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MEH > The Hypothalamic Pituitary Axis + Growth Hormone > Flashcards

The Hypothalamic Pituitary Axis + Growth Hormone Flashcards

1
Q

Location of the pituitary gland

A

Inferior to hypothalamus within the sella turcica of the sphenoid bone

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2
Q

What processes do the hypothalamus and pituitary gland modulate?

A

Body growth
Reproduction
Adrenal gland function
Water homeostasis
Milk secretion
Lactation
Thyroid gland function
Puberty

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3
Q

Why is the anterior part of the pituitary gland a gland but the posterior part isn’t?

A

Anterior - produces hormones it releases
Posterior - site of release

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4
Q

Embryological origin of anterior pituitary gland

A

Arises from evagination of oral ectoderm (primitive gut tissue)

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5
Q

Embryological origin of posterior pituitary

A

Originates from neuroectoderm (primitive brain tissue)

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6
Q

What connects the posterior pituitary to the hypothalamus?

A

Infundibulum

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7
Q

Outline the neurocrine function of the posterior pituitary

A
  • oxytocin and ADH are produced by neurosecretory cells in the supraoptic + paraventricular nuclei of the hypothalamus
  • hormones transported down the nerve cell axons to the posterior pituitary
  • stored + released to act on distant targets
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8
Q

Outline the synthesis, secretion, release and action of hormones acting on the anterior pituitary gland

A
  • hormones synthesised in hypothalamus
  • hormones transported down axons + stored in median eminence
  • released into hypophyseal portal system
  • hormones stimulate/inhibit target endocrine cells in anterior pituitary gland
  • effect distant cells - endocrine function
  • effect neighbouring cells - Paracrine function
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9
Q

What hormones are released from the posterior pituitary and what are their actions?

A

OT - oxytocin - milk let down + uterus contractions during birth
ADH - antidiuretic hormone/vasopressin - regulation of body water volume

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10
Q

What does it mean if a hormone is tropic?

A

Effects production and release of another hormone

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11
Q

What are the 6 tropic hormones produced in the hypothalamus

A

RH - releasing hormone
TRH - thyrotropin releasing hormone
CRH - corticotropin releasing horomone
GnRH - gonadotropin releasing hormone
GHRH - growth hormone releasing horomone

IH - inhibitory hormone
PIH - prolactin release-inhibiting hormone - dopamine
GHIH - growth hormone-inhibiting hormone/somatostatin

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12
Q

What hormones are produced by the anterior pituitary gland?

A

TSH - thyroid stimulating hormone
ACTH - adrenocorticotropic hormone
LH - luteinising hormone
FSH - follicle stimulating hormone
PRL - prolactin
GH - growth hormone

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13
Q

What is TRH and what does it act on?
What does this cause?

A
  • Thyrotropin releasing hormone
    .
  • Acts on thyroid stimulating hormone + (prolactin)
    .
  • Causes secretion of thyroid hormone (T3/4) from thyroid gland
  • (Causes mammary gland development and milk secretion (PRL))
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14
Q

What is CRH and what does it act on?
What does this cause?

A
  • Corticotropin releasing hormone
    .
  • Acts on adrenocorticotropic hormone (ACTH)
    .
  • Causes secretion of hormones e.g. cortisol from adrenal cortex
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15
Q

What is PIH and what does it act on?
What does this cause?

A
  • Prolactin release-inhibiting hormone - dopamine
    .
  • Acts on prolactin
    .
  • Causes a decrease in mammary gland development + milk secretion
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16
Q

What is GHRH and what does it act on?
What does this cause?

A
  • Growth hormone releasing hormone
    .
  • Acts on growth hormone
    .
  • Causes growth, energy metabolism + IGFs stimulation - insulin like growth factors
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17
Q

What is GHIH and what does it act on?
What does this cause?

A
  • Growth hormone-inhibiting hormone - somatostain
    .
    Acts on growth hormone
    .
    Causes a decrease in growth + energy metabolism + IGF stimulation
18
Q

What is GnRH and what does it act on?
What does this cause?

