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58 Cards in this Set
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- Back
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The pancreatic islets contain 2 hormones responsible for glucose homeostasis. What are these hormones?
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1. Insulin
2. Glucagon |
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Which pancreatic islet cells release insulin?
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beta cells
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What other secretory product do beta cells release?
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islet amyloid polypeptide (IAPP)
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Which pancreatic cells release glucagon?
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alpha cells
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Where are beta cells distributed within the islet?
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core of islet (medulla)
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How much of the islet is composed of beta cells?
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majority - 60%
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How much of the islet is composed of alpha cells?
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25%
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Where are alpha cells distributed within the islet?
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in the periphery (mantle)
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You are more likely to find alpha cells over PP cells in the head of the pancreas (duodenal end). True or False?
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False!
Tail of pancreas (splenic end): alpha > PP Head of pancreas (duodenal end): PP > alpha |
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What is the blood flow within the islet?
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beta to alpha to delta (BAD)
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Following its release from the alpha cell, glucagon is thought to travel downstream to the beta cell via the intra-islet microcirculation to inhibit insulin secretion. True or False?
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False. (for 2 reasons)
1. Glucagon actually stimulates insulin release to limited degree. 2. Intra-islet blood flow is beta to alpha to delta cells (BAD), therefore the beta cell is not downstream of the alpha cell. |
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Following its release from the beta cell, insulin is thought to travel to the alpha cell via the intra-islet microcirculation to stimulate glucagon secretion. True or False?
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False.
Although the direction of blood flow is correct (the alpha cell is downstream of the beta cell), insulin inhibits glucagon secretion. |
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Pancreatic islets are richly innervated. True or False?
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True.
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Islets have both sympathetic and parasympathetic autonomic innervation. True or false?
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True.
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How are islets parasympathetically innervated?
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Vagus
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What are the parasympathetic neurotransmitters?
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ACh
VIP to a lesser degree |
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Where do the parasympathetic preganglionic fibres synapse?
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Within the target organ (pancreas).
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Which nerve is responsible for (preganglionic) sympathetic innervation of the pancreas?
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greater splanchnic nerve
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Which spinal cord segments make up the greater splanchnic nerve?
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T5-T9
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Where do the post-gangionic fibres innervating the pancreas arise from? (ie. where does the GSN synapse?)
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celiac ganglion
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What is the sympathetic neurotransmitter?
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norepinephrine
also neuropeptides to a lesser extent (eg. NPY) |
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The adrenal gland can also act on the pancreas by releasing epinephrine into the blood stream (endocrine effect). True or False?
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True.
Epinephrine will bind to alpha and beta adrenergic receptors in the pancreas to inhibit insulin and stimulate glucagon. (ie. increase blood sugar to fight or flee) |
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Hyperglycemic effect of epinephrine.
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N.B. that alpha and beta refer to type of adrenergic receptor (NOT alpha or beta islet cells!!!!)
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What is the primary stimulus for insulin secretion?
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glucose
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Why is it evolutionarily advantageous to have glucose-dependent insulin secretion?
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To prevent hypoglycemia.
Normally, you should not be releasing insulin in the absence of glucose. If you are, it is pathological: insulinoma or due to excess exogenous insulin. |
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What contributes to the neural regulation of insulin secretion?
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Autonomic NS: PNS and SNS
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What are the effects of parasympathetic stimulation on insulin secretion?
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Stimulatory.
Rest and digest - and store your excess glucose as glycogen or fat! |
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What are the effects of sympathetic stimulation on insulin secretion?
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Inhibitory.
Need to mobilize glucose to fight or flee, therefore can't be storing it. |
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What are some of the hormones that modulate insulin release?
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1. incretins: GLP-1 and GIP
2. Somatostatin 3. Glucagon |
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What is the incretin effect?
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Insulin release (and consequently, glucose uptake into cells leading to lower blood glucose levels) is enhanced when glucose is given via enteral routes rather than parenteral.
It is thought that the incretins, (released enterally by intestinal L cells following food absorption), are responsible for potentiating the effects of insulin. |
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What effect does somatostatin FROM THE GUT have on insulin release? And how does this hormone act (ie, endocrine, paracrine, juxtacrine, etc.)?
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Inhibitory.
Endocrine. |
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What effect does somatostatin from the ISLET DELTA CELLS have on insulin release? And how does this hormone act (ie, endocrine, paracrine, juxtacrine, etc.)?
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Inhibitory.
Paracrine. |
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Which other hormone may have a paracrine effect on beta cells, impacting the release of insulin?
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Glucagon.
Stimulatory effect via glucagon receptors on beta cells. |
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Which nutrients have a stimulatory effect on insulin release?
