Basic Physiology - Digestive System PDF

27/05/2024 BPT 132 BASIC PHYSIOLOGY – DIGESTIVE SYSTEM SARA AGYEMANG ANTWI (Mrs.) 1 COURSE OBJECTIVES This course introduces the student to the structures and...

27/05/2024 BPT 132 BASIC PHYSIOLOGY – DIGESTIVE SYSTEM SARA AGYEMANG ANTWI (Mrs.) 1 COURSE OBJECTIVES This course introduces the student to the structures and functions of the digestive system. 2 2 1  27/05/2024 COURSE OUTLINE General introduction Anatomy of the Digestive system Individual structures Mouth, Oesophagus, stomach, Small intestines, Large intestines, Rectum, Anum. Innervation of the Digestive system Hormones related to the Digestive system Clinical Significance 3 3 INTRODUCTION The digestive system is made up of the gastrointestinal tract (GIT) and accessory organs (liver, pancreas and gallbladder). The GIT consists of mouth, esophagus, stomach, small intestine, large intestine, and anus. 4 2  27/05/2024 5 HISTOLOGY OF THE GIT Mucosa – which secretes gastric juices, absorbs nutrirents and protects tissues through mucus production. Single layer of epithelial tissue attached to a layer of connective tissue called lamina propria. Submucosa – holds blood, lymphatic and nervous tissues that serve to nourish, protect and communicate. Muscular layer – consists of circular and longitudinal muscle that contract and relax to make a wavelike motion called peristalsis. Serosa – the outermost layer, which consists of connective tissue covered by squamous epithelium. 6 3  27/05/2024 7 INTRODUCTION CONT’D Digestion: The process of breaking and resolving foods (large insoluble food molecules) in the digestive tract so they can be absorbed by the body. Absorption: Digested foods move cross the mucosa of alimentary tract and enter blood or lymph fluid. 8 4  27/05/2024 DIGESTION CONT’D Bacteria are present in the GI tract. They are also called microbiome or gut flora. They help with digestion. Parts of the nervous and circulatory systems help digestion to take place. Digestion is important because nutrients needs to be absorbed from the food and drinks we ingest daily for the body to work properly. 9 DIGESTION CONT’D Nutrients include; proteins, carbohydrates, fats, vitamins, minerals and water. The digestive system breaks these down into small units for the body to absorb and use for energy, growth and cell repair. Proteins break into amino acids Fats into fatty acids and glycerol Carbohydrates into simple sugars 10 5  27/05/2024 TYPES OF DIGESTION Mechanical Digestion: Breaking down the foods through the movement of digestive tract(grinding , agitating and pushing forward) Chemical Digestion: The process of decomposing the macro molecules of food into micro-molecule through the digestive enzymes, bile and stomach acid. 11 MOUTH tongue pushes the food into your throat. A small flap of tissue, called the epiglottis, folds over your windpipe to prevent choking and the food passes into your esophagus. 12 6  27/05/2024 MOUTH CONT’D There are 3 pairs of salivary glands that empty into the mouth Parotid glands – 25% Sublingual glands – 5% Submandibular glands – 70% Salivary glands are controlled by both the sympathetic and parasympathetic 13 14 7  27/05/2024 MOUTH CONT’D Salivary glands make saliva (pH near 7), a digestive juice which moistens food. Saliva contains;  Water – about 99.4% Electrolytes (Na+, K+, Cl-, HCO3-) to regulate osmotic pressure Glycoprotein Antibody (IgA) and Lysozyme Enzyme – amylase to digest carbohydrate Urea (a waste product) 15 MOUTH CONT’D Functions of saliva Salivary amylase breakdown starch to maltose. Saliva prevents inflammation and has some antibacterial effect by the lysozyme. Cleaning and lubrication to make swallowing easier. 16 8  27/05/2024 PHARYNX The throat is called Pharynx. It connects the oral and nasal cavities with the esophagus. The pharynx has three main parts. The nasopharynx The oropharynx Hypopharynx/Laryngopharynx The pharynx has two skeletal muscles lined with stratified squamous epithelium. 