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Metabolism in H&D > 2 Digestion And Absorption > Flashcards

2 Digestion And Absorption Flashcards

0
Q

What does saliva contain?

A

Electrolytes, mucus, bicarbonate

And the following enzymes: lysozyme, lingual lipase

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1
Q

How are nutrients delivered to the liver?

A

Hepatic portal vein

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2
Q

How does food enter the oesophagus and what stops food reentering from he stomach?

A

Peristalsis and gravity

Cardiac sphincter

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3
Q

What happens in the stomach? Draw and label the structure

A

Mixing of food into chyme
Bulk storage of digested food in the fundus
Some salivary amylase denatured
50% dietary starch digested
Secretion of HCL and pro enzymes
Absorption of water and some other substances
(Refer to lecture slide for diagram)

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4
Q

HCL secretion _____ stomach contents to ph__
Gastric mucosa is folded into ________
Gastric glands are located at the _______
The entire stomach mucosa is replaced every ___ days

A

Acidified to ph 2
Invagination aka gastric pits
Th base of the gastric pits
Every 3 days

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5
Q

Name the gastric secretory cells and what they do

A

Mucous cells : release thick mucus to prevent auto digestion
Parietal cells: release HCL and intrinsic factor
Enterochromaffin-like cells: release histamine
Chief cells: release pepsinogen, chymosin, gastric lipase
Enterendocrine g cells: secrete gastrin
Enterendocrine d cells: secrete somatostatin

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6
Q

What substances control HCL secretion? Why is HCL important?

A

Histamine
Acetylcholine
Gastrin (+ve in presence of food) (-ve at low ph)

HCL maintains optimum ph for pepsin

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7
Q

What is the target of omeprazole? Why are ther few siDe effects? What is a prodrug?

A

Google it

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8
Q

What is nervous control of gastric emptying?
What is endocrine control?
What is hormone release controlled by?

A
  • nervous: when duodenum is distended, the sphincter is closed
  • secretin eg GIP and cholecystokinin CCK released by small intestine inhibit opening
  • acidic chyme and high fat content
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9
Q

What are the roles the endocrines

GIP and CCK?

A

GIP: insulin secretion
CCK: produced in the duodenum and jejenum and stimulates secretion of bile and pancreatic juice

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10
Q

Draw a diagram representing the inside of the intestinal tract.

A

Diagram on lecture slide
Duodenum contains sub mucosal glands and plica
Jejunum contains serosa, muscular is externa, sub mucosa, muscularis mucosa and mucosa… Plus plica
Ileum contains aggregate lymphoid nodules and villi

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11
Q

The Small Intestine
The duodenum is __ m in length and it is the _____ site of digestion
The jejunum is ___ m in length, ___ digestion and ___ absorption
The ileum is ___m in length, ___ digestion

A

The duodenum is ~0.3 m in length and it is the primary site of digestion
The jejunum is 1-2 m in length, some digestion and most absorption
The ileum is ~1.5 m in length, little digestion

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12
Q

What is pancreatic juice made of?

A

bicarbonate; carbohydrases; lipase; nucleases; proteolytic enzymes; endocrine hormones

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13
Q

What does plasma secretin regulate?

A

The release of bicarbonate

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14
Q

What is passive diffusion?
Facilitated diffusion?
Active transport?

A

Passive: Some short chain fatty acids, down a concentration gradient by osmosis
Facilitated: Protein channel, against a conc gradient, may require co-transport
Active transport: Uses ATP against an electro or chemical gradient

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15
Q

Compare the appearance, and the enzymes used in Lumenal epithelial cells and Contralumenal EC’s

A 
Lumenal: Ordered microvilli
enzymes - Di- and oligosaccharidases
Aminopeptidase, Dipeptidases
g-Glutamyltransferase, Alkaline phosphatase
Guanylate cyclase

Contralumenal: Few microvilli
enzymes - Na+/K+ ATPase, Adenylate cyclase

16
Q

Compare the transport systems of
Lumenal SI Epithelial cells (enterocytes)
and Contralumenal enterocytes

A 
Lumenal: Na+-monosaccharide cotransport (SGLT-1).... Facilitated fructose transport (GLUT-5)
Facilitated monosaccharide transport (GLUT-2)
Na+-neutral amino acid cotransport
H+-peptide cotransport (PEPT1)
Na+-bile cotransport (ASBT)
Fatty acid translocase (FAT)
Fatty acid transport portein (FATP)
Passive diffusion

Contralumenal:
Facilitated monosaccharide transport (GLUT-2)
Facilitated amino acid transport
Export into lacteal in chylomicrons

17
Q

Give the first 5 glucose transporters, their locations and their functions.

