The Endocrine System and Hormones
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The Endocrine System and Hormones
Endocrine System
Regulates, coordinates and controls :
Growth and development
Male and female development
How body uses energy
Levels of salts and sugars in blood
The amount (volume) of fluid in body
Appetite
Many other body functions
Endocrine Glands
organs of the Endocrine System
produce and secrete (release) Hormone
located all over your body
Hormones
Biochemical classification
Mechanism of action
Signal transduction
Definition
Hormones - chemical messengers that are secreted
(released) from glands into the blood and affect cells in
another part of the body.
General Principles
Cells of an organism do not live in isolation.
The communication between cells ultimately controls growth, differentiation, and metabolic processes within the organism.
Communication between cells is often by direct cell to cell contact.
Communication frequently occurs between cells over short and long distances.
In the target cell, a specific response is induced.
Cells use an amazing number of signaling chemicals.
These signaling molecules are termed “hormones.”
The ability of a hormone to induce a response in a target cell
is usually mediated by a hormone receptor on, or in, the
target cell
General characteristics of hormones
are secreted directly into the blood
Carried to their sites of action
are present at very low levels in the circulatory system
specifically affect or alter the activities of the responsive
tissue (target tissue)
act specifically via receptors located on, or in, target tissue
Specific stimulus for hormones
secretion
nerve impulse
concentration of the certain compound in blood passing
through the endocrine gland
Brain reacts by way of secretions
from neurons in hypothalamus
(neurohormones)
Brain also reacts by way of
nerves from hypothalamus and
brainstem
Classification of hormones
1.Proteins: hormones of anterior pituitary, insulin, parathyroid hormone.
2.Peptides: ACTH, calcitonin, glucagon, vasopressin, oxytocin, hormones of hypothalamus.
3.Derivatives of amino acids: catecholamins (epinephrine and norepinephrine), thyroxin, triiodthyronin.
4.Steroid (derivatives of cholesterol): hormones of the cortex of epinephrine lands, sex hormones.
5.Derivatives of polyunsaturated fatty (arachidonic) acids: prostaglandins.
Hormone Source Function Insulin Pancreas Controls blood sugar level and
storage of glycogen Glucagon Pancreas Stimulates conversion of
glycogen to glucose Oxytocin Pituitary gland Stimulates concentration of the
uterine muscles and secretion of milk by the mammary glands
Vasopressin Pituitary gland Controls water excretion by the kidneys; stimulates contraction of the blood vessels
Growth hormone Pituitary gland Stimulates growth Adrenocorticotrophic hormone Pituitary gland Stimulates the adrenal cortex
Prolactin Pituitary gland Stimulates milk production by the mammary glands after birth of baby
Epinephrine Adrenal glands Stimulates rise in blood pressure, acceleration of heartbeat, decreased secretion of insulin and increased blood sugar.
Hormone Source Function
Cortisone Adrenal glands Helps control carbohydrate metabolism, salt and water balance, formation and storage of glycogen.
Thyroxine and Triiodothyronine Thyroid gland Increases the metabolic rate of carbohydrates and proteins
Calcitonin Tryroid gland Prevents the rise of calcium and phosphate in the body
Parathyroid Parathyroid gland Regulates the metabolism of calcium and phosphate in hormone in the body
Gastrin Stomach Stimulates cesretion of gastric juice
Secretin Duodenum Stimulates secretion of pancreatic juice
Estrogen Ovaries Stimulates development and maintenance of female sexual characteristics
Progesterone Ovaries Stimulates female sexual characteristics and maintains pregnancy
Testosterone Testes Stimulates development and maintenance of male sexual characteristics
Transport of hormones in the blood
Protein and peptide nature – in free state
Steroid hormones and hormones of thyroid gland – bound with alpha-globulins or albumins
Catecholamines – in free state or bound with albumins, sulphates or glucuronic acid
Reach the target organs
Cells have the specific receptors to certain hormone.
Hormone receptors
Model of insulin receptor
Target cells
Hormones only work on certain cells - target cells
The target cells have special receptors
“recognize” the hormones and allow them to influence that
cell
These receptors recognize the hormones.
