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WP 19 Biomed > Physiology > Flashcards

Physiology Flashcards

1
Q

How are fat soluble vitamins (A,D,E,K) absorbed?

A

With lipids as part of the chylomicron

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2
Q

How are Water Soluble Vitamins (B,C) absorbed?

A

Active transport by specific transporter proteins.

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3
Q

How are Na ions absorbed?

A
  • Secondarily actively transported through the brush-border via Na/glucose co-transporter, Na/amino acid co-transporter and Na/H exchanger.
  • Powered by the Na/K ATPase pump on the basolateral (Facing ECF) membrane.
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4
Q

How is Water absorbed in the intestine?

A

Via transcellular and paracellular (tight junctions between the apical borders of epithelial cells) routes.
Osmosis

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5
Q

What effect does Aldosterone have on Na, Cl and water absorption?

A

dehydration -> aldosterone secretion by cornices of adrenal gland -> aldosterone increased activation of enzyme -> increased Na absorption -> secondary increase in Cl and water absorption.

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6
Q

How is Cl absorbed in the small And large intestine?

A

Small intestine = diffusion.
Large intestine = Cl-bicarbonate exchanger.
Cl exits the cell on the basolateral membrane through Cl channels.

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7
Q

How are bicarbonate ions absorbed in the duodenum and jéjunum?

A

Large amounts of bicarbonate ions are secreted by the pancreas and in bile. Thus it must be reabsorbed:
When Na ions are absorbed, moderate amounts of H ions are secreted into the lumen of the gut in exchange for some Na -> H ions combine with bicarbonate to form carbonic acid -> dissociates into water and carbon dioxide -> water remains in chyme but CO2 is absorbed into blood.
This is active absorption of bicarbonate ions.

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8
Q

How are carbs absorbed in the small intestine?

A

Mainly absorbed as monosaccharides (glucose 80%, galactose and fructose 20%).
Active transport.

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9
Q

How is glucose absorbed in the small intestine?

A

Requires Na in the Na-glucose co-transporter.
1. Na active transport through the basolateral membrane of intestinal epithelial cells.
2. Decrease of Na inside the cell drives the Na-glucose co-transporter via secondary active transport.
3. Glucose crosses basolateral membrane via facilitated diffusion.
Galactose transport is similar.

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10
Q

How is fructose transported in the small intestine?

A

Facilitated diffusion through the intestinal epithelium but isn’t coupled with Na. On entering the cell, fructose becomes phosphorylation and converted to glucose -> diffusion into blood.

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11
Q

How are proteins absorbed in the small intestine?

A

Absorbed in the form of dipeptides, tripeptides and free amino acids. Energy supplied by Na co-transporter.
Similar to glucose.

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12
Q

How are lipids absorbed in the small intestine?

A

Monoglycerides and FFA dissolve in the central portion of the bile micelles -> carried to apical membrane -> penetrate the recesses among the moving, agitating microvilli -> Monoglycerides and FFA diffuse out of micelles and into the interior of the epithelial cells -> taken up by smooth ER where they are used to form new triglycerides -> released as chylomicrons through the basolateral membrane -> flow through lymphatic to the thoracic duct -> enter the blood.

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13
Q

What part of the colon does the most absorbin?

A

Proximal 1/2 of the colon - absorbing colon.

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14
Q

What are the main substances absorbed in the large intestine?

A 
Water
Vitamin K
Vitamin B12
Thiamine (B1)
Riboflavin (B2)
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15
Q

How is H2O absorbed in the large intestine?

A

Absorption of Na and Cl creates an osmotic gradient.

Tighter gap junctions in the large bowel make it difficult for electrolytes to pass back into the lumen.

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16
Q

What is the composition of faeces?

A

3/4 water

1/4 solid matter -> 30% dead bacteria, 10-20% fat, 10-20% inorganic matter, 2-3% protein and 30% other.

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17
Q

How are carbs digested?

A

Salivary amylase and pancreatic amylase break down starch and disaccharides (lactose, maltose, sucrose) to oligosaccharides and disaccharides and brush border enzymes (dextrinase, glucoamylas, lactase, maltase and sucrase) break down these to monosaccharides (galactose, glucose and fructose).

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18
Q

How are proteins digested?

A

Begins in stomach with HCl. Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) then further degrade proteins to smaller polypeptides and peptides. Small peptides are freely absorbed with brush border enzymes which convert peptides -> amino acids.

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19
Q

How are lipids digested?

A

Begins with lingual lipase secreted from the tongue glands which initiates the hydrolysis of triglycerides -> fatty acids and monoglycerides. This is continued in the stomach.
Pancreatic lipase action is facilitated by bile salts and involves the hydrolysis of triglycerides -> FA + monoglycerides.

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20
Q

Where are Ca, Fe and folate most absorbed?

A

Gastro-duodenal junction.

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21
Q

Where are bile acids most absorbed?

A

Start of ileum.

22
Q

Where are the most carbs, proteins and lipids absorbed?

A

Most absorbed at the proximal duodenum and become less absorbed moving distally into the small bowel.

23
Q

What are the 4 layers of the small intestine and their constituents?

A

Mucosa: simple columnar epithelium, brush border, high immune cell density, Peyer’s patches in ileum, goblet cells.
Submucosa: Brunner’s glands in duodenum.
Muscularis: inner circular and outer longitudinal.
Serosa

24
Q

List the hormones that control digestion and their function.

