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Endocrine > Pituitiary, Hypothalamus, Thyroid > Flashcards

Pituitiary, Hypothalamus, Thyroid Flashcards

1
Q

Anterior Pituitiary

A

The adenohypophysis

  • pars distalis
  • pars intermedia
  • pars tuberalis
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2
Q

Posterior Pituitary

A

Neurohypophysis

  • pars nervosa
    • extension of hypothalamus
    • median eminence
    • infundibulum
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3
Q

Histogenesis of Rathke’s pouch

A

Oral ectoderm in roof of mouth proliferates and evaginates superiorly

  • constricts at base & separates from oral epithelium
  • Forms Rathke’s pouch
    • rostral epith thickens (pars distalis)
    • reduces pouch to cleft (Rathke’s cysts)
    • separates distalis from intermedius
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4
Q

Histogenesis of Pars nervosa

A

Diencephalon forms pocket

  • hypothalamic median eminence proliferates and forms infundibulum
    • pars nervosa
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5
Q

Hypophysial Portal Sytem

A

Superior hypophysial aa

  • feed 1st capillary bed in hypothalamus

Inferior hypophysial aa

  • feed capillary beds in neurohypophysis

2nd capillary bed forms in pars distalis

  • supplies anterio pituitary and drains via hypophyseal veins
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6
Q

The Adenohypophysis cells

A

Chromophobes

  • follicular cells

Chromophils

  • acidophils
    • somatotropes
    • mammotropes
  • basophils
    • corticotropes
    • thyrotropes
    • gonadotropes
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7
Q

Follicular cells

A

Large portion of cells don’t take up stain

Stellate in shape and appear to be supportive/phagocytic

Contain few secretion granules

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8
Q

Somatotropes

A

Secrete GH

  • Affect epiphysial cartilage
    • indirect growth stim
  • Stimulates somatomedin production
    • hypersecretion leads to gigantism, acromegaly, GH diabetes
    • hyposecretion leads to hypopituitary dwarfism
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9
Q

Mammotropes

A

Secrete PRL

  • Stims mammary gland development in preparation for lactation and milk ejection
  • Regulate glucose sensitivity of islet B-cells
  • role in immune function
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10
Q

Corticotropes

A

POMC

  • precursor to secretory products of corticotropes

ACTH

  • stimulates adrenal corticosteroid secretion
  • most important product of POMC

MSH

  • large doses lead to hyperpig
  • 1st product from pars intermedia

Liptropin

  • mobilizes fat
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11
Q

Gonadotropes

A

FSH

  • females - follicular development
  • males - gametogenesis

LH/ICSH

  • females - maturation of graafian follicle, development of corpus luteum, progesterone secretion
  • males - stim androgen secretion by testicular interstitial cells
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12
Q

Thyrotropes

A

Secrete TSH to stim thyriod gland

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13
Q

Adenohypophysis regulation

A

Pituitary cells under influence of hypothalamus

  • regulatory hormones released in median eminence
  • transported to anterior pituitary via hypothalamic - hypophysial portal system
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14
Q

Neurohypophysis is extension of the brain

A

Projection of supraoptic and paraventricular nuclei

  • give rise to hypothalamic-hypophysial tract
  • nerve terminals store hormones and abut on capillaries
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15
Q

Cell Types of Neurohypophysis

A

Pituicytes - most cells

  • specialized neurons secrete into capillaries of the hypophyseal-portal system
  • neurons ramify & form large discernible dilatations called Herring Bodies
  • contain numerous secretion granules have multi-laminated membrane structure major store of secretary material
  • filled with secretion granules granule content:
    • oxytocin & neurophysin I
    • vasopressin & neurophysin II
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16
Q

Hormones released in Pars Nervosa

A

vasopressin (ADH) - supra-optic nucleus in hypothalamus

oxytocin - paraventricular nucleus in hypothalamus

17
Q

Neurophysins

A

Carrier proteins of vasopressin & oxytocin

Stored in secretion granules & co-released

  • neurophysin I - oxytocin
  • neurophysin II - vasopressin
18
Q

Epiphysis (Pineal Gland)

