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Systems Physiology > Gastrointestinal Tract > Flashcards

Gastrointestinal Tract Flashcards

1
Q

What is the overall function of the GI Tract

A

Digestion and absorption of nutrients

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2
Q

What are the major organs of the GI Tract

A 
Oral Cavity (mouth)
Pharynx (throat)
Oesophagus
Stomach
Small Intestine
Large Intestine
rectum lol
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3
Q

What is the mucosa

A

The luminal lining of the trac

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4
Q

What are the 4 layers of the GI tract from inside to out

A

Mucosa
Submucosa
Muscularis
Serosa - squamous epithelial cells, separated from muscularis by loose CT.

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5
Q

What are the 3 layers of the mucosa

A

Epithelium
Lamina Propria - loose CT
Muscularis Mucosae - thin layer of smooth muscle that supports the mucosa and provides it with the ability to move and fold.

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6
Q

What are the roles of the epithelium in the mucosa

A

Mainly protective in the mouth, oesophagus and anal canal

Secretion and Absorption in the stomach/intestines

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7
Q

What is the role of the lamina propria

A

Contains blood and lymphatic vessels - loose CT between muscualris mucosae and epithelium

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8
Q

What is the muscularis mucosae and what is its role

A

Thin layer of smooth muscle fibres pull mucosa into folds to increase the absorptive surface area

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9
Q

Describe the neuronal networks in the highly vascular submucosa

A

Has a submucosal plexus AKA Meissner’s plexus - part of the enteric nervous system

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10
Q

What do the neuronal networks of the highly vascular submucosa control

A

Primarily secretions but also the smooth muscle and blood vessel tone

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11
Q

What parts of the muscularis are skeletal muscle and under voluntary control

A

Muscularis of the mouth, upper oesophagus and external anal sphincter - these are skeletal muscles

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12
Q

What is the rest of the muscularis, that is not under voluntary control controlled by

A

Contains intrinsic nerve supply - myenteric plexus AKA auerbach’s plexus
This part is smooth muscle btw

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13
Q

What does the intrinsic nerve supply in the muscularis control

A

Controls the GI tract motility

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14
Q

What is the serosa

A

It is the superficial layer of those portions of the GI tract suspended in the abdominopelvic cavity

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15
Q

What are the 2 distinct nervous systems that control GI tract activity

A

Autonomic nervous system

Enteric/internal nervous system

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16
Q

What effect do the SNS and PNS have on GI tract activity

A

SNS - inhibitory action on GI tract activity

PNS - excitatory

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17
Q

What plexuses make up the enteric nervous system

A 
Myenteric plexus (Auerbach's)
Submucosal plexus (Meissner's)
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18
Q

Describe the myenteric plexus and what it mainly controls

A

Situated between the longitudinal and circular muscle of the muscularis. Consists of a linear chain of interconnecting neurones and extends the full length of the GI tract.
Mainly controls motor activity along length of GI tract.

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19
Q

Where is the submucosal plexus and what does it mainly control

A

Lies in the submucosa

Mainly controls secretions and local absorption function within the inner wall of each segment of the gut.

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20
Q

What is mastication

A

The breakdown of food mechanically and initial enzymatic digestion of ptyalin (alpha-amylase)

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21
Q

What is another word for swallowing

A

Deglutition

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22
Q

What are the stages of swallowing

A
  1. Oral stage - bolus to the back of the oral cavity
  2. Pharyngeal stage (involuntary)
  3. Oesophageal phase (involuntary)
23
Q

What are the main muscles involved in chewing

A

Masseter
Temporalis
Pterygoids

24
Q

What innervates the main muscle of mastication

A

The mandibular division of the trigeminal nerve

25
Q

What innervates the tongue

A

Hypoglossal nerve

26
Q

What nerve mainly supplies the buccinator and orbicularis iris muscles

A

Facial

27
Q

What does the bolus pass through in the pharyngeal stage

A

Oropharynx
Cricopharynx
Into the upper oesophagus

28
Q

What prevents nasal regurgitation of masticated food

A

The nasopharynx is shut off from the oropharynx in the pharyngeal stage by the contraction of muscles of the soft palate and posterior pharyngeal wall.

