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human nutrition and physiology > Physiology lecture 5 > Flashcards

Physiology lecture 5 Flashcards

1
Q

Regulation of pancreatic secretion by?

A

Acetylcholine
Cholecystokinin
Secretin

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2
Q

How is acetylcholine released in pancreatic secretion?

A

Acetylcholine, released from parasympathetic nerve ending and from enteric nervous system

Acetylcholine is believed to be the main neurotransmitter which regulates the cephalic phase (the gastric secretion that occurs before ingestion).

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3
Q

How is CCK released in pancreatic secretion?

A

it is secreted by the duodenal and upper jejunal mucosa when food enters the small intestine (to 80% of the total secretion of the pancreatic digestive enzymes)

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4
Q

How is secretine released in pancreatic secretion?

A

Also secreted by duodenal and jejunal mucosa when highly acidic food enters small intestine

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5
Q

What do acetylcholine and CCK do?

A

stimulate the acinar cells in pancreas causing production of large quantities of pancreatic digestive enzymes

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6
Q

What do secretin stimulate?

A

secretion of large quantities of water solution of sodium bicarbonate by the pancreatic ductal epithelium

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7
Q

Name 2 roles of bile acids

A

1) they help emulsify large fat particles into many small particles, so the surface can be attacked by lipase enzymes (oancreatic juice)
2. help in absorption of digested fat end products through intestinal mucosal membrane

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8
Q

Give two exemples on end products bile help to take care of

A

bilirubin - end product from hemoglobin destruction

and excess of cholesterol

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9
Q

Short function of bile

A

important in the role of fat digestion and absorption

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10
Q

Where is bile stored and what is the maximum volume?

A

gallbladder

30-60milliliters

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11
Q

How is bile produced?

A

Bile is continually produced by the liver and then concentrated and stored in the gallbladder
Water, sodium, chloride and most other small electrolytes are continually absorbed through gallbladder mucosa.
–> the concentrated remaining bile constituents are bile salts, cholesterol, lecithin and bilirubin

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12
Q

When does the gallbladder begin to empty? What is the mechanism?

A

When food begins to be digested in the upper gastrointestinal tract
mechanism is rhytmical contractions of the gallbladder wall and simultaneous relaxation of the sphincter of Oddi

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13
Q

What stimulates gallbladder emptying?

A

Most potent stimulus is hormone CCK

but also less strongly by acetylcholine-secreting nerve fibers

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14
Q

What is the precursor for bile salts?

A

Cholesterol

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15
Q

How much bile salt is synthesized daily?

A

6 grams

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16
Q

How do bile salts help fat be absorbed?

A

They form complex with fatty acids, monoglycerides and cholesterol called micelles - which can cross intestinal mucosa

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17
Q

What happens to the bile salts in the small intestine?

A

94% is reabsorbed into the blood
half by diffusion through mucosa in small intestine and remainder by active transport through intestinal mucosa in distal ileum

enter portal blood and back to liver.

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18
Q

How is cholesterol gallstones formed?

A

Under abnormal conditions

cholesterol may precipitate in gallbladder -

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19
Q

Where are the Brunner’s Glands, what do they do and why?

A
  • in the wall of the first few centimeters of duodenum
  • protects duodenal wall against highly acidic gastric juice from stomach
  • secrete large amounts of alkaline mucus
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20
Q

What stimuli does Brunner’s respond to?

A

Secrete mucus in response to:

  1. tactile or irritating stimuli on duodenal mucosa
  2. Nervous stimulation
  3. Gastrointestinal hormones especially secretin

Are inhibited by sympathic stimulation.

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21
Q

What are the Crypts of Lieberkühn?

Function etc?

A

A gland found in between villi in the intestinal epithelium lining of the small intestine and large intestine.
Consist of:
1. a moderate number of goblet cells which secrete mucus that lubricates and protects the intestinal surfaces
2. A large number of enterocytes, which in the crypts, secrete large quantities of water and electrolytes
(which help the absorption of ex. amino acids)

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22
Q

Small intestinal enzymes:
The enterocytes of the mucosa, especially those that cover the villi, contain digestive enzymes that digest specific food substances

A
  1. Several peptidase for splitting small peptides into amino acids
    2- four enzymes for splitting disaccharides into monosaccharides - sucrase, maltase, isomaltase and lactase
  2. Small amounts of intestinal lipase for splitting neutral fats into glycerol and fatty acids
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23
Q

What are the two major tissues in the pancreas and what do they do?

A

The acini - which secrete digestive juices into the duodenum
2. the islet of Langerhans, which secrete insulin and glucagon directly into the blood

24
Q

What do alpha cells in the pancreas produce?

A

Glucagon

25
Q

What do delta cells in the pancreas produce?

A

somatostatin

26
Q

What kind of system is the islets of Langerhans?

A

an endocrine system – produce different hormones which goes straight to the blood

27
Q

What does somatostatin do?

A

Somatostatin inhibits insulin and glucagon secretion

28
Q

How much of the islets is beta cells and what is secreted from them?

A

60%

Insulin and amylin (contributes to glycemic control.

29
Q

How much of islets is alpha and delta cells?

A

25% and 10%

30
Q

Where is glycogen stored and what happens to the excessive carbs?

