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autonomic final > 24 > Flashcards

24 Flashcards

1
Q

describe function of mouth

A
  • digestion of food begins in the mouth
  • saliva moistens and lubricates mouth and food (important for taste and swallowing)
  • mechanical breakdown by teeth
  • enzymatic breakdown (salivary amylase to digest complex carbs)
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2
Q

name the 3 main pairs of salivary glands in humans

A
  • parotid
  • submandibular
  • sublingual
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3
Q

what units make up salivary glands

A
  • salivons = acini and ducts
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4
Q

salivary acini are made up of what types of cells

A
  • mucous cells: produce mucin = lubricant
  • serous cells: produce watery secretion and proteins (ie salivary amylase)
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5
Q

describe mucous cells

A
  • mucus contains mucin proteins (forms a protective barrier and acts as lubricant)
  • mucins are heavily glycosylated proteins = N and C term contain cysteine residues > allow polymerization
  • central region contains serines and threonines = glycosylation > blocks degradation by peptidases
  • mucins retain large amounts of water on the epithelial surface
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6
Q

describe serous cells

A
  • salivary amylase catalyzes the hydrolysis of starches
  • hydrolyze up to 75% of ingested starches
  • amylase is degraded in the stomach by high acidic environment
  • produces initial saliva
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7
Q

describe where aquaporins are expressed and their functions

A
  • aquapoirins present in the acini (but not in ductal cells)
  • allow water to flow into tubules
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8
Q

describe how saliva is formed

A
  • saliva begins as fluid secreted by acinar serous cells
  • composition of this fluid changes as it travels thru ductal system to reach mouth
  • ductal cells reabs Na and Cl and secrete K and bicarb
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9
Q

how does ductal cells modify initial saliva produced by acinar cells

A
  • epithelium of duct is largely impermeable to water
  • more Na and Cl removed than K and HCO3 added = saliva is hypotonic with respect to plasma
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10
Q

what innervate salivary glands

A
  • salivary glands receive inputs from SNS and PNS
  • but PNS inputs predominates
  • salivation rate can be increased by variety of stimuli
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11
Q

how is salivation regulated (what factors affect salivary flow)

A
  • by the salivatory nuc of the medulla
  • food in mouth - Acidic taste stimulates salivation; Sweet tastes are least potent stimulators
  • psychic factor - Thinking about or smelling food stimulates salivation
  • circadian rhythm - Highest in afternoon, lowest during sleep
  • dehydration
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12
Q

describe PNS input to salivary glands

A
  • primary input via M3R = increases fluid and protein secretion (activation of M3R > cal dependent translocation of aquaporins from intracellular vesicles to the plasma mem in the parotid glands)
  • similar to vasopressin in renal interstitium
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13
Q

describe SNS input to salivary glands

A
  • indirect effect on salivary glands via a1R expressed in vasculature
  • vasocon decreases blood flow to salivary glands > less production of saliva
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14
Q

describe function of stomach

A
  • chemical breakdown of ingested food
  • Acid is pumped into lumen of stomach = Pepsinogen is released > Converted into active peptidase by acid in stomach > Pepsin
  • mechanical breakdown of ingested food
  • Chyme is formed = Liquified material that will be released into small intestine
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15
Q

name the specialized cells of the stomach (brief function)

A

Parietal cells = Secrete HCl
Chief cells = Secrete pepsinogen
Mucous neck cells = Secrete mucus that helps protect the stomach lining
Enteroendocrine cell

