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Animal Physiology > Endocrinology > Flashcards

Endocrinology Flashcards

1
Q

How do positive feedback loops influence the parameter?

A

pushes the parameter further from the set point

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2
Q

how do negative feedback loops influence the parameter?

A

bring the parameter closer to the set point

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3
Q

What are the 4 types of feedback regulation?

A

direct feedback loop
first-order
second order
third order

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4
Q

Describe direct feedback loops

A

the tissue/organ that senses the parameter change is the same one that releases the hormone that will cause a response from the target organ to bring the parameter closer to the set point

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5
Q

describe first order feedback loops

A

sensor sends a signal messenger (neurotransmitter) to the integration centre which sends a messenger (neurotransmitter) to the target organ which produces a response to bring the parameter closer to the set point

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6
Q

describe second order feedback loop

A

the sensor sends a messenger (neurotransmitter) to the integration centre which sends a message (neurotransmitter) to the endocrine gland which releases a hormone into the circulatory system to the target organ to elicit a response to bring the parameter closer to the set point

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7
Q

Explain how there’s 2 negative feedback loops in second order feedback loops

A

there’s one that includes the entire system from the response to the stimulus

the endocrine gland has it’s own negative feedback loop: the response from the target organ can negatively regulate the endocrine gland and the hormones it releases

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8
Q

describe third order feedback loops

A

the sensor organ sends a neurotransmitter to the integrating centre which sends a neurotransmitter to an endocrine gland which releases a hormone into the circulatory system

this causes a second endocrine gland to release a second hormone into the circulatory system to find the target organ

target organ responds to bring the parameter closer to the set point

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9
Q

How does a third order feedback loop have 3 points of regulation?

A

there’s 3 negative feedback loops

1 for the entire system

1 from the response to the first endocrine gland

1 from the response to the 2nd endocrine gland

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10
Q

What’s a major difference between direct feedback regulation and different ordered loops?

A

direct feedback loops only involve endocrine glands, whereas the ordered loops involve the nervous system (neurons and neurotransmitters)

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11
Q

In direct regulation, what could be the sensor organ?

A

an endocrine gland could sense the stimulus and also release the hormone directly into the circulatory system to reach the target organ

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12
Q

Explain how the atrial natriuretic peptide is an example of direct feedback regulation

A

the atrium is the sensor that senses the high blood pressure and releases the atrial natriuretic peptide hormone to stretch the cells of the atrium and lower blood pressure

organ is both sensor and releaser of hormone

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13
Q

What are the 2 anatomic sections of the pituitary gland?

A

anterior pituitary (adenohypophysis)

posterior pituitary (neurohypophysis)

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14
Q

What part of the brain is the pituitary gland connected to? explain how

A

hypothalamus

the neurons that grow into the posterior pituitary gland originate in the hypothalamus

the cell bodies are in the hypothalamus and the axons extend into the posterior pituitary

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15
Q

What type of feedback regulation occurs in the pituitary gland? explain

A

first order endocrine pathway

hypothalamus senses a stimulus and acts as the integrating centre to send information to the posterior pituitary gland (target organ) via a neuron causing the pituitary gland to release a hormone into the blood causing a response

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16
Q

Explain how oxytocin is released and regulated by the endocrine system

A

first order positive feedback loop

oxytocin stimulates uterine contraction during child birth

fetus presses against uterus = stimulus

cervix stretch cells (sensor) receive signal and send neurotransmitter to hypothalamus (integrating)

hypothalamus sends a neurotransmitter via a neuron to the posterior pituitary gland (target organ)

posterior pituitary gland releases oxytocin into the blood stream to increase uterine contractions

this response causes a stronger signal to be sent to the stretch cells of the cervix to increase the release of oxytocin and cause more contractions = pushes the parameter further from the set point (positive feedback)

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17
Q

What order of endocrine pathways (feedback regulation) is the anterior pituitary gland involved in?

