Chapter 45: the endocrine system

Chemical signaling

• A molecule released by one cell that may influence the activity of another cell • Local regulator: the molecule travels a short distance through the interstitial fluid, the

cell influenced in nearby • Neurotransmitter • Paracrine signals

• Histamines, cytokines, nitric oxide, prostaglandins (inflammation, pain), adenosine diphosphate

• Autocrine signal

• Hormones: the molecule travels through the circulatory system, the cell influenced may be far away

• Pheromone: the molecule is released by organism, the cell influenced is in another organism

Hormones:

• Polar or non polar • Steroid or amine/polypeptide/protein In order to work, the chemical signals need to come in contact with a receptor protein:

• Required for a cell to respond to a chemical signal • They are very specific (lock and key) • Different cells may respond differently to the same chemical signal • They could be found on the plasma membrane or inside the cell (intracellular)

• Polar molecules can't pass through the plasma membrane, non polar molecules can

Signal transduction: the linkage of a mechanical, chemical or electromagnetic stimulus to a specific cellular response.

• Second messengers: • cAMP ( cyclic adenosine mono phosphate) is a common second messenger • Cascade of reactions: amplifies the response

• Ex: 1 molecule can trigger the release of about 100 million molecules of glucose

• Ca+

Endocrine system

• Hormone system • Endocrine gland: ductless gland that secretes hormones directly into the interstitial

fluid, from which they diffuse into the bloodstream • Coordinating the activity of cells in different parts of the body

• The human endocrine system • Pineal gland: in the brain • Pituitary gland • Hypothalamus • Thyroid gland in neck

• Parathyroid glands on thyroid gland • Adrenal glands in abdomen ( on top of kidneys) • Pancreas • Ovary and testis

Hypothalamus and pituitary gland

• Master endocrine gland • Releases many hormone

• Some influence other endocrine glands • Hypothalamus produces hormones but it doesn't release them, they are sent to the

posterior pituitary, where they are released • Posterior pituitary releases 2 hormones

• ADH: anti diuretic hormone = vasopressin • Polypeptide • Released in response to increased osmolarity of blood plasma • Receptors:

• Distal tubules of nephridia (nephrons) • Response: increased permeability to water, which allows more water

to be absorbed from the filtrate • Collecting ducts:

• Response: increased permeability to water and urea, which allows more water and urea to be reabsorbed

• Thick ascending limb of loop of henle of nephridia • Response: increased active transport of sodium from filtrate

• Increased absorption of salt • Oxytocin

• Muscle of uterus • contraction

• Pressure on cervix • Mechanoreceptors (neurons that respond to pressure) that

stimulate the production of more oxytocin (positive feedback) • Induced labor: when a small amount of oxytocin is injected

• Anterior pituitary also produces hormones

• Thyroid and parathyroid fig 45.20 • Involved in maintaining homeostasis of blood ca2+ levels • A blood calcium levels drop, PTH is produced

• stimulates calcium release from bones • Stimulates calcium uptake in kidneys