Download The Endocrine System

The Endocrine System
Interacts with nervous system to
coordinate and integrate activity of body
cells
Nervous System v. Endocrine System
Control
Nervous System
 Regulation by
electrochemical
impulses (electrical
signals &
neurotransmitters)
 Neurons deliver
impulses to muscles &
glands
 Rapid response
 Short duration
Endocrine System
 Regulation by chemical
messengers
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Hormones: long distance
chemical signals travel in
blood & lymph
Hormones released into
blood & transported to
all cells
Lag time (sec. to days)
Prolonged response
Endocrine System
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Controls growth & reproduction
Mobilizes body defenses
Maintains blood electrolytes, water & nutrient
balance
Maintains cellular metabolism
Maintains energy balance
Endocrine organs scattered about the body
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Two kinds of glands
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Exocrine – gland that secretes its product into an
area of the body via ducts
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Nonhormonal
Endocrine – gland that secretes its product into
the blood without the use of ducts
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Produces hormones
Local-acting molecules – i.e prostaglandin effect on smooth
muscle cells
Exocrine Glands
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Substances are routed to membrane surface
through ducts – not systemically distributed
Unicellular
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Goblet cells secrete mucus to lubricate internal surfaces.
Found in epithelium of respiratory, digestive, urinary and
reproductive systems
Multicellular
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Sweat glands (secrete sweat), mammary glands (milk),
sebaceous glands (sebum), salivary glands (saliva),
pancreas (digestive enzymes), prostate gland (seminal
fluid)
Endocrine glands
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Produce hormones which are released into
the blood that is passing through the gland
Examples:
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Pineal gland
Pituitary gland
Thyroid gland
Parathyroid gland
Thymus gland
Adrenal gland
Mixed-Functioning Glands
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Pancreas
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Gonads
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Secretes digestive juices into pancreatic duct to small
intestine (exocrine)
Secretes insulin & glucagons into blood from Islets of
Langerhans cells to regulate blood glucose levels
(endocrine)
Ovaries and testes produce steroid sex hormones
Seminal vesicles produce seminal fluid
Hypothalamus
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Neuroendocrine organ – regulates body homeostasis
(neural) and acts on pituitary (endocrine)
Other organs containing hormoneproducing cells
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Stomach – Gastrin, serotonin
Small intestine- intestinal gastrin, secretin,
cholecystokinin
Kidney - Erythropoietin
Skin- Cholecalciferol
Heart- atrial natriuretic peptide
Adipose tissue – leptin, resistin
Hormones - Chemistry
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Hormones are either steroids, polypeptides,
glycoproteins, or derivatives of amino acids
Most hormones are amino acid based
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Simple amino acid derivatives – amines &
thyroxine
Peptides – short chains of amino acids
Proteins – long polymers of amino acids
Of major endocrine organs, gonadal &
adrenocortical hormones are steroids
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Steroids are synthesized from cholesterol
Mechanism of Hormone Action
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Alters plasma membrane permeability and/or
membrane potential by opening or closing ion
channels
Stimulates production of regulatory molecules
within cell
Activates or deactivates enzymes
Induces secretions
Stimulates mitosis
Mechanisms of Hormone Communication
Second-Messenger Systems
 Amino acid-based hormones cannot
penetrate cell plasma membrane
 Hormone binds to plasma membrane
receptor which generates second
messengers
 Examples
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Cyclic AMP
PIP-calcium
Cyclic AMP
3’5’-cyclic adenosine monophosphate
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Hormone (1st messenger) binds to plasma
membrane receptor activating the signal
transducer, G protein (light switch)
G protein activates an effector enzyme,
adenylate cyclase (GTP)
GTP generates cAMP (2nd messenger)
cAMP triggers cascade of chemical reactions
within the cell (amplification effect)
Cyclic AMP
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Chemical reactions set in motion by cAMP depend on
 Type of target cell
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Target cell is a cell that has proper receptors to react with a specific
hormone
Enzymes in the target cell
Which hormone is 1st messenger
cAMP action persists briefly, therefore no extracellular controls are
necessary to stop activity
Direct Gene Activation
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Steroid hormones (and thyroid hormone) can
diffuse into target cells (lipid soluble)
Steroid hormones bind to receptor and
hormone-receptor enters nucleus and binds
to DNA-associated receptor protein
Thyroid receptors are on the DNA
This “turns on” a gene → transcription of
DNA → produce mRNA → translation →
protein molecules (enzymes) → metabolic
processes
Interaction of Hormones at Target Cells
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Permissive effect: enhancement of a target
organ’s responsiveness to a hormone from
prior exposure to a different hormone
Synergistic effect: effect of two or more
hormones acting on an organ
Antagonistic effect: occurs when the effect
of one hormone opposes the effect of another
on a target organ
Interaction of Hormones at Target Cells
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Permissive effect
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Synergistic effect
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Thyroid hormone is necessary for normal
reproductive system development
Glucagon (pancreas) and epinephrine cause liver
to release glucose to the blood efficiently
