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ENI 2 > pancreas anatomy and physiology > Flashcards

pancreas anatomy and physiology Flashcards

1
Q

discuss the pancrease as an exocrine organq

A
  • secretes digestive enzymes in response to gastrointestinal hormones
  • secretes bicarbonate to neutralize acid produced in the stomach (in response to secretin)
  • digestive enzymes: trypsin, lipase, amylase, phospholipase, ribonuclease and deoxyribonuclease
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2
Q

where are the endocrine cells of the pancrease located

A

in islets (islets of langerhans)

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3
Q

name the 3 different types of islet cells and what they produce

A
  • beta = insulin (60-70%)
  • alpha = glucagon (20-25%)
  • delta = somatostatin (10%)
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4
Q

what other substances are released by the islet cells

A
  • pacreatic polypeptide
  • ghrelin
  • vasoactive intestinal peptide
  • secretin
  • motilin
  • substance P
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5
Q

what is somatostatin

where is it produced and what is the function

A
  • produced by the hypothalamus, stomach, intestine and pancrease (delta cells)
  • has paracrine function
  • secreted by delta islet cells
  • supresses insulin and glucagon secretion by local beta and alpha cells
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6
Q

what is insulin

A
  • peptide hormone
  • secreted by the beta cells of the islets of langerhans
  • first synthesised as a preprohormone
  • then converted to a prohormone called proinsulin
  • stored as an intracytoplasmic pool of proinsulin waiting for secretion
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7
Q

describe the structure of insulin

A
  • secretion involves removal of C-peptide from proinsulin
  • insulin molecule consists of two polypeptide chains
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8
Q

describe the synthesis and secretion of insulin

A

synthesis:
1. preproinsulin
2. proinsulin
3. C-peptide cleaved from proinsulin = insulin (alpha and beta chains only)

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9
Q

discuss insulin kinetics and secretion

A
  • insulin secreted by pancreatic cells
  • only has a plasma half life of 5-8 minutes
  • enters veins then into the portal system to act upon the liver first
  • the insulin enters the general circulation
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10
Q

what are the 3 mechanisms for regulating insulin secretion

A
  • increased nutrients (glucose and amino acids) recognized by islet cells, which secrete insulin to store excess
  • gastrointestinal hormones (incretins) such as gastric inhibitory peptide and glucagon peptide prompts pancreatic cells to produce insulin
  • ANS (PSNS stimulates insulin, SNS inhibits)
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11
Q

the release of insulin from beta cells occurs through the process of:

A

calcium mediated exocytosis

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12
Q

the action of insulin is to:

A

move excess nutrients into storage

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13
Q

describe how GLP-1 works

A
  • released by small intestinal cells
  • increase in secretion of GIP and GLP-1 when food reaches intesting
  • causes insulin release from pancrease BEFORE nutrient absorption occurs
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14
Q

describe how the parasympathetic nervous system regulates insulin secretion

A
  • increase in parasympathetic activity stimulates insulin secretion
  • via the vagus nerve
  • vagus nerve increases gastrointestinal motility and digestion
  • higher insulin secretion after feeding
  • SNS activity decreses insulin secretion
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15
Q

describe how the sympathetic nervous system regulates insulin secretion

A
  • direct innervation
  • indirect responses via adrenaline
  • stress response = hyperglycemia
  • insulin secretion is inhibited (as well as insulin action)
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16
Q

what are the key players in the release of insulin

A
  • glucose transportes (GLUT 2: the islet glucose sensor)
  • calcium
  • potassium
  • glucose
17
Q

describe the sequence of events within the beta cells resulting in the release of insulin

A
  1. GLUT 2 transporters allow glucose to enter cell
  2. phosphorylation of glucose by glucokinase traps glucose in the cell
  3. increase in ATP production
  4. inhibits ATP-sensitive potassium channels
  5. increased intracellular potassium concentration leads to depolarization
  6. volatage gated calcium channels activated
  7. influx of calcium triggers exocytosis of insulin
18
Q

explain the connection between insulin and insulin transporters

A
  • insulin water soluble peptide hormone
  • therefore requires receptor proteins to cross cell membrane
  • density of receptors is determinant of insulin sensitivity
  • activates the tyrosine kinase signal transduction pathway
19
Q

what is mechanism of GLUT4

A
  • insulin stimulates translocation of glucose transporter 4 proteins from cytoplasmic vesicles to plasma membrane
  • GLUT 4 proteins are the insulin responsive glucose transporters
  • they are in the skeletal muscles and adipose tissues (major sites of nutrient storage
  • requires insulin!!
20
Q

describe GLUT 1

A
  • insulin independent
  • found in CNS, RBCs
  • high affinity for glucose
  • ensures contant supply of glucose to essential cells (brain cells, RBC)
21
Q

describe GLUT 2

A
  • facilitated insulin independent glucose transport
  • primarily in the liver, pancreatic beta cells, kidney and small intestine
  • low affinity for glucose, allows bidirectional transport
  • facilitates glucose uptake after meal for storage
    -participates in glucose sensing by beta cells and triggers insulin secretion
22
Q

explain how insulin influences metabolism of carbohydrates in muscles

A
  • promotes muscle glucose uptake by GLUT4
  • increases glycogen synthase activity (stimulates glycogenesis)
23
Q

explain how insulin influences carbohydrate metabolism in the liver

A
  • glucose uptake by GLUT2
  • inactivates liver glycogen phosphorylase to inhibit glycogenolysis
  • increases glycogen synthase activity, stimulating glycogenesis
  • promotes conversion of glucose into fats
  • inhibits glyconeogenesis
24
Q

describe how insulin impacts fat metabolism

A
  • inhibits hormone sensitive lipase
  • stimualtes de novo lipogenesis (production of fatty acids from glucose)
  • promotes lipoprtein lipase (increases delivery of fatty acids into tissues)
25
Q

discuss how insulin influences protein metabolism

A
  • increases amino acid uptake by tissues
  • increases the rate of transcription and translation
  • inhibits catabolism of proteins
  • depresses the rate of gluconeogenesis within the liver (inhibits enzymes and lowers supply of amino acids from tissues
26
Q

what is glucagon

A
  • secreted by alpha cells of the islets of langerhans
  • peptide hormone
  • synthesised as preproglucagon
  • rapidly converted into glucagon
  • short plasma half life :5-6 minutes
  • metabolised in the liver and kidneys
27
Q

what are the actions of glucagon

A
  • generally a catbolic hormone
  • primary site of action is liver
  • metabolic processes respond to: glucagon increasing in concentration and insulin decreasing in concentration
  • insulin/glucagon ration determines actions
  • alpha cells primarily respond to a low blood glucose level
28
Q

how is glucagon secreted

A
  • inhibited by high blood gluose levels
  • stimulated by high amino acid levels
  • protects from post prandial hypoglycemia after protein rich meal

ENI 2 (81 decks)

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