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1. glucose
2. arginine and lysine (potentiate glucose stimulus for insulin secretion) |
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What are the main counter-regulatory hormones to insulin?
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1. glucagon
2. cortisol 3. GH 4. catecholamines |
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How is glucagon secretion neurally regulated?
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1. PNS via vagus
2. SNS via Epi and NE |
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SNS activation is stimulatory for glucagon release, while PNS stimulation is inhibitory. True or false?
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True.
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There are 2 primary sources of hormones regulating glucagon release. What are these sources?
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1. GI tract
2. Pancreatic islets |
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Which hormones released by the GI tract have a stimulatory effect on the release of glucagon?
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1. CCK
2. GIP |
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Which hormones released by the GI tract have an inhibitory effect on the release of glucagon?
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1. GLP-1
2. SS (GI form) |
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Which hormones released by the pancreatic islets have an inhibitory effect on glucagon release?
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1. insulin
2. SS (islet form) |
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Insulin inhibits glucagon via a paracrine effect while islet SS inhibits glucagon via an endocrine effect. True or false?
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False!
Insulin inhibits via an endocrine effect (through pancreatic circulation BAD). Islet SS inhibits via paracrine effect. |
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Which nutrients are important for glucagon secretion?
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1. lack of glucose ** most important
2. amino acids (alanine and arginine) vs. insulin stimulus is arginine and lysine |
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What is the function of IAPP?
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-inhibits gastric emptying
-suppresses appetite -forms islet amyloid deposits which are toxic to Beta cells (role in DM type 2) |
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What is the role of PP (pancreatic polypeptide)?
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Rat studies:
-suppresses food intake and gastric emptying -increases energy expenditure net = (-) energy balance |
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What other hormones are important in regulating appetite?
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1. Ghrelin - stimulatory
2. Leptin - inhibitory |
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What is the general biological action of insulin on CHO metabolism?
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ANABOLISM - increased glucose storage and utilization
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At which sites does insulin act to increase glucose storage and utilization?
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1. Muscles
2. Adipocytes 2. Liver |
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What are the actions of insulin on muscle?
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1. Translocation of GLUT4 to membrane to uptake glucose (*** 1 effect)
2. Promotion of glycogen storage or use of glucose for energy. 3. stimulation of amino acid uptake (esp. branch chain eg. valine) 4. increase rate of protein synthesis and inhibition of protein catabolism |
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What are the actions of insulin on adipocytes?
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1. Translocation of GLUT4 to membrane to uptake glucose (*** 1 effect)
2. Promotion of storage of glucose as triglycerides. 3. Stimulation of lipoprotein lipase on endothelial cells to break down lipoproteins to FFAs that can enter the adipocyte. 4. Inhibition of lipolysis via inhibition of lipase. |
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What are the effects of insulin on the liver?
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1. stimulation of glycogen synthesis (by activation of glycogen synthase).
2. stimulation of glycolysis (by activation of glucokinase, phosphofructokinase, pyruvate kinase). 3. Inhibition of glycogenolysis (via inactivation of liver glycogen phosphorylase) 4. inhibition of gluconeogenesis (vian inhibition of pyruvate carboxylase, PEPCK, fructose-1,6-diphosphatase) 5. increase rate of protein synthesis and inhibition of protein catabolism |
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What are the chronic metabolic effects of insulin?
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- increased expression of anabolic enzymes
- decreased expression of catabolic enzymes |
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What are the effects of insulin on cell growth?
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-stimulates growth
-stimulates DNA synthesis -essential for normal growth |
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Where is the major site of glucagon action?
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Liver
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How does glucagon affect the liver?
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Increases hepatic glucose output to increase blood glucose via:
1. increased glycogenolysis (via stimulation of glycogen phosphorylase) 2. increased gluconeogenesis (via increased uptake of amino acids which are gluconeogenic precursors = alanine, glutamine; inhibition of pyruvate kinase; stimulation of PEPCK and pyruvate carboxylase) |
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Where do glucocorticoids act to modulate glucose homeostasis?
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1. liver
a. increase gluconeogenesis (via stimulation of PEPCK and glucose-6-phosphatase) b. increase liver's responsiveness to glucagon and catecholamines 2. Adipose tissue a. inhibit glucose uptake |
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Where does GH act to modulate glucose homeostasis?
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inhibits insulin action in many tissues
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In the normal glucose counter-regulation, there is a hierarchy of hormonal action. At which blood glucose level do the following hormones begin to act?
a) insulin b) glucagon c) epinephrine d) growth hormone e) cortisol |
a) insulin release is inhibited at 4.6 mM
b) glucagon release is stimulated at 3.8 mM c) epinephrine release is stimulated at 3.8 mM d) GH is stimulated at 3.7 mM e) cortisol is stimulated at 3.2 mM |
