related to smoking and inhaling the carcinogens in tobacco smoke. Even exposure to second-hand smoke can damage cells so that cancer forms. Cancer symptoms are quite varied and depend on where the cancer is located, where it has spread, and how big the tumor is. Lung cancer symptoms may take years before appearing, usually after the disease is in an advanced stage. Many symptoms of lung cancer affect the chest and air passages. These include: Persistent or intense coughing, Pain in the chest shoulder, or back from coughing, Changes in color of the mucus that is coughed up from the lower airways (sputum), Difficulty breathing and swallowing, Hoarseness of the voice, Harsh sounds while breathing (stridor), Chronic bronchitis or pneumonia, Coughing up blood, or blood in the sputum. If the lung cancer spreads, or metastasizes, additional symptoms can present themselves in the newly affected area. Swollen or enlarged lymph nodes are common and likely to be present early. If cancer spreads to the brain, patients may experience vertigo, headaches, or seizures. In addition, the liver may become enlarged and cause jaundice and bones can become painful, brittle, and broken. It is also possible for the cancer to infect the adrenal glands resulting in hormone level changes. As lung cancer cells spread and use more of the body's energy, it is possible to present symptoms that may also be associated with many other ailments.

Lung cancer treatments depend on the type of cancer, the stage of the cancer (how much it has spread), age, health status, and additional personal characteristics. As there is usually no single treatment for cancer, patients often receive a combination of therapies and palliative care. The main lung cancer treatments are surgery, chemotherapy, and/or radiation. However, there also have been recent developments in the fields of immunotherapy, hormone therapy, and gene therapy. Surgery is the oldest known treatment for cancer. If a cancer is in stage I or II and has not metastasized, it is possible to completely cure a patient by surgically removing the tumor and the nearby lymph nodes. After the disease has spread, however, it is nearly impossible to remove all of the cancer cells. Radiation treatment, also known as radiotherapy, destroys or shrinks lung cancer tumors by focusing high-energy rays on the cancer cells. This causes damage to the molecules that make up the cancer cells and leads them to commit suicide. Radiotherapy utilizes high-energy gamma-rays that are emitted from metals such as radium or high-energy x-rays that are created in a special machine. Radiation can be used as the main treatment for lung cancer, to kill remaining cells after surgery, or to kill cancer cells that have metastasized.

Digestion:

Addendum Questions:

1.

- A living system controls its activity through enzymes. An enzyme is a protein molecule that is a biological catalyst with three characteristics. First, the basic function of an enzyme is to increase the rate of a reaction. Most cellular reactions occur about a million times faster than they would in the absence of an enzyme. Second, most enzymes act specifically with only one reactant (called a substrate) to produce products. The third and most remarkable characteristic is that enzymes are regulated from a state of low activity to high activity and vice versa. Gradually, you will appreciate that the individuality of a living cell is due in large part to the unique set of some 3,000 enzymes that it is genetically programmed to produce. If even one enzyme is missing or defective, the results can be disastrous. The activity of an enzyme depends, at the minimum, on a specific protein chain. In many cases, the enzyme consists of the protein and a combination of one or more parts called cofactors. This enzyme complex is usually simply referred to simply as the enzyme.

Apoenzyme: The polypeptide or protein part of the enzyme is called the apoenzyme and may be inactive in its original synthesized structure. The inactive form of the apoenzyme is known as a proenzyme or zymogen. The proenzyme may contain several extra amino acids in the protein which are removed, and allows the final specific tertiary structure to be formed before it is activated as an apoenzyme.

Cofactors: A cofactor is a non-protein substance which may be organic, and called a coenzyme. The coenzyme is often derived from a vitamin with specific examples discussed later. Another type of cofactor is an inorganic metal ion called a metal ion activator. The inorganic metal ions may be bonded through coordinate covalent bonds. The major reason for the nutritional requirement for minerals is to supply such metal ions as Zn+2, Mg+2, Mn+2, Fe+2, Cu+2, K+1, and Na+1 for use in enzymes as cofactors.

