Jasmine's Biology Blog : Endocrine System

System of organs that releases hormones into the blood
Function of endocrine system

endocrine system uses blood vessels to carry chemical information

Organs of the endocrine system (overview)

hormones

chemical messenger molecules that are made by cells in one part of the body and changes cells in another part of the body
regulate many functions that keep you alive
made and secreted by cells in endocrine glands

endocrine glands

ductless organs that secrete hormones directly into blood or fluid surrounding a cell
primary function is to make and secrete hormones
collectively make up endocrine system
other organs, such as stomach, heart, and kidneys, secrete hormones and are considered as part of the endocrine system

exocrine glands

organs that secrete products into ducts (duct glands)
secrete substances, but do not secrete hormones
secrete things like water, mucus, enzymes, and other proteins

Hormones (in detail)

body produces many different hormones
each hormone very specific for target cells
target cell

cell on which hormone has effect

affected by hormones because they have receptor proteins that are specific for hormone
hormones will travel through bloodstream until they find target cells
amino acid based hormones

made of amino acids
can be simple in structure or very large
not fat-soluble and cannot diffuse through plasma membrane of target cell
bind to receptors found on cell membrane

cholesterol based hormones

made of lipids such as phospholipids and cholesterol
hormones are also called steroid hormones
fat soluble and able to diffuse through plasma membrane
found within cell cytosol and nucleus

hormone-like substances

group of signaling molecules derived from certain types of fatty acids and proteins
do not travel around body in blood and are broken down quickly
effects of hormone-like substances are localized in tissue where they are produced
prostaglandins: made from essential fatty acids and produced by most cells in body
have many different effects, like causing constriction or dilation of blood vessels
neuropeptides: signaling peptides found in nervous tissue
many different effects on nerve cells
some have effects on non nerve cells and are called hormones
hormones exit their cell of origin by exocytosis or some kind of membrane transport
cells that respond to hormone may be one of several cell types found in tissues throughout body

Hormone receptors

cells that respond to hormones have two things in common: have receptors that are specific for certain hormones, and receptors are joined with processes that control metabolism of target cell
two ways receptor-bound hormones activate processes within cells
second messenger system

water soluble hormone molecules does not enter cell
binds to membrane bound receptor molecule, triggering change within cell
changes activated by second messenger molecules

direct gene activation

fat soluble hormone diffuses across membrane and binds to receptor within cytosol or nucleus
hormone-receptor complex acts as transcription factor that affects gene expression

Action of glucagon: second messenger system

majority of amino acid based hormones bind to membrane bound receptors
binding of hormone triggers signal transduction pathway

process of molecular changes that turns hormones extracellular signal into intracellular response

activation of receptors by hormones make the intracellular production of second messengers as part of signal transduction pathway
second messenger is a small molecule that starts change inside cell in response to binding of specific signal to receptor protein
glucagon: hormone involved in carbohydrate metabolism

released when glucose level is low
released by pancreas and circulates blood until it binds to glucagon receptor
receptor found in plasma membrane of liver cells
binding of glucagon changes shape of receptor, which activates a G protein
G protein is enzyme that activates next enzyme, activating the next, etc.
end result: enzyme that breaks apart glycogen molecule in liver cell to release glucose molecules in blood
signal transduction pathway, a domino effect in the cell, allows a little bit of hormone to have large effect on cell or tissue

Action of cortisol: direct gene activation

steroid hormones diffuse through cell membrane and bind to receptors in cytosol or nucleus
cortisol

steroid hormone produced by adrenal glands
often called stress hormone because it is involved in body's response to stress
increases blood pressure, blood sugar levels, and has immunosuppressive action
crosses cell membrane and binds to steroid receptor in cytoplasm
enters nucleus of cell and binds to DNA, either activating or deactivating gene transcription

Effects of hormones

effects varies widely
tropic hormones (tropins) regulate production and release of other hormones
other effects

stimulation or inhibition of growth
induction or suppression of programmed cell death (apoptosis)
activation or inhibition of immune system
regulation of metabolism
preparation for new activity
preparation for new phase of life (ex. puberty, caring for offspring, or menopause)
control of reproductive cycle

Hypothalamus

links nervous system to endocrine system by pituitary gland
located below thalamus
found in all mammalian brains
about the size of an almond
complex area of brain, and nerve cells are involved in many different functions
coordinates seasonal and circadian rhythms, complex homeostasis mechanisms, and ANS
circadian rhythm

24 hour cycle in biological processes carried out within organisms

ANS controls activities such as body temperature, hunger, and thirst
hypothalamus must respond to different signals, both outside and outside
connected with many parts of CNS, including brainstem, olfactory bulbs, and cerebral cortex
produces hormones that are stored in pituitary gland

