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MD4001 Physiology > Hypothalamus and Pituitary > Flashcards

Hypothalamus and Pituitary Flashcards

1
Q

What does the pineal gland control?

A

Sleep patterns, light dark cycles, releases melatonin

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2
Q

What are secretions called that act locally?

A

Paracrine secretion

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3
Q

What are secretions called that act on themselves?

A

Autocrine secretion

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4
Q

What kind of capillaries are located in endocrine glands?

A

Fenestrated

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5
Q

What are the 3 main factors which control the release of hormones from endocrine glands?

A
  • Humoral (hormone released due to a factor/metabolite/solute in the blood)
  • Neural
  • Hormonal
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6
Q

What is an example of humoral control of endocrine release?

A
  • Capillary blood contains low concentration of Ca2+ which stimulates parathyroid glands to release PTH
  • Also insulin release in response to glucose
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7
Q

What is an example of neural endocrine release?

A
  • Adrenal medulla

- Chromaffin cells release catecholamines and dopamine through sympathetic innervation

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8
Q

What is an example of hormonal endocrine release?

A
  • Hypothalamus secretes hormones that stimulate the pituitary gland to secrete hormones that then stimulate endocrine
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9
Q

What are ‘neurohormones’?

A
  • Modified neurons in hypothalamus with cell bodies, axons and post axonal terminals which terminate in a capillary network. Hormones are released here which tare carried to anterior pituitary and stimulate hormones which are stored there
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10
Q

What do the adrenal cortex and medulla secrete?

A
  • Glucocorticoids
  • Mineralocorticoids
  • Catecholamines
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11
Q

What does the thyroid secrete?

A
  • Thyroid hormones (T3 and T4)

- Calcitonin

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12
Q

What do the parathyroid gands secrete?

A
  • Parathyroid hormone (PTH)
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13
Q

What hormones are released by the pancreas?

A
  • Insulin
  • Glucagon
  • Pancreatic polypeptide
  • Somatostatin
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14
Q

What hormones are released by the the thymus?

A

Thymopoietin

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15
Q

What hormones are released by the heart?

A
  • Natriuretic peptides
  • ANP
  • BNP
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16
Q

What hormones are released by the gonads?

A
  • Sex steroids
  • Inhibins (feedback)
  • Activins (feedback)
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17
Q

What hormones are released by the liver?

A
  • Insulin-like growth factors
  • Leptin
  • Angiotensinogen
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18
Q

What hormones are released by the kidney?

A
  • Erythropoietin (EPO)

- Renin

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19
Q

What hormone is released by adipose tissue?

A

Leptin

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20
Q

What is another name for the pituitary?

A

Hypophysis (2 glands in 1)

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21
Q

What is the anterior pituitary also known as?

A
  • Anterior lobe

- Adenohypophysis

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22
Q

What is the posterior pituitary also known as?

A
  • Posterior lobe

- Neurohypophysis

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23
Q

What are the 3 parts of the anterior pituitary?

A
  • Pars anterior (distalis) (main part)
  • Pars tuberalis (PT) (upgrowth of tissue from pars anterior) (nealry surrounds pituitary stalk)
  • Pars intermedia (quite atrophied, in between ant and post pituitary)
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24
Q

What lobe is the pituitary stalk part of?

A

The posterior pituitary

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25
Q

What is the pars intermedia derived from?

A

Rathke’s pouch

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26
Q

What is contained within the pars intermedia?

A
  • Colloid-filled, epithelial lined follicles

- Numerous basophilic cells - may have some connection with the secretion of melanocyte stimulating hormone MSH

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27
Q

What is the anterior pituitary developed from?

A

Up-growth of epithelium from the oral cavity (Rathke’s pouch)

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28
Q

What is the posterior pituitary developed from?

A

Down-growth from brain (infundibulum)

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29
Q

Where may craniopharyngiomas grow?

A

Along track of Rathke’s pouch (slow growing)

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30
Q

In what week does Rathke’s pouch lose contact with the oral cavity?

A

Week 8

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31
Q

What are the cells that take up the stain in the anterior pituitary?

A
  • Chromophils

- Chromophobes do not take up the stain

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32
Q

What are the 2 types of chromophil?

A
  • Acidophils (65%) (orange colour) - GH and prolactin

- Basophils (35%) (purple colour) - the others

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33
Q

What is the function of the different regions / nuclei of the hypothalamus?

A

Different roles / functions

- Involved in synthesising storing and releasing neural hormones that control the release of hormones from the pituitary

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34
Q

What are the names of the different nuclei of the hypothalamus?

