Intestinal microanatomy Flashcards

1
Q

Things that increase SA of the small intestine?

A

Plicae, villi, crypts of lieberkuhn and microvilli

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2
Q

Purpose of blood vessels to the small intestines?

A

They carry Oxygen-rich blood to the SI, allowing metabolic activity

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3
Q

Purpose of the venous system of the SI

A

Carries away nutrient-rich blood to the liver for processing and redistribution (Hepatic Portal Vein)

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4
Q

Purpose of lacteal lymphatic vessels and the SI

A

transport lipids

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5
Q

What is in the core of a villus

A

Blood vessels and lacteals, embedded in CT support. muscle fibres extend in from muscularis mucosae

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6
Q

What is the purpose of the smooth muscle fibres in the lamina propria?

A

Help milk and squeeze the lacteals

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7
Q

Another name for intestinal glands? What is their purpose?

A

Crypts of Lieberkuhn. To increase SA

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8
Q

What is an issue that can happen to the elderly around blood supply.

A

Sometimes, especially in elderly, blood supply and circulation can decrease.
> less absorption taking blood away from gut > malabsorption and malnutrition

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9
Q

What is studded in the lipid bilayers?

A

1000’s of digestive enzymes eg) glycosidase breaks down carbs

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10
Q

What are the cells of the SI

A
columnar absorptive cells (enterocytes)
Goblet cells
Enteroendocrine cells
undifferentiated cells
Paneth cells
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11
Q

Microvilli are

A

projections of membrane filled with cytoplasm. Have a core of actin filaments. Found at the apical surface of columnar absorptive cells. (enterocytes)

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12
Q

Why do microvilli have a core of actin filaments

A

Bc the actin filaments are connected to the cytoskeleton network
SM in LP contract > BM of epi. cells move > Cells atop BM move > Microvilli atop epi cells move

This creates localised, homogenous mixing of contents, via ‘microwhisks’.

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13
Q

What is the glycocalyx?

A

a slippery biological film made of glycoproteins and acidic mucopolysaccharides. Sits atop and coats microvilli

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14
Q

Function of the glycocalyx?

A

Selective gate keeper, attracts desirable contents and blocks unwanted.

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15
Q

Goblet cells

A
  • no microvilli on apical surface
  • secrete mucus for lubrication
  • theories that mucus contributes to glycocalyx
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16
Q

Undifferentiated cells are?

A

Stem cells that can divide and migrate to replace epithelium.

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17
Q

What stimulates enteroendocrine cells, and what do they release?

A

Stimulus: acidic chyme, FA, amino acids

Release: Cholecystokinin, serotonin, secretin and somatostatin.

18
Q

Purpose of Cholecystokinin

A

1) + gall bladder to contract (bile released into duodenum)

2) + pancreas to increase enzyme production and secretion

19
Q

Purpose of secretin

A

1) + pancreas to produce bicarbonate (from ductule cells)

2) - acid production by stomach

20
Q

Purpose of serotonin

A

1) + peristalsis

2) + intestinal secretion (goblet, paneth etc)

21
Q

Purpose of somatostatin

A

1) Reduce gastrin
2) Facilitates SM contraction
3) enhances absorption

22
Q

Paneth cells around found? what are they for? What do they produce

A

Found at bottom of crypts

important for antimicrobial and antibacterial purposes

produce TNF-alpa, lysozymes, defensins

23
Q

acidic chyme, amino acids and FAs from the stomach stimulate?

A

pancreas and gallbladder > release digestive enzymes, HCO3- and bile into the duodenum

24
Q

How does the pH of the duodenum change and how does this occur?

A

from acidic pH 1-2 to eventual 7-8 (neutral).
This is due to submucosal ‘Brunners glands’ (as well as bile)
that secrete an alkaline mucus that counteracts the acidic chyme.
(lots initially, less distally)

25
Length of the Duodenum, jejunum and ileum
D: 25cm J: 2.5m I: 3.5m
26
Purpose of the pyloric sphincter
To control the volume and frequency of chyme into the duodenum
27
Features of the jejunum?
Heavily twisted suspended with mesentery increased plicae
28
Identifying feature of the ileum? What is this for?
Macroscopically visible lymphatic aggregates "Peyers Patches" These have a B cell core, and a M cell outer (antigen presenting/sensing cells for sampling) This is for defence against the large amount of bacteria in the LI
29
What is in the lamina propria
BVs, lacteals, SM, lymphocytes, fibroblasts
30
Muscle type of the anal sphincters
Internal sphincter = smooth muscle | external sphincter = skeletal muscle
31
The rectum and anal canal has different types of epithelium. What are these?
Rectum: Simple columnar enterocytes + goblet cells Superior half: simple columnar epithelium Inferior half: Stratified squamous epithelium
32
Purpose of the SS epithelium in the anal canal?
protects against the friction of faecal matter leaving
33
How does the frequency of goblet cells change throughout the colon and why?
Start of colon: Watery substances, few goblet cells Water is absorbed End of colon: viscous, dry, dehydrated, many goblet cells
34
Features of the colon mucosa?
smooth with no plicae or villi Numerous crypts of lieberkuhn Main two cells: 1) Columnar absorptive cells (absorb, water, electrolytes and vitamins B&K) 2) Goblet cells (secrete mucus for lubrication) also have enteroendocrine cells (not visible by light microscope) undifferentiated cells: at base of glands (migrate upwards
35
Features of the colons lamina propria
Lots of lymphatics | dense layer of collagen immediately beneath the surface epithelium
36
Features of the colons muscularis externa.
Still has inner circular and outer longitundinal muscle layers But outer longitudinal forms three strips 'teniae coli' that run along the colon - this allows segments of the colon to contract independently - contraction pulls colon into sac like pockets 'haustraccoli'
37
is the colon covered in serosa or adventitia?
Posterior surface = adventitia | elsewhere = serosa
38
Describe the purpose of the rectum/ anus
temporary storage of faecal material (movement of material into leads to the urge to defecate
39
What are the sections of the rectum/anus
final portion = anal canal (mucosa has anal columns) distal margin = pectinate line (transverse folds) anal sphincters = internal and external end of anal canal = anus
40
What is the general trend around cell replacement rates
surface/ SF cells: high replacement rate (days) Deeper cells: replaced every few months Deeper cells are more specialised, require more energy to replace.
41
What are some common GI effects of chemo
diarrhoea, nausea. This is due to the mitotically targeting anticancer drugs affecting the highly replaced surface cells