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Sem 2 - MEH > HPA Axis and Growth Hormone > Flashcards

HPA Axis and Growth Hormone Flashcards

1
Q

What is the HPA axis?

A

The hypothalamus and pituitatary gland form a major complex functional unit that serves as the major link between the endocrine and nervous system.

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2
Q

Where are are hypothalamus and pituitary located?

A

Hypothalamus = just below thalamus

Pituitary = Just below the hypothalamus, in a socket of bone called the sella turcica.

The posterior pituitary gland is physically connected to the hypothalamus since the hypothalamus drops down through the infundibulum to form the posterior pituitary.

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3
Q

What processes do the hypothalamus and the pituitary gland modulate?

A
  • Body growth
  • Reproduction
  • Adrenal gland function
  • Water homeostasis
  • Milk secretion (ocytosin)
  • Lactation (Lactin)
  • Thyroid gland function
  • Puberty
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4
Q

What are the two parts to the pituitary and what are their roles?

A

Anterior pituitary gland (adenopophysis) and Posterior pituitary gland (Neurohypohysis)

Productions of posterior petuitary are made by the hypothalamus but are transfered via neurocrine communication then released from there. This means it is not strictly a gland.

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5
Q

What are the embryonic origins of anterior and posterior pituitary?

A

Anterior pituitary arises from evagination of oral ectoderm (Rathke’s pouch) - Primitive gut tissue.

Posterior pituitary origionates from the neuroectoderm. - Primitive brain tissue.

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6
Q

Whar are the neurocrine functions of the posterior pituitary?

A
  • Oxytocin and ADH are produced by neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus.
  • Transported down the nerve cell axons to the posterior pituitary
  • Stored and released fron the posterior pituitary into general circulation to act on distant targets.
  • BUT, hormones are MADE in the hypothalamus.
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7
Q

What are the functions of the anterior pituitary?

A
  • Hormones synthesied in hypothalamus and transported down axons and stored in median eminance before released into hypophyseal portal system.
  • These hormones stimulate (or inhibit) target endocrine cells in the anterior pituitary gland (neurocrone function)
  • Endocrine cells of the anterior pituitary secretes a variety of hormones into the bloodstream to act on distand target cells (endocrine function)
  • Anterior pituitary hormones also effect neighbouring cells (autocrine and paracrine function)
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8
Q

What are the two distinct neurocrine pathways that hormones produced by the nerve cells in the hypothalamus can act via?

A
  1. Direct effects on distant target tissues via oxytocin and ADH from the posterior pituitary.
  2. Hormones secreted exclusively into hypophyseal portal system affect endocrine cells within the anterior pituitary.
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9
Q

What is the role of ADH?

A

Regulation of body water volume via aquaporins

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10
Q

What is the role of oxytocin?

A

Milk let down (milk produced via breasts) and uterus contractions during birth.

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11
Q

What is the difference between tropic and trophic?

A

Tropic - Stimulate another hormone.

Trophic - involved in growth

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12
Q

What are the six tropic hormones produced in the hypothalamus?

A

These have direct effects on the release of anterior pituitary hormones

  • TRH - Thyrotropin releasing hormone
  • PIH - Prolactin releasing-inhibiting hormone
  • CRH - Corticotropin releasing hormone
  • GnRH - Gonadotropin releasing hormine
  • GHRH - Growth hormone releasing hormone
  • GHIH - Growth hormone-inhibitng hormone (Somatostatin)
  • They used to believe there was a PRH BUT this doesnt exist. Instead, TRH hs a slight positve effect on prolactin.
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13
Q

What are the six hormones produced by the anterior pituitary and what are their function?

A
  • TSH - Thyroid stimulating hormone - secretion of thyroid hormone from thyroid gland.
  • ACTH - Adenocorticotropic hormone - Secretion of hormones fron adrenal cortex
  • LH - Luteinising hormone - Ovulation and secretion of sex hormones
  • FSH - Follicle stimulating hormone - Development of eggs and sperm
  • PRL - Prolactin - Mammary gland development and milk secretion
  • GH - Growth hormone - Growth and energy level metabolism. Stimulates IGFs.
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14
Q

How are the pathways by which hypothalamic and anterior pituitary hormones regulated?

A

The pathways by which hypothalamic and anterior pituitary hormones are produced are often regulated by NEGATIVE FEEDBACK

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15
Q

What is the HPA axis?

A
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16
Q

What factors influence growth?