A

Mainly in liver and muscles

Converted to fats and stored in adipose

31
Q

Name a few roles of insulin in energy abundance and absorption

A
  • Storing excess energy
    (glycogen and convert to fats)
  • Also direct effect in promoting amino acid uptake by cells and conversion of these to protein
    Insulin inhibits breakdown of proteins in the cells
32
Q

What are the last steps before insulin is formed and ready for secretion?

A

proinsulin consist of 3 peptides (A-chain, C-chain and B-chain) in the golgi apparatus broken down (A and C-chain connected via disulphide bonds and make insulin whilst C peptide hang loose)→ packed into secretory granules and ready for carbohydrates –
(There is one C peptide per insulin molecule)

33
Q

What can C peptide be used for?

A

The levels of C peptide can be measured in insulin-treated diabetic patients to determine how much of their own natural insulin they are still producing

34
Q

what is the half life of insulin and how is it degraded?

A

Its plasma half-life is about 6 min
mainly cleared from circulation within 10-15
it is defreaded by enzyme insulinase, mainly in liver to lesser extent in the kidneys and muscles

35
Q

How do the insulin receptors look like?

A

They are a combination of four subunits held together by disulfide linkages

36
Q

What happens when insulin binds to receptor?

A

Binds to the alpha subunits on the outside of the cell so the beta subunits on the cellmembrane become autophosphorylated
This activated a local tyrosine kinase which then activates insulin receptor substrates

37
Q

What happens when insulin receptor substrates have been activated?

A

There are phosphorylation of enzymes triggering several responses:

  • Growth and gene expression
  • Glycogen synthesis
  • Fat synthesis
  • Protein synthesis
  • Vesicles with glucose transporter goes to membrane
38
Q

What does GLUT4 do?

A

The proteins are inside the cell in vesicles (each carry several GLUT4)
In response to insulin, goes to the membrane of the cell and can transport glucose inside

39
Q

What happens to the cell membrane as a response to insulin?

A

It becomes more permeable to many amino acids, potassium iona and phosphate ions

40
Q

What can branched amino acids in the blood indicate?

A

Risk of diabetes

41
Q

How can GLUT4 be stimulated without insulin?

A

Through exercise! It acts independently then

42
Q

What happens to most of the absorbed glucose?

A

Stored as glycogen in the liver

43
Q

How does insulin inhibit gluconeogenesis?

A

Insulin inactivates liver phosphorylase, the principal enzyme that causes liver glycogen to split into glucose

44
Q

How is glucose trapped in the liver?

A

Insulin increases the activity of the enzyme glucokinase which phosphorylate glucose making it negatively charged and therefore not able to leave
Then made to glycogen

45
Q

What happens to the excess of glucose that the liver doesn’t need?

A

They are converted to fatty acids which are sybsequently packed as triglycerides in a LDL and transported this way by the blood to adipose tissue.
In adipose tissue insulin activated lipoprotein lipase in the capillary walls which splits triglycerides into fatty acids again

46
Q

How is hormone -sensitive lipase regulated by insulin?

A

Insulin inhibit
When insulin not present – start break down fat in adipose tissues
Insulin deficiency –> lipolysis of storage fat and release of FFA

47
Q

Insulin stimulates transport of many amino acids into the cell but most strongly…

A

valine, leucine, isoleucine, tyrosine and phenylalanine

48
Q

How does insulin promote protein synthesis?

A

Insulin increases translation of messenger RNA turning in the ribosomal machinery
increases rate of transcription of selected DNA
also inhibits catabolism of protein

Also decreasing activity of enzymes promote gluconeogenesis and save amino acids

49
Q

Can fat be converted to glucose?

A

Nope!
Can be acetyl coa (2c)
but to be glucose you need 3 carbon (pyruvate)

50
Q

What is needed for us to grow in addition to insulin?

A

Growth hormone and insulin interact synergistically to promote growth

51
Q

Explain the mechanism for insulin secretion of the beta cells

A

In beta cells have GLUT2 – independent of insulin

  • Glucose goes inside beta cells – make ATP – when high enough it blocks channel of K+
  • Then get a lot of potassium inside so the cell gets more positive (usually it is negative) which leads to depolarization (when charge between in and outside of cell is less) –> activate sensitive Calcium channels
  • The insulin vesicles can be incorporated into membrane and release insulin through exocytosis
52
Q

How does amino acid effect insulin?

A

Amino acid produce little insulin

- Amino acid + glucose produce a lot of insulin

53
Q

What regulates glucagon?

A

Glucose levels in the blood

54
Q

Explain the multiple inhibitory effect of somatostatin produced by delta cells

A

1- Acts locally within the islets of Langerhans to deoress secretion of both insulin and glucagon
2- Decreases motility of the stomach, duodenum and gallbladder
3- decreases both secretion and absorption in the gastrointestinal tract

Goal is to make satiety last longer!

55
Q

How can GLP-1 help diabetes type 2 patients?

A

It signal insulin secretion

56
Q

What kind of drugs can be used for T2D besides insulin?

A

Drugs that increase insulin sensitivity
Supress liver glucose production
cause additional release of insulin by pancreas

human nutrition and physiology (17 decks)

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