Flashcards in Physiology Deck (68):
what does the small intestine receive from the stomach?
chyme - via the pyloric sphincter
what does the small intestine receive from the pancreas?
what does the small intestine receive from the gallbladder?
what does the small intestine secrete?
intestinal juices and moves remaining residue to the large intestine
name the adaptations of the small intestine which increases surface area
arranged in circular folds
villi contain microvilli
Name the peptide hormones that the small intestine secretes (7)
Glucagon like insulinotropic peptide (GIP)
Glucagon like peptide-1 (GLP 1)
which cells are the peptide hormones secreted from in the small intestine?
endocrine cells within the mucosa into the blood
where does gastrin come from?
G cells of the gastric antrum and duoenum
where does CCK come from?
cells of the duodenum and jejunum
where does secretin come from?
s cells of the duodenum
where does motilin come form?
m cells of the duodenum and jejunum
where does GIP come from?
K cells of the duodenum and jejunum
Where does GLP-1 come from?
incretin from L cells of the gut
Where does ghrelin come from?
Gr cells of the gastric antrumm, small intestine and pancreas
which receptors do peptide hormones from the small intestine act on?
g-protein coupled receptors
what does incretin do?
acts on b-cells of the pancreas to stimulate the release of insulin
Control mechanisms of the succus entericus
arrival of chyme
parasympathetic nerve activity - enhances activity
sympathetic nerve activity - decreases activity
what does secretion of the small intestine contain?
mucous and aqueous salt
steps of mixing of chyme
1. moved back and forth
2. contraction and relaxation initiate by pacemaker cells
3. segmentation of duodenum
4. segmentation in the ileum (empty) triggered by gastrin
5. overall net movement
what controls the segmentation of the small intestine during the mixing of chyme?
parasympathetic and sympathetic stimulation
what inhibits the migrating motor complex of peristalsis
feeding and vagal activity
what does peristalsis clear from the small intestine?
debris, mucus and endotheliac cells between meals
what are the components of the endocrine secretion of the pancreas?
insulin and glucagon onto the blood
what are the components of the exocrine secretion of the pancreas?
digestive enzymes and sodium bicarbonate
what do acinar cells secrete in the pancreas?
procarboxypeptidase A and B
what does trypsinogen become in the duodenum?
trypsin (enterokinase is added)
what is autocatalysis
the process by which a substance catalyses its own production e.g. trypsin
what does chymotrypsinogen become in the duodenum?
chymotrypsin (trypsin is added)
what does procarboxypeptidase A and B become?
carboxypeptidase A and B (acted on by trypsin)
why do duct cells secrete alkaline fluid into the duodenum?
neutralises chyme to make optimum pH for pancreatic function and protects mucosa from acid erosion
What are the three phases of pancreatic secretion?
what mediates the cephalic stage of pancreatic secretion?
vagal stimulation of the acinar cells
what does the large intestine recieve from the ileum?
unabsorbed biliary compounds
what is the function of the ilieocaecal sphincter?
1. maintains positive resting pressure
2. relaxes in response to distension of duodenum
3. contracts in response to ascending colon
4. prevents bacteria getting from the colon
What are the functions of the Large intestine?
1. absorbs water, Na and Cl
2. secrets K, bicarbonate and mucus
3. absorbs short chain fatty acids
4. storage for colonic content
5. elimination of faeces
what is haustration?
caused by contraction of the circular muscle which occurs in the proximal colon and mixes its content
what are peristaltic propulsive movements?
joint contraction of large sections of the circular muscle of the ascending and transverse colon
what are peristaltic propulsive movements triggered by?
after a meal via gastrocolic responses (gastrin and extrinsic nerve plexuses)
Where does most of the water in the body come from?
Secreted within the body itself
what is the absorption of water driven by?
The transport of Na from the lumen of the intestine to the blood stream
define diarrhoea in terms of fluid loss?
Loss of fluid and solutes from the GI tract in excess of 500ml per day
What are the 5 main ways that is Na reabsorbed?
1. Na+/glucose co-transport
2. Na+/amino acid co-transport
3. Na+/H+ exchange
4. Parallel Na+/H+ and Cl-/HCO3- exchange
5. Epithelial Na+ channels
where does Na+/glucose and Na+/amino acid co-transport take place?
where does Na+/H+ exchange take place and what is it facilitated by?
duodenum and jejunum - facilitated by luminal HCO3-)
where does Parallel Na+/H+ and Cl-/HCO3- exchange take place?
ileum and colon
where are Epithelial Na+ channels and what facilitates reabsorption here?
colon - facilitated by aldosterone
Na+/H+ exchange in the jejunum occurs where?
both the apical and basolateral membranes
what is exchange of Na+/H+ stimulated by in the apical membrane of the jejunum?
the alkaline environment of the lumen due to the presence of bicarbonate from the pancreas
Does the lumen have a lower or higher concentration of protons compared to the cytoplasm?
what is the primary mechanism of absorption of Na in the interdigestive period?
Na+/H+ and CI-/HCO3- exchange
How is the absorption through Na+/H+ and CI-/HCO3- exchange described?
what is Na+/H+ and CI-/HCO3- exchange regulated by?
intracellular cAMP, cGMP and Ca2+, all of which reduce NaCl absorption
What can a reduction in NaCl cause?
what does Epithelial Na+ channels mediate?
electrogenic Na absorption in the distal colon
what increases Epithelial Na+ channels?
What are the three actions of Aldosterone?
1. opens ENaC
2. inserts more ENaC into membrane from intracellular vesicle pool
3. increases synthesis of ENaC and Na+/K+-ATPase
what is the driving force of Cl absorption in the small intestine?
electrogenic transport of Na+ - Na+/glucose and Na+/amino acid
what is the driving force of Cl absorption in the late intestine?
electrogenic movement of Na+ through ENaC
What are the two other ways Cl is absorbed?
Na+-H+ and Cl--HCO3- exchange
where does Na+-H+ and Cl--HCO3- exchange take place?
ileum and proximal colon
where does Cl--HCO3- exchange take place?
ileum and proximal and distal colon
What are the benefits of colonic flora?
increase intestinal immunity
synthesise vitamin K2 and free fatty acids
activate certain drufs
How is intestinal immunity increased by colonic flora?
by competition with pathogenic microbes
where do gases released from the anus arise from?
bacteria in the colon attacking carbohydrate
gas which is not absorbed in the large intestine
Presence of hard dried faeces within the colon from a delay in deification and enhanced absorption of water
what is constipation caused by?
ignoring the urge to defecate
decreased colonic motility
obstruction of faecal movement
impairment of defecation reflex
What symptoms can constipation cause?
loss of apetite