Download - Introduction to Endocrine System
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The Endocrine System
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Endocrine Glands
• Controls many body functions– exerts control by releasing special chemical substances
into the blood called hormones– Hormones affect other endocrine glands or body
systems
• Ductless glands• Secrete hormones directly into bloodstream– Hormones are quickly distributed by bloodstream
throughout the body
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Hormones
• Chemicals produced by endocrine glands.• Act on target organs elsewhere in body.• Control/coordinate widespread processes:• Homeostasis.• Reproduction.• Growth & Development.• Metabolism.• Response to stress.
• Overlaps with the Sympathetic Nervous System
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Hormones
Hormones are classified as:ProteinsPolypeptides (amino acid derivatives)Lipids (fatty acid derivatives or steroids)
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Hormones
Amount of hormone reaching target tissue directly correlates with concentration of hormone in blood.
Constant level hormones• Thyroid hormones
Variable level hormones• Epinephrine (adrenaline) release
Cyclic level hormones• Reproductive hormones
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The Endocrine System Consists of several glands located in various parts of
the body Specific Glands
Hypothalamus Pituitary Thyroid Parathyroid Adrenal Kidneys Pancreatic Islets Ovaries Testes
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Pituitary Gland
Small gland located on stalk hanging from base of brain.
“The Master Gland” Primary function is to control other glands.Produces many hormones.Secretion is controlled by hypothalamus in base of brain.
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Pituitary Gland Two areas
Anterior PituitaryPosterior Pituitary
Structurally, functionally different
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Pituitary Gland
Anterior Pituitary HormonesThyroid-Stimulating Hormone (TSH)
stimulates release of hormones from Thyroid thyroxine (T4) and triiodothyronine (T3): stimulate
metabolism of all cellscalcitonin: lowers the amount of calcium in the blood by
inhibiting breakdown of bone
released when stimulated by TSH or coldabnormal conditions
hyperthyroidism: too much TSH releasehypothyroidism: too little TSH release
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Pituitary Gland
Anterior PituitaryGrowth Hormone (GH)
stimulates growth of all organs and increases blood glucose concentration
decreases glucose usage increases consumption of fats as an energy source
Adreno-Corticotrophic Hormone (ACTH)stimulates the release of adrenal cortex hormones
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Pituitary Gland
Anterior PituitaryFollicle Stimulating Hormone (FSH)
females - stimulates maturation of ova; release of estrogen
males - stimulates testes to grow; produce spermLuteinizing Hormone (LH)
females - stimulates ovulation; growth of corpus luteum
males - stimulates testes to secrete testosterone
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Pituitary Gland
Anterior PituitaryProlactin
stimulates breast development during pregnancy; milk production after delivery
Melanocyte Stimulating Hormone (MSH)stimulates synthesis, dispersion of melanin pigment
in skin
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Pituitary Gland
Posterior PituitaryStores, releases two hormones produced in
hypothalamusAntidiuretic hormone (ADH)Oxytocin
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Pituitary Gland
Posterior Pituitary Hormones: Antidiuretic hormone (ADH)
Stimulates water retention by kidneys reabsorb sodium and water
Abnormal conditionsUndersecretion: diabetes insipidus (“water diabetes”)Oversecretion: Syndrome of Inappropriate Antidiuretic
Hormone (SIADH)
OxytocinStimulates contraction of uterus at end of pregnancy
(Pitocin®); release of milk from breast
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Hypothalamus Produces several releasing and inhibiting factors
that stimulate or inhibit anterior pituitary’s secretion of hormones.
Produces hormones that are stored in and released from posterior pituitary.
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Hypothalamus Also responsible for:
Regulation of water balanceEsophageal swallowingBody temperature regulation (shivering)Food/water intake (appetite)Sleep-wake cycleAutonomic functions
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Pineal Gland Located within the Diencephalon Melatonin
Inhibits ovarian hormonesMay regulate the body’s internal clock
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Thyroid Gland
Located below larynx and low in neckNot over the thyroid cartilage
Thyroxine (T4) and Triiodothyronine (T3)Stimulate metabolism of all cells
Calcitonin Decreases blood calcium
concentration by inhibiting breakdown of bone
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Parathyroids Located on posterior surface of
thyroid Frequently damaged during
thyroid surgery Parathyroid hormone (PTH)
Stimulates Ca2+ release from bone Promotes intestinal absorption and
renal tubular reabsorption of calcium
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Parathyroids Underactivity
Decrease serum Ca2+
Hypocalcemic tetanySeizures Laryngospasm
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Parathyroids
Overactivity Increased serum Ca2+
Pathological fracturesHypertensionRenal stonesAltered mental status
“Bones, stones, hypertones, abdominal moans”
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Thymus Gland
Located in anterior chest Normally absent by ~ age 4Promotes development of immune-system
cells (T-lymphocytes)
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Adrenal Glands
• There are 2 adrenal glands, one on top of each kidney.
