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Endocrine > Pituitary and Hypothalomus > Flashcards

Pituitary and Hypothalomus Flashcards

1
Q

Another term for pituitary

A

hypophysis

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2
Q

Pituitary gland definition

A

An endocrine gland, weighing 0.5g in humans, that secretes hormones and acts as the master gland.

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3
Q

Location of pituitary

A

Protrusion of the hypothalamus as the base of the brain.

rests upon the hypophysial fossa of the sphenoid bone - sits in the pituitary fossa

attached to the brain via the pituitary stalk

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4
Q

Development of the pituitary gland

A
  • Rathke’s pouch grows up from oropharyngeal ectoderm (roof of mouth) to form the anterior pituitary
  • infundibular process grows down from the forebrain vesicle to form the posterior pituitary
  • portion of Rathke’s pouch in contact with the infundibular process forms the intermediate lobe
  • in humans, the cells become interspersed with those of the anterior pituitary
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5
Q

structure of anterior pituitary

A

consists of numerous individual endocrine cells

distinct cell types that produce and secrete different hormones

different cells arranged in a network, where they all interconnected via gap junctions and junctional proteins

glial like folliculostellate cells surround and support endocrine cells

internal carotid branch forms the jugular vein

PALE CHROMATIN- LOTS OF TRANSCRIPTION

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6
Q

How is the anterior pituitary regulated?

A

neurohormones from the hypothalamus- central control (stimulatory for all anterior pituitary hormones apart from PRL)

systemic hormones- feedback control, mainly negative by target hormones

paracrine interactions in the anterior pituitary

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7
Q

how are hypothalmic releasing factors released?

A

pulsatile manner, stimulates pulses of anterior pituitary hormones

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8
Q

structure of posterior pituitary

A

formed by the axons and terminals of magnocellular neurosecretory neurones that originate in the hypothalamus

pituicytes, type of glial supporting cells, surround and support the terminals

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9
Q

how is the posterior pituitary regulated?

A

controlled entirely by the hypothalamus

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10
Q

How are hormones secreted?

A

hormones synthesised in the hypothalamus packed into granules, transported down axons and released by exocytosis into systemic veins draining neyropophysis

neuroendocrine system, meaning that the neurones secrete the hormones directly into the blood stream (neurosecretion)

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11
Q

Alternative names for the anterior and posterior pituitary

A

adenohypophysis and neurohypophysis

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12
Q

How many cell types in adenohypophysis?

A

6

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13
Q

name 6 cells + what they secrete

A

somatotrophs- growth hormone

gonadotrophs- LH, FSH

corticotrophs- stimulate the adrenal cortex, ACTH

lactotrophs- prolactin

thyrotrophs- thyroid stimulating hormone

folliculo-stellates

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14
Q

What types of hormones are released + definition?

A

trophic hormones- directly affect growth either as hyperplasia or hypertrophy

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15
Q

Two main ways in which the adenohypophysis is stimulated to release hormones

A

hypothalamo-hypophyseal portal vessels

negative feedback of hormones

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16
Q

Hypothalamo-hypophyseal portal vessel definition

A

system of blood vessels in the microcirculation at the base of the brain connecting the hypothalamus and anterior pituitary

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17
Q

hypothalamo-hypophyseal portal vessel function

A

quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland

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18
Q

Examples of the hormones and function

A

gonadotropin-releasing hormone- regulates the release of LH and FSH

corticotropin-releasing hormone- regulates the release of adrenocorticotropic hormone

growth-hormone releasing hormone

thyrotropin releasing hormone

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19
Q

How do these hormones reach the anterior pituitary?

A

neuroendocrine cells in the hypothalamus project axons into the median eminence at the base of the brain

cels secrete substances into small blood vessels that travel directly to the anterior pituitary

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20
Q

How can different cells be identified?

A

immunocrystochemistry- FSH/LH cells always form a boundary with blood vessels

shape and size of secretory granules under TEM

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21
Q

Feedforward control definition

A

command signal from an external operator

control variable adjustment is not error based

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22
Q

Thyroid stimulating hormone chemical nature + RECEPTORS

A

glycoprotein hormone made of alpha and beta subunits- beta specific to TSH, whereas alpha is common in LH and FSH

GPCR- linked to cAMP on thyroid gland follicular cells

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23
Q

TSH actions

A

acts on the thyroid which stimulates thyroid hormone production (T3 - T4)

increases iodine uptake by thyroid (needed for synthesis of thyroid hormone) and stimulates thyroid growth

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24
Q

control of TSH

A

TSH release stimulated by thyrotropin releasing hormone from the hypothalamus

secretion of TSH is stimulated by cold and by stress via the CNS

released in pulses with a diurnal rhythm

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25
Q

What inhibits TSH?

A

Inhibited by T3 and T4 negative feedback

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26
Q

corticotrophin chemical nature

A

polypeptide cleaved from the prohormone, ProOpioMelanoCortin POMC

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27
Q

corticotrophin receptor type

A

G protein coupled cAMP in adrenal cortex

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28
Q

adrenocorticotrophic hormone action

A

stimulates production and thus secretion of cortisol (glucocorticoid steroid hormone) from the cortex of the adrenal gland

ACTH produces an increase in adrenal sex steroids and stimulates the growth of the adrenal cortex

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29
Q

What also is produced by the cleaving of Pro-opio-melano-cortin? + function

A

melanocyte-stimulating hormones

MSH stimulate pigmentation of the skin via actions on melanocytes

30
Q

control of ACTH

A

secretion is increased by hypoglycaemia stress

secreted by corticotrophin releasing hormone

diurnal rhythm- high at 7am and low at midnight

31
Q

What is it inhibited by?

