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After the MSA > Hypothalamo pituitary axis > Flashcards

Hypothalamo pituitary axis Flashcards

1
Q

Endocrine secretion

A

Hormones diffuse directly into capillaries to act on distant target organs

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2
Q

Paracrine secretion

A

Secreted and act more locally

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3
Q

Autocrine secretion

A

Act on themselves

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4
Q

What are the major endocrine glands?

A
  • Pineal gland
  • Hypothalamus
  • Pituitary
  • Thyroid
  • Parathyroid
  • Thymus
  • Adrenal gland
  • Pancreas
  • Gonads - ovary and testes
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5
Q

What are the 3 categories of factors controlling hormone release from endocrine glands?

A
  • Humoral
  • Neural
  • Hormonal
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6
Q

Describe the humoral factors affect hormone release

A

Response to changes in extracellular fluid e.g.
• Capillary blood has a low concentration of Ca2+ which stimulates the secretion of parathyroid hormone by parathyroid glands
• Release of insulin in response to blood glucose

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7
Q

Describe the neural factors affecting hormone release

A

Preganglionic sympathetic nervous system fibres stimulating the adrenal medulla cells to secrete catecholamines

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8
Q

What are the hormonal factors affecting hormone release?

A
  • Hypothalamus secretes hormones/neurohormones that stimulate the anterior pituitary to secrete hormones that stimulate other glands to release hormones
  • Amplifiable response
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9
Q

What is the pituitary gland enclosed by?

A
  • Sella tunica of the sphenoid

* enclosed superiorly by diaphragma sellae

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10
Q

Where does the pituitary gland lie?

A

Immediately posterior to the optic chiasma and sphenoid sinus, on the floor of the midbrain

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11
Q

What are the parts of the anterior pituitary?

A
  • Pars anterior (distalis)
  • Pars tubercles (PT) surrounds the neural stalk
  • Pars intermedia - exists between anterior and posterior pituitary
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12
Q

What is the anterior pituitary derived from?

A

• Rathke’s pouch

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13
Q

Describe the embryological development of the pituitary

A
  • Anterior pituitary: upgrowth of epithelium from the oral cavity (Rathke’s pouch) - hypophysial diverticulum
  • Posteiror pituitary: down growth from the brain (infundibulum) - neurohypophyseal
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14
Q

Craniopharyngiomas

A

Slow growing tumours that can develop along the track of Rathke’s pouch

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15
Q

Describe chromaphils

A
  • Take up stain, there are two types
  • Acidophils
  • Basophils
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16
Q

What is the name given to cells that do not take up stian

A

Chromophobes

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17
Q

Describe the nuclei in the hypothalamus

A 
• Large cell bodies: 
- paraventricular 
- supraoptic 
- infundibular 
• Small cell body nuclei
18
Q

Describe the course of the axons of the large cell bodied nuclei

A
  • Extend down through the median eminence
  • Come together to form a nerve tract: hypothalmo-hypophyseal tract
  • Fibres terminate in the posterior pituitary on a capillary network supplied by the inferior hypophyseal artery
  • Herring bodies
19
Q

Describe the course of the axons of the small cell bodied nuclei

A
  • Axons terminate higher up on a capillary network in the median eminence or pituitary stalk
  • Capillary network is supplied by the superior hypophyseal artery: called the primary capillary plexus
  • Neurohormones released into the network drain into the hypothalmo-hypophyseal portal system which goes on to form a secondary capillary network within the anterior lobe of the pituitary
  • The neurohormones diffuse out of the fenestrated capillaries and act on receptors (trophic cells) in the anterior pituitary to regulate secretions from adenohypophyseal cells
20
Q

What ar the neurohormones released from the posterior pituitary?

A
  • Vasopressin/ADH

* Oxytocin

21
Q

What are the trophic hormones of the anterior pituitary

A
  • Thyrotropin/ thyroid stimulating hormone
  • Corticotropin/adrenocorticotropic hormone
  • Gonadotropins: LH and FSH
22
Q

What hormones released from he anterior pituitary act on peripheral targets?