A
  • found in posterior portion of third ventricle
  • flattened, conical organ covered by pia mater connected by a short stalk
  • CT septae with vessels & unmyelinated nerves penetrate pia mater form irregular lobules w/ cellular cords
  • contains lammellar structures called corpa arenacea
19
Q

Epiphysial cells

A

pinealocytes

  • basophilic cytoplasm
  • large irregular or lobate nuclei w/ sharply defined nucleoli
  • produce melatonin and other pineal peptides.

glial cells (astrocytes)

  • elongate nuclei & long cytoplasmic processes
  • between pinealocytes and around vessels
20
Q

Epiphysis secretes melatonin

A

secreted in response to absence of light
photostimuli relayed by sympathetic nerves secretion increased during hours of darkness
even without visual cues level of melatonin in blood rises & falls in daily (circadian) cycle effects change in secretory activities of: gonads other organs

21
Q

Thyroid gland development

A

median evagination of endoderm from base of tongue

  • thyroglossal duct attaches to tongue thru foramen caecum duct can remain patent and develop thyroglossal cysts

proliferating cellular mass breaks up into cords of cells

  • cell cords develop lumen upon formation of colloid thyroid uniquely stores hormone extracellularly
22
Q

Parafollicular cells of the thyroid

A

scattered throughout thyroid gland

  • located between follicles (may be part of follicular wall)
  • usual characteristics of secreting endocrine cells contain

secrete calcitonin (32 amino acid polypeptide) regulates

  • blood Ca2+ levels increase in plasma Ca2+ leads to increase in calcitonin inhibits bone Ca2+ resorption by direct inhibition of osteoclasts
23
Q

Thyroid follicular cells

A

produce large glycoprotein thyroglobulin

  • secreted into follicle
  • iodinated & stored
  • T4 (thyroxine)/T3 active forms

continuous layer of cuboidal epithelium surrounding central mass of colloid

  • colloid is largely thyroglobulin

follicular diameter varies with activity (50-900m)

  • less active follicles - flattened follicular cells & increased colloid
  • more active follicles - tall columnar follicular cells & reduced colloid
24
Q

Synthesis of Thyroid Hormones

A
  1. Synthesis of thyroglobulin (TG) and exocytosis to the lumen
  2. Transport of I- into cell- against chemical and electrochemical gradients
  3. Oxidation of I-* - thyroid peroxidase
  4. Organification of iodine into MIT and DIT*; MIT = monoiodothyronine, DIT = diiodothyronine
  5. Coupling reaction*; DIT + DIT = T4, DIT + MIT = T3
  6. Endocytosis of TG
  7. Proteolysis of iodinated thyroglobulin; releases T3 and T4
  8. Deiodination of residual MIT and DIT; recycling of I- and TG
25
Q

Transportation and Deiodination of Thyroid Hormone

A
  1. T4 and T3 circulate bound to thyroid-binding globulin (TBG) and to a lesser extent albumin and transthyretin (TTR)
    • TBG buffers hormone levels in the blood
    • 99.98% of T4 is bound in circulation and 99.5% of T3 is bound
  2. T3 is the more active thyroid hormone as it has a higher affinity for thyroid receptor (10 fold); however the ratio of T4 to T3 is 10:1
    • Tissues contain deiodinases to convert T4 to T3
    • People without thyroid function will have T3 upon treatment with T4 only
26
Q

Iodine deficiency Goiter

A

Hyperplasia of follicular cells with decreased colloid

  • due to positive feedback of thyroid
    *
27
Q

Hypothyroidism

A

Hashimoto’s autoimmune thyroiditis most common

  • causes autoimmune destruction of follicular cells
    • myxedema in adults
    • cretinism in children
28
Q

Hyperthyroidism

A

Graves disease most common

  • circulating IgG binds follucular cell & mimics TSH
  • constant unregulated stimulation of gland

Endocrine (2 decks)

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