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Endocrinology > The Hypothalamic pituitary axis > Flashcards

The Hypothalamic pituitary axis Flashcards

1
Q

location of the hypothalamus and pituitary gland

A
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2
Q

Hypothalamus and pituitary gland form a complex functional unit that serves as the

A

major link between the endocrine and nervous system

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3
Q

what structure links the hypothalamus and pituitary gland

A

the infundibulum

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4
Q

hypothalamus and pituitary gland modulate (8)

A
  • Body growth
  • Repro
  • Milk secretion
  • Lactation
  • Adrenal gland function
  • Water homeostasis
  • Thyroid gland function
  • Puberty
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5
Q

structure of the pituitary gland

A

consists of two parts: anterior portion and posterior portion

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6
Q
A
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7
Q

anteiror pitutiary gland also known as

A

adenohypophysis

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8
Q

the a.pituitary is embryologically derived from

A

Rathkes pouch- primitive gut tissue

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9
Q

why is the posterior pituitary gland technically not a gland

A

since doesn’t produce the hormones that is releases- releases hormones produced in the hypothalamus

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10
Q

what is the p.pit also known as

A

neurohypophysis

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11
Q

the p.pit is embryologically derived from

A

neuroectoderm (primitive brain tissue)

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12
Q

p.pits anatomical position in relation to the hypothalamus

A

PP is physically connected to the hypothalamus, since the hypothalamus drops down through the infundibulum to form the posterior pituitary

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13
Q

what does the posterior pituitary release

A

Oxytocin and ADH produced by neurosecretory cells in supraoptic and paraventricular nuclei (collection of cell bodies with a similar function) of the hypothalamus

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14
Q

how are Oxytocin and ADH transported from the hypothalamus to the PP

A

Transported down nerve cell axons to the posterior pituitary

Prime example of neurocrine signalling (where hormone is transported down the axon of a neurone before it is released to act on a tissue)

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15
Q

Oxytocin and ADH are hormones because

A

Stored and released from posterior pituitary into general circulation to act on distant targets

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16
Q

oxytocin action

A
  1. Milk let down
  2. Uterus contraction during birth- Ferguson reflex
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17
Q

ADH (vasopressin) action

A

regultion of body water volume

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18
Q

the anterior pituitary endocrine function

A

Synthesises and releases many hormones

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19
Q

how is the AP controlled

A

by the hypothalamus

  • Hormones synthesised in hypothalamus are transported down axons and stored in median eminence before release into hypophyseal portal system
  • These hormones stimulate (or inhibit) target endocrine cells in the a.pituitary gland (neurocrine function)
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20
Q
A
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21
Q

hormones released by the AP

A
  • TSH
  • ACTH
  • LH
  • Prolactin
  • GH
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22
Q

TSH

A
  • thyroid stimulating hormone- secretion of thyroid hormone from thyroid gland
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23
Q

ACTH

A

Adrenocorticotropic hormones- secretion of hormones from adrenal cortex

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24
Q

LH

A
  • Luteinising hormone- ovulation and secretion of sex hormones
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25
Q

PRL

A
  • Prolactin- mammary gland development and milk secretion
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26
Q

GH

A
  • Growth hormone- growth and energy metabolism- stimulates IGF
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27
Q

The hormones produced by nerve cells in hypothalamus act via two distance neurocrine pathways

A
  1. Direct effects on distant target tissues via oxytocin and ADH hormones from PP
  2. Hormones secreted exclusively onto hypophyseal portal system affect endocrine cells within the anterior pituitary
28
Q

tropic

A

hormones that are affecting the synthesis and release of another hormone

29
Q

tropic hormones of the hypothalamus

A

6 tropic hormones that have a direct effect on the release of anterior pitutiary hormoens

  • TRH
  • PRH
  • PHI
  • CRH
  • GnRH
  • GHRH
  • GHIH
30
Q

TRH

A

Thryotropin releasing hormone

  • stimulates release of TSH from the AP
  • stimulates the thryoid gland to release T3 and T4 to icnrease metabolic rate
31
Q

PRH

A

prolacting releasing hormone (TRH)

  • minor +ve control on prolactin release in AP
  • stimulates mammary glands grow and secrete milk
32
Q

PIH

A

prolactin inhibiting hormone

  • inhibits release of prolactin from the AP
  • inhibits milk secretion from mammary glands
33
Q

CRH

A

corticotropin releasing hormone

  • stimulates the AP to release Adrenocorticotropic hormones
  • ACTH stimulates the adrenal glands to secrete cortisol
  • stimulates stress response and metabolic actions
34
Q