Pituitary gland

about the size of a pea
attached to hypothalamus by thin stalk at base of the brain
secretes hormones that regulate homeostasis
secretes hormones that stimulate other endocrine glands
anterior pituitary (front lobe) makes many important hormones
posterior pituitary (rear lobe) releases two hormones, oxytocin and ADH
hormones transported down the nerve cell's axons to posterior pituitary where they are stored
most hormones are released from anterior pituitary under influence from hormones in hypothalamus
hypothalamus hormones travel to anterior lobe down special capillary system that surrounds pituitary

Thyroid gland

one of the largest endocrine glands in body
butterfly gland found in the neck, wrapped around trachea
hormones released by thyroid control how quickly the body uses energy, makes proteins, and how sensitive the body should be to other hormones
controlled by hypothalamus and pituitary
thyroid hormones generally controls pace of all processes in body
pace is related to metabolism
hyperthyroidism (overactive thyroid) and hypothyroidism (under active thyroid) are common problems of the thyroid gland
thyroxin (T4) and triiodothyronine (T3) regulate rate of metabolism and affect growth of different systems in the body
iodine is very important for making T3 and T4
if not enough iodine, person developed iodine deficiency called goiter

low amounts of T3 and T4 causes pituitary to secrete large amounts of thyroid stimulating hormone (TSH) which causes abnormal growth of thyroid gland
addition of iodine to mass produced foods, like salt, helps reduce the iodine-deficiency in developed countries

also produces the hormone calcitonin, which plays a role in calcium homeostasis

Parathyroid glands

usually located behind the thyroid gland
parathyroid hormone (PTH) maintains blood calcium levels within a narrow range

maintains calcium levels so that nervous and muscular systems can work properly

if blood calcium levels drop below certain point, calcium sensing receptors in parathyroid releases hormone PTH in the blood

PTH increases blood calcium levels by stimulating bone cells to break down bone and release calcium
increases gastrointestinal calcium absorption by activating vitamin D
promotes calcium uptake by kidneys

Pineal gland

melatonin is made in pea-sized pineal gland
located at the base of the brain
production is under control of hypothalamus

receives information from retina about daily pattern of light and darkness

melatonin is involved in sleep cycles, onset of puberty, and immune function
responds to seasonal changes in light

could be reason why getting out of bed on a dull, rainy morning can be so difficult

Pancreas

both exocrine gland and endocrine gland

exocrine gland because it secretes pancreatic juice containing digestive enzymes
endocrine gland because it produced several important hormones

located below and behind stomach
endocrine cells in pancreas are grouped together in areas called inslets of Langerhans

islets produce amino acid-based hormones insulin, glucagon, and somatostatin

insulin

produced by beta cells
causes excess blood glucose to be taken up by liver and muscle cells
stored as glycogen, a polysaccharide

glucagon

produced by alpha cells and stimulates liver cells to break down glycogen into glucose
released into blood

alpha cell

another type of endocrine cell found within the islets of Langerhans

Adrenal glands

located each above the kidneys
separated into two structures

adrenal medulla (center of gland)
adrenal cortex (outer layer)
work as two separate endocrine glands

adrenal medulla

core of adrenal gland
surrounded by adrenal cortex
secretion of hormones from medulla is controlled by sympathetic nervous system
cells of medulla are main source of epinephrine and norepinephrine
hormones are part of fight-or-flight response
boots supply of oxygen and glucose to brain and muscles, suppressing other non-emergency bodily processes

adrenal cortex

site od steroid hormone synthesis
some cells make cortisol, and others make testosterone (or more)
other cells secrete aldosterone, which helps regulate blood pressure
regulated by hormones secreted by pituitary gland and hypothalamus

cortisol (see above)
epinephrine (adrenaline)

fight or flight hormone
released from adrenal medulla when stimulated by sympathetic nervous system
plays central role in short term stress reaction
body's response to threatening, exciting, or environmental stressors, like high noise levels and bright light
binds to multiple receptors when secreted into bloodstream
increases heart rate, dilates pupils, and constricts blood vessels in skin and gut while dilating arterioles in leg muscles
also increases blood sugar levels
begins breakdown of lipids in fat cells
"turns down" non-emergency bodily processes like digestion
depresses the immune system

norepinephrine

similar actions on the body as adrenaline
psychoactive because it affects alertness, helpful for studying

Gonads

ovaries of females and testes of males are gamete producing organs
ovaries are homologous to testes in males
producing gametes is an exocrine action
gonads are endocrine glands that produce steroid sex hormones
sex hormones

responsible for secondary sex characteristics that develop at puberty

puberty

process of physical changes during which the sex organs mature and a person becomes capable of reproducing

gonadotropes

luteinizing hormone (LH) and follicle stimulating hormone (FSH) both secreted by pituitary gland
tropic hormones of the gonads
triggers production of hormones in other glands
secretion of LH and FSH are controlled by gonadotropin-releasing hormone for hypothalamus
pulses are subject to estrogen feedback from gonads

androgens

in males, LH triggers production of sex hormones androgens in testes
main androgen is testosterone
causes increase in skeletal mass and bone density
also responsible for secondary sex characteristics of males, such as facial hair
also produce small amounts of estrogen in the form of estradiol

estrogen and progesterone

rise in LH concentration triggers production of estrogen and progesterone by ovaries
estrogen causes release of an egg from ovaries
progesterone prepares uterus for possible implantation by fertilized egg
placenta is endocrine gland for pregnancy
secrets hormones estrogen, human chorionic gonadatropin, and progesterone
important for maintaining pregnancy