Final Enzyme: The type of association between the cofactor and the apoenzymes varies. In some cases, the bonds are rather loose and both come together only during the course of a reaction. In other cases, they are firmly bound together by covalent bonds. The activating role of a cofactor is to either: activate the protein by changing its geometric shape, or by actually participating in the overall reaction. The overall enzyme contains a specific geometric shape called the active site where the reaction takes place. The molecule acted upon is called the substrate.

2.

- Mouth: The mouth is the beginning of the digestive tract; and, in fact, digestion starts here when taking the first bite of food. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use.

Esophagus: Located in your throat near your trachea (windpipe), the esophagus receives food from your mouth when you swallow. By means of a series of muscular contractions called peristalsis, the esophagus delivers food to your stomach.

Stomach: The stomach is a hollow organ, or "container," that holds food while it is being mixed with enzymes that continue the process of breaking down food into a usable form. Cells in the lining of the stomach secrete a strong acid and powerful enzymes that are responsible for the breakdown process. When the contents of the stomach are sufficiently processed, they are released into the small intestine.

Small intestine: Made up of three segments - the duodenum, jejunum, and ileum - the small intestine is a 22-foot long muscular tube that breaks down food using enzymes released by the pancreas and bile from the liver. Peristalsis also is at work in this organ, moving food through and mixing it with digestive secretions from the pancreas and liver. The duodenum is largely responsible for the continuous breaking-down process, with the jejunum and ileum mainly responsible for absorption of nutrients into the bloodstream.

Contents of the small intestine start out semi-solid, and end in a liquid form after passing through the organ. Water, bile, enzymes, and mucous contribute to the change in consistency. Once the nutrients have been absorbed and the leftover-food residue liquid has passed through the small intestine, it then moves on to the large intestine, or colon.

Pancreas: The pancreas secretes digestive enzymes into the duodenum, the first segment of the small intestine. These enzymes break down protein, fats, and carbohydrates. The pancreas also makes insulin, secreting it directly into the bloodstream. Insulin is the chief hormone for metabolizing sugar.

Liver: The liver has multiple functions, but its main function within the digestive system is to process the nutrients absorbed from the small intestine. Bile from the liver secreted into the small intestine also plays an important role in digesting fat. In addition, the liver is the body's chemical "factory." It takes the raw materials absorbed by the intestine and makes all the various chemicals the body needs to function. The liver also detoxifies potentially harmful chemicals. It breaks down and secretes many drugs.

Gallbladder: The gallbladder stores and concentrates bile, and then releases it into the duodenum to help absorb and digest fats.

Colon (large intestine): The colon is a 6-foot long muscular tube that connects the small intestine to the rectum. The large intestine is made up of the cecum, the ascending (right) colon, the transverse (across) colon, the descending (left) colon, and the sigmoid colon, which connects to the rectum. The appendix is a small tube attached to the cecum. The large intestine is a highly specialized organ that is responsible for processing waste so that emptying the bowels is easy and convenient.

Rectum

The rectum (Latin for "straight") is an 8-inch chamber that connects the colon to the anus. It is the rectum's job to receive stool from the colon, to let the person know that there is stool to be evacuated, and to hold the stool until evacuation happens. When anything (gas or stool) comes into the rectum, sensors send a message to the brain. The brain then decides if the rectal contents can be released or not. If they can, the sphincters relax and the rectum contracts, disposing its contents. If the contents cannot be disposed, the sphincter contracts and the rectum accommodates so that the sensation temporarily goes away.

Anus

The anus is the last part of the digestive tract. It is a 2-inch long canal consisting of the pelvic floor muscles and the two anal sphincters (internal and external). The lining of the upper anus is specialized to detect rectal contents. It lets you know whether the contents are liquid, gas, or solid. The anus is surrounded by sphincter muscles that are important in allowing control of stool. The pelvic floor muscle creates an angle between the rectum and the anus that stops stool from coming out when it is not supposed to. The internal sphincter is always tight, except when stool enters the rectum. It keeps us continent when we are asleep or otherwise unaware of the presence of stool. When we get an urge to go to the bathroom, we rely on our external sphincter to hold the stool until reaching a toilet, where it then relaxes to release the contents.

3.

