Lect 7 Small Intestine.pdf

Introduction, Anatomy, and Physiology Overview of the Lower GI Chapter 15 Lecture # 7 Lower GI Anatomy Small Intestine Duodenum Jejunum Ileum Large Intestine Transverse Ascending Descending Lower GI Rectum Anus Lower GI Functions • • • • Motility Secretion Digestion Absorption Small Intes...

Introduction, Anatomy, and Physiology Overview of the Lower GI Chapter 15 Lecture # 7 Lower GI Anatomy Small Intestine Duodenum Jejunum Ileum Large Intestine Transverse Ascending Descending Lower GI Rectum Anus Lower GI Functions • • • • Motility Secretion Digestion Absorption Small Intestines Anatomy • Maximum surface area for digestion and absorption – Folds of Kerckring – Villi – Microvilli – brush border A cell of intestinal lining • Specialized enterocytes from stem cells of crypts ‫الخاليا املعوية املتخصصة من الخاليا الجذعية الخبايا‬ – High turn over = high nutrient need Small Intestine Motility • Hormonal stimulation – gastrin • Peristaltic reflex – segmental contractions • Mixing of chyme Small Intestine Secretions • Other hormones: CCK, secretin • Own secretions + digestive enzymes, • CCK, gastrin, and secretin stimulate release of - Bicarbonate – neutralizes gastric HCL – Bile – emulsifies fat • Other small intestine secretions include – 1.5 liters of intestinal “juices” – water and mucous Gastrointestinal Hormones Small Intestine Digestion • Starch digestion – Pancreatic amylase, Lactase, alpha-dextrinase, sucrase, maltase, and glucosidase from brush border • Protein digestion – Trypsinogen, chymotrypsinogen,procarboxypeptidases, and elastase – Enterokinase from brush border • Lipid digestion – Pancreatic lipase, and colipase – Bile Small Intestine Absorption • Active transport utilizing Na/K pump at brush border – Glucose, galactose, and amino acids • Facilitated diffusion – Fructose • Paracellular route – Glucose (in part) • These end products enter the liver via the portal vein Small Intestine Absorption – Lipids and Nutrients • Lipids enter lymph via passive diffusion – First converted to micelles and packaged as chlylomicrons – Steatorrhea – if lipid not absorbed B12 absorbed only at specific sites in ileum Sites of Nutrient Absorption Anatomy of the Large Intestine • Ascending, transverse, descending, sigmoid colon – Nearly straight rather than curved like small intestine – No villi or microvilli – Crypts produce specialized epithelial cells including goblet cells Large Intestine Anatomy Large Intestine Motility • Haustration – Circular muscles forms small sacs (haustra) • Propulsion • Mass movement • Defecation ‫الدفع‬ ‫حركة الكتلة‬ ‫التغوط‬ Haustration Segmentation, also known as haustration occurs in the large intestine Segmentation moves food backwards and forwards in a local intestinal segment. This type of intestinal motility enhances mixing of the food with enzymes and mucus Large Intestine Secretions • Goblet cells produce mucus • Potassium and bicarbonate Large Intestine Digestion & Absorption • No enzymatic digestion occurs • Reabsorption of water, electrolytes, some vitamins • Formation and storage of feces – Insoluble fiber and bilirubin – 400 species of bacteria – Fermentation of fiber and sugar alcohols Digestion and Absorption Fermentation • Fermentation produces SCFA (acetate, propionate and butyrate) and lactate • Energy produced used by bacteria, for tissue growth in colon or utilization in body • Excess substrate results in gas, flatulence Digestion & Absorption – Maintaining Balance • Maintaining balance of intestinal flora – – – – Resistant starches Prebiotics Probiotics Synbiotics • Vitamin K and biotin – endogenously produced ‫تُنتج داخليًا‬ Pre and Probiotics • Pro – Products containing microorganisms manufactured and sold as food products and supplements • Live active cultures • Expressed as colony forming units - CFU – Suppress the inflammatory response – Contribute to a healthy microflora ‫املساهمة في البكتيريا الصحية‬ – Examples • Lactobacillus acidophilus and Lactobacillus helveticus (bulgaricus), Lactobacillus GG – Food Sources • Yogurt, kefir, buttermilk Pre and Probiotics • Prebiotics – Substances found in food that stimulate the beneficial flora of the large intestines – Increases production of SCFA – Examples • • • • Inulin, fermentable fiber oligosaccharides Resistant starch (potatoes, bananas and some legumes) – Food sources • Bread, cereals and pastas Bacterial Overgrowth • Definition – Resulting from cross contamination of bacteria from colon to small intestine • Pathophysiology – Motility of GI tract delayed – Bacteria competes with host for nutrients Bacterial Overgrowth – Clinical Manifestations and Treatment • Clinical manifestations ‫سوء الهضم‬ – Maldigestion, malabsorption, and weight loss • Treatment ‫املضادات الحيوية واسعة الطيف‬ – Broad spectrum antibiotics Summary • Anatomy of the lower GI includes the small and the large intestines as well as the rectum. • Functions of the small intestines includes motility, secretions, digestion and absorption. • The major site for digestion and absorption is the small intestines • Knowing about the anatomy and physiology will be helpful when trying to make recommendations