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2 - MEH > Hypothalamic Pituitary Axis > Flashcards

Hypothalamic Pituitary Axis Flashcards

1
Q

Describe the location of the pituitary gland

A

Pituitary gland sits beneath the hypothalamus in a socket of bone called sella turcica

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2
Q

State the embryonic source of pituitary gland development

A
  • Anterior pituitary gland derived from primitive gut tissue
  • Posterior pituitary gland derived from primitive brain tissue
    • Connected to hypothalamus through infundibulum (pituitary stalk)
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3
Q

State the hormones synthesised in the hypothalamus and pass to posterior pituitary

A

Oxytocin, antidiuretic hormone

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4
Q

How are posterior pituitary hormones made and secreted

A
  • Oxytocin and antidiuretic hormone secreted from posterior pituitary but synthesised by neurosecretory cells in the supraoptic and paraventricular nuclei of hypothalamus
  • Transported down nerve cell axons to posterior pituitary
  • Stored and released from posterior pituitary into circulation (neurocrine secretion)
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5
Q

State the role of oxytocin in the body

A
  • Stimulus of sucking transmitted from breast to hypothalamus, resulting in release of oxytocin
    • Oxytocin travels to mammary glands and causes lactation
  • During childbirth, stimulus of pressure on cervix and uterine wall transmitted to hypothalamus
    • Release of oxytocin stimulates powerful uterine contractions
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6
Q

Explain the role of ADH in the body

A
  • Antidiuretic hormone (vasopressin) - reduces urine production
    • When produced, increase permeability of collecting duct by inducing translocation of aquaporin to allow water retention
    • § Alcohol inhibits ADH release - increased urination and dehydration
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7
Q

How do hormones secreted in hypothalamus reach anterior pituitary

A
  • Hormones synthesised in hypothalamus travel down axons and stored median eminence before secreted into hypophyseal portal system (neurocrine function)
  • These hormone stimulate or inhibit target endocrine cells in anterior pituitary gland
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8
Q

What are tropic hormones

A

Hormone involved in control of 2nd hormone

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9
Q

State the tropic hormones produced by hypothalamus and its function

A
  • TRH - thyrotropin releasing hormone - stimulates TSH
  • PRH - prolactin releasing hormone - stimulates prolactin
  • PIH - prolactin inhibiting hormone (dopamine) - inhibit prolactin
  • CRH - corticotropin releasing hormone - stimulate ACTH
  • GnRH - gonadotropin releasing hormone - stimulate LH and FSH
  • GHRH - growth hormone releasing hormone - stimulate growth hormone
  • GHIH - growth hormone-inhibiting hormone (somatostatin) - inhibit growth hormone
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10
Q

State the hormones produced in anterior pituitary and their functions

A
  • TSH - thyroid stimulating hormone - stimulates secretion of thyroid hormone from thyroid gland
  • ACTH - adrenocorticotropic hormone - stimulate glucocorticoid (cortisol) secretion from 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 metabolism, stimulate IGFs
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11
Q

Describe the different negative feedback loops for anterior pituitary hormones

A
  • Ultra short loop - tropic hormone to hypothalamus
  • Short loop - anterior pituitary hormone to hypothalamus
  • Direct long loop - endocrine gland hormone (eg. cortisol, IGF, thyroxine) to anterior pituitary
  • Indirect long loop - endocrine gland hormone to hypothalamus
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12
Q

Where is IGF (somatomedin) produced

A

In response to GH, cells of the liver and skeletal muscle produce and secrete IGF (somatomedin)

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13
Q

How is growth hormone metabolically controlled

A
  • Decrease in glucose or fatty acids leads to increase in GH secretion
  • Increase in glucose or free fatty acid leads to decrease in GH secretion
    • Give oral glucose tolerance test and see if GH becomes depressed to test GH function
  • Fasting increase GH secretion, obesity decrease GH secretion
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14
Q

How is growth hormone controlled by CNS

A
  • CNS regulates GH secretion via inputs into the hypothalamus effecting GHRH and somatostatin levels
    • Surge in GH secretion after onset of deep sleep (good sleep)
      Rapid eye movement sleep (light sleep) decreases GH secretion
    • Stress (trauma, surgery, fever) increase GH secretion
      • Exercise promote GH secretion
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15
Q

Explain how feedback loops control growth hormone levels

A
  • Long loop negative feedback mediated by IGF
    • Inhibit release 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
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16
Q

What are the effects on cells of growth hormone

A
  • GH stimulates long bone growth - both length and width increases prior to epiphyseal closure
    • Only increase width after epiphyseal closure
  • In response to GH, cells of the liver and skeletal muscle produce and secrete IGF (somatomedin)
  • IGF stimulate both bone and cartilage growth
  • In adults, growth hormone and IGFs help maintain muscle and bone mass and promote healing and tissue repair as well as modulating metabolism and body composition
17
Q