A

second and third order

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18
Q

Explain the endocrine pathway the anterior pituitary gland is involved in

A

second and third order

sensor: hypothalamus senses stimuli and releases neurohormones to the

integration center: hypothalamus-pituitary portal system which releases another hormone to

endocrine gland/target organ: anterior pituitary releases a hormone into the circulatory system to cause a response

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19
Q

What’s a tropic hormone?

A

a hormone that causes the release of another hormone

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20
Q

What are the 3 neurohormones (tropic hormones) that the hypothalamus will release to reach the anterior pituitary?

A

prolactin-releasing hormone (PRH)

prolactin-inhibiting hormone (PIH/dopamine)

corticotropin-releasing hormone (CRH)

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21
Q

describe the endocrine pathway related to the prolactin-releasing hormone (PRH)

A

sensor: hypothalamus senses stimulus and releases PRH

integration centre: hypothalamus-pituitary portal system

endocrine gland: PRH stimulates the anterior pituitary to release prolactin (PRL)

target organ: prolactin stimulates breast tissue to produce breast milk

this is second order positive feedback (prolactin production causes breast milk production which increases the signal and causes the parameter to move further from the set point)

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22
Q

describe the endocrine pathway related to the prolactin-inhibiting hormone (PIH/dopamine)

A

sensor: hypothalamus senses stimulus and releases PIH

integration centre: hypothalamus-pituitary portal system

endocrine gland: PIH inhibits the anterior pituitary to stop the release of prolactin into the blood stream

target organ: prolactin does not reach the breast tissue and the lack of response causes the parameter to come back to the set point

negative feedback second order

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23
Q

describe the endocrine pathway for the corticotropin-releasing hormone (CRH)

A

sensor: hypothalamus senses stimuli and releases CRH

integrating: hypothalamic-pituitary portal

endocrine gland: CRH stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH) into the circulatory system

2nd endocrine gland: ACTH stimulates the adrenal cortex to release cortisol (hormone steroid) into the circulatory system

target organ: multiple

positive third order regulation

related to stress response

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24
Q

What endocrine function does the pancreas have?

A

blood-glucose regulation

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25
Q

Describe the cellular structure of the pancreas and its relation to glucose and blood-glucose levels

A

alpha cells produce glucagon

beta cells produce insulin

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26
Q

Why is the regulation of blood glucose levels essential?

A

glucose provides energy for brain cells so having a balanced level of blood-glucose is essential for brain function

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27
Q

What are the consequences of low blood glucose levels?

A

brain cannot function

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28
Q

What are the consequences of high blood glucose levels?

A

the osmotic balance of blood is disturbed

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29
Q

Which 2 hormones are involved in controlling blood-glucose levels?

A

insulin to lower blood glucose levels

glucagon to raise blood glucose levels

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30
Q

What does insulin do?

A

lower blood-glucose levels

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31
Q

What does glucagon do?

A

raise blood glucose levels

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32
Q

Who won the Nobel prize for discovering insulin?

A

Frederick Banting and John Macleod of University of Toronto in 1923

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33
Q

What endocrine organ secretes the hormones insulin and glucagon?

A

pancreas

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34
Q

What type of feedback loop/regulation is involved in the pancreas’s regulation of blood-glucose levels?

A

direct feedback loops

the pancreas receives neural and hormonal signals and releases hormones to trigger a response

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35
Q

What is antagonistic pairing?

A

when hormones have opposing effects

ex. insulin and glucagon

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36
Q

How does the pancreas reduce elevated blood glucose levels?

A

by secreting insulin

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37
Q

How does the pancreas increase lowered blood glucose levels?

A

by secreting glucagon

38
Q

How many amino acids make up insulin?

A

51

39
Q

How many amino acids make up glucagon?

A

29

40
Q

What are the 2 major functions of the pancreas?

A

exocrine: secretes digestive enzymes

endocrine: secretes insulin and glucagon

41
Q

What are the Islets of Langerhans?

A

clusters of cells in the pancreas with endocrine function (secrete insulin and glucagon)

42
Q

What are the 2 types of cells found in Islets of Langerhams in the pancreas?