GnRH

A

gonadotropin releasing hormone

  • stimulates the release of LH and FSH from the AP
  • LH stimulates ovaries in females and testes in male to secrete sex hormones
  • FSH stimulates ovaries in females and testes in males in gamate production
35
Q

GHRH

A

growth hormone releasing hormone

  • stimulates growth hormone to be released from the AP
  • the GH stimualtes many tissues including the liver to produce IGFs to increase growth
36
Q

GHIH

A

growth hormone-inhibitng hormone (somatostatin)

  • inhibits the release of GH from the AP
  • reducing growth of tissue and release of IGF from the liver
37
Q

how are pathways by which hypothalamic and AP hormoens are produced regulated

A

most often by negative feedback

(Prolactin is under tonic inhibitory control by dopamine

Anything blocking stalk will lead to prolactin disinhibition )

38
Q

feedback loop for the hypothalamic pituitary-adrenala xis

A
  • 2 levels of feedback
  • ACTH can also feedback to the hypothalamus and inhibit the release of CRH
  • E.g. when cortisol levels increase, negative feedback is sent to the hypothalamus (reducing CRH release) and AP (reducing ACTH release)
39
Q

name the factors which influence growth

A
  • genetics
  • nutrition
  • environment
  • hormones (Growth Hormoen)
40
Q

hyerplasia

A

increase in cell number

41
Q

hypertrophy

A

increase in cell size

42
Q

atrophy

A

decrease in cell size and number

43
Q

necrosis

A

cell death by damage

44
Q

apoptosis

A

programme cell death e.g. when structures such as the hands are forming

45
Q

GH structure

A

Protein hormone (191 aa) hass a signal peptide that must be cleaved before proper folding

46
Q

what stimulates GH production in AP

A

GHRH (growth hormone releasing hormone)

47
Q

what inhibits GH production in AP

A

somatostatin

48
Q

growth promitng effects of GH mainly promoted

A

indirectly via insulin-like growth factors (somatomedins)

49
Q

in response to GH the liver and s. muscle produce and secrete

A

IGF

50
Q

function of GH in children

A

Essential for normal growth during childhood and teenage years

  • Stimulates long bone growth
  • Length and width prior to epiphyseal closure
  • Width after epiphyseal closure
51
Q

function of GH in adults

A

GH and IGF help maintain muscle and bone and promote healing, tissue repair as well as modulating metabolism and body composition

52
Q

when does a surge of GH secretion occur

A

after onset of deep sleep

53
Q

what sort of sleep decreases GH secretion

A

REM

54
Q

what else increases GH secretion

A
  • stress
  • exercise
  • less glucose or fatty acids
  • fasting
55
Q

what else decreases GH secretion

A

obesity

56
Q

Feedback loop of GH

A

Long loop

  • Mediated by IGF
  • Inhibits release of GHRH from hypothalamus
  • Stimulates release of somatostatin from hypothalamus
  • Inhibit release of GH from anterior pituitary

Short loop

  • Mediated by GH itself via stimulation of somatostain release
57
Q
A
58
Q

GH deficiency can cause

A

pituitary dwarfism

  • Proportionate type of dwarfism
  • Complete or partial deficiency
  • Both types respond to GH therapy
  • Height below 3rd percentile on standard growth charts
  • growth rate slower than expected for age
  • Delayed or no sexual development during teen years
59
Q

GH excess in childhood

A

Gigantisms

  • rare
  • pituitary adenoma
60
Q

GH excess in adulthood

A

acromegaly

  • large extremities: hand, feet and lower jaw
61
Q
A
62
Q

other hormones which influcne growth

A

isnulin, thyroid hormones, androgens, estorgens and glucocorticoids

63
Q

molecular mechanism of GH

A
  1. GH binds to janus kinase (JAK) receptors
  2. Activating signalling pathway which leads to the activation of transcription factors and IGF
64
Q

IGF action

A

Act through IGF receptors (distinct from GH receptors) to modulate

  • Cell growth- hypertrophy
  • Cell number – hyperplasia
  • Increase in rate of protein synthesis
  • Increase in rate of lipolysis in adipose tissue
65
Q

major IGF in adults vs for fetal growth

A

Adult- IGF-1

Fetal growht- IGF3

66
Q

what sort of signalling does IGF do

A

paracrine, autocrine and endocrine

67
Q

IGF has some

A

homology with insulin receptors

e.g. can get hybrid receptros (half insulin/ half IGF receptors)

Endocrinology (12 decks)

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