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medicine > Pituitary gland > Flashcards

Pituitary gland Flashcards

1
Q

Embryological origins of anterior and posterior pituitary

A

Anterior pituitary: Rathke’s pouch grows up from oropharyngeal ectoderm

Posterior pituitary: Infundibular process grows down from the forebrain vesicle

They detach from their origins and meet at the intermediate lobe, the cells of which in humans become part of the anterior pituitary

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2
Q

Histology of adenohypophysis

[Clue]
–>type of capillary?

A

Endocrine cells with surrounding folliculostellate cells (glial-like) and capillary network

Endocrine cells have extensive RER, full of secretory granules and many mitochondria

Capillaries are fenestrated

Five types of endocrine cell, identifiable only by fluorescent labelling:

  • Lactotroph
  • Gonadotroph
  • Somatotroph
  • Corticotroph
  • Thyrotroph
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3
Q

Histology of neurohypophysis

A

Made predominantly of axons and axon terminals of neuro-secretory cells originating from the hypothalamus

Sparse nuclei belong to pituicytes or red blood cells in capillary network

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4
Q

What regulates the adenohypophysis?

A

CNS - pulsatile neurohormone secretions from hypothalamus into the hypothalamo-hypophysial portal veins of the pituitary stalk that supply the anterior pituitary.

Feedback control by target hormones, mainly negative feedback

Paracrine interactions between endocrine and folliculostellate cells

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5
Q

Control of neurohypophysis

A

Entirely by hypothalamus as hormones packaged in granules within the cell bodies located in the hypothalamus and are released into systemic veins

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6
Q

Describe the chemical nature of the hormone secreted by thyrotrophs

A

Thyroid Stimulating Hormone (TSH)

Chemical nature: Glycoprotein with alpha and beta subunit - alpha is common to TSH, FSH and LH, beta is TSH specific

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7
Q

Receptor of the hormone secreted by thyrotrophs

A

Thyroid Stimulating Hormone (TSH)

Found on basolateral surface of follicular cells
Gs-protein coupled receptor

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8
Q

Actions of the hormone secreted by thyrotrophs

A

Thyroid Stimulating Hormone (TSH)

  • Stimulates thyroid gland to release T3 and T4
  • Increases iodine uptake by thyroid
  • Stimulates thyroid growth
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9
Q

Control of the hormone secreted by thyrotrophs

A

Thyroid Stimulating Hormone (TSH)

  • Stimulated by diurnal release of thyrotrophin releasing hormone (TRH) from hypothalamus, which itself is released in response to cold and stress sensed by CNS
  • Inhibited by T3 & T4 negative feedback
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10
Q

Dysfunctions of the hormone secreted by thyrotrophs

A

Thyroid Stimulating Hormone (TSH)

Rare

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11
Q

What are the two hormone(s) secreted by corticotrophs

A

Adreno Cortico Trophic Hormone (ACTH)

Melanocyte-stimulating hormones (MSH)

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12
Q

Describe the receptor of the hormone secreted by corticotrophs

A

Adreno Cortico Trophic Hormone (ACTH)

Gs-protein coupled in adrenal cortex, mostly zona fasciculata

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13
Q

Describe the actions of the hormone(s) secreted by corticotrophs

A

Adreno Cortico Trophic Hormone (ACTH)

  • Stimulates production and secretion of cortisol from adrenal gland
  • Some increase in adrenal sex steroids

MSH acts on melanocytes stimulating skin pigmentation

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14
Q

Describe the control of the hormone secreted by corticotrophs

A

Adreno Cortico Trophic Hormone (ACTH)

  • Pulsatile diurnal release of corticotrophin releasing hormone (CRH) from hypothalamus stimulates ACTH release
  • Negative feedback from cortisol/glucocorticoids
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15
Q

Describe dysfunctions of the hormone secreted by corticotrophs

A

Adreno Cortico Trophic Hormone (ACTH)

Cushing’s disease - corticotrophinoma causes excess ACTH secretion leading to increased glucocorticoid secretion

Addison’s disease - ACTH deficiency due to autoimmune mechanism or tuberculosis leading to diminished cortisol and adrenal secretions

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16
Q

Describe the chemical nature of the hormone secreted by gonadotrophs

A

Follicle stimulating hormone and Luteinising Hormone (FSH and LH)

Glycoprotein hormones, alpha subunits common to TSH

17
Q

Describe the receptor of the hormone secreted by gonadotrophs

A

Follicle stimulating hormone and Luteinising Hormone (FSH and LH)