A
  • Gonadotropin releasing hormone
    .
  • Acts on luteinising hormone + follicle stimulating hormone
    .
  • Causes ovulation + secretion of sex hormones (LH)
  • Causes development of eggs + sperm (FSH)
19
Q

What is TSH and what is its action?
What is it produced by?

A

Thyroid stimulating hormones

Causes secretion of T3+T4 from thyroid gland

Produced by anterior pituitary gland

20
Q

What is ACTH and what is its action?
What is it produced by?

A

Adrenocorticotropic hormone

Causes secretion of hormones from adrenal cortex

Produced by anterior pituitary gland

21
Q

What is LH what is its action?
What is it produced by?

A

Luteinising hormone

Causes ovulation and secretion of sex hormones

Produced by anterior pituitary gland

22
Q

What is FSH what is its action?
What is it produced by?

A

Follicle stimulating hormone

Causes development of eggs an sperm

Produced by anterior pituitary gland

23
Q

What is PRL what is its action?
What is it produced by?

A

Prolactin

Causes mammary gland development + milk secretion

Produced by anterior pituitary gland

24
Q

What is GH what is its action?
What is it produced by?

A

Growth hormone

Causes growth, energy metabolism + IGF stimulation

Produced by anterior pituitary gland

25
Q

What factors influence growth?

A

Hormones - growth hormone
Environment
Nutrition
Genetics

26
Q

Outline the HPA axis using cortisol as an example of a negative feedback loop

A

Stress > hypothalamus > CRH > anterior pituitary > ACTH > adrenal cortex > cortisol > target cells

  • High levels of cortisol will have negative feedback on anterior pituitary + hypothalamus to lower their production of ACTH + CRH to lower cortisol levels
27
Q

What stimulates and inhibits growth hormone release?

A

Stimulated by GHRH
Inhibited by somatostatin/GHIH

28
Q

How do growth hormones exert their effects?

A
  • indirectly via insulin like growth factors
  • in response to GH cells of the liver and skeletal muscle produce + secrete IGFs
29
Q

Explain the role of GH + IGFs in bone development during childhood

A
  • GH: stimulates long bone growth
  • IGFs: stimulate bone + cartilage growth
30
Q

Explain the role of GH + IGFs in bone development during adulthood

A
  • Help maintain muscle + bone mass
  • Promote healing + tissue repair
  • Modulating metabolism + body composition
31
Q

How is GH secretion regulation by long loop negative feedback?

A

Mediated by IGFs
- inhibit release of GHRH from hypothalamus
- stimulates the release of somatostatin/GHIH from hypothalamus
- inhibit release of GH from anterior pituitary

32
Q

How is GH secretion regulation by long loop negative feedback?

A

Mediated by GH itself via stimulation of somatostatin/GHIH release

33
Q

What does growth hormone deficiency result in?

A

Pituitary dwarfism
- proportionate type of dwarfism due to partial or complete deficiency

34
Q

What does excess growth hormone in childrenhood cause?

35
Q

What does excess growth hormone in childrenhood cause in adulthood?

A

Acromegaly

Large extremities: hands, feet + lower jaw

36
Q

How does GH exert its effects on cells?

A

GH receptors activate Janus kinases JAKs

  • GH binds to GHR
  • JAK activated
  • cross phosphorylation of JAK
  • phosphorylation of GHR
  • activates signalling pathway > IGR production
37
Q

Actions of the 2 growth factors in mammals

A

IGF1- main growth factor in adults
IGF2- mainly involved in fetal growth

38
Q

What are the three ways IGFs communicate?

A

Paracrine
Autocrine
Endocrine

39
Q

IGFs act through IGF receptors to modulate what?

A
  • hypertrophy
  • hyperplasia
  • increase in the rate of protein synthesis
  • increase in the rate of lipolysis in adipose tissue
40
Q

What other hormones influence growth?

A

Insulin
Thyroid hormones
Androgens
Estrogens
Glucocorticoids

41
Q

What organ produces IGFs?

MEH (23 decks)

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