What happens when growth factor binds to its receptor

A
  • GH receptors activate Janus kinases (JAK) - tyrosine kinase receptor
    • When growth factor binds to its receptor, cross phosphorylation of JAK occur
    • Then phosphorylation of GH receptor and activation of signalling pathway
      • Transcription factor activation and IGF production
18
Q

Differentiate between two types of IGF

A
  • IGF1 - major growth factor in adults

- IGF2 - mainly involved in fetal growth

19
Q

What are the effects of IGF

A
  • IGF act through IGF receptors to:
    - Modulate hypertrophy
    • Modulate hyperplasia
    • Increase in rate of protein synthesis]
    • Increase in rate of lipolysis in adipose tissue
      • Decrease in glucose uptake
20
Q

What symptoms do pituitary tumours have

A
  • Visual loss, headache, vomiting, nausea
  • If tumour grows superior, it pushes and creates pressure against optic chiasm (chiasmal legion)
    • Bitemporal hemianopsia - vision missing in the outer half of visual field
  • Lateral growth of tumour can cause pain and double vision
    • Ptosis (droopy eye) - causes eye compressive problems
21
Q

What effect does pituitary tumour have on pituitary gland

A
  • A tumour blocking portal system decreases production of pituitary hormones (hypopituitarism)
    • Leads to increase in prolactin but decrease in other 5 hormones
22
Q

How would you investigate pituitary tumour

A
  • Identify anatomy, size and location of pituitary mass through MRI
  • Assessment of visual field - bitemporal hemianopsia
  • Assessment of endocrine function - hormone level in blood
23
Q

What are the causes of effects of hypopituitarism

A
  • Most commonly due to pituitary adenoma
    • Sometimes due to radiation therapy, inflammatory disease, head injury
  • Usually secondary to mass effect from adenoma
  • Progressive loss of anterior pituitary function with GH and LH/FSH first hormones to be affected
  • Deficiency in all tumours - panhypopituitarism
24
Q

What are the effects of growth hormone deficiency

A
  • Short stature in children, delayed or no sexual development
    • May be due to gene mutation or autoimmune inflammation
  • Adults - decrease tolerance to exercise, decrease muscle strength, increase body fat
    • Usually due to mass effects from pituitary adenoma
  • First hormone to become deficient
25
Q

What are the effects of gonadotropin deficiency

A
  • Delayed puberty in child
  • Loss of secondary sexual characteristics in adults
  • Loss of periods and early sign in women
26
Q

What are the effects of TSH/ACTH deficiency

A
  • Late feature of pituitary tumours
  • TSH deficiency - symptoms of hypothyroidism
  • ACTH deficiency - low cortisol levels, dizzy, low BP, low Na
27
Q

What are the effects of ADH deficiency

A
  • Excess excretion of dilute urine resulting in dehydration and polydipsea (increased sensation of thirst)
  • Represents cranial form of diabetes insipidus
  • Very high sodium levels (hypernatraemia)
  • Reduced consciousness, coma and death
28
Q

What are symptoms of hyperprolactinaemia

A
  • Menstrual disturbance
  • Fertility problems
  • Galactorrhoea (milk secreted when not pregnant), erectile dysfunction
  • Hypogonadism (diminished activity of gonads)
  • Gynectomastia (hard breast tissue)
29
Q

What are the causes of hyperprolactinaemia

A
  • Most commonly due to prolactinoma - pituitary adenoma that secretes prolactin
  • Could also be pregnancy, suckling, stress, exercise, drugs
30
Q

What is the treatment of prolactinoma

A
  • Dopamine agonist taken to shrink prolactinoma - no operation needed
    • Dopamine inhibits prolactin
  • Eg. Cabergoline
31
Q

What are the symptoms of growth hormone excess

A
  • Changes in physical appearance - broad nose, coarse facial features, thick lips, prominent supraorbital ridge (crest of bone on frontal bone of skull)
  • Acromegaly
    • Large extremities - large hands and feet
    • Gigantism
    • Growth factor secreting tumour
    • Premature cardiovascular death, tumours, thyroid cancer, disfiguring body symptoms, hypertension
32
Q

What is the treatment for acromegaly

A
  • Surgical removal of tumour
  • Radiation therapy - shrink tumour
  • Drug therapy - dopamine receptor agonists to reduce GH secretion
    - Synthetic somatostatin analogs to prolong suppression of GH secretion
33
Q

What does ACTH excess cause

A

Cushing’s disease

2 - MEH (16 decks)

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