The Endocrine System
Dr. Anderson
GCIT
Endocrine System
• A collection of glands
that work together to
maintain the
homeostasis of the
body by:
• Coordinating
___________________
_________and activity
via chemical
communication
The Theory of Communication
• All communication has at least three parts
• Sender – entity that releases information
• Message – the forms of the information itself
• Receiver – the entity that collects and
interprets the information contained in the
message
Hormones
• Hormones are chemicals released by glands
that control the function/activity of cells
generally far from the source of production
Body Communication
• Sender?
Tissue that creates the hormone
• Message?
The hormone itself
• Receiver?
The target tissue
Autocrines vs. Paracrines
Autocrines – cells
produce hormones that
effect themselves
Paracrines – cells
produce hormones that
effect other nearby cells
How can chemicals alter cellular
function?
Hormones can…
•
•
•
•
•
1. Alter cell membrane permeability
2. Stimulate synthesis of proteins or enzymes
3. Activates or deactivates enzymes
4. Induces exocytosis
5. Stimulates mitosis
Human Growth Hormone –
Normal Amounts
Examples – HGH
Abnormally High Amounts
Testosterone – Normal Amounts
Testosterone – Abnormal Amounts/
Gender Differences
Hormone Classification
• 3 Chemical classes
– Amino acid based
– Steroid-based (sterols)
– Eicosanoid (lipid-based)
• What is the most important functional
difference between these molecules?
Amino acid-Based Hormones
• Water soluble, so can diffuse through blood
and body fluids easily
• However, they are generally fat-insoluble
• How do they enter and affect cells?
Receptor Proteins
• Target cells have receptors for each hormone
– Not every cell has all receptors
• Receptors bind with hormones to start a series
of events, ultimately changing cell function
Water Soluble (Amino acid-based)
Hormones
Fat-Soluble Hormones
• Can go right through the cell membrane!
• Bond with receptor proteins in the cytoplasm
instead of the cell membrane
• Receptor-hormone complex can bond to DNA
to initiate gene expression
Fat-Soluble Hormones
Hormone Life (Half-life)
• Presence of a
hormone in the blood
is limited by:
1.
2.
3.
Hormone Release
• What controls the release/retention of
hormones?
1. Humoral Stimulus – Blood levels of certain
ions/nutrients
2. Neural Stimulus- Nerve fibers stimulate
hormone release
3. Hormonal Stimuli – hormones tell glands to
release/retain hormones
Regulation
• Hypothalamus –
regulates most
hormonal release in
the body
– Monitors body
homeostasis (blood
sugar, wastes,
hormone levels)
– Direct link to pituitary
gland
Pituitary gland
Hypothalamus Hormones
• The hypothalamus makes two hormones that
are stored in the posterior pituitary gland
– ADH
– Oxytocin
• These hormones travel down the
infundibulum ( nerve extensions) into the
posterior pituitary where they are stored
Pituitary Gland
• Bi-lobed structure that stores and produces
hormone
• Under the direct control of the hypothalamus!
Pituitary Gland (Hypophysis)
Posterior Pituitary
• Does not create, but rather stores hormones
that are made in the hypothalamus
• Derived from nervous tissue
– Anti-diuretic hormone (ADH) – Oxytocin
Anterior vs. Posterior Pituitary
Anterior Pituitary
• Derived from epithelial tissue (secretory cells)
• Creates MANY hormones de novo
–
–
–
–
–
–
Human growth hormone (HGH)
Thyroid Stimulating Hormone (TSH)
Adrenocorticotropic Hormone
Prolactin
Leutinizing Hormone
Follicle Stimulating Hormone
• Released or inhibited as directed by hormones
from hypothalamus (stimulates or inhibits AP
hormone production and release)
Pituitary Perfusion (Posterior)
• Posterior Pituitary
(PP) is perfused with
one major artery and
vein
• Carries PP hormones
out to body
Pituitary Perfusion (Anterior)
• Capillaries are “split”
(form plexi) twice!
– Primary capillary
plexus
– Secondary capillary
plexus
• Why???
Primary plexus
Secondary plexus
Thyroid Gland
• Surrounds the
trachea (bilateral
lobes)
• Produces the
hormone thyroxin
• Why is this not
considered to be an
exocrine gland?
