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Antidiuretic hormone

Stimulates the kidneys to reabsorb water



- stimulates the contraction of uterine muscles during childbirth (an example of positive feedback) - stimulates milk release in breastfeeding


Mechanism for posterior pituitary hormone secretion

1) stimulus: neural input to hypothalamus 2) hypothalamus signals posterior pituitary to release stored hormones by neural stimulation 3) ADH or oxytocin released into blood


How the hypothalamus communicates with the posterior pituitary

- hypothalamus is connected to the posterior lobe by neurons - PP hormones are made in hypothalamus, travel down axon and stored at axon ending until required


How the hypothalamus communicates with the anterior pituitary

- hypothalamus communicates with the anterior lobe by hormones in blood vessel - AP hormones are made in AP by specific cells


Mechanism for anterior pituitary hormone secretion

1) stimulus: neural input into hypothalamus 2) hypothalamus signals the anterior pituitary to release hormones by hormonal stimulation, releasing hormones (or inhibiting hormones) 3) hormone binds to receptor on membrane of a specific cell type and a specific peptide hormone is secreted


Growth hormone secretion sequence

1) Stimulus - stress, sleep, exercise, fasting 2) Hypothalamus - releases GHRH into bloodstream 3) Anterior pituitary - secretes growth hormone into bloodstream 4) Liver and other cells - increase in IGF-1 (growth factor) secretion 5) Metabolic effects


metabolic effects of GH

increased protein synthesis and decreased glucose uptake in muscle, increased glucose synthesis in liver, increased fat breakdown by mobilising fatty acids


GH disorders

- hyposecretion (too little) - dwarfism - hypersecretion (too much) - gigantism - Hyposensitivity (little or no response) - Hypersensitivity (respond too much)


GH function

promotes the growth of bones, muscles and other tissues by stimulating cell division


pituitary gland location

base of brain, attached to hypothalamus



chemical messengers produced in one location and transported to a second location where they cause a response in those cells


functions of endocrine system

Regulates our internal environment by secreting hormones into the bloodstream.


Endocrine gland

secrete hormones


major endocrine glands

hypothalamus, pituitary, thyroid, thymus, adrenal, testes


Specificity of Hormone action

Target cells have specific receptors proteins that allows for specific and close hormone-target cell interaction


hormone receptors for peptides and catecholamines

located on plasma membrane of target cell because they are water-soluble to cannot cross lipid bilayer


hormone receptors for lipid-soluble hormones

located in cytoplasm (steroid hormones) or nucleus (thyroid hormones) because can diffuse across the cell membrane into target cell


response to receptor activation of water-soluble hormones

  1. Water-soluble hormone binds to cell surface receptor
  2. Hormone binding allows activation of associated (G-) protein
  3. G- protein activates adenylyl cyclase
  4. Second messenger production e.g. cyclic AMP (cAMP)
  5. cAMP activates protein kinase
  6. Protein kinase activates specific enzyme Enzyme converts specific substrate to product (cell’s specific response)


what determines amount of hormone in blood

  • Rate of production – controlled by negative feedback loops (usually)
  • Rate of removal – controlled by enzymes in the bloodstream 


response to  receptor activation for lipid-soluble hormones (steroid and thyroid hormones)

  1. Lipid-soluble hormone dissociates from carrier protein
  2. Hormone diffuses across cell membrane
  3. Hormone binds to INTRACELLULAR receptor
  4. Hormone-receptor complex acts as a specific transcription factor
  5. New mRNA is generated
  6. New protein is generated by translation of mRNA
  7. New protein mediates cell’s specific response (SLOW PROCESS)


lipid soluble vs water soluble hormones


comparison of endocrine and neural control systems

Neuronal (action potentials in axons and neurotransmitter release at synapse)

  • Targeting achieved by specific wiring
  • Fastest transmission speed to minimise response delays
  • Good for brief responses

Hormonal (hormones released into blood)

  • Targeting by expression of specific receptors on target cells
  • Relatively slow, but long-lasting action
  • Good for widespread and sustained responses


pancreas and islets

  • Head and neck in the C-shaped curve of the duodenum and the body extends behind the stomach
  • Endocrine tissues called pancreatic islets are dispersed throughout the pancreas (~2% of mass)
  • Beta cells secrete insulin
  • Alpha cells secrete glucagon


fed state

cellular uptake of nutrient and anabolic metabolism (synthesis of glycogen, protein and fat)


fasting state

mobilisation of nutrient and catabolic metabolism (breakdown of glycogen, protein and fat)


blood glucose regulation

  • If blood glucose concentration rises above 6mmol/L insulin is secreted
  • If blood glucose concentration drops below 3.5mmol/L glucagon is secreted
  • Negative feedback for insulin release
  • Also feedforward reaction- while eating, the pancreas releases insulin (signal from gastro-intestinal tract to pancreas)


sequence of events that occurs when blood glucose concentration increases above the reference range

effects on muscle cells:

  • amino acid uptake so protein synthesis
  • glucose uptake so glycogen synythesis

effects on adipose cells:

  • glucose uptake so fat synthesis

effects on liver cells: