11. GIT - physiology 4 Flashcards
Why are muscle contractions important in the small intestine?
Mixing content
Ensures luminal content contracts with epithelial cells
Transport chyme along the tract
What are the 2 types of contractions in the small intestine?
Segmentation (mixing movements)
Peristalsis (propulsive movements)
What is the function of the migrating motility complex during the interdigestive period?
- “sweeps” the intestine clean between meals
- between periods of peristaltic contractions
- gets rid of bacteria and sloughed off epithelial cells
What is another name for pacemaker cells?
Interstitial cells of cajal (ICC)
what are pacemaker cells?
modified smooth muscle cells
how do propulsive movements happen?
the longitudinal muscle relaxes, circular muscle contracts which move the chyme. Then they swap
What are the pacemaker cells of the small intestine?
- Insterstitial Cells of Cajal (ICCs)
- Modified smooth muscle cells
- Form an interconnected lattice of cells that
surround circular + longitudinal muscle in SI - Create the slow-wave potential which runs constantly over the smooth muscle in the GIT.
How does the smooth muscle in the GIT contract?
- Needs to be enough membrane polarisation to cause action potentials
- slow wave frequency = not enough
- Muscle contractions = same or lesser frequency than slow wave potential
- ENS releases peptides + neurotransmitters
affects membrane potential, when depolarised - action potential.
When are the pacemaker cells activated?
When chyme enters the small intestine.
Where is the frequency of slow waves the highest?
Proximal small intestine
What nervous activity increases or decreases contraction strength?
Increased parasympathetic vagal fibre activity increase contraction strength
Increased sympathetic activity decreases contraction strength
Which nervous system primarily regulates strength of peristaltic and segmentation contractions?
Enteric nervous system
Which nervous system primarily regulates strength of peristaltic and segmentation contractions?
Enteric nervous system
What does the ENS release that affects membrane potential in the small intestine?
Peptides and neurotransmitters in the vicinity of smooth muscle cells
What does the ENS release that affects membrane potential in the small intestine?
Peptides and neurotransmitters in the vicinity of smooth muscle cells
Where does most of the digestion and absorption occur in non-ruminants?
What happens to the rest?
mall intestine
Carbohydrates and protein are digested in the small intestine
If not digested there, they are moved to the large intestine for microbial digestion
Which 3 structures increase the surface area of the small intestine?
Folds in the inner surface of small intestine (mucosa)
Inner surface covered with villi
Villi have microvilli
what us the structure of an enterocyte?
- apical membrane: contact with intestinal lumen
- tight junctions: connect adjacent enterocytes
- basolateral membrane: extracellular space ( EC fluid)
what are the 2 mechanisms of absorption?
- transcelluar
- paracellular
what is transcellular absorption?
organic nutrients are transported from intestinal lumen to the interstitial fluid across the enterocyte
what is paracellular absorption?
inorganic ions and water can diffuse through tight junctions connecting enterocytes
what is absorption?
transfer of substances from the lumen of the GIT to blood/lymph capillaries
what are the 3 transport mechanisms across the intestine?
Simple Diffusion:
cell membrane = barrier
allows water + lipid soluble substances
water can diffuse rapidly because of aquaporins in the membrane
Carrier Proteins:
Large water-soluble nutrients can go via protein pumps
Exocytosis/endocytosis:
vesicle forms around nutrient + transports to cell.
what are the 2 phases of digestion?
- luminal
- membranous
How is starch digested + absorbed?
Degraded by amylase in proximal portion of stomach
Pancreatic juice in simple stomached animals (EXCEPT HORSES) have lots of amylase
Final step = occurs across membrane of microvilli
What is maltose digested into?
Glucose
What is sucrose digested into?
Glucose and fructose
What is lactose digested into?
Glucose and galactose
What is glucose absorption linked to?
Sodium absorption via Na-K-ATPase pump
What is glucose absorption linked to?
Sodium absorption via Na-K-ATPase pump
What happens to monosaccarides after absorption?
Transported to liver via portal vein + stored as glycogen.
How is protein digested?
- Pepsin in the stomach/SI creates peptides
- Peptides are broken down into short-chain peptides in SI
- Final degradation to AAs = membrane of epithelial cells.
How is protein digested?
- Pepsin in the stomach/SI creates peptides
- Peptides are broken down into short-chain peptides in SI
- Final degradation to AAs = membrane of epithelial cells.
How are amino acids absorbed?
- Active transport (linked to Na uptake)
- Mostly transported into cells as tri-/di- peptides
- Transported to liver via portal vein.
How are triglycerides broken down during non-microbial degradation?
Broken down into x2 FAs and 1 mono-glyceride.
Why are bile salts important for fat digestion?
- Lipase = water soluble
can only be used at the water/fat interface - Bile salts needed to emulsify fats
*increases SA for lipase enzymes - Bile salts form micelles which are water soluble and act as transporters of digested products
- Lipid-soluble vitamins (A/D/E/K) absorbed at same time.
How is water absorbed?
- Mucosa = freely permeable
- aquaporins
- Water lost from intestine = replaced w/ blood’s water
- 12 L absorbed by small intestine
- Simple stomached herbivores = lots of water needed in Large intestine for fermentation
How is water absorbed?
- Mucosa = freely permeable
- aquaporins
- Water lost from intestine = replaced w/ blood’s water
- 12 L absorbed by small intestine
- Simple stomached herbivores = lots of water needed in Large intestine for fermentation
Where does water absorption occur?
villi
Where does water secretion into the intestinal lumen occur?
Crypts
Where does water secretion into the intestinal lumen occur?
Crypts
