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nuero > small bowel > Flashcards

small bowel Flashcards

1
Q

Q. What is the function of the small bowel?

A

To absorb nutrients, salt & water

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2
Q

what is the duodenum

A

The duodenum is the first segment of the small intestine. It’s largely responsible for the continuous breaking-down process

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3
Q

whta is the jejunum

A

The middle part of the small intestine. It is between the duodenum (first part of the small intestine) and the ileum (last part of the small intestine). The jejunum helps to further digest food coming from the stomach.

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4
Q

what is the ileum

A

The ileum is the final section of the small intestine. The function of the ileum is mainly to absorb vitamin B12, bile salts, and any products of digestion that were not absorbed by the jejunum

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5
Q

what is the transition between them

A

no sudden transition between them

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6
Q

how do the histological organistaion differ

A

All have same basic histological organisation

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7
Q

what is the mesentry

A

The mesentery attaches your intestines to the wall of your abdomen. This keeps your intestines in place, preventing it from collapsing down into your pelvic area.

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8
Q

functions

A

Suspends small & large bowel from posterior abdominal wall
anchoring them in place
whilst still allowing some movement

Provides a conduitfor blood vessels, nerves & lymphatic vessels.

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9
Q

where can you find villi

A

only occur in the small intestine

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10
Q

what is the blood and lymph supply like

A

Have a rich blood supply & lymph drainage for absorption of digested nutrients

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11
Q

what is the nerve innervation like

A

Have good innervation from the submucosal plexus.

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12
Q

describe the structure of the villi

A

Have simple epithelium
1 cell thick
dominated by enterocytes (columnar absorptive cells)
motile

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13
Q

what are enterocytes

A

(columnar absorptive cells)

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14
Q

what are villi lined with

A

simple columnar epithelium consisting of:
primarily enterocytes (absorptive cells)
scattered goblet cells
enteroendocrine cells

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15
Q

what is in the crypt epithelium

A

Crypts of Lieberkühn - epithelium includes:
Paneth cells
Stem cells

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16
Q

what is the most abundant cell in the small bowe,

A

enterocystes

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17
Q

describe their structure

A

Tall columnar cells with microvilli & a basal nucleus.

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18
Q

function

A

Specialised for absorption & transport of substances.

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19
Q

lifespan

A

Short lifespan of 1-6 days.

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20
Q

how is the surface area increased

A

Folds, villi & microvilli ^ surface area

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21
Q

what does the microvilli make up

A

brush border

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22
Q

what are the microvilli made up of

A

glycocalyx

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23
Q

what is a glycocalyx

A

rich carbohydrate layer on apical membrane

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24
Q

function

A

serves as protection from digestional lumen
yet allows for absorption.
regulates rate of absorption from intestinal lumen

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25
Q

what is the unstirred layer

A

the glycocalyx traps a layer of water & mucous known as “unstirred layer”

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26
Q

what do mucous cells contain apical

A

Mucous containing granules accumulate at apical end

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27
Q

what is mucous

A

→ large glycoprotein that facilitates passage of material through bowel.

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28
Q

how does the compisition of goblet cell change through the legnth of the bowel

A

^ abundance of goblet cells along entire length of bowel

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29
Q

what are enterendocrine cells

what is their structure

A

Columnar epithelial cells

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30
Q

where are they commonly found

A

most often found in lower part of crypts.

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31
Q

function

A

Hormone secreting

e.g. to influence gut motility (see Regulation of function lecture)

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32
Q

where are paneth cells found

A

Found only in the bases of crypts

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33
Q

what do they contain

A

Contain large, acidophilic granules

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34
Q

what are the contents of the granules

A

antibacterial enzyme lysozyme (protects stem cells)

Glycoproteins & zinc (essential trace metal for a no. of enzymes)

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35
Q

what is another function

A

Also engulf some bacteria & protozoa

May have a role in regulating intestinal flora

36
Q

what are stem cells

A

Undifferentiated cells which remain capable of cell division to replace cells which die

37
Q

why does the GI tract have stem cells

A

Epithelial stem cells are essential in the GI tract to continually replenish the surface epithelium
Differentiate into various cell types (pluripotent)

38
Q

describe their life cycle

A

Migrate up to tip of villus, replacing older cells that die by apoptosis -> digested and reabsorbed

39
Q

what is the relative life cycle of enterocytes and goblet cells of the small bowel

A

short life span (about 36 hrs)

40
Q

what is their relative lifespan in comparison to other epithelial cells

A

Rapid turnover contrasts with lifespan of weeks/months for other epithelial cell types (e.g. lung, blood vessels)

41
Q

why are the lifespans so different

A

Enterocytes are first line of defense against GI pathogens & may be directly affected by toxic substances in diet.

Effects of agents which interfere with cell function, metabolic rate etc will be diminished.

Any lesions will be short-lived.

If escalator-like transit of enterocytes is interrupted through impaired production of new cells (e.g. radiation) severe intestinal dysfunction will occur

42
Q

how can you distniguish between the duodenum and the jeunum and iluem

A

Distinguished by presence of Brunner’s glands

43
Q

how does the duodenum secreate alkaline fluid

A

Submucosal coiled tubular mucous glands secreting alkaline fluid

44
Q

why the alkaline secreation

A

Neutralizes acidic chyme from stomach, protecting proximal small bowel
Help optimise pH for action of pancreatic digestive enzymes.