Thyroid Structure
• Principal (Follicle)
Cells – produce
thyroglobulin
• Colloid – stores
thyroglobulin and
iodine molecules
• Parafollicular cells –
produce calcitonin
Thyroid Synthesis
1. Thyroglobulin made by follicular cells and goes
into follicle
2. Iodine trapped from the blood (active transport)
3. Iodide converted to iodine
4. Iodine attached to tyrosine
5. Iodinated tyrosines are linked
6. Thyroglobulin is endocytosed
7. Thyroid hormone is processed by enzymes and
diffuse from the cell into the blood stream
Thyroid Production
Calcitonin
• Produced by the
parafollicular cells in the
thyroid
• Release of calcitonin results
in lowered blood Calcium
– 1. Inhibits osteoclast activity
– 2. Enhances bone absorption
of Ca.
The Parathyroid Glands
• Paired glands located on the posterior aspect
of the thyroid
• They produce parathyroid hormone which
control Calcium levels in the blood
– Antagonist of calcitonin (inhibited by rising Ca
levels)
The Adrenal Glands
• Divided into two
sections
– Adrenal Medulla (the
core of the gland)
– Adrenal Cortex (the
outermost layer of
tissue)
• Zona glomerulosa
• Zona fasciculate
• Zona reticularis
Adrenal Cortex
• Produces
corticosteroids (derived
from cholesterol!)
• Each zone of the cortex
produces its own suite
of hormones that are
functionally specific
Adrenal Cortex – Zona glomerulosa
• Produce mineralocorticoids
– Regulate ion concentration in blood and
interstitial fluid
– Aldosterone reduces excretion of Na + from the
body and enhances resorption
• Production triggered by low blood volume, low blood
pressure and increases in K+ ion concentration.
• Why is this important?
Glucocorticoids
• Synthesized in zona
fasciculata
• Cortisol – steroid-based
hormone
– Release of cortisol promoted
by ACTH release
– Depresses inflammation,
increases blood sugar by
provoking gluconeogenesis
Gluconeogenesis
• Where do sugars normally come from?
• Gluconeogenesis -
Gonadocorticoids
• Secreted in the zona
fascicularis/reticularis
• Most are weak androgens
(precursors to testosterone
and estrogen)
– Not really (anabolic)
steroids?
• Play a large role during
puberty (both sexes) and
female sex drive
The Adrenal Medulla
• Chromaffin cells produce
catecholamines
– Epinephrine
– Norepinephine
• Released during fight-orflight stress
– Increases heart rate,
constricts blood vessels
(increasing blood pressure)
for a short time
Pineal Gland
• Located in the diencephalon
• Produces melatonin, which
causes drowsiness
• Decreased light, received by
the eyes (to brain) stimulate
the release of melatonin
Pancreas
• Organ most directly related in regulating
blood sugar
• Two hormones produced
– Glucagon – produced by alpha cells when blood
sugar is low (hypoglycemia)
– Insulin – produced when blood sugar is high
(hyperglycemia)
Pancreas
Glucagon
• When released from the pancreas,
1. causes the breakdown of glycogen (liver starch)
into sugar
2. Gluconeogenesis
3. Release of glucose from liver cells into the blood
Insulin
• When released from the pancreas, insulin…
1. Enhances cellular uptake of blood glucose
2. Inhibits gluconeogenesis
3. Inhibits the breakdown of glycogen to
glucose
Diabetes mellitus
• Due to low or non-functional insulin
• Since sugar cannot be absorbed into body
cells:
– Blood sugar levels rise (hyperglycemia)
– This stress causes the body to release MORE
glucose into the blood!
• Gluconeogenesis from fat and protein conversion, the
waste products of which lead to ketoacidosis (nail
polish breath)
Diabetes Symptoms
• In the kidneys, sugar lost in urine pulls water
from the blood at excessive rates (polyuria)
• Dehydration leads to excessive thirst
(polydipsia)
• Excessive hunger (polyphagia) results as fat
stores are used in a effort to get sugar into
body cells
Ovaries
• Ovaries – produce
estrogen and
progesterone
– Estrogen – regulates
monthly menstrual
cycle
– Progesterone – support
pregnancy and
menstruation
Menstrual Cycle
Testes
• Produce testosterone
leading to puberty
(secondary sex
characteristics),
aggression, muscle
growth