Pituitary gland

Question 1

Embryological origins of anterior and posterior pituitary

Answer 1

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

Question 2

Histology of adenohypophysis

[Clue]
–>type of capillary?

Answer 2

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

Question 3

Histology of neurohypophysis

Answer 3

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

Question 4

What regulates the adenohypophysis?

Answer 4

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

Question 5

Control of neurohypophysis

Answer 5

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

Question 6

Describe the chemical nature of the hormone secreted by thyrotrophs

Answer 6

Thyroid Stimulating Hormone (TSH)

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

Question 7

Receptor of the hormone secreted by thyrotrophs

Answer 7

Thyroid Stimulating Hormone (TSH)

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

Question 8

Actions of the hormone secreted by thyrotrophs

Answer 8

Thyroid Stimulating Hormone (TSH)

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

Question 9

Control of the hormone secreted by thyrotrophs

Answer 9

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

Question 10

Dysfunctions of the hormone secreted by thyrotrophs

Answer 10

Thyroid Stimulating Hormone (TSH)

Rare

Question 11

What are the two hormone(s) secreted by corticotrophs

Answer 11

Adreno Cortico Trophic Hormone (ACTH)

Melanocyte-stimulating hormones (MSH)

Question 12

Describe the receptor of the hormone secreted by corticotrophs

Answer 12

Adreno Cortico Trophic Hormone (ACTH)

Gs-protein coupled in adrenal cortex, mostly zona fasciculata

Question 13

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

Answer 13

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

Question 14

Describe the control of the hormone secreted by corticotrophs

Answer 14

Adreno Cortico Trophic Hormone (ACTH)

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

Question 15

Describe dysfunctions of the hormone secreted by corticotrophs

Answer 15

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

Question 16

Describe the chemical nature of the hormone secreted by gonadotrophs

Answer 16

Follicle stimulating hormone and Luteinising Hormone (FSH and LH)

Glycoprotein hormones, alpha subunits common to TSH

Question 17

Describe the receptor of the hormone secreted by gonadotrophs

Answer 17

Follicle stimulating hormone and Luteinising Hormone (FSH and LH)

Gs-protein coupled receptors located in ovaries and testes

Question 18

Describe the actions of the hormone secreted by gonadotrophs

Answer 18

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

Question 19

Describe the control of the hormone secreted by gonadotrophs

Answer 19

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

Question 20

Describe dysfunctions of the hormone secreted by gonadotrophs

Answer 20

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

Question 21

Describe the chemical structure of the hormone secreted by lactotrophs

Answer 21

Prolactin

Protein

Question 22

Describe the receptor of the hormone secreted by lactotrophs

Answer 22

Prolactin

Tyrosine kinase receptor in breast

Question 23

Describe the actions of the hormone secreted by lactotrophs

Answer 23

Prolactin

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

Inhibits ovary function - lactational amenorrhoea

Question 24

Describe the control of the hormone secreted by lactotrophs

Answer 24

Prolactin

Suckling increases PRL production

Hypothalamus inhibits PRL production by pituitary by secreting dopamine

Circulating oestrogen stimulates PRL production

Question 25

Describe dysfunctions of the hormone secreted by lactotrophs

Answer 25

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

Question 26

Describe the chemical nature of the hormone secreted by somatotrophs

Answer 26

Growth hormone Protein

Question 27

Describe the receptor of the hormone secreted by somatotrophs

Answer 27

Growth hormone Tyrosine Kinase

Question 28

Describe the action of the hormone secreted by somatotrophs

Answer 28

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

Question 29

Describe the control of the hormone secreted by somatotrophs

Answer 29

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

Question 30

Describe dysfunctions of the hormone secreted by somatotrophs

Answer 30

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

Question 31

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

Answer 31

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??