• Each gland has 2 endocrine parts:– An inner adrenal medulla– A surrounding adrenal
cortex.
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Adrenal Glands
• Adrenal Medulla– the Adrenal Medulla secretes the catecholamine
hormones norepinephrine and epinephrine– Epinephrine and Norepinephrine.
• Prolong and intensify the sympathetic nervous system response during stress.
• More epinephrine than norepinephrine is secreted.
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Adrenal Glands• Adrenal Cortex– Aldosterone (Mineralocorticoid)
• Regulates electrolyte (potassium, sodium) and fluid homeostasis in the body.
– Cortisol (Glucocorticoids)• Anti inflammatory, anti-immunity, and anti-allergy
effects.• Increases blood glucose concentrations
– Androgens (Sex Hormones)• Stimulate sexual drive in females
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Adrenal Glands
Adrenal Cortex Glucocorticoids
accounts for 95% of adrenal cortex hormone production the level of glucose in the bloodReleased in response to stress, injury, or serious
infection - like the hormones from the adrenal medulla
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Ovaries Located in the abdominal cavity adjacent to the
uterus. Under the control of LH and FSH from the
anterior pituitary gland. Produce eggs for reproduction. Produce hormones
estrogen progesterone Functions include sexual development and preparation
of the uterus for implantation of the egg.
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Ovaries
Estrogen Development of female secondary sexual characteristics. Development of endometrium.
Progesterone Promotes conditions required for pregnancy. Stabilization of endometrium.
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Testes
Located in the scrotum. Controlled by anterior pituitary hormones FSH and
LH. Produce sperm for reproduction. Produce testosterone -
promotes male growth and masculinization. promotes development and maintenance of male sexual
characteristics.
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Pancreas
Located in retroperitoneal space between duodenum and spleen.
Has both endocrine and exocrine functions. Exocrine Pancreas:• Secretes key digestive enzymes
Endocrine Pancreas:• Alpha Cells - glucagon production.• Beta Cells - insulin production.• Delta Cells - somatostatin production.
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Pancreas
• Exocrine function• Secretion of:
amylaselipase
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Pancreas
Alpha Cells Glucagon
Raises blood glucose levels
Beta Cells Insulin
Lowers blood glucose levels
Delta Cells Somatostatin
Suppresses release of growth hormone
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Classes of hormones
Three broad classes of hormones:Amine Hormones - Derivative of the amino acid
tyrosine.T3,T4.Peptide Hormones - The majority of hormones.These
hormones may also serve as neurotransmitters. Eg:; Calcitonin.
Steroid Hormones- Produced by the adrenal cortex and the gonads.
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Hormone Transport in Blood
• Water-soluble hormones are transported dissolved in blood plasma.
• Others circulate in blood, bound to plasma proteins.
• The free hormone diffuses across capillary walls to encounter its target cells.
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Hormone Metabolism and Excretion
• Concentration of a hormone in plasma depends upon its rate of secretion and rate of removal.
• Hormones are either excreted by kidneys or metabolized in blood or the target cells.
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Mechanisms of Hormone Action
• Hormones reach all tissues via blood but only cells that have receptors to bind the hormone act as target cells for the hormone.
• A low concentration of hormone is compensated for by an increase in the number of receptors - up-regulation.
• while a high concentration of hormones leads to a decrease in the number of receptors - down-regulation.
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• A hormone can reduce the number of receptors available for a second hormone, resulting in decreased effectiveness of the second hormone (antagonism).
• A hormone can also induce an increase in the number of receptors for a second hormone, increasing the latter's effectiveness (permissiveness).
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Events Elicited by Hormone-Receptor Binding
• Receptors for peptide hormones and catecholamines are present on the extracellular surface of the plasma membrane.
• Receptors for steroid and thyroid hormones are mainly present on the intracellular surface of the membrane.
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Hormone-receptor binding influences:
1- Ion channels.
2- Enzyme activity that is part of the receptor.
3- Activity of kinases.
4- Gene proteins and second messengers.
Genes could also be activated or inhibited, causing a change in the synthesis rate of proteins coded for by these genes.
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