Nutrition and Digestion PART-III - PowerPoint Presentation

1. Nutrition and Digestion PART-IIIDr. Keshav SinghAssociate ProfessorDepartment of ZoologyD.D.U Gorakhpur University,Gorakhpur

2. 1- The caecumThis is the first part of the colon. It is a dilated region which has a blind end inferiorly and is continuous with the ascending colon superiorly.Just below the junction of the two, the ileocaecal valve opens from the ileum.The vermiform appendix is a fine tube, closed at one end, which leads from the caecum. It is usually about 13 cm long and has the same structure as the walls of the colon but contains more lymphoid tissue.2- The ascending colonThis passes upwards from the caecum to the level of the liver where it curves acutely to the left at the hepatic flexure to become the transverse colon.3- The transverse colonThis is a loop of the colon which extends across the abdominal cavity in front of the duodenum and the stomach to the area of the spleen where it forms the splenic flexure and curves acutely downwards to become the descending colon.4- The descending colonThis passes down the left side of the abdominal cavity then curves towards the midline. After it enters the true pelvis it is known as the sigmoid colon.5- The sigmoid colonThis part describes an S-shaped curve in the pelvis then continues downwards to become the rectum.

3. 7- The Rectum and anusIt is a slightly dilated section of the colon about 13 cm long. It leads from the sigmoid colon and terminates in the anal canal.The anal canal is a short passage about 3.8 cm long in the adult and leads from the rectum to the exterior.Two sphincter muscles control the anus; the internal sphincter, consisting of smooth muscle fibers, is under the control of the autonomic nervous system and the external sphincter, formed by skeletal muscle, is under voluntary control.

4. The exocrine pancreasIt consists of a large number of lobules made up of small alveoli, the walls of which consist of secretory cells.Each lobule is drained by a tiny duct and these unite eventually to form the pancreatic duct, which extends the whole length of the gland and opens into the duodenum.Just before entering the duodenum the pancreatic duct joins the common bile duct to form the hepatopancreatic ampulla. The duodenal opening of the ampulla is controlled by the hepatopancreatic sphincter (of Oddi).The function of the exocrine pancreas is to produce pancreatic juice containing enzymes that digest carbohydrates, proteins and fats.The endocrine pancreasDistributed throughout the gland are groups of specialized cells called the pancreatic islets (of Langerhans).The islets have no ducts so the hormones diffuse directly into the blood.The function of the endocrine pancreas is to secrete the hormones insulin and glucagon, which are principally concerned with control of blood glucose levels.

5. Functions of the PancreasAs part of the exocrine system, the pancreas secretes enzymes that work in tandem with bile from the liver and gallbladder to help break down substances for proper digestion and absorption.Enzymes produced by the pancreas for digestion include:1- lipase to digest fats2- amylase to digest carbohydrates3- chymotrypsin and trypsin for digesting proteins4- The pancreas produces enzymes as soon as food reaches the stomach.5- These enzymes travel through a series of ducts until they reach the main pancreatic duct.6- The main pancreatic duct meets the common bile duct, which carries bile from the gallbladder and liver towards the duodenum. This meeting point is called the ampulla of Vater.7- Bile from the gallbladder and enzymes from the pancreas are released into the duodenum to help digest fats, carbohydrates, and proteins so they can be absorbed by the digestive system.

6. Endocrine FunctionAs part of the endocrine system, the pancreas secretes two main hormones that are vital to regulating glucose (also known as blood sugar) level:Insulin. The pancreas secretes this hormone to lower blood glucose when levels get too high.Glucagon: The pancreas secretes this hormone to increase blood glucose when levels get too low.Balanced blood glucose levels play a significant role in the liver, kidneys, and even brain. Proper secretion of these hormones is important to many bodily systems, such as your nervous system and cardiovascular system.

7. LiverThe liver is the largest gland in the body, weighing between 1 and 2.3 kg.It is situated in the upper part of the abdominal cavity occupying the greater part of the right hypochondriac region, part of the epigastric region and extending into the left hypochondriac region.Its upper and anterior surfaces are smooth and curved to fit the undersurface of the diaphragm; its posterior surface is irregular in outline.The liver is enclosed in a thin inelastic capsule and incompletely covered by a layer of peritFolds of peritoneum form supporting ligaments attaching the liver to the inferior surface of the diaphragm. oneum.

