Endocrine System

Chemical signals transported by the bloodstream that stimulate physiological responses in cells of another tissue or organ

• Nervous System communicates through neurotransmitters and release signals through the synapse and effect specific areas.
• Endocrine System communicate through hormones and release signals in bloodstream, effecting general areas.

• Ductless glands that secrete hormones
• Lots of capillaries to carry hormones

• Target organ cells have receptors specific to that hormone
• Some hormones have target organs through the body, others have only one.

Anterior pituitary: True gland

Posterior Pituitary: neural tissue

Adenohypophysis and Neurohypophysis

• Oxytocin is produced by neurons in the paraventricular nucleus.
• Antidiuretic hormone (vasopressin) produced by neurons in the supraoptic nucleus

• Receptor locations: mammary gland, uterus, and heart
• Causes uterine contractions during labor
• Allows letdown reflex during breastfeeding
• Some role in orgasm
• Some role in trust and empathy

• Receptor locations: kidney, liver, and vasculature
• Regulates water retention by kidneys
• Ethanol is ADH antagonist
• Increases blood pressure

• Characterized by excessive thirst and excretion of lots of dilute urine
• Typically caused by inability to make sufficient amounts of ADH

• Neurosecretory neurons in hypothalamus release "releasing hormone"
• RH enters hypophyseal portal system (small capillaries between hypothalamus and pituitary)
• Anterior pituitary cells with receptors for that RH are activated and secrete tropic hormones into general circulation

• Stimulates milk production in mammary glands
• Released after orgasm (refractory period?)

• Stimulated by GHRH
• Inhibited by somatostatin
• Widespread effects on body
• Induces mitosis and cellular differentiation in cartilage, bone, muscle, and fat
• Promotes protein synthesis, decreases protein metabolism
• Promotes lipid release and metabolism to spare the proteins and carbohydrates for growth and brain function
• Promotes electrolyte retention

• Stimulate GH:
• Sleep
• Vigorous exercises
• Good nutrition
• GOnadal hormones during puberty

Stress

GH stimulates IGF-I and II release from the liver, which prolongs GH's effects

• Bone, cartilage, and muscle growth
• Secret about 700 mg/day in adolescence

• Bone thickening and remodeling
• Secrete about 400 mg/day

Caused by a tumor in the pituitary gland that leads to excess GH secretion

• Expansion of soft tissue and bones, often accompanies gigantism.
• Due to excess GH secretion.

• Short Stature
• Delayed puberty
• Slow muscular development
• Causes: genetic mutation, pituitary tumor, radiation, trauma, or surgery to the head

• In normal adults, GH causes increase in water retention, increase in connective tissue, decrease in fat
• No increase in muscle strength
• Recover faster from injury
• Stamina may be decreased

• GH is given to cows to increase milk production
• Not legal to use GH in cows raised for beed or in poultry or pigs
• rBST milk: higher IGF-I levels, more pus (sours faster), sometimes lower nutritional quality

Causes target organ to release its own hormone

• Largest endocrine gland
• Reddish brown due to lots of blood flow
• In response to thyroid stimulating hormone from the pituitary, it secretes "thyroid hormone"
• Thyroxine or Tetraiodothyronine (T4)
• Triiodothyronine (T3)

• Synthesized by iodine
• Increase metabolic rate
• Increase heart and respiratory rates
• Increase heat production
• TH levels in rise in cold environments
• Promote alertness, growth hormone secretion, growth of bones, skin, hair, nails and teeth, development of fetal nervous system

• Follicular cells produce T3 and T4
• C cells secrete calcitonin in response to high blood calcium levels (promotes bone formation)

• Typically caused by iodine deficiency
• People living in inland regions of developing countries are susceptible
• Thyroid swells in attempt to capture more iodine

Hyperthyroidism: fatigue, heat intolerance, hyperactivity, weight loss

Hypothyroidism: fatigue, cold intolerance, joint pain, weight gain, bradycardia (slow heart rate)

• Estrogen, progesterone, some androgens, and inhibin secreted from granulosa and thecal cells
• Hormones secreted in response to FSH and LH from pituitary

• 3 estrogens: estradiol, estrone, and estriol
• Promotes secondary sexual characteristics
• Increase metabolic rate
• Reduce muscle mass
• Increase uterine growth
• Increase bone formation
• Influence mood, cognitive function, and libido

• Prepares the body for pregnancy
• Regulates immune response
• Decreases anxiety
• Probably neuroprotective effects

Interstitial (Leydig) cells secrete androgens in response to LH from pituitary

• Include testosterone and several weaker androgens (DHEA, DHT, and androstenedione)
• Promote sperm production
• Important for development of male genitalia
• Inhibit fat storage
• Promote muscle development
• Influence aggression, libido, cognitive function

Outer "bark"

• Mineralocorticoids from zona glomerulosa
• Glucocorticoids from zona fasciculata
• Sex steroids from zona reticularis

• Promotes salt and water retention by kidney
• Increases blood volume and blood pressure

• Cortisol (primary human glucocorticoid) released when ACTH binds
• Produces stress response by increasing alertness and blood glucose, inhibiting immune system, and affecting memory.

• Androgens: small amounts of testosterone, DHT, and DHEA; a major source of androgens for females
• Estrogens: small amounts of estradiol; important for postmenopausal women

• Caused by dysfunction of one of the enzymes needed to produce glucocorticoids and mineralocorticoids
• Result is overproduction of androgen

Excess testosterone in prenatal development can lead to masculinized genitalia, infertility, masculinized behavour

• Inner "Core"
• Modified part of sympathetic nervous system
• Chromaffin cells release epinephrine and norepinephrine into the bloodstream when SNS neurons release Acetylcholine

• Similar effects as remainder of sympathetic nervous system
• Increases heart rate and blood pressure, dilates airways, increases blood glucose levels, increases circulation to muscles, and inhibits digestion and reproduction