17 18 9  27/05/2024 ESOPHAGUS Brain signals the muscles of the esophagus and peristalsis begins. When food reaches the end of your esophagus, a ringlike muscle—called the lower esophageal sphincter or cardiac sphincter—relaxes and lets food pass into your stomach. This sphincter usually stays closed to keep what’s in your stomach from flowing back into your esophagus. 19 CLINICAL RELEVANCE Gastroesophageal reflux happens when the stomach contents come back into the esophagus. GERD (Gastroesophageal reflux Disease) is characterized by repeated GER. It causes symptoms of heartburn. It may develop when the lower esophageal sphincter becomes weak or relaxes when it should not. Lifestyle changes such as weight loss, eating meals 2- 3 hours before lying down can be combined with medicines or surgery to correct it. 20 10  27/05/2024 STOMACH The stomach lies below the diaphragm in the upper left region of the abdominal cavity. The stomach muscles mix the food and liquid with gastric juices. The stomach starts protein digestion. The stomach slowly empties its contents, called chyme, into your small intestine. 21 22 11  27/05/2024 STOMACH CONT’D The gastric glands found in the fundus and the body of the stomach are composed of; Mucous cells – produce alkaline mucous, which protects the stomach wall itself from being damaged by the acid. Parietal cells – produce HCl Chief cells – Produce pepsinogen. G-cells – Produces Gastrin hormone D-cells – secretes somatostatin 23 STOMACH CONT’D Gastric juice and its secretion Color: colorless, pH: 0.9～1.5, liquid with the lowest pH in the body Volume: 1.5～2.5L/D Components: hydrochloric acid, pepsinogen, mucus, intrinsic factor and HCO3-. 24 12  27/05/2024 STOMACH CONT’D Functions of HCl Activate the pepsinogen, provide suitable environment to pepsin(pH 2.0). Cause degeneration of proteins, and help pepsin to break down proteins( proteolysis). Promote the secretion of pancreatic juice, bile and Small intestinal juice Help small intestine mucosal cells to absorb iron and calcium 25 STOMACH CONT’D Pepsin/Pepsinogen Function： to break down protein Characteristic： inactive when it is secreted , requires activation; At pH＞６.0, it is inactive; it is secreted in small amounts and at stable rate 26 13  27/05/2024 STOMACH CONT’D Mucus and HCO3- The main component of mucus is glycoprotein, with higher glutinousness and gelating characteristics. The pH is neutral. The primary function of the mucosal bicarbonate secretion is to neutralize acid diffusing into the mucus gel layer and to be quantitatively sufficient to maintain a near- neutral pH at the mucus-mucosal interface. 27 STOMACH CONT’D Surface mucosa cells in the pyloric region secrete a thick, alkaline-rich mucus that protects the epithelium of the stomach and duodenum from harsh acid conditions of the lumen. This is known as the gastric mucosal barrier. These cells are stimulated by mechanical and chemical irritation and parasympathetic inputs. This protective mucus barrier can be damaged by bacterial and viral infection, certain drugs such as aspirin and NSAIDs 28 14  27/05/2024 INTRINSIC FACTOR Source: secreted by parietal cell. Effects: promote the absorption of Vitamin B12 by the terminal segment of the ileum. Clinical: when the parietal cells are damaged or decreased, megaloblastic anaemia may happen. 29 GASTRIC EMPTYING Concept: the process of chymus movement from stomach to duodenum Velocity: different with foods : H2O> starch>protein>fats Influential factor: Factors which can promote evacuation in stomach: intramural plexus local reflex and vagus -vagus reflex; gastrin. 30 15  27/05/2024 SMALL INTESTINE The small intestine has three parts. The first part is Duodenum – shortest part has fingerlike lumps called villi The middle part is Jejunum – has specialized absorptive cells (simple columnar epithelial) called enterocytes. The last part is the Ileum – absorbs B12, bile salts and left-over that were not absorbed by the jejunum. 31 32 16  27/05/2024 SMALL INTESTINE CONT’D The muscles of the small intestine mix food with digestive juices from the pancreas, liver, and intestine, and push the mixture forward for further digestion. The walls of the small intestine absorb water and the digested nutrients into your bloodstream. As peristalsis continues, the waste products of the digestive process move into the large intestine. 