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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
16
Q
Epithelial cell types in the small intestine
5
A
- enterocytes: absorb nutrients
- goblet cells: produce mucus
- enteroendocrine cells: secrete hormones
- paneth cells: exocrine cells, secrete anti-microbial peptides
- 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
