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HUBS192 Missing Cards > Lecture 25: Secretion > Flashcards

Lecture 25: Secretion Flashcards

1
Q

What are the types of secretions?

A
  • salivary
  • gastric
  • pancreatic
  • biliary (liver and gallbladder)
  • intestinal
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2
Q

define secretion

A

movement of solutes and water from body to the lumen

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3
Q

define absorption

A

movement of solutes and water from the lumen into the body

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4
Q

what is the difference between endocrine and exocrine secretion?

A
  • endocrine secretions move into the body (so they aren’t really secretions)
  • exocrine secretions are produced by the epithelia and move into the lumen
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5
Q

what are the components of exocrine secretion and their function?

A

Mucus
- protection and lubrication
- aids mechanical digestion

Electrolyte solution
- dilutes food and provides optimal pH
- essential for chemical digestion of food

Digestive enzymes
- essential for chemical digestion of food
- aids absorption

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6
Q

what volume of electrolyte solution is secreted everyday from each region? what is the pH?

A

Plasma - 3L/day, 7.4pH
Saliva - 1.5L/day 7.5 pH
Stomach - 3L/day 1
Pancreas - 1.5L/day 7.8
Liver - 0.5L/day 7.5
Small Intestine - 1.5L/day 7.5

In total 8L/day is secreted from 3L of plasma meaning reabsorption is important!

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7
Q

how much salivary secretion is there?

A
  • 3 pairs of salivary glands
  • produce 1.5L fluid per day
    basal secretion is 0.3ml/min
    stimulated secretion 1.5ml/min
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8
Q

what is the composition of the salivary secretion?

A
  • Mucus for lubrication
  • Dilute solution of bicarbonate and NaCl for dilution of food and optimal pH of digestive enzymes
  • Digestive enzymes: lingual lipase and alpha amylase
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9
Q

what are the functions of salivary secretions?

A
  • aids talking, chewing and swallowing by dissolving food and lubrication
  • hygiene by irrigation
  • xerostomia (dry mouth)
  • digestion by dissolving food to allow taste. lingual lipase digests fats, alpha amylase dissolves starch
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9
Q

what regulates salivary secretion?

A

Nervous regulation
- thought, smell, sight of food, presence of food in mouth

Autonomic nervous system
- parasympathetic stimulates secretion of copious quantities of fluid
- sympathetic secretes small volumes of viscous fluid which augements parasympathetic response

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10
Q

What is gastric (stomach) secretion per day?

A

2-3L/day

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11
Q

what are the gastric (stomach) secretion between meals?

A
  • slow rate (15-30ml/h) of secretion
  • surface epithelium cells secrete mucous and bicarbonate
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12
Q

what are the gastric (stomach) secretion when eating?

A

superimposed on basal rate

  • surface epithelial cells secrete mucus (goblet cells) and bicarbonate
  • parietal cells secrete HCl (gastric acid) (150ml/h, pH 1.0) and intrinsic factor
  • chief cells secrete pepsinogen
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13
Q

what is the function of mucus in the gastric (stomach) secretions

A
  • protects against abrasion
  • buffers acid with surface bicarbonate
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14
Q

what is the function of intrinsic in the gastric (stomach) secretions

A
  • absorption of vitamin b12 in small intestine
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15
Q

what is the function of pepsinogen in the gastric (stomach) secretions

A
  • pepsinogen is inactive form of pepsin (known as gastric proteolytic enzyme)
  • converted to active form pepsin by acid
  • starts digestion of proteins
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16
Q

what is the function of gastric acid in the gastric (stomach) secretions

A
  • dilutes food
  • denatures protein
  • activates pepsinogen to pepsin
  • creates optimal pH for pepsin
  • protection
17
Q

what is the secretion of acid by parietal cells?

A

it is a source of acid

  • by the formation of carbonic acid by carbonic anhydrase
  • and by the dissociation of carbonic acid to give H+ and bicarbonate
18
Q

how does the secretion of HCl by parietal cells work? link to diagram

A
  1. carbonic anhydrase forms carbonic acid which gives H+ and bicarbonate
  2. Secretion of acid (H+)
    - via the H+K+ ATPase on the apical membrane of parietal cells
    - it pumps H+ ions into the lumen in exchange of potassium ions (K+)
    - K+ return to the lumen through membrane channel
  3. Source of chloride (Cl-)
    - via the anion counter transporter on the serosal membrane of parietal cells
    - ejects bicarbonate into interstitial fluid
    - then imports Cl- ions into cell
  4. Secretion of chloride (Cl0)
    - Cl- diffuses across the cell
    - enters the lumen via Cl- channel in apical membrane
19
Q

what is the regulation of gastric (stomach) secretion coordinated with and named after?

A
  • coordinated with eating and arrival of food
  • named after region of body that controls the secretion
20
Q

what are the 3 phases of gastric (stomach) secretion?

A
  1. cephalic phase (head controls secretion)
  2. gastric phase (stomach controls secretion)
  3. intestinal phase (intestine controls secretion)
21
Q

what are the features of cephalic phase, its stimuli and regulation?

