Download Endocrine System

Endocrine System
Collection of specialized cells, tissues and glands
that produce and secrete hormones that control
many body functions.
Endocrine glands are ductless and secrete their
hormones into interstitial fluid, lymph, and blood.
• Exocrine glands secrete products into ducts
• Hormones are bloodborne “information” units.
– Come from endocrine glands
– Circulate in the bloodstream
– Act on specific cells in the body
rev 12-12
Endocrine-BIO 102 HANDOUT
1
Endocrine glands are stimulated in one of three
ways:
1. By nervous impulses
2. By hormones
3. By humoral stimulation (usually a chemical
[glucose, calcium] )regulated by the
hormone which activates or inhibits hormone
release
Endocrine-BIO 102 HANDOUT
2
Endocrine System Characteristics
• Access to every cell because hormones circulate
in the blood
• Each hormone acts only on specific cells
(target cells) because only the hormone’s
target cells have the appropriate receptor to
fit it;
• Endocrine control slower than nervous system
• Endocrine and nervous systems interact i.e.
timing of growth and sexual maturation involves
a complex sequence of changes in both
endocrine and nerve signals; release of some
hormones is dependent on input from sensory
neurons.
Endocrine-BIO 102 HANDOUT
3
Classification of Hormones
Hormones are classified as “steroid” or “nonsteroid”
based on their structure and mechanism of action.
• Steroid hormones:
– Lipid soluble, chemically derived from cholesterol
– Enter target cells, bind to an intracellular receptor
and activate genes that produce new proteins
– Slower acting than nonsteroid hormones
Endocrine-BIO 102 HANDOUT
4