33 SMALL INTESTINES CONT’D The blood carries the absorbed nutrients to the liver where they are stored and processed and distributed to the rest of the body. The lymph system which carries white blood cells and lymph also absorbs fatty acids and vitamins. 34 17  27/05/2024 GIT HORMONES HORMONE FUNCTIONS STIMULUS FACTORS Gastrin (Stomach) 1. Promotes secretion of gastric acid 1. Breakdown product and propepsin. of protein 2. Promotes contraction of sinus 2. Vagus excitation ventriculi 3. Promotes mucosa growth of alimentary tract Secretin 1. Promotes secretion of pancreatic 1. Vagus excitation (Duodenum) fluid (water and bicarbonate) 2. HCl>protein 2. Promotes secretion of bile product>fatty acid Cholecystokinin 1. Promotes gallbladder contraction 1. Vagus excitation (CCK) and bile secretion 2. Protein (Duodenum) 2. Promotes enzyme secretion in product>fatty pancreatic juice acid>HCl Gastrin Inhibitory 1. Promote insulin secretion 1. Fats and Polypeptide 2. Inhibits gastric secretion and breakdown (Duodenum) gastrointestinal motility products 2. Saccharide, amino acid 35 DIGESTION IN THE SMALL INTESTINE Water and bicarbonates – neutralize gastric acid and protect the intestinal mucosa from erosion by gastric acid. Pancreatic amylase (diastase) – converts starch to maltose and glucose. Lipase – pancreatic lipase digests fats. Trypsin and chymotrypsin – helps to digest proteins. 36 18  27/05/2024 DIGESTION IN THE SMALL INTESTINE Gallbladder secretes bile. Bile does the following; Promotes fat digestion and absorption Promotes fat soluble vitamin absorption 37 ENTEROHEPATIC CYCLING After entering the small intestine, above 90% of the bile salt is absorbed by mucosa of terminal ileum. The bile salts then pass the portal vein to go back to the liver, then become the raw materials to form “new” bile. The “new” bile is then secreted into intestine. This process is named enterohepatic cycling of bile salts. 38 19  27/05/2024 LARGE INTESTINE The large intestine consists of Appendix, Cecum, Colon and rectum The appendix is a finger-shaped pouch attached to the cecum. The cecum is the first part of the large intestine The colon is the middle and largest part. It consists of the ascending, transverse and descending colon. The rectum is the end of the large intestine. 39 DIGESTION IN THE LARGE INTESTINE Secretion in the Large Intestine and Bacteria Activity The main components of the large intestine juice: mucous and supercarbonate. The main effects of the large intestine juice : protect the intestinal mucosa , lubricate stool. Bacteria in the large intestine “Normal” types of bacteria: coliform bacterium ,staphylococci etc, according microbial population concentrate style, each microbial population can restrict each other and propagate. Some bacteria can use food residue to synthesize vitamin B and vitamin k. The enzymes which produced by bacteria can breakdown food residue to produce poisonous matters such as marsh gas, ammonia etc. 40 20  27/05/2024 LARGE INTESTINES CONT’D Bacteria in the colon produce three vitamins; Vitamin K Biotin Vitamin B5 41 LARGE INTESTINES CONT’D Waste products from the digestive process include undigested parts of food, fluid, and older cells from the lining of your GI tract. The large intestine absorbs water and changes the waste from liquid into stool. Peristalsis helps move the stool into your rectum. The rectum stores stool until it pushes stool out of your anus 42 21  27/05/2024 43 ABSORPTION Absorption of iron - superior segment of the small intestine by active transportation. Absorption of calcium - small intestine , especially in the duodenum by active transport. Condition of calcium absorption: solubility calcium. Influential factors of calcium absorption ：Vitamin D & fatty acid can promote calcium absorption; Quantity of calcium absorption is influenced by the body requirement. 44 22  27/05/2024 45 46 23  27/05/2024 CLINICAL RELEVANCE Appendicitis is an inflammation of the appendix. Most common cause of acute abdominal pain requiring surgery and antibiotics. Left untreated, it can lead to peritonitis or abcess. Confirmed with abdominal ultrasound and the symptoms such as abdominal pain, vomiting, diarrhea or constipation, lack of appetite. 