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Gastrointestinal > Transport Across Alimentary Tract > Flashcards

Transport Across Alimentary Tract Flashcards

1
Q

What nervous systems are present in the gut?

A

The gut has an intrinsic and enteric nervous system

- large neuronal connections in the gut

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2
Q

Name the 2 intrinsic neural plexus of the gut

A

Submucosal Meissner Plexus
- regulates digestive glands

Myenteric Auerbach’s Plexus
- connected to gut motility

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3
Q

What are the intrinsic neural controls of the GI tract?

A

Nerve plexus’ near GI tract initiate short reflexes mediated by local ENS plexus

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4
Q

What are the extrinsic neural controls of the GI tract?

A

Long reflexes arising within/outside GI tract

Involve CNS and extrinsic Parasympathetic reflexes

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5
Q

What type of neurons are within the plexi?

A

The nerve plexi contain local sensory + motor neurones as well as inter-neurons for communication

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6
Q

What stimulates the motor neurons in the myenteric plexus?

A

Motor neurons stimulated by Ach (m receptors) and substance P release

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7
Q

What do inhibitory Motor neurons release?

A

Cause the release of VIP/NO

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8
Q

What is the Serosa?

A

tissue of the outer serous membrane of the gut

Is continuous with the mesentery containing blood vessels, lymph vessels and nerve fibres

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9
Q

Where are sensory neurons found in the gut?

A

Connected to mucosal chemoreceptors and stretch receptors

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10
Q

What is the function of sensory neurons in the GI tract?

A

Respond to gut wall tension caused by food and chyme

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11
Q

What type of cells is the small intestine composed of?

A

epithelial folds
villi + microvilli
- to provide a large SA of 200 m²

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12
Q

What is the fate of the small intestine contents?

A

all dietary nutrients, water and electrolytes that enter the upper small intestine are absorbed

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13
Q

What are crypt cells?

A

Cells located where the epithelia of villi extend down into the lamina propria to form crypts

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14
Q

Where us the lamina propria located?

A

Beneath the epithelium

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15
Q

Which cells are located within the crypts?

A

Many important cells reside in the crypts including host defence + signalling cells, and stem cells for replacement

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16
Q

What is transcellular transport (give an example)?

A

Transport of solutes by a cell through a cell

e.g. glucose transport from intestinal lumen →ECF by epithelial cells

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17
Q

What is paracellular transport?

A

Passage of solutes between cells; passive but selective, variable and regulated
e.g. Na+, Cl-, H₂O

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18
Q

How are carbohydrates absorbed?

A

Can only be absorbed as Monosaccharides

complex CHO need to be reduced to disaccharides by amylase

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19
Q

How are disaccharides converted to monosaccharides?

A

Specific brush border enzymes convert disaccharides → monosaccharides (e.g. glucose and galactose)

20
Q

Give examples of disaccharides conversions to monosaccharides via their specific enzymes

A

Sucrose → Glucose + fructose
- via sucrase

Starch →glucose oligomers
- via salivary + pancreatic amylase
Glucose oligomers →glucose
- via glucoamylase

Lactose→glucose + galactose
- via lactase

21
Q

How are glucose and galactose transported?

A

Rapidly absorbed by a secondary active transport mechanism

22
Q

Explain how glucose and galactose are transported

A
  1. Na generates an electrochemical gradient
    • Na+ flux out of cell
    • K+ moves into cell
  2. Glucose moves out along with Na+ as it’s pumped out
    due to SGLT1 transporter binding site
  3. Galactose also joins due to a similar binding site
  4. GLUT2 transporters transport glucose → bloodstream
  5. Fructose →blood via passive diffusion through GLUT5
    transporter
23
Q

Which molecules does SGLT transport?

A

Glcose and fructose

24
Q

Which enzyme facilitates protein production?

A

Pepsin action produces polypeptides

25
Q

Which enzymes aid digestion and absorption of polypeptides?

A

Pancreatic proteases

Dipeptidases in the brush border cause complete digestion into amino acids

26
Q

How are amino acids transported within the small intestine?

A

On a sodium coupled carrier system (similar to glucose)

Separate carriers for different amino acids

27
Q

How are some di/tri-peptides transported in the small intestine?

A

On a carrier system using inwardly directed H+ gradient

28
Q

What dietary lipids do we obtain?

A

90% TGs
Phospholipids
Cholesterol
Fat soluble vitamins A,D,E,K

29
Q

How is lipid absorption facilitated?

A

Dietary TGs are broken down into simpler units to facilitate absorption

30
Q

Where along the GI tract are lipids digested?

A

Small fraction digested by salivary lipases (in mouth)
Most TGs digested in small intestine
Gastric lipase hydrolyses 10-30%
remainder digested by pancreatic lipases

31
Q

Explain why TGs are harder to dissolve

A

Water insoluble
Chyme (emulsion of fat particles in water
Lipase is water soluble
TGs must be dissolved in the aqueous phase before they can be digested

32
Q

Which two processes facilitate lipid digestion + absorption?

A
  1. emulsification

2. micelle formation

33
Q

Describe the composition of TGs

A

1 glycerol + 3 fatty acids

34
Q

Explain how TG emulsification enables digestion by lipases

A

Lipase action requires emulsification of TGs by bile salts which dissolve TG in water
Pancreatic lipase then binds to the surface of the small emulsion particles

35
Q

What is the role of bile salts in emulsification of lipids?

A

Break large fat globules → smaller globules

SA for lipase to act on is increased

36
Q

What are micelles?

A

lipid molecules that arrange themselves in spherical formation in aqueous solutions

37
Q

How are micelles transported?

A

small enough to be taken up by enterocytes → lacteals→ lymphatics before travelling to blood via thoracis duct → subclavian vein

38
Q

Explain why TG formation occurs?

A

to form chylomicrons

39
Q

What are chylomicrons?

A

Largest lipoprotein

40
Q

What is a lipoprotein?

A

Protein and lipid components

41
Q

What is an apo?

A

coenzyme/cofactor attached to protein

42
Q

Explain the milky appearance of lymph

A

Lymph has a milky appearance during drainage from small intestine due to chylomicrons

43
Q

Explain the route chylomicrons take to reach the blood

A

Chylomicrons enter lymphatic system via lacteals and then travel via lymph vessels and enter blood

44
Q

What are the disorders of fat digestion?

A

Gallstones
Pancreatitis
Crohn’s disease
Liver disease

45
Q

What is the consequence of fat digestion disorders?

A

Can lead to fat malabsorption (steatorrhoea)

; excess fat in faeces

Gastrointestinal (18 decks)

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