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ENI > Pancreas anatomy and physiology > Flashcards

Pancreas anatomy and physiology Flashcards

1
Q

Which is the larger component of the pancreas - exocrine or endocrine component?

A

Exocrine = larger component

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2
Q

What is the function of the exocrine pancreas?

A
  • Secrete digestive enzymes in response to gastrointestinal hormones e.g. CCK
  • Secrete bicarbonate to neutralise acid produced in the stomach (this is in response to secretin produced by intestinal cells)
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3
Q

What do trypsin and carboxypeptidase act on?

A

Peptides and proteins

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4
Q

What does lipase act on?

A

Triglycerides

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5
Q

What does amylase act on?

A

Starch

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6
Q

What does phospholipase act on?

A

Phospholipid

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7
Q

What does ribonuclease act on?

A

RNA

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8
Q

What does deoxyribonuclease act on?

A

DNA

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9
Q

Where are endocrine cells concentrated in the pancreas?

A

In the Islets of Langerhans

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10
Q

What 3 types of cells are found in the Islets of Langerhans?

A

Alpha, beta and delta cells

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11
Q

What hormone is produced by alpha cells?

A

Glucagon

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12
Q

What hormone is produced by beta cells?

A

Insulin

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13
Q

What hormone is produced by delta cells?

A

Somatostatin

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14
Q

Where is somatostatin produced?

A
  • Delta islet cells
  • Periventricular nucleus of the hypothalmus
  • Stomach
  • Intestine
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15
Q

What is the effect of somatostatin?

A

It has a paracrine function, suppressing the secretion of insulin and glucagon.

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16
Q

Describe the synthesis of insulin

A
  • Insulin = peptide hormone
  • First synthesised as a preprohormone → then converted to a prohormone (proinsulin)
  • There is an intracytoplasmic pool of proinsulin
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17
Q

What is the significance of C-peptide in insulin secretion?

A
  • Secretion of insulin requires removal of C-peptide from proinsulin
  • C-peptide = connecting peptide released in equal amounts to insulin; it is biologically inactive and removed from the body at a much slower rate
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18
Q

Describe the structure of insulin

A

Insulin consists of 2 polypeptide chains: alpha and beta amino acid chains connected by two disulphide bonds

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19
Q

What is the plasma half-life of insulin?

A

5-8 mins

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20
Q

Describe the kinetics of insulin

A

Secreted by beta islet cells of pancreas → enters veins → portal system → insulin acts upon liver first → insulin enters general circulation

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21
Q

Where and how is insulin degraded?

A
  • Liver or kidney
  • This occurs via cleavage of 2 disulphide bonds within target cells after receptor binding
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22
Q

How is insulin secretion regulated?

A
  • Nutrients: glucose and amino acid levels
  • GI hormones: incretins such as gastric inhibitory peptide (GIP) and glucagon-like peptide (GLP-1)
  • Autonomic nervous system: parasympathetic nervous system stimulates, sympathetic nervous system inhibits
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23
Q

How does the parasympathetic nervous system stimulate insulin secretion?

A
  • Via the vagus nerve
  • The vagus nerve increases GI motility and digestion
  • There is higher insulin secretion after feeding
24
Q

How does the sympathetic nervous system inhibit insulin secretion?

A
  • Direct innervation via sympathetic neurones
  • Indirect response via adrenaline
  • The stress response produces hyperglycaemia

Note: both insulin secretion and action are inhibited.

25
Q

True/false: it is not a specific level of insulin or glucagon in the body that determines the actions in the body.

A

True: it is not a specific level of insulin/glucagon that determines the actions in the body; it’s the ratio between the two which leads us to anabolism vs. catabolism

26
Q

This diagram describes the events in the beta cell that lead to insulin secretion. Fill in the blanks.

A
27
Q

Describe how events in the intestinal tract affect insulin secretion

A
  • GIP and GLP-1 are released by small intestinal cells. Their release stimulates insulin secretion.
  • GIP and GLP-1 are increased when food reaches the intestine. This causes insulin secretion in advance of nutrient absorption.
28
Q

Describe the 2 phases of insulin release that occurs in humans and some animals

A
  • First phase: release of intracytoplasmic pool of proinsulin
  • Second phase: insulin secretion resulting from new protein synthesis
29
Q

True/false: the release of insulin from beta cells occurs through the process of potassium-mediated exocytosis.

A

False.

The release of insulin from beta cells occurs through the process of calcium-mediated exocytosis.

30
Q

Give some examples of glucose transporters

A

GLUT-1

GLUT-2

GLUT-4

31
Q

Which of the following glucose transporters (GLUT1, GLUT2, GLUT4) are insulin dependent vs independent?

A
  • GLUT1 and GLUT2 = insulin independent
  • GLUT4 = insulin dependent
32
Q

True/false: insulin is a water soluble peptide hormone.

What receptors would it therefore bind to/would it move straight into the cell?

A

True: insulin is a water soluble peptide hormone.

It binds to insulin receptors on the plasma membranes. The density of receptors is one determinant of insulin sensitivity.

33
Q

The binding of insulin to insulin receptors on the plasma membrane activates what signal transduction pathway?

A

It activates the tyrosine kinase signal transduction pathway.

34
Q

Which of the glucose transporters allows glucose to enter cells in a concentration-dependent manner, working independently of insulin?

