Week 2

• Circulatory system

  1. Capillary bed allows diffusion of hormones

  2. Hormones diffuse into the capillary by a primary plexus of the hypophyseal portal system (vein to the second plexus of the hypophyseal portal system) – target cells in the anterior pituitary
• Anatomy of the pituitary

  1. Infundibular = stalk

  2. Pars intermedia = develops from roof plate tissue (anterior pituitary)

  3. Posterior – ectoderm goes to neurohypophysis
• Adrenocorticotrophic hormone (ACTH)

  1. ACTH is a peptide

  2. Corticotropin-releasing hormone (CRH) causes ACTH release from anterior pituitary

  3. ACTH stimulates adrenal cortex to release glucocorticoids

  4. Glucocorticoids have negative feedback effect on CRH and ACTH

  5. Control metabolism, skeletal, reproduction, cognition
• Anatomy of the pituitary

  1. Pars intermedia produces - Melanocyte stimulating hormone (MSH)

  2. Regulates pigment containing cells

  3. Acts on neurons in brain, inhibits hunger
• Hormones release from the anterior pituitary

  1. Thyroid stimulating hormone (TSH)

  2. Adrenocorticotropic hormone (ACTH)

  3. Follicle stimulating hormone (FSH)

  4. Luteinising hormone (LH)

  5. Prolactin (PRL)

  6. Growth hormone (GH) –(both tropic and non-tropic effects)

  7. Melanocyte stimulating hormone (MSH)

  8. Act as TROPIC hormones –(regulate function of endocrine cells/glands)
• MSH/Ghrelin regulation of appetite

  POMC gene expresses MSH, balanced out by Ghrelin when stomach is empty
• Thyroid stimulating hormone (TSH)


  1. TRH controls release of TSH (a Glycoprotein)

  2. TSH stimulates release of T3 and T4 from the thyroid (control body's metabolism)

  3. Thyroid hormones T3 and T4 inhibit release of TRH and TSH (negative feedback)

  4. T3 = triiodothyronine

  5. T4 = thyroxin
• Hypophyseal portal system

  1. Communication from hypothalamus to the anterior pituitary gland

  2. Linked by capillary beds by portal veins

  3. Regulatory hormones from hypothalamus transported to anterior pituitary via the hypophyseal portal system
• Regulation by the hypothalamus and pituitary

  1. Hypothalamus produces Releasing hormone (RH) causes Hormone 1 release from anterior pituitary

  2. Hormone 1 causes Hormone 2 release from target endocrine organ

  3. Hormone 2 inhibits release of RH and Hormone 1

  4. Hormone 2 has effect upon target cells

  5. Levels of these hormones need to be carefully controlled
• Embryonic formation of pituitary

  1. Ectodermal tissue derives from evagination of roof of the oral cavity

  2. The Rathke pouch loses connection to Pharynx
• Mammalian endocrine system

  • The hypothalamus and pituitary gland
• Melanocytes respond to MSH


  1. Dynamic cells- Sit in the basement membrane

  2. Finger-like projection to contact keratinocytes

  3. Produces melanin which darkens skin colour

  4. If mutated, can become cancerous

  5. Sun exposure triggers the release of MSH

  6. May influence brain activity

  7. Dopamine inhibits MSH release

  8. Corticotropin-releasing hormone stimulates MSH release
• Glucocorticoids have negative feedback effect on CRH and ACTH


  Inhibit CRH and ACTH
• Hypothalamus can give you the sensation of thirst
• Prolactin release is stimulated by prolactin releasing factor (PRF) and inhibited by prolactin inhibiting hormone (PIH, known as dopamine)


  Stimulated by hypothalamus
• The thyroid gland sits on the windpipe with a central isthmus and right and left lobes
• GH stimulates somatomedin (Insulin-like Growth Factor - IGF)


  1. Influence carbohydrate metabolism

  2. Production

  3. Enter bloodstream from the liver
• ADH binds receptors in the DCT

  Increases expression of the Aquaporin-2 channel and its insertion in the membrane of DCT cells → Increase in permeability → water retention in blood
• Inhibin inhibits FSH production


  In both sexes
• Effects of FSH and LH

  • Promote egg and sperm production
  • Secretion of sex steroids
  • Control the negative hormone inhibin
• T4 has 4 iodine atoms, T3 has 3 iodine atoms
• Growth hormone abnormalities

  • Pituitary Gigantism
  • Acromegaly
  • Pituitary growth failure
• CRH causes ACTH release from corticotrophs in the anterior pituitary


  Diffuses through wall system
• Hormones of the posterior pituitary

  • ADH
  • Oxytocin
• GH release is inhibited by growth hormone-inhibitory hormone (GHIH) (somatostatin)

  Anterior pituitary
• FSH and LH (gonadotropins)


  Produce diffuses hypothalamic portal system to pituitary controls FSH and LH production
• Too much prolactin


  • Men = erectile dysfunction
  • Women = galactorrhea (inappropriate lactation) and absence of menstrual cycles
• ACTH stimulates adrenal cortex to release glucocorticoids


  Act directly
• Functions of glucocorticoids


  • Control metabolism
  • Control skeletal functions
  • Control reproduction
  • Control cognition
• Effects of growth hormone (GH)

  • Stimulates bone and cartilage growth
  • Fat and glycogen breakdown
  • Increases blood glucose levels
  • Increases release of fatty acids for ATP production
  • Affects protein and lipid metabolism
• The fine structure of the thyroid includes follicles containing thyroglobulin surrounded by a capsule and C cells important in calcium homeostasis
• Oxytocin may be responsible for the feeling of pleasure after sex
• Effects of Prolactin

  • Stimulates milk production
  • Stimulates mammary glands
  • Responsible for breast tenderness just before a period as levels rise
• Congenital hypothyroidism results in poor skeletal and nervous system development, low metabolic rate, low body temperature
• Function of thyroid hormone

  • T3 more active than T4, important for development, metabolism, bone formation, brain function, increase metabolic rate, ATP production, glycolysis, heart rate, blood pressure
• Between T4 (4 iodine) and T3 (3 iodine) is the number of iodine atoms, derived from tyrosine
• Parathyroid hormone (PTH) and calcium homeostasis


  Increases blood calcium, released in response to low calcium levels, stimulates osteoclasts, stimulates calcium reabsorption in kidneys and intestine via vitamin D production
• If there is a mutation or cancer in the adrenal cortex
• Hyperthyroidism results in high metabolic rate, high body temperature, sweating, high heart rate, high blood pressure, central nervous system effects
• Synthesis of thyroid hormones

  TSH-sensitive pump transports iodide ions into thyroid follicle cells, Thyroid follicular cells synthesise thyroglobulin rich in tyrosine amino acids, Iodide ions are oxidised to atoms via thyroid peroxidase, Iodine atoms react with tyrosines on thyroglobulin to form T1 or T2, T1 and T2 react to form T3 or T4, TSH enhances endocytosis of colloid, T3 and T4 diffuse into blood via transport proteins