Gastro-intestinal system Flashcards
Anatomy of GI tract
-from mouth to anus, 8 metre long tube
-passes through thoracic and abdominopelvic cavities
-this tube consists of 4 layers that are specialised for specific functions (mucosa, submucosa, muscular layer, serosa)
Mucus membrane
-what is it, structure (2), function, clinical relevance
Mucosa
-surface epithelium
-some regions it is folded with projections which increases absorption
-also patches lymphatic tissue called mucosa-associated lymphoid tissue (MALT)
-carries out secretion and absorption
-in contact with food
-no sensory nerves, damages easily
Ulceration-
1. In mucosa
2. In submucosa
3. muscular layer
1.mucosa damage causing discomfort
2. bleeding occurs
3. causes extensive bleeding (fatal)
Submucosa
what is it, what it contains, function (2)
-loose connective tissue
-contains glands, blood vessels, lymphatic vessels and nerves
-nourishes surrounding tissue
-carries away absorbed material
Muscular layer
function, structure (detail)
-moves the tube
-constructed of 2 smooth muscle tissue coats
1. circular fibres on inner coat cause contraction
2. longitudinal fibres run length ways and cause shortening
Serous layer
structure(2), function(2)
Serosa
-visceral peritoneum on outside
-connective tissue beneath
-protects underlying tissues
-secretes serous fluid
4 layers of GI tract from deep to superficial
-mucosa
-submucosa
-muscular layer
-serosa
Peritoneum
what is it, 2 layers and gap between them
-largest serous membrane of the body
-parietal peritoneum lines wall of abdominopelvic cavity
-visceral layer covers organs
-space between them is where serous fluid is
Ascites-
where fluid accumulates in the abdomen
Retroperitoneal organs
Examples and what they are
-kidneys, pancreas
-covered by peritoneum only on anterior surfaces
Mesentery
what is it, structure (3)
-fold of peritoneum
-fan shaped
-binds small intestine to the posterior abdominal wall
-extends from posterior abdominal wall wraps around small intestine and returns to origin
Mesocolon
-fold of peritoneum binds large intestine to posterior wall
-carries blood and lymphatic vessels
Functions of GI tract
-ingestion
-mechanical processing
-digestion
-secretion
-absorption
-excretion
Ingestion
-food enters GI tract through mouth
-starts process with mechanical and chemical actions
Mechanical processing
what is it, what has main influence on chewing, numbers
-mastication- chewing, crushing and breaking into smaller fragments
-pressure changes in mouth have main influence on chewing, teeth are secondary
-not chewing properly reduces digestion by 50%
-pressure changes of 37psi are achieved by the mouth
Digestion
-chemical breakdown of food into small particles that can be absorbed by epithelium
-simple molecules stay intact while others are broken down before being absorbed
Secretion
-release water, acids, buffer enzymes and salts by epithelium and glandular organs
Absorption
-movement of molecules acted upon by enzymes, electrolytes, vitamins and water across epithelium into interstitial fluid
Excretion
-removal of waste products
-becomes faeces eliminated by defecation
Nervous control of GI tract
specific NS, types neurone and what they do, branch of NS
-enteric NS= brain of gut
-consists of 100 million neurones
-motor neurone- control motility and secretion by epithelial cells
-sensory neurones- chemo and stretch receptors
-ANS- sympathetic decreases digestion, parasympathetic increases digestion
Mouth
proper name, structure, function
-oral/ buccal cavity
-oral cavity= space extends from gums to fauces
-salivary glands- secrete just enough to keep mouth and pharynx moist
Salivary glands
branches ANS, 3 gland names
-parasympathetic increases secretion, sympathetic decreases salivation
-3 pairs major glands secrete most saliva
1. parotid- watery texture
2. submandibular- mucus rich
3. sublingual- mucus rich
Composition of saliva
99.5% water
0.05% solutes eg. ions and salivary amylase
Tongue
-accessory digestive organ
-skeletal muscle covered by mucus membrane
-manoeuvres food for chewing, swallowing
-lingual glands secrete salivary lipase (triglycerides)
Oesophagus
-secrete mucus, transports food
-purely for transportation, no enzymes of absorption
-mucosa for protection of wear and tear
