Download Chapter 35.3 The Endocrine System (pages

Chapter 35.3 The Endocrine System (pages 1031-1037)
NOTES
A. Action of Hormones
a. Steroid Hormones
i. Examples : estrogen and testosterone
ii. All steroid hormones work by causing target cells to initiate protein
synthesis
iii. Soluble in lipids, can diffuse through plasma membrane of target cell
iv. Diagram - A steroid hormone passes through a cell membrane, binds to a
receptor within the cell, and stimulates protein synthesis
b. Amino Acid (non-steroid)Hormones
i. Examples: insulin and growth hormones
ii. Bind to receptors on plasma membrane of target cell because can’t diffuse
through plasma membrane
iii. Biochemical pathway initiated causing cell to produce desired response
iv. Diagram – An amino acid hormone binds to a receptor on plasma
membrane before entering cell
B. Negative Feedback
a. Homeostasis in the body is maintained by internal feedback mechanisms called
negative feedback
b. Negative feedback returns a system to a set point once it departs enough from
that set point
c. Example : thermostat in the home
i. House maintained at a certain temperature
ii. Gets cold, thermostat turns on to heat the house
iii. Once desired temperature is reached, thermostat turns off
iv. Process continues or “loops” at temperature drops and increases
C. Endocrine Glands and Their Hormones
a. Endocrine system includes all the glands that secrete hormones – pituitary,
thyroid, parathyroid, and adrenal glands, pancreas, ovaries, testes, pineal gland,
and thymus gland.
b. Pituitary gland
i. Located at base of brain
ii. “Master gland” because it regulates so many body functions
iii. Regulates other glands – thyroid gland, adrenal glands, ovaries, and testes
iv. Human growth hormone (hGH) regulates body’s physical growth by
stimulating cell division in muscle and bone tissue (especially active during
childhood and adolescence)
c. Thyroid and parathyroid glands
i. Thyroid gland produces
1. Thyroxine - doesn’t act on specific organs, causes cell to have higher
rate of metabolism
2. Calcitonin – partly responsible for regulation of calcium, blood
clotting, nerve function, muscle contraction; lowers blood calcium
levels by signaling bones to increase calcium absorption and kidneys
to excrete more calcium
ii. Parathyroid gland
1. Parathyroid hormone – increases blood calcium levels by stimulating
bones to release calcium, causing kidneys to reabsorb more calcium,
and intestines to absorb more calcium from food
iii. Thyroid and parathyroid glands have opposite effects on blood calcium
levels but work together to maintain homeostasis
d. Pancreas
i. Crucial role in production of enzymes that digest carbohydrates, proteins,
and fats
ii. Secretes insulin and glucagon which work together to maintain
homeostasis
1. High glucose levels
a. Causes pancreas to release insulin, which signals body cells
(liver and muscle cells) to increase conversion of glucose to
glycogen (stored in liver)
2. Low glucose levels
a. Glucagon released from pancreas, which binds to liver cells,
signaling them to convert glycogen to glucose and release
glucose into blood
e. Adrenal glands
i. Located just above kidneys
ii. Cortex
1. Outer part of adrenals
2. Makes steroid hormone aldosterone and glucocorticoids
a. Aldosterone primarily affects kidneys and important for
absorbing sodium
b. Cortisol (glucocorticoid) raises blood glucose levels and
reduces inflammation
3. Adrenaline rush
a. A sudden burst of energy during s stressful situation
b. Adrenaline (epinephrine) and norepinephrine increase heart
rate, blood pressure, breathing rate, and blood sugar levels
which are important in increasing activity of body cells
D. Link to the Nervous System
a. Nervous and endocrine systems both involved in regulating activities of body and
maintaining homeostasis
b. Hypothalamus involved in maintaining homeostasis
i. Produces two hormones – oxytocin and antidiuretic hormone (ADH)
ii. Transported through axon and stored in axon endings in pituitary gland
c. Antidiuretic hormone
i. Functions in homeostasis by regulating water balance
ii. Travels in blood to kidney
iii. Causes kidney to reabsorb more water and decrease amount of water in
urine, increasing water level in blood
iv. Hypothalamus decreases ADH release and urine tends to be more dilute
v. ADH production stimulated by nausea and vomiting – both cause
dehydration
vi. Blood loss of 15 or 20 percent by hemorrhage results in release of ADH