Download Chapter 9 - Endocrine System Overview coordinate and directs the

Chapter 9 - Endocrine System
Overview
coordinate and directs the activity of the body's cells
more slowly acting than nervous system
uses chemical messengers (hormones) released into the blood
hormones transported leisurely throughout the body
controls:
reproduction
growth and development
mobilization of body defenses against stressors
maintenance of electrolyte, water, and nutrient balance of the blood
regulation of cellular metabolism and energy balance
organs are small, unimpressive, lack the structural or anatomical continuity typical of most organs
bits and pieces of endocrine tissue are tucked away in widely separated regions of the body
The Chemistry of Hormones
chemical substances
secreted by cells into the extracellular fluids
regulate the metabolic activity of other body cells
amino acid- based molecules (including proteins, peptides, and amines)
steroid hormones
made from cholesterol
include sex hormones made by the gonads (ovaries and testes)
also hormones produced by the adrenal cortex
prostaglandins
made from highly active lipids found in plasma membranes
increases blood pressure by acting as vasoconstrictors
cause constriction of respiratory passageways
stimulates muscle of the uterus (promoting labor)
enhance blood clotting
increase inflammation and pain
increase output of digestive secretions stomach
causes fever
Mechanisms of Hormone Action
blood-borne hormones circulate to all the organs of the body
a given hormone affects only certain tissue cells or organs (target cells/organs)
specific protein receptors must be present on plasma membrane or in its interior
hormone attaches
affects body cells primarily by altering cellular activity
(increasing or decreasing the rate of a normal/usual metabolic process)
precise changes depend on the specific hormone and the target cell type but may include:
changes in plasma membrane permeability or electrical state
synthesis of proteins/regulatory molecules in the cell
activation or inactivation of enzymes
stimulation of mitosis
steroidal hormones (lipid-soluble molecules)
diffuse through the plasma membranes of target cells
enters the nucleus and binds to a specific receptor protein
hormone-receptor complex binds to specific genes in the cell's DNA
mRNA transcribed and translated in the cytoplasm
results in the synthesis of new proteins
nonsteroidal hormones
bind to receptors on plasma membrane
sets off a series of reactions that activates an enzyme
enzymes catalyzes a reaction that produces a second messenger molecule
2nd molecule oversees additional intracellular changes
causes the typical response of the target cell to the hormone
Control of Hormone Release
negative feedback mechanisms regulate blood levels of nearly all hormones
secretion triggered by internal or external stimulus
rising hormone levels inhibit further hormone release
stimuli fall into three major categories (hormonal, humoral, neural)
hormonal
endocrine organs are stimulated into action by other hormones
hypothalamic hormones stimulate the anterior pituitary gland to secrete its hormones
humoral
changing blood levels of certain ions/nutrients/body fluids
insulin produced by the pancreas
neural
nerve fibers stimulate hormone release
sympathetic nervous system stimulating release of norepinephrine and epinephrine
Endocrine Organs/Glands
major glands include the pituitary, thyroid, parathyroid, adrenal, pineal, thymus, pancreas, and gonads
also includes the hypothalamus (part of the nervous system) because it produces several hormones
Know Table 9.1
Pituitary Gland
size of a grape
on the inferior surface of the hypothalamus surrounded by the sphenoid bone
two functional lobes - anterior pituitary (glandular tissue) and posterior pituitary (nervous tissue)
anterior pituitary
growth hormone and prolactin
(affects non-endocrine targets)
thyrotropic hormone, adrenocorticotropic hormone, and two gonadotropic hormones
(stimulate target organs to secrete hormones which affects other organs/tissues)
all are proteins, have 2nd messenger systems, regulated by hormonal stimuli/negative feedback
growth hormone (GH)
general metabolic hormone
growth of skeletal muscles and long bones
amino acids built into proteins and stimulates growth/division of target cells
causes fats to be broken down and used for energy
hyposecretion in childhood leads to pituitary dwarfism
hypersecretion during childhood results in gigantism
hypersecretion after long bone growth has ended results in acromegaly
prolactin (PRL)
protein hormone structurally similar to growth hormone
only known target in humans is the breast (stimulate/maintain milk production)
adrenocorticotropic hormone (ACTH)
adrenal gland
thyroid-stimulating hormone (TSH)
growth and activity of the thyroid gland
gonadotropic hormone
regulate the hormonal activity of the gonads (ovaries and testes)
follicle-stimulating hormone (FSH)
stimulates follicle development in the ovaries
stimulates sperm development by the testes
luteinizing hormone (LH)
triggers ovulation of an egg from the female ovary
causes ruptured follicle to be converted to a corpus luteum
stimulates the corpus luteum to produce progesterone and some estrogen
stimulates testosterone production by the interstitial cells of the testes
**anterior pituitary gland controls several endocrine glands - called the master endocrine gland
**release of its hormones is controlled by releasing/inhibiting hormones produced by the hypothalamus
posterior pituitary
not an endocrine gland (it does not make the peptide hormones it releases)
acts as a storage area for hormones made by hypothalamic neurons
oxytocin
during childbirth and in nursing women