A

Beta cells: secrete insulin

alpha cells: secrete glucagon

43
Q

Describe the endocrine pathway that follows elevated blood-glucose levels

A

direct feedback loop

sensor: pancreas receives signal that blood-glucose levels are high and releases insulin into the circulatory system

insulin causes:

glucose to be transported into beta cells via the glucose transporter GLUT2 = increases glucose in the cells and increases intracellular ATP

increased ATP closes ATP-dependent potassium channels

membrane potential is depolarized = activates voltage-gated Ca2+ channels

vesicles fuse and insulin is secreted into the blood

insulin binds to insulin receptors (RTKs)

the receptor tyrosine kinase signal transduction pathway causes phosphorylation of GLUT4 intracellular glucose transporters

GLUT4 translocates to the cell surface and glucose is transported out of the cell

44
Q

What are the glucose transporters involved when insulin is released?

A

GLUT2 transporters bring glucose from the bloodstream into the beta cells of the pancreas

GLUT4 translocates to the cell surface to move glucose out of the cell and into muscle and fat tissue

45
Q

Describe the endocrine pathway that follows lowered blood-glucose levels

A

direct feedback loop

sensor: pancreas receives signal that the blood-glucose levels are too low and releases glucagon into the circulatory system

glucagon is released by alpha cells in the pancreas and binds to G-protein coupled receptors in the liver (G alpha s)

activated Gas stimulates adenylate cyclase signal transduction

PKA activated

PKA phosphorylates glycogen phosphorylase kinase which breaks down glycogen (storage form of glucose) into glucose

GLUT2 carries glucose out of the cell and into the bloodstream

46
Q

Which glucose transporters are involved in the release of glucagon?

A

GLUT2 carries glucose out of the cell into the blood stream

47
Q

What is glycogenolysis?

A

the breakdown of glycogen into glucose

48
Q

What is gluconeogenesis?

A

the formation of glucose

49
Q

Why does glucose require transporters to bring it across cell membranes?

A

glucose is hydrophilic and cannot pass the hydrophobic membrane on its own

50
Q

what’s the resting level of glucose?

A

4-6 mM

51
Q

What’s the level of glucose after eating?

A

9-11 mM

52
Q

What are the different isoforms of glucose transporters?

A

GLUT 1, 2, 3, 4

53
Q

Where does GLUT1 function and how does it function?

A

in all tissues

constantly working on cell surfaces

54
Q

Where does GLUT3 function and how does it function?

A

only in the brain

works constantly

55
Q

Where does GLUT4 function and how does it function?

A

intracellular in muscle and fat tissue

involved in bringing glucose out of the beta cells and into fat and muscle tissues by translocating to the cell surface when insulin has been released to lower blood glucose levels

56
Q

Where does GLUT2 function and how does it function?

A

in pancreatic beta cells and liver

brings glucose into and out of the beta cells

57
Q

Which of the 2 hormones stimulates glycogenolysis and gluconeogenesis?

A

glucagon

58
Q

Describe the insulin regulating pathways that occurs when you’ve eaten a meal

A

eat a meal

  1. increased blood glucose signals to the pancreas and the pancreas secretes insulin into the circulatory system to negatively regulate the blood glucose levels and lower them (direct)
  2. the glucose receptors in the digestive tract bind glucose and release CCK into the bloodstream > CCK stimulates secretion of insulin into the bloodstream by the pancreas > lowers blood glucose levels (2nd order)
  3. stretch receptors in the digestive tract sense increased glucose and send a signal to the integrating centre which sends a neuronal message to the pancreas > pancreas releases insulin into the blood stream and lowers blood glucose (2nd order)
59
Q

Describe the antagonistic pairing in the regulation of blood-glucose that work to reduce glucose levels

A

when there’s an increase in blood glucose levels:

STIMULATING:
beta cells of pancreas are stimulated
increase of insulin secretion
target tissues increase uptake of glucose
blood glucose levels reduced
sends negative feedback to the sensor

INHIBITING:
alpha cells of pancreas stimulated
decreased glucagon secretion
target tissues reduce glucose release
blood glucose levels reduced
sends negative feedback to sensor

60
Q

Describe Type 1 Diabetes Mellitus

A

occurs when blood-glucose levels are abnormally high due to lack of insulin production because the beta cells of the pancreas are attacked and destroyed (autoimmune)

10% of diabetics, usually diagnosed at young age

it’s insulin-dependent diabetes
alpha cells are spared

61
Q

is type 1 diabetes the autoimmune disease? how is it treated?