8. The liver has four lobes. The two most obvious are the large right lobe and the smaller, wedge-shaped, left lobe. The other two, the caudate and quadrate lobes, are areas on the posterior surface.The lobes of the liver are made up of tiny lobules just visible to the naked eye.These lobules are hexagonal in outline and are formed by cubical-shaped cells, the hepatocytes, arranged in pairs of columns radiating from a central vein.Between two pairs of columns of cells, there are sinusoids (blood vessels with incomplete walls) containing a mixture of blood from the tiny branches of the portal vein and hepatic artery.Amongst the cells lining the sinusoids are hepatic macrophages (Kupffer cells) whose function is to ingest and destroy any foreign particles present in the blood flowing through the liver.Blood drains from the sinusoids into central or centrilobular veins. These then join with veins from other lobules, forming larger veins, until eventually, they become the hepatic veins which leave the liver and empty the inferior vena cava just below the diaphragm.

9. Functions of the liverSecretion of bile. The hepatocytes synthesize the constituents of bile from the mixed arterial and venous blood in the sinusoids. These include bile salts, bile pigments, and cholesterol.Carbohydrate metabolism. Conversion of glucose to glycogen in the presence of insulin, and converting liver glycogen back to glucose in the presence of glucagon. These changes are important regulators of the blood glucose level.Fat metabolism. Desaturation of fat i.e. converts stored fat to a form in which it can be used by the tissues to provide energy.Protein metabolism. Deamination of amino acids removes the nitrogenous portion from the amino acids not required for the formation of new protein; urea is formed from this nitrogenous portion which is excreted in the urine.It also breaks down the genetic material of worn-out cells of the body to form uric acid which is excreted in the urine.Transamination — removes the nitrogenous portion of amino acids and attaches it to other carbohydrate molecules forming new non-essential amino acids.

10. Synthesis of plasma proteins and most of the blood clotting factors from the available amino acids occur in the liver.Breakdown of erythrocytes and defense against microbes. This is carried out by phagocytic Kupffer cells (hepatic macrophages) in the sinusoids.Detoxification of drugs and noxious substances. These include ethanol (alcohol) and toxins produced by microbes.Metabolism of ethanol.Inactivation of hormones. These include insulin, glucagon, cortisol, aldosterone, thyroid and sex hormones.Synthesis of vitamin A from carotene. (Carotene is the pro-vitamin found in some plants, e.g. carrots and green leaves of vegetables).Production of heat. The liver uses a considerable amount of energy, has a high metabolic rate and produces a great deal of heat. It is the main heat-producing organ of the body.It is involved in the storage of:1- fat-soluble vitamins: A, D, E, K2- iron, copper3- some water-soluble vitamins, e.g. riboflavin, niacin,4- pyridoxine, folic acid, and vitamin B12.

11. Gastrointestinal TractThe Gastrointestinal System is responsible for the breakdown and absorption of various foods and liquids needed to sustain life. The GI tract starts with the mouth and proceeds to the oesophagus, stomach, small intestine (duodenum, jejunum, ileum), and then to the large intestine (colon), rectum, and terminates at the anus. You could probably say the human body is just like a big donut. The GI tract is the donut hole. Layers of the Gastrointestinal TractThere are 4 layers in gastrointestinal tract: from inside to outside these are :-Mucosa, Submucosa, Muscular layerSerosa.

12. Mucosa: The mucosa is the absorptive and secretory layer. It is composed of simple epithelium cells and a thin connective tissue. There are specialized goblet cells that secrete mucus throughout the GI tract located within the mucosa. On the mucosa layer there are Villi and Micro Villi.Submucosa: The submucosa is relatively thick, highly vascular, and serves the mucosa. The absorbed elements that pass through the mucosa are picked up from the blood vessels of the submucosa. The submucosa also has glands and nerve plexuses.Muscularis: The muscularis is responsible for segmental contractions and peristaltic movement in the GI tract. The muscularis is composed of two layers of muscle: an inner circular and outer longitudinal layer of smooth muscle. These muscles cause food to move and churn with digestive enzymes down the GI tract.Serosa: The last layer is a protective layer. It is composed of avascular connective tissue and simple squamous epithelium. It secretes lubricating serous fluid. This is the visible layer on the outside of the organs.