stimulates powerful contractions of the uterine muscle during labor, causes milk ejection
antidiuretic hormone
inhibits/prevents urine production
causes kidneys to reabsorb more water from forming urine
as a urine volume decreases - blood volume increases
Thyroid Gland
base of the throat inferior to the Adam's apple
thyroid hormone
major metabolic hormone
controls rate at which glucose is burned/oxidized and converted to body heat/chemical energy
important for normal tissue growth and development
calcitonin
decreases blood calcium levels by causing calcium to be deposited in the bones
released directly to the blood in response to increasing levels of blood calcium
Parathyroid Glands
tiny masses of glandular tissue on the posterior surface of the thyroid gland
parathyroid hormone (PTH)
most important regulator of calcium ion homeostasis of the blood
released when calcium levels drop below a certain level
stimulates osteoclasts to break down bone matrix and release calcium into the blood
**PTH is a hypercalcemic hormone (acts to increase blood levels of calcium)
**calcitonin is a hypocalcemic hormone (acts to decrease blood levels of calcium)
Adrenal Gland
top of the kidneys
structurally and functionally two endocrine organs in one - glandular (cortex) and neural tissue (medulla)
adrenal cortex
produces three major groups of steroid hormones collectively called corticosteroids
mineralocorticoids
regulates mineral (or salt) content of the blood (particularly sodium and potassium ions)
target is kidney tubules that reabsorb minerals or allow them to be flushed out in urine
help regulate both water and electrolyte balance in body fluids
glucocorticoids
promote normal cell metabolism
help the body to resist long-term stresses
increases blood glucose levels, decreases edema, inhibits some pain-causing molecules
sex hormones
produced by throughout life in relatively small amounts
adrenal medulla
develops from a knot of nervous tissue
stimulated by sympathetic nervous system neurons
release two similar hormones - epinephrine (adrenaline) and norepinephrine as (noradrenaline)
fight-or-flight response stimulates the adrenal medulla
hormones pumped into the bloodstream
heart rate, blood pressure, blood glucose levels increase
body is better able to deal with a short-term stressor
**glucocorticoids operate during resistance stage of the stress response
**prolonged/continuing stressors (death of a family member/having a major operation)
Pancreatic Islets
little masses of hormone-producing tissue scattered among enzyme-producing tissue of the pancreas
more than a million
insulin and glucagon regulate the amount of glucose in the blood
insulin
acts on just about all body cells
increases ability to transport glucose across their plasma membranes
glucose oxidized for energy or converted to glycogen or fat for storage
as blood glucose levels fall, the stimulus for insulin release ends (negative feedback)
absolutely necessary for the use of glucose by body cells
glucagon
antagonist of insulin
primary target is the liver
breaks down stored glycogen to glucose to be released into the blood
Pineal Gland
roof of the third ventricle of the brain
somewhat of a mystery
melatonin secreted in substantial amounts
important role in establishing the body's day-night cycle
helps regulate mating behavior and rhythms
coordinates the hormones of fertility
inhibits reproductive system (sexual maturation is prevented from occurring during childhood)
Thymus
upper thorax, posterior to the sternum
large in infants and children but decreases in size throughout adulthood
incubator for the maturation of T lymphocytes (important in the immune response)
Gonads, Ovaries
paired, almond-sized organs located in the pelvic cavity
produces female sex cells and two groups of steroid hormones (estrogens and progesterone)
begin to function at puberty (stimulated by anterior pituitary gonadotropic hormones)
corpus luteum produces both estrogen and progesterone
estrogens
stimulate development of secondary sex characteristics in females
prepare the uterus to receive a fertilized egg
causes cyclic changes in the uterine lining (menstrual cycle)
helps maintain pregnancy
prepares the breasts to produce milk
progesterone
acts with estrogen to bring about the menstrual cycle
quiets the muscles of the uterus so that an implanted embryo will not be aborted
helps prepare breast tissue for lactation
Gonads, Testes
suspended in the scrotum outside the pelvic cavity
produce male sex hormones (androgens)
testosterone
most important androgen
causes development of adult male sex characteristics
responsible for growth and maturation of the reproductive system
necessary for continuous production of sperm
Other Hormone Producing Tissues and Organs
hormone-producing cells are found in the walls of the small intestine, stomach, kidneys, and heart
also in the placenta and certain tumor cells (lung and pancreatic cancers)
placenta
formed temporarily in the uterus of pregnant women
acts as the respiratory, excretory, and nutrition-delivery systems for the fetus
also produces hormones to help maintain the pregnancy and deliver the baby
- human chorionic gonadotropin
stimulates the corpus luteum of the ovary to continue producing
estrogen/progesterone so the uterine lining is not sloughed off in menses
- human placental lactogen
works cooperatively with estrogen/progesterone to prepare breasts for lactation
- relaxin
causes pelvic ligaments/pubic symphysis to relax and become more flexible
Developmental Aspects
most endocrine organs seem to operate smoothly until old age
efficiency of the endocrine system as a whole gradually declines with age
target organs also become less productive