Endocrinology

• what is a hormone?

  chemical agent secreted by cells and acting at a distance from origin site (e.g. gland)
• what type of hormones are there?

  • neuroendocrine - secreted by neurons into circulating blood (e.g. hypothalamic releasing hormones)
  • endocrine - secreted by endocrine glands into circulating blood (e.g. insulin by pancreas)
  • cytokine - secreted by tissue (e.g. leptin)
• lipid insoluble

  • chains of amino acids
  • proteins (> 100 aa) or peptides (< 100 aa)
  • e.g. insulin
• lipid soluble

  • have a common precursor - cholesterol
  • is a fat like molecule, abundant in cell membranes
  • e.g. testosterone
• how do hormones work?

  • they can only affect a cell if that cell has a receptor that fits
  • receptors are large proteins - cell needs >= 200 receptors to be affected by hormone
  • down-regulation and up-regulation of receptors are tools to regulate bodily response to hormones
• mechanism of action depend on their chemistry

  • lipid insoluble via ion channels and g protein-liked receptors
  • lipid soluble via intracellular receptors, acting on DNA
  • thyroid hormones via acting on cell nucleus
• how do g protein-linked receptors work?

  1. hormones activate receptor on extracellular membrane
  2. activates alpha unit of G protein (GDP -> GTP)
  3. detaches from beta and gamma units, then activates intracellular enzyme
• how do intracellular receptors work?

  1. hormone freely passes membrane
  2. binds to receptors in plasma
  3. receptors bind to hormone-response element strand of DNA
• how do hormones act on cell nucleus?

  1. thyroid hormone passes cell membrane via carrier channels
  2. enter nucleus
  3. receptor on hormone sensitive element of some genes causing transcription of DNA into mRNA
  4. synthesis of new proteins
• hypothalamic releasing and inhibitory hormones
• thyrotropin-releasing hormone

  • TRH
  • stimulates secretion of thyroid-stimulating hormone in anterior pituitary
• gonadotropin-releasing hormone

  • GnRH
  • stimulates secretion of luteinising and follicle stimulating hormones in anterior pituitary
• growth hormone-releasing hormone

  • GHRH
  • stimulates secretion of growth hormone in anterior pituitary
• growth hormone-inhibitory hormones

  • somatostatin
  • inhibits secretion of growth hormone in anterior pituitary
• prolactin-inhibiting hormone

  • PIH
  • inhibits secretion of prolactin in anterior pituitary
• corticotropin-releasing hormone

  • CRH (from paraventricular nucleus)
  • stimulates secretion of adrenocorticotropic hormone in anterior pituitary
• anterior pituitary hormones
• growth hormone (somatropin)

  • GH
  • stimulates body growth, cell multiplication and differentiation
• thyroid-stimulating hormone

  • TSH
  • stimulates secretion of thyroid hormones
• follicle-stimulating hormone

  • FSH
  • stimulates development of ovarian follicles and spermatogenesis in testis
• luteinising hormone

  • LH
  • causes ovulation and stimulates the corpus luteum; stimulates secretion of oestrogen and progesterone in ovaries; stimulates testosterone in testes
• adrenocorticotropic hormone

  • ACTH
  • stimulates secretion of glucocorticoids and androgens in adrenal cortex
• prolactin

  • PRL
  • inhibited in non-pregnant, biologically female women by hypothalamic prolactin inhibitory hormone (dopamine)
  • after birth, sudden loss of oestrogen and progesterone from placenta -> PRL stimulates lactation in post partum birthing parent
  • mechanical stimulation of nipples during nursing stimulates PRL secretion
  • PRL facilitates birthing beh and monogamy
• how do PRL and the brain interact?

  • PRL can cross BBB, brain has PRL receptors in hypothalamus and other regions
  • PRL counteracts effects of stress-related hormones and has anxiolytic effects
• Smith et al. (2004)


  PRL improves mood after birth and opposes detrimental effects of stress during pregnancy on depression-like beh of offsrping
• posterior pituitary, also known as?

  Neurohypophysis
• posterior pituitary hormones
• vasopressin

  • antidiuretic hormone
  • regulates blood press., blood vol., kidney functioning
  • social behaviours -> territorial beh., aggression
• oxytocin

  • contractions during birth and lactation
  • social behaviours -> bonding inc.
  • "love hormone"
• hypothalamus

  • master hormone regulator
  • will tell the pituitary gland to release more hormones
  • through the anterior and posterior
• metabolism-related hormones

  • thyroid hormones
  • insulin
  • leptin
  • ghrelin
  • oestrogens
  • androgens
  • cortisol
• how do hormones affect mental health condition?

  they affect behaviour which in turn affects mental health
• what effect do thyroid hormones have?

  widespread effects throughout the body:

  • increased metabolism
  • increased heart rate and strength of heart contraction
  • increased respiration
  • growth, CNS dev.
• what effect do thyroid hormones have on the brain?

  very slow effects (days to weeks)
• hypersecretion

  • excitation of CNS -> increased speed of cog., cost = disorganised
  • nervousness, anxiety, restlessness, impaired concentration, worries, paranoia, depression, manic ep in severe thyrotoxicosis
• hyposecretion

  • cog. impairment -> lack of concentration, memory deficits, psychomotor slowing
  • psychiatric symptoms inc. delusions, hallucinations, depression, impaired sleep, apathy
• how do thyroid hormones affect mood and depression?

  • serotonin and noradrenaline main mood regulatory systems
  • depression -> decreased serotoninergic activity
  • animal experiments -> presence of thyroid receptors in many brain areas, esp. phylogenetically younger regions
  • thyroid hormones increase serotonin prod. in brain stem nuclei
  • hypothyroid states -> decrease in serotonin production
• where is insulin secreted from?

  beta-cells in pancreas
• why is insulin hormone of energy abundance?

  allows transport of glucose into cells in presence of high blood glucose lvl, formation of stores (glycogen) and fat store (adipose tissue), and supports proteosynthesis (creating proteins)
• insulin and its role in diabetes?

  • type 1 -> lack of insulin secretion
  • type 2 -> decreased sensitivity of insulin receptors (insulin resistance)