A

glucocorticoid negative feedback

32
Q

What may the dysfunction of this regulation cause?

A

Cushing’s disease- excess ACTH causes excess glucocorticoid secretion

Addison’s disease- deficiency of ACTH causes glucocorticoid deficiency

Nelson’s syndrome- increased pigmentation, via excess MSH secretion due to lack of negative feedback after adrenal cortex surgery

33
Q

What do LH and FSH stand for?

A

luteinising hormone and follicle stimulating hormone

34
Q

chemical nature of gonadotrophins

A

glycoprotein made up of alpha and beta subunits

alpha subunit common in TSH beta specific

35
Q

receptors of gonadotrophins

A

GPCR linked to cAMP in ovaries and testes

36
Q

Actions of LH and FSH in female

A

Control growth and development of follicles, ovulation, synthesis of steroid hormones in the ovary

growth and secretion of the sex steroid progesterone by the corpus luteum

37
Q

Actions of LH and FSH in male

A

LH controls testosterone production by the Leydig cells

FSH stimulates the Sertoli cells and sperm production

38
Q

two types of control of gonadotrophins

A

hypothalamic and systemic

39
Q

explain hypothalamic control

A

LH and FSH release is stimulated by hourly pulses of gonadotrophin releasing hormone during reproductive life

40
Q

explain systemic control

A

inhibited by sex steroid oestrogen/testosterone/ovarian peptides such as inhibin and follistatin by negative feedback

switch to positive feedback triggers LH surge during ovulation

41
Q

dysfunctions linked to gonadotrophins

A

genetic mutations can cause infertility in adults and lack of sexual maturation in children

inappropriate hypothalamic GnRH secretion can lead to excess LH or FSH secretion, or receptor overactivity can cause precocious puberty

42
Q

prolactin chemical nature

A

protein

43
Q

prolactin receptor

A

single transmembrane tyrosine kinase present in mammalian breast

44
Q

Actions of prolactin

A

principle role is preparation for lactation

marked increase in lactotroph cells in pregnancy (pituitary almost doubles in size)

PRL stimulates the development ad growth of secretory alveoli in the breast and milk production

inhibits the reproductive system at the level of the gonads and pituitary - can cause lactational amenorrhoea

45
Q

what is lactational amenorrhea?

A

postpartum infertility- when woman is not menstruating and is fully breastfeeding

46
Q

control mechanisms of prolactin

A

secretion increased by suckling

PRL inhibited by the dopamine released from the hypothalamus

PRL synthesis stimulated by oestrogen

47
Q

dysfunctions linked to prolactin

A

prolactinomas- hypersecretion of PRL from tumours in the pituitary gland- causes galactorrhea, infertility and impotence

dopamine agonist drugs, such as bromocryptine, are used to suppress PRL release from tumours

48
Q

Growth hormone chemical nature

A

protein

49
Q

growth hormone receptor

A

single transmembrane tyrosine kinase

50
Q

Growth hormone actions

A

stimulates release of IGFs (insulin like growth factors) from the liver which stimulates long bone and soft tissue growth, also via direct action

exerts complex action on metabolism- has insulin like effects to promote the uptake of amino acids by the liver and muscle and therefore promotes protein synthesis

GH chronically increased it has anti insulin effects - switches metabolism away from glucose and towards increased oxidation of fat

51
Q

frequency of GH release

A

in pulses, every 4h and on entering deep sleep

52
Q

control of GH release

A
  • increased via hypothalamus by hypoglycaemia, stress and exercise

growth hormone releasing hormone stimulates production

somatostatin inhibits release

53
Q

Dysfunctions linked to GH

A

GH insufficiency leads to dwarfism, excess causes gigantism in children and acromegaly in adults,

54
Q

Acromegaly symptoms

A

enlargement of feet and hands, forehead, jaw and nose

joint pain, thicker skin, deepening of the voice

55
Q

two main hormones of the neurohyophysis

A

anti-diuretic hormone and oxytocin

56
Q

another name for ADH

A

vasopressin

57
Q

chemical nature of vasopressin

A

peptide of 9 amino acids

58
Q

receptors of ADH

A

GPCRs linked to cAMP

V1- vasculature

V2- kidneys

59
Q

ADH actions

A

increases water reabsorption from collecting ducts of kidney (V2)

vascular pressor effects- constrict peripheral arterioles and veins

60
Q

control of ADH

A

osmotic- sensitive to 1% increase from normal plasma OP- sensed by hypothalamic osmoreceptors

also sensitive to decreases in blood volume or pressure

61
Q

what is the normal plasma OP?

A

285mOsm

62
Q

dysfunction linked to vasopressin

A

diabetes insipidus

lack of ADH production and action- leads to very dilute urine and large quantities

63
Q

Two different types of diabetes insipidus explained

A

hypothalmic- due to lack of hormone vasopressin

nephrogenic- kidneys do not respond to vasopressin

64
Q

Oxytocin chemical nature

A

peptide of 9 amino acids

65
Q

oxytocin receptors

A

acts on membrane GPCRs coupled to PLC in breast and uterine muscle

66
Q

oxytocin actions

A

contraction of uterine myometrium in childbirth and causes contraction of breast myoepithelium to eject milk

67
Q

controls of oxytocin

A

Ferguson reflex- stretch of cervix during parturition

milk ejection reflex- stimulation of nipple

68
Q

dysfunction linked to oxytocin + why is there uncertainty?

A

deficit may cause prolonged labour

knockout mice- labour is normal but no milk ejection

69
Q

what causes acromegaly?

A

too much GH

70
Q

What does abnormal juvenile secretion of GH result in?

A

either excess or short stature

Endocrine (5 decks)

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