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Endocrine System
Biology 211: Anatomy & Physiology 1
Tony Serino, Ph.D.
Biology Department
Misericordia University
Endocrine System
• Controls and modifies the internal
environment by releasing chemicals
(hormones) into the blood
• Slower response time but longer duration
of action compared to nervous system
Chemical Messengers (hormones)
• Hormone –secreted by cell into blood and
acts on another cell some distance away
• Neurohormone –secreted by neuron into
blood to affect a target cell some distance
away
• Local hormones –secreted by cell into
interstitial fluid to affects cells nearby
– Paracrines –affect neighboring cells
– Autocrines –affect the secreting cell
• Pheromones –secreted by cell onto body
surface to affect cells of another individual
Hormones
• Chemical Classification
– Amines –single or few amino acids, most water soluble
• Epinephrine, Thyroxine (but water insoluble), Melatonin
– Proteins –short to long chains of amino acids; water
soluble
• GH, FSH, LH, Insulin, Glucagon, ADH, etc.
– Steroids –derivatives of cholesterol; water insoluble
• Estrogen, Testosterone, Progesterone, Cortisol, Aldosterone
Steroid Hormones
Characteristics Common to all Hormones
• Must have target cell with appropriate
receptor molecules
• Receptor-hormone complex must trigger
events in target cell that changes its
physiology
• Mechanisms for deactivating the hormone
response must be present
Controlling Hormone Response
• Half-life of the hormone
• Physiological range
• Modifying target cell response
– Up and down regulation
• Turning off secretion
– Negative feedback
– Control by other hormones, neurons and
metabolites
Control of Hormone Secretion
Mechanisms of Hormone Action
2nd messengers
Water
Soluble
Water
Insoluble
Carrier protein
nd
2
Messengers: cAMP
2nd Messengers: IP3 and Ca++-Calmodulin
Steroid Hormone Transduction
Different Styles of Secretion
• Prohormone –a hormone that is made as a
larger (inactive form) that must be changed
prior to secretion (allows for storage of
hormone in secreting cell)
Ex.: proinsulin, pro-opiomelanocortin
• Prehormone –a hormone that is secreted in
an inactive form that must be changed near
or in the target cell
Ex.: Thyroxine, Angiotensinogen
Proinsulin
Types of Endocrine Disorders
• Hypersecretion
– Too much secretion of the hormone
• Hyposecretion
– Too little secretion of hormone
• Hyporesponsiveness
– Normal secretion, but little to no response by
target cells
Endocrine Glands
Hypothalamus Control of Pituitary
Posterior Pituitary
Anterior Pituitary
Control of Growth
• Growth periods: prenatal and postnatal
(consists of pre-puberal (especially the first
2 years –infancy) and puberty
• Several factors influence growth: genetics,
diet, health, and hormonal balance
• Prenatal growth dominated by insulin
secretion, post-natal dominated by GH,
thyroxine, and sex hormones
GH secretion and effects
Increase protein
synthesis
(increase mitosis)
Increase
differentiation
GH secretion
stimulated by
exercise, fasting,
sleep (diurnal
rhythm), stress,
decreased plasma
glucose, increased
plasma AA (such
as after a high
protein meal)
GH interactions with other Hormones
• Thyroxine: essential and permissive for GH
– Needed to maintain energy levels for growth
– Increases sensitivity of target cells to GH effects
• Insulin: essential for GH effects
– Dominant hormone for pre-natal growth
• Estrogen and Testosterone: surge at puberty
stimulates GH release, synergistic with GH
anabolism; also trigger epiphyseal closure
• Cortisol: anti-growth effects; decrease GH
secretion, cell division, and increase catabolism
GH pathologies
• Hypersecretion:
– Gigantism –in children
with responsive
epiphyseal plates
– Acromegaly –in
adults, with closed
epiphyseal plates
GH pathologies
• Hypofunction:
– Dwarfism –in children
• Pituitary –decreased GH secretion
• Laron –decreased responsiveness due to
lack of GH receptors
28 yo woman with
pituitary dwarfism; 45” tall
Achondroplastic Dwarfism (genetic dwarf) due to failure of
cartilage to form in epiphyseal plate
Thyroid Location
Thyroid Follicle
(follicular cells  thyroxine)
Parafollicular cells  calcitonin
T3 & T4 Formation and Secretion
T3 & T4
Control of Thyroxine Secretion
Short loop
Long loop
Thyroid Malfunction
• Hypothyroidism
• Endemic goiters –due to iodine
deffeicency
• Cretinism –i thyroxine in child
results in igrowth (dwarf) and
severe mental retardation
• Myxedema –i thyroxine in adult,
leads to swelling of tissues plus
other symptoms
Cretinism
Thyroid Malfunction
• Hyperthyroidism
• Toxic goiters (Graves disease) –Ab
may stimulate thyroid without
negative feedback control
• Exophthalmos –symptom present in
many hyperthyroid patients
Parathyroid Location
Parathyroid
PTH Actions
• Stimulates resorption of
bone  hCa+ and PO4- in
blood
• Stimulates Ca+ absorption in
intestine (active Vit. D3
necessary for Ca+
absorption)
• Stimulates Ca+ reabsorption
and PO4- excretion in kidney
• Stimulates Vit. D3 formation
(skin) and activation
(kidney)
• Vital for life
Adrenal Location and Structure
Adrenal Layers
(Epinephrine (adrenalin))
(Androgens)
(Glucocorticoids
(cortisol))
(Mineralocorticoids,
(Aldosterone))
GAS (General Adaptation Syndrome)
Adrenal Malfunction
• Hypersecretion
Cushing’s syndrome –increase in glucocorticoids
– Usually due to over secretion of ACTH by pituitary or from
adrenal cortex tumors stimulating an increase in glucocorticoids.
Characteristic obesity of trunk only and development of “buffalo
hump” (a fat pad behind the shoulders). Will develop hypertension,
atherosclerosis, muscular weakness and fatigue.
Conn’s syndrome –excess amount of aldosterone
– Salt imbalance, water retention, hBP, muscle weakness
Adrenogenital syndrome –too much androgen
– Premature sexual development in children or masculinization in
women
Cushings
(buffalo hump)
Obesity of trunk
Adrenogenital
syndrome
A 15 yo girl, note typical masculine
build, under developed breasts, and
excessive body hair
Adrenal Cortex Malfunction
• Hyposecretion –Addison’s disease
– Due to decrease amounts of mineral and
glucocorticoids
– Can be due to over use of steroids or an
autoimmune mechanism resulting in destruction
of the gland
– Dehydration, K+ loss, iBP, fatigue,
pigmentation deepening (bronzing of skin) may
be symptom of loss of negative feedback
Pineal Gland
• Plays a major role in
circadian rhythm
control through its
sympathetic
connection to the
hypothalamus
• Melatonin increases at
night and decreases
during daylight
• Implicated in the
control of major life
changes (such as the
onset of puberty and
adulthood
Thymus Gland
• Bilobed organ that is
largest in children, but
begins to regress sharply
at the onset of puberty
(around age 11)
• It is the site of T-cell
lymphocyte production
and produces hormones
(such as, thymosin) that
modifies their physiology