Gs-protein coupled receptors located in ovaries and testes

18
Q

Describe the actions of the hormone secreted by gonadotrophs

A

Follicle stimulating hormone and Luteinising Hormone (FSH and LH)

FSH

Female ovaries: stimulates follicle development and ovulation, and oestrogen release

Male testes: initiates and maintains spermatogenesis in Sertoli cells

LH

Female ovaries: stimulates progesterone production via growth of corpus luteum

Male testes: stimulates testosterone production in Leydig cells

19
Q

Describe the control of the hormone secreted by gonadotrophs

A

Follicle stimulating hormone and Luteinising Hormone (FSH and LH)

Release stimulated by hourly release of gonadotrophin releasing hormone (GnRH) from hypothalamus

Systemic control:

Females - Inhibited by oestrogen via negative feedback, switches to positive feedback at ovulation (causing LH surge) … cyclical variations in LH and FSH during menstrual cycle

Males - testosterone inhibits LH via negative feedback, whereas follistatin and inhibin inhibit FSH

20
Q

Describe dysfunctions of the hormone secreted by gonadotrophs

A

Follicle stimulating hormone and Luteinising Hormone (FSH and LH)

Genetic mutations in LH and FSH gene and receptor gene can cause infertility and lack of sexual maturation

Overstimulation of gonadotrophs by excess GnRH from hypothalamus or overactivity of LH and FSH receptors can lead to precocious puberty

21
Q

Describe the chemical structure of the hormone secreted by lactotrophs

A

Prolactin

Protein

22
Q

Describe the receptor of the hormone secreted by lactotrophs

A

Prolactin

Tyrosine kinase receptor in breast

23
Q

Describe the actions of the hormone secreted by lactotrophs

A

Prolactin

Growth and development of secretory alveoli in the breast and milk production

Inhibits ovary function - lactational amenorrhoea

24
Q

Describe the control of the hormone secreted by lactotrophs

A

Prolactin

Suckling increases PRL production

Hypothalamus inhibits PRL production by pituitary by secreting dopamine

Circulating oestrogen stimulates PRL production

25
Q

Describe dysfunctions of the hormone secreted by lactotrophs

A

Prolactin

Prolactinomas causes increased PRL release, causing galactorrhoea, infertility and impotence

26
Q

Describe the chemical nature of the hormone secreted by somatotrophs

A

Growth hormone

Protein

27
Q

Describe the receptor of the hormone secreted by somatotrophs

A

Growth hormone

Tyrosine Kinase

28
Q

Describe the action of the hormone secreted by somatotrophs

A

Growth hormone

Stimulates long bone and soft tissue growth by

  • stimulating the release of insulin-like growth factors from the liver
  • direct actions on target tissues

Necessary for growth 2 years postnatally but only with sufficient nutrition

Metabolic actions due to insulin like affects, such as promoting amino acid uptake by liver and muscle hence promoting protein synthesis

Switches metabolism to oxidising fats in starvation

Anti-insulin-like effects with chronic over production

29
Q

Describe the control of the hormone secreted by somatotrophs

A

Growth hormone

Every 4 hours, and during deep sleep, growth hormone releasing hormone (GHRH) released by hypothalamus stimulates GH release

Secretions of GHRH increase with hypoglycaemia, stress and exercise

Somatostatin secreted from hypothalamus inhibits release of GH

GH inhibits release via negative feedback

30
Q

Describe dysfunctions of the hormone secreted by somatotrophs

A

Growth hormone

Dwarfism with GH insufficiency

Gigantism in children and acromegaly in adults with excess GH release, often caused by pituitary adenoma

31
Q 
What are the two hormones secreted by the posterior pituitary gland? 
Describe the
-chemical nature
-receptor
-actions
-control
-dysfunction
A

ADH:

Chemical nature - peptide

Receptor - V2 receptors in kidney are Gs-protein coupled; V1 receptors in vasculature are PLC-coupled

Actions - V2 causes fusion of aquaporins with membrane in collecting ducts to increase water reabsorption in kidneys; V1 constricts peripheral blood vessels

Control - Changes in osmotic pressure sensed by hypothalamic osmoreceptors and also sensitive to changes in blood pressure and volume

Dysfunction - Diabetes insipidus, where large amounts of urine are produced irrespective of water consumed, either due to hypothalamic problems or kidney insensitivity to ADH

Oxytocin:

Chemical nature - peptide

Receptor - PLC-coupled receptor

Actions - contraction of uterine myometrium in childbirth; contraction of breast myoepithelium in lactation; social behaviours

Control - cervix/vagina stretch; suckling

Dysfunction - deficit = perhaps prolonged labour and no milk production??

medicine (62 decks)

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