Answer: <h3>B. The accessory organs of digestive system</h3>
<p>These are glands situated on the alimentary tract. Their function is to secrete digestive juice which is poured into GI tracts by ducts. They are:</p>
<p>I. The salivary glands<br />II. The liver<br />III. The pancreas<br />IV. The gall bladder and bile duct.</p>
<h4>1) The salivary glands &ndash;</h4>
<p>There are three pairs of compound racemose glands, which pour their secretion into the mouth. They are:<br /><strong>Parotid glands</strong> &ndash; they are paired and lies one on each side. They lie below and slightly in front of each earlobe.<br /><strong>Sub &ndash; mandibular glands &ndash;</strong> they are paired and each is situated just cover of the angle of the mandible. The sub &ndash; mandibular duct or Wharton duct passes forwards on the floor of the mouth and open by a papilla at the side of the frenulum of the tongue.<br /><strong>Sublingual glands &ndash;</strong> they lie in the anterior part of the floor of the mouth between the tongue and the mandible, close to the midline.</p>
<h4>Structures of the salivary glands</h4>
<p>A fibrous capsule surrounds all the glands. They consist of a number of lobules made up of small alveoli lined with secretary cells. The secretions are poured into small ducts, which join up to form larger ducts leading into the mouth.</p>
<h4>Functions of Salivary gland:</h4>
<p>i. Saliva constantly moistens the mouth and tongue<br />ii. It moistens and lubricates food so that it can be rolled into a soft mass or bolus, suitable for swallowing<br />iii. Ptyalin begins to act on cooked starches and converts them to dextrin and maltose<br />iv. Saliva dissolves the part of the food, which stimulates the taste buds<br />v. It has a cleansing action and helps to keep the mouth and teeth free of debris<br />vi. Saliva contains lysozymes, immunology- tubulin.</p>
<h4><br />2) The pancreas</h4>
<p>The pancreas is a pale yellowish gray gland weight about 60 grams and having 10-15 cm long.it is situated in the epigastric and the left hypochondriac regions of the abdominal cavity.it consists of three parts:<br /><br />a) Head, which lies in the curve(c shaped) of the duodenum and is closely attached to it.<br />b) A body which lies behind the body of the stomach.<br />c) Tail, it is a narrow part, which lies in the front of the left kidney and which just reaches the spleen.</p>
<h4><br />Structure of the pancreas:</h4>
<p>The pancreas is both an endocrine and exocrine gland. The exocrine parts consist of a large number of lobules made up of small alveoli consisting secretory cells (acini).each lobule is drained by a tiny duct and these units eventually to form the pancreatic duct that extends the whole length of the gland and opens into the duodenum at its midpoint.<br />The islets of Langerhans are the endocrine part, consisting of groups, of specialized cells distributed throughout the gland. They secrete the hormone insulin, glucagon and somatostatin (Growth hormone inhibiting hormone) by beta, alpha and cells respectively.</p>
<h4>Function of the pancreas:</h4>
<p><strong>a. Exocrine function</strong>: The acinar cells of the pancreas secrete pancreatic juice containing digestive enzymes amylase, lipase, trypsinogen and chymotrypsinogen that digest carbohydrates, protein and fats respectively.<br /><strong>b. Endocrine function</strong>: The beta cell of pancreas secretes insulin, alpha cell secretes glucagons and gamma cell secretes somatostatin hormone. Insulin is important in the metabolism of carbohydrates, fats, and protein. Glucagon is concerned with the breakdown of liver glycogen. Somatostatin is growth hormone inhibiting hormone.</p>
<h4>3) The Liver &ndash;</h4>
<p>liver is the largest organ or gland in the body, weighing about 11.5 to 2.5 kg and is heavier in the male than in the female. It occupies 2% of total body weight in adult and about 5% of body weight in newborn.it is a wedge shaped (triangular) organ lying immediately below the diaphragm in the right hypochondriac and epigastrium and extending into the left hypochondrium. Its upper and interior surface are smooth and fit the under surface of the diaphragm; its posterior surface is irregular in outline. The liver is a storehouse for glycogen.</p>
<h4>Structure of the Liver</h4>
<p>The liver is composed of a large number of hexagonal lobules, each about 1mm in diameter and formed by cubical shaped cells known as hepatocytes. A small branch of the hepatic vein extends through the center of each lobule. The liver cells are arranged in plates, or sheets, one cell thick, around the central vein. The plates of cells from an irregular anatomizing system throughout the liver between the places of cells lie spaces, which contains the sinusoids. The sinusoids are the blood vessels with incomplete walls and are irregular in shape and wider than blood capillaries.</p>
<h4>Functions of the Liver:</h4>