A
  • Pre-optic nuclei
  • Suprachiasmic nuclei
  • Paraventricular nuceli
  • Supraoptic nuclei
  • Dorsomedial nucleus
  • Posterior nucleus
  • Infundibular nucleus (part of arcuate nucleus)
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35
Q

Where do the axons of the large bodied cell nuclei in the hypothalamus extend to?

A

Through median emminance forming a nerve tract (forms hypothalamo-hypophyseal nerve tract)

  • Terminates in capillary network in posterior pituitary
  • Releases neurohormones from the body in vesicles
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36
Q

The capillary bed of the posterior pituitary is fed by what artery?

A

Inferior hypophyseal artery

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37
Q

What are the swellings of axons near nerve endings called that store neurohormones?

A

Herring bodies

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38
Q

Where are small bodied neurons found?

A

Inside the nuclei

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39
Q

Where do small bodied neurons axonal terminals terminate?

A

Higher up

  • Median emminance
  • Or para tubulares
  • Pituitary stalk
  • Feeds into capillary network which feeds into a series of portal veins (hypothalamo-hypophyseal portal system)
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40
Q

What artery supplies the pituitary stalk?

A

Superior hypophyseal artery

41
Q

Where does the hypothalamo-hypophyseal portal system form another capillary network?

A

In anterior pituitary (hormones produced by small bodied neurons in hypothalamus carried down and meet target cells in anterior pituitary)

42
Q

What are the neurohormones controlling the secretions from the anterior pituitary?

A
  • Thyrotropin-releasing hormone (TRH, 3 amino acid peptide)
  • Corticotropin-releasing hormone (CRH, 41 aa polypeptide)
  • Growth hormone-releasing hormone (GHRH, 43 aa polypeptide) or somatotropin-releasing hormone (SRH)
  • Somatostatin/Growth hormone release-inhibiting hormone (SS/GHRIH; cyclic 14 aa peptide)
  • Gonadotropin-releasing hormone (GnRH, 10 aa peptide) (or Follicle -stimulating hormone releasing hormone - FSH-RH) (or Luteinising hormone releasing hormone - LH-RH)
  • Prolactin releasing factor (PRF); TRH
  • Prolactin release inhibiting factor (PIF); Dopamine
43
Q

What are the neurohormones released from the posterior pituitary?

A
  • Vasopressin (VP) / ADH (9 aa peptide)

- Oxytocin (OT, 9 aa peptide)

44
Q

What is thyrotopin-releasing hormone derived from?

A

A precursor protein that is 250 amino acids long which is then cleaved to create 6 or 7 TRH peptides

45
Q

What is the structure of the first amino acid on the amino terminal end of TRH?

A

Pyroglutamic acid residue (circulised glutamic acid)

- Modifi

46
Q

Why is TRH given a circulised glutamic acid?

A

Small peptides in the circulation like TRH (even if only going from hypothalamus to pituitary) are actively degraded by extracellular proteases (modification protects the TRH)

47
Q

What are the trophic hormones?

A

Hormones which have primary actions on other endocrine glands

  • Thyrotropin / TSH
  • Corticotropin/ Adrenocorticotropic hormone (ACTH)
  • Gonadotropins (LH and FSH)
48
Q

What cells are TSH synthesised stored and released from?

A

Thyrotrophs

49
Q

What are hormones which act on peripheral target cells?

A
  • Somatotropin / Growth hormone (GH)
  • Prolactin (PL)
  • alpha, Beta and gamma Melanotropin / Melanocyte-stimulating hormone (MSH)
50
Q

How many amino acids are presnt in oxytocin and ADH?

A

9

51
Q

What cells release Thyrotropin / TSH?

A

Thyrotrophs (are basophils)

52
Q

What cells release corticotropin / adrenocorticotropic hormone (ACTH)?

A

Corticotrophs (basophils)

53
Q

What cells release gonadotropins?

A

Gonadotrophs (basophils)

54
Q

What is the precursor protein of corticotropins/ Adrenocorticotropic hormones and melanotropin / Melanocyte-stimulating hormone?

A

Pro-opiomelanocortin (POMC)

55
Q

What cells release Somatotropin / Growth hormone (GH)?

A

Somatotrophs (acidophils)

56
Q

What cells release Prolactin?

A

Lactotrophs or mammotrophs (acidophils)

57
Q

What cells release melanotropin / Melanocyte-stimulating hormone (MSH)?

A

Melanotrophs (basophils)

58
Q

What is the prevelance of the different cell types in the anterior pituitary?

