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Gastrointestinal > Session 8 > Flashcards

Session 8 Flashcards

1
Q

What is the main purpose the the intestines?

A

To absorb nutrients, water and electrolytes from chyme

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2
Q

How are the intestines adapted for their purpose?

A

Have a large surface area (Villi)

Contents moves slowly through

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3
Q

What is the structure of the small intestine?

A

The mucosa is folded in Villi which is separated by the Crypts of Leiberkuhn (Glands in the epithelium, also in the Colon)

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4
Q

How are cells released into the small intestine?

A

Cells multiply in the Crypts of Leiberkuhn and migrate to the top of the villi (Mature as they go and acquire the capacity to absorb and microvilli to increase the surface area)
Then shed from top of Villus

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5
Q

What forms an unstirred layer in the intestine?

A

Villi secrete enzymes into the brush border which forms the unstirred layer.

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6
Q

What does the unstirred layer do?

A

Partially digested nutrients get trapped in it and the enzymes complete digestion. Steadily release the small molecules for absorption.

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7
Q

When can digestion be disturbed?

A

If the brush border is disturbed then there are less enzymes to digest the nutrients

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8
Q

What is the structure of the 2 parts of Starch?

A

Amylose has long straight chains with alpha 1,4 bonds

Amylopectin has branches with alpha 1,6 bonds

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9
Q

What enzyme breaks down starch?

A

Amylase acts on alpha 1,4 bonds yielding Glucose and Maltose from Amyloses.
Cannot get many dextrins from Amylopectin due to it not being able to break the alpha 1,6 bond

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10
Q

What released Amylase?

A

Salivary amylase in the mouth

Pancreatic amylase in the small intestine

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11
Q

What completes the breakdown of starch?

A

The enzymes in the brush border of the small intestine. (Maltase breaks Maltose to glucose, isomaltase breaks branched molecules at alpha 1,6 bonds)

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12
Q

How is Glucose absorbed from the lumen of the small intestine?

A

Active transport up a concentration gradient using energy form the Na/K ATPase. Uses the Na+/Glucose symporter (SGLT1)

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13
Q

How is Fructose and Lactose absorbed from the lumen of the small intestine

A

Facilitated diffusion not linked to Na+

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14
Q

How does Glucose leaves the luminal cells?

A

Facilitated diffusion (GLUT2 Transporter)

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15
Q

What is in oral hydration fluid?

A

Na+ and Glucose because the uptake of Na+ generates an osmotic gradient for water to follow.Glucose uptake stimulates Na+ uptake and generates an osmotic gradient as well.

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16
Q

What are proteins digested into?

A

Oligopeptides (Which release small peptides and sometimes single Amino Acids)

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17
Q

What breaks down proteins in the stomach?

A

Pepsin released from Chief cells

18
Q

What breaks down proteins in the duodenum?

A

Peptidases from the pancreas eg Trypsin & Chymotrypsin. Carboxypeptidase.

19
Q

What breaks down the oligopeptides?

A

Enzymes in the brush border of the intestine. The Amino Acids and peptides are then absorbed by active and passive processes

20
Q

What are the 5 Na+/AA co-transporters in the small intestine?

A 
Small neutral AA
Neutral AA, basic AA and Cystine
Acidic AA
Imiuo AA
Beta AA (Mainly Taurine)
21
Q

What is the difference between newborn absorption of protein and adults?

A

Adults cannot absorb proteins that haven’t been broken down, but newborn babies can - useful for immunoglobulins which would lose their effect if broken down.

22
Q

How is Na+ absorbed in the small intestine?

A

Diffusion into the cell then active transport through the baso lateral membrane

23
Q

How is Cl- absorbed in the small intestine?

A

Follows Na+ due to the electrical gradient it causes

24
Q

How is Ca2+ absorbed in the small intestine?

A

Enters the cells via facilitated diffusion as there is a low intracellular concentration. It is then pumped out via a Ca2+ ATPase on the basolateral membrane of the cell.
Both of these processes need vitamin D (Cofactor) and PTH

25
Q

How is Iron absorption aided?

A

Gastric acid solubises the iron complexes

Gastroferrin (Secreted from the stomach) also solubises

26
Q

How is Iron absorbed into the cells?

A

The mucosal cells secrete transferrin which binds iron in the lumen
The complex is then endocytosed (Receptor mediated endocytosis)
Iron is then liberated and exported into the blood where it can bind to transferring again

27
Q

How are water soluble vitamins absorbed in the small intestine? (Vitamin B & C)

A

Passive diffusion

28
Q

How is vitamin B12 absorbed?

A

In the terminal ileum ONLY

Needs a co factor to carry it through the GI system (Intrinsic factor which is made and secreted by the stomach mucosa)

29
Q

What is Pernicions anaemia?

A

The red blood cells and haemoglobin cannot be made due to B12 deficiency which is due to stomach damage so it cannot make intrinsic factor

30
Q

How are the contents of the small intestines moved?

A

Slow agitation of the contents - Segmenting (NOT peristalsis)

31
Q

Where are the intestinal pacemakers of the small intestine?

A

At intervals along the length of the small intestine
Higher frequency at the stomach end (Makes the intestinal gradient that causes slow caudal progression)
Each pacemaker drives a small section of the intestine to cause intermittent contraction along its length

32
Q

What is the aim of segmenting in the small intestine?

A

Mixes and agitates the content

33
Q

What are the 2 elements to the large intestine motility?

A 
Haustal shuttling (Similar to segmenting, but slower)
Mass movement (Peristsaltic wave)
34
Q

What is colon divided into?

A

Haustra (Circular & Longitudinal muscle)

Contraction of smooth muscle in the walls of Haustra moves the contents

35
Q

How often does Mass movement occur?

A

Around once or twice a day

36
Q

What is Mass movement?

A

A peristaltic propulsive pattern from the transverse colon through the descending colon.
It forces the faeces rapidly into the rectum (Which is usually empty) inducing an urge to defecate.

37
Q

What often triggers Mass movement?

A

Eating (Called the Gastro-Colic reflex and is part of receptive relaxation)
Swelling of the stomach causes the colon to empty as it knows soon food will be there.

38
Q

Why is there an urge to defecate when the rectum is full?

A

Pressure receptors in the wall of the rectum

Waves of contraction in the rectal muscle forces the faeces into the anus

39
Q

What are the 2 anal sphincters?

A

Internal - Smooth muscle, parasympathetic control relaxes

External - Striated muscle, Somatic motor system.

40
Q

How is faeces expelled from the anus?

A

External sphincter relaxes first which then causes the internal sphincter to relax.
There is an increase in intra abdominal pressure leading to expulsion of faeces.
It is controlled via the sacral reflexes by higher centres, but this is overridden if the rectal pressure is too high.

Gastrointestinal (13 decks)

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