<p>1. Determinates amino acid: (urea formation)<br /><br />2. Carbohydrates metabolism:<br />a) Glycogenesis: conversion of glucose to glycogen in the presence of insulin for storage.<br />b) Glycogenolysis: conversion of glycogen to glucose in the presence of glucagon and release of glucose into the blood. Epinephrine and glucagon accelerate glycogenolysis. <br />c) Gluconeogenesis: formation of glucose from protein or fats; glucocorticoid (hydrocortisone, corticosterone) have an accelerating effect on gluconeogenesis.<br /><br />3. Desaturation of fat: converting stored fat to a form in which it can be used by the tissue to provide energy.<br /><br />4. Heat production: the liver uses a considerable amount of energy, has a high metabolic rate and produces a great deal of heat.<br /><br />5. Secretion of bile: the liver cell synthesizes the constituents of bile from the mixed arterial and venous blood in the sinusoids.<br /><br />6. Synthesis of: plasma protein(albumin and fibrinogen), anticoagulant &ndash;heparin, vitamin K-dependent clotting factors.<br /><br />7. Storages of fat-soluble vitamins &ndash; A, D, E and K and B12. It also stores iron and copper. Iron in the form of ferritin and copper in the form of ceruloplasmin.<br /><br />8. Metabolism of some steroid hormones and some polypeptide hormone.<br /><br />9. Detoxifies drugs and toxins.</p>
<h4>4) The gall bladder &ndash;</h4>
<p>The gallbladder is a pear-shaped sac attached to the posterior surface of the liver by connective tissue. It is described as having a fundus, (expanded end), a body (main part) and neck (narrowing part) which is continuous with the cystic duct. Its capacity is approximately 60ml.</p>
<p>The structure of the gallbladder: the gall bladder consist of three coats:<br /><br /><strong>i. Peritoneum</strong> &ndash; it is continuous with peritoneum covering the liver, which binds the gall bladder in position on the undersurface of the liver.<br /><strong>ii. Muscle layer</strong> &ndash; the muscular layer consists of a layer of smooth muscle with longitudinal, oblique and circular fibers.<br /><strong>iii. Mucous membrane &ndash;</strong> The inner lining is of mucous membrane, which displays very small rugae when the gallbladder is empty. The rugae are disappeared when the organ is distended with bile.</p>
<h4>Functions of the gall bladder:</h4>
<p>a. It acts as a reservoir for bile<br />b. The lining membrane adds mucus to the bile<br />c. It absorbs water so that it is 10 to 15 times more concentrated than liver bile<br />d. By the contraction of the muscle walls, bile is expelled from the gallbladder and passed via the bile duct into the duodenum.</p>
<h4>5) The Biliary tract &ndash;</h4>
<p>The biliary tract is the apparatus of the liver and consists of:<br /><br /><strong>I. Right and left hepatic duct</strong><br /><strong>II. The common hepatic duct</strong><br /><strong>III. The gall bladder the cystic duct</strong><br /><strong>IV. The common bile duct.</strong></p>
<p><br />Structure of the biliary tract: the walls of the bile ducts consisting of the following layer<br />I. The outer covering &ndash;peritoneum<br />II. The middle layer - smooth muscle layer which exhibits peristaltic contraction.<br />III. The inner layer - lining of a mucous membrane.</p>
<h4>The function of the digestive system</h4>
<p>a. It helps in food entering into the digestive tract through the mouth.<br />b. Physical manipulation of solid food first by the tongue and teeth and then by swirling and mixing motion of the digestive tract.<br />c. Chemical breakdown of food so it can be absorbed by the digestive tract.<br />d. Secretion or release of the water, acids, enzymes and buffer <br />e. The movement of small organic molecules, electrolytes, vitamins and water across the digestive epithelium and into the interstitial fluid of the digestive tract<br />f. The removal of waste products from body fluids, these waste products are compacted and discharge as feces through the process of defecation.</p>
<h4>Physiology of Digestion:</h4>
<p>Digestion is the process by which the nutrients materials (food substances) are altered or changed physically and chemically so that they are reduced to simple chemical substance ready for absorption from the alimentary tract into the blood and lymph capillaries in the villi of the small intestine. The process is divided into two main parts. <br /><br />1<strong>. Mechanical digestion</strong> &ndash; mechanical digestion consists of the liquefying of food by the digestive juice, mastication, swallowing and thereafter onwards movements through the tract by peristalsis. The rate at which onward movements takes place does, to some extent, depends on upon the state of the food e.g. the contents of the stomach do not pass through the pyloric sphincter until they have reached a considerable degree of liquefaction.<br /><br /><strong>2. Chemical digestion</strong> - chemical digestion takes place by a breakdown of food through chemical substances of enzymes presence of the secretion of the different organs of the gastrointestinal tract. The different juice and enzymes are:</p>
<ul>
<li>Saliva in the mouth &ndash; analysis (ptyalin)</li>
<li>Gastric juice in the stomach &ndash; pepsinogen, rennin</li>
<li>Pancreatic juice in the duodenum &ndash; amylase, lipase, trypsinogen, chymotrypsinogen</li>
<li>Bile in the duodenum</li>
<li>Intestinal juice in the small intestine &ndash; enteropeptidase enterokinase, maltase, lactase, sucrase, isomaltase, lipase.</li>
</ul>
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