GIT Seminar 1 PDF

DIGESTIVE SYSTEM Gastrointestinal tract- part 1  GIT FUNCTION GIT is responsible for breaking down food and supplying the body with water and many nutrients essential for life. Before nutrients can be used they should be ingested, digested and absorbed. Ingestion: p...

DIGESTIVE SYSTEM Gastrointestinal tract- part 1  GIT FUNCTION GIT is responsible for breaking down food and supplying the body with water and many nutrients essential for life. Before nutrients can be used they should be ingested, digested and absorbed. Ingestion: placing into the mouth, chewing the food into smaller pieces, moistening with saliva and swallowing. Digestion: breaking down the food into small parts and degradation with enzymes into useful nutrients. Absorption: transport of nutrients from the bowels through blood to all body organs. SALIVARY GLANDS  SALIVA Chewing has both voluntary and involuntary components. Chewing center is in the brain stem. Chewing allows to mix food with saliva which enables easy swollowing. Saliva is produced ( app. 1000 ml daily) in 6 salivary glands and has digestive and protective functions. Saliva’s pH is app.7 (neutral). Saliva contains also organic compounds: α-amylase, lingual lipase, mucin glycoproteins. It contains also 2 antibacterial factors: muramidase lysing bacterial wall and lactoferrin that binds iron depriving microbes of sources of iron essential to their growth.  BALANCE IN GIT FLUID INPUT FLUID OUTPUT Food and drinks-2,0 l Absorption-small bowel-7,5 l large bowel- 1,5 l Secretion- saliva-1,5 l Excretion - faeces- app. 100 gastric juice-2,0 l ml bile- 0,5 l pancreatic juice-1,5 l intestinal juice- 1,5 l Total 9,0 l Total 9,0 l  SWALLOWING Three phases of swallowing: oral, pharyngeal, esophageal. LES- LOWER ESOPHAGEAL SPHINCTER- REFLUX ACHALASIA  STOMACH The three functional regions of the stomach. The regions have different secretions and patterns of smooth muscle activity.  GASTRIC SECRETION Gastric cell types: 1/ Mucous neck cells- mucus 2/ Peptic cells (main cells) –pepsynogen, rennin 3/ Parietal cells- HCl, intrinsic factor-IF 4/ Endocrine cells- gastrin, ghrelin, somatostatin, serotonin, histamine  GASTRIC SECRETION Mucus- covers and protects against harmful action of HCL and e.g. drugs Pepsinogen- is inactive enzyme essential for peptide absorption Small amount of amylase and lipase Hormones - gastrin, somatostatin , ghrelin Intrinsic factor- binding vitamin B12 HCL-contributes to protein digestion by supplying H+ which activates pepsynogen-the precursor to pepsin. Without adequate HCl secretion, larger fragments of proteins enter the small intestine and may compromise the efficacy of digestive processes. It also serves as a barrier against harmful microorganisms that may enter the digestive system through ingested food.  HCL SECRETION-PROTON PUMP Proton pump is integral membrane protein in parietal cells. By using ATP an acidic hydrogen ion replaces non-acidic potassium ion. Potassium follows through channels and hydrogen ion is pumped out in exchange for potassium via proton pump (potassium is recycled).  GASTRIC SECRETION Gastric secretion is stimulated by neural, paracrine and endocrine mechanisms. Acetylcholine - HCl secretion, mucus, pepsinogen, and gastrin Histamine - HCl secretion Gastrin - HCl secretion (1500x more powerful compared to histamine) HCL SECRETION CONTROL  HCL SECRETION CONTROL Protection against HCL is provided by mucous layer of stomach. DISRUPTION OF GASTRIC MUCOSAL BARRIER GASTRIC SECRETION  GASTRIC SECRETION CONTROL Gastrin releasing peptide (GRP)- stimulates gastrin release from G-cell Somatostatin - inhibits gastrin release from G-cell Antrum acidification - pH < 3 inhibits gastrin release Small peptides and amino acids - directly stimulate gastrin release form G-cel.  GASTRIN Gastrin has 4 molecular forms: G-4, G-14, G-17 and G-34. Response to meal large amounts of G-17 are released from antrum and small amounts of G-34 are released from duodenum. G-34 acts as a stymulator of regeneration for mucous membrane of the whole GIT Stimulation of gastrin release: 1. protein digestion products 2. nervous stimulation; physical distention Inhibition of release: acidification of antrum.  PEPTIC ULCER DISEASE Complication s of the disease: 1/ bleeding 2/ perforation 3/ cancer  HELICOBACTER PYLORI H. pylori is found in app.100% patients with gastric ulcer (when alcohol, aspirin, NSAIDS are eliminated) It is a Gram- negative bacterium with a high urease activity H. pylori can withstand acid environment and damages epithelial cells. It is strictly associated with a high risk of gastric cancer in future. GASTRINOMA INTRINSIC FACTOR MEGALOBLASTIC ANEMIA  SMALL BOWEL Average adult length of app. 7m. Three parts: duodenum, jejunum and ileum. Absorbtion of vitamin B12, bile salts and ingested nutrients. Movement the intestinal contents—consisting of gastric and pancreatic juices and bile and partly digested food—along the GIT into the large intestine. Peristaltic movements.  