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SGUL - Physiology 1 > Transport Along and Across GI Tract PART 2 > Flashcards

Transport Along and Across GI Tract PART 2 Flashcards

1
Q

Describe the motor activity in the small intestine in the fed state.

A
  • Mixing contractions, i.e segmentation, which mixes and stirs the contents with enzymes, and prevents an unstirred layer formation.
  • Peristaltic contractions - move the contents in an oral to anal direction
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2
Q

Describe motor activity in the small intestine in the fed state with reference to the nervous system.

A
  • Usually a reflex mediated by ENS
  • Sympathetic innervation inhibits motility
  • Parasympathetic innervation stimulates motility
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3
Q

What two emotions can decrease intestinal motility?

A

PAIN
FEAR

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4
Q

Describe storage in the large intestine.

A
  • Occurs whilst water is absorbed from the contents.
  • Intensive mixing and slow movements of waste and indigestible material occur aborally.
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5
Q

What are the purpose of fermentation chambers in the large intestine?

A

Hydrolysis of fibre and indigestible nutrients, leading to faeces formation.

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6
Q

Describe the motility of the large intestine. PART 1

A
  • Segmental contractions mix the contents - using taenia coli longitudinal muscle.
  • Peristalsis: slow in the large intestine in comparison to the small intestine, moves the contents towards the anus; distention initiates contraction.
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7
Q

Describe the motility of the large intestine. PART 2

A

Mass movement: powerful contraction of the mid-transverse colon that sweeps the colon contents into the rectum (responsible for colonic evacuation).

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8
Q

SUMMARY - What are the three main features of motility in the large intestine?

A

Fermentation
Intensive mixing and slow aboral flow

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9
Q

How does the hypothalamus detect food in the gut? PART 1

A
  • Outer muscle layer of the gut is covered by the serosa, which is continuous with the mesentery containing blood vessels and nerve fibres.
  • Sensory neurones are connected to the mucosal chemoreceptors, which detect different chemical substances in the gut lumen
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10
Q

How does the hypothalamus detect food in the gut? PART 2

A
  • Sensory neurons also connected to stretch receptors, which respond to the tension in the gut wall, caused by the food and chyme.
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11
Q

FPP RECAP: Describe the sympathetic ganglia and where they are found.

A
  • Found along length of sympathetic trunk
  • Distinguished as cervical, thoracic, lumbar, and sacral - based on position on spinal cord
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12
Q

Describe carbohydrate (CHO) digestion and absorption.

A
  • Can only be absorbed in the form of monosaccharides
  • Complex carbohydrates reduced to disaccharides by amylase
  • Brush border enzymes convert disaccharides to monosaccharides (eg. glucose)
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13
Q

Describe the transport of galactose across the apical membrane.

A
  • Actively transported by the luminal glucose carrier system
  • Competitive inhibitor of glucose transport.
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14
Q

Describe the transport of fructose across the apical membrane.

A
  • No effect on the absorption of glucose and galactose.
  • Absorbed by a carrier-mediated, facilitated diffusion system - energy is not required.
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15
Q

For active transport, where is the sodium-potassium ATPase pump found?

A

Basolateral membrane.

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16
Q

Describe the movement of fructose from the intestinal lumen to the blood and various tissues.

A
  • After apical transport mediated by GLUT5, fructose is transported across the basolateral membrane by GLUT2.
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17
Q

How is GLUT2 different to GLUT5?

A
  • GLUT2 transports fructose, glucose and galactose. GLUT5 is only specific to fructose
  • GLUT2 is sensitive to phloretin and cytochalasin B. GLUT5 is not.
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18
Q

What is the role of GLUT2?

A
  • Fructose uptake across hepatic plasma membrane into liver
  • Fructose uptake across basolateral membrane of intestinal/renal epithelial cells
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19
Q

Describe protein digestion.

A
  • Polypeptides produced by action of pepsin.
  • Polypeptides, di- and tri- peptides produced by action of pancreatic proteases.
  • Di-peptidases in the brush border complete digestion to amino acids.
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20
Q

Describe protein absorption.

A

Hydrolytic digestive products are absorbed intact across the intestinal mucosa and into the blood.

21
Q

Describe amino acid transport.

A
  • Transported on a sodium-coupled carrier system.
  • Separate carriers for different types of amino acids.
22
Q

Describe di/tripeptide transport.

A

Carrier system using an inwardly directed H+ gradient.

23
Q

Give examples of dietary lipids.

A
  • Triglycerides(TGs) - make up majority of dietary lipids.
  • Phospholipids
  • Cholesterol
  • Vitamins (A,D,E,K)
24
Q

Generally, describe the digestion of lipids.

