The endocrine system

• What are the functions of the endocrine system?

  • Regulating of the production and secretion of other hormones
  • Maintenance of the glands
  • Homeostasis
  • Growth promotion
  • Facilitate reproduction
• What are the classes of hormones (solubility) and how they differ?


  • Hydrophilic (e.g, peptides, catecholamine and indole amines): opening channels/intracellular second messengers. Biochemical actions. FAST
  • Lipophilic (e.g, steroid, thyroid hormones): intracellular receptors, tend to change gene activity. SLOW
• Explain regulation of hormones?


  • Physiological by-products generated in response to their actions
  • Action from other hormones
  • Nervous system
• Explain the pituitary gland?


  • The cell bodies of the neurones that makes up the posterior gland lie on the hypothalamus
  • The posterior lobe is a collection of the axon terminals of these neurones which descend as the hypothalamic-hypophyseal tract
  • The posterior pituitary gland stores and secretes hormones produced by the hypothalamus (oxytocin and antidiuretic hormone; ADH)
• What is the effect of Antidiuretic hormone?


  Stimulates water reabsorption by kidneys
• What is the effect of oxytocin?


  It stimulates uterine contractions and dilation of the cervix during childbirth
• Explain the anterior pituitary gland?


  The anterior lobe of the pituitary produces its own hormones which are released into the secondary capillary plexus of the hypophyseal portal system
• 1. Explain the release of growth hormone?


  • Hypothalamus releases growth hormone-releasing hormone (GHRH)
  • GHRH stimulates the anterior pituitary to release growth hormone (GH)
• 2a. Glucose-sparing effect?

  • Stimulates adipose cells to break down stored fat, fuelling growth effects.
• 2b) Growth effects and targets?

  • Increases uptake of amino acids from the blood
  • Enhances cellular proliferation and reduces apoptosis
  • Targets: Bone cells, muscle cells, nervous system cells and immune system cells
• 2C) Diabetogenic effects


  • GH stimulation liver to break down glycogen into glucose, fueling growth effects.
• 3) Inhibition of growth hormone?

  • High IGF-1 levels perceived by hypothalamus
  • Growth hormone-inhibiting hormone (GHH) is released to inhibit GH release
  • GHH inhibits GH release in the anterior pituitary
• What are the mechanisms and effect of growth hormone release?

  • 1 Release of growth hormone
  • 2a. Glucose-sparing effect
  • 2b. Growth effects and targets
  • 2c. Diabetogenic effects
  • 3. Inhibition of growth hormone.
• Explain the thyroid gland?


  • The thyroid gland lies anterior to the trachea
  • The medial portion is called the isthmus, and on either side are the right and left lobes
  • The parathyroid glands are embedded into the posterior surface of the two lobes
• Associated hormones produced by the thyroid gland?

  • Thyroxine (T4), triiodothyronine (T3)
  • Calcitonin (by C-cells)
• Effects of Thyroxine (T4), triiodothyronine (T3)


  • Stimulate basal metabolic rate
  • Stimulate sympathetic activity
  • Stimulate growth and CNS development
• Effect of calcitonin?


  • Reduces blood Ca2+ levels
• Functions of calcium?


  • Hormonal secretion
  • Coagulation system
  • Contraction of smooth an striated muscles
  • Neuronal regulation
  • Bone/Teeth resistance
  • Cardiac contractility and conduction
• Explain the parathyroid gland?


  • There are four parathyroid glands in most individuals, but some might have more.
  • There are two cell types:
  • oxyphil cells - unknown function
  • Chief cells
• What is the function of chief cells?


  Produce and secrete parathyroid hormone (PTH) in response to low blood calcium levels.
• What are the pancreatic hormones?


  • Insulin
  • Glucagon
• Describe the pancreas?

  The pancreas is both exocrine and endocrine
• What does the exocrine portion secrete?


  Digestive enzymes
• Explain the endocrine portion (the islets of Langerhans) of the pancreas?


  It is made up of different cell types:

  • Alpha cells - produce glucagon
  • Beta cells - produce insulin
• What are the functions of insulin?


  • Facilitates glucose transport into the cells
  • Accelerates glucose use
  • Stimulates glycogenesis (skeletal muscles and liver cells)
  • Inhibits glycogenolysis
  • Inhibits gluconeogenesis
• What is type 1 insulin deficiency (diabetes mellitus)?


  • Autoimmune
  • Does not produce insulin
• What is type 2 insulin deficiency (diabetes mellitus)?


  The body does not respond to insulin
• Explain the adrenal gland?


  • The adrenal glands lie on the superior surface of the kidneys
  • They have an inner medulla and an outer cortex layer which is subdivided into 3 regions
• What are the three subdivisions of the cortex layer?

  • Zona glomerulosa
  • Zona fasciculata
  • Zona reticularis
• What are the hormones released by zona glomerulosa?


  Mineralocorticoids (regulate mineral balance). Example Aldosterone
• What are the hormones released by zona fasciculata?


  Glucocorticoids (regulate glucose metabolism). Example cortisol, corticosterone, cortisone
• What are the hormones released by zona reticularis?


  Androgens (stimulate masculinisation). Example Dehydroepiandrosterone
• What are the hormones released by adrenal medulla?


  Stress hormones (stimulate sympathetic ANS). Example Epinephrine and norepinephrine.
• What is the effect of aldosterone?


  Increase blood Na+ levels
• What is the effect of cortisol, corticosterone and cortisone?


  Increase blood glucose levels, protein breakdown, anti-inflammatory effects, depression of immune response.
• What is the effect of adrenaline and noradrenaline?


  Stimulate fight-or-flight response
• Describe the pineal gland?


  The pineal gland is made up of pinealocytes; cells that produce and secrete the hormone melatonin (derived from serotonin)
• How does the regulation of melatonin production by the pineal gland relate to light exposure?

  •Melatonin production varies with the level of light in the external environment. Light in the retinas triggers a nerve impulse to the suprachiasmatic nucleus (SCN) in the hypothalamus.

  •The SCN then signals the pineal gland, inhibiting melatonin production. This promotes wakefulness and also influences appetite and body temperature.
• How does the heart have secondary endocrine function?


  • The atrial natriuretic peptide (ANP) is produced in the walls of the atria in response to stretch. It is a vasodilator and triggers sodium excretion in the kidneys reducing blood volume. It also inhibits renin secretion
• How does the stomach and small intestine have secondary endocrine function?

  Hormones are secreted by cells in the mucosa

  •Gastrin is secreted in response to stomach distention.

  •Secretin is secreted in the small intestine to trigger the regulation of the pH of the acidic chyme

  •Cholecystokinin (CCK) is also secreted in the small intestine. It stimulates secretion of pancreatic enzymes and bile