A
  • Somatotrophs - 50%
  • Lactotrophs/ mammotrophs - 20% (more in lactating female)
  • Corticotrophs - 20%
  • Thyrotrophs - 5%
  • Gonadotrophs - 5%
  • Melanotrophs
59
Q

Where does the receptor specificity lie in hormones of the anterior pituitary?

A

Beta subunit (TSH, LH, FSH)

60
Q

What is the purpose of the alpha subunit?

A

Similar in all hormones - induces second messanger response - stimulates cAMP

61
Q

What is the structure of Corticotropin/ Adrenocorticotropic hormone (ACTH)?

A

39 amino acid polypeptide

62
Q

What is the structure of somatotropin / Growth hormone (GH)?

A

191 amino acid protein

63
Q

What is the structure of prolactin?

A

199 amino acid protein

64
Q

What is the structure of alpha, Beta and gamma(y) melanotropin / Melanocyte-stimulating hormone (MSH)?

A

12, 13 and 18 amino acid peptides

65
Q

Describe the mechanism controlling Growth Hormone release?

A
  • Neurosecretory cells in the arcuate nucleus secrete growth-hormone-releasing hormone (GHRH), which reaches the somatotrophs via the hypophyseal portal blood supply
  • Cells in the periventricular region release somatostatin, a hormone that is a potent inhibitor of GH secretion, into portal blood supply
  • GHRH causes somatotrophs to synthesize and release GH
  • Binds to G-protein coupled receptor (serpentine) causes conformational change - G protein disssociates, alpha subunit binds to adenylate cyclase take ATP to cAMP, cAMP activates PKA - this phosphorylates a calcium channel causes depolarisation and exocytosis of GH
  • Somatostatin inhibits the release of GH by somatotrophs (binds to inhibitory G-protein, suppresses cAMP)
66
Q

How does the negative feedback mechansim work in supppressing GH?

A
  • GH stimulates secretion of IGF-I from peripheral target tissue
  • IGF-I then directly inhibits GH release by suppressing the somatotrophs
  • IGF-I indirectly inhibits GH release by suppressing GHRH release from the arcuate nucleus in the hypothalamus
  • IGF-I indirectly inhibits GH release by increasing secretion of somatostatin from nuclei in the periventricular region
  • GH also inhibits own secretion via short loop feedback on somatotrophs
67
Q

What organ produces Insulin-like Growth Factor I (IGF-I)?

A

Liver

68
Q

Describe the manner in which GH is released?

A

Pulsatile, circadian rhythm release (More released at night, during sleep)

69
Q

What are the effects of GH (other than negative-feedback effects)?

A

Anti-insulin actions

  • Increased lipolysis
  • Increased blood glucose and other anti-insulin effects

Insulin-like growth factors (IGFs)

  • Negative feedback
  • Increased cartilage formation and skeletal growth
  • Increaased protein synthesis, and cell growth and proliferation
70
Q

What condition is caused by GH deficiency?

A

Dwarfism - treated with GH

- Due to predictable effects on linear bone growth and decreased availibility of lipids and glucose for energy

71
Q

What is gigantism caused by?

A

GH excess before puberty - leads to excess stimulation of epiphseal plates

72
Q

What is GH excess (acromegaly) often due to?

A

Pituitary adenoma

73
Q

What are the effects of GH excess (acromegaly) after puberty (e.g pituitary adenoma)?

A
  • No stimulation of linear growth due to fusion of epiphyses
  • Periosteal bone growth causing enlarged hand, jaw and foot size (ring may not fit, shoe size increases)
  • Soft tissue growth leading to enlargement of the tongue and coarsening of facia lfeatures
  • Insulin resistance and glucose intolerance (diabetes)
74
Q

How is acromegaly treated?

A

Synthetic long-acting somatostatins (e.g Octreotide) with varying success

75
Q

What are physical signs of gigantism?

A
  • Enlargement of hands and feet
  • Rapid growth (6 ft by 12, 8 ft as adult)
  • Swelling of soft tissue
  • Skin tags
  • Muscle weakness / fatigue
  • Skin changes, thickening, oiliness, acne
  • Hirsutism (abnormal/unusual hair growth)
  • Coarsening of facial features, including forehead, nose, lips, tongue and jaw
76
Q

What are symptoms of acromegaly?

A
  • Arthralgia (pain in joints) - 75%
  • Amenorrhea - 72%
  • Hyperhidrosis (excessive perspiration) - 64%
  • Sleep apnea 60%
  • Headaches - 55%
  • Paresthesia or carpel tunnel syndrome - 40%
  • Loss of libido or impotence - 36%
  • Hypertension - 28%
  • Thyroid disorders (goitre) - 21%
  • Visual field defects - 19%
77
Q

GnRH is released from what nuclei?

