endocrine system Flashcards
endocrine system action
one of 2 communication systems in the body, acts by glands releasing chemicals (hormones) into the blood stream, the hormones come in contact with all of the body tissues but only react with those that contain receptors specific for that hormone. when this happens, it triggers the body to either do something or release a different hormone.
how is the amount of hormone released regulated?
positive and negative feedback loops. all hormones have different half-lives or amounts of time they stay present in the blood stream
GnRH
triggers the release of hormones affecting the gonads, such as FSH and LH
what systems does the endocrine system affect?
the endocrine system effects many different tissues in the cardiovascular, digestive, reproductive and renal systems
how is the repro system controlled?
by the fluctuation of hormones triggered by various external and internal stimuli
progesterone
pregnancy hormone produced by a corpus luteum, stopped by prostaglandin, trade names=regumate, LAP4
estrogen
causes “in heat” behavior, produced by the developing follicle and increases as the follicle grows
FSH
stimulates the growth of a follicle, used to get horses to start cycling. governs sperm production in stallions
LH
causes ovulation, causes the formation of the corpus luteum in the follicle after the ovulation in mares, stimulates testosterone production in stallions trade names=hCG, deslorelin
what type of breeders are horses?
polyestrous seasonal breeders, they have multiple estrus cycles within their breeding season, but will go into a period of anestrous during the off season
when do horses birth their young?
in the spring, horses naturally begin cycling in mid to late spring.
what induces estrus?
the amount of daylight perceived in the pineal gland
pineal gland
when no light is available, the pineal gland produces a hormone called melatonin, preventing the release of GnRH. As day length increases the amount of melatonin produced decreases and the hypothalamus produces more GnRH.
what does GnRH act on?
the pituitary gland, stimulating the release of FSH and LH. this happens in both mares and stallions
hypothalamus
gland located in the brain, exerts primary control over the so-called sympathetic response of the autonomic nervous system by means of both hormones and nerves. indirectly controls most of the other glands
ovaries
found only in females, located in the upper hindquarters. hold and release ova (female gametes) for reproduction. hormones produced by the ovaries include estrogen and progesterone
pancreas
located at the small intestine, plays a crucial role in digestion. maintains the body’s sugar level through insulin which removes sugar from the blood and glycogen
pituitary
located in the base of the brain stem, “the master gland” because it has a strong influence over growth, over milk production, over adrenal gland production, over the thyroid gland etc.
testes
found only in males, part of the external genitalia, produce sperm, hormone produced is testosterone, responsible for muscle growth
thymus
located near the lungs, crucial to the immune system because it is essential for the production of both white blood cells and antibodies
thyroid
located in the throat, controls the level of certain chemicals or minerals in the blood, especially calcium and regulates metabolism
prostiglandin F2alpha
lyses the porous luteum and causes the mare to begin another cycle, causes smooth muscle contractions. trade names=lutalyse, estrumate
oxytocin
causes smooth muscle contractions, allows for milk let down, it can also remove fluid from uterus and induce parturition
testosterone
promotes muscle growth, increases appetite. can cause aggressive behavior and other major side effects, trade name=equipoise, winstrol/stanozol