-muscularis divided into 3
1. superior= skeletal muscle
2. middle= skeletal and smooth
3. inferior= smooth muscle
-2 sphincters:
1. upper oesophageal sphincter- reg movement in oesophagus
2. lower oesophageal sphincter- reg movement in stomach
Deglutition
what is it, facilitated by, 3 stages
-act of swallowing
-facilitated by saliva and mucous
-3 stages:
1. voluntary- bolus passed oropharynx
2. pharyngeal- involuntary passage through pharynx to oesophagus
3. oesophageal- involuntary passage through oesophagus to stomach
Stomach
what is it, capacity, structure, absorption, vomiting
-muscular bag
-1.5l capacity
-higher portion= fundus
-lower portion= pylorus (thickest muscle)
-small amount of absorption
-when vomiting, pylorus contracts first
-pylorus is more liquefied, fundus has more undigested chunks
Digestion in stomach
2 types and how they work
Mechanical digestion
-mixing waves, rippling peristaltic movements
Chemical digestion
-digestion by saliva continues until deactivated by acid
-parietal cells secrete H+ and Cl- which create HCl
-pepsin secreted by chief cells digests proteins. secreted as pepsinogen which is inactive
-gastric lipase splits triglycerides into fatty acids and monoglycerides
Adrenaline and drugs/ alcohol effect on stomach
Adrenaline
-suppress mucus production
Alcohol/ drug misuse
-causes pepsinogen malfunction
-pepsin is produced and causes digestion of the own stomach
Pancreas
location, structure, function
-posterior to greater curvature of stomach
-has head, body and tail
-connects duodenum via pancreatic duct and accessory duct
-endocrine islets secrete hormones
-exocrine acini secrete pancreatic juice
Liver
structure, composition
-left and right lobes
-composed of hepatocytes (cells) and hepatic sinusoids
-sinusoids= permeable capillaries receive oxygenated blood from hepatic artery and deoxygenated nutrient rich from hepatic portal vein
Functions liver and gallbladder
-carb metabolism- glycogen to glucose
-fat metabolism
-protein metabolism
-breakdown erythrocytes
-detoxification drugs etc
-secretion bile
-storage- glycogen, iron, water etc.
Gallbladder
-smooth muscle contracts which ejects contents into cystic duct
-stores bile produced by liver until needed by SI
-absorbs water and ions to concentrate bile up to ten-fold
Liver blood flow
-ox blood hepatic artery
-HPV deoxy blood from digestive system
-this flows into sinusoid which absorbs nutrients then flows into hepatic vein
Composition bile
-mostly water, salts, cholesterol, lecithin, bile pigments
-bilirubin= principal bile pigment, derived from haeme of recycled RBCs
Small intestine
3 regions
-duodenum
-jejunum
-ileum
Structures in GI tract increase SA
- circular folds
-ridges mucosa and submucosa
-causes chyme to spiral - villi
-finger-like projections of mucosa
-contain lots blood vessels - microvilli
-protects of apical membrane of absorptive cells
Mechanical digestion
-governed by myenteric plexus
-divided into segments which are localised and cause mixing contractions
-peristalsis keeps food moving from the lower portion of the stomach
Absorption in SI
Electrolytes:
-from GI secretions of food
Vitamins:
-fat soluble eg. A, D, E and K
Water:
-most absorbed SI some in LI
-all absorbed by osmosis
Large intestine
function, 4 regions, sphincter, division of colon
-completes absorption, produces vitamins, forms and expels faeces
-4 regions: caecum, colon, rectum, and anal canal
-ileocaecal sphincter between SI and LI
-colon divides into ascending, transverse, descending and sigmoid
-internal anal sphincter= smooth muscle
-external anal sphincter= skeletal muscle
Digestion of LI
Mechanical
-haustral churning
-peristalsis
Chemical digestion
-final stage digestion through bacterial action
-mucous no enzymes
What does metabolism use nutrients to do
-provide energy by chemical oxidation of those nutrients
-make new or replace body substances
Anaerobic respiration
-glycolysis
-glucose + insulin= pyruvic acid + lactic acid
Aerobic respiration
-krebs cycle
-pyruvic acid + oxygen -> CO2 + H2O + ATP
Absorptive state
period in which the GI tract is full and anabolic (build) processes exceed catabolism (break)
Post absorptive state
period where GI tract is empty of nutrients and body stores must supply required energy