29
Q

Where does food pass to in the oesophageal stage

A

Propels food bolus down the oesophagus.

30
Q

What nerves mediate the oesophageal stage

A

The vagus nerve and sympathetic nerves

31
Q

What is the primary peristaltic wave

A

The positive pressure peristaltic wave that coincides with the entry of the bolus into the oesophagus

32
Q

What is the stripping wave

A

This is the smaller positive wave that clears the left over food material from the oesophagus.

33
Q

What are secondary peristaltic waves

A

Waves generated in the oesophagus in response to dilation of the oesophagus

34
Q

Describe tertiary peristaltic waves

A

Irregular, non-propulsive contractions involving large segments of oesophagus, that occur during emotional stress

35
Q

How does the rate of progression of peristaltic wave vary in different portions of the oesophagus

A
  • upper part of oesophagus, the peristaltic wave progresses rapidly
  • Waves are more sluggish in the lower third of the oesophagus
36
Q

Why is there a difference in the rate of progression of peristaltic waves in different portions of the oesophagus

A

Due to the musculature being striated in the upper portion of the oesophagus and smooth at the lower 1/3 of the oesophagus

37
Q

What are the 3 layers of the smooth muscle in the muscularis

A
  • Outer longitudinal
  • Middle circular
  • inner oblique
38
Q

What are the 3 types of exocrine gland cells in the gastric glands

A

Mucous Neck cells
Chief (zymogenic) cells
Parietal (oxyntic) cells

39
Q

What do mucous neck cells secrete

A

Mucus and HCO3-

40
Q

What do chief (zymogenic) cells secrete

A

The principal gastric enzyme precursor - pepsinogen

41
Q

What do parietal (oxyntic) cells secrete

A

HCl and an intrinsic factor involved in the absorption of Vit. B12

42
Q

What is gastric juice

A

This is the combined secretions of the 3 types of exocrine gland cells

43
Q

What are G cells (enteroendocrine) and what do they do

A

In mucosa, secrete gastrin

44
Q

What are the 4 major digestive secreted by enteroendocrine cells

A

Gastrin
Secretin
Choleocystokinin (CCK)
Gastric Inhibitory Peptide (GIP)

45
Q

What does gastrin do

A

stimulates G cells of stomach to secrete gastric juice, a mix of HCl and pepsinogen

46
Q

What does CCK act on and what reaction does it cause

A

Acts on gall bladder
Simulates it to contract and release bile
Acts on pancreas to release pancreatic digestive enzymes into the pancreatic fluid

47
Q

When is secretin released

A

Secreted by cells in the duodenum when exposed to acidic contents of the emptying stomach
(causes bicarbonate release to neutralise acid)

48
Q

What does secretin stimulate

A

Stimulates the pancreas to secrete bicarbonate into the pancreatic fluid (neutralising the acidity of the intestinal contents)

49
Q

What are the phases of gastric secretion

A

Cephalic
Gastric
Intestinal

50
Q

What is the cephalic phase of gastric secretion

A

Sight/sound/smell initiates reface via medulla, hypothalamus and vagal output to stimulate submucosa plexus to increase gastrin release, gastric peristalsis and HCl release

51
Q

What is the gastric phase of gastric secretion

A

Food stretches stomach wall, stretch receptors and chemoreceptors increase submucosal plexus activity that increases gastric juice secretion
Increased myenteric plexus activity increases stomach peristalsis.
Increased parasympathetic = release of gastrin by enteroendocrine cells

52
Q

What is the intestinal phase of gastric secretion

A

Activation of receptors in duodenum results in hormonal/neuronal reflexes that are inhibitory on gastric motility and gastric acid secretion.
3 hormones, Secretin inhibits gastric juice secretion,
CCK inhibits motility and GIP inhibits both.

53
Q

What is the submucosa

A

The submucosa is a thick connective tissue layer that contains arteries, veins, lymphatics, and nerves.

Systems Physiology (28 decks)

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