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HUBS192 2022 > lecture 22 - the small intestine > Flashcards

lecture 22 - the small intestine Flashcards

1
Q

What are the 3 regions of the small intestine?

A

Duodenum, Jejunum, ileum

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2
Q

What are the relative lengths oof the 3 regions of the small intestine?

A

Duodenum < jejunum < ileum

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3
Q

What structure holds the SI in place and prevents it from getting tangled?

A

Mysentery

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4
Q

What part of the SI is retroperitoneal?

A

Initial segment of the SI - the duodenum

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5
Q

Where does chyme enter the SI?

A

The duodenum, from the stomach

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6
Q

How is the epithelium of the duodenum protected from the acidic chyme?

A

Mucus secreting cells and glands in the submucosa. The pH is neutralised by bicarbonate from the pancreas

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7
Q

What chemical, secreted by the pancreas, neutralises acidic chyme in the duodenum?

A

Bicarbonate - HCO3-

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8
Q

Where is the bicarbonate secreted into the duodenum produced?

A

The pancreas

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9
Q

Why does the SI need a large surface area?

A

Specialised for digestion and the majority of GI absorption

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10
Q

What are the 3 structural adaptions of the SI that increase its surface area?

A

Plicae circulares, villi, microvilli

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11
Q

What are plicae circulares?

A

Permanent, large circular folds of the SI that have a pleated appearance.

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12
Q

What is the function of the plicae circulares?

A

Increase surface area of SI and spiral material to slow it down for effective digestion and absorption

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13
Q

What is the structure of the plicae circulares?

A

A core of folded submucosa with overlying mucosa

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14
Q

What is the fundamental structural and functional difference between rugae and plicae circulares?

A

Rugae are temporary for stomach expansion & storage, while plicae circulares are permanent to increase SI surface area. However, they both have a core of submucosa with overlying mucosa

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15
Q

What is the approximate size of plicae circulares?

A

1cm long

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16
Q

What structure is found on the surface of plicae circulares to increase surface area further?

A

Villi

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17
Q

What is found at the base of villi?

A

Intestinal glands/crypts

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18
Q

What is the structure of SI villi?

A

Folds in the mucosa layer, in all parts except the muscularis mucosae

19
Q

What layer of the SI mucosa is not folded in SI villi?

A

muscularis mucosae

20
Q

What is the function of muscularis mucosae for villi?

A

Helps them ‘wiggle’ back and forth

21
Q

What are the vessels found within villi?

A

Lymph lacteals, capillary network - input by arterioles and output by venule

22
Q

What is a lymph lacteal?

A

A lymphatic vessel found in SI villi that absorbs the products of fat digestion

23
Q

What does the capillary network of SI villi absorb?

A

Products of protein and carbohydrate digestion (amino acids and monosaccharides respectively)

24
Q

Where does blood from the venules leaving SI villi drain to?

A

Nutrient rich, deoxygenated blood enters the superior or inferior mesenteric veins, which drain into the hepatic portal vein

25
Q

Where do the mesenteric veins drain?

A

The hepatic portal vein

26
Q

Where does the hepatic portal vein drain?

A

The liver

27
Q

Where do lymphatic lacteals drain?

A

Ultimately drained/collected into the cisterna chyli

28
Q

Where does the cisterna chyli drain?

A

The thoracic duct and then left subclavian vein, where fat laden lymph enters the blood stream for use in the body

29
Q

What is the name for the epithelial cells found in the SI?

A

Enterocytes or intestinal absorptive cells

30
Q

What is the structure of the epithelium of the SI?

A

Simple columnar layer of enterocytes

31
Q

How is the surface area of enterocytes increased to facilitate efficient absorption?

A

Brush border/microvilli on apical surface

32
Q

What sits on the surface of the epithelium of the SI as a surface coat?

A

Glycocalyx

33
Q

What is the fucntion of the glycocalyx?

A

A surface coat that is made up of glycoproteins and branched filaments that tether digestive enzymes for contact digestion

34
Q

What is the structure of the glycocalyx?

A

Made up of glycoproteins and branched filaments

35
Q

What substances can diffuse through the plasma membrane of enterocytes?

A

Lipid-soluble molecules such as fats

36
Q

What is a transcellular pathway in terms of GI absorption?

A

A pathway in which molecules cross the apical cell membrane to enter enterocytes before leaving via the basolateral membrane

37
Q

What is a paracellular pathway in terms of GI absorption?

A

When molecules diffuse between the gaps between cells through tight junctions, down their concentration gradient

38
Q

What junctions facilitate paracellular pathways of absorption?

A

Tight junctions

39
Q

What are the 5 key cell types found in the epithelium of the small intestine?

A

Enterocytes, goblet cells, stem cells, endocrine cells, paneth cells

40
Q

What is the function of the goblet cells in the epithelium of the SI?

A

secrete mucus for protection

41
Q

What is the function of the paneth cells of the epithelium of the SI?

A

Contain granules that produce antibacterial enzymes such as defensins and lysozyme that prevent colonisation by unwanted bacteria

42
Q

What are examples of secretions by paneth cells

A

Antibacterial enzymes - defensins, lysozyme

43
Q

What is the function of the endocrine cells of the epithelium of the SI?

A

Secrete regulatory hormones that control SI and provide negative feedback to other organs, such as the stomach

HUBS192 2022 (38 decks)

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