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Gastrointestinal > GI Physiology > Flashcards

GI Physiology Flashcards

1
Q

What gastric factors influence the rate of gastric emptying?

A

The amount of chyme - stomach distension triggers increased gastric motility through a direct effect of stretching on smooth muscle and ghe involvement of intrinsic and extrinsic nerve plexuses and GI hormones

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2
Q

What duodenal factors can affect the rate kf gastric emptying?

A 
Presence of fat in the duodenum
Presence of acid in the duodenum
Hypertonicity of the duodenum 
Distension of the duodenum
All of these will reduce the rate of gastric empyting
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3
Q

In what areas of the stomach are oxyntic glands, which mostly contain parietal cells and secrete lots of HCL, mostly present?

A

Fundus and body

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4
Q

Which cells secrete pepsinogen?

A

Chief cells

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5
Q

What do D cells in the gastric pits secrete?

A

Somatostatin

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6
Q

What do eneterochromaffin-like cells in the gastric pits secrete?

A

Histamime

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7
Q

What do G cells in the gastric pit secrete?

A

Gastrin

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8
Q

What is the role of hydrochloric acid in the stomach?

A

Act as an antimicrobial
Activate pepsinogen to pepsin
Denature protein

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9
Q

Explain the process by which parietal cells secrete hydrochloric acid into the stomach lumen.

A

First water is broken down into hydrogen and hydroxyl ions. The hydrogen ions are actively transported out of the cell using a H+/K+-ATPase. (Potassium passively leaks back out of the cell. Meamwhile the hydroxyl ions are reacted woth carbon dioxide from cellular metabolism to create bicarbknate ions which are actively transported out of the cell and into the plasma in exchange for chloride ions. This builds up a concentration gradient to allow chloride ions to diffuse into the gastric lumen through a protein channel.

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10
Q

What type of signal is the histamine released by ECL cells?

A

Paracrine

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11
Q

What kind fo signal is the somatostatin released from D cells?

A

Paracrine

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12
Q

What type of signal is the gastrin secreted from G cells?

A

Hormone

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13
Q

What is the function of ECL cells?

A

To release histamine which stimulates parietal cells to produce HCL

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14
Q

What is the function of G cells?

A

To secrete gastrin which stimulates parietal, chief and ECL cells to increase the secretion of HCl and pepsinogen

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15
Q

What is the function of D cells?

A

Inhibits parietal, G and ECL cells

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16
Q

How does acetylcholine work to increase HCL secretion?

A

By stimulating parietal cells, chief cekks, G cells and ECL cells

17
Q

What is the normal pH of the stomach when not eating?

A

1.5

18
Q

Why does the pH of the stomach increase when digesting a meal despite the increased acid secretions?

A

Because the food (particularly the protein component) is acting as a buffer

19
Q

Describe the cephalic phase of digestion

A

When thinking about, smelling, tasting, chewing or swallowing food the vagus nerve sends signals to stimulate increased hydrochloric acid and pepsinogen secretion through the neurotransmitter ACh

20
Q

Describe the intestinal phase of digestion

A

The removal of food from the stomach into the duodenum removes protein which js a major stimulus for enhanced gastrin secretion. This removal of food also lowers the pH of the stomach and the acidic environment stimulates D cells to secrete somatostatin. This all leads to decreased gastric secretions

21
Q

The small intestine secretes a vast amount of water into the lumen. Why does it do this?

A

In order to help fix pancreatic and gastric secretions with food to aid digestion

22
Q

What two factors cause the small intestine to secrete water into the lumen?

A

Luminal osmotic pressure increases as the osmolarity of the foodstuffs imcreases with digestion
Secretion of electrolytes (sodium chloride) into the lumen draws water into the lumen by osmosis

23
Q

Describe the action of the CFTR channel in The secretion of water into the lumen of the small intestine

A

Chloride ions enter the enterocyte via cotransport with sodium and potassium ( sodium and potassium are then exported out of the cell again)
This activates adenylyl cyclade to generate cAMP
Elevated intracellular levels of cAMP activates CFTR resulting in the secretion of chloride ions into the lumen of the small intestine
The accumulation of these negatively charged ions in the lumen attracts sodium ions into the lumen
This secretion of sodium chloride into the lumen creates an osmotic gradient which draws water i to the lumen

24
Q

Explain how cholera infection leads to increased water secretion via CFTR

A

The cholera toxin binds to crypt cells to cause an elevation in cAMP which results in the abnormal activation of CFTR. This causes hyper-secretion of sodium chloride into the lumen and thus sets up a concentration gradient which leads to the hyper-secretion of eater into the lumen. This can lead to severe and dangerous dehydration

25
Q

Most proteins are digested before absorption in the small intestine. What protein is an exception to this?

A

Antibodies in colostral milk

26
Q

Glucose and galactose are actively absorbed in the small intestine but there is limited absorption of fructose. T/F?

A

True

27
Q

Protein is predominantly absorbed in the small intestine as amino acids by active co transport with which ion?

A

Sodium

28
Q

In which part of the small intestine is vitamin b12 primarily absorbed?

A

The terminal ileum

29
Q

Coeliac disease, whipple’s disease and giardiasis can all result in malabsorption. T/F?

A

True

30
Q

What is the name of the glands in the small intestine which secrete bicarbonate ions to neutralise acidic secretions from the stomach?

A

Brunner’s glands

31
Q

What is the function of peyers patches in the small intestine?

A

These are lymphatic areas which protect against ingested pathogens

32
Q

Bobesin is secreted by the small intestine. What does it do?

A

Stimulates gastrin release

Gastrointestinal (22 decks)

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