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endocrine system
is composed of endocrine glands and specialized endocrine cells located throughout the body
hormones
Endocrine glands and cells secrete very small amounts of chemical messengers called — into the bloodstream, rather than into a duct
target tissues
The hormones diffuse into the blood to be transported to their target. Hormones circulate through the bloodstream to specific sites called — or effectors
autocrine chemical messengers
paracrine chemical messengers
neurotransmitters
endocrine chemical messengers
the study of the endocrine system includes several of the following categories (classes of chemical messengers) :
autocrine chemical messengers
chemical messenger stimulates the cell that originally secreted it
have local effect on same cell type
ex. eicosanoids and secreted by white blood cells
paracrine chemical messengers
chemical messengers act locally on neighboring cells
released by cells that affect other cell types in close proximity
ex. somatostatin and histamine
neurotransmitter (and neuromodulators)
chemical messengers secreted by neurons that activate an adjacent cell, whether it is another neuron, a muscle cell, or a glandular cell
secreted by nerve cells
ex. nervous system function
endocrine chemical messenger (hormones and neurohormones)
secrete into blood and bind to receptors on target tissues
ex. epinephrine and insulin
lipid-soluble hormones
water-soluble hormones
Hormones fit into one of two chemical categories:
lipid-soluble hormones
are nonpolar, and include steroid hormones
thyroid hormones, and fatty acid derivative hormones, such as certain eicosanoids.
hormones bind to nuclear receptors due to their lipid solubility and small molecular size allowing to easily pass through the cell membrane
water-soluble hormones
are polar molecules and cannot pass through the cell membrane
they include protein hormones, peptide hormones, and most amino acid derivative hormones.
bind to membrane-bound receptors.
humoral
neural
hormonal
Three types of stimuli regulate hormone release:
humoral stimuli
Blood-borne chemicals can directly stimulate the release of some hormones.
These chemicals are referred to as —- because they circulate in the blood
hormonal stimuli
It occurs when a hormone is secreted that, in turn, stimulates the secretion of other hormones
negative feedback
positive feedback
Two major mechanisms maintain hormone levels in the blood within a homeostatic range:
negative feedback
Most hormones are regulated by a — mechanism, whereby the hormone’s secretion is inhibited by the hormone itself once blood levels have reached a certain point
it is a self-limiting system.
positive feedback
Some hormones, when stimulated by a tropic hormone, promote the synthesis and secretion of the tropic hormone in addition to stimulating their target cell. In turn, this stimulates further secretion of the original hormone.
Thus, it is a self-propagating system.
pituitary gland
It is a small gland about the size of a pea
controlled by hypothalamus
divided into 2 regions: anterior and posterior
hypothalamus
serves as a control center for the autonomic nervous system as well as the endocrine system
anterior pituitary gland
synthesizes hormones under the control of the hypothalamus
posterior pituitary gland
stores and releases hormones produced by neuroendocrine cells in the hypothalamus
growth hormone
thyroid-stimulating hormone
adrenocorticotropic hormone
melanocyte-stimulating hormone
luteinizing hormone
follicle-stimulating hormone
prolactin
anterior pituitary gland hormones
growth hormone
target tissues: most tissues
Functions: stimulates growth of bones, muscles, and organs
giantism
too much growth hormone causes —
pituitary dwarfism
too little growth hormone causes
thyroid-stimulating hormone
binds to membrane-bound receptors on cells of the thyroid gland and stimulates the secretion of thyroid hormone
target tissue: thyroid gland
thyroid gland enlarges (goiter)
too much thyroid-stimulating hormone causes —
thyroid gland shrinks
too little thyroid-stimulating hormone causes—
adrenocorticotropic hormone
binds to membrane-bound receptors on cells of the adrenal cortex.
increases the secretion of corticosteroids
luteinizing hormone
females: promotes the secretion of the reproductive hormones, estrogen and progesterone, from the ovaries
males: stimulates interstitial cells of the testes to secrete the reproductive hormone testosterone
follicle-stimulating hormone
female: follicle in ovaries and estrogen secretion
male: sperm production
prolactin
binds to membrane-bound receptors in cells of the breast, where it helps promote development of the breast during pregnancy
stimulates the production of milk following pregnancy.
