GI tract Flashcards
Describe the peritoneum
Double layered serous membrane covering abdominal and pelvic cavities
Parietal peritoneum lines the body wall
Visceral peritoneum lines the organs
Peritoneal cavity lies in between parietal and visceral and contains serous fluid
Intraperitoneal organs
Organs fully covered by the peritoneum eg. stomach
Retroperitoneal organs
Organs pushed up against posterior abdominal wall and partially covered by peritoneum eg. pancreas
Mesentery
A double layer of visceral peritoneum, attaches an organ to the body wall
Omentum
A double layer of visceral peritoneum that attaches one organ to another eg. lesser and greater omentum
Name the 4 basic layers of the GI tract
Mucosa - epithelium, lamina propia and muscularis mucosa
Submucosa - dense irregular connective tissue
Muscalaris externa - smooth muscle cells, peristalsis
Serosa/adventia - serous membrane
Arterial supply to tract
Celiac trunk
Superior mesenteric artery
Inferior mesenteric artery
Venous drainage
Blood from stomach, pancreas, S and L intestines drain to liver via hepatic portal vein
Hormonal control
Enteroendocrine glands secrete gastrin, secretin and CCK
Functional processes of digestive system
Motility Digestion Secretion Absorption Protection
Motility
Mechanical digestion: - chewing - churning - segmentation Propulsion: - swallowing - peristalsis - mass movements - elimination
Mechanical digestion
Breaks down food into bolus so easier to move through tract and increases SA
Chewing - teeth, tongue, salivary glands
Churning - includes stomach and L intestine
Segmentation - cycles of contraction that fragment the bolus and mix it with digestive juices, in S intestine
Propulsion
The movement of digestive materials along the tract
Swallowing - 3 stages, oral, pharyngeal and oesophageal
Peristalsis - waves of muscular contraction that move bolus along
Mass movements - occur in L intestine, powerful contractions that push bolus into rectum, produce urge to defecate
Elimination - defecation reflex, internal anal spincter relaxes, external anal spincter contarcts, conscious effort requires to relax external sphincter
chemical digestion
Breakdown of food into smaller fragments that can be easily absorbed Carbs = simple sugars Proteins = amino acids Lipids = fatty acids Secretion Absorption Protection
Secretion
Exocrine glands (salivary, pancreas) release enzymes, water, salts, buffers and mucus Cells of stomach, S intestine and liver release enzymes, water, bile, salts and buffers Endocrine glands eg. pancreas release hormones
Absorption
Passage of substances across digestive epithelium into blood or lymph
Occurs in stomach and S intestine
Protection
GI tract protects itself against:
- acids
- mechanical trauma
bacteria
Mouth
Mechanical digestion = chewing
Chemical digestion = salivary amylase causes carb digestion, lingual lipase causes lipid digestion
Salivary glands
1-1.5 L saliva a day - salivary amylase - serous fluid - mucin (lubrication) lysozyme immunoglobulin A
Oesophagus
Extends from pharynx to stomach
25cm long
Lined by stratified squamous epithelium
Innervated by ANS
Stomach
Located in epigastrium - storage - mechanical and chemical digestion - protection - absorption - production of intrinsic factor Extra layer of muscle: > inner - obliqe > middle - circular > outer - longitudinal
Cells of the stomach
Mucous cells and mucous neck cells - secrete mucous
Parietal cells - hydrochloric acid and intrinsic factor
Chief cells - pepsinogen
Enterendocrine - gastric
Gastric juice
1.5/2 L/day
Secretion activated by low pH, gastrin, histamine and Ach
HCl = kills microbes, breaks down connective tissue
Pepsin = protein digestion
Gastrin = stimulates secretion of pepsinogen and HCl, contractions of gastric wall
Intrinsic factor aids absorption of Vit. B12
Regulation of gastric activity
- cephalic phase - site, smell and taste of food
- gastric phase - food in stomach = gastrin secretion, stimulates gastric juice production
- intestinal phase - partially digested food arriving in duodenum slows down production of gastric juices
