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GI Health > Small Intestine Structure and Function > Flashcards

Small Intestine Structure and Function Flashcards

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1
Q

Small Intestine Functions

A

Mix food + digestive enzymes, absorb nutrients and propel undigested molecules towards large intestine

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2
Q

3 segments of small intestine

A

Duodenum, jejunum and ileum. Not physiologically distinct. Have different absorbent and secretive properties

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3
Q

Layers in the small intestine

A

Mucosa, submucosa, muscularis and serosa

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4
Q

Structures unique to small intestine physiology

A

Villi (containing lacteals)

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5
Q

Small Intestine Mucosa Organisation

A

Kerckring Folds (circular folds in duodenum and jejunum small increase surface area), villi (contains arterioles, venule and lacteal. Intermediate increase surface area) and microvilli (digestive enzymes, largest surface area increase)

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6
Q

Villus Def

A

Functional unit of small intestine. Lamina propia layer in small intestine contains blood vessels (amino acids + sugars) and lacteals (fat).

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7
Q

Cells in Small Intestine

A

STEM cells (in crypt), enterocyte (absorption), goblet (mucus production), enteroendocrine (hormone and peptide production), Paneth (immune) and M cells (antigen transport to immune cells)

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8
Q

Brunners Gland Outline

A

Duodenum only, submucosa linking to mucosa via ducts. Produce alkaline mucus. Neutralises acid, provides optimal digestive enzyme pH, fluid medium from diffusion and wall lubrication

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9
Q

Peyer Patches Outline

A

Mainly in ileum. Round lymphoids in mucosa and submucosa. Contain B and T lymphocytes. Covered by M cells

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10
Q

Small Intestine M cell Function

A

Transfer of antigens to immune cells in peyer patches

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11
Q

S Cell Outline

A

Mucus in duodenum. Secretin produced in response to acid, producing bicarbonate and inhibiting gastric acid

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12
Q

D Cells Outline

A

Found in mucosa throughout small intestine. Produce somatostatin in response to acid inhibit gastric acid and prevent pepsinogen production

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13
Q

I Cells Outline

A

Found in mucosa in duodenum/jejenum. Stimulated by lipid produces cholecystokinin. Pancreatic enzyme secretion

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14
Q

Main Function of cells in small intestine mucosa

A

Neutralise stomach contents and recruiting accessory digestive organs (eg pancreas and liver)

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15
Q

Duodenal Cluster Unit

A

Organs contributing to substance entering small intestine. Stomach (chyme), duodenum (Brunners gland), biliary tract (bile) and gall bladder (pancreatic juice)

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16
Q

Factors contributing to composition of substance in small intestine

A

Food volume, nutrient type and amount, enteroendocrine hormones and parasympathetic and sympathetic innervation

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17
Q

Pancreas Endocrine vs Exocrine

A

Endocrine (islets of Langerman) = metabolism (blood sugar regulation). Exocrine (acinar cells) = digestion (digestive enzymes). Ducts secrete H2O and Bicarbonate

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18
Q

Pancreatic Duct cells mode of action

A

Acid in duodenal lumen triggers secretin release. Secretin stimulates pancreatic duct cells producing NaHCO3. This decreases acid (self regulating)

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19
Q

Pancreatic Acinar Cells Mode of Action

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A

Fat and protein in duodenal lumen. Increased cholecystokine secretion stimulating acinar cells. Acinar cells release digestive enzymes (eg lipase and pepsin)

20
Q

Proteases Outline and Examples

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A

Proteases are released as zymogens (inactive precursors). Eg trypsin, chymotrypsin and carboxypeptidase

21
Q

Trypsin Mode of Action

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A

Secreted as trypsinogen (inactive). Cleaved by enteropeptidase on microvilli. Trypsin cleaves trypsinogen, chymotripsinogen and procarboxypeptidase

22
Q

Pancreatic Lipase Mode of Action

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A

Digests triglycerides into monoglycerides and 2 fatty acids

23
Q

Amylase Mode of Action

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A

Hydrolyses starch to maltose

24
Q

Bile Outline

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A

Synthesised by hepatocytes. Bile acids, bile pigments, cholesterol, phospholipids and bicarbonate. Stored in gall bladder. Facilitates fat digestion and absorption in small intestine

