ENDOCRINE SYSTEM Flashcards
primary regulators of the coordination of cell activities
Chemical messengers of nervous and endocrine system
allow cells to communicate with each other to regulate body activities
Chemical messengers
the controlled release of chemicals from a cell
secretion
stimulates the cell that originally secreted it
Autocrine chemical messengers (ex. Eicosanoids; those secreted by white blood cells during an infection)
(T/F) the total number of white blood cells increases rapidly
T - Several types of white blood cells can stimulate their own replication
act locally on neighboring cells that are secreted by one cell type into the extracellular fluid and affect surrounding cells
Paracrine chemical messengers (ex. histamine, Somatostatin, eicosanoids)
stimulates vasodilation in nearby blood vessels
histamine
widening of blood vessels as a result of the relaxation of the blood vessel’s muscular walls and a mechanism to enhance blood flow to areas of the body that are lacking oxygen and/or nutrients
Vasodilation
chemical messengers secreted by neurons that activate an adjacent cell, whether it is another neuron, a muscle cell, or a glandular cell
Neurotransmitters (ex. Acetylcholine, epinephrine)
secreted into the bloodstream by certain glands and
cells
Endocrine chemical messengers
composed of endocrine glands and specialized endocrine cells located throughout the body
endocrine system (ductless release)
very small amounts of chemical messengers
hormones
Hormones circulate through the bloodstream to specific
sites called?
target tissues, or effectors
endo in Greek means?
within
krino means?
to secrete
have ducts that carry their secretions to the outside
of the body, or into a hollow organ
Exocrine glands (ex. secretions of saliva, sweat, breast milk, and
digestive enzymes)
study of the endocrine system
endocrinology
neuron’s chemical messenger which enters the bloodstream where it functions as a hormone
neuropeptides, or neurohormones (ex. oxytocin)
hormones secreted by most endocrine glands can be described as
amplitude-modulated signals (concentration)
the all-or-none action potentials carried along axons can be described as
frequency-modulated signals (frequency)
hormon in Greek means?
set into motion
General Characteristics of Hormones (3)
Stability
Communication
Distribution
(T/F) Larger, more complex hormones are more stable
T
(T/F) simpler hormones are less stable
T
A hormone’s life span
half-life
amount of time it takes for 50% of the circulating hormone
to be removed from the circulation and excreted.
half-life
thyrotropin-releasing hormone (TRH)
short half-life
cortisol
longer half-life
(T/F) Small, water- soluble hormones are quickly digested by hydrolytic enzymes in the blood and are easily filtered from the blood in the kidneys
T
(T/F) lipid-soluble hormones, have low solubility in the blood plasma
T
Hormones requiring a transport chaperone bind to blood proteins
binding proteins (protects water-soluble hormones from degradation by hydrolytic enzymes and from being filtered from the blood in the kidney; causes lipid-soluble hormones to become more water-soluble)
Once hormones attach to a binding protein, they are then called
bound hormones
(T/F) The binding of hormones to binding proteins is reversible
T
Once the hormones detach from the binding protein,
they are then called
free hormones
(T/F) Hormones that attach to binding proteins tend to have longer half-lives than hormones that do not require binding proteins
T
two chemical categories of hormones based on chemical behavior
lipid-soluble hormones
water-soluble hormones
nonpolar and include steroid hormones, thyroid hormones, and fatty acid derivative hormones, such as certain eicosanoids
Lipid-Soluble Hormones (ex. Steroids (all cholesterol-based)
Testosterone, aldosterone, thyroxine)
lipid-soluble hormones are removed from the
circulation when specific enzymes in the liver attach water-soluble molecules to the hormones,
conjugation
polar molecules: they include protein
hormones, peptide hormones, and most amino acid derivative
hormones
Water-Soluble Hormones (ex. Proteins, Insulin, Peptides, Amino Acid Derivatives; Epinephrine)
many of these circulate as free hormones
water-soluble hormones
The three main patterns of hormone secretion
chronic (constant; thyroid hormones)
acute (Irregular; epinephrine)
episodic (intervals; steroid reproductive hormones)
lipid-soluble hormones exhibit the two regular secretion patterns
(chronic and episodic)
water-soluble hormones tend to exhibit the secretion pattern __
acute (sometimes episodic)
Three types of stimuli regulate hormone release:
humoral stimuli (circulate in blood)
neural stimuli (neurotransmitters into synapses)
hormonal stimuli (hormones stimulate the secretion of other hormones)
a term usually reserved for hormones from the hypothalamus
releasing hormones
hormones from the anterior pituitary gland,
tropic hormones
Three types of stimuli regulate hormone inhibition:
humoral stimuli
neural stimuli
hormonal stimuli
hormones from the hypothalamus that prevent the
secretion of tropic hormones from the pituitary gland
inhibiting hormones
Two major mechanisms maintain hormone levels in the blood
within a homeostatic range:
negative feedback and positive feedback
the hormone’s secretion is inhibited by the hormone itself once blood levels have reached a certain point and there is adequate hormone to
activate the target cell.
