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Regulatory Physiology > Hormonal regulation of the GI tract (Week 5) > Flashcards

Hormonal regulation of the GI tract (Week 5) Flashcards

1
Q

what is the capacity of the stomach

A

50>1000ml

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2
Q

what is the starting point for digestion

A

the mouth
mechanical (chewing) and chemical (saliva, amylase) digestion

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3
Q

what digests carbohydrates

A

salivary amylase in the mouth
pancreatic amylase in the small intestine
disaccharides (on the surface of the small intestine)

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4
Q

what digests proteins

A

pepsin in the stomach
trypsin, chymotrypsin, and carboxypeptidase in the small intestine
peptidases on the surface of the small intestine

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5
Q

what are the parts of the stomach

A

Cardia - uppermost part
Fundus - dome shaped portion
Body - central largest part
Antrum - lower part of the stomach closer to the small intestine

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6
Q

what is the orad stomach

A

the upper part

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7
Q

what is the caudad stomach

A

the lower part

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8
Q

what are the tonic contractions

A

tonic contractions are particularly relevant in the upper regions, such as the fundus and proximal body. The fundus is the upper part of the stomach, and tonic contractions in this area help to maintain a constant pressure for the storage and initial processing of ingested food. This sustained contraction contributes to the stomach’s ability to accommodate varying amounts of food without a significant increase in pressure.

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9
Q

what are phasic contractions

A

Phasic contractions are more typical in the lower regions of the stomach, such as the antrum, and are involved in the mixing and propulsion of partially digested food (chyme) into the small intestine.

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10
Q

what is the pyloric sphincter

A

a muscular valve that opens to allow food to pass from the stomach to the top of the small intestine

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11
Q

what are some factors affecting the volume of chyme

A

The rate of emptying is proportional to the volume of chyme in the stomach
The more chyme present, the faster the stomach empties its contents.

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12
Q

what are some factors affecting the distension of the stomach

A

stretch of smooth muscle
stimulation of intrinsic nerve plexuses
increased vagus nerve activity
gastrin release

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12
Q

explain the factors affecting the distension of the stomach

A

Explanation: When the stomach wall stretches due to the presence of food (distension), several responses occur:
The smooth muscle of the stomach is stimulated.
Intrinsic nerve plexuses (networks of nerves within the stomach wall) are activated.
Vagus nerve activity increases.
Gastrin, a hormone that stimulates stomach activity, is released.
Outcome: These responses collectively increase motility, promoting the movement of chyme through the digestive system

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13
Q

why must the duodenum be ready

A

ensures smooth transition for further digestion and nutrient absorption in the small intestine

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14
Q

Factors Delaying Gastric Emptying:

Neuronal Response - Enterogastric Reflex
explain the mechanism, the effect and the outcome

A

mechanism: The enterogastric reflex is a neural response that involves signals from intrinsic nerve plexuses (nerve networks within the gastrointestinal tract) and the autonomic nervous system (ANS)
effect: This reflex decreases antral activity. The antrum is the lower part of the stomach responsible for mixing and propelling chyme.
outcome: By reducing antral activity, the enterogastric reflex slows down gastric emptying.

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15
Q

Factors delaying gastric emptying
Hormonal Response - Enterogastrones (e.g., Cholecystokinin - CCK)
explain the mechanism, the effect and the outcome

A

mechanism: Hormones like cholecystokinin (CCK) are released from the duodenum.
effect: Enterogastrones inhibit stomach contraction.
outcome: The release of these hormones signals the stomach to slow down its contractions, further delaying gastric emptying.

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16
Q

Stimuli within the duodenum that drive the neuronal and hormone responses include

A

Fat – particularly potent – delay in gastric emptying required for digestion and absorption in small intestine
Acid – time is required for neutralization of gastric acid by bicarbonate secreted from the pancreas – important for optimal function of pancreatic digestive enzyme so
Hypertonicity – products of carbohydrate and protein digestion are osmotically active and draw water into the small intestine – danger of reduced plasma volume and circulatory disturbances (e.g.‘dumping syndrome’)
Distension

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17
Q

what is the combined effect of both neuronal and hormonal responses

A

The neuronal and hormonal responses work in conjunction to ensure that the duodenum is adequately prepared before receiving chyme from the stomach.

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18
Q

what is the oxyntic gland area

A

proximal stomach including the fundus and body

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19
Q

what is the pyloric gland area

A

distal stomach, designated the antrum

20
Q

what is the gastric mucosa composed of

A

a surface lining the stomach
pits, invaginations of the surface
glands, at the base of the pits responsible for several secretions

21
Q

in the oxyntic mucosa what is the function of HCL

A

activated pepsinogen and pepsin
denatures protein
kills most (not all) microorganisms ingested with food

22
Q

in the oxyntic mucosa what is the function of Pepsinogen

A

inactivates precursor of the peptidasem, pepsin.