A
  • head controls this secretion
  • 20% of secretion associated with meal
  • prepares for arrival of food

Stimuli:
- higher centers in CNS detect thought, smell, sight of food
- chewing action, taste

Regulated by parasympathetic nervous system via enteric nervous system:
- stimulates parietal cells, chief cells and goblet cells
- stimulate secretion of hormone gastrin which is released into blood and stimulates parietal cells and chief cells

22
Q

what are the features of gastric phase, its stimuli and regulation?

A
  • stomach regulates secretion
  • 70% of secretion associated with a meal
  • ensures sufficient secretion to handle ingested food

Stimuli:
- stretch/distension stomach wall
- products of digestion stomach lumen
- elevated pH

Has nervous and hormonal regulation:
- local nervous reflex by enteric nervous system
- external nervous reflex by parasympathetic nervous system
- stimulates secretion from gastric glands
- stimulates motility
-stimulates gastrin secretion for further stimulation of secretion and motility

23
Q

what are the features of intestinal phase, its stimuli and regulation?

A
  • small intestine regulates secretion
  • 10% of secretion associated with meal
  • controls delivery to small intestine

Stimuli:
- distension of duodenum
- arrival of chyme, lipids and carbohydrates in the duodenum

Nervous and hormonal regulation:
- hormones: gastric inhibitory peptide, cholecystokinin, secretin
- nerves: enterogastric reflex
- hormones and nerves inhibit secretion and motility

24
Q

what type of organ is the pancreas?

A

endocrine and exocrine organ

25
Q

what is the volume of pancreatic secretions?

A

1-1.5L per day

26
Q

what is the composition of pancreatic secretions?

A

Enzymes
- secreted by acinar cells
- used for chemical digestion of food

Alkaline fluid
- secreted by duct cells
- used for neutralise acid and optimal pH for enzymes

27
Q

what is the pancreas important for?

A

most important source of digestive enzymes

28
Q

what are the types of pancreatic enzymes? what are they secreted by?

A

Lipolytic e.g. lipase, phospholipase
Amylytic e.g. pancreatic amylase
Proteolytic e.g. trypsin, chymotrypsin, carboxypeptidase
Nucleolytic e.g. ribonuclease, deoxyribonuclease

all secreted by acinar cells

29
Q

what stimulates pancreatic secretions?

A
  • secretion of digestive enzymes by acinar cells stimulated by hormone cholecystokinin (CCK)
  • arrival of lipids and carbohydrates in duodenum stimulates CCK secretion
30
Q

what is the function of pancreatic secretions?

A

luminal chemical digestion of food

31
Q

how are proteolytic enzymes activated?

A
  • proteolytic enzymes are secreted as inactive precursors and activated in the duodenum (e.g. trypsin/trypsinogen, chymotrypsin/chymotrypsinogen, carboxypeptidase/procarboxypeptidase)
  • in the small intestine, activated involves enterokinase (aka enteropeptidase). it is bound to the duodenal membrane and converts trypsinogen to trypsin
  • trypsin converts other enzymes to active form
32
Q

how is alkaline fluid secreted? what is its function?

A
  • produced by duct cells in pancreas
  • secretion of alkaline fluid is stimulated by secretin
  • secretion of secretin is stimulated by arrival of chyme in duodenum
  • alkaline fluid neutralises acid chyme delivered from the stomach. it creates optimal pH (6.7-9) for pancreatic and intestinal digestive enzymes
33
Q

what is the volume of biliary secretions?

A

0.5L/day

34
Q

what is the composition of biliary secretions?

A

products associated with digestion:
- bile salts
- bicarbonate rich fluid

excretory products
- bile pigments (waste products)
- cholesterol

35
Q

what are the functions of biliary secretions?

A

bile salts - fat digestion
bicarbonate rich fluid - neutralise acid
bile pigments - excretion

36
Q

what is the regulation of biliary secretion?

A

Bile is secreted constantly by the liver
- stored and concentrated in the gallbladder
- delivered to the duodenum with arrival of food

Initial delivery of bile is under hormonal control
- cholecystokinin is produced in response to products of digestion in the duodenum
- initiates contraction of gallbladder and relaxation of hepatopancreatic ampulla
- secretin has mild stimulation of bile by the liver

37
Q

what is the enterohepatic circulation?

A
  • bile is metabolically expensive to produce
  • 95% is reabsorbed in ileum
  • transported back to liver in enterohepatic circulation
  • reabsorbed and secreted to stimulate bile secretion
38
Q

how much small intestinal secretion is there?

A

1.5L/day from crypts/glands

39
Q

what are the components of small intestinal secretion? what is their function?

A

Mucus - lubrication

Isosmotic fluid
- alkaline, mixture of NaCl and sodium bicarbonate
- helps neutralise acid
- dilutes food to aid digestion

Digestive enzymes
- shed cells

40
Q

what does the large intestine secrete? what is its function?

A

mucus - lubrication

HUBS192 Missing Cards (31 decks)

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