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Endocrine System > Endocrine Functions of the Pancreas > Flashcards

Endocrine Functions of the Pancreas Flashcards

1
Q

What hormones are secreted by the pancreas?

A

Insulin
Glucagon
Somatostatin
Pancreatic Polypeptide

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2
Q

What are the pancreatic cells known as?

A

Islets of Langerhans

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3
Q

Types of Islets of Langerhans and their secretions:

A
  1. A cells - Glucagon
  2. B cells - Insulin
  3. Delta cells - Somatostatin
  4. F cells or PP cells - Pancreatic Polypeptide
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4
Q

What is the only anti-diabetic hormone secreted by the body?

A

Insulin

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5
Q

Insulin characteristics:
a. Number of amino acids
b. Molecular weight
c. half life
d. basal level in plasma

A

Insulin is a polypeptide hormone
a. 51 amino acids
b. 5808
c. 5 minutes
d. 10 µU/mL

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6
Q

What links the 2 amino acid chains (a and b chains) in Insulin?

A

Disulphide bridges

alpha chain contains 21 amino acids
beta chain contains 30 amino acids

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7
Q

Describe the synthesis of Insulin

A

Occurs in the Rough Endoplasmic Reticulum of beta cells in the Islets of Langerhans
1. It is first synthesised as preproinsulin
2. Preproinsulin gives rise to proinsulin
3. Proinsulin is converted to Insulin and C peptide through a series of peptic cleavages

C peptide - connecting peptide that connects an and b chains. It is detached at the time of Insulin secretion

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8
Q

Where is insulin degraded and what enzyme does that?

A

Insulin is degraded in the liver and kidneys by enzyme Insulin Protease or Insulin-degrading Enzyme

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9
Q

Name the actions of Insulin on:
a. Carbohydrate Metabolism:

or
Insulin decreases blood glucose level by:

A
  1. Increases transport and uptake of glucose by the cells
  2. Promotes peripheral utilisation of glucose
  3. Promotes storage of glucose by glycogenesis
  4. Inhibits glycogenolysis
  5. Inhibits gluconeogenesis
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10
Q

Name the actions of Insulin on:
b. Protein Metabolism

A

Insulin facilitates the synthesis and storage of proteins and inhibits the cellular utilization of proteins by:
i. Facilitating the transport of amino acids into the cell from blood, by increasing the permeability of cell membrane for amino acids
ii. Accelerating protein synthesis by influencing the transcription of DNA and by increasing the translation of mRNA
iii. Preventing protein catabolism by decreasing the activity of cellular enzymes which act on proteins
iv. Preventing conversion of proteins into glucose.

Insulin is responsible for the conservation
and storage of proteins in the body.

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11
Q

Name the actions of Insulin on:
c. On Fat Metabolism

A

Insulin stimulates synthesis of fat
It also increases storage of fat in adipose tissue

  1. Synthesis of fatty acids and triglycerides
    activates enzymes which convert glucose to fatty acids and fatty acids into triglycerides
  2. Transport of fatty acids into adipose tissue
  3. Storage of fat
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12
Q

What is a Houssay Animal?

A

One in which both the anterior pituitary gland and the pancreas have been removed.
Used to show that GH and Insulin have synergistic effects on growth

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13
Q

Ways in which insulin secretion is regulated:

A
  1. Blood glucose level
  2. Amino acids, especially arginine and lysin
  3. Lipid derivatives, eg β-ketoacids such as acetoacetate
  4. Gastrointestinal hormones like gastrin, secretin, CCK and GIP.
  5. Endocrine hormones like diabetogenic hormones such as glucagon, growth hormone and cortisol; increase blood glucose level, leading to insulin secretion
  6. Autonomic nerve fibers - Stimulation of parasympathetic nerve to the pancreas (right vagus) increases insulin secretion; chemical neurotransmitter involved is acetylcholine. Stimulation of sympathetic nerves inhibits the secretion of insulin and the neurotransmitter is noradrenaline
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14
Q

What is the normal blood glucose level?

A

80 to 100 mg/dl

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15
Q

Where do the alpha and beta subunits face/protrude?

A

The alpha subunits protrude out of the cell while the beta subunits protrude into the cell

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16
Q

What is the molecular weight of Insulin receptor?

A

It is a glycoprotein with a weight of 340,000

Insulin receptor is a tetramer, formed by four glycoprotein subunits (two α-subunits and two β-subunits).

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17
Q

Explain the events leading to autophosphorylation

A

When insulin binds with α-subunits of the receptor protein, the tyrosine kinase at the β-subunit (that protrudes into the cell) is activated by means of autophosphorylation.
Activated tyrosine kinase acts on many intracellular enzymes by phosphorylating or dephosphorylating them so that some of the enzymes are activated while others are inactivated.

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18
Q

Where is Glucagon secreted?

