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Y2S2 VETS2012 physiology > L2 - hypothalamus pituitary and pineal gland > Flashcards

L2 - hypothalamus pituitary and pineal gland Flashcards

1
Q

Hypothalamus is made up of

A

Made up of :
Nuclei (concentrations of neuronal cell bodies)
Nerve tracts (axons)
Regulates and coordinates responses to changes in the external and internal environment
Vegetative – maintains homeostasis
Behaviour – eg. Reproductive, feeding, rage

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2
Q

what is the role of the hypothalamus, simplified

A

integrating neural and endocrine systems

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3
Q
A
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4
Q

Hypothalamus-putuary adrenal axis (HPA) axis

A
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5
Q

Hormones in the hypothalamus control secretion of hormones in the pituitary

A
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6
Q

hormones of hypothalamus and pituitary gland

A
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7
Q

Pineal gland

A

Receives input from retina on light/dark
Not directly, via hypothalamus (suprachiasmatic nuclei (SCN))and sympathetic innervation
Fossils indicate originally there may have been direct light exposure (3rd eye)
Along with SCN, pineal is responsible for circadian rhythms through production of melatonin
Circadian rhythms seem to have evolved to match environment with internal metabolism, including at the cellular level (eg, low O2 levels and UV damage)

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8
Q

Circadian rhythms

A

Endocrine rhythms
Body temperature
Glucose homeostasis
Lipogenesis
Locomotor activity

For more information on circadian rhythms, see this link

http://patient.info/doctor/pineal-gland-and-circadian-rhythms

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9
Q

morning’ people have lowest core temp at 4am whereas ‘evening’ people have lowest core temp at 6am

A
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10
Q
A
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11
Q

Neurohypophysis

A

(Posterior Pituitary gland)
Stores neurohormones from hypothalamus in Herring bodies and releases them into bloodstream
2 hormones:
Oxytocin
Anti-diuretic Hormone (ADH or vasopressin)
Both hormones short peptides consisting of 9 amino acid residues

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12
Q

ADH and Oxytocin

A

Being small peptide hormones, both ADH and oxytocin are synthesized as preprohormones in the neurosecretory cells
Prohormone portion is cleaved as it is transported down the axon and results in the active hormone and peptide fragments known as neurophysins
No known functions (yet) for neurophysins which are also released into blood stream
Release of hormone is due to calcium influx triggered by electrical impulses travelling down the axons from the hypothalamus

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13
Q

Anti-diuretic Hormone

A

Actions:
Decrease in water excretion by kidneys (anti-diuretic)
Vasoconstriction (=vasopressin)
Secretion is regulated by:
[solute] in ECF (extracellular fluid)
Osmoreceptors in hypothalamus
Blood volume
Atrial volume ‘stretch’ receptors
See renal lectures for more info

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14
Q

Cellular action of ADH

A

ADH binds to V2 receptor on distal tubule of kidney
Activates 2nd messenger (cAMP)
Activates protein kinases
Affect membrane protein on apical surface of distal tubule cell
Water flows from distal tubule, down concentration gradient, through tubule cell to interstitium of renal medulla
Water retention
ADH binds to V1 receptor in smooth muscle
Vasoconstriction
Increased blood pressure
May be used in emergency med for treatment of vasodilatory shock

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15
Q

Oxytocin

A

Actions:
Parturition – stimulates contraction of uterine smooth muscle
Lactation – milk ejection during suckling due to contraction of smooth muscle
Secretion is stimulated by:
Pressure of foetus in birth canal
Suckling baby
Secretion is inhibited by fear or anxiety
May also play important roles in males
Has been called the ‘trust chemical’
Neurotransmitter, neuromodulator & neurohormone
More in repro

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16
Q

neural Input - hormal output (oxytocin release)

A
17
Q

Suckling feedback loop,

A
18
Q

explain the secretion of oxytocin and why it is like that

A
19
Q

Other roles of oxytocin

A

Oxytocin impairs uterine blood flow (necessary post-partum)
Increase oxytocin release during positive social interaction – also found to be associated with wound healing (decrease in chemokines)
Increased oxytocin promotes trust and reduces fear and generally modulates emotional behaviour to promote social bonding (presumably to enhance reproduction), however also promotes defensive behaviours, depending on the situation
Oxytocin receptor deficiency has been shown to be associated with autism (not all autism) and oxytocin administration trials show promise with improvement of speech, decrease in repetitive behaviours and increase in reading others’ emotions

20
Q

Adenohypophysis

A

Or anterior pituitary
Hormone production and secretion triggered by regulating hormones produced in the hypothalamus
5 different types of endocrine cells, each producing their own hormone(s)

21
Q

Interms of normal actions there are 2 groupings

A

Trophic hormones control the activity of another endocrine gland
ACTH (adrenocorticotrophic hormone)
TSH (thyroid stimulating hormone)
LH (luteinising hormone)
FSH (follicle stimulating hormone)

Hormones that have a direct effect in their own right
Prolactin
Growth hormone

22
Q

Control anterior pituitary gland

A

Secretions are in response to neurohormones called ‘releasing hormones/factors’ from hypothalamus
Secreted from nerve endings into capillaries at specialised region of hypothalamus (median eminence)
Transported in hypothalamus-hypohyseal portal system to adenohypophysis
Act on their target cells to stimulate synthesis and secretions of adenohypophysis hormones
Often small peptides 3-40 amino acid residues
Eg. GnRH is a decapeptide (10 aa’s)

23
Q

Secretion of hypothalamic releasing and release inhibiting factors

A

Integrated response from neural and hormonal inputs
Can be excitatory and inhibitory
Target gland hormones exert negative feedback to maintain homeostasis
Also can get positive feedback
Eg. Oestrogen induced preovulatory LH surge

24
Q

Prolactin

A

Action:
Stimulates alveolar epithelium of mammary gland to synthesise and secrete milk
Many other non-reproductive roles
Eg. Immune system, behaviour, haematopoiesis
Secretion:
Inhibited by dopamine
Negative feedback maintains low prolactin in non-lactating animals
Prolactin has a multitude of post-translational forms and other variants such as phosphorylation and glycosylation
Prolactin in its many forms has been shown to be produced in many tissues such as the CNS, the immune system and reproductive tissues

25
Q

Disorders involving prolactin

A

Hyposecretion:
Poor milk secretion
Hypersecretion (pituitary tumour):
Galactorrhea and infertility in females
Low libido and gynecomastia in males

26
Q

Regulation of prolactin secretion

A
27
Q

regulation of PRL in lactation

A
28
Q

suckling pathway including prolactin

A
29
Q

Pro-opiomelanocortins

A

ACTH (corticotropin) and β-lipoprotein originate from common prohormone (pro-opiomelanocortin)
Prohormone produced by corticotropes in pars distalis and from cells in pars intermedia
Corticotropes in pars distalis produce ACTH
In pars intermedia, ACTH is cleaved to form -MSH predominantly, and small amount of ACTH

30
Q

Pro-opiomelanocortin derivatives

A
31
Q

MSH

A

Melanocyte stimulating hormone
MSH stimulate the production and release of melanin by melanocytes in skin and hair
MSH actions in the brain have effects on appetite and sexual arousal.
Get increased pigmentation in Cushing’s disease due to xs ACTH due to common pathway
Get Cushing’s symptoms in horses when have pituitary tumours involving intermediate lobe due to common pathway

Y2S2 VETS2012 physiology (16 decks)

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