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Gastroenterology > Small Bowel > Flashcards

Small Bowel Flashcards

1
Q

What is the function of the small bowel?

A

Absorb nurtrients salt and water

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2
Q

Describe the structure of the small bowel

A

du 25cm
je 2.5 m
ile3.75

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3
Q

What functions does the Mesentary have?

A

Suspends small and larger bowel from posterior abdominal wall: anchoring them in place

provides a conduit for blood vessels, nerves and lymphatics

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4
Q

What does the superior mesenteric artery supply?

A

COMES OUT FROM THE inferior border of the pancreas

supplies duodenum and jejunum and ilieum

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5
Q

What is the serosa?

A

Outer covering of digestive epithelium.

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6
Q

What are plicae circulares

A

Also known as the valves of krekhering …

circular folds, termed the plicae circulares, which amplify the organ’s surface area, promoting efficient nutrient absorption.

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7
Q

Describe the structure of the villus?

A

Found on the pilcae circulares

Have endocrine, goblet, paneth, enterocyte cells.

Have a brush border - microvilli

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8
Q

What are the adaptations of the villi?

A

Only in small bowel

Motile

rich blood supply and lymph drainage

simple epothelial
1 cell thick

sominated by enterocytes

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9
Q

What provides innervation to the villi?

A

good innervation from submucosal plexus

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10
Q

What cells are the villi lined with?

A

Simple columnar epithelial consisting of:
enterocytes (most)
scattered goblet cells
enteroendocrine cells

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11
Q

What are the crypts of lieberkuhn? What cells make it up?

A

Epithelium in the cell bowel that contain:

Paneth cells
Stem cells

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12
Q

What are the characteristics of enterocytes?

A

Abundant in s.bowel

Columnar with microvili and basal nuclei

Absorption and transport

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13
Q

measurements of microvlli?

A

Surface area
Cylindrical internal surface area of small bowel is 0.4m2.
Folds, villi & microvilli ↑ surface area to ~200m2 (size of a tennis court)
At least a 500 fold ↑

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14
Q

Why do enterocytes and goblet cells have a short life span ( 36 hrs )

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

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15
Q

What covers the surface of the microvilli?

A

Glycocalyx :

rich carb layer on apical membrane

protection from digestional lumen

Traps water and mucous known as “unstirred layer” which :

regulates rate of absorption from intestinal lumen

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16
Q

What are the characteristics of Goblet cells?

A

2nd most abundant cell type

mucous: larger glycoprotein

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17
Q

What gives goblet cells their goblet shape?

A

mucous containing granules accumulation at apical end of cell - goblet shape

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18
Q

How do goblet cells change down the bowel ( arrangement )

A

Increased abundance of goblet cells along entire length of bowel
↓ in duodenum
↑ in colon

19
Q

What are enteroendocrine cells?

A

Columnar epithelial cells

scattered among enterocytes

most often found in lower part of crypts.

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

*referred to as chromaffin cells (affinity for chromium/silver salts).

20
Q

Paneth cells contain large acidophilic granules, what are in these?

A

Granules contain:
antibacterial enzyme lysozyme (protects stem cells)
Glycoproteins & zinc (essential trace metal for a no. of enzymes)

21
Q

What roles can paneth cells play?

A

Also engulf some bacteria & protozoa

May have a role in regulating intestinal flora

22
Q

Where do stem cells in the Gi tract migrate?

A

To the tip of villus as they divide mitotically

Replace dead cells ( apoptosis )

23
Q

How is the duodenum distinguised?

A

Distinguished by presence of Brunner’s glands

24
Q

What are Brunner’s glands?

A

Submucosal coiled tubular mucous glands secreting alkaline fluid

Open into the base of the crypts

Alkaline secretions of Brunner’s glands
Neutralizes acidic chyme from stomach, protecting proximal small bowel
Help optimise pH for action of pancreatic digestive enzymes.

25
Q

What are the functions of the 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

26
Q

How does segmentation occur ( mixing ) in the small bowel?

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

27
Q

How does Peristalsis occur ( propelling) in the small bowel?

A

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

28
Q

How does Migrating motor complex occur in the small bowel?

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

29
Q

What are the anatomical differences between the jejnum and the ileum?

A

Jejunum is wider, thicker walled and redder than the ileum

thicker because plicae circulares are larger, more numerous and closely set

  • jejunal mesentray is attached to the above and left of aorta whereas ileal mesenatary which is attached below and to the right of the aorta

jejunal mesenteric branches have 1 arterial arcades and long arterial vessels whereas ileum has multiple arcades and shorter vessels.

30
Q

What envinronment does digestion in the duodenum take place?

A

Digestion in small bowel occurs in an alkaline environment

Pancreatic digestive enzymes & bile enter duodenum from MPD & CBD

Duodenal epithelium also produces its own digestive enzymes

Digestion occurs in lumen & in contact with the membrane

31
Q

Name some simple carbohydrates?

A

monosaccharides - glucose & fructose

disaccharides - sucrose & maltose

32
Q

Describe some complex carbohydrates

A

starch, cellulose, pectins

→ sugars bonded together to form a chain

33
Q

How does digestion of carbohydrates start in the mouth?

A

salivary a-amylase (destroyed in stomach (acid pH)

*Most of digestion of carbohydrates occurs in small intestine

34
Q

When is pancreatic a-amylase secreted into the duodenum

A

In response to a meal

Digestion of starch and glycogen in S.B

Acts in the lumen

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

35
Q

WHat does pancreatic a-amylase need for optimum activity?

A

Cl- ions

Slightly alkaline pH

36
Q

What carrier protein absorbs glucose and galactose?

A

SGLT-1 on apical membrane

Secondary active transport

  • GLUT 2 facilitates exit at basolateral membrane
37
Q

How is fructose absorbed?

A

Diffusion through GLUT-5 on apical membrane

  • GLUT 2 facilitates exit at basolateral membrane
38
Q

Where does the digestion of protein begin?

A

in the lumen of stomach by PEPSIN

it is then inactivated in alkaline duodenum

39
Q

What protein digestion occurs in the small bowel?

A

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

Trypsin activated by enterokinase
an enzyme located on duodenal brush border

Trypsin → activates other proteases
hydrolyse proteins → single amino acids (AA) & oligopeptides (AA)n

40
Q

Where do multi amino acids get broken down into monoaminoacids ?

A

Variety of peptidases at brush borders of enterocytes progressively hydrolyse (AA)n → AAs

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

These small peptides are digested to AAs by peptidases in cytoplasm of enterocytes

41
Q

What are the four stages of digestion of lipids?

A
  • Secretion of bile salts & pancreatic lipases
  • Emulsification (↑s surface area for digestion)
  • Enzymatic hydrolysis of ester linkages
  • Solubilisation of lipolytic products in bile salt micelles
42
Q

What is enzymatic hydrolysis of ester linkages?

A

Colipase complexes with lipase – prevents bile salts displacing lipase from fat droplet

43
Q

How is the ileum separated from the colon?

A

Ileocaecal valve

44
Q

What does the relaxation and contraction of the ileocaecal valve do?

A

Relaxation & contraction controls passage of material into colon

Also prevents back flow of bacteria into ileum

Gastroenterology (10 decks)

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