Human Biology Lecture 10: Digestive System PDF

Human Biology Lecture 10 : Digestive system The Digestive System: the consumed food consists of protein, fat, complex carbohydrates. macromolecules should convert into the simple molecules food conversion into nutrients by processes of digestion & absorption. food particles are broken down to smalle...

Human Biology Lecture 10 : Digestive system The Digestive System: the consumed food consists of protein, fat, complex carbohydrates. macromolecules should convert into the simple molecules food conversion into nutrients by processes of digestion & absorption. food particles are broken down to smaller components ( digestion ). consuming more food energy than is used in activity leads to storage of the excess in the form of fat deposits. Result in rise obesity and diseases like type 2 diabetes. DIGESTIVE SYSTEM 1. Digestive tract ( from mouth to anus) 2. Accessory organs (teeth, salivary glands, liver, pancreas, gall bladder) Layers of digestive tract: Mucosa : Innermost layer, moist membrane surface epithelium, small amount of connective tissue (lamina propria) Small smooth muscle layer Submucosa: beneath submucosa, soft connective tissue with blood vessels, nerve ending, lymphatics Muscularis externa: smooth muscle Serosa: outermost layer Layers of digestive tract: Oral cavity : ❖ mucus in saliva that moistens food and buffers the pH of the food. ❖ Saliva contains lysozyme (has antibacterial action.) ❖ Saliva contains salivary amylase enzyme (begins the process of converting starches in the food into a maltose disaccharide). ❖ lipase enzyme produced by tongue cells to break down fats. ❖ Bolus mass result from the chewing and wetting action by the teeth and saliva Oral cavity : ❖ The tongue helps in swallowing moving the bolus from the mouth into the pharynx. ❖ The pharynx opens to two passageways: the esophagus leads to the stomach & the trachea leads to the lungs. ❖ The epiglottis is a flap‒like structure covers the tracheal opening during swallowing to prevent food from entering the lungs. Esophagus : ❖ a tubular 20 cm organ connects the pharynx to the stomach. ❖ The chewed and softened food (i.e. the bolus) passes through the esophagus after being swallowed. ❖ The smooth muscles of the esophagus undergo peristalsis (contractions) that pushes the food toward the stomach. ❖ The peristaltic wave is unidirectional it moves food from the mouth the stomach, and reverse movement is not possible, except in the case of the vomit reflex Esophagus : ❖ The peristaltic movement of the esophagus is an involuntary reflex ❖ Sphincter is a ring-like muscles structure ( valves in the digestive system). ❖ Cardioesophageal sphincter between esophagus& stomach Esophagus : ❖ In response to swallowing and the pressure exerted by the bolus of food, this sphincter opens, and the bolus enters the stomach. ❖ Acid reflux or heartburn occurs when the acidic digestive juices escape back into the esophagus and the low pH irritates the unprotected surface. Stomach : ❖ A saclike J shape organ that secretes gastric digestive juices. ❖ Protein digestion is carried out by an pepsin enzyme ❖ The highly acidic environment (pH between 1.5 and 2.5) kills many microorganisms in the food and, combined with the action of enzyme pepsin, results in the catabolism of protein in the food. ❖ Chemical digestion is facilitated by the churning action of the stomach caused by contraction and relaxation of smooth muscles. Stomach : ❖ Chyme is the partially digested food & gastric juice mixture ❖ Themovementofchymefromthestomachinto the small intestine is regulated by hormones, stomach distension and muscular reflexes that influence the pyloric sphincter. ❖ The stomach lining is unaffected by pepsin and the acidity because pepsin is released in an inactive form (pepsinogen) that is activated by the low pH and the thick mucus lining that protects the underlying tissue (rugae is internal folds of mucosa)) Stomach : ❖ ❖ ❖ ❖ ❖ ❖ chemical digestion of starches & fats ↓ in stomach Gastric cell secrete gastric juice Chief cell produce pepsinogens Parietal cells produce HCL Endocrine cells produce gastrin Gastric emptying occurs within two to six hours after a meal. Small Intestine : ❖ the digestion of protein, fats, and carbohydrates is completed here. ❖ The small