The Endocrine System: Chemical Signals in Animals

Regulatory systems Hormone~ chemical signal secreted into body fluids (blood) communicating regulatory messages Target cells~ body cells that respond to hormones (usually by having the correct “receptor sites”) Endocrine system/glands~ hormone secreting system/glands (ductless); as opposed to….. Exocrine glands which secrete chemicals (sweat, mucus, enzymes) through ducts Neurosecretory cells~ nerve cells that secrete (not actually produce) hormones Feedback mechanisms ~ negative and positive

Some Hormones are just Local Regulators: cells adjacent to or near point of secretion Examples include: Growth factors ~ proteins for cell proliferation Nitric oxide (NO) ~ neurotransmitter; cell destruction; vessel dilation Prostaglandins ~ modified fatty acids. Secreted by placenta and immune system; also found in semen

2 main Modes of Action: 1- Plasma membrane reception. Sometimes referred to as “peptidal”. Use signal-transduction pathways. Neurotransmitters, some growth factors, most hormones. Very quick acting, but also wear off quickly. 2- Cell nucleus reception. Sometimes referred to as “steroidal”. Sex hormones, many growth factors, thyroid hormones, some local regulators. Slower to act, but longer lasting than peptidal hormones. Animation!l

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 Pituitary: Anterior pituitary: Consists of 2 Lobes: Anterior & Posterior Anterior pituitary: aka “adenohypophysis” Growth Hormone(GH)~stimulates production of growth factors √gigantism/dwarfism √acromegaly Prolactin (PRL)~mammary glands; milk production Follicle-stimulating (FSH) and… Luteinizing (LH)~ both tropic hormones for spermatogenesis, egg maturation, ovulation. Thyroid-stimulating (TSH)~ tropic for thyroid hormones. Adrenocorticotropic (ACTH)~ tropic for adrenal cortex hormones… Melanocyte-stimulating (MSH) Endorphins~natural ‘opiates’; brain pain receptors

The Pituitary continued…. The Posterior Pituitary: Aka _ Neurohypophysis Technically only stores and secretes hormones which are actually produced in the hypothalamus. Only 2 this time: Oxytocin~uterine and mammary gland cell contraction. (Pitosin- Synthetic version of oxytocin used to induce contractions.) Antidiuretic Hormone(ADH)~ regulates blood osmolarity. Causes retention of water by kidneys by increasing permeability of tubules. Alcohol inhibits production. Osmorecepters in hypothalamus shrink from low water levels to start production.

The pineal, thyroid, & parathyroid Pineal gland: Melatonin~; biological rhythms Thyroid Gland hormones: Thyroxine- regulates metabolism by increasing rates of oxygen consumption. Regulated by TRH (from hypothalamus) & TSH (from the pituitary) Hyperthyroidism- high temps, sweating, weight loss Hypothyroidism- cretinism, weight gain, cold Calcitonin~lowers blood calcium is antagonistic to…. Parathyroid Gland- Parathyroid Hormone(PTH)~ raises blood calcium by decomposing bones to release calcium into the blood.

The Pancreas “Islets of Langerhans” which have... Link …is mostly an exocrine gland for digestive enzymes except for clusters of cells called: “Islets of Langerhans” which have... Alpha cells which produce: •Glucagon~ raises blood glucose levels by hydrolyzing the glycogen in the liver and Beta cells which produce: •Insulin~ lowers blood glucose levels by causing cells to take in more and slowing glycogen breakdown. (antagonistic to glucagon) Type I diabetes- juvenile onset, insulin-dependent; autoimmune disorder, little or no insulin production. Type II diabetes- adult onset. non-insulin-dependent; reduced responsiveness in insulin targets. Link

The Adrenal Glands Adrenal medulla (catecholamines): •epinephrine & norepinephrine~(you might know these collectively as “Adrenaline”) secreted in times of stress when excited nerves release extra acytlecholine which rapidly increases basal metabolic rate by: Mobilizing glucose to skeletal muscle Increasing rate & stroke volume of heart, shunting more blood to muscles Dilating the bronchioles. Important for short term stress.

The Adrenal Glands, continued…. Adrenal cortex (corticosteroids): 2 types: •glucocorticoids (cortisol)~ raise blood glucose, has immunosuppressive effects. •mineralocorticoids (aldosterone)~ reabsorption of Na+ and K+, raises blood pressure. Initiated by ACTH (AdrenoCorticoTropic Hormone) Cortical hormones important in maintaining homeostasis during extended stress.

The gonads Steroid hormones: Androgens –Male Hormones Testosterone- precursor is cholesterol Androgens –Male Hormones Testosterone- Produced by the testes sperm formation; male secondary sex characteristics The female sex hormones include: Estrogens- (estradiol)~uterine lining growth; female secondary sex characteristics and Progestins- (progesterone)~uterine lining growth All of these are controlled by gonadotropin

More Hormone Animations!! D:\bc_campbell_biology_7\0,7052,3117253-,00.html