Gastrointestinal Tract Presentation PDF

University of Babylon Hammurabi Medical college Gastrointestinal tract  Structural & functional adaptations of the digestive Structural & functional adaptations of the digestive system system  OBJECTIVES 1. Outline functio...

University of Babylon Hammurabi Medical college Gastrointestinal tract  Structural & functional adaptations of the digestive Structural & functional adaptations of the digestive system system  OBJECTIVES 1. Outline function & a general structural plan of the digestive tract. 2. Introduce some regional variations in structure that relate to functional. 3. describe the fluid balance of the gut. 4. Describe properties of hormonal and enteric nervous system.  Function of GIT system ► Digestion allows food to be converted to a sterile, neutral, and isotonic structure containing small sugars, amino acids, small peptides, small particles of lipids and other small molecules. This is now ready for absorption and excretion ,which is accomplished by the action of HCl , bile and a variety of enzymes secreted by exocrine glands – secretion Motility the contractions of the smooth muscles in the walls of the tract, mix and move the ingested food from mouth to anus. Absorption products of digestion are then taken into the blood. Initial physical disruption 🡪 Ingestion and transport to storage 🡪 Initial chemic disruption and creation of suspension (chyme) 🡪 Disinfection 🡪 Controlled release of Chyme 🡪 Dilution and neutralisation 🡪 Completion of chemical breakdown 🡪 Absorption of nutrients and electrolytes 🡪 Final absorption of water and electrolytes 🡪 Producing faeces for controlled excretion.  Digestion ► The process of digestion can be divided into : ❖ The non-specific phase involves making the larger food particles physically smaller. ❖ the specific phase breaks down the food molecules chemically via specific enzymes to smaller molecules. ► This process involves the production of chyme, ► Chyme: which is a semiliquid form of ingested food & it is sterile due to the action of the stomach acid on any ingested microbes. Digestion  Absorption ► Absorption is the specific (active or passive) uptake of nutrients molecules, water, and electrolytes. ► Fluid passes very slowly through the small intestine and the small intestine also has a very high surface area due to the villi and microvilli, allowing for greater rate of absorption. ► In the large intestine, the remaining water and electrolytes are absorbed. The slow transit through the large intestine allows water to be reabsorbed by the gut and leaves dry faeces to accumulate in the sigmoid colon and anal canal. Small intestine absorbs about (12.5 L )of the fluid, Large intestine absorbs about 1.5 L.  Excretion ► Faeces are propelled periodically into the rectum, causing an urge to defecate. When the sphincters relax around the anus, the faeces are expelled. ► it is easy to understand why diarrhoea and vomiting are major causes of dehydration as water added to the solution is lost before being reabsorbed. There will also be GI disturbances such as constipation as a result. broad functions of the various regions of the GI tract Mouth and Oesophagus ► Mastication ► Saliva production 1. Protects mouth Wets / Bacteriostatic / Alkaline / High Ca2+ 2. Lubricates food for mastication and swallowing Wet / Mucus 3. Starts digestion Sugars ► Swallowing ► Formation of bolus ► Rapid oesophageal transport Stomach Storage Relaxes to accommodate food Initial disruption Contracts rhythmically to mix and disrupt Secretes acid and Proteolytic enzymes to break down tissues & disinfect as Chyme Delivers Chyme slowly into the Duodenum Duodenum Dilution and neutralisation of Chym o Water drawn in from ECF. Stomach impermeable, Duodenum permeable. o Alkali (bile) added from Liver and Pancreas o Enzymes added from pancreas  Balance of gut Description Water in GI tract lumen Eat 1kg a food per day 1L Add 1.5l of saliva 2.5L Add 2.5l of gastric secretion 5L Addition of 9l of fluid for isotonic and neutral 14L Small intestine absorbs 12.5l of water 1.5L Large intestine absorbs 1.35l 0.15 L Remaining in faeces 0.15kg  Small Intestine ❖ Absorption of nutrients & electrolytes o Fluid passes very slowly through the small intestine o Large surface area o Epithelial cells absorb molecules, some actively some passive o Often coupled to Na+ ,absorption pass into hepatic portal circulation (first pass…) ❖ Absorbs the majority of water (1.5L vs. 0.15L large intestine)  Large Intestine Final absorption of water (0.15) Very slow transit Faeces form and accumulate in the descending and sigmoid colon  Rectum Faeces propelled periodically into rectum Urge to defecate Controlled relaxation of sphincters and expulsion of faeces Enteric nervous system and its relationship to the autonomic nervous system The enteric nervous system is a subdivision of the autonomic nervous system that directly controls motility the GI system. The enteric nervous system is made up of two nerve plexuses in the wall of the gut which may act independently of the CNS (short reflex pathway). Parasympathetic control is the most significant. It coordinates both secretion and motility using a range of neurotransmitters. Hormonal Activations ► A dozen or more peptide hormones are released by endocrine cells in the walls of the gut. Some of these 1. -hormone with a paracrine action, 2. - hormone with true endocrine action. hormones comprise 2 structurally related "groups" : gastrin group and secretin group. ► These hormones are released from one part of the gut to affect the secretions or the motility of other parts. THANK YOU