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Medsci 312 > Lecture 22; Neuroendocrinology 2 > Flashcards

Lecture 22; Neuroendocrinology 2 Flashcards

1
Q

How do the endocrine and neural systems work together?

A
  • Many endocrine systems are under control of BOTH nervous system and endocrine system
  • Work together by way of REFLEX PATHWAYS
  • The response of the pathway usually serves as a negative feedback signal that turns off the reflex
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2
Q

What is a reflex pathway comprised of?

A

Comprised of

  1. Stimulus (out of homeostasis)
  2. Input signal
  3. Integration of signal (Neural or Endocrine system)
  4. Output signal
  5. Response (turning off stimulus)
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3
Q

Describe a simple endocrine reflex

A
  • Internal or external change in signal
  • Endocrine system sensory-intergrative system
  • Efferent signal hormone
  • effectors
  • response
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4
Q

Describe a simple neural reflex

A
  • Internal or external change in signal
  • Receptor
  • Afferent pathway sensory neuron
  • Neural system integrating system
  • Efferent neuron
  • Effector
  • Response
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5
Q

Describe a complicated neuroendocrine reflex;

A
  • Internal or external change in signal
  • Receptor
  • Afferent pathway sensory neuron
  • Neural system integrating system
  • EFFERENT NEURON OR NEUROHORMONE (i.e POMC neurons can work through Leptin or Neurotransmitters, i.e GABA)
  • ENDOCRINE INTERGRATING CENTER
  • Efferent SIGNAL #2 HORMONE
  • Effector
  • Response
    i. e LH regulation…

ACTH -> LH -> estrogen

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6
Q

What are the differences between an endocrine and neural reflex?

A

Specificity; Neural reflex only targets/ acts on a single cell. Where as in the endocrine reflex most cells are exposed to the hormone.

Nature of the signal; Neural = electrical and chemical. Endocrine = Chemical

Speed; Neural = rapid, endocrine = much slower b/c distribution of hormones

Duration of action; Neural ; very short, encodrine = much longer

Coding for stimulus intensity; Neural = Hz of APs, Endocrine = Hormone Conc.

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7
Q

Give an example for a simple endocrine reflex;

A

Endocrine Cell = sensor and integrating center (No afferent pathway)
Efferent pathway = hormone Target = cell with receptor
Example: Glucose stimulation of insulin Increased glucose: Increased intracellular ATP exceeds threshold Pancreatic β cells secret insulin
Target cells express insulin receptor; increased glucose uptake Glucose levels fall; negative feedback

Insulin triggers glucose uptake into liver, muscle and adipose tissue.

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8
Q

Describe a simple neural reflex;

A

Example: Knee jerk reflex
Knock on knee (stimulus) activate stretch receptor
Electrical and chemical signal through afferent neuron to
Spinal cord = integrating center
Signal travels through efferent neuron to muscles of thigh (target = effector)
Response = muscles contract = knee jerk

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9
Q

Describe a neuroendocrine reflex.

A

Identical to neural reflex except neurohormone released by neuron travels in blood to target

Example:
Baby’s suckling stimulates breast sensory signals (afferent pathway)

Signals travel to mother’s brain = integrating center

Electrical signal in the efferent neuron triggers release of neurohormone, oxytocin

Oxytocin is carried in the circulation to the breast Breast smooth muscle (effector) contracts Ejection of milk = response

Hint hint** should be able to do this for the appetite regulation from lecture 21 exam

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10
Q

Whats the sensor/ receptor for endocrine reflexes?

A

Endocrine cells as is the integrating centre!!!

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11
Q

What noteable tissue does the nervous system actually innervate?

A

Adipose tissue

= Thermogenesis

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12
Q

In reality what sort of pathway is the insulin system?

A

Complex Reflex Control Pathway

Example: Control of insulin release by nervous system

Both excitatory and inhibitory neurons terminate on the endocrine cells of the pancreas

Endocrine cells must integrate information from 3 sources;

Two antagonistic inputs from the nervous system and their direct detection of blood glucose levels

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13
Q

What tissue structures does it become difficult to seperate the nervous and endocrine systems?

A
  1. Hypothalamus
  2. Adrenal medulla
  3. Pineal gland
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14
Q

In what three ways does the hypothalamus control the endocrine system?

A
  1. Synthesises Anterior pituitary releasing and inhibiting hormones
  2. Neuroendocrine hormones of post. piuitary
  3. Regulates the secretion of catecholamines in the adrenal medulla.
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15
Q

How does the endocrine system regulate the PVN?