13. Hormones of Gastrointestinal Tract and their RolesThere are different hormones related to gastrointestinal system which plays important role in digestion of the food. These hormones are related to each other and in different pathological condition, their production may increase or decrease leading to derangement of digestive process. Some important hormones are :-

14. Hormones of gastrointestinal tract and their role

15. Classification of GI Hormones

16. Gastrin Family1- GastrinRelease is stimulated by presence of protein in stomach.Secretion inhibited by accumulation of acid in stomach.FunctionsActs in several ways to increase secretion of HCl and pepsinogen.Enhances gastric motility, stimulates ileal motility, relaxes ileocecal sphincter, induces mass movements in colon.Helps maintain well-developed, functionally viable digestive tract lining.Stimulate insulin secretionStimulate Exocrine pancreas secretion.Stimulate mass movement of large intestine.Stimulate Histamine secretion from ECL cells.Trophic (growth) effects on the mucosa of the small intestine, colon, and stomach.

17. 2- CHOLECYSTOKININ (CCK)Cholecystokinin (CCK) – Pancreozymin (PZ) is peptide hormone produced by I cells of the small intestine (duodenum > jejunum, ileum) and stimulates the digestion of protein and fats.FunctionsContraction of the gallbladder with simultaneous relaxation of the sphincter of OddiInhibits gastric emptyingStimulates secretion of pancreatic enzymes: lipases, amylase, and proteasesSecretion of bicarbonate from the pancreasTrophic effects on the exocrine pancreas and gallbladderCCK receptors are of two types mainly, CCK- A and CCK- B, CCK- A primarily located in GIT, and CCK- B primarily located in CNS. CCK also acts in hypothalamus inducing satiety and it augments effect of secretin for production of alkaline pancreatic juice. It also exerts tropic effect on pancreas.CCK secretion in enhanced by lipid >>> peptones, amino acids, CCK releasing factors.

18. Secretin Family1- SecretinSecretin is peptide hormone (27 amino acids) produced by S cells of duodenum and jejunum. It is stored as prosecretin. It stimulates secretion of fluid and bicarbonate from the pancreas. It acts through cAMP causing increase secretion of watery alkaline pancreatic juice.Inhibits gastrin, H+ secretion, and growth of stomach mucosaStimulates biliary secretion of bicarbonate and fluidSecretion of bicarbonate from the pancreasTrophic effect on the exocrine pancreas2- Gastric inhibitory peptide (GIP)– Inhibitory effects on gastric acid secretion– Glucose-dependent insulinotrophic peptide– Stimulates insulin release by pancreas

19. SOMATOSTATINSomatostatin /Growth hormone inhibitory hormoneThere are two forms of Somatostatin ( 14 and 18). Somatostatin 14 is primarily located in hypothalamus and Somatostatin 18 in GIT. Secretion is more in gastric lumen as compared to circulation and it acts through G protein coupled receptor. In GIT , it is secreted by D cells present in stomach, duodenum and pancreatic islet and is released in response to acid in stomach.It decreases:-Gall bladder contraction /Bile flowPancreatic secretion ( both endocrine and exocrine)Intestinal secretionGastric acid secretionMotilityAbsorption of glucose amino acids, triglycerides.

20. It increases:-Fluid absorption.It inhibits secretion from:Gastrin /SecretinVIP/GIPInsulin/GlucagonMotilin/Growth hormoneMotilinMotilin is 22 amino acids polypeptide secreted by enterochromaffin cells and Mo cells in the stomach, small intestine, and colon.Produces contraction of smooth muscle in the stomach and intestines in injection.Major regulator of the migrating motor complexes (MMCs) that control gastrointestinal motility between meals.

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