intestine is a long (over 6 meters) tube-like organ with a highly folded surface containing finger-like projections (the villi) ,with many microscopic projections microvilli on top surface , epithelial cells at the surface of them absorb nutrients from the digested food and release them to the bloodstream on the other side. Small Intestine : Small Intestine : ❖ three parts: the duodenum, the jejunum and the ileum. ❖ The pyloric sphincter between duodenum and the stomach ❖ The chyme is mixed with pancreatic juices, an alkaline/basic solution rich in bicarbonate that neutralizes the acidity of chyme from the stomach and creates an appropriate environment for enzymes ❖ Pancreatic juices contain digestive enzymes (amylase, trypsin, and lipase) that break down starches, proteins, and fats, respectively. Small Intestine : ❖ Bile is produced in the liver and stored and concentrated in the gallbladder; enters the duodenum through the bile duct. ❖ Bile contains bile salts,which make emulsification so lipid will be accessible to the water-soluble enzymes. Bile keeps fat droplets from coming back together again, thus increasing the surface area available to lipase. ❖ The wall of the small intestines secrete disaccharidases enzymes , faciltate digestion of disaccharides (e.g. maltose, sucrose, and lactose) into their respective monosaccharides. Small Intestine : ❖ ❖ ❖ ❖ ❖ ❖ Absorb 80% ingested water Vitamins Minerals CHO (monosccharides) Proteins (amino acid) lipids Large Intestine : ❖ The undigested food is sent to the colon from the ileum via peristaltic movements. ❖ ileocecal valve between ileum and large intestine beginning. ❖ The vermiform, worm-like, appendix (accumulation of lymphatic tissue)is located at the ileocecal valve. The appendix of humans has a minor role in immunity. ❖ The large intestine reabsorbs the water from indigestible food material and processes the waste material ❖ much smaller in length (1.5 m) compared to the small intestine but larger in diameter Large Intestine : ❖ It has three parts: the cecum, the colon, and the rectum. ❖ many bacteria or intestinal flora that aid in the digestive processes found at colon. ❖ The colon has four regions, the ascending colon, the transverse colon, the descending colon and the sigmoid colon. ❖ The main functions of the colon are to extract the water and mineral salts from undigested food, absorb vitamin B ,K and to store waste material Large Intestine : ❖ The rectum stores feces until defecation. ❖ The feces are propelled using peristaltic movements during elimination. The anus is an opening at the far-end of the digestive tract and is the exit point for the waste material. ❖ Two sphincters regulate the exit of feces, the inner sphincter is involuntary and the outer sphincter is voluntary. Large Intestine : Accessory Organs : ❖ Not part of food path ❖ Accessory organs add secretions and enzymes that break down food into nutrients. ❖ include the teeth ,salivary glands, the liver, the pancreas, and the gall bladder. ❖ The secretions of the liver, pancreas, and gallbladder are regulated by hormones in response to food consumption. ❖ The liver produces bile Accessory Organs : ❖ The liver processes the absorbed vitamins and fatty acids. ❖ The liver filter toxins and waste. ❖ The gallbladder aids the liver by storing bile and concentrating bile salts. ❖ The pancreas secretes bicarbonate that neutralizes the acidic chyme and a variety of enzymes (trypsin, amylase, and lipase) for the digestion of proteins, carbohydrates, and fats, respectively. Accessory Organs : Nutrition : During digestion, digestible carbohydrates broken down into glucose and used to provide energy within the cells of the body. humans do not produce the enzyme necessary to digest cellulose (fiber). intestinal flora able to extract some nutrition from plant fibers. excess sugars in the body are converted into glycogen and stored for later use in the liver and muscle tissue to used in prolonged exertions and to provide energy during food shortage. Nutrition : Fats are stored for insulation and energy reserves. Proteins in food are broken down into amino acid the essential nutrients are the nutrient that must be eaten, because the body cannot produce them. Essential nutrients include some fatty acids, some amino acids, vitamins, and minerals.