DUODENUM The first part of lower GIT. It has ampulla of Vater where main pancreatic duct and bilary duct end.  LARGE BOWEL FUNCTION The large intestine includes the colon, rectum and anus. Functions: 1/ absorption of water and electrolytes, 2/ production and absorption vitamins, 3/ formation of feces and moving it toward the rectum for elimination 4/ housing beneficial bacteria that aid in the breakdown of remaining undigested food particles and can synthetize vitamins, 5/ elimination waste products from the body: undigested food, bacteria and toxins.  HIRSCHPRUNG’S DISEASE It is a congenital disorder associated with constipation, large colon, and narrowed segment of colon in the rectum. Histologic examination of this narrowed segment reveals an absence of ganglion cells from both submucosal (or Meissner’s) and myenteric (or Auerbach’s) plexuses. The basic defect is due to arrest of the caudal migration of neural crest cells, which are precursors of ganglion cells. The patient’s constipation and resulting megacolon are secondary to failure of this „aganglionic” segment to relax in response to proximal distention. HIRSCHPRUNG’S DISEASE  MICROBIOME- BACTERIA IN LARGE BOWEL It is now well established that a healthy gut flora is largely responsible for overall health of the host. Majority of the gut bacteria are non-pathogenic and, exist with the bowel cells (enterocytes) in a symbiotic relationship. Functions: 1/ fermentation of food and vitamin production 2/ protection against pathogens and toxins 3/ stiumlation of immune response MICROBIOME  ENTERIC NERVOUS SYSTEM- ENS C ON T R OL AN D R E GU L AT I ON OF GI T 1/ intrinsic neurons- 2 nerve plexus and glial cells within the wall of GIT 2/ neurotransmitters and neuromodulators- serotonion, nitric oxide, vasoactive intestinal peptide 3/diffusion barrier- created by capillars- similar to BBB in CNS 4/ short reflexes 5/long reflexes-transmission through a sensory nerves to the CNS; then it’s integrated and acted on Neuron network is its own intergrating center- reflexes begin and end in GIT- ”little brain”.  GIT MOTILITY S T OM AC H 1/ Hunger contractions are the first contractions to appear in the empty stomach, when the tone of the gastric muscles is low. Each contraction lasts for about 20 seconds. The interval between contractions is about 3 to 4 seconds. 2/ Receptive relaxation is the relaxation of the upper part of the stomach when food enters the stomach from esophagus. It involves the fundus and upper part of the body of stomach. Its significance is to accommodate the food easily, without much increase in pressure inside the stomach. 3/ When food enters the stomach, the peristaltic contraction or peristaltic wave appears with a frequency of 3 per minute. It starts from the lower part of the body of stomach, passes through the pylorus till the pyloric sphincter. 4/ This digestive peristalsis because it is responsible for the grinding of food particles and mixing them with gastric juice for  GIT MOTILITY S T OM AC H Food that is swallowed enters the stomach and remains there for about 3 hours and then is emptied from stomach into the intestine slowly, with the help of peristaltic contractions. It takes about 3 to 4 hours for emptying. This slow emptying is necessary to facilitate the finaI digestion and maximum (about 80%) absorption of the digested food materials from small intestine.  GIT MOTILITY S M A L L BOW E L Movements of small intestine are essential for mixing the food with digestive juices, propulsion of food and absorption. The contractions occur at regularly spaced intervals along a section of intestine. The segment of the intestine involved in each contraction is about 1 to 5 cm long. The segments of intestine in between the contracted segments are relaxed. Peristaltic contractions start at any part of the intestine and travel towards anal end, at a velocity of 1 to 2 cm/sec.  GIT MOTILITY L AR GE BOW E L Mixing movements Mass movements-these movements usually occur only one to three times each day. A mass movements are a modified type of peristalsis. Irritation in the colon can also initiate intense mass movements. Appearance of mass movements after meals is facilitated by gastrocolic and duodenocolic reflexes. These reflexes result from distention of the stomach and duodenum. GIT MOTILITY  MOTILITY IN FASTING-MMC Migrating motor complex is a type of peristaltic contraction, which occurs in stomach and small intestine during the periods of fasting for several hours. It is also called migrating electric complex. It is different from the regular peristalsis because a large portion of stomach or intestine is involved in the contraction. The contraction extends to about 20 to 30 cm of stomach or intestine. This type of movement occurs once in every 11⁄2 to 2 hours. It travels at a velocity of 6 to 12 cm/min.-it takes about 10 minutes to reach the colon after taking origin from the stomach. MMC sweeps the excess digestive secretions into the colon and prevents the accumulation of them in stomach and intestine.