A
  • Dietary TGs are broken down into simpler units to facilitate absorption.
  • In the mouth, salivary lipase digests a small fraction of the TGs.
  • Most dietary TGs are digested in the small intestine.
25
Q

What must happen to triglycerides before digestion?

A

Dissolved in the aqueous phase

26
Q

In detail, describe the digestion of lipids. PART 1

A
  • Facilitated by emulsification and micelle formation
  • Gastric lipase breaks down approximately 10-30% of fats, the remainder is digested by pancreatic lipase.
27
Q

In detail, describe the digestion of lipids. PART 2

A
  • Lipase action requires the emulsification of TGs by bile salts (which dissolve TGs in water).
  • Pancreatic lipase binds to the surface of the small emulsion particles.
28
Q

Describe micelles.

A
  • Lipid molecules that arrange themselves in a spherical form in aqueous solutions.
  • Micelle formation is response to the amphipathic nature of fatty acids
29
Q

FLC RECAP: What does it mean for a fatty acid to be amphipathic?

A

Contain both hydrophilic and hydrophobic regions (polar head group and long hydrophobic chain).

30
Q

Describe mixed micelle formation.

A
  • Simple lipid molecules diffuse into the lipophilic core of the simple bile micelle and form mixed micelle.
31
Q

What are some of the simple lipid molecules used in mixed micelle formation?

A
  • Cholesterol, phospholipids, fatty acids, 2-monoglycerides, fat-soluble vitamins, and lyso-lecithin
32
Q

What happens to the mixed micelle following formation?

A

Carry the lipids that are absorbed by intestinal microvilli

33
Q

Summarise the digestion and transport of lipids. PART 1

A
  • Dietary fat composed of TGs is emulsified by the action of bile salts into a suspension of fat droplets.
  • Lipid emulsion prevents the fat droplets from coalescing and increases surface area available for attack by pancreatic lipase.
34
Q

Summarise the digestion and transport of lipids. PART 2

A
  • Lipase hydrolyses TGs into monoglycerides and free fatty acids.
  • Water-insoluble products are carried in the interior of water-soluble micelles, to the luminal surface of the small intestine epithelial cells.
  • Micelles formed by bile salts and other bile constituents
35
Q

Summarise the digestion and transport of lipids. PART 3

A
  • When a micelle approaches the absorptive epithelial surface, the MGs and fatty acids leave the micelle and passively diffuse through the lipid bilayer of the luminal membranes.
36
Q

Summarise the digestion and transport of lipids. PART 4

A
  • Monoglycerides and free fatty acids are resynthesised into TGs in the epithelial cells.
  • TGs aggregate and are coated with a layer of lipoprotein to form water-soluble chylomicrons
37
Q

Summarise the digestion and transport of lipids. PART 5

A
  • Chylomicrons extrude through the basal membrane of the cells by exocytosis.
  • Chylomicrons are unable to cross the basement membrane of blood capillaries, so instead they enter the central lacteals.
38
Q

Describe disorders of fat digestion/ absorption.

A

Gallstones, pancreatitis, Crohn’s Disease, and liver disease can lead to fat malabsorption (steatorrhoea or fat-diarrhoea = excess fat in the faeces).

39
Q

Where do bile salts go following lipid digestion?

A

→ Recycled by enterohepatic circulation

40
Q

How do bile salts work?

A

→ They make the lipid molecules much smaller
→ Enzymes from the pancreas can break down the lipid and get to the core

41
Q

What does the duodenum detect?

A

Lipids which must be emulsified

42
Q

How is pepsin secreted and how is it activated?

A

→ Secreted as a zymogen (pepsinogen)
→ HCl converts it into pepsin

43
Q

List the equations for the breakdown of the following?

SUCROSE
LACTOSE
GLUCOSE OLIGOMERS

A

Sucrose (+ sucrase) → Glucose + fructose
Lactose (+lactase) →Glucose + galactose
Glucose oligomers (+glucoamylase) → glucose

44
Q

Describe the way glucose and galactose are transported.

A

→ On the basolateral side Na+ is transported into the blood
→ Gradient is created for Na+ to come into the lumen
→ Driving force of Na+ allows glucose to come with it

45
Q

What is the glucose/galactose co-transporter called?

A

SGLT-1

46
Q

What are adaptations of the small intestine to absorb food?

A

→ Epithelial folds
→ Villi + microvilli
→ Increase SA

47
Q

What is absorbed when it enters the upper small intestine?

A

→ Dietary nutrients
→ Water
→ Electrolytes

48
Q

The intestines contain crypt cells. What is kept within these cells?

A

Stem cells

49
Q

What are the two modes of transport across enterocytes?

A

→ Transcellular
→ Paracellular

SGUL - Physiology 1 (68 decks)

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