Intestinal Physiollogy: Fluid, Electrolytes And Digestion In The Intestines Flashcards
Why is shape important in multicellular organisms?
If the shape is not hollow: Greater Ratio of Volume to Exterior Surface Area than in a Single Cell
Cavity or lumen for optimal digestion and absorption
Organisation into shapes that maximise surface area for exchange
More complicated multicellular organisms are terrestrial
not living in an aqueous solution filled with nutrients
Specialized tube through the body for getting nutrients to the circulatory system for delivery to tissues
Take relatively large solids and digest them into smaller molecules that can be absorbed as nutrients, while still serving as a barrier to toxins, bacteria, parasites, etc
Transport of fluid and electrolyte is a key function of the GI tract
Epithelial cells may:
Secrete water and electrolytes
Absorb water and electrolytes
Secretion: transport from blood to gut
Absorption: gut lumen to blood
Daily gut fluid balance
Slide 12
Movement of H2O and electrolytes
Water moves down an osmotic gradient
Electrolytes move down electrochemical gradients
To move against concentration gradients requires energy
Energy is supplied by sodium gradients (generated by the sodium pump) and by proton gradients
Small intestine 3 segments
Duodenum
Jejunum
Ileum
2 stage transcellular process
1st stage: membrane transport protein
2nd stage: Na+K+ATPase transporter
Intestinal secretion
Chloride ions enter the crypt epithelial cell by cotransport with sodium and potassium; sodium is pumped back out viasodium pumps, and potassium is exported via a number of channels
Activation ofadenylyl cyclase by a number of so-called secretagogues leads to generation of cyclic AMP
Elevated intracellular concentrations of cAMP in crypt cells activate the CFTR, resulting in secretion of chloride ions into the lumen
Accumulation of negatively-charged chloride anions in the crypt creates an electric potential that attracts sodium, pulling it into the lumen, apparently across tight junctions - the net result is secretion of NaCl
Secretion of NaCl into the crypt creates an osmotic gradient across the tight junction and water is drawn into the lumen
Factors influencing absorption
Number and structures of electrolytes
Blood and lymph flows
Nutrient intake
GI motility- hormonal and neural
Secretion
Irritants
Bile
Bacterial
Toxins
Hormonal
Neural
Vibrio cholerae can survive in the water without a host for a long enough time to be ingested by its next host
Cholera is transmitted by either contaminated food or water
Source of contamination is typically other cholera sufferers when their untreated diarrheal discharge is in waterways, groundwater, or drinking water supplies
It rarely spreads from person to person.
Major sources:
In developed world: seafood is typically the cause
In developing world: it is often water
Toxin induces diarrhoea
Cholera toxin released from bacteria in infected intestine
Binds to Intestinal cells
Stimulates adenylate cyclase to produce cAMP
Dramatic efflux of ions and water
Watery Diarrhoe
Oral rehydration
Water passively follows the osmotic gradient
SGLT1- sodium glucose co-transporter which moves Na and glucose from the luminal membrane into the enterocyte
Define digestion
Breakdown of large, complex organic molecules that can be used by the body.
Mechanical (eg. chewing, churning of food)
Chemical (eg. enzymes)
Small intestine
is primary site for digestion and absorption of food
Digestion occurs in the GI lumen by secreted enzymes and on surface of enterocytes by membrane-bound enzymes
Absorption occurs by simple diffusion, facilitated diffusion, active transport, endocytosis, and paracellular transport.
Surface area of small intestine is greatly increased by extensive folding and the projection of fingerlike villi covered with microvilli.
Enterocytes
absorb glucose and galactose through an Na-dependent secondary active transport process, while fructose is absorbed by facilitated transport
Digestion of fats
Fat and water tend to separate
Enzymes are in the water and they cant get at the fat
Bile (an emulsifier) arrives
Bile has an affinity for both fat and water and can therefore bring the fat into the water
After emulsification, the fat is mixed in the water solution, so fat-digesting enzymes have access to it
Bile acids: what do they do?
Released into the small intestine
After function performed- recycled back to the liver
Leads to bile acid diarrhoea
Digestive enzymes
Slide 39
3 pairs of Salivary glands
Parotid
Sublingual
Submandibular
Functions of saliva
Lubricates, cleans oral cavity
Dissolves chemicals
Suppresses bacterial growth
Digest starch by amylase
GI secretion in stomach
Slide 42
Pancreas endocrine function
secretes insulin and glucagon from islets of Langerhans
Exocrine functions of pancreas
Secretion of pancreatic juice
Relevant functions of the liver
1) Metabolic regulation
Store absorbed nutrients, vitamins
Release nutrients as needed
2) Haematological regulation
Plasma protein production
Remove old RBCs
3) Production of bile
Required for fat digestion and absorption