A

yes, the beta cells of the pancreas are attacked and destroyed

treated with insulin injections

62
Q

What mediates the destruction of the beta cells when someone has type 1 diabetes?

A

T cell lymphocytes

63
Q

Describe Type 2 Diabetes Mellitus

A

non-insulin dependent diabetes
80-90% of diabetics, often diagnosed later in life

often related to other health factors such as obesity

blood-glucose levels are too high because cells become unresponsive to insulin (insulin resistance) as a result of impairment to the insulin receptor or the transduction mechanism causing beta cells to stop secreting insulin

64
Q

What’s the major differences between type 1 and 2 diabetes?

A

Type 1 is insulin-dependent, type 2 is not

Type 1 is an autoimmune disease in which the beta cells are destroyed and cannot produce insulin to lower blood-glucose ; type 2 is not an autoimmune disease, likely due to an impairment in the signal transduction pathway of insulin secretion that prevents beta cells from secreting insulin

~10% of diabetics are insulin-dependent, type 1
~80-90% are NID, type 2

65
Q

Describe how glucose levels are controlled in crustaceans

A

Low hemolymph-glucose causes:

Crustacean hyperglycemic hormone (CHH) to be released from the crab’s eyestalk (X-organ/sinus gland)

CHH binds to receptor guanylate cyclase

higher cGMP levels activate signaling pathway to release glucose and raise glucose levels (negative feedback)

under anaerobic conditions, glycolysis and lactate release cause the release of CHH

66
Q

How does CHH regulate hemolymph glucose levels?

A

low glucose = increased CHH
high glucose = decreased CHH

low lactate = decreased CHH
high lactate = high CHH

67
Q

How are lactate, glucose, and CHH related in crabs in a positive feedback loop?

A

low glucose levels cause build of lactate which increases CHH levels to release more glucose and increase glucose levels

68
Q

How are glucose and CHH related in crabs in a negative feedback loop?

A

low glucose stimulates guanylate cyclase to stimulate glycogenolysis to breakdown glycogen and release glucose

high glucose levels inhibit guanylate cyclase and prevent glycogenolysis and the release of glucose

69
Q

Which two physiological systems interact to stimulate the fight-flight response to stress in vertebrates?

A

the sympathetic nervous system and the hypothalamus-pituitary-adrenal cortex (HPA axis) of the endocrine system

70
Q

Explain how the sympathetic nervous system is involved the vertebrate stress response

A

sense organ: brain receives stress signal and activates the sympathetic nervous system

a) sympathetic nerves increase heart rate, respiration, airway dilation

b)

71
Q

What are the 4 major vertebrate stress responses onset by the sympathetic nervous system?

A
  1. SNS activates pancreas to decrease insulin secretion = increase blood-glucose
  2. SNS activates pancreas to increase glucagon secretion = increase blood-glucose
  3. SNS activates adrenal medulla to increase epinephrine in blood = increase heart rate, respiration, airway dilation, blood glucose levels, and to redistribute blood flow
  4. SNS directly targets other tissues to have the same physiological responses

these work together to increase delivery of nutrients, glucose and oxygen to fuel the body for survival

72
Q

How does the endocrine system function in vertebrate stress response?

