1. The Endocrine System:
Chemical Signals in Animals

2. 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

3. 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

4. 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

5. 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)

6. 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

7. 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.

8. 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.

9. 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

10. 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.

11. 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.

12. 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

13. More Hormone Animations!!
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