Exocrine glands
release enzymes to the external environment through ducts
ex: sweat, oil, mucous, digestive glands
endocrine glands
release hormones directly into the blood stream
Receptors
Hormones act by binding to protein receptors. Receptors are highly specific to a particular hormone. Some hormones have receptors on virtually all cells, while others have receptors only on specific tissues.
Three basic chemical types of hormones
- peptides
- steroids
- tyrosine derivatives
Peptide hormones
Are water soluble and thus move easily through blood but cannot diffuse through the cell membrane of the target tissue (effector)
How peptide hormones are synthesized
- Manufactured in the rough ER as preprohormones that are larger than the active hormones
- Preprohormone is cleaved in the ER lumen to become a prohormone
- Transported to Golgi apparatus where the pro hormone is cleaved and sometimes modified with carbohydrates to produce the hormone’s final form
Anterior pituitary hormones
- FSH
- LH
- ACTH
- HGH
- TSH
- prolactin
Posterior pituitary hormones
ADH and oxytocin
parathyroid hormone
PTH
pancreatic hormones
glucagon and insulin
thyroid C cell hormone
calcitonin
steroid hormones
derived from cholesterol
This is a lipid so hydrophobic, which means it usually requires a protein transport molecule (carrier protein) to dissolve in the bloodstream
How steroid hormones work
They diffuse through the cell membrane of the effector and inside the cell combine with a receptor in the cytosol or nucleus and act at the level of transcription. Thus, the typical effect of a steroid hormone is to increase certain membrane or cellular proteins within the effector.
steroid hormones from the adrenal cortex
glucocorticoids and mineral corticoids cortisol and aldosterone
gonadal hormones
estrogen, progesterone, testosterone
Tyrosine derivative hormones
T3, T4, and catecholamines formed in the adrenal medulla: epinephrine and norepinephrine
thyroid hormones
- -T3 and T4
- -lipid-soluble so need to be carried by protein carriers
- -Slowly released to their target tissues and bind to receptors inside the nucleus
- -increase the transcription of large numbers of genes in nearly all cells of the body
epinephrine and norepinephrine
are water-soluble so they dissolve in the blood
–Bind to receptors on the target tissue and act mainly through the second messenger cAMP
