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ENDOCRINE > A. HYPOTHALAMUS AND PITUITARY > Flashcards

A. HYPOTHALAMUS AND PITUITARY Flashcards

1
Q

what is the anterior pituitary also known as

A

adenohypophysis (Adeno = gland)

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2
Q

what is the appearance of the anterior pituitary

A

vascularised

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3
Q

what is the posterior pituitary also known as

A

neurohypophysis

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4
Q

what is the appearance of the posterior pituitary

A

neural

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5
Q

what is in close proximity with the pituitary gland

A

optic chiasm (where optic nerves cross) and the carvenous sinus (with cranial nerves)

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6
Q

characteristics of pituitary tumours

A
  • called adenomas
  • benign and don’t spread
  • slow growing (years)
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7
Q

what are the consequences of pituitary gland tumours due to the mass pressure on surrounding structures

A
  • increased intracranial pressure causing headaches
  • compression of optic nerves/chiasm causing visual field defects
  • compression on cavernous sinus causing cranial nerve palsies (partial paralysis of nerves which supply eye, ear etc)
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8
Q

what are the consequences of pituitary gland tumours due to effects on hormones

A
  • over-production of a pituitary hormone due to tumour arising from hormone-secreting pituitary cells
  • inadequate production of other remaining hormones due to tumour mass causing compression of other pituitary cells
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9
Q

pathway of hormones for anterior pituitary

A
  • cell bodies and neurones secrete hypothalamic-releasing factors (hormones)
  • they pass along portal vessels to reach capillary bed in anterior pituitary
  • control secretion of hormones from specific endocrine cells of anterior pituitary into circulation
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10
Q

pathway of hormones for posterior pituitary

A
  • cell bodies of paraventricular and supraoptic nuclei secrete hypothalamic-releasing factors (hormones)
  • neurones carry oxytocin and vasopressin (ADH) down axon fibres to posterior pituitary
  • stored and released here
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11
Q

what is the endocrine axis

A

Interactions between hypothalamus, pituitary gland and peripheral endocrine glands, with feedback regulation of hormone secretion, to maintain physiological homeostasis

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12
Q

what kind of hormones are hypothalamus and anterior pituitary hormones

A

tropic (ie affect activity of an endocrine gland)

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13
Q

what are the hormones of the anterior pituitary

A
  • growth hormone (somatotropin) secreted by specific endocrine cells (eg - somatotroph cells secrete GH)
  • prolactin
  • adrenocorticotropic hormone (ACTH) (corticotropin)
  • thyroid-stimulating hormone (TSH) (thyrotropin)
  • luteinising hormone: gonadotropin
  • follicle-stimulating hormone (FSH): gonadotropin

*a different specific endocrine cells secrete each of these

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14
Q

gonadotrophin pathway

A
  • GnRH in hypothalamus
  • releases LH and FSH in anterior pituitary
  • stimulatory effect (+) on LH and FSH
  • affects gonads (peripheral endocrine gland)
  • sex hormones produced
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15
Q

growth hormone pathway

A
  • GHRH in hypothalamus
  • releases GH in anterior pituitary
  • stimulatory effect (+) on GH
  • GH affects liver (peripheral endocrine gland)
  • IGF-1 produced (insulin-like growth factor 1)
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16
Q

thyroid-stimulating hormone pathway

A
  • TRH (thyrotropin-releasing hormone) in hypothalamus
  • releases TSH in anterior pituitary
  • stimulatory effect (+) on TSH
  • TSH affects thyroid (peripheral endocrine gland)
  • thyroid hormones produced
  • has a stimulatory effect on prolactin production aswell
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17
Q

somatostatin (a GH) pathway

A

inhibitory effect on GH and TSH

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18
Q

prolactin pathway

A
  • dopamine in hypothalamus
  • releases prolactin in anterior pituitary
  • inhibitory effect on prolactin
  • affects breast tissue (exocrine gland - therefore prolactin isn’t a tropic hormone)
19
Q

ACTH pathway

A
  • CRH in hypothalamus (also CRF - factor)
  • releases ACTH in anterior pituitary
  • stimulatory effect on ACTH
  • ACTH affects adrenal cortex (peripheral endocrine gland)
  • cortisol produced
20
Q

what effects does GH have

A
  • linear growth (ie long bones)
  • effects on metabolism
  • effects via GH receptor on target cells
21
Q

what is the direct action of GH

A

metabolism - has anti-insulin effects (ie - diabetogenic) as increases blood glucose

22
Q

how does GH increase blood glucose

A

Muscle:
- increases amino acid uptake
- increased protein synthesis
- decreases glucose uptake

Adipose tissue
- increases lipolysis
- decreases glucose uptake

Liver:
- increases gluconeogenesis

23
Q

what is the indirect action of GH

A

promotes growth (IGF-1)