A
  • Somatotropin/ Growth hormone
  • Prolactin
  • Melanocyte stimulaitng hormone
23
Q

Describe growth hormone release control

A
  • Neurosecretory cells in the arcuate nucleus of the hypothalamus secrete growth hormone releasing hormone
  • Reaches somatotrophs via the hypophyseal portal blood supply
  • GHRH causes somatotrophs to synthesise and release growth hormone (in the anterior pituitary) by activating a stimulating g protein coupled receptor
24
Q

Describe the inhibition of growth hormone release

A
  • Somatotropin is released from the periventricular region
  • Inhibits the release of GH by the somatotrophs
  • Activates an inhibiting G protein coupled receptor
25
Q

Describe feedback of growth hormone

A

• IGF-1 directly inhibits GH release by suppressing the somatotrophs
• IGF-1 indirectly inhibits GH release by:
- suppressing GHRH release
- increasing the secretion of somatostatin
• GH inhibits its own secretion via short loop feedback on somatotrophs

26
Q

Describe the circadian rhythms for growth hormone secretion

A
  • Pulsatile release of GH throughout the day

* Spikes during sleep

27
Q

What are the physiological action fo growth hormone?

A

• Direct anti insulin effect:
- increased lipolysis in adipose tissue
- increased blood glucose
• Indirect actions (IGF-1 release from the liver)
- Increased cartilage formation and bone growth
- increased general protein synthesis and cell growth/division

28
Q

What are the physiological consequences of growth hormone?

A

• Increased linear growth and lean body mass
• Vital importance for normal post natal development and rapid growth throughout puberty
• Maintenance of protein synthesis and tissue function in adults
- maintains protein turnover rate

29
Q

GH deficiency

A
  • Dwarfism in children

* Decreased availability of lipids and glucose for energy: treat with growth hormone

30
Q

GH excess- before puberty

A

• Gigantism due to excess stimulation of the epiphyseal plates

31
Q

GH excess after puberty

A
  • Periosteal bone growth causing enlarged hands, jaw and foot size
  • Soft tissue growth leading to enlargement of the tongue and coarsening of facial features
  • Insulin resistance and gluten intolerance
  • Treat with synthetic long acting somatostatins
32
Q

Where is ADH synthesised?

A

In the neurosecretory cells in the supra-optic nucleus and paraventricular nucleus

33
Q

What increases ADH release?

A
  • Increased blood osmolarity detected by osmoreceptors in the brain
  • Decreased blood volume detected by volume receptors (carotid, aorta, left atrium)
  • RAAS - angiotensin II
34
Q

What is the effect of ADH release?

A

Recruitment of aquaporin water channels -> water retention

35
Q

ADH deficiency

A
  • Diabetes insipidus

* Neural or nephrogenic

36
Q

What are causes of cranial diabetes insipidus?

A
  • Tumours - 30%
  • Disease induced/trauma -> damage to the hypothalamus
  • Familial disorders of the neurosecretory cells
37
Q

What are the causes of nephrogenic diabetes insipidus?

A
  • Sex linked genetic defect in the collecting tubule (receptor doesn’t recognise ADH)
  • Non sex linked genetic defect in the aquaporin water channel
38
Q

Describe the control of milk production

A
  • Suckling stimulus travels through the spinal cord to the hypothalamus
  • Neurones from the hypothalamus inhibit dopamine release from the arcuate nucleus leading to prolactin release -> milk production
  • Neurones from the spinal cord stimulate the production and release of oxytocin from the paraventricular and supraoptic nuclei in the posterior pituitary -> systemic circulation -> breast and my-epithelial cells
  • neurones in the spinal cord inhibit neurones in the arcuate nucleus and preoptic area of the hypothalamus causing a fall in GnRH, inhibiting the ovarian cycle
39
Q

Where is the pineal gland?

A

• In the midline in the posterior part of the 3rd ventricle

40
Q

What are the functions of the pineal gland?

A
  • In darkness the pineal gland secretes melatonin
  • Regulates circadian rhythm
  • Regulates reproductive processes including the onset of puberty in humans
  • Effects on ageing and regulation fo the immune system
  • Accumulate calcium phosphate

After the MSA (22 decks)

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