Pituitary gland Flashcards
Embryological origins of anterior and posterior pituitary
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
Histology of adenohypophysis
[Clue]
–>type of capillary?
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
Histology of neurohypophysis
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
What regulates the adenohypophysis?
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
Control of neurohypophysis
Entirely by hypothalamus as hormones packaged in granules within the cell bodies located in the hypothalamus and are released into systemic veins
Describe the chemical nature of the hormone secreted by thyrotrophs
Thyroid Stimulating Hormone (TSH)
Chemical nature: Glycoprotein with alpha and beta subunit - alpha is common to TSH, FSH and LH, beta is TSH specific
Receptor of the hormone secreted by thyrotrophs
Thyroid Stimulating Hormone (TSH)
Found on basolateral surface of follicular cells
Gs-protein coupled receptor
Actions of the hormone secreted by thyrotrophs
Thyroid Stimulating Hormone (TSH)
- Stimulates thyroid gland to release T3 and T4
- Increases iodine uptake by thyroid
- Stimulates thyroid growth
Control of the hormone secreted by thyrotrophs
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
Dysfunctions of the hormone secreted by thyrotrophs
Thyroid Stimulating Hormone (TSH)
Rare
What are the two hormone(s) secreted by corticotrophs
Adreno Cortico Trophic Hormone (ACTH)
Melanocyte-stimulating hormones (MSH)
Describe the receptor of the hormone secreted by corticotrophs
Adreno Cortico Trophic Hormone (ACTH)
Gs-protein coupled in adrenal cortex, mostly zona fasciculata
Describe the actions of the hormone(s) secreted by corticotrophs
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
Describe the control of the hormone secreted by corticotrophs
Adreno Cortico Trophic Hormone (ACTH)
- Pulsatile diurnal release of corticotrophin releasing hormone (CRH) from hypothalamus stimulates ACTH release
- Negative feedback from cortisol/glucocorticoids
Describe dysfunctions of the hormone secreted by corticotrophs
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
Describe the chemical nature of the hormone secreted by gonadotrophs
Follicle stimulating hormone and Luteinising Hormone (FSH and LH)
Glycoprotein hormones, alpha subunits common to TSH
Describe the receptor of the hormone secreted by gonadotrophs
Follicle stimulating hormone and Luteinising Hormone (FSH and LH)
Gs-protein coupled receptors located in ovaries and testes
Describe the actions of the hormone secreted by gonadotrophs
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
Describe the control of the hormone secreted by gonadotrophs
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
Describe dysfunctions of the hormone secreted by gonadotrophs
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
Describe the chemical structure of the hormone secreted by lactotrophs
Prolactin
Protein
Describe the receptor of the hormone secreted by lactotrophs
Prolactin
Tyrosine kinase receptor in breast
Describe the actions of the hormone secreted by lactotrophs
Prolactin
Growth and development of secretory alveoli in the breast and milk production
Inhibits ovary function - lactational amenorrhoea
Describe the control of the hormone secreted by lactotrophs
Prolactin
Suckling increases PRL production
Hypothalamus inhibits PRL production by pituitary by secreting dopamine
Circulating oestrogen stimulates PRL production
Describe dysfunctions of the hormone secreted by lactotrophs
Prolactin
Prolactinomas causes increased PRL release, causing galactorrhoea, infertility and impotence
Describe the chemical nature of the hormone secreted by somatotrophs
Growth hormone
Protein
Describe the receptor of the hormone secreted by somatotrophs
Growth hormone
Tyrosine Kinase
Describe the action of the hormone secreted by somatotrophs
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
Describe the control of the hormone secreted by somatotrophs
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
Describe dysfunctions of the hormone secreted by somatotrophs
Growth hormone
Dwarfism with GH insufficiency
Gigantism in children and acromegaly in adults with excess GH release, often caused by pituitary adenoma
What are the two hormones secreted by the posterior pituitary gland? Describe the -chemical nature -receptor -actions -control -dysfunction
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??