A

Leptin regulates (high) POMC and (low) ARGP neurons in the ARC which then regulates MC4R on the PVN (aMSH vs AGRP).

Complex neuroendocrine system (but not key way this system actually works, (GABA))

Regulates Body weight, appetite, thermogenesis

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16
Q

Where did leptin really work (reminder)

A

Mainly on GABA neurons that synapsed onto POMC neurons

therefore leptin indirectly regulates POMC

17
Q

How was the cre loxp mouse produced?

A

F0 , make two mice. Cre mouse, expresses cre recombinase which cleaves and recombines DNA. But only for gabaergic neurons.

Also the LoxP mouse (LoxP sites either side of target gene, cre tragets this)

Combine the mouse = F1 gen. Cre LoxP mouse, doesnt express the gene in those receptors.

18
Q

What determines the strength of the GABAergic neurons on the POMC neurons?

A

Interplay between glucose and leptin signalling determines the strength of GABergic synapses at POMC neurons.

19
Q

Do POMC and ARGP only signal through aMSH and AGRP?

A

No!

They can signal through a range of other neurotransmitters too

20
Q

What does MS4R do?

A

Regulates energy homeostasis in the brainstem (energy expenditure and glucose homeostasis)

Satiety elsewhere in the brain

BUT appetite regulation in the PVN

21
Q

What can brown white adipose tissue?

A

Enriched environment induces ‘browning’ of white fat and this can happen independent of exercise. Suggests feeling good/happy induces browning of white adipose tissue

This means more thermogenesis / energy expenditure = healthier

22
Q

Describe the adrenal medulla;

A

• Structurally and developmentally part of the nervous system
• Yet in the adrenal gland which is an endocrine structure
• Adrenal medulla - modified sympathetic ganglion whose
neurons secret catecholamines into the blood
• Catecholamines (epinephrine, norepinephrine and dopamine) are neurohormones (synthesised from dopamine)
• Catecholamines bind to cell membrane receptors (GPCRs)

23
Q

What modulates the hypothalamic centers?

A

Neural inputs from higher centers modulate the hypothalamic system

24
Q

What causes neural regulation of the hypothalamic centers?

A

Environmental changes: psychological stress, exercise, temperature, light/dark
Effects: pulsatility of hormone release, circadian rhythm of hormone release

25
Q

Whats an example of the environment affecting the hypothalamus?

A

Pineal gland: in mammals this appears to transduce neural information on day-night cycle from retina into the circadian rhythm of melatonin secretion

26
Q

Describe melatonin release;

A

Increases around 10pm peaks mid sleep then is back to low levels 8-9am

27
Q

Give some examples of circadians rhythms;

A

Body temperature changes day/night

Plasma cortisol- peaks 9am, then reduces

28
Q

Therefore because of pulsatile release and circadian rhythms whats the clinical importance of this?

A
  • Set points can vary in individuals in response to the daily light-dark cycles and the seasons
  • Changing set points cause certain variables to vary in predictable ways over a period of time, forming patterns of change known as biorhythms

therefore measuring must occur at certain times i.e 24hr urinary cortisol is measured as this peaks 9am

29
Q

What do biological rhythms create?

A

• Biological rhythms create an anticipatory response to a predictable environmental variable

30
Q

Give some examples of biorhythms;

A
  • Cortisol release
  • Growth hormone release
  • Sex hormones (LH, FSH, sex steroids)
  • Blood pressure
  • Body temperature (drops at night - sleep)
31
Q

What does melatonin effect?

A
  • Circadian rhythms
  • Mediates reproduction in seasonally breeding animals
  • Regulation of sleep
  • Cardiovascular function
  • Immune function
  • Cancer cell growth

Not the only driver of biorhythms as each cell has a clock and the brain does too. Some of these are driven by food intake.

32
Q

What does the timing that you eat affect?

A

Your body weight

33
Q

What regulates the periphery clocks?

A

Master clock in hypothalamic suprachiasmatric (SCN) nucleus sends signals to extra-SCN regions, which in turn entrain peripheral tissues via hormonal, autonomic nervous system (ANS), and behavioural pathways in order to
regulate peripheral clock control of fuel utilization and energy harvesting.

i.e through hormone and neural input

34
Q

What can changes in biological clocks lead to?

A

Insulin insensitivity

Obesity

35
Q

What can regulate the central clock?

A

Food and Light

There is nerual and hormonal regulation of all peripheral clocks from this

Medsci 312 (28 decks)

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