They “fit” like a lock and key.
Inactivation of hormones
After biochemical effect hormones are released and metabolized
Hormones are inactivated mainly in liver
Inactive metabolites are excreted mainly with urine
Half-time life
-from several min to 20 min – for the majority of hormones
-till 1 h – for steroid hormones
-till 1 week – for thyroid hormones
The final effects of hormone actions
1.Change the permeability of cell membrane, accelerate the penetration of substrates, enzymes, coenzymes into the cell and out of cell.
2.Acting on the allosteric centers affect the activity of enzymes (Hormones penetrating membranes).
3.Affect the activity of enzymes through the messengers (cAMP).
4.Act on the genetic apparatus of the cell (nucleus, DNA) and promote the synthesis of enzymes (Steroid and thyroid hormones).
Hormone systems are negative
feedback systems
Negative feedback - when enough hormone is in the body, the
body stops producing the hormone until it is needed again
You eat. Glucose (sugar)
in the blood increases.
Increased glucose is detected by receptors
that notify the brain. It sends a message
to the pancreas to produce insulin.
Insulin tells muscle and liver to take up
glucose from the bloodstream and use it for energy
or store it for later. Brain reduces appetite.
Blood glucose level drops as
it is removed by the cells.
Pancreas stops making insulin
Few hormone systems are positive
feedback systems
pituitary gland sends a signal by way of the hormone
oxytocin to the uterus causing contractions
pressure of the fetus on the cervix sends a signal back to the
brain which then stimulates the release of more oxytocin
This causes more contractions
The fetus pushes harder on the cervix.
More oxytocin is released. The system continues until birth
occurs
Types of Hormones
Catecholamines and Thyroid Hormones
Small and derived from amino acids (epinephrine, thryoxine.)
Steroid Hormones and Vitamin D
Relatively small and derived from cholesterol
Prostaglandin's
Relatively small and derived from fatty acids
Proteins or Polypeptides
relatively large and derived from translation of hormone specific mRNA (growth hormone, insulin)
Catecholamines
synthesized in nervous tissues from which the adrenal medulla is derived.
Adrenal medulla is the major source for circulating epinephrine.
Synthesized from tyrosine which is converted to dihydroxyphenylalanine (DOPA) by tyrosine hydroxylases.
Subsequent conversions to dopamine and then to nor epinephrine which is released by most catecholamine-producing cells of the body.
In the adrenal medulla and a few other tissue, nor epinephrine is converted to epinephrine.
The half life is 1-2 minutes.
Adrenaline
Where it comes from: Adrenal Gland
Where it acts: heart, blood vessels, eyes
What it does: stimulates heart rate, increases blood pressure, dilates pupils
Causes "Adrenaline Rush”
A 'fight and flight' hormone.
It is released in high stress conditions or in excitement or fear.
Loud noise, high temperature etc. may also trigger its release since these are also high stress situations.
Progesterone
Where it comes from: ovary
(where an egg was released)
Where it acts: uterus
What it does: controls
menstruation in women and
plays a role in pregnancy.
One of the components of
birth control pills
Thyroid Hormones
Synthesized solely in the thyroid gland ( T4; 3’,5’,3,5-L-tetra-iodothyronine).
Majority of the active form, T3 (3’,3,5-L-tri-iodothyronine), is produced in the peripheral tissues through deiodination of T4.
Thyroid gland cells concentrates iodine for thyroid hormone synthesis.
Iodine is attached to tyrosine residues on a protein, termed thyroglobulin. Tyrosine residues are then coupled together to yield thyronines.
Proteolytic digestion of thyroglobulin then yields T4 and T3 in a 10:1 ratio.
Helps in the metabolism of sugars.
The half life of T4 is 7 days and that of T3 is 1 day.
Thyroxine
Where it comes from: thyroid gland
Where it acts: most cells of the body
What it does: controls the rate of metabolic processes (how energy is used) in the body and influences physical development
People may not produce enough of this hormone and get a condition known as hypothyroidism. They can take thyroxine to treat this condition.
Steroid hormones
Produced in the adrenals, ovaries, testes, and placenta.