A

Gastrin: stimulates gastric glands to secrete pepsinogen and HCl; stimulated by arrival of food and is inhibited by low pH.
Secretin: signals the secretion of NaHCO3 in the pancreas, thus stimulating the secretion of bile in the liver; responds to the acidity of chyme.
CCK: Stimulates the release of digestive pancreatic enzymes, emptying of bile into gallbladder; released in response to fat in chyme.
Gastric Inhibitory Peptide (GIP): Decreases stomach churning in order to slow the emptying of the stomach, also induces insulin secretion.
Motilin: Increasing MMC and stimulates the production of pepsin.
Glucagon-like Peptide 1 (GLP-1): Inhibits gastric emptying and appetite and stimulates insulin release.

25
Q

List the hormones that control appetite and describe their function.

A

Gherkin: released by stomach and signals pituitary gland when body needs to eat.
PYY: released by hypothalamus, aiding in suppression of appetite.
Insulin: Rise in blood-sugar levels and signals suppression of appetite.
Leptin: Produced by adipose fat tissue targeting the hypothalamus -> suppresses appetite.

26
Q

Define digestion.

A

The process of converting food into chemical substances which can be absorbed into the blood and used by the body tissue.
Carbs —> monosaccharides.
Proteins —> amino acids.
Fats —> Glycerol and fatty acids.

27
Q

How is Ca absorbed and where?

A

Ca is mostly actively absorbed in the duodenum and requires Vitamin D which is activated by parathyroid hormone.

28
Q

What type of transport does Fe utilise?

A

Active transport.

29
Q

What type of transport does K, Mg, PO4 use?

A

Uses active transport

30
Q

How much of absorbed carbohydrates does glucose account for?

A

80%.

20% = fructose or galactose.

31
Q

What is a central lacteal and where are they located?

A

A central lacteal is a lymph vessel located in the centre of the villus of the intestines.

32
Q

What are the four enzymes which are secreted by the pancreas as precursors?

A

Trypsin from trypsinogen (activated by enterokinases).
Chymotrypsin from chymotrypsinogen.
Elastase from proelastase.
Carboxypeptidase from procarboxypeptidase.

33
Q

Where are the majority of carbs, proteins and lipids absorbed from?

A

The duodenum mostly, then the jéjunum, then the ileum.

34
Q

Where is the most Ca, Fe and folate absorbed from?

A

Ca is absorbed throughout the small intestine, Fe and folate is mostly in the duodenum.

35
Q

Where in the bowel are bile acids mostly absorbed from?

A

Mostly at the jejunoileal junction, less so in the jéjunum and ileum.

36
Q

Where are Peyer’s Patches found?

A

Ileum

37
Q

What type of epithelium is found in the small and large intestine?

A

Simple columnar epithelium.

38
Q

How long is the small and large intestine?

A

SI - 6m

LI - 1.5m.

39
Q

What is the role of gastrin?

A

Stimulates gastric glands to release pepsinogen which is converted to pepsin in the presence of HCl.

40
Q

What is the role of secretin? Where is it found?

A

Signals the secretion of NaHCO3 in the pancreas, thus stimulating the secretion of bile.
In the duodenum.
Stimulated by the acidity of chyme.

41
Q

What is the role of cholecystokinin (CCK)? Where is it found? How is it stimulated?

A

CCK stimulates the release of digestive enzymes in the pancreas. It is found in the duodenum and stimulated by the presence of fat in chyme.

42
Q

What is the role of gastric inhibitory peptide (GIP)? Where is it found?

A

Decreases stomach churning to slow gastric emptying. It also induces insulin secretion. Found in the duodenum.

43
Q

What is the role of Motilin? Where is it found?

A

Increases MMC and stimulates the production of pepsin. Found in the duodenum.

44
Q

What is the role of Glucagon-like peptide (GLP-1)? Where is it found?

A

Inhibits gastric emptying and appetite. Stimulates the release of insulin. Found in the small intestine and colon.

45
Q

What is the role of ghrelin?

A

Released by the stomach and targets pituitary gland, signalling the need to eat.

46
Q

What is the role of PYY? Where is it released?

A

PYY is a hormone released but the small intestine to counter ghrelin. It is also released by the hypothalamus and signals that you have just eaten.

47
Q

What is the role of insulin? Where is it released?

A

Increases blood sugar. Released by pancreatic beta cells to target hypothalamus —> suppresses appetite.

48
Q

What is the role of leptin?

A

Suppresses appetite. Produced by adipose tissue to target hypothalamus.

49
Q

What is the role of somatostatin? Where is it released?

A

Decreases gastrin release ad secretion, increases smooth muscle contraction and fluid absorption. Secreted from D cells of the stomach and duodenum.

50
Q

What is the role of Vasoactive intestinal peptide (VIP)? Where is it found?

A

Stimulates secretion of water into the pancreatic juice and bile, inhibits gastric acid secretion and causes smooth muscle relaxation. It is found in the pancreas, intestine and CNS.

51
Q

What is non-tropical sprue?

A

Malabsorption cause by coeliac disease, lactose intolerance. Unlike tropical sprue which is caused by tropical pathogens.

WP 19 Biomed (4 decks)

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