Negative feedback (self-limiting system)
ex. thyroid hormones inhibit the
secretion of TRH from the hypothalamus and TSH from the
anterior pituitary
hormones promote the further synthesis and secretion of the tropic hormone in addition to stimulating their target cell.
Positive feedback (self-propagating system)
ex. prolonged estrogen stimulation
promotes a release of luteinizing hormone
target cell proteins
receptors
specific portion of each receptor molecule where a hormone bind is called
receptor site
tendency for each type of hormone to bind to one type
of receptor, and not to others
specificity
drug that binds to a hormone receptor and activates
agonist
A drug that binds to a hormone receptor and inhibits
its action
antagonist
Desensitization occurs when the number
of receptors rapidly decreases after exposure to certain hormones
down-regulation
results in an increase in the rate of receptor synthesis in the target cells,
which increases the total number of receptor molecules in a cell
Up-regulation
Classes of Receptors
- Lipid-soluble hormones bind to nuclear receptors.
- Water-soluble hormones bind to membrane-bound receptors.
proteins that extend
across the plasma membrane, with their hormone-binding sites
exposed on the plasma membrane’s outer surface
membrane-bound receptors
sequences in the DNA called
hormone- response elements
The combination of the hormone and its receptor forms
a
transcription factor
when the hormone-receptor
complex binds to the hormone-response element, it activates the
transcription of ___ which codes for proteins.
messenger ribonucleic acid (mRNA)
Nuclear receptors have portions that allow them to bind to the DNA
in the nucleus once the hormone is bound:
The hormone-receptor complex activates genes, which in turn
activate the DNA to produce mRNA.
The mRNA increases the synthesis of certain proteins that produce
the target cell’s response.
(T/F) Nuclear receptors cannot respond immediately, because it takes time to produce the mRNA and the protein
T
produced inside a cell once a hormone or another chemical messenger binds to certain membrane-bound receptors
intra cellular mediator
an enzyme that converts ATP to cAMP
adenylate cyclase
functions as a second messenger, an intracellular mediator that
carries out cellular metabolic processes in response to hormonal activation
Cyclic AMP
enzymes that regulate the
activity of other enzymes by attaching phosphates to them, a
process called phosphorylation
protein kinase
breaks down cAMP to AMP
phosphodiesterase
Membrane-Bound Receptors and Signal
Amplification
- Membrane-bound receptors activate a cascade of events once the
hormone binds. - Some membrane-bound receptors are associated with membrane
proteins called G proteins.
■ Hormone binds to a membrane-bound receptor, and G proteins are
activated.
■ The α subunit of the G protein binds to ion channels and causes
them to open or change the rate of synthesis of intracellular mediators,
such as cAMP, cGMP, IP3, and DAG. - Intracellular enzymes can be activated directly, which in turn causes
the synthesis of intracellular mediators, such as cGMP, or adds a
phosphate group to intracellular enzymes, which alters their activity. - Second-messenger systems act rapidly, because they act on already
existing enzymes to amplify the signal.
