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GI: Key Information > Physiology > Flashcards

Physiology Flashcards

1
Q

four layers of the GI tract

A

mucosa
submucosa
muscularis externa
serosa/adventitia

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2
Q

where is the muscularis mucosae located?

A

mucosa

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3
Q

where is the submucous plexus located?

A

submucosa

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4
Q

where is the myenteric plexus located

A

muscularis externa

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5
Q

which layer is made up of the circular and longitudinal muscle layers?

A

muscularis externa

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6
Q

function of the circular muscle layer?

A

makes the lumen longer and narrower

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7
Q

function of the longitudinal muscle layer

A

makes the lumen shorter and fatter

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8
Q

what initiates slow wave activity in the GI tract?

A

interstitial cells of Cajal (pacemaker cells between the two muscle layers)

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9
Q

major patterns of motility in the stomach and small intestine

A
  1. peristalsis
  2. segmentation
  3. colonic mass movement (faeces into rectum)
  4. migrating motor complex (stomach to terminal ileum)
  5. tonic contractions
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10
Q

gastric factors affecting stomach emptying

A

volume and consistency of chyme

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11
Q

patterns of motility in the large intestine

A
  • haustration (slow wave)
  • peristalsis propulsion
  • defecation
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12
Q

two areas of secretion in the stomach

A
  • oxyntic gland area

- pyloric gland area

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13
Q

cells in the oxyntic gland area

A
  • chief cells (pepsinogen)
  • parietal cells (HCl, intrinsic factor and gastroferrin)
  • enterochromaffin (histamine)
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14
Q

cells in the pyloric gland area

A
  • D cells (somatostatin)

- G cells (gastrin)

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15
Q

role of intrinsic factor and gastroferrin

A

bind B12 and Fe2+

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16
Q

role of somatostatin

A

inhibit HCl secretion

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17
Q

how does the mucosa protect itself from being digested?

A

secretes PGE2 and PGI2

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18
Q

two motility regions in the stomach

A
  • orad: tonic contractions- vagus

- caudad: slow wave (retropulsion)

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19
Q

two types of secretions in the pancreas

A
  1. endocrine: islets of Langerhans

2. exocrine: acinar cells

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20
Q

five pancreatic enzymes (precursors)

A
  1. trypsinogen
  2. chymotrypsinogen
  3. carboxypeptidase
  4. pancreatic amylase
  5. pancreatic lipase
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21
Q

how is Cl- secreted

A

through CFTR on apical membranes (overstimulated causes secretory diarrhoea- loss of K+)

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22
Q

describe luminal digestion

A

pancreatic enzymes secreted into the duodenum

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23
Q

describe membrane digestion

A

mediated by enzymes at the brush border of epithelial cells

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24
Q

in carbohydrate digestion what is the role of alpha-amylase

A

breaks alpha-1,4-links

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25
Q

in carbohydrate digestion what is the role of isomaltase?

A

breaks alpha-1,6 links

26
Q

what are oligosaccharidases

A

integral membrane proteins with a catalytic domain that faces the lumens

27
Q

examples of oligosaccharidases

A

lactase, maltase, sucrase and isomaltase

28
Q

substances involved in protein digestion

A
  • HCl and pepsin in stomach

- pancreatic enzymes function as either endopeptidases or exopeptidases in the small intestine

29
Q

describe lipid digestion

A

converted to an emulsion by lipases which is reduced by pancreatic lipase

30
Q

what does failure to secrete bile salts result in?

A

lipid malabsorption (steatorrhoea and vitamin deficiency- A, D, E and K)

31
Q

how are glucose and galactose absorbed?

A

secondary active transport mediated by SGLT1 (Na+)

32
Q

how is fructose absorbed

A

facilitated diffusion mediated by GLUT5

33
Q

how do all monosaccharides exit enterocytes

A

facilitated diffusion by GLUT2

34
Q

how are peptides absorbed at the brush border?

A

by PepT1 (co-transport with H+)

35
Q

how is cholesterol absorbed

A

NPC1L1 (ezetimibe)

36
Q

what is the taeniae coli

A

longitudinal smooth muscle in the colon is divided into three strands to cause the production of haustra

37
Q

how is the appendix connected to the caecum?

A

appendiceal orifice

38
Q

three major functions of the large intestine

A
  • secretion of K+, HCO3- and mucus
  • absorption of Na+, Cl- and H2O (& short chain fatty acids)
  • reservoir for periodic elimination
39
Q

what enhances Na+ absorption and K+ secretion

A

aldosterone

40
Q

is the absorption of water a passive process?

A

yes, it follows solutes (usually Na+)

41
Q

three mechanisms of water absorption in the jejunum

A
  • Na+/glucose co-transport
  • Na+/amino acid co-transport
  • Na+/H+ exchange
42
Q

mechanism of water absorption in the ileum and proximal colon

A

Na+/H+ and Cl-/HCO3- exchange (reduced NaCl absorption causes diarrhoea)

43
Q

mechanism of water absorption in the distal colon

A

epithelial Na+ channels (enhanced by aldosterone)

44
Q

define assimilation

A

overall process of digestion and absorption

45
Q

major functions of the liver

A
  • metabolism
  • deactivation of hormones (insulin, glucagon, ADH, steroids)
  • storage of A, D, E, K vitamins, iron, copper and glycogen
  • synthesis of protein (acute phase proteins, coagulation, albumin, etc.)
  • protection: Kupffer cells
  • detoxification
  • secretion of bile
46
Q

describe the secretion of bile by the liver

A

secreted by hepatocytes into canaliculi which drains into bile ducts, neutralising chyme an forms micelles

47
Q

two phases of drug metabolism in the liver

A

Phase 1: oxidation (CYP450s), reduction and hydrolysis.

phase 2: conjugation e.g. glucuronidation

48
Q

what is the enteric nervous system

A

it is the autonomic nervous system that supplies the GI tract

49
Q

parasympathetic neurotransmitter in the ENS

A

both preganglionic and postganglionic synapse with ACh

50
Q

role of the parasympathetic in the ENS

A

‘rest and digest’

  • increases blood flow, secretion and smooth muscle contraction
  • relaxation of sphincters
51
Q

neurotransmitters in the sympathetic of the ENS

A

preganglionic release ACh and postganglionic release NA

52
Q

role of the sympathetic in the ENS

A
  • increased sphincter tone

- decreased motility, secretion and blood flow

53
Q

define retching

A

rhythmic reverse peristalsis with forceful contraction of abdominal muscles and the diaphragm

54
Q

define emesis

A

forceful expulsion of gastric-intestinal contents out of the mouth

55
Q

what stimuli act directly on the VC

A
  • pain, repulsive sights, smells and emotional factors

- motion (signals via the vestibular nucleus)

56
Q

what stimuli act on the NTS

A

pharyngeal stimulation, gastric/duodenal distension or irritation

57
Q

what stimuli act on the CTZ (no BBB)

A
  • pharyngeal stimulation, gastric/duodenal distension or irritation
  • toxins, drugs and vagal afferents
58
Q

consequences of severe vomiting

A
  • dehydration
  • metabolic alkalosis
  • hypokalaemia
  • oesophageal damage e.g. Mallory-Weiss tear
59
Q

which area of the brain ‘causes’ obesity

A

lesioning ventromedial hypothalamus (leptin and insulin report fat status)

60
Q

define satiety

A

period of time between termination of one meal and the next (gherlin is the hunger signal)

GI: Key Information (24 decks)

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