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GI Lectures > Intestinal physiology: fluid, electrolytes and digestion > Flashcards

Intestinal physiology: fluid, electrolytes and digestion Flashcards

1
Q

What is important for diffusion?

A

Shape:
- If the shape is not hollow: greater ratio of volume to exterior surface area than in a single cell
- The cavity or lumen is important for optimal digestion and absorption

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2
Q

What does terrestrial mean?

A

Not living in an aqueous solution filled with nutrients

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3
Q

What is the function of the gut (tube)?

A
  • Take relatively large solids and digest them into smaller molecules that can be absorbed as nutrients, while still serving as a barrier to toxins, bacteria, parasites etc…
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4
Q

What are some functional anatomy points about the GI system?

A
  • GI system is a hollow organ, a tube through the body.
  • The lumen is “outside” the body’s tissues, but its environment is tightly controlled by the body.-
  • Specialised organs for secretion of enzymes & bile.
  • Epithelial cells line the entire GI tract and serve as the primary barrier.
  • Structure maximises surface area for secretion and absorption (folds, villi, and crypts).
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5
Q

What functions do the epithelial cells have?

A
  • Secrete water and electrolytes
  • Absorb water and elecrolytes
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6
Q

How much fluid should we ingest a day?

A

2L/day

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7
Q

How much fluid does the small intestine absorb a day?

A

7.5 L/day

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8
Q

How much fluid do we excrete a day?

A

<200ml

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9
Q

How does water move in an osmotic gradient?

A
  • Water moves down the osmotic gradient
  • Electrolytes move down electrochemical gradient
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10
Q

How is energy supplied to move up the conc gradient?

A

Energy is supplied by the sodium gradients (generated by the sodium pump) and by proton gradients

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11
Q

How much fluid does the small intestine ingest a day?

A

7.5L/day

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12
Q

What are the three segments of the small intestine?

A
  • Duodenum
  • Jejunum
  • Ileum
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13
Q

How long is the small intestine circa?

A

6m long

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14
Q

How does Na+ help with water movement?

A

1st stage: membrane transport protein - Transports glucose from intestinal lumen into epithelial cells via Na+
2nd stage: Na+/K+/ATPase transporter uses ATP to shift sodium into blood/ baso-lateral membrane. This shifts water with it from the gut to body (blood)
This happens because water always follows sodium

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15
Q

How does Cl- help with movement of fluids?

A
  • cAMP (cyclic AMP) shifts Cl from body to intestinal lumen
  • This makes the basolateral end of the lumen very negative
  • So the Cl- moves across lumen to a positive end and it takes Na+ and K+ with it (as it uses a Na+/K+/2Cl- transporter)
  • This therefore takes water with it
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16
Q

What factors affect absorption?

A
  • Number and structure of enterocytes
  • Blood and lymph flows
  • Nutrient intake
  • GI motility (e.g. if take medication that influences movement)
  • GI motility also affected by hormonal and neural factors
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17
Q

What factors affect secretion?

A
  • Irritants
  • Bile
  • Bacterial toxins
  • Hormonal and neural factors also affect secretion
18
Q

What are some clinical conditions that can arise if the intestines can not absorb/secrete properly?

A
  • Diarrhoea
  • Weight loss
  • Failure to thrive
19
Q

Why does coeliac disease affect absorption?

A
  • Attacks small bowels and so you lose villi
  • Therefore can’t absorb nutrients properly
20
Q

What toxin induces diarrhoea?

A
  • Cholera toxin is released from bacteria in infected intestine
21
Q

How does cholera toxin induce diarrhoea?

A
  • Released
  • Then binds to intestinal cells
  • Stimulates adenylate cyclase to produce cAMP
  • Dramatic efflux of ions and water
  • Profuse Cl- excretion so lots of water movement into body
  • So watery diarrhoea
22
Q

How do oral rehydration packets work?

A
  • Packet contains lots of SGLT-1 or sodium glucose so lots of sodium ions in the intestinal wall. So Na moves into blood and takes water with it as a co-transporter, therefore rehydrating the body
23
Q

What is the definition of digestion?

A

Breakdown of large, complex organic molecules that can be used by the body
- Mechanical (chewing, churning food)
- Chemical (enzymes)

24
Q

Where is the primary site for digestion and absorption of food?

A

Small intestine

25
Q

Where does digestion occur more specifically?

A

In the GI lumen by secreted enzymes and on the surface of enterocytes (intestinal absorptive cells) by membrane-bound enzymes

26
Q

Which types of transports facilitate absorption?

A

Simple diffusion, facilitated diffusion, active transport, endocytosis, paracellular transport

27
Q

How is the small intestine adapted for absorption?

A

By extensive folding and the projection of fingerlike villi covered with microvilli

28
Q

How is CHO (carbohydrate) digested?

A
  • Starts as a glucose polymer then amylase in the mouth and pancreas breaks it down into…
  • Disaccharides (e.g. maltose, sucrose)
  • These are then broken down further into monosaccharides (e.g. glucose, fructose)
29
Q

How is digested carbohydrate absorbed?

A

Enterocytes absorb glucose and galactose through an Na+ dependent secondary active transport process, while fructose is absorbed by facilitated transport.

30
Q

How are proteins digested?

A

Only really digested and acted on in the stomach by pepsin and then in the small intestine by trypsin and chymotrypsin breaking them down into amino acids

31
Q

How are proteins absorbed?

A

Facilitated diffusion and co-transport into the intestinal mucosa with the help of peptidases and then via Facilitated diffusion and co-transport into the blood stream

32
Q

How are fats digested?

A
  • Fat and water separate
  • So bile (an emulsifier) has an affinity for both fat and water and can thus bring the fat into the water
  • This allows fat-digesting enzymes to have access to it and break the fat down
33
Q

What do bile acids do?

A
  • Gallbladder contracts and releases contents (bile)
  • They are released into the small intestine
  • After they have emulsified fats, they are reabsorbed in the terminal ileum and recycled back to the liver
34
Q

How are lipids absorbed?

A
  • Bile salts help absorb from the lumen into the intestinal epithelia
  • Then chylomicrons help transport triglycerides and lipids from intestinal epithelia to vessels
  • Then they are transported through the lymph system
35
Q

What enzymes do the salivary glands release?

A
  • Amylase (starch)
  • Lipase (triglycerides)
36
Q

What enzymes does the stomach release?

A
  • Pepsin (proteins)
  • Lipase (triglycerides)
37
Q

What enzymes does the pancreas release?

A
  • Amylase (Starch)
  • Lipase and Colipase (Triglycerides)
  • Phospholipase (Phospholipids)
  • Trypsin (Peptides)
  • Chymotrypsin (Peptides)
38
Q

What enzymes does the intestine release?

A
  • Enterokinase (Activates trypsin)
  • Disaccharidases (Complex sugars)
  • Peptidases (peptides)
39
Q

What are the three pairs of salivary glands?

A

Parotid
Sublingual
Submandibular

40
Q

What are the functions of saliva?

A
  1. Lubricates, cleans oral cavity
  2. Dissolves chemicals
  3. Suppresses bacterial growth
  4. Digest starch by amylase
41
Q

What regulates the secretion of saliva?

A

Neural (voluntary and involuntary) secretions

GI Lectures (14 decks)

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