Antagonistic effect
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Insulin (lowers blood sugar) is antagonized by
action of glucagon (raises blood sugar)
Control of Hormone Release
Synthesis and release of most hormones are
regulated by a negative feedback system
 Hormone secretion triggered by stimuli
 Hormone levels rise
 Target organ effects are produced
 Further hormone release inhibited
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As a result, concentration of hormones in
blood varies within narrow range
Control of Hormone Release
Endocrine glands are stimulated by 3 types of stimuli
 Humoral Stimuli
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Response to changing levels of ions and nutrients
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Neural Stimuli
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Response to nerve fiber stimuli
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Ca2+ levels monitored by parathyroid (PTH)
Release of norepinephrine & epinephrine by adrenal medulla
during stress
Hormonal Stimuli
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Response to other hormones
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Hypothalamic-pituitary-target feedback loop
Pituitary Gland (Hypophysis)
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Located in the hypophyseal fossa of the sella turcica
of the sphenoid bone
Attached to the base of the brain underneath
hypothalamus
Composed of two separate lobes
“pea on a stalk”
Stalk, infundibulum, connects the gland to the
hypothalamus
Anterior lobe composed of glandular tissue which
produces hormones and releases them into blood
Posterior lobe composed of neurological tissue
which releases neurohomones from hypothalamus
Pituitary Gland
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Anterior lobe is called adenohypophysis and is
referred to as master endocrine gland
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Now known to be controlled by hypothalamus
Produces 6 hormones (proteins)
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Growth hormone (GH)
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Gonadotropins
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Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin (PRL)
All affect target cells via cyclic AMP
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Pituitary Gland
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Posterior pituitary is called the
neurohypophysis and is made up of axons of
hypothalamic neurons
Produces 2 hormones
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Oxytocin
Antidiuretic hormone (ADH)
Both use PIP-calcium second-messenger
mechanism
Pituitary Gland Hormones
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Growth Hormone (GH)
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Stimulates growth in all organs
Promotes fat mobilization
Inhibits blood sugar utilization
Secretion of GH regulated by Growth hormone-releasing
hormone (GHRH) opposed by the Growth hormoneinhibiting hormone (GHIH)
Gigantism caused by hypersecretion in children
Acromegaly occurs when hypersecretion occurs after
epiphyseal plates have closed
Pituitary dwarfism is caused by hyposecretion
Pituitary Gland Hormones
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Thyroid-stimulating hormone (TSH)
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Stimulates normal development of thyroid
Release is triggered by thyrotropin-releasing
hormone (TRH)
Rising blood levels of thyroid hormones acts on
pituitary and hypothalamus to inhibit TSH
In response, hypothalamus releases GHIH which
helps block TSH
Hyposecretion: Cretinism and myxedema
Hypersecretion: Graves disease
Pituitary Gland Hormones
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Adrenocorticotropic hormone (ACTH)
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Secreted by anterior pituitary lobe
Stimulates adrenal cortex to release corticosteroid
hormones that help body resist stressors
Release triggered by corticotropic-releasing
hormone (CRH)
Rising levels of glucocorticoids block CRH and
thus ACTH release
Hypersecretion: Cushing’s disease
Pituitary Gland Hormones
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Follicle-stimulating hormone (FSH) and Luteinizing
hornmone (LH)
Regulate function of the gonads
Stimulate gamete production
Promotes production of gonadal hormones
LH works with FSH to cause egg maturation
(ovarian follicle)
LH triggers ovulation
LH stimulates production of testosterone in males
Hyposecretion: failure of sexual maturation
Pituitary Gland Hormones
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Prolactin (PRL)
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Stimulates milk production in breasts
Controlled by hypothalamic hormones
Oxytocin
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Made by hypothalamic neurons and stored in
posterior pituitary
Strong stimulant of uterine contraction
Stimulated by stretching of uterus and cervix
Pituitary Gland Hormones
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Antidiuretic hormone (ADH) (vasopressin)
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Made by hypothalamic neurons and stored in posterior
pituitary
Diuresis is urine production: an antidiuretic inhibits urine
formation
Prevents wide swings in water balance
Hypothalamic neurons monitor solute concentration of
blood: when too concentrated, ADH released
Targets kidney tubules to reabsorb more water from urine
thus lowering urine volume
Alcohol inhibits ADH thus causing copious urine output with
resulting dry mouth and dehydration
Diuretics antagonize ADH (manage hypertension, edema)
Thyroid Gland
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Thyroid Hormone (TH)
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Thyroxine (T4) (4 bound iodine atoms) and triiodothyronine
(T3) (3 iodine atoms)
Except for adult brain, spleen, testes, uterus, and thyroid, TH
affects every cell of body
Stimulates protein synthesis
Promotes maturation of nervous system
Increases rate at which energy is used by body
Thyroid-stimulating hormone (TSH) stimulates thyroid to
produce thyroxine
Hypothyroidism in adults – myxedema; in children –cretinism
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Goiter caused by lack of iodine
Hyperthyroid – Graves disease (autoimmune disease?)
