Digestive System PDF

Digestive system Dr. Udeshika Yapa Bandara BSc. (Hons) Human Biology (USJP), PhD (UOC) Learning Outcomes At the end of the session, you should be able to: List the parts of the digestive tract Describe the functions of oesophagus, stomach, liver, gall bladder, intestines describe me...

Digestive system Dr. Udeshika Yapa Bandara BSc. (Hons) Human Biology (USJP), PhD (UOC) Learning Outcomes At the end of the session, you should be able to: List the parts of the digestive tract Describe the functions of oesophagus, stomach, liver, gall bladder, intestines describe mechanical digestion describe chemical digestion describe the digestive functions of the small intestine and its secretions outline how nutrients are absorbed in the small intestine Main Function of the GIT - Supply the body with nutrients and water Nutrients required by cells are - Large quantities of carbohydrates - Monosaccharides (Glucose & Fructose) - Fats (Glycerol & Fatty acids) - Proteins (Amino acids) - Small amounts of vitamins & minerals Digestion - Process of breaking down of food into small particles enough to be absorbed by -Mechanical digestion -Chemical digestion  Digestion Phases Include 1. Ingestion 2. Movement 3. Mechanical and chemical digestion 4. Absorption 5. Elimination Mechanical digestion in the mouth Teeth Break up food into smaller pieces - Which provides larger surface area to act digestive chemicals - Easy to swallow Saliva Food Mix with saliva (bolus) Easy to swallow Starch & glycogen Amylase Maltose Deglutition (Swallowing) 1. Oral Phase – Bolus moves from oral cavity into the oropharynx; voluntary process 2. Pharyngeal Phase - Bolus moves from the oropharynx into the oesophagus; involuntary process 3. Oesophageal phase - Bolus moves through the oesophagus and into the stomach; involuntary process  Functions of oesophagus Transfer of food from mouth to stomach Prevent regurgitation of gastric content by lower oesophageal sphincter (LOS) Prevent regurgitation of oesophageal content into respiratory passage by UOS Secretion of mucus by compound and simple mucous glands Gastro – oesophageal reflux Due to weakness of LOS leading to reflux of the acidic gastric content to the lower part of the oesophagus Risk factors: Obesity Pregnancy Smoking Connective tissue disorder (Scleroderma) Hiatal hernia Delayed emptying of stomach Functions of stomach Temporary storage – allowing time to act digestive enzymes like pepsin Chemical digestion – pepsin breaks proteins into polypeptides Mechanical breakdown Limited absorption (Alcohol, drugs) Non specific defence against microbes Preparation of iron for absorption Production and secretion of intrinsic factors needed for absorption of Vit. B12 Regulation of the passage of gastric content into duodenum Gastric mucosal barrier A compact epithelial cell lining A special mucous covering Protects the cells from contents of the stomach Luminal membranes of cells are impermeable to protons Cells are tightly adjoined Rapid turnover If damaged, peptic ulcer may result  Chemical digestion in the stomach Mucus Main components of gastric juice are; - Sticky - Mucus, Pepsin, HCL, Water - Alkaline secretion - Protects GIT from damage by the other gastric secretions Pepsin - An enzyme - Helps to digest proteins Large protein Short strands of AA HCl Pepsinogen Pepsin Control of gastric secretions See/Smell/Taste Food - Brain via parasympathetic nerve Gastric juice Gastrin (From gastric glands) (From stomach &SI) Gastrin production enhanced when - food is present in the stomach - pH of the stomach contents - parasympathetic nerves send signals  Food mixed with gastric juice - Chyme (partially digested CHO & proteins) Peristaltic movements of stomach force small amounts of chyme through the pyloric sphincter, into SI Chemical digestion completes in SI Chemical digestion in the SI Pancreatic juice - Polysaccharides Amylase Disaccharide (Maltose) - Fats Lipase Glycerol & Fatty acid - Long chains of amino acid Peptidases Short chains of AA - Sodium bicarbonate Neutralize acidity of chyme Bile - Consists with water, bile salts, cholesterol, bilirubin & other substances - Bile salts help to digest fats Intestinal enzymes - Peptidase - Completes the digestion of peptides to AA - Lipase - Completes the digestion of fats to glycerol & fatty acids - Sucrase, Maltase & Lactase - Digest disaccharide to monosaccharides (Glucose & Fructose) Pancreatic juice - Release pancreatic juice when arrival of chyme - Two components i. Digestive enzymes Amylase, Lipase & Peptidase ii. Alkaline secretion Contains sodium bicarbonate which neutralize the acidic chyme Absorption in the SI - CHO Glucose & fructose, absorbed via carrier proteins, active or passive - Proteins AA, enter brood via active transport mechanisms - Fats Glycerol & fatty acids, diffuse across the epithelial layers to the lacteals & transported through lymphatic system and enter the blood - Water, electrolytes & vitamins Large intestine - Very little digestion - Absorb water and electrolytes from the chyme - Formation and storage of faeces - Stretch receptors in sigmoid colon & rectum trigger the reflex Strong peristaltic movements Opening of the anal sphincters Faeces excrete from the body Vomiting reflex  Liver and gall bladder Functions of liver- Removing metabolic waste products Producing bile to aid in digestion Processing nutrients absorbed from the digestive track Storing glycogen, certain vitamins, minerals Maintaining normal blood sugar Synthesizing plasma proteins, albumin, clotting factors Producing immune factors and removing bacteria Removing senescent RBC from the circulation Excreting bilirubin Functions of gall bladder Regulate equalization of pressure in biliary system Effect on pH of bile Concentration of bile – becomes thicker, viscous and darker Storage of bile – (30-50 mL) Secretion of bile Functions of bile Most of the functions of bile due to presence of bile salts. Digestive function Absorptive function Excretory function Laxative action Antiseptic action (unconjugated bile acids) Maintenance of pH in GI tract Prevention of gallstone formation (cholelithiasis) Lubrication function Question 1. 24 years old Nimal had a lunch with rice, pork and green beans and green leaves. Outline the digestion of complete meal of Nimal.