25
How bile is released in gall bladder
I cells release cholecystokine in response to lipid in lumen. Gallbladder constriction and Oddi sphincter relaxation
26
How bile acids digest lipid
Bile acid acts as detergent (solubilises and emulsified lipid). Enables fat droplets to form micelles (hydrophobic component separating lipid from water nuetralises surface tension, oil droplets forming micelles). Pancreatic amylase enters micelles and digest tri/monoglycerides and fatty acids
27
2 types of small intestine motility
segmentation (circular) and peristalsis (circular and longitudinal)
28
Relationship between motility and nervous system
parasympathetic = increased motility
29
Major Migrating Complex Outline
Contractions push indigestible materials towards colon from small intestine. Stimulated by motilin
30
Enteroendocrine M Cells Outline
In response to high pH motilin is produced. Increases stomach contractions stimulating Major Migration Complex
31
Jejunum and Ileum Functions
complete digestion and absorption of molecules
32
Location of amylase
Small intestine lumen
33
Location of lactase, sucrase and maltase
Brush boarder (small intestine)
34
Carbohydrate transporters on apical membrane
SGLT1 (glucose + galactose) and GLUT5 (fructose). Facilitated diffusion
35
Carbohydrate transporters on basolateral membranes
Glut2 (monosaccharides). Facilitated diffusion
36
Oligopeptides digestion and absorption
Digested by brush boarders (carboxypeptoidase, aminopeptidase and dipeptidase). Amino acids and dipeptidases abslorbed through apical membrane (further digested in membranes where tri/di peptidases broken down to free amino acids). Diffusion of amino acids in blood
37
Fat digestion
Mainly in duodenum. Triglycerides, fat soluble vits and cholesterol are emulsified and solubilised into micelles by bile acids. Triglycerides in micelles are broken down into monoglycerides and fatty acids by lipase. Micelles diffuse actrioss epithelium and release fatty acids and monoglycerides inside cells
38
Fat Absorption Outline
Fatty acids and monoglycerides in epithelial cell are stored in endoplasmic recticulum where they resynthesise triglycerides. Triglycerides moved to Golgi apparatus and formed chylomicrons. Chylomicrons excreted on basolateral side and are absorbed by lacteals
39
Water Absorption Outline
Na/K pumps push Na out of cell onto baslateral side. SGLT 1 (Na/gulucose cotransporter) pumps Na into cell to counterbalance (GLUT2 transporter removes excess glucose and K+ pump removes excess K+). Cl- diffuses through tight junction to basolateral side. Na+ and Cl- combine to form NaCl. Water moves by osmosis from lumen across epithelial (selectively permeable) membrane to area of high solute (NaCl) conc
40
Ileum Outline
Similar to jejunum but with thinner walls, fewer blood vessels, les prominent circular folds and more peyers patches. Remaining fatty acids, fat soluble nutrients, cholesterol, sugars and amino acids are absorbed.
41
Site of bile acid reabsorption
Terminal ileum. 90% recirculated back to liver, 10% progress to colon.
42
Coeliac Disease Outline
Autoimmune response to dietary gluten. Causes atrophy of villi resulting in malabsorption of nutrients. Symptoms: diahorrea, weight loss, fatigue and anaemia. Avoidance of gluten is only solution
43
Lactose Intolerance Outline
Deficiency of lactase resulting in body inability to matabolise lactose. Lactose then metabolised by bacteria in colon. Results in bloating, cramps and diahorrea. Lactase product (eg lactaid) can be taken with meal to avoid symtoms
44
Crohn's Disease Outline
Chroic severe inflammtion in GIT due to genetics/environmental/ immunological factors. Treatment anti-inflammatory drugs or surgery
45
Irritable Bowel Syndrome outline
Small intestinal bacteria overgrowth (bacteria from colon migrate to small intestine). Results in cramps, bloating and diahorrea. Diagnosed bt aspiration of 10^5 bacteria/ml and halogen breath tests
46
Drug absorption factors (drug)
molecular weight, particle size, pKa, lipo/hydrophilicity, physical + chamical structures, formulation and concentration
47
Drug absorption factors (body)
Surface area, vascularity, pH, food vol, gastric emptying rate, disease and secreted substances

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