Thyroid and Parathyroid Glands
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Calcitonin
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Produced by the thyroid
Promotes decrease in blood calcium
Direct antagonist of parathyroid hormone
Parathyroid hormone (PTH)
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Secreted by parathyroid glands
Helps increase calcium blood levels
Affects the bones, kidneys and intestines
Adrenal Glands
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Steroid hormones (corticosteroids) are
synthesized from cholesterol by adrenal
cortex
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Not stored in cells, so rate of release depends on
rate of synthesis
Mineralocorticoids (aldosterone) – act on the
kidneys to regulate sodium and potassium
balance
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Hypersecretion – aldosteronism
Hyposecretion – Addison’s disease
Adrenal Glands
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Aldosteronism
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Hypertension and edema due to excessive
sodium ion and water retention
Accelerated excretion potassium ions, which can
lead to unresponsive neurons
Addison’s disease
 Hyposecretory disorder of adrenal cortex
 Deficits in mineralocorticoids and glucocorticoids
 Severe dehydration and hypotension
Adrenal Glands
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Steroid hormones (cont.)
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Glucocorticoids (cortisol) – regulate metabolism of
blood sugar and other organic compounds,
essential to life
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Modify gene activity
Help respond to stressors
Cortisol release promoted by ACTH
Rising cortisol levels feed back to act on hypothalamus
and anterior pituitary, preventing CRH release and
shutting off ACTH and cortisol
Adrenal Glands
Stress response
 Stress results in rise in blood levels of glucose, fatty
acids, amino acids caused by cortisol
 Cortisol provokes formation of glucose from fats &
proteins
 Cortisol enhances epinephrine’s vasoconstrictive
effects with rise of blood pressure
 Anti-inflammatory and anti-immune effects are
associated with cortisol excess
 Cushing’s disease- may be caused by ACTHreleasing pituitary tumor, adrenal cortex tumor, or
other malignancy
Adrenal Glands
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Sex hormones (Gonadocorticoids)
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Androgens (weak male sex hormone)
Estradiol (estrogen)
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Small amounts compared to those produced in sex
organs
Contribute to onset of puberty
Gonads
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Produce steroid sex hormones
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Estrogens
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Progesterone
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Stimulates female secondary sex characteristics,
stimulates maturation, help stimulate mammary gland
development
Helps maintain endometrium during pregnancy,
increases uterine sensitivity to oxytocin, suppresses
gonadotropin secretion
Testosterone
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Stimulates development of male genitalia and secondary
sex characteristics
Pancreas
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Located behind stomach in abdomen
Islets of Langerhans produce hormones
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Alpha (α) cells synthesize glucagon
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Glucagon is hyperglycemic; its target is the liver;
increases blood glucose levels
Beta (β) cells synthesize insulin
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Insulin is hypoglycemic; lowers blood sugar levels;
inhibits breakdown of gylcogen
Pancreas
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Diabetes mellitus (DM)
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Results from hyposecretion or hyperactivity of insulin
Blood sugar levels remain high after a meal
High hyperglycemia triggers hypoglycemic response and
sugar levels go higher
High sugar levels begin to be lost in urine
Fats are mobilized: high fatty acid (and ketones) levels
result; lowers pH
Nervous systems initiates rapid breathing to raise pH
Ketoacidosis can lead to coma and death if untreated
Pancreas
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Diabetes mellitus (DM)
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Hyperinsulinism – excessive insulin secretion
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Results in low blood sugar levels (hypoglycemia)
Triggers hyperglycemic hormones which cause anxiety,
nervousness, tremors, weakness
Insufficient delivery of glucose to brain cause
disorientation and can lead to unconsciousness and
death
Treated by ingesting sugar
Pineal Gland and Thymus
Pineal Gland
 Hangs from the roof of the third ventricle in the
diencephalon
 Endocrine function still a mystery
 Melatonin is produced (derived from serotonin) and
peak levels cause drowsiness
 Related to day/night cycles
Thymus
Located in thorax, appears to be essential for
development of immune response