Intestinal Physiollogy: Fluid, Electrolytes And Digestion In The Intestines

Question 1

Why is shape important in multicellular organisms?

Answer 1

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

Question 2

More complicated multicellular organisms are terrestrial

Answer 2

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

Question 3

Transport of fluid and electrolyte is a key function of the GI tract

Epithelial cells may:

Answer 3

Secrete water and electrolytes

Absorb water and electrolytes

Secretion: transport from blood to gut
Absorption: gut lumen to blood

Question 4

Daily gut fluid balance

Answer 4

Slide 12

Question 5

Movement of H2O and electrolytes

Answer 5

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

Question 6

Small intestine 3 segments

Answer 6

Duodenum

Jejunum

Ileum

Question 7

2 stage transcellular process

Answer 7

1st stage: membrane transport protein

2nd stage: Na+K+ATPase transporter

Question 8

Intestinal secretion

Answer 8

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

Question 9

Factors influencing absorption

Answer 9

Number and structures of electrolytes

Blood and lymph flows

Nutrient intake

GI motility- hormonal and neural

Question 10

Secretion

Answer 10

Irritants

Bile

Bacterial
Toxins

Hormonal
Neural

Question 11

Vibrio cholerae can survive in the water without a host for a long enough time to be ingested by its next host

Answer 11

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

Question 12

Toxin induces diarrhoea

Answer 12

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

Question 13

Oral rehydration

Answer 13

Water passively follows the osmotic gradient

SGLT1- sodium glucose co-transporter which moves Na and glucose from the luminal membrane into the enterocyte

Question 14

Define digestion

Answer 14

Breakdown of large, complex organic molecules that can be used by the body.

Mechanical (eg. chewing, churning of food)
Chemical (eg. enzymes)

Question 15

Small intestine

Answer 15

is primary site for digestion and absorption of food

Question 16

Digestion occurs in the GI lumen by secreted enzymes and on surface of enterocytes by membrane-bound enzymes

Answer 16

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.

Question 17

Enterocytes

Answer 17

absorb glucose and galactose through an Na-dependent secondary active transport process, while fructose is absorbed by facilitated transport

Question 18

Digestion of fats

Answer 18

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

Question 19

Bile acids: what do they do?

Answer 19

Released into the small intestine

After function performed- recycled back to the liver

Leads to bile acid diarrhoea

Question 20

Digestive enzymes

Answer 20

Slide 39

Question 21

3 pairs of Salivary glands

Answer 21

Parotid

Sublingual

Submandibular

Question 22

Functions of saliva

Answer 22

Lubricates, cleans oral cavity

Dissolves chemicals

Suppresses bacterial growth

Digest starch by amylase

Question 23

GI secretion in stomach

Answer 23

Slide 42

Question 24

Pancreas endocrine function

Answer 24

secretes insulin and glucagon from islets of Langerhans

Question 25

Exocrine functions of pancreas

Answer 25

Secretion of pancreatic juice

Question 26

Relevant functions of the liver

Answer 26

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