FUNCTIONS OF ENDOCRINE SYSTEM
- Regulation of metabolism
- Control of food intake and digestion
- Modulation of tissue development
- Regulation of ion levels
- Control of water balance
- Changes in heart rate and blood pressure
- Control of blood glucose and other nutrients
- Control of reproductive functions
- Stimulation of uterine contractions and milk release
- Modulation of immune system function. The endocrine system
helps control the production of immune cells
secretes nine major hormones that regulate numerous body functions and the secretory activity of several other endocrine glands.
pituitary gland
regulates the secretory activity of the pituitary gland in
response to other hormones, sensory information, and emotions.
hypothalamus
connected to the base of the brain, just inferior to the hypothalamus; rests in the sella turcica (depression) of the sphenoid bone and is roughly the size of a pea
pituitary gland
stalk of tissue that connects the pituitary gland to the
hypothalamus
infundibulum
The pituitary gland is divided into which two lobes?
posterior pituitary gland, or neurohypophysis
anterior pituitary gland, or adenohypophysis
is called the neurohypophysis because it is
continuous with the hypothalamus in the brain
posterior pituitary (neural tissues)
Because the posterior pituitary is a part of the nervous system, its hormones are called?
neuropeptides, or neurohormones
develops as an outpocketing of the roof of
the embryonic oral cavity called the pituitary diverticulum, or
Rathke pouch
anterior pituitary (epithelial tissues)
not functional in adult humans
pars intermedia
a circulatory system
portal systrem
a circulatory system
portal system
one of the major portal systems in the body
hypothalamohypophysial portal system
provides a means by which the hypothalamus, using
neurohormones as chemical messengers, regulates the secretory
activity of the anterior pituitary
hypothalamohypophysial portal system
HORMONES OF HYPOTHALAMUS (8)
Growth hormone–releasing
hormone (GHRH)
Growth hormone–inhibiting
hormone (GHIH), or somatostatin
Thyrotropin-releasing hormone (TRH)
Corticotropin-releasing hormone
(CRH)
Gonadotropin-releasing hormone
(GnRH)
Prolactin-releasing hormone (PRH)
Prolactin-inhibiting hormone (PIH)
HORMONES OF POSTERIOR PITUITARY (2)
Antidiuretic Hormone (vasopressin)- a water conservation hormone that also constricts blood vessels and raises blood pressure when large
amounts are released
Oxytocin - an important reproductive hormone; increased uterine contractions; increased milk expulsion from mammary glands; unclear function in males
HORMONES OF ANTERIOR PITUITARY (6)
Growth hormone (GH), or somatotropin - Increased growth in tissues; increased amino acid uptake and protein synthesis; increased breakdown of lipids and release of fatty acids from cells; increased glycogen synthesis and increased blood glucose levels; increased somatomedin production
Thyroid-stimulating hormone (TSH) - Increased thyroid hormone secretion
Adrenocorticotropic hormone (ACTH) - Increased glucocorticoid hormone secretion
Luteinizing hormone (LH) - Ovulation and progesterone production in ovaries; testosterone synthesis and support for sperm cell production in testes
Follicle-stimulating hormone (FSH) - Follicle maturation and estrogen secretion in ovaries; sperm cell production in testes
Prolactin - Milk production in lactating women; increased response of follicle to LH and FSH; unclear function in males
Increased lipid breakdown
Lipotropins
Analgesia in the brain; inhibition of gonadotropin-releasing
hormone secretion
β endorphins
Chronic hyposecretion, or insufficient secretion, of GH in
infants and children lead to a condition called
pituitary dwarfism
There are two types of pituitary dwarfism:
(1) GH and other anterior pituitary hormones are
secreted in reduced amounts (additional disorders; 2/3)
(2) GH secretion is reduced, and the secretion of other anterior pituitary hormones is closer to normal (no additional; 1/3)
Chronic hypersecretion of GH before the epiphyseal plates
have ossified causes exaggerated and prolonged growth in long bones,
a condition called
gigantism (childhood)
In adults, chronically elevated GH levels result in
acromegaly (No height increase occurs because the epiphyseal
plates have ossified)
binds to membrane-bound receptors on skin melanocytes and stimulates
increased melanin deposition in the skin.