A

the brain senses the stressful stimulus

hypothalamus secretes corticotropin-releasing hormone (CRH)

CRH targets the anterior pituitary and causes the release of adrenocorticotropic hormone (ACTH)

ACTH activates the adrenal cortex to release cortisol

increased cortisol causes many cells in tissues to increase blood glucose levels

73
Q

Describe additivity

A

a target cell’s response to combinations of hormones is the sum of the responses to the individual hormones

Ex. the glucose secretion caused by just glucagon + glucose secretion caused by just epinephrine = the glucose release when the two are combined

74
Q

Describe synergism

A

When hormones increase the effect of other hormones and the response by the target cell to combinations is more than additive

ex. cortisol has a really small effect on glucose secretion, but when combined with glucagon + epinephrine, the result is significantly higher than if the individual responses were added up

75
Q

What hormones does the adrenal cortex release?

A

cortisol, aldosterone

76
Q

Where is the adrenal cortex? What type of cells exist there?

A

in the outer shell of the adrenal gland on the kidney

interrenal cells

77
Q

Where is the adrenal medula? what type of cells exist there?

A

the inner layer of the adrenal gland on the kidney

chromaffin cells

78
Q

What type of hormones does the adrenal medula secrete?

A

epinephrine (adrenaline)

79
Q

What are circadian rhythms?

A

the mechanisms that control behaviour, activity, and physiology in response to light and dark periods (periodic activity)

80
Q

What physiological parameters are controlled by circadian rhythms?

A

activity
body temperature
hormones
metabolism
sleeping/waking
feeding

81
Q

What are circadian rhythms in sync with?

A

light and dark cycles, roughly over 24 hours

82
Q

What part of the brain has been linked to circadian rhythms?

A

suprachiasmatic nucleus of the hypothalamus

83
Q

How did researchers discover the connection between the suprachiasmatic nucleus and circadian rhythms?

A

used a control mouse with no surgery etc and found that activity was mostly during the dark periods of 12 hours and little during the light 12 hour periods

blind mouse, no surgery: activity still followed 12 hour cycles of activity and no activity though over time started to drift more into the light periods = still maintained circadian rhythm

mouse with SCN lesion: constant activity and no connection to 12 hour cycles or periods of light or dark = lose circadian rhythm

84
Q

Explain the study on circadian rhythm in reindeer in the Arctic (both the 70 and 78 degrees north)

A

in the 70 degrees north population:
there were shorter periods of no light or all light
animals were still relatively rhythmic in their activity

in the 78 degree north:
in periods of 24 hours of darkness, the animals lost their circadian rhythms and were less active regardless of the time of day
in periods of 24 hours of light, the connection to their circadian rhythms were also disrupted as the animals were much more active regardless of time

85
Q

How is the circadian clock in the SCN generated?

A

by a rhythmic cycle of changes to gene expression regulated by a negative feedback loop

86
Q

What are the transcription factors involved in regulating the gene expression involved in circadian rhythms?

A

BMAL1 and CLOCK

87
Q

Describe the steps involved in the negative feedback loop of gene expression involved in regulating circadian rhythms?

A

BMAL1 and CLOCK (transcription factors) heterodimerize

the heterodimer binds to E-box activator sequence located in the promoters of period (per) and cryptochrome (cry) genes

this produces proteins PERs and CRYs which heterodimerize in the cytoplasm

PER:CRY translocate into the nucleus to inhibit CLOCK:BMAL1 activity = inhibit PER:CRY transcription

because transcription is involved, there’s a time lag and PER and CRY increase or decrease cyclically

88
Q

Describe what’s occurring in the SCN during the circadian day

A

BMAL1:CLOCK dimer actively binding to E-box and transcribing period and cryptochrome genes

this takes a long time to produce the protein products

89
Q

Describe what’s occurring in the SCN during the circadian night

A

When transcription of period and cryptochrome genes is complete, the protein products CRY and PER heterodimerize in the cytoplasm and are translocated to the nucleus to inhibit the binding of BMAL1:CLOCK to the activator E-box sequence

prevents more transcription

90
Q

Are circadian clock genes positively or negatively regulated?

A

negative feedback regulation on the transcription of circadian clock genes period and cryptochrome

91
Q
A

Animal Physiology (13 decks)

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