45
Q

Functions of small intestine motility

A

To mix ingested food with digestive secretions & enzymes

To facilitate contact between contents of intestine & the intestinal mucosa

To propel intestinal contents along alimentary tract

46
Q

what are the 3 phases of motility

A

Segmentation (mixing)

  1. Peristalsis (propelling)
  2. Migrating Motor Complex
47
Q

what is the segmentation

A

Mixes contents of lumen
Occurs by stationary contraction of circular muscles at intervals.
More frequent contractions in duodenum cf. ileum
allow pancreatic enzymes & bile to mix with chyme
Although chyme moves in both directions, net effect is movement → colon

48
Q

what is peristalisis

A

. Peristalsis (propelling)
Involves sequential contraction of adjacent rings of smooth muscle
Propels chyme towards colon
Most waves of peristalsis only travel about 10cm
Segmentation & peristalsis result in chyme being segmented, mixed & propelled → colon

49
Q
  1. Migrating Motor Complex
A

Cycles of smooth muscle contractions sweeping through gut
Begin in stomach → small intestine → colon → next wave starts in duodenum
Prevents migration of colonic bacteria into ileum

50
Q

describe the digestion in the small bowel

A

Digestion in small bowel occurs in an alkaline environment

51
Q

how do digestive enzyme enter the duodenum and bile enter

A

Pancreatic digestive enzymes & bile enter duodenum from MPD & CBD

52
Q

why doesn’t the duodenal epithelial produce any of its oen digestive enzymes

A

Duodenal epithelium also produces its own digestive enzymes

53
Q

where does digestion occur in the dueodnum

A

Digestion occurs in lumen & in contact with the membrane

54
Q

what are the 2 carbihydrate strcutures

A 
Simple carbohydrates 
(monosaccharides -  glucose & fructose
disaccharides -  sucrose & maltose)

Complex carbohydrates
(starch, cellulose, pectins
→ sugars bonded together to form a chain)

55
Q

what is the first step in digetsion of carbs

and where does most of it take place

A

Digestion begins in mouth by salivary -amylase (destroyed in stomach (acid pH)
Most of digestion of carbohydrates occurs in small intestine

56
Q

when is Pancreatic a-amylase released

A

Secreted into duodenum in response to a meal

57
Q

what is the optimum envoroment

A

Needs Cl- for optimum activity & neutral/slightly alkaline pH

58
Q

where does pancreatic a-amylase act

A

Acts mainly in lumen (some also adsorbs to brush border)

Digestion of amylase products & simple carbohydrates occurs at the brush border

59
Q

how is glucose and galactose absorbed

A

2o

active transport

60
Q

what carrier protien

A

= SGLT-1 on apical membrane

61
Q

how is fructose absorbed

A

by facilitated diffusion.

62
Q

how

A

= GLUT-5 on apical membrane

63
Q

what is the function of glut 2

A

facilitates exit at basolateral membrane

64
Q

where are protiens first digested

A

Protein digestion begins in lumen of stomach by pepsin

pepsin then inactivated in alkaline duodenum

65
Q

what then occurs in the small bowel

A

5x pancreatic proteases secreted as precursors → lumen of small bowel (e.g. trypsinogen)

66
Q

what activates trypsin

A

enterokinase

67
Q

where is enterokinase

A

an enzyme located on duodenal brush border

68
Q

what does trypsin do

A

activates other proteases

hydrolyse proteins → single amino acids (AA) & oligopeptides (AA)n

69
Q

what is the junction between the duodenam and jejunum

A

duodenojejunal flexure

70
Q

what is the outer part of the small bowel called

A

serosa

71
Q

what os under that

A

longitudinal and then circular muscle layer

72
Q

what is cu=ircular muscle iimportant for

A

motility

73
Q

what is brunners gland

A

submucosal coiled tubular mucous glands secreting alkaline fluid

74
Q

where do they open

A

in the cypt

75
Q

what is the difference between the jejunum and ileum

A

jejunum is wider and thicker walled

redder

76
Q

where is the cypt

A

base of the villi

77
Q

why is the jejunum more thicker

A

more plicae circulares

78
Q

where do peptidases act

A

Action of luminal, brush-border & cytosolic peptidases

79
Q

what do enterocytes absorb

A

Enterocytes directly absorb some of small (AA)n via action of H+/oligopeptide cotransporter PepT1

80
Q

are lipids soluble in water

A

Lipids are poorly soluble in water

more complicated to digest.

81
Q

how are they digested

A

Secretion of bile salts & pancreatic lipases

Emulsification (↑s surface area for digestion)

Enzymatic hydrolysis of ester linkages (Colipase
complexes with lipase – prevents bile salts displacing lipase from fat droplet)

Solubilisation of lipolytic products in bile salt micelles

82
Q

how are lipids absorbed

A

Unlike AAs & simple sugars -> lipids transformed as absorbed via enterocytes

83
Q

describe their absoroption

A

Fatty acids (FAs) & monoglycerides (MG) leave micelles and enter enterocytes

FAs & MG resynthesized into tri-glycerides (TGS) by 2x pathways:

Monoglyceride acylation (major)
Phosphatidic acid pathway (minor)

Chylomicrons - lipoprotein particles synthesised as an emulsion (80-90% TGs, 8-9% phospholipids, 2% cholesterol, 2% protein, trace carbohydrate) in Golgi apparatus

Chylomicrons secreted across basement membrane by exocytosis

Chylomicrons enter a lacteal (lymph capillary) → lymph transports them away from bowel

84
Q

what is the Ileocaecal valve

A

Ileum is separated from the colon by the ileocaecal valve

85
Q

function

A

Relaxation & contraction controls passage of material into colon

Also prevents back flow of bacteria into ileum

nuero (36 decks)

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