Other hormone-producing tissues and organs

stomach, small intestine, kidneys, and heart
have cells that secrete hormones

Homeostatic imbalance: endocrine system disorders

diseases are common
includes diseases such as diabetes, thyroid disease, and obesity
usually characterized by hyposecretion or hypersecretion of hormones
also inappropriate response to hormone signaling by cells
cancer can occur in endocrine glands (thyroid)
some hormones can signal distant cancer cells to multiply

hyposecretion

production of no hormone or too little of a hormone
can be caused by destruction of hormone-secreting cells

such as Type 1 diabetes, an autoimmune disease that results in destruction of insulin producing beta cells in pancreas

also can be caused by deficiency in nutrient that is important for hormone synthesis
can be treated with hormone-replacement therapies
diabetes insipidus is characterized by excretion of large amounts of dilute urine

caused by inability of kidney to concentrate urine because of lack of ADH
insensitivity of kidneys to hormone
blood glucose levels are not affected in diabetes insipidus

growth hormone deficiency

caused by lack of GH production in pituitary gland
affects bone growth development
have low bone density and small stature, called pituitary dwarfism
treated by growth hormone replacement

hypothyroidism

not enough thyroid hormones are made
autoimmune disease where body's antibodies attack cells of thyroid and destroy it
plays important part in brain development during fetal growth
hypothyroidism in child is major cause of physical and mental growth impairment in developing countries
iodine deficiency is most common cause of preventable mental retardation and brain damage in the world

hypersecretion

body produces too much of a hormone
hormone can be hypersecreted if gland develops a tumor and grows out of control
hyperthyroidism

result of excess thyroid hormone production
causes overactive metabolism
increased speed of all body's processes
most common cause of goiter in developed world

hypersecretion of growth hormone causes acromegaly

common cause of acromegaly is benign tumor of pituitary glands that releases too much GH
also caused by overproduction of hypothalamus hormone GHRH
most commonly affects middle aged adults and can result in illness and premature death
symptoms: enlarged hands and feet, protruding brow and chin, and enlarged internal organs
disease is hard to diagnose in early stages
frequently missed for many years due to slow progression
if pituitary produced too much GH during childhood, the person will be taller than normal
called pituitary gigantism, which is very rare, and some of the tallest people on record have this condition

Hormone insensitivity: Type 2 diabetes

sometimes, the body makes enough hormones, but body cells do not respond
can be due to missing or defective hormone receptors
body cells became resistant to normal concentration of hormone, and don't respond to it
Type 2 diabetes

characterized by hyperglycemia
body cells that don't respond to normal amounts of insulin
resulting inability of pancreas to produce enough insulin
high amounts of free fatty acids and glucose in blood
high plasma levels of insulin and glucose lead to metabolic syndrome and type 2 diabetes
type 2 diabetes can be controlled by improving diet, increasing levels of activity, and sometimes medication

gestational diabetes

form of diabetes that affects pregnant women
no known single cause
hormones produced during pregnancy reduce ability of cells in pregnant woman's body to respond to insulin
results in high blood glucose concentrations

Hormones as medicines

hormone-replacement therapy
most commonly prescribed hormones are estrogens and synthetic progesterone
progestin used to prolong pregnancy in women to have experienced miscarriage due to premature drop in progesterone levels

Epinephrine

anti inflammatory effect on immune system

used to treat anaphylaxis
sudden and severe allergic reaction that involved entire body
histamine causes blood vessels to dilate
lowers blood pressure, and fluid leaks from bloodstream into tissues
can cause difficulty breathing

Anabolic androgenic steroids

synthetic androgens have many medical uses

used to stimulate bone growth and appetite
induce puberty in boys
treat muscle-wasting conditions in patients

promotes protein synthesis and growth of muscle tissue and other tissues
blocks effects of stress hormone cortisol, so breakdown of muscle is greatly reduced

Anabolic steroid abuse

used in sport and bodybuilding to increase muscle size and strength to gain competitive edge or to assist in recovery from injury
steroids used to gain competitive advantage are forbidden by rules in many sports
hearth risks can be produced by long term use or excessive doses of anabolic steroids
most side effects are dose dependent

most common side effects: increase in bad cholesterol, and decrease in good cholesterol
acne is common among anabolic steroid users
more testosterone is produced, which leads to more oil being produced

teenage boys who take anabolic steroids are more likely to be involved in sports that depend on weight and shape
have higher rates of disordered eating, drug abuse, and have poorer attitude towards health
steroids may prematurely stop lengthening of bones (stunted growth)
accelerated bone maturation, increased acne outbreaks, and premature sexual development

Jasmine's Biology Blog

Friday, April 11, 2014

Endocrine System

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