A

Small bodied cell nuclei

78
Q

What hormones control the release of GH?

A

GHRH and SS

79
Q

What does TRH stimulate the release of?

A
  • TSH

- Prolactin

80
Q

What does TSH cause the release of?

A
  • T3: triiodothyronine

- T4: Thyroxine

81
Q

What hormones control the production of prolactin?

A
  • TRH increases secretion

- Dopamine decreases production

82
Q

What does Prolactin stimulate?

A

Breast development and milk production

83
Q

WHat does corticotrophin-releasing hormone (CRH) cause the release of?

A

ACTH (Adrenocorticotropic hormone)

84
Q

What does ACTH (Adrenocorticotropic hormone) affect?

A

Adrenal cortex - secretes cortisol

85
Q

Where are ADH/AVP and Oxytocin stored?

A

Large bodied cell nuclei in the hypothalamus

86
Q

What is a signal peptide?

A

First 20-25 amino acids in the polypeptide (precursor protein) recognised by proteins in the endoplasmic reticulum which causes the protein to be transported into vesicles

87
Q

What is the precursor protein of ADH cleaved into?

A
  • Signal peptide
  • ADH (first 9 aa)
  • Neurophysin II (98 aa long) (ADH and Neurophysin II bind to each other)
  • C terminal Glycopeptide (Partly glycosylated during processing) - is then set for degradation
88
Q

What is the precursor protein of Oxytocin cleaved into?

A
  • Signal peptide
  • Oxytocin
  • Neurophysin I (97 aa)
    OT and neurophysin I bind to each other
89
Q

What is the purpose of the neurophysin I and II?

A

They protect ADH and oxytocin by binding on to them - means they are not broken down by proteases in circulation

90
Q

Where is ADH synthesised?

A

Neurosecretory cells within the supra-optic and paraventricular nuclei

91
Q

What factors lead to ADH release?

A
  • Osmoreceptors detect increased blood osmolarity
  • Volume receptors (carotid, aorta, Left atrium) detect decreases blood volume
  • RAAS system stimulates Angiotensin II release
92
Q

What factors can cause diabetes insipidus (polyuria, polydispia)?

A
  • Cranial (30% trauma/disease induced, 30% familial disorders of NS cells, 30% tumours)
  • Nephrogenic - sex-linked genetic defect in collecting tubule
93
Q

What is oxytocin produced by?

A

Hypothalamic neurones in the paraventricular and supraoptic nuclei

94
Q

How is oxytocin stored and secreted?

A
  • Bound to glycoproteins it is carried in the axons to the posterior pituitary where it is stored in vesicles in the expanded ends of the axons
  • Herring bodies
  • Release (neurosecretion) is contolled directly by nervous impulses from the hypothalamus
95
Q

How does oxytocin affect the female reproductive system?

A

Smooth muscle contraction in uterus - helps expel the fetus during partuirition

96
Q

How does oxytocin affect the female reproductive system?

A

Smooth muscle contraction in uterus - helps expel the fetus during partuirition

97
Q

Explain the hypothalamic control of milk production and ejection and the role oxytocin plays in the mother?

A
  • Stimulus of suckling travels from breast, through spinal cord to the hypothalamus
  • Neurons from the spinal cord inhibit dopamine release from the aarcuate nucleus. The decreased level of dopamine removes inhibition that DA normally produces on lactotrophs in the anterior pituitary, leading to prolactin release. Prolactin stimulates milk prodction in the breast
  • Neurons from the spinal cord also stimulate and release oxytocin from the paraventricular nuclei and supraoptic nuclei. Oxytocin is released in posterior pituitary and into systemic blood, where it then makes its way to the breast and myoepithelial cells
  • Neurons from the spinal cord inhibit neurons in the arcuate nucelus and the preoptic area of the hypothalamus, causing a fall in GnRH production. Reduced stimulation of gonadotrophs inhibits the ovarian cycle
98
Q

Where does the pineal gland lie?

A

Midline in the posterior part of the roof of the 3rd ventricle

99
Q

What are the functions and actions of the pineal gland?

A
  • Pinealocytes have neural connections with the hypothalamus
  • In darkness pineal secretes melatonin (from tryptophan)
  • Regulates circadian rhythms (melatonin has a hypnotic effect)
  • Regulates reproductive processes including onset of puberty
  • Effects aging and regulation of immune system
  • Accumulates calcium phosphate with time ‘brain sand’ visible in the mid line on X rays and other scans

MD4001 Physiology (22 decks)

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