23
Q

in the oxyntic mucosa what is the function of Intrinsic factor and Gastroferrin

A

binds vitamin B12 and Fe2+ respectively, facilitating subsequent absorption

24
Q

in the oxyntic mucosa what is the function of histamine

A

stimulates HCL secretion

25
Q

in the oxyntic mucosa what is the function of Mucus

A

protective

26
Q

in the pyloric gland area, what is the function of gastrin

A

stimulates HCL secretion and motility

27
Q

in the pyloric gland area, what is the function of somatostatin

A

inhibits HCL secretion

28
Q

in the pyloric gland area, what is the function of Mucus

A

protective

29
Q

explain the action of histamine

A

histamine is secreted by enterochromaffin-like cells in the gastric glands in response to stimulation by acetylcholine.
Binds to H2 receptors with subsequent activation of adenlyl cyclase.
Increase in cAMP increases number of proton pumps, increasing gastric acid secretion from the parietal cells.

30
Q

explain the action of acetylcholine

A

released by parasympathetic cholinergic neurons

ACh binds to muscarinic (M3) receptors on parietal cells with the subsequent activation of PLC

Increase in intracellular Ca2+ evokes cell signalling pathways that increase the number of proton pumps, increasing gastric acid secretion from parietal cells

31
Q

explain the action of gastrin

A

released by G cells.

binds to CCK2 receptors on parietal cells with subsequent activation of PLC

increase in intracellular Ca2+ increases the number of proton pumps, increasing gastric acid secretion from parietal cells.

32
Q

explain the action of somatostatin

A

secreted by d cells in the gastric glands

binds to SST2R receptorrs inhibiting adenylyl cyclase

increase in intracellular Ca2+ evokes cell signalling pathways that increase the number of proton pumps, increasing gastric and acid secretion in parietal cells

33
Q

Receptors and Signal-transduction Pathways Modulating Acid Secretion from the Gastric Parietal Cell

A

Stimuli for secretion of H+act by both PLC - IP3(gastrin, ACh) and cAMP -PKA (histamine) signalling pathways

Stimuli for inhibition of secretion of H+ act by cAMP - PKA (somatostatin,prostaglandins) signalling pathways

34
Q

what are the three phrases of gastric secretion

A

cephalic phase (in the head) before food reaches the stomach preparing it stomach to receive food
- driven directly and indirectly by the CNS and vagus nerve

Gastric phase - when food is in stomach
- involves both physical and chemical mechanism

intestinal phase - after food has left the stomach
-chyme entering the upper small intestine causes weak stimulation of gastric secretion via neuronal and hormonal mechanisms

35
Q

the cephalic phase

A

vagus stimulations enteric neurons that:
-release ACh directly activating parietal cells
-via release of GRP cause release of gastrin from the G cells in to systemic circulation that activates parietal cells
- via release of histamine from ECL cells that locally activates parietal cells
- via inhibition of D cells decreases the inhibitory effects of ss on g cells

36
Q

the gastric phase

A

-distension of stomach activates reflexes that cause acid secretion
-food buffers pH, D cells inhibition via ss of gastrin release is decreased
- amino acids (e.g. tryptophan, phenylalanine) stimulates G cells. Other stimulants include Ca2+, caffeine and alcohol.

37
Q

what does the small intestine release into the blood

A

various peptide hormones from endocrine cells within the mucosa

38
Q

what does gastrin from the G cells of gastric Antrum release

A

stimulates H+ secretion by gastric parietal cells
stimulates growth of gastric mucosa (a tropic effect)

39
Q

what does secretin from the S cells of the duodenum release in response to H+ and fatty acids in lumen

A

promotes secretion of pancreatic and biliary HCO3-

40
Q

what does the secretion of chloecystokinin (CCK) - from I cells of duodenum and jejunum released in response of monoglycerides, free fatty acids, amino acids, small peptides in lumen do

A

-inhibits gastric secretion
-causes secretion of pancreatic enzymes required for digestion
-stimulates relaxation of sphincter of Oddi and contraction of the gall bladder to eject bile into duodenum
-potentiates the action of secretin

41
Q

what does GIP (gastric inhibitory peptide) released from the K cells in response to glucose, amino acids and fatty acids

A
  • stimulates release of insulin from pancreatic B-cells (incretin)
  • inhibits gastric emptying
42
Q

Glucagon Like Peptide 1(GLP-1) from the L cells

A

-stimulates insulin secretion
- inhibits glucagon secretion from pancreatic a- cells
-decrease gastric emptying and appetite

43
Q

motolin from the M cells

A

initiates the migrating motor complex

43
Q

ghrelin- from Gr cells

A

stimulates appetite

44
Q

what are the endocrine hormones released from the pancreas

A

insulin and glucagon - secreted into the blood

45
Q

what are the exocrine hormones released from the pancres

A

digestive enzymes acinar cells), aqueous NaHCO- solution (duct cells)- secreted to the duodenum collectivley pancreatic juice

46
Q
A

Regulatory Physiology (13 decks)

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