Ch. 5 Endocrinology

neuroendocrine system

• interaction between the hypothalamus and the pituitary gland

• endocrine system releases hormones into the blood, nervous system releases neurotransmitters to relay messages

glands

• secrete hormones directly into the blood

• endocrine glands do not possess ducts, hormones just go right into the bloodstream

2 types of hormones

steroid and amino acid

steroid hormones

• come from cholesterol

• need a blood transporter but can pass easily through the membrane

• acts directly on DNA in the cell

• ex: testosterone

AA hormone

• come from amino acids

• flow freely in the blood but need a receptor protein to start a secondary messenger cascade

• ex: cyclic AMP

how to remove hormones from the blood

excrete by the urinary system, or turn off/metabolize by the liver

the effect of a hormone acting on a tissue is determined by…

• plasma concentration

• number of active receptors

what is plasma concentration determined by?

• rate of secretion of a hormone from a gland

• rate of metabolism or excretion by the liver and kidneys respectively

• number of transport proteins

• changes in plasma volume

the magnitude of the effect for a peptide hormone is dependent on…

• concentration of the hormone

• number of the receptors in the cell

• affinity of the receptor for the hormone

downregulation

decrease in receptor number in response to high concentration of a hormone (diabetes)

upregulation

increase in receptor number in response to low concentration of the hormone (resistance training increases receptor content 48-72 hours after exercise)

3 ways hormones act

• activate genes to alter protein synthesis (steroid only)

• 2ndary messenger cascade (peptide only)

• alter membrane transport

major endocrine glands

• hypothalamus and pituitary glands

• thyroid and parathyroid

• adrenal glands

• pancreas

• testes and ovaries

hypothalamus and posterior pituitary

• direct innervation between these 2 glands (neurohypophysis)

• hormones release directly into the blood

• main hormones from PP: ADH and oxytocin

hypothalamus and anterior pituitary

• uses portal system to communicate (capillary bed)

• releasing hormone travels from hypo to AP to release another hormone

• major hormones: ACTH, FSH, LH, MSH, TSH, GH, prolactin

ACTH (cortisol from adrenal glands)

corticotropin-releasing hormone

FSH and LH (estrogen and testosterone); gonads

gonadotropin-releasing hormone

TSH (thyroid hormone release from thyroid gland)

thyroid-releasing hormone

Prolactin; mammary gland

thyrotropin-releasing/prolactin-releasing hormone

GH; liver and all body

GHRH (positive affect) and Somatostatin (negative affect)

Growth hormone

• both tropic and non-tropic (goes to liver to release IGF-1s and also acts on rest of bodily tissues)

• both pulsatile and diurnal (levels fluctuate; levels are higher at night)

• higher release during exercise

• acutely catabolic from exercise and chronically anabolic due to IGF-1s (responsible for muscle growth)

what does GH do during exercise?

• blocks insulin to reduce usage of blood glucose (use fats for longer)

• increase gluconeogenesis in the liver

• increase lipolysis for beta-oxidation

ADH

• acts in the kidneys

• works in conjunction with aldosterone to control water and salt retention to chronically control BV which controls BP

• levels increase during exercise (60% VO2max) to maintain plasma volume