Module 16: Endocrine System

Endocrine System

Acts with nervous system to coordinate & integrate activity of body cells. Influences metabolic activities is hormones transported in the blood. Response is slower, but lasts much longer longer than signals from nervous system

Exocrine glands

Secrete non-hormonal substances(sweat, saliva) into a network of ducts

Endocrine glands

directly secrete hormones into the bloodstream

Hormones

Long-distance chemical signals that work at very low concentrations

Half-life

The rate of hormone breakdown in circulation, the amount of time required to reduce the concentration of hormone by one-half. How long a hormone is active in the body.

Preprohormone

Contains one or more copies of the peptide hormone, including a signal sequence directing movement into the Rough ER

Peptide/Protein Hormones

Made in advance and stored in secretory vesicles. Water-soluble/hydrophilic←degradation enzyme, short half-life, must bind to membrane bound receptors to signal via secondary messenger systems (fast)

Steroid Hormones

Synthesized from cholesterol, hydrophobic, and must be transported by carrier proteins into the blood. Longer half-life and ability to diffuse across the plasma membrane. Hormones secreted by gonads and adrenal cortex, heavily modified with smooth ER

Amino Acid derived Hormones

Derived from either tryptophan (melatonin) or tyrosine

Water soluble hormones

Protein/peptide and all amino acid based hormones except thyroid hormone. A on plasma membrane receptors and work through secondary messenger systems

Lipid soluble hormones

Steroid and thyroid hormones. Act on intracellular receptors that directly activate genes

Up-regulation

Target cells form more receptors in response to low hormone levels, making them more sensitive to the signal

Down-regulation

Target cells loose receptors in response to high hormone levels, making them less sensitive to the signal

Humoral stimuli

Changing blood levels of ions/nutrients directly stimulate secretion of hormones (sensed by chemoreceptors)

Neural stimuli

Nerve fibers directly stimulate hormone release. NS can override endocrine functions esp during periods of extreme stress

Hormonal stimuli

Hormones stimulate other endocrine organs to release their hormones

Tropic hormones

Cause hormones to be released from other endocrine tissues

Trophic hormones

Tropic hormone that additionally triggers growth in the target tissue

Parathyroid hormone PTH

Controls Ca2+ homeostasis. Detects low [Ca2+] in the plasma

Posterior Pituitary

An extension of the hypothalamic neural tissue where the hormones are synthesized in the cell body (residing in. The hypothalamus) but released from the axon terminals (in the posterior pituitary). Oxytocin and ADH/Vasopressin

Oxytocin

Strong stimulant of uterine contractions as it is released during childbirth, but it also acts a neurotransmitter in the brain & a hormonal trigger for milk ejection

ADH/Vasopresin

Inhibits excessive urine production by regulating water balance in the kidneys