- Liver is an organ in the upper abdomen that aids in digestion and removes waste products and worn-out cells from the blood. The liver is the largest solid organ in the body. The liver weighs about three and a half pounds (1.6 kilograms). It measures about 8 inches (20 cm) horizontally (across) and 6.5 inches (17 cm) vertically (down) and is 4.5 inches (12 cm) thick. The liver has a multitude of important and complex functions. Some of these functions are to: Manufacture (synthesize) proteins, including albumin (to help maintain the volume of blood) and blood clotting factors, Synthesize, store, and process (metabolize) fats, including fatty acids (used for energy) and cholesterol, Metabolize and store carbohydrates, which are used as the source for the sugar (glucose) in blood that red blood cells and the brain use, Form and secrete bile that contains bile acids to aid in the intestinal absorption (taking in) of fats and the fat-soluble vitamins A, D, E, and K, Eliminate, by metabolizing and/or secreting, the potentially harmful biochemical products produced by the body, such as bilirubin from the breakdown of old red blood cells and ammonia from the breakdown of proteins, Detoxify, by metabolizing and/or secreting, drugs, alcohol, and environmental toxins.

Bile acids are derivatives of cholesterol synthesized in the hepatocyte. Cholesterol, ingested as part of the diet or derived from hepatic synthesis is converted into the bile acids cholic and chenodeoxycholic acids, which are then conjugated to an amino acid (glycine or taurine) to yield the conjugated form that is actively secreted into cannaliculi. Bile acids are facial amphipathic, that is, they contain both hydrophobic (lipid soluble) and polar (hydrophilic) faces. The cholesterol-derived portion of a bile acid has one face that is hydrophobic (that with methyl groups) and one that is hydrophilic (that with the hydroxyl groups); the amino acid conjugate is polar and hydrophilic. Their amphipathic nature enables bile acids to carry out two important functions: Emulsification of lipid aggregates: Bile acids have detergent action on particles of dietary fat which causes fat globules to break down or be emulsified into minute, microscopic droplets. Emulsification is not digestion per se, but is of importance because it greatly increases the surface area of fat, making it available for digestion by lipases, which cannot access the inside of lipid droplets, Solubilization and transport of lipids in an aqueous environment: Bile acids are lipid carriers and are able to solubilize many lipids by forming micelles - aggregates of lipids such as fatty acids, cholesterol and monoglycerides - that remain suspended in water. Bile acids are also critical for transport and absorption of the fat-soluble vitamins.

4.

- There are a number of influences than can change the efficiency of enzyme, but the four most important factors are inhibitors, allosteric factors, pH, and temperature. pH plays an important role in affecting the rate of an enzyme's activity. Remember that pH is a measure of how acidic or basic a solution is; that is, how many H+ or OH- ions there are. These ions are charged, and charged molecules tend to pull on other molecules. So, if too many ions are present, the enzyme may be denatured (twisted and pulled so out of shape that it can no longer function). However, this is not to say that all enzymes work best when the pH is neutral. Some enzymes actually work best in acidic or basic environments, but these characteristics are particular to the enzyme.

The final factor that influences an enzyme's efficiency is temperature. To a certain extent, a high temperature increases the rate of an enzyme's activity, because at high temperatures, molecules move around faster, so an enzyme is likely to come in contact with a substrate very quickly. However, at too high temperatures, the enzyme can become denatured and lose all function. Low temperatures slow the rate of formation of the enzyme-substrate complex because the molecules move at slower speeds and so do not come in contact with one another as frequently.

5.

- Enzymes are catalysts. Most are proteins, A few ribonucleoprotein enzymes have been discovered and, for some of these, the catalytic activity is in the RNA part rather than the protein part. Enzymes bind temporarily to one or more of the reactants of the reaction they catalyze. In doing so, they lower the amount of activation energy needed and thus speed up the reaction. Catalyst is a substance that can cause a change in the rate of a chemical reaction without itself being consumed in the reaction; the changing of the reaction rate by use of a catalyst is called catalysis. Substances that increase the rate of reaction are called positive catalysts or, simply, catalysts, while substances that decrease the rate of reaction are called negative catalysts or inhibitors. Substrate is the substance that is affected by the action of a catalyst; for example, the substance upon which an enzyme acts in a biochemical reaction. A hydrolase is an enzyme that catalyzes the hydrolysis of a chemical bond. For example, an enzyme that catalyzed the following reaction is a hydrolase: A-B + H2O → A-OH + B-H. Ph is a measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.

