Endo 1

• Roles:

  1. Homeostasis: Maintenance of the internal environment
  2. Metabolic regulation: Storage and use of energy substrates
  3. Responses to external stimuli
  4. Control of growth, reproduction and development
• Hormone is a chemical substance released by a group of cells to control the function of other type of cells
• Types of hormone

  • Affect many different types of cells (GH and Thyroxine)
  • Affect only specific target cells (ACTH and Estrogen)
• Other tissues and organs that produce hormones: Adipose cells, pockets of cells in the walls of the small intestine, stomach, kidneys, and heart
• Neurohormone: Specialized neurons that secrete chemicals into the blood rather than synaptic cleft

  • Chemical secreted is called neurohormone
• Endocrine signaling: Released into the blood
• Paracrine signaling: Acts on neighboring cells
• Autocrine signaling: Acts on the same gland or cell
• The multiple hormone systems play a key role in regulating almost all body functions: Metabolism, Growth and development, Water and electrolyte balance, Reproduction, Behavior
• Released into and carried via bloodstream to target tissues
•  Target cells refer to cells that contain specific receptors (binding sites) for a particular hormone
• Steroids

  • Secreted by gonads, adrenals cortex, and placenta
  • Derived from cholesterol --> Fat-soluble

  1. Cross membrane (no storage)

  • Usually bound to carrier proteins
  • Secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and progesterone), the testes (testosterone), and the placenta (estrogen and progesterone)
• Protein and polypeptide

  • Can dissolve in water

  1. Pancreas (insulin and glucagon), the parathyroid gland (parathyroid hormone), and many others
• Amine hormone

  • Derived from amino acid tyrosine

  1. Thyroid hormones, epinephrine and norepinephrine (produced by the adrenal medulla), and dopamine (produced by the hypothalamus)
• Nonsteroid hormones (first messengers) mechanism

  1. Hormone-receptor interaction (first messenger)
  2. Enzyme activation
  3. Release of the second messenger which is cyclic AMP (cAMP)
  4. Effects on cellular function
• Steroid hormones mechanism: Pass through the cytoplasm and enter nucleus where they bind with a receptor (lock-and-key model)
• Receptors

  1. Hormonal receptors are large proteins
  2. 2000-100,000 receptors/cells
  3. Receptors are highly specific for a single hormone
• Receptors location: Surface of cell membrane (peptides and catecholamines), cytoplasm (steroids), nucleus (thyroid hormones)
• Two factors that control the concentration of a hormone in the blood

  1. Rate of secretion
  2. Rate of removal
• Hormones are cleared by:

  • Metabolic destruction by tissues
  • Excretion by the liver into bile
  • Excretion by the kidney into urine
• Clearance of protein-bound hormones is slower than clearance of peptide hormones
• Negative feedback: Returns the body back to normal, most feedback in the body is negative
• Positive feedback: Enhances the stimuli, usually seen during childbirth