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ENI > Pancreas Anatomy > Flashcards

Pancreas Anatomy Flashcards

1
Q

What does the pancreas develop from?

A

The organ develops as outgrowth of the foregut (dorsal and ventral) and the Langerhans islets bud off from the developing exocrine pancreas.

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2
Q

What is the function of the exocrine pancreas?

A

Secretes digestive enzymes- Secreted in response to gastrointestinal hormones (e.g. cholecystokinin; CCK)

Also secretes bicarbonate (base) to neutralize acid produced in the stomach-
Secreted in response to secretin (hormone produced by intestinal cells)

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3
Q

Where is the endocrine pancreas situated?

A

The endocrine compartment of the pancreas is concentrated in the islets of Langerhans (1-2% of the pancreas)

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4
Q

What cells does the endocrine pancreas consist of?

A

β-cells (dog:75 %)
α-cells (dog: 20 %)
δ (delta)-cells

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5
Q

What do the cells of the islet produce?

A

β-cells which produce Insulin (dog:75 %)
α-cells which produce Glucagon (dog: 20 %)
δ (delta)-cells which produce Somatostatin

Other hormones also produced by the islet cells include:Pancreatic polypeptide, ghrelin, vasoactive intestinal peptide (VIP), secretin, motilin, and substance P

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6
Q

What is different about the horse pancreas?

A

The lobes are fused

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7
Q

Which species have fused pancreas lobes (partially)?

A

Ox, sheep and pig

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8
Q

Where does the pancreas arise from

A

The final liver and pancreas are made from glandular tissue from the gut plus connective tissue from mesenchyme.

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9
Q

Where is somatostatin produuced?

A

Hypothalamus (periventricular nucleus)
Stomach
Intestine
Pancreas (delta cells)

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10
Q

What does somatostatin from the delta cells do?

A

Acts to supress insulin and glucagon secretion by local beta and alpha cells

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11
Q

Why does insulin need to be injected rather than taken orrally?

A

Insulin is a peotide hormone which means that it needs to be injected otherwise it would be digested

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12
Q

How is insulin produced?

A

It is Secreted by the beta cells of the Islets of Langerhans where it is first synthesized as a preprohormone and then converted to a prohormone called proinsulin

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13
Q

What is the purpose of making insulin as a prohormone?

A

This forms an Intracytoplasmic pool of proinsulin

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14
Q

What is the C-peptide and how is it formed?

A

Secretion of insulin involves the removal of C-peptide from proinsulin, C-peptide is the connecting peptide.
The C-peptide is then released with the insulin but it is biologically inactive

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15
Q

How can we use C-peptide?

A

Because it is removed from the body at a slower rate it is useful to measure pancreatic function (but not often done in animals)

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16
Q

What does the insulin molecule consist of?

A

Insulin molecule consists of two polypeptide chains of length 21 (α) and 30 (β) amino acids.
These two chains are connected by two disulphide bonds

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17
Q

Where is insulin degraded?

A

Degradation of insulin is done in the liver and kidneys within target cells after the insulin binds to the receptor and is broken by cleavage of these disulphide bonds

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18
Q

What is the half life of insulin?

A

Once insulin is secreted by the pancreas it has a half life of only 5-8 min

19
Q

Once secreted by the liver what is the action of insulin?

A

It enters the veins and goes into the portal system where it travels to the liver where the insulin acts first.
After this insulin enters the general circulation although the C-peptide is not removed from circulation by the liver

20
Q

Insulin secretion is regulated by…

A 
Nutrients: glucose and amino acids
Gastrointestinal hormones (incretins) such as gastric inhibitory peptide (GIP) and glucagon like peptide (GLP-1)

Autonomic nervous system

a. Parasympathetic stimulates
b. Sympathetic inhibits

21
Q

Insulin is an anabolic hormone, what does this mean?

A

Increased secretion when nutrients are abundant eg. After feeding

22
Q

How does calcium have an effect on insulin release?

A

The release of insulin from β cells occurs through the process of calcium-mediated exocytosis and acts to move energy substrates into storage

23
Q

How do GI hormones regulate insulin release?

A

Insulin secretion is stimulated by gastric inhibitory peptide (GIP) and GLP-1 which are Released by small intestinal cells
There is an Increase in GIP and GLP-1 when food reaches intestine which causes insulin release from pancreas before nutrient absorption occurs

24
Q

What effect does parasympathetic stimulation have on insulin secretion?

A

The parasympathetic nervous system stimulates insulin secretion via the the vagus nerve (the vagus also increases GI motility and digestion) so this creates higher insulin after feeding

25
Q

What effect does sympathetic stimulation have on insulin secretion?

A

There is also direct innervation by sympathetic neurons (and indirect sympathetic stimulation via adrenaline) which initiates a stress response, hyperglycemia, so insulin secretion is inhibited

26
Q

What is first and second phase insulin release?

A

First phase represents release of the intracytoplasmic pool of proinsulin
Second phase insulin secretion results from new protein synthesis

27
Q

How does insulin bind to receptors?

A

Insulin is a water-soluble peptide hormone so it binds to insulin receptors on plasma membranes

28
Q

The density of insulin receptors is dependant on…

A

The density of receptors is one determinant of insulin sensitivity

29
Q

Activation of these insulin receptors causes activation of what pathway?

A

Activation of these receptors activates the tyrosine kinase signal transduction pathway

30
Q

What are GLUT4 proteins and what does insulin stimulate them to do?

A

GLUT4 proteins are the insulin-responsive glucose transporters in skeletal muscle and adipose tissues (Major sites for nutrient storage)

Insulin stimulates translocation of glucose transporter 4 (GLUT4) proteins from the cytoplasmic vesicles to the plasma membrane

31
Q

Insulin increases glycogen ……………….

A

synthesis

32
Q

In the liverthere are no GLU4 receptors so how is insulin taken up?

A

Via GLUT2 receptors?

33
Q

Liver uptake of insulin acts to …..

A

Inactivate liver glycogen phosphorylase (which inhibits glycogenolysis)

Increase glycogen synthase activity (which stimulates glycogenesis)

Promotes conversion of glucose into fats (stimulates lipogenesis)

Inhibits gluconeogenesis

34
Q

There are no GLUT4 receptors in the brain so how is insulin taken up?

A

GLUT1

The Exception is where insulin is taken up into satiety and appetite centres (without insulin appetite increases)

35
Q

What effect does insulin have on hormone sensitive lipase?

A

Insulin also inhibits hormone sensitive lipase (HSL) which decreases lipolysis and stimulates lipogenesis (production of fatty acids from glucose)

36
Q

What are the steps in lipogenesis?

A

Excess glucose increases TCA cycle intermediates: citrate and isocitrate
Activate acetyl CoA carboxylase (ACC)
Forms malonyl CoA (fat precursor)

37
Q

What is the effect of insulin on protein metabolism?

A

Increasing amino acid uptake by tissues and increasing the rate of transcription and translation, it also inhibits the catabolism of proteins.

38
Q

What is the effect of insulin on the rate of gluconeogenesis?

A

Insulin depresses the rate of gluconeogenesis within the liver and inhibits enzymes so lowers supply of AA from tissues.

39
Q

Where is glucagon secreted from?

A

Glucagon is secreted by by alpha cells of the Islets of Langerhans

40
Q

What is glucagon and how is it synthesised?

A

It is a petide hormone consisting of 29 amino acids that is synthesized as preproglucagon which is rapidly converted to glucagon.

41
Q

What is the half life of glucagon? Where is it metabolised?

A

It has a short half life of 5-6 mins and is metabolized in the liver and kidneys

42
Q

What triggers the alpha cells to produce more glucagon?

A

Alpha cells primarily respond to a low blood glucose level (hypoglycemia)

43
Q

What is the function of glucagon?

A

Glucagon acts to maintain blood glucose levels between meals and is activated during negative energy balance, it stimulates glycogenolysis and gluconeogenesis.

44
Q

What stimulates and inhibits glucagon?

A

Glucagon is inhibited by by high blood glucose levels and Stimulated by high amino acid levels (eg. After a protein rich meal, it responds best to Alanine and arginine) which promotes gluconeogenesis to act in a protective mannor.

ENI (33 decks)

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