47 CLINICAL RELEVANCE Diarrhea is passing of watery stools 3-4times a day or more frequently than the individual’s defecation pattern. May be caused by infection of the GIT, food allergies and intolerances, GIT disorders. Treated with appropriate hydration (Oral rehydration salts, zinc and the appropriate anti-infectives). 48 24  27/05/2024 CLINICAL RELEVANCE Constipation is a condition in which there is fewer than 3 bowel movements in a week. The stools are hard, dry or lumpy and painful or difficult to pass. There is the feeling that not all the stool has passed. Lifestyle changes like food and liquid intake, being more active and some OTCs may help. Surgery may be recommended if there is a blockade. Constipation can also be caused by some medications. 49 INNERVATION OF THE GIT Autonomic Nerves The GI is also supplied by autonomic nerve system. Enteric Nerves These are nerves within the walls of the GIT. When food stretches the walls the nerves of the ENS release substances to speed up or delay the movement of food and the production of digestive juices. Somatic Nerves Oral cavity, superior extremity of the esophagus and external anal sphincter are controlled by somatic nerves. 50 25  27/05/2024 INNERVATION OF THE GIT The enteric nerves has Submucous and mucosal nerve plexus : mainly regulate secretion cells and blood vessels. Myenteric nerve plexus: mainly regulate smooth muscle cells. 51 52 26  27/05/2024 INNERVATION OF GIT The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulating GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. 53 INNERVATION OF THE GIT The parasympathetic system exerts its effects primarily via the vagus (innervates the esophagus, stomach, pancreas, upper large intestine) and pelvic nerves (innervates the lower large intestine, rectum, and anus.) The vagus nerve regulates tone and volume by activating the enteric motor neurons. 54 27  27/05/2024 LIVER Liver is an organ that  Detoxifies – inactivation or activation of some substances and drugs.  Deamination of amino acids and its conversion to urea.  synthesizes proteins – plasma proteins eg: albumin, globulins and fibrinogen.  produces chemicals needed for digestion – bile  Red blood cells are destroyed in the spleen and hemoglobin is broken down in the liver. The iron released is stored in the liver. Bile pigments are formed from the breakdown of hemoglobin.  Production of bile which is stored in the gallbladder.  Regulation of blood glucose – glucose is converted to glycogen for storage  Nutrients and vitamin metabolism  Production of cholesterol. 55 GALL BLADDER Gallbladder is a small sac The gallbladder serves as Storage of bile which leaves the liver via the common hepatic ducts and enters the duodenum via the common bile duct. Bile is a yellow-to-green substance containing bile salts, pigments, cholesterol, phospholipids and electrolytes. Bile helps to emulsify fats. 56 28  27/05/2024 PANCREAS Pancreas acts as an organ of the digestive system and the endocrine system. As an endocrine gland, it secretes hormones such as insulin, glucagon, somatostatin and pancreatic polypeptide. As an exocrine gland, it secretes pancreatic digestive enzymes. The pancreatic enzymes secreted into the duodenum is alkaline (pH 8) which neutralizes the acidic chyme. 57 PANCREAS CONT’D The acini glands of the pancrease produces 1- 1.5L of juice daily. Pancreatic juice consist of; Amylase – digest carbohydrates Lipase – digests fats Trypsin and Chymotrypsin – digests protein 58 29  27/05/2024 59 CLINICAL RELEVANCE Pancreatitis is the redness and swelling (inflammation) of the pancreas. Happens when the digestive juices or enzymes attack the pancreas. Pancreatitis can be acute or chronic Caused by alcohol abuse. Solid lumps (gallstones) can block the ducts. Belly injury or surgery, high levels of calcium or fats in the blood can also cause it. Tumor can also cause it. It is diagnosed by Ultrasound or CT scan. Treated with IV fluids, pain medicines and antibiotics. Then surgery to remove gall stones or tumor. 60 30  27/05/2024 THANK YOU 61 31