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Anat and Phys > Gastrointestinal tract IV > Flashcards

Gastrointestinal tract IV Flashcards

1
Q

The small intestine

A
  • the major organ of digestion and absorption
  • production of gastrointestinal hormones
  • small diameter of 2.5-4cm
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2
Q

Digestion

A
  • catabolic process that breaks macromolecules down into chemical buidling blocks (monomers) by enzymes so they are small enough for absorption across wall of small intestine
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3
Q

Absorption

A
  • process of moving substances from lumen of gut through apical membrane of epithelial cells into the body through basolateral membrane
  • most nutrients are absorbed before chume reaches ileum
  • occurs via diffusion, facilitated transport, osmosis and active transport
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4
Q

Modifications to increase surface area

4

A
  • modificatoins of mucosa and submucosa
  • reflects function -> achieve maximal digestion and absorption
    1. length of SI = 4-7m
    2. plicae circulates = 1 cm
    3. villi = 1mm
    4. microvilli = 1um
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5
Q

Small intestine length

A
  • 4-7m length
  • stretched from pyloric sphincter to ileocecal valve
  • propulasion of chyme
  • allows for sufficient time for digestion and absorption
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6
Q

Plicae circulates

A
  • permanent circular folds of mucosa and submucosa
  • form transverse to sprial ridges, 1cm deep
  • absent fro the firstfew cm, of the duodenum, then all the way to the missle of the ileum
  • increase surface area 3 fold
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7
Q

Plicae circulates function

A
  • force chyme to slowly spiral through lumen
  • increased contace with mucosa
  • allow more time for nutrient absorption
  • promote more through mixing
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8
Q

Villi and crypts

A
  • each of the plicae circulates contain many villi
  • projection sinto SI lumen
  • Crypts of Lieberkuhn
  • invaginations of the epithelium between villi
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9
Q

Villi

A
  • finger-like projections of the mucosa
  • folds of the epithelum, 1 mm high
  • epithelium of villi made up mainly of tall columnar absorptive cells = enterocytes and mucus secreting goblet cells
  • increase surface area 10 fold
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10
Q

Core of villi contains

A
  • dense capillary bed = transports sugars and amino acids away to maintain concentration gradient
  • capillaries unite to form larger blood vessels -> hepatic portal vein -> liver
  • dense lymphatic bed = lacteal
    absorption of dietary fats
    associates with gut immune response
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11
Q

The lymph vessels

A
  • lymphatic system fluids leaked from blood vessels back to blood
  • circulates 3L interstitial fluid per day
  • lymph entering the lymphatic between the capillaries = interstital fluid plus bigger fragments not fitting into capillaries (viruses, bacteria, cells)
  • contains water salts, amino acids, proteins, hormones, cellular waste products
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12
Q

Lymphatic capillaries

A
  • lacteals = specialised lymph capillaries present in intestinal mucosa -> absorb digested fat
  • capillaries drain into larger lymph vessels
  • lymph vessels are more permaeable and can take up larger molecules and particles than blood capillaries
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13
Q

Crypts of Lieberkühn

A
  • between the villi are crypts of cells which contain various cell types
  • extend through lamina propria down to muscularis mucosae
  • secretion of intestinal juice
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14
Q

Microvilli

A
  • projections of the columnar epithelial cells lining the small intestine -> on apical surface of enterocytes
  • microvilli look like a “brush-border”
  • brush border has fuzzy appearance as it contains membrane-bound enzymes = brush border
  • enzymes -> used for final carbohydrate and protein digestion
  • increase of absorptive surface 20 fold
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15
Q

Specialised structures

A

microvilli:
- 1um in length, 90nm diameter
- contain bundles of parallel actin filaments held together into a bundle by cross-linking proteins
- on enterocytess in SI to increase absorption

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16
Q

Epithelial cell types in the small intestine

5

A
  1. enterocytes: absorb nutrients
  2. goblet cells: produce mucus
  3. enteroendocrine cells: secrete hormones
  4. paneth cells: exocrine cells, secrete anti-microbial peptides
  5. stem cell: replace cells
17
Q

