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DS > Lecture 12 > Flashcards

Lecture 12 Flashcards

1
Q

What are prominent features found in the small intestine?

A

Place circulars (valves of kercking).

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2
Q

What do the plicae serve as?

A

Increasing SA of small intestine.

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3
Q

What is on top of the plica?

A

Villi - fingerlike projections.

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4
Q

What is the part that ingavinates the lumen of the plica?

A

Villus.

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5
Q

What is the depression of the plica?

A

Intestinal glands (crypts of lieberkuhn).

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6
Q

What is the functional purpose of the glands and villus?

A

Increase SA for digestion and absorption.

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7
Q

What is in the core of the villus?

A

Support structures -

i. blood vessels - carry O2 rich blood toward the SI for metabolism. As capillaries become venous all the absorbed nutrients are carried away in the venous system towards the liver for processing and redistribution.

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8
Q

What is the middle vessel?

A

Lacteal. This is a lymphatic vessel.

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9
Q

What extends from muscular mucosa?

A

Smooth muscle fibres, which are found in the core of the villus (spindle tapered cells).

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10
Q

What is the key function of the smooth muscle fibres?

A

Contraction produces rhythmic beating of the villi, which is enhanced during digestion. This makes the contents are mixed to maximise exposure to epithelial cells. Smooth muscles help to squeeze the lacteals (milk) and the contents along.

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11
Q

What happens in elderly people?

A

Blood supply/circulation functions decrease. There will be decreased absorption (taking blood away from the gut). Lead to malabsorption and malnutrition.

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12
Q

What are microvilli?

A

Projections of membranes, filled with plasma membrane, into the luminal surface.

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13
Q

What is the primary function of microvilli?

A

Increase SA for absorption.

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14
Q

What is in the core of microvilli? and describe the function.

A

Actin filaments. These filaments are connected to cytoskeletal network within the cell. When the smooth muscle cells contract and move basement membrane of the epithelial cells, moves the cells on top of the basement membrane, mechanical movement transferred to cytoskeleton and transferred to actin filaments. Lots of micro whisks producing localised mixing of contents.

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15
Q

What is embedded within the lipid bilayer?

A

Digestive enzymes e.g. glycosidase. Helps to digest carbohydrates.

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16
Q

What coats the microvilli?

A

Glycocalyx. It is a slippery film, made up of glycoproteins, and acidic much polysaccharides.

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17
Q

What does the glycocalyx do?

A

Becomes a selective gate keeper. The desirable molecules are attracted by the glycocalyx, and unwanted molecules the glycocalyx becomes a physical barrier.

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18
Q

What can cause enterocyte disfunction?

A

Tumors, infection, surgery and certain drugs can aggregate and inflame enterocytes. Outcome can be diarrhoea (inadequate absorption), fatty poo, abdominal pain discomfort and weight loss.

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19
Q

What do goblet cells do?

A

Secrete mucus. Apical surface do not have microvilli and mucus serves to help lubricate the process.

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20
Q

Where are enteroendocrine cells found?

A

Deeper in the crypts. But they are spread out.

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21
Q

What is the role of undifferentiated stem cells?

A

Found in the gland region and migrate upwards and downwards to replace cells positioned above or below them.

22
Q

Where are paneth cells found? and what is their role?

A

Bottom of the crypts where the gland turns around.
Important for anti-microbial and anti-viral functions, they produce lysozyme, TNF-alpha (inflammatory mediator) and defensins (increase permeability of membrane of microorganism).

23
Q

What do acidic chyme, amino acids and fatty acids do?

A

Trigger release of certain hormones into the basal lateral membrane via enteroendocrine cells.

24
Q

What is the function of secretin?

A
  1. Stimulate pancreas to produce bicarbonate for the ductal cells in the pancreas.
  2. Inhibit acid production by the stomach.
25
Q

What is the function of cholecystokinin?

A
  1. Stimulates the gallbladder to contract. Bile is stimulated to be injected into the duodenum.
  2. Stimulate the pancreas to increase its production of digestive enzymes.
26
Q

What is the function of serotonin?

A
  1. Increase peristalsis.

2. Increase intestinal secretions by the goblet cells, paneth cells etc.

27
Q

What is the function of somatostatin?

