Download The Endocrine System Chapter 10

The Endocrine System
Chapter 10
Endocrine System
 “Control system” along with nervous
system
 Helps maintain homeostasis
 Allows for communication among cells
Comparison of Nervous & Endocrine
Nervous system
 quick response (milliseconds)
 relatively short duration of effect
 works via electrical impulses (action potentials) and direct
release of chemicals (neurotransmitters) across interstitial fluid to
adjacent cells
 affects specific sets of cells (neuron, muscle, gland) resulting in
specific responses (eg. muscle contraction or glandular
secretion)
Endocrine system
 slower response (minutes to hours)
 potentially long duration of effects (hours to days)
 works via chemical signals (“hormones”) which are released
through interstitial fluid into blood capillaries
 affects multiple cells throughout the body that have specific
hormone receptors (“target cells”) resulting in change of
metabolic activities of cells (eg. affects protein synthesis)
Overview of Endocrine System
 Endocrine system includes
all endocrine cells, tissues,
and endocrine glands
(organs) of the body
 Many different organs have
some endocrine cells/tissues
within their structure, but the
organ’s primary function is not
endocrine (ie: heart, kidney,
digestive organs, pancreas
hypothalamus, gonads,
thymus)
 Some organs are primarily
endocrine organs (endocrine
glands) (ie. pituitary, thyroid,
parathyroid, adrenal, pineal)
Secretion, Distribution & Effect of Hormones
 Hormones are released on demand – only when needed
 Hormone release is primarily regulated by negative feedback
mechanisms

changes in ECF (ISF/plasma) concentration/composition

changes in circulating levels of hormone itself or regulating
hormones

neural stimuli
 Hormones secreted by endocrine cells into interstitial fluid, and
distributed through bloodstream
 Only cells that posses receptors for that particular hormone can be
affected (“target cell/target organ”)
 Effect of hormones is on metabolic activity of cells, via
activation/inactivation of specific genes, affecting protein synthesis
and/or ATP production
Secretion, Distribution & Effect of Hormones
Structure of Hormones
Hormones classified based on their chemical structure:
 Amino acid derivatives – eg. epinephrine,
norepinephrine, thyroid hormones, melatonin
 Peptide/protein hormones – eg. ADH, oxytocin,
growth hormone, hypothalamic hormones, pancreatic
hormones, thymic hormones
 Lipid derivatives – include steroid hormones (eg.
estrogens, testosterone, adrenal hormones) &
eicosanoids (aka cytokines/local hormones) (eg.
prostaglandins)
Mechanism of Hormonal Action
Depends on whether hormone can cross cell membrane
& enter cell:

Epi, norepi, peptide hormones are not lipid soluble
& therefore will bind to receptors on cell membrane
(membrane receptors). Eicosanoids also bind to
membrane receptors