A

GLUT1 - red cells, brain placenta - basal glucose uptake
GLUT2 - Liver, Kidney, pancreatic b cells, intestine
- allows glucose to equilibrate across cell membran
CLUT3 - Brain - Allows constant glucose uptake
GLUT 4 - muscle, fat - insulin-sensitive
GLUT5 - jejunum - fructose transporter

18
Q

What are SGLT genes? what do they depend on?

A

They enable transport of glucose against a concentration gradient. They depend on the sodium gradient actively to accumulate glucose.
They have different stoichiometries
SGLT 1 - 1 glucose/2NA+ e.t.c

19
Q

Na/K exchanging ATPase is present on the ___________ membrane of the enterocyte and is responsible for _________ from the cell to maintain an _________ gradient

A

Na/K exchanging ATPase is present on the contraluminal membrane of the enterocyte and is responsible for removing Na+ from the cell to maintain an electrochemical gradient.

20
Q

What secretions and absorptions is the NA/K exchanging ATPase responsible for?

A
  • Absorption of NaCL in small and large intestine
  • Glucose and amino acid absorption in the SI enterocytes
  • NaCl/bicarbonate secretion by intestinal crypt cells and secretary cells of the pancreas
21
Q

How are amino acids absorbed?

A

Digested by pepsin, break down into free amino acids and oligo peptides. Oligo peptides are further digested by enzymes on the brush border -> free amino acids and di/tri-peptides. These are absorbed through non-specific luminal transport proteins. Free mino acids are co-transported with Na+, di/tripeptides are co-transported with H+.

22
Q

What are the 5 phases of lipid digestion/absorption?

A
  • Hydrolysis of TAG to FFA and MAG within the lumen
  • Large oil phase TAG droplets are emulsified to smaller emulsion droplets by the stomach,
  • Mixed micelles are formed by bile acids and other pancreatic enzymes
  • Uptake of FFA and MAG via specific FAT transport proteins
  • These are packaged into chylomicrons which enter the lacteal and lymphatic circulation.
23
Q

1) What are the primary bile acids?
2) What are the secreted as?
3) How are they recirculated?

A

1) Cholic and chenodeoxycholic acids
2) Secreted as a conjugate - taruine+cholic acid = taurocholate
3) From hepatocytes -> illeum -> enterocytes -> blood -> hepatocytes
* and bound to albumin in plasma

24
Q

Describe the role of the Na+/K+ATPase in electrolyte (and water) absorption

A

NaCl uptake proceeds by different mechanisms in small and large intestine
Majority absorbed by small intestine (electroneutral)
Requires a luminal Na+/H+ exchanger (driven by contraluminal Na+/K+ ATPase)
Release of H+ drives Cl- absorption
Remainder ‘scavenged’ by large intestine (depending on the NaCl balance of the body)
Also driven by Na+/K+ ATPase
Luminal Na+ channel is regulated by glucocorticoid hormones

25
Q

In the colon, what are undigested carbohydrates broken down by and into?

A

By resident microflora by fermentation - into short chain fatty acids.

26
Q

Explain how impaired activity of the Na+/K+ ATPase may contribute to the symptoms of IBD

A

Net decrease in Na+ and Cl- absorption in the large intestine
Reduced activity (<70%) of the Na+/K+ exchanger
Collapse of electrochemical gradient
Reduced activity of a luminal Na+ channel
Electrochemical imbalance reduces Cl- uptake
Decreased water uptake secondary to impaired NaCl absorption contributes to diarrhoea
Treatment with glucocorticosteroids

27
Q

What system drives water uptake into the intestine?

A

K/Na exchanging ATPase system - electrochemical gradient

28
Q

What disease is associated with lowering water uptake into the small intestine and what is it treated with?

A

Irritable bowel syndrome

Glucocorticosteroids

29
Q

What are the stages that lipids are transported around the body?

A 
Lipids ->
Lumen triacylglycerol ->
Micelles ->
Enterocyte triacylglycerol ->
Chylomicron -> to the lymph

Metabolism in H&D (14 decks)

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