melanocyte-stimulating hormone
binds to membrane-bound receptors on melanocytes and causes them to synthesize melanin
darken
The structure of MSH is similar to that of ACTH, and over secretion of either hormone causes the skin to
antidiuretic hormone
oxytocin
hormones of the posterior pituitary gland
antidiuretic hormone
target tissues: kidney
function: conserve water
diabetes insipidus
A lack of ADH secretion
which is the production of a large amount of dilute urine
can lead to dehydration and thirst
oxytocin
target tissue: uterus
function: increases uterine contractions during labor
thyroid gland
one of the largest glands
require iodine to function
thyroid hormone
calcitonin
thyroid gland secretes —
thyroid hormones
secreted by follicular cells
Target tissues: most tissues
Functions: regulates metabolic rates and is needed for growth
calcitonin
secreted by parafollicular cells:
Target tissues: bone and some other tissues
Function: reduces blood calcium level when high
hypothyroidism
lack of thyroid hormones
Decreased metabolism
Weight gain, reduced appetite, fatigue
Low temp. and pulse
Dry, cold skin
Myxedema in adults
Cretinism in infant
hyperthyroidism
elevated rate of thyroid hormones
increased metabolism
Weight loss, increased appetite, nervousness
Higher temp. and pulse
Warm, flushed skin
Graves’ disease is autoimmune disease that cause —
parathyroid glands
Four tiny — are embedded in the posterior wall of the thyroid
parathyroid hormone
target tissues: bones and kidneys
functions: essential for the regulation of blood calcium levels
adrenal gland
are two small glands located superior to each kidney
adrenal medulla
adrenal gland inner part
adrenal cortex
adrenal gland outer part
epinephrine and norepinephrine
adrenal medulla secrete 2 hormones —
are called the fight-or-flight hormones. They prepare the body for intense physical activity.
aldosterone
cortisol
androgens
adrenal cortex hormones
aldosterone
type of mineralocorticoid
target tissues: kidneys
functions: regulate ion balance, causes Na+ and H2O to be retained and K+ to be secreted, indirectly involved with blood pressure and blood volume
cortisol
type of glucocorticoid
target tissues: most
functions: increases breakdown of fat and protein for energy uses reduces inflammatory and immune responses
androgens
males: which stimulate the development of male secondary sex characteristics.
female: sex drive
pancreas
is a mixed gland, with an exocrine portion and an endocrine portion
pancreatic islets (islets of Langerhans)
The endocrine part of the pancreas consists of —-, which are dispersed throughout the exocrine portion of the pancreas
alpha cells
beta cells
delta cells
The islets consist of three cell types, each of which secretes a separate hormone
These three hormones regulate the blood levels of nutrients, especially glucose
alpha cells
secretes glucagon
beta cells
secrete insulin
delta cells
secrete somatostatin
insulin
target tissues: liver, skeletal muscle, adipose tissue
Functions:
regulates blood glucose levels
after a meal glucose levels are high and — is secreted
diabetes mellitus
Causes: too little insulin or faulty insulin receptors
Symptoms: hyperglycemia, exaggerated appetite, excess urine, dehydration, thirst, fatigue
type 1 diabetes mellitus
occurs when too little insulin is secreted from the pancreas
insulin dependent (daily injections required)
type 2 diabetes mellitus
is caused by either too few insulin receptors on target cells or defective receptors on target cells
insulin independent, often found in obese people and can be treated with diet
glucagon
is released from the alpha cells when blood glucose levels are low
target tissues: liver
between meals glucose levels drop and —is secreted
allows glycogen to be broken down into glucose
testosterone
which is secreted by the testes.
It regulates the production of sperm cells by the testes and the development and maintenance of male reproductive organs and secondary sexual characteristics
estrogen and progesterone
In the female, two main classes of reproductive hormones, secreted by the ovaries, affect sexual characteristics
involved in uterine and mammary gland development and menstrual cycle
thymus
lies in the upper part of the thoracic cavity and is important in the function of the immune system
thymosin
The thymus secretes a hormone called—
which aids the development of white blood cells called T cells
promotes immune system development and function
pineal gland
is a small, pinecone-shaped structure located superior and posterior to the thalamus of the brain
melatonin
pineal gland produces a hormone called
plays a role in onset of puberty and controls circadian rhythms.
Light affects its function