Endocrine System 7M

endocrine glands secrete very small amounts of chemical messengers in the extracellular fluid called

hormones

hormones circulate through the bloodstream to be transported to specific sites (for a specific response) called

target tissues or effectors

endocrine

from Greek words

endo - “within”

krino - “to secrete”

exocrine glands

have ducts that carry out their secretion to outer side of body

ex. saliva, sweat, breast milk, and digestive enzymes

study of endocrine system

endocrinology

chemical messengers

• allow cells to communicate with each other to regulate body activities

• some produced by nervous system, some by endocrine system

• most of these are produced by a specific collection of cells or by a gland

gland

an organ consisting of epithelial cells that specialize in secretion

the controlled release of chemicals from a cell

secretion

four (4) classes of chemical messenger based on source and way of transport

• autocrine chemical messengers

• paracrine chemical messengers

• neurotransmitters

• endocrine chemical messengers

autocrine chemical messengers

stimulates cell that originally secreted it

ex. WBC during infection - stimulate own replication to increase cell number rapidly

paracrine chemical messengers

secreted by one cell type, out in the extracellular fluid, and affect surrounding cells

ex. Histamine by WBC - stimulates vasodilation in nearby blood vessels

neurotransmitters

• secreted by neurons that activate an adjacent cell; whether another neuron, a muscle cell, or a glandular cell

• secreted by synaptic cleft rather than in bloodstream

• are like “paracrine” chemical messengers

endocrine chemical messengers

• secreted into bloodstream by certain glands and cells

• travels to reach target cells

functions of the endocrine system

1. regulation of metabolism

2. control of food intake and digestion

3. modulation of tissue development

4. regulation of ion levels

5. control of water balance

6. regulation of cardiovascular functions

7. control of blood glucose and other nutrients

8. control of reproductive functions

9. stimulation of uterine contractions

10. modulation of immune system function

regulation of metabolism (TH, Cortisol)

control rate of nutrient utilization and energy production

control of food intake and digestion (Insulin, GI hormones)

regulate level of satiation (fullness) and the breakdown of food into individual nutrients

modulation of tissue development (GH, TH)

influence the development of tissues i.e. nervous system

regulation of ion levels (Aldosterone, ANP, PTH, Calcitonin)

help monitor blood pH, aslo:

Na⁺, K⁺, and Ca⁺ concentrations in the blood

control of water balance (ADH, Aldosterone, ANP)

control solute concentration of blood as well as controlling membrane permeability

regulation of cardiovascular functions (TH, Cortisol, Aldosterone)

helps regulate heart and blood pressure and prepare the body for physical activity

control of blood glucose and other nutrients (Insulin, Glucagon)

regulate levels of glucose and other nutrients in the blood

control of reproductive functions (Androgens, Estrogen, Testosterone)

controls the development and function of reproductive systems in males and females

stimulation of uterine contractions (Oxytocin, Prolactin)

regulate uterine contractions during delivery and stimulate milk release from breast in lactating females

modulation of immune system function (Thymosin, Cortisol)

help control the production of immune cells

chemical nature of hormones

1. lipid - soluble hormones

2. water - soluble hormones

lipid - soluble hormones

• nonpolar

• insoluble in water based fluids, like plasma/blood

• travel in bloodstream attached to binding proteins

• degraded slowly and are not rapidly eliminated from circulation

water - soluble hormones

• polar molecules

• can dissolve in blood

• free hormones

• short lived lives because they are rapidly degraded by enzymes