A
  1. Alpha cells in Islets of Langerhans of the pancreas
  2. A cells of stomach
  3. L cells of intestine
19
Q

Glucagon characteristics:
a. Number of amino acids
b. Molecular weight
c. half life

A

Glucagon is a polypeptide hormone
a. 29 amino acids
b. 3485
c. 3-6 minutes

20
Q

Describe the synthesis of Glucagon

A
  1. Glucagon is synthesized from the preprohormone precursor called preproglucagon in the α-cells of islets.
  2. Preproglucagon is converted into proglucagon
  3. Proglucagon gives rise to glucagon.
21
Q

Describe the metabolism of Glucagon

A
  1. About 30% of glucagon is degraded in liver
  2. 20% is degraded in kidney.
    The cleaved glucagon fragments are excreted through urine.
  3. 50% of the circulating glucagon is degraded in blood itself by enzymes such as serine and cysteine proteases.
22
Q

Name the actions of Glucagon on:
a. Carbohydrate metabolism

A

Glucagon increases the blood glucose level by:
i. Increasing glycogenolysis in liver and releasing glucose from the liver cells into the blood.
Glucagon does not induce glycogenolysis in
muscle
ii. Increasing gluconeogenesis in liver by:
a. Activating the enzymes, which convert pyruvate into phosphoenol pyruvate
b. Increasing the transport of amino acids into the liver cells. The amino acids are utilized for glucose formation.

23
Q

Name the actions of Glucagon on:
b. Protein Metabolism

A

Glucagon increases the transport of amino acids into liver
cells. The amino acids are utilized for gluconeogenesis.

24
Q

Name the actions of Glucagon on:
c. Fat Metabolism

A

Glucagon shows lipolytic and ketogenic actions. It increases lipolysis by increasing the release of free fatty acids from adipose tissue and making them available for peripheral utilization. The lipolytic activity of glucagon, in turn promotes ketogenesis (formation of ketone bodies) in liver.

25
Q

Name the actions of Glucagon on:
d. Other actions

A

Glucagon:
i. Inhibits the secretion of gastric juice
ii. Increases the secretion of bile from liver.

26
Q

Ways in which glucagon secretion is regulated

A
  1. Decrease in blood glucose level
  2. Increase in amino acid level in blood
  3. Exercise
  4. Stress
  5. Gastrin
  6. Cholecystokinin (CCK)
  7. Cortisol
27
Q

Ways in which glucagon secretion is inhibited:

A
  1. Somatostatin
  2. Insulin
  3. Free fatty acids
  4. Ketones.
28
Q

Sources of Somatostatin secretion:

A
  1. Hypothalamus
  2. D cells in Islets of Langerhans of Pancreas.
  3. D cells in stomach and upper part of small intestine
29
Q

a. Forms in which somatostatin is synthesised:
b. Number of amino acids:
c. Half life:

A

Somatostatin is a polypeptide hormone
a and b. Somatostatin-14 (contains 14 amino acids)
Somatostatin-28 (contains 28 amino acids)

c. 2 to 4 minutes

30
Q

Where does Somatostatin metabolism take place?

A

Liver and kidneys

30
Q

Describe the synthesis of Somatostatin

A

Somatostatin is synthesized from the precursor prosomatostatin.

  1. Prosomatostatin is converted mostly into somatostatin-14 in the D cells of islets in pancreas.
  2. However, in the intestine, large amount of somatostatin- 28 is produced from prosomatostatin.
30
Q

What are the actions of Somatostatin?

A
  1. Somatostatin acts within islets of Langerhans and, inhibits β and α cells, i.e. it inhibits the secretion of both glucagon and insulin
  2. It decreases the motility of stomach, duodenum and gallbladder
  3. It reduces the secretion of GIT hormones: gastrin, CCK, GIP and VIP
  4. Hypothalamic somatostatin inhibits the secretion of GH and TSH from anterior pituitary. That is why, it is also called growth hormone-inhibitory hormone (GHIH)
31
Q

What is the mode of action of Somatostatin?

A

It brings out its actions through cAMP

32
Q

Describe the regulation of:
a. Pancreatic Somatostatin
b. GIT Somatostatin

A

a. Secretion of pancreatic somatostatin is stimulated by:
i. glucose
ii. amino acids
iii. CCK.
The tumor of D cells of islets of Langerhans causes hypersecretion of somatostatin. It leads to hyperglycemia and other symptoms of diabetes mellitus.

b. Secretion of somatostatin in GIT is increased by the presence of chyme-containing glucose and proteins in stomach and small intestine.

33
Q

Sources of Pancreatic Polypeptide secretion:

A
  1. F cells or PP cells in Islets of Langerhans of Pancreas
  2. Small intestine
34
Q

Pancreatic Polypeptide characteristics:
a. Number of amino acids
b. half life

A

a. 36 amino acids
b. 5 minutes

35
Q

Describe the synthesis of Pancreatic Polypeptide.

A

PP is synthesized from pre-prohormone precursor called prepropancreatic poly- peptide in the PP cells of islets.

36
Q

Describe the metabolism of Pancreatic Polypeptide

A

PP is degraded and removed from circulation mostly by the kidneys

37
Q

Action of PP:

A

Increases secretion of glucagon for a cells in the Islet and Langerhans

38
Q

Mode of action of PP:

A

PP brings out its actions through cAMP

39
Q

Regulation of PP secretion:

A

Secretion of pancreatic polypeptide is stimulated by the presence of chyme containing more proteins in the small intestine.

40
Q

Hormones that increase blood glucose level:

A
  1. Glucagon
  2. Growth Hormone
  3. Thyroxine
  4. Cortisol
  5. Adrenaline
41
Q

Role of liver in the maintenance of blood glucose level:

A

The liver serves as a glucose buffer system.
When blood glucose level increases after a meal, the excess glucose is converted into glycogen and stored in liver. Afterwards, when blood glucose level falls, the glycogen in liver is converted into glucose and released into the blood. The storage of glycogen and release of glucose from liver are mainly regulated by insulin and glucagon.

Endocrine System (3 decks)

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