Enterocytes

A
  • make up the bulk of all epithelial cells
  • simple columnar cells lining villi and crypts
  • contain many microvilli on apical surface
  • bound by tight junctions
  • main function absorption of nutrients and electrolytes
    e. g. ions, water, simple sugars, vitamins, lipids, peptides and amino acids
  • in crypts production of intestinal juice
18
Q

Goblet cells

A
  • mucus-secreting cells
  • giblet cells secrete mucin, which absorbs water and becomes mucous
  • mucous lubricates and protects the epithelium from the luminal contents
19
Q

Enteroendocrine cells

A
  • group of different cells, secreting various gastrointestinal hormones
    e. g. secretin, pancreozymin, enteroglucagon
  • found scattered in villi but some in crypts
20
Q

Enterogastrone

A

hormone secreted bythe duodenal mucosa when fatty food is in the stomach or small intestine

21
Q

Paneth cells

A
  • found in deep in crypts
  • exocrine cell -> specialised secreotory cells
  • Secrete antimicrobial agents: secrete defensins and lysozyme
  • can destroy bacteria as part of the body’s innate immune protection from pathogens
22
Q

Stem cell

A
  • found deep in crypts
  • 1-4 per crypt
  • can self-renew but also continuously divide to produce other cell types (progenitor cells)
  • depending on the transcriptional signal they can produce all other epithelial cell types
  • new cells migrate up the side of the villi
  • epithelium renewed every 3rd day
  • also targets rapidly dividing GI tract epithelium
  • symptoms of nausea, vomiting and diarrhoea
23
Q

Duodenum

A
  • Approximately 0.25m long
  • Receives chime from the stomach
  • Receives bile and pancreatic enzymes from hepatopancreatic ampulla
  • Stomach acids is neutralised
  • Pepsin is inactivated by increased pH
  • Fats are emulsified by bile salts
  • Chemical digestion by pancreatic enzymes
24
Q

Pancreas juice composition

A 
1.Proteases: digest proteins
Secreted in inactive form to prevent self-digestion
Zymogen granules contained proenzymes
2.Lipases: digest fat
3.Amylase: digest carbohydrates
4.Nucleases: nor nucleic acids
5.Bicarbonate (HCO3-): neutralises chime
6.Watery, alkaline solution (pH 8) to neutralise acidic chime coming from stomach
25
Q

exocrine pancreas

A

-The exocrine secretes: secretions of the acini empty into ducts lined with a simple cuboidal epithelium, which becomes stratified cuboidal in the larger ducts

26
Q

Functions of bile in digestion

A

-Far is water repellent, but enzyme responsible for fat digestion (lipase) is water soluble
-Bile salts emulsify fats in the intestine
They surround fat droplets to form micelles, providing a greater surface area for pancreatic lipase to break down the fat

27
Q

Brunner glands

A
  • only found deep in the duodenum
  • Ducts of individual glands unite with overlying intestinal glands (crypts of Lieberkühn)
  • Produce more mucous and bicarbonate
  • Protect underlying mucosa from gastric acids, pancreatic enzymes by neutralising the stomach acid in the duodenum (increased pH)
28
Q

Jejenum

A
  • Approx. 2.5m long
  • Most digestion
  • Most nutrient absorption
  • Contains more plicae and villi than the duodenum
  • Lined with simple columnar epithelium
  • Very similar to duodenum but Brunner’s glands are absent
29
Q

Ileum

A

-Approx. 3.6m long
-Thinner
-Less muscular
-Less vascular
-Function: absorption
•Particularly vit B12 and bile salts
Contains Payer’s patched in the lamina propria of

30
Q

Peyer’s patches

A
  • Lymph nodules immune function
  • Found in great numbers in distal part of small intestine where bacterial numbers increase
  • Involves in immune regulation… decide which bacteria are good flora or pad pathogens
  • part of the gut associated lymphoid tissue (GALT)
31
Q

Ileocecal valve

A
  • At junction of ileum and cecum
  • Regulates passage of food residue into the large intestine
  • Prevents reflux of colonic contents into the ileum
  • When food residue containing gastrin approaches the valve, the gastrin causes sphincter to relax

Anat and Phys (19 decks)

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