Derived from cholesterol.
Enzymes in the various glands control the final product. For example, cytochrome P450c11 which is located in the adrencortical cells, is involved in coritsol production. This enzyme is lacking in the gonads, that do not produce cortisol or aldosterone.
Gonads, however, can produce dihydroxytestosterone, estradiol, or progesterone depending upon the enzymes present in the gonadal tissue.
Over 50 different steroid metabolites have been described.
STEROID HORMONES
Testosteron
Where it comes from: testicles
Where it acts: body-hair cells, muscle, reproductive structures
What it does: stimulates development of male sexual characteristics
Testosterone is a steroid and has been administered to athletes in order to improve performance. This is considered to be a form of doping in most sports and is a very dangerous practice.
Females also produce small amounts of testosterone in their ovaries that affect muscle development and other body functions.
Estrogen
Where it comes from: ovary
Where it acts: breast tissue, reproductive structures in female
What it does: stimulates development of female sexual characteristics
Estrogen levels may be related somehow to migraine headaches in women.
Cortisol
Where it comes from: outer part of adrenal gland
Where it acts: multiple tissues
What it does: mental stimulation, breaks down fat and protein to glucose, anti-inflammation
It is usually referred to as the "stress hormone" as it is involved in response to stress and anxiety.
Prostaglandins and Leukotrienes
can be produced by most cells depending upon lipid and enzyme content of the cells.
Arachidonic acid - is the precursor compound.
Cyclooxygenase (involved in PGG2 synthesis) is widely distributed throughout the body
Is inhibited by aspirin, indomethacin, and other nonsteroidal and anti-inflammatory agents.
The half-life: a few seconds
Insulin
Where it comes from: Insulin is produced in the pancreas
Where it acts: liver, muscle, and fat tissue
What it does: Insulin causes cells to take up glucose (sugar) from the blood, storing it in the liver and muscle, and stopping use of fat as an energy source.
Problems with insulin production or use in the body can lead to diabetes.
The hormones of the pancreas
blood glucose levels are too high - pancreas releases the
hormone insulin
tells the liver to convert glucose into glycogen - stored in
the liver and muscles
blood glucose levels are too low - pancreas releases the
hormone glucagon
tells the liver to convert glycogen into glucose - release it
into the blood
Hormone receptors
Nuclear receptors – estrogens
Cytoplasmic receptors – most steroid and thyroid
hormones
Cell surface membrane receptors – polypeptide
hormones and catecholamines
Rules
Interaction - All hormones interact with target cells by first binding to specific receptors located either on the plasma membrane or as a cytosolic protein
Linkage - The receptor for hormones must be linked to a component that is able to respond to the binding of hormone with its receptor
Agonists - Substances that fool the responder into thinking a hormone has bound
Antagonists - Substances that prevent the binding of the natural hormone and do not elicit a response from the receptor
Signal transduction
The series of events and components that take part in transmitting a
hormonal signal to a the interior of the cell
Primary areas of hormone action
Reproduction
Growth and development
Maintenance of internal environment
Energy production, utilization and storage
Definitions related to hormones Endocrine - Refers to the internal secretion of biologically
active substances.
Exocrine - Refers to secretion outside the body, for example, through sweat glands, mammary glands, or ducts lead to the gastrointestinal
Paracrine - Hormones that act locally on cells that did not produce them
Autocrine - Hormones that act on cells that produced them.
Examples of hormone antagonists
used in therapy
Antagonist to Use
Growth hormone Acromegaly, Diabetes
Progesterone Contraceptive, abortion
Glucocorticoid Spontaneous Cushing's Syndrome
Mineralocorticoid Primary and secondary mineralocorticoid Excess
Androgen Prostate cancer
Estrogen Breast cancer
Adreneric Hypertension, hyperthyroidism
Prostaglandin Acute and chronic inflammatory disease
Summary What are the functions of the Endocrine System?
Name Endocrine Glands and what they do.
What are hormones?
How do hormones work?
Name hormones and what they do.
At what times in your life do you think your Endocrine System is most active?
Hormone receptors
Rules
Signal Transduction
Definitions (!)
Antagonists and their use
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