24
Q

how does GH promote growth

A
  • stimulates release of growth factors (ie: IGF-I, IGF-II - somatomedins) from liver and other cell types
  • growth is via action of IGF-I on cells
  • promotes growth of soft tissue (increase cell size - hypertrophy and cell number - hyperplasia)
  • promotes skeletal growth (length and thickness)
25
Q

what can a deficiency in GH cause (hypopituitarism)

A

stunted growth in children (pituitary dwarfism - proportional dwarfism) and deficiency in adult

26
Q

non-specific symptoms of GHD in adults

A
  • Psychological changes
  • Malaise, excessive tiredness, anxiety and depression
  • Osteoporosis
  • Poor muscular tone, decrease in lean body mass
  • Impaired hair growth
  • Increase in adipose tissue (especially around the waist)
27
Q

treatment of GHD

A
  • in the past, from human cadaver pituitaries
  • now, recombinant HGH licensed in UK
  • used in sport?
28
Q

what can an excess in GH cause

A

accelerated growth in children (gigantism) and acromegaly in adults

29
Q

what causes excessive GH

A
  • GH-secreting pituitary tumour
30
Q

treatment of excess GH

A
  • surgery or radiotherapy
  • inhibit GH release with somatostatin analogues (eg - octreotide)
  • some tumours respond to dopamine receptor agonists (eg - bromocriptine) as they acquire expression of dopamine receptors
  • resistance to above: use pegvisomant which is highly selective GH receptor antagonist
31
Q

symptoms of excess GH in adults

A
  • Coarsening of facial features (look older) due to increased thickening of bone, cartilage and soft tissue development
  • Enlarged hands and feet
  • Headaches, vision disturbance due to GH tumour
  • Sleep apnoea, general tiredness due to enlargement of body tissue
  • Hypertension, cardiomegaly due to enlargement of heart
  • Glucose intolerance (diabetes) as GH increases blood glucose
32
Q

what effects does prolactin have

A
  • stimulates mammary glands to produce milk (lactation)
  • promotes growth and development of the breasts
  • high prolactin concentrations inhibit GnRH release
33
Q

what type of hormone is prolactin

A

trophic - promotes growth and tissue integrity

34
Q

what causes hyperprolactinaemia

A

prolactinoma - non-cancerous tumor of the pituitary gland

35
Q

symptoms of hyperprolactinaemia

A
  • loss of fertility/libido as inhibits GnRHs
  • galactorrhoea (in non-pregnant) f>m
  • gynaecomastia: benign development of breast tissue (m>f)
36
Q

treatment for hyperprolactinaemia

A
  • dopamine receptor agonists (Eg - cabergoline, bromocriptine) which inhibit prolactin secretion and shrink the tumour
  • surgery/radiotherapy for tumours resistant to drug therapy
37
Q

what are the 2 hormones of the posterior pituitary

A
  1. vasopressin AVP or aka ADH: pituitary gland releases AVP when the amount of water in the body becomes too low
  2. oxytocin
  • love hormones for attachment?

(stored in axon terminals)

38
Q

what is AVP/ADH release stimulated by

A
  • increase in body fluid osmolality
  • fall in blood volume/pressure (also angiotensin II, nausea, acute stress)
39
Q

treatment of excess AVP/AHD

A
  • blood vessels: vasoconstrictors (eg - vasopressin) via V1 receptors (at higher AVP concs)
  • kidney: to increase permeability and hence reabsorption of water via V2 receptors block ADH action using V2 receptor antagonists (tolvaptan)
40
Q

what can a deficiency of AVP/ADH cause

A

diabetes insipidus
1. pituitary DI
- excretion of large volumes of dilute urine (polyuria and hence polydipsia)
- use desmopressin (analogue of ADH)

  1. nephrogenic DI
    - lack of response in collecting tubes to ADH (polyuria and hence polydipsia)
    - use diuretics (thiazide-like diuretics)

*You just need to increase the amount of water you drink to compensate for the fluid lost through urination sometimes

41
Q

what can an excess of AVP/ADH cause

A

syndrome of inappropriate ADH secretion (SIADH)
- retention of water so small volume of urine, highly concentrated
- hyponatraemia (due to dilution effect)

42
Q

when is oxytocin released

A
  • produced in males and females
  • stimulated release by suckling and by cervical stimulation (parturition)
43
Q

what effects does oxytocin have

A
  • stimulates milk let-down and hence expression of breast milk
  • contraction of uterine smooth muscle
  • parental/reproductive behaviour, social bonding
44
Q

clinical use of oxytocin

A

induction/enhancement of labour

ENDOCRINE (17 decks)

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