6.

- Swallowing is the process in the human or animal body that makes something pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. If this fails and the object goes through the trachea, then choking or pulmonary aspiration can occur. In the human body it is controlled by the swallowing reflex. Peristalsis is a series of wave-like muscle contractions that moves food to different processing stations in the digestive tract. The process of peristalsis begins in the esophagus when a bolus of food is swallowed. The strong wave-like motions of the smooth muscle in the esophagus carry the food to the stomach, where it is churned into a liquid mixture called chyme.

Next, peristalsis continues in the small intestine where it mixes and shifts the chyme back and forth, allowing nutrients to be absorbed into the bloodstream through the small intestine walls. Peristalsis concludes in the large intestine where water from the undigested food material is absorbed into the bloodstream. Finally, the remaining waste products are excreted from the body through the rectum and anus.

7.

- In addition to breaking down food, stomach acid and enzymes also help to kill bacteria or other infectious organisms that you may have eaten. The stomach is protected from corrosive stomach acid by a layer of mucus lining its walls. This mucus layer also protects other internal organs from stomach acid. When the mucus lining is damaged, stomach acids can burn through the lining of the stomach and damage other organs in the body. The Pancreas completes the job of breaking down protein, carbohydrates, and fats using digestive juices of pancreas combined with juices from the intestines. It secretes hormones that affect the level of sugar in the blood. It Produces chemicals that neutralize stomach acids that pass from the stomach into the small intestine by using substances in pancreatic juice. It Contains Islets of Langerhans, which are tiny groups of specialized cells that are scattered throughout the organ. These cells secrete: Glucagon raises the level of glucose (sugar) in the blood, Insulin-stimulates cells to use glucose, Somatostatin may regulate the secretion of glucagons and insulin. The duodenum is responsible for secreting hormones that trigger the pancreatic duct to release pancreatic juice and bile. The duodenum also serves to neutralize the acidity of the chyme that exits the stomach, an intermediate product in the digestive process. Both the Brunner's glands and the pancreatic duct secrete alkaline fluids to temper the acidity of the chyme. In addition, the mucus secreted by the Brunner's glands helps protect the duodenum from the acidity, making the duodenum much less sensitive than the rest of the small intestine to the acidic chyme. Therefore, the duodenum helps protect the rest of the small intestine by neutralizing the chyme to some extent before it passes into the jejunum. The function of the ileum is mainly to absorb vitamin B12 and bile salts and whatever products of digestion that were not absorbed by the jejunum. The main functions of the colon are absorption of water and minerals, and the formation and elimination of feces. The colon contains nearly 60 varieties of micro flora or bacteria to aid digestion, promote vital nutrient production, to maintain pH (acid-base) balance, and to prevent proliferation of harmful bacteria.

8.

- Sphincter muscles prove effective in the mediation of the entrance or release of liquids and fluids; this is evident, for example, in the blowholes of numerous marine mammals. Many sphincters are used everyday in the normal course of digestion. For example, the epiglottis is used to seal off the windpipe when swallowing, so as to ensure that no food or liquid enters.the lungs. The function of the epiglottis is a typical example of an involuntary action by the body. The hepatic portal vein is responsible for draining blood from the gastrointestinal tract and spleen into the liver. It receives blood from the stomach, small intestine, large intestine, pancreas, spleen and gall bladder through the inferior mesentric, gastric, and cystic veins. It carries the blood received from all these parts of the body to the liver. The blood that is brought to the liver by the hepatic portal vein is cleaned by the liver and flows into the inferior vena cava through the hepatic veins. It is then taken to the heart for systemic circulation. The blood coming from the different parts of the digestive system is fully loaded with nutrients and toxins that have been absorbed along the tract from the ingested food. The liver detoxifies the blood by filtering it and that is the main reason why the blood is brought to the liver by the hepatic portal vein. The blood can enter the systemic circulation of the body after all the toxins have been removed.