A
  1. Reduce gastrin.
  2. Facilitates smooth muscle contraction.
  3. Enhances absorption.
28
Q

What does the stomach secrete into the duodenum?

A

Acidic chyme, amino acid chains and fatty acids. Come through the pyloric sphincter (controls how much chyme released into SI but the timing i.e. volume and frequency).

29
Q

What happens as the acidic chyme enters the SI?

A

Stimulates the enteroendocrine cells to signal the pancreas and the gall bladder.

30
Q

What do the gall bladder and pancreas do when chyme comes into the SI?

A

Contribute digestive enzymes, bicarbonate and bile into the duodenum.

31
Q

What is the pH in the lumen?

A

Very acidic: 1-2. As we progress down the duodenum pH becomes neutral due to secretion of bicarbonate and submucosal structures.

32
Q

What causes the pH to increase?

A

Brunners Glands. Submucosal glands which produce an alkaline secretion (mucus). This helps to neutralise acidic chyme coming in.

33
Q

What happens as we progress down the duodenum?

A

Brunners glands become less and less.

34
Q

How long is the duodenum?

A

25cm and it is curved (C-shaped).

35
Q

How long is the jejunum?

A

2.5m and it is wound up and it is suspended by mesentery.

36
Q

What is the definite feature of the jejunum?

A

Pronounced plicae.

37
Q

How long is the ileum?

A

3.5m last stop before LI.

38
Q

What is the key function of ileum?

A

To be rich in defence.

39
Q

What is the definite feature of the ileum?

A

Enriched with massive lymphatic aggregates that are macroscopically visible - “Peyer’s Patches.

40
Q

Describe Peyer’s Patches?

A

Lymphatic aggregates. In the core there are B cells and B lymphocytes that are surrounded by rim of M cells which are antigen sensing/sampling cells.

41
Q

What is the mucosal of the colon?

A

Smooth, no plicae or villi.

42
Q

What lines the crypts?

A

Superficial surface columnar absorptive cells. Absorb water and electrolytes and vitamins produced by gut bacteria.
Goblet cells which secrete mucus for lubrication.

43
Q

What happens to the texture of the contents?

A

Becomes harder and dehydrated. Thus the frequency of goblets (from ascending to descending colon) increase; more lube.

44
Q

What do the undifferentiated stem cells help to do in the colon?

A

Help to replace goblet cells.

45
Q

What does the outer longitudinal layer of the muscular externa do?

A

Forms three distinct strips running along the colon as teniae coli. When these contract they allow segments of the colon to contract independently, this pulls the intestinal tune into sac-like pockets (haustra coli).

46
Q

What happens at the rectum/anus in terms of epithelial cells?

A

Transition from columnar absorptive goblet cells to stratified squamous. This is due to sharing forces of the faecal matter being expelled, so need protection against friction.

47
Q

What happens to the anal sphincter?

A

The inner sphincter is made up of smooth muscle (involuntary control) whilst the external anal sphincter is made up of the skeletal muscle.

48
Q

Where is the location of the stem cells in the oesophagus? and what is the replacement rate?

A

Basal part of the epithelium. Migrate downwards. Days.

49
Q

Where is the location of the stem cells in the stomach? and what is the replacement rate?

A

Near the neck between the gastric pits and glands. Migrate upwards. The superficial epithelial cells replace in days. Where as the deep epithelial cells replace in months. This is due to them being more sheltered from the acidic chyme.

50
Q

Where is the location of stem cells in the SI? and what is the replacement rate?

A

Located in the lower 1/2 of glands. Migrate upwards to replace enterocytes. Superficial epithelial cells replace in days. And deep epithelial cells in months.

51
Q

Where is the location of stem cells in the LI? and what is the replacement rate?

A

Located in the lower 1/3 of glands. Migrate upwards. Days.

52
Q

How does chemotherapy and drugs affect mitotic division in GI?

A

Diarrhoea, nausea. Closely tied with the impact of mitoticly targeted anti-cancer drugs on the highly replaced cells normally. Cancer is more cell growth than death. So chemotherapy drugs non-distinctly target all mitotic dividing cells and impact on the normal replacement of superficial cells. Huge impact on the digestive system, normally a high baseline level of mitotic activity.

DS (32 decks)

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