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Chemical Signals in Animals 9. c. Students know how
feedback loops in the nervous and endocrine systems regulate conditions in the body.
9. i.* Students know how hormones (including digestive, reproductive, osmoregulatory) provide internal feedback mechanisms for homeostasis at the cellular level and in whole organisms.
Feedback Loops
Feedback loops are how the nervous system uses the endocrine system to regulate body conditions.
The presence or absence of hormones in blood brought to the brain by the circulatory system will trigger an attempt to regulate conditions in the body.
Hormone Example The hormone leptin, which fat cells
produce as they become filled with storage reserves.
Leptin is carried by the blood to the brain, where it normally acts to stop hunger
An example of negative feedback. When fat reserves diminish, the concentration of leptin decreases, a phenomenon that in turn causes the appetite center in the brain to start the hunger stimulus and activate the urge to eat.
Hormones work with the Nervous System
For ex-ample, in the digestive system, where insulin released from the pancreas into the blood regulates the uptake of glucose by muscle cells.
The pituitary master gland produces growth hormone for controlling height.
Mode of Action: Chemical Signaling 1- Plasma membrane reception
• signal-transduction pathways (neurotransmitters, growth factors, most hormones)
2- Cell nucleus reception • steroid hormones, thyroid hormones, some local regulators
Vertebrate Endocrine System Tropic hormones ~
a hormone that has another endocrine gland as a target
Hypothalamus~pituitary Pituitary gland Pineal gland Thyroid gland Parathyroid glands Thymus Adrenal glands Pancreas Gonads (ovary, testis)
The hypothalamus & pituitary, I Releasing and inhibiting hormones Anterior pituitary: Growth (GH)~bones
√gigantism/dwarfism √acromegaly
Prolactin (PRL)~mammary glands; milk production
Follicle-stimulating (FSH) & Luteinizing (LH)~ovaries/testes Thyroid-stimulating (TSH)~ thyroid Adrenocorticotropic (ACTH)~
adrenal cortex Melanocyte-stimulating (MSH)
Endorphins~natural ‘opiates’; brain
pain receptors
The pituitary, II
The posterior pituitary: Oxytocin~
uterine and mammary gland cell contraction
Antidiuretic (ADH)~ retention of water by
kidneys
Pituitary Hormones
Follicle-stimulating hormone [FSH] and luteinizing hormone [LH] control the gonads
Thyroid-stimulating hormone [TSH] controls the thyroid, and adrenocorticotropic hormone [ACTH] regulates the formation of glucocorticoids by the adrenal cortex).
This master gland is itself controlled by the hypothalamus of the brain.
The pineal, thyroid, & parathyroid Melatonin~ pineal gland;
biological rhythms
Thyroid hormones: Calcitonin~
lowers blood calcium Thyroxine~ metabolic processes
Parathyroid (PTH)~ raises blood calcium
The pancreas
Beta cells: •insulin~ lowers blood glucose levels
Type I diabetes mellitus (insulin-dependent; autoimmune disorder)
Type II diabetes mellitus (non-insulin-dependent; reduced responsiveness in insulin targets)
The adrenal glands Adrenal medulla (catecholamines): •epinephrine &
norepinephrine~ increase basal metabolic rate (blood glucose and pressure)
Adrenal cortex (corticosteroids): •glucocorticoids (cortisol)~ raise blood glucose •mineralocorticoids (aldosterone)~ reabsorption of Na+ and K+
The gonads
Ovaries estrogens
(estradiol)~uterine lining growth; female secondary sex characteristics; gonadotropin
progestins (progesterone)~uterine lining growth
Testes Steroid hormones:
precursor is cholesterol
androgens (testosterone)~ sperm formation; male secondary sex characteristics;
gonadotropin
Regulatory systems Hormone~ chemical signal
secreted into body fluids (blood) communicating regulatory messages
Target cells~ body cells that respond to hormones
Endocrine system/glands~ hormone secreting system/glands (ductless); exocrine glands secrete chemicals (sweat, mucus, enzymes) through ducts
Neurosecretory cells~ actual cells that secrete hormones
Feedback mechanisms ~ negative and positive