A
  • Genetics
  • Nutrition
  • Hormones - growth hormone is the most important regulator of postnatal growth
  • Environment
17
Q

What are the terms used to decribe cell growth or decline?

A

Necrosis - cell death by damage

Apoptosis - Programmed cell death

Atrophy - Decrease in cell size or cell nember

Hyperplasia - Increase in cell number (e.g. cancer growth)

Hypertrophy - Increase in cell size (e.g. muscles)

18
Q

What is growth hormone?

A

It is produced in the anterior pituitary.

Stimulated by GHRH and inhibited by hypothalamic Somatostatin.

It is a protein hormone and it has a signal peptide that must be cleaved before proper folding.

Growth promoting effects mainly exerted indirectly via insulin-like growth factors (Somatomedins)

In response to GH cells of the liver and skeletal muscle produce and secrete IGFs.

19
Q

What is GH essential for?

A

GH is essential for normal growth during childhood and teenage years.

It stimulates long bone growth - length and width prior to epiphysela closure and width after.

IGFs stimulate both bone and cartilage growth.

20
Q

How does GH stimulate growth in children?

A

GH stimulates long bone growth – length and width prior to epiphyseal closure but can only increase in width after.

IGFs stimulate bone bone and cartilage growth.

21
Q

What is the role of GH and IGF in adults?

A

Gh and IGFs help maintain muscle and bone mass and promote healing and tissue repair as well as modulating metabolism and bdy composition.

22
Q
A
23
Q

How is GH secretion controlled?

A

GHRH increases GH secretion and Somatostatin decreased GH secretion.

CNS regulates GH secretion via inputs into the hypothalamus effecting GHRH and somatostatin levels.

  • Surge of GH secretion after onset of deep sleep
  • REM (rapid eye movement) sleep decreases GH secretion
  • Stress increases GH secretion
  • Exercise increases GH secretion
  • A decrease in glucise or fatty acids leads to an increase in GH secretion
  • An increase in glucose or free fatty acid leads to a decrease in GH secretion
  • Fasting increases GH secretion
  • Obeisity decreases GH secretion
24
Q

How is GH secretion regulated?

A

It is regulated by long loop and short loop negative feedback.

Long loop: Negative feedback

Mediated by IGFs

  • Inhibits relased of GHRH from hypothalamus
  • Stimulates the release of somatostatin from hypothalamus
  • Inhibit release of GH from anterior pituitary.

Short loop: negative feedback

  • Mediated by GH itself via stimulation of somatostatin release.
25
Q

What are the consequences of growth hormone deficiency?

A

In childhood it results in pituitary dwarfism.

  • This is a proportionate type of dwarfism
  • Can occur as a result of a complete or partiall deficiency.
  • Both types respond to GH therapy
  • Height below 3rd percentile on standard hrowth chart
  • Growth rate slower than expected
  • Delayed or no sxual development during teenage years.
26
Q

What are the consequences of excess growth hormone?

A

In childhood, excess GH results in gigantism. This is rare and is often caused by pituitary adenoma.

In adulthood,excess GH results in acromegaly – Literally means large extremities so large hands, feet and lower jaw. Also deep voice. (JAWS actor in James Bond)

27
Q

How does GH exert its effects on cells?

A

GH receptors activate Janus kinase (JAKs) – bidning of the receptor results in dimerization.

This results in cross talk which causes phosphorylation.

Causing ducking site to form signal scaffold. This activated downstream signalling pathways such as transcription factor activation and IGF 2 activation.

28
Q

What is IGF?

A

This is insulin like growth factor.

There are IGF 1 which is the major growth factor in adults and IGF 2 which Is mainly involved in foetal growth.

Binding proteins modulate their availability.

Actions of IGFs can be paracrine and aurocrine as well as endocrine.

29
Q

What processes do IGFs modulate?

A

IGFs act through IGF receptors (distinct from GH receptors) to modulate:

  • Cell growth (hypertrophy)
  • Cell number (Hyperplasia)
  • Increase in the rate of protein synthesis
  • Increase in the rate of lipolysis in adipose tissue
30
Q

What other hormones influence growth?

A
  • Insulin - Enhance somatic growth; interacts with IGF receptors
  • Thyroid hormones - Promote CNS development and enhance GH secretion
  • Androgens - Accelerate pubertal growth spurt; increase muscle mass; promote closure of epiphyseal plate
  • Oestogen - Decrease somatic growth; promote closure of epiphyseal plates
  • Glucocorticoids - Inhibit somatic growth

Sem 2 - MEH (22 decks)

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