Steroid hormones & thyroid hormones can enter
cell & therefore will bind to receptors within the cell
(intracellular receptors)
Mechanism of Hormonal Action
 Hormones that bind to
membrane receptors
work indirectly, via
“second messengers”
 Most common second
messenger is cyclic
AMP (cAMP)
Mechanism of Hormonal Action
Hormones that can enter
the cell and bind to
intracellular receptors can
directly affect the structure
or function of the cell, via
affect on protein synthesis
&/or energy production
Pituitary Gland (Hypophysis)
 “master gland”
 Sits within sella turcica
 Attached to
hypothalamus via
infundibulum
Two regions – anterior
pituitary & posterior
pituitary
 Regulated by
hypothalamus
 Secretes 9 hormones
Anterior Pituitary Gland
 Comprised of endocrine cells that
produce & secrete 7 hormones:
 Adrenocorticotropic hormone (ACTH)
Thyroid stimulating hormone (TSH)
 Growth Hormone (GH)
 Prolactin (PRL)
 Follicle stimulating hormone (FSH)
 Luteinizing hormone (LH)
 Melanocyte-stimulating hormone (MSH)
 Controlled by regulatory hormones
(releasing hormones &/or inhibiting
hormones) from hypothalamus
Hypothalamic regulatory hormones
reach anterior pituitary via
“hypophyseal portal system”
Effects of Anterior Pituitary Hormones
Adrenocorticotropic hormone (ACTH) Targets adrenal cortex to secrete glucocorticoids (cortisol, corticosterone), which
affect glucose metabolism
Thyroid stimulating hormone (TSH) Targets thyroid gland to secrete thyroid hormones (thyroxine (T4), triiodothyronine (T3)),
which affect metabolism, growth and development
Growth Hormone (GH) Targets most body tissues, but especially liver, bone, muscle & cartilage, affecting growth,
repair & mobilization of energy reserves. Works indirectly through release of “somatomedins”
(hormones) from liver.
Prolactin (PRL) Targets mammary gland for development & lactation. Targets prostate gland in males.
Follicle stimulating hormone (FSH) Targets gonads (ovaries/testes) for gamete (egg/sperm) production & development.
Also causes secretion of estrogens by ovaries.
Luteinizing hormone (LH) Targets ovaries causing ovulation & release of estrogens and progesterone, and testes
causing secretion of testosterone
Melanocyte-stimulating hormone (MSH) Produced primarily during fetal development; targets melanocytes. No secretion in heathy adults
Overview
of Anterior
Pituitary
Hormones
ACTH
Adrenal
cortex
GH
TSH
Liver
MSH
PRL FSH
LH
Somatomedins
Thyroid
gland
Glucocorticoids
(cortisol,
corticosterone)
Melanocytes (uncertain
significance)
Testes
Bone, muscle,
cartilage, other
Thyroid hormones
(T3, T4)
Ovaries
Mammary glands
(& prostate)
Sperm
Testosterone
Estrogen
Progesterone
ovulation
Egg
Posterior Pituitary Gland
 Comprised of axons,
telodendria and terminals of
neurons that originate in the
hypothalamus
 2 hormones (antidiuretic
hormone (ADH) & oxytocin (OT)
are produced by the
hypothalamic neurons &
transported through the axons
running within infundibulum to
terminals
 Hormone release controlled
via AP stimulation
Effects of Posterior Pituitary Hormones
 Antidiuretic hormone
(aka vasopressin) –
targets kidneys to decrease
amount of urine produced
(increased water
reabsorption), & blood vessels
causing vasoconstriction to
increase BP
 Oxytocin – targets
uterus during childbirth
(positive feedback), mammary
glands for milk release (“letdown”); In non-pregnant
females & in males, may
contribute to orgasm;
“bonding” hormone
Thyroid Gland
 Located anterior to trachea, just
below thyroid cartilage of larynx
 Two lobes connected by isthmus
 Lobes contain thyroid follicles
 Follicular cells secrete 2
hormones under the influence of
TSH – Thyroxine (T4) &
Triiodothyronine (T3)
Thyroid Gland
 Thyroid hormones target almost every body cell
 Can enter cells & bind to intracellular receptors on
mitochondria & in nucleus
 Effects include:
 increased ATP production
 increased cellular metabolism, energy utilization
& oxygen consumption
 increased body temperature
 growth & development of skeletal, muscular &
nervous system in fetus & children
Thyroid Disorders
Hyperthyroidism – different causes but resulting increased
production of thyroid hormones may lead to: increased metabolic rate,
increased heart rate & blood pressure, increased body temperature,
excitability & nervousness, weight loss, possible goiter, possible
exopthalmos
Hypothyroidism – decreased secretion of thyroid hormones
may cause: lower metabolic rate, sluggishness, fatigue, decreased
heart rate & BP, decreased body temperature, weight gain, possible
goiter, subcutaneous swelling (myxedema), hair loss, dry skin
Hypothyroidism during pregnancy or in early childhood may lead to
“cretinism” – abnormal skeletal & nervous development
Adrenal (Suprarenal) Glands
 Lie superior to each
kidney
 Comprised of two parts
– outer adrenal cortex &
inner adrenal medulla
Adrenal Cortex
 Divided into 3 functional zones with each zone
producing different types of “corticosteroids”
 Middle zone secretes steroid hormones known as
“Glucocorticoids” (cortisol (hydrocortisone),
corticosterone, cortisone), under the control of ACTH
 Glucocorticoids target most body cells, especially liver,
muscle, adipose & white blood cells
Effects include:
 increased glucose synthesis, “gluconeogenesis” & glycogen
formation mainly in liver
 release of fatty acids from adipose tissue & protein breakdown in
muscle cells for energy use
 helps provide resistance to stress due to increase in available
energy
 inhibits activity of WBCs & immune responses – anti-inflammatory
effects but slow wound healing & resistance to disease
Adrenal Medulla
 Comprised of cells that are postganglionic sympathetic neurons
 Sympathetic stimulation results
in release of epinephrine
(adrenaline) and norepinephrine
(noradrenaline) into bloodstream
 Effects are sympathomimetic
Pancreas
 Endocrine & exocrine (digestive) gland
 Endocrine function by cells within pancreatic islets (islets of
Langerhans)

Alpha (α) cells secrete glucagon

Beta (β) cells secrete insulin
 Both regulate blood glucose levels
Regulation of
Blood Glucose
Diabetes Mellitus
Most common endocrine disorder of the pancreas
2 major types:

Type 1 (insulin dependent/ ”juvenile”) – actual deficiency of beta
cells; sudden onset; may be autoimmune

Type 2 (non-insulin dependent/ “adult”) – insulin resistance due to
decreased sensitivity (or number) of insulin receptors
Initial symptoms include: hyperglycemia, glycosuria, polyurea, polydipsia,
polyphagia, weight loss, fatigue
Long term symptoms: neuropathy, retinopathy, gangrene, kidney failure…
Hormones & Stress – General
Adaptation Syndrome (GAS)