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16
Q

how does parietal cells secrete HCl

A
  • CO2 in bloodstream enters parietal cells > combines with water > form H2CO3
  • carbonic anhydrase convert the carbonic acid into H and HCO3
  • HCO3 transported out as Cl transported in
  • H is transported into lumen of the stomach while K transported in via ATP transporter
  • Cl diffuses into lumen of stomach where it combines with H
17
Q

describe role of chief cells

A
  • secrete pepsinogen (precursor to active pepsin - group of proteases)
  • pepsinogen is release by exocytosis from vesicles
  • pepsinogen is converted to active pepsins by acidic condition in stomach (most active ph 3 and below)
18
Q

describe the role of mucous neck cells

A
  • located in narrow neck of the gastric gland
  • mucins are heavily glycosylated peptides > the sugars protect them from pepsins = line gastric mucosa = trap bicarb released by epithelial cells of the stomach > bicarb trapped in mucous at surface of stomach lining to form alkaline barrier to acidic environment of stomach = prevent stomach from digesting itself
19
Q

describe how food in the stomach causes release of gastrin

A

food in stomach stim IPANs > causes release of gastrin from G cells in stomach > either
- short-loop reflex = excitation of IPANs activates intrinsic ENS reflex > secretomotor neurons release gastrin releasing peptide (GRP)
- gastrin released into circulatory system > increases the release of H+ from parietal cells

20
Q

describe gastrin relationship with histamine

A
  • gastrin released into the circulatory system > increases the release of histamine from ECL cells
  • histamine = strongest activator of HCl release from parietal cells
21
Q

describe the long-loop reflex when food in stomach stim IPANs

A
  • long-loop reflex involves PNS input
  • excitation of IPANs increase PNS input to ENS > vagus release ACh to increase histamine release from ECL cells + vagus releases ACh to increase H+ release from parietal cells
22
Q

describe somatostatin release and action

A
  • presence of highly acidic contents of the distal stomach increases release of somatostatin from D cells
  • somatostatin binds to inhibitory receptors > inhibit the further release of gastrin from G cells > inhibition of acid secretion
23
Q

what happens with entry of food into the stomach and gastrin

A
  • food buffers concentration of H+
  • decreased H+ inhibits somatostatin release
  • decreased somatostatin > less inhibition on gastrin release
  • increased release of gastrin causes increased secretion of HCl
24
Q

what happens with no food in the stomach and gastrin

A
  • pH in lumen is low > increased concentration of H+ increases release of somatostatin from D cells = inhibits secretion of gastrin > HCl secretion into stomach is decreased
25
Q

what happens if stomach acid comes into contact with surface of GI lumen?

A
  • ulcers may develop
  • gastric, esophageal, duodenal
26
Q

describe the components of gastrointestinal barriers

A
  • has two components
  • extrinsic barrier - made up of secretions from epithelium = help maintain barrier function
  • intrinsic barrier - made up of the epithelial cells lining the digestive tube (tight junctions between cells)
27
Q

how does SNS act on ENS

A
  • SNS inhibits ENS functions
  • vasoconstriction = decreased blood flow limits removal of excess protons
  • decreased secretions = decreased secretion of mucus
  • stress may contribute to erosion of the gastric mucosa > gastrointestinal hemorrhage
28
Q

describe how chyme is emptied from the stomach

A
  • chyme is emptied from the stomach into the duodenum of the small intest via peristalic contraction > pushes chyme towards pyloric sphincter (which is partially relaxed) > small quantity of the chyme is forced through the sphincter into the duodenum
29
Q

describe anatomy of small intestine

A
  • 3m long divided into sections
  • duodenum proximal to stomach
  • jejunum between duodenum and ileum
  • ileum final section of small intest which leads to colon
30
Q

how does anatomy of intestine help aid absorption of nutrients

A
  • very large surface area from:
  • villi + microvili which contains brush border that has some digestive enzymes
  • crypts
31
Q

what is the main function of the small intestine

A
  • further liquefaction and digestion of ingested food: Water and NaCl are increased in the lumen + Pancreatic juices and bile from liver are introduced
  • absorption of nutrients into blood
  • distal reabsorption of water and electrolytes ( water and sodium removed from lumen)
32
Q

what happens when theres a decrease in fluid volume or plasma sodium levels? (think sympathetic inputs)

A
  • increases activity of SNS input to sevretomotor neurons > decreases secretion of Cl- > causes decrease in amount of water and sodium released into lumen of GI tract

autonomic final (8 decks)

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