A

GLUT2

is a type of glucose transporter that allows glucose to enter cells in a concentration-dependent manner. It provides facilitated, insulin-independent glucose transport.

35
Q

Where are GLUT1 transporters found?

A
  • CNS
  • RBCs

They supply the basic energy requirements of the cells here.

36
Q

Where are GLUT2 transporters found?

A
  • Liver
  • Islet glucose sensor
37
Q

Where are GLUT4 transporters found?

A
  • Muscle
  • Fat
38
Q

Describe the action of insulin on muscle (where carbohydrates are concerned)

A
  • Insulin promotes uptake of glucose via GLUT4 into muscle
  • Insulin increases glycogen synthase activity, stimulating glycogenesis
39
Q

Describe the action of insulin on energy metabolism in the liver (with respect to carbohydrates)

A
  • There is no GLUT4 in the liver. Glucose uptake occurs via GLUT2
  • Insulin inactivates glycogen phosphorylase → inhibit glycogenolysis
  • Insulin increases glycogen synthase activity → stimulates glycogenesis
  • Insulin promotes the conversion of glucose into fats = de novo lipogenesis
  • Insulin inhibits gluconeogenesis (glucose creation from breakdown of stores)
40
Q

Describe the action of insulin on energy metabolism in the brain

A
  • There is no GLUT4 in the brain. Glucose uptake occurs via the insulin independent GLUT1 transporter
  • The exception to this is satiety and appetite centres, where insulin is required for glucose uptake
  • Without insulin (i.e. diabetes mellitus) appetite increases
41
Q

Describe the effect of insulin on fat metabolism

A
  • Insulin inhibits hormone-sensitive lipase (HSL) so thus decreases lipolysis
  • Insulin stimulates de novo lipogenesis; excess glucose increases TCA cycle intermediates (e.g. citrate) and malonyl CoA (fat precursor) is formed
  • Insulin increases delivery of fat to tissues
42
Q

Describe the effect of insulin on protein metabolism

A
  • Insulin increases amino acid uptake by tissues
  • Insulin increases the rate of transcription and translation
  • Insulin inhibits catabolic of proteins
  • Insulin depresses the rate of gluconeogenesis in the liver by inhibiting enzymes and by lowering the supply of amino acids from tissues e.g. muscle
43
Q

Which of these statements is false?

  • Glucagon is a peptide hormone secreted by the alpha islet cells
  • Glucagon is synthesised as preproglucagon which is rapidly converted to glucagon
  • Glucagon has a short plasma half-life of 8-9 mins
A

✅ Glucagon is a peptide hormone secreted by the alpha islet cells

✅ Glucagon is synthesised as preproglucagon which is rapidly converted to glucagon

❌ Glucagon has a short plasma half-life of 8-9 mins → glucagon’s half life is 5-6 mins

44
Q

True/false: glucagon is generally an anabolic hormone.

A

False.

Glucagon is generally a catabolic hormone and its primary site of action is the liver.

45
Q

Where is the primary site of action of glucagon? Where is it metabolised?

A

Primary site of action = liver

Metabolised in liver and kidneys

46
Q

What is the function of glucagon?

A
  • To maintain blood glucose levels between meals (in the inter-prandial period)
  • It is activated during negative energy balance
  • It stimulates glycogenolysis and gluconeogenesis
47
Q

What factors inhibit glucagon secretion?

A
  • Glucagon secretion is inhibited by high blood glucose levels
48
Q

What factors stimulate glucagon secretion?

A
  • Glucagon secretion is stimulated by high amino acid levels
  • This occurs after a protein-rich meal
  • This means glucagon promotes gluconeogenesis
  • This is “protective” after a protein-rich meal, otherwise, insulin stimulated by the amino acids of a protein meal would cause low blood glucose
49
Q

Which of the following hormones cause gluconeogenesis?

Insulin

Glucagon

Cortisol

Epinephrine

A

Glucagon and cortisol

Glucagon - glucose levels are low between meals. We need more glucose so must make some.

Cortisol - we are stressed. Cortisol is a glucocorticoid. We must increase the availability of glucose to the brain and thus may need to make some more. Cortisol acts on liver, muscle, adipose tissue and pancreas to achieve this.

50
Q

Which of the following hormones increase glucose uptake into cells?

Insulin

Glucagon

Cortisol

Epinephrine

A

Insulin

51
Q

Which of the following hormones promote glycogenolysis?

Insulin

Glucagon

Cortisol

Epinephrine

A

Glucagon and epinephrine

Glucagon - glucose is low between meals. Let’s release some from glycogen.

Epinephrine - we’re scared. Let’s release some glucose from glycogen ASAP.

52
Q

Which of the following hormones increases protein synthesis? Which inhibits it?

Insulin

Glucagon

Cortisol

Epinephrine

A

Insulin increases protein synthesis.

Cortisol inhibits protein synthesis. This is presumably to free up amino acids for gluconeogenesis/provision of energy.

53
Q

Fill in the blanks.

A
54
Q

Which type of glucose transporter is shown here? Where is this transporter found?

A

GLUT4 = insulin dependent glucose transporter found in muscle and fat.

55
Q

What cell is shown here? What is the significance of the glucose transporter type?

A

Beta islet cell.

GLUT2 transporter = faciliatated insulin-independent glucose transporter. Allows glucose to enter the islet “glucose sensor” in a concentration-dependent manner, therefore influencing insulin secretion.

ENI (11 decks)

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