Melanocyte-stimulating hormone (MSH)
are glycoprotein hormones capable of promoting the growth and function of the gonads, the ovaries and testes.
Gonadotropins
composed of two lobes connected by a narrow band of thyroid
tissue called the isthmus and is one of the largest endocrine glands
thyroid gland
small spheres whose walls are composed of a single layer of
cuboidal epithelial cells
follicles
The center of each
thyroid follicle is filled with a gelatinous material called
colloid (composed of a highly concentrated protein called
thyroglobulin)
stores a huge amount of thyroid hormones (Storage of such a large amount of hormone is unique to the thyroid gland.)
thyroglobulin
secretes calcitonin
parafollicular cells
plays a role in reducing
the concentration of calcium in the body fluids when calcium
levels become elevated
calcitonin
THYROID HORMONES (2)
triiodothyronine or T3 (10%) & tetraiodothyronine or T4/thyroxine (80%) - Increased metabolic rate; increased protein synthesis; essential for normal growth and maturation
Calcitonin (10%) - Decreased rate of breakdown of bone by osteoclasts; prevention of a large increase in blood Ca2+ levels
should be consumed by humans to support thyroid hormone synthesis
iodine
Causes inadequate T3 and T4 synthesis, which results in elevated thyroid-stimulating hormone (TSH) secretion
Iodine deficiency
Inhibit T3 and T4 synthesis; found in certain drugs and in small amounts in certain plants, such as cabbage
Goitrogenic (goiter-causing) substances
Caused by maternal iodine deficiency or congenital errors in thyroid hormone synthesis
Neonatal hypothyroidism
Results from lack of TSH secretion
Pituitary insufficiency
Autoimmune disease in which thyroid hormone secretion can be normal or depressed
Hashimoto disease
Partial or complete surgical removal or drug-induced destruction of the thyroid gland as a treatment for Graves
disease (hyperthyroidism)
Lack of thyroid gland
Characterized by goiter and exophthalmos
Graves disease
Result in either normal secretion or hypersecretion of thyroid hormones (rarely hyposecretion)
Tumors—benign adenoma or cancer
Produces painful swelling of the thyroid gland with normal or slightly increased T3 and T4 production
Thyroiditis—a viral infection
Thyroid storm Sudden release of large amounts of T3 and T4; caused by surgery, stress, infections, or other, unknown factors
Thyroid storm
abnormal enlargement of the thyroid gland
goiter
results when dietary
iodine intake is so low that there is not enough iodine to synthesize T3 and T4
iodine-deficiency goiter
most common preventable cause of mental defects,
iodine-deficiency diseases
may be the most common endemic disease on the planet
hypothyroidism
secretes excess T3 and T4, and it can result from
elevated TSH secretion or elevated TSH-like immunoglobulin
toxic goiter
most common cause of hyperthyroidism
Graves disease
usually embedded in
the posterior part of each lobe of the thyroid gland
parathyroid glands
parathyroid glands are made up of two cell types:
chief cells (secrete parathyroid hormone,)
oxyphils
polypeptide hormone that is important in regulating calcium levels in body fluids
Parathyroid hormone (PTH), also called parathormone
Increased rate of breakdown of bone by osteoclasts;
increased reabsorption of Ca2+in kidneys; increased absorption of Ca2+from the small intestine; increased vitamin D synthesis; increased blood Ca2+ levels
Parathyroid hormone (PTH)
abnormally low levels of calcium in the blood
hypocalcemia
produce a diverse set of hormones, is retroperitoneal and they are surrounded by abundant adipose tissue
adrenal glands (suprarenal)
adrenal glands are composed of: (2)
medulla - arises from neural crest cells
cortex - derived from mesoderm
LAYERS OF ADRENAL CORTEX (3)
zona glomerulosa - secretes aldosterone (mineralocorticoid)
zona fasciculata - secretes cortisol (glucocorticoid)
zona reticularis - secretes androgens and estrogen (and glucocorticoid)
modified sympathetic nervous system
ganglion
adrenal medulla
ADRENAL MEDULLA HORMONES (2)
epinephrine (80%; increases blood glucose levels) & norepinephrine (20%) - increased cardiac output; increased blood flow to skeletal muscles and to the heart; vasoconstriction of blood vessels, especially in the viscera
and skin; increased release of glucose and fatty acids into the blood; in general, preparation for physical activity
ADRENAL CORTEX HORMONES (3)
mineralocorticoids - regulate ion balance in the blood and are the major secretory products of the zona glomerulosa of the adrenal cortex; produces aldosterone
glucocorticoids - help to provide energy for cells by stimulating the
increased use of lipids and proteins
androgens
secreted under low blood pressure conditions; secreted under low blood pressure conditions
aldosterone
the synthesis of new glucose from precursor molecules,
such as amino acids in the liver),
gluconeogenesis
generic term for steroid hormones that cause the development of male secondary sex characteristics
Androgen
both an exocrine gland and an endocrine gland
pancreas
exocrine portion of pancreas
acini produce pancreatic juice, and a duct system, which carries the
pancreatic juice to the small intestine
endocrine portion of pancreas
pancreatic islets (islets of Langerhans) secrete hormones that enter the plasma of the blood
secrete glucagon
alpha (α) cells (20%) - Increased breakdown of glycogen; release of glucose into the blood
secrete insulin (lowers blood glucose levels by
stimulating glucose transport into body cells)
beta (β) cells (75%) - Increased uptake and use of glucose and amino
acids
secrete somatostatin
delta (δ) cells - Inhibition of insulin and glucagon secretion
a collection of neurons in the hypothalamus that
controls appetite
satiety center
intense sensation of hunger in spite of high blood glucose levels
polyphagia
results primarily from
the inadequate secretion of insulin or
the inability of tissues to respond to
insulin.
Diabetes mellitus
also called insulin-dependent diabetes mellitus (IDDM),
results from diminished insulin secretion. It develops as a result of
autoimmune destruction of the pancreatic
islets, and symptoms appear after approximately 90% of the islets have been destroyed
Type 1 diabetes mellitus
also called noninsulin-dependent diabetes mellitus
(NIDDM), usually develops in people older than 40–45 years
of age
Type 2 diabetes mellitus (more common)
companion hormone to insulin
glucagon
elevated blood levels of glucose
hyperglycemia
low blood levels
of glucose
hypoglycemia
main endocrine
glands of the male reproductive system
testes
main hormone secreted by the
testes
testosterone
regulates the
production of sperm cells by the testes and the development and
maintenance of male reproductive organs and secondary sexual
characteristics.
testosterone
inhibits the secretion of FSH from the anterior
pituitary gland.
inhibin
main endocrine glands of the female reproductive system
ovaries
main hormones secreted by the ovaries
estrogen and progesterone
Inhibits FSH secretion
inhibin
Aids in uterine and mammary gland development and function, maturation of genitalia, secondary sex characteristics, sexual behavior (only estrogen), and menstrual cycle
estrogen and progesterone
Increases the flexibility of connective tissue in the pelvic area, especially the symphysis pubis
relaxin
act on the hypothalamus and the gonads to
inhibit reproductive functions, such as by inhibiting the secretion
of certain reproductive hormones
pineal gland
Two substances have been proposed as secretory products:
melatonin - decrease hypothalamic GnRH secretion, may
inhibit reproductive functions, and also help regulate sleep
cycles by increasing the tendency to sleep
arginine vasotocin – regulate the function of the reproductive system in some animals; Possible inhibition of gonadotropin-releasing hormone secretion
In some animals, pineal secretions are regulated by the
____, the amount of daylight and darkness that occurs
each day and changes with the seasons of the year
photo period
important for immune function that is in
the neck and superior to the heart in the thorax
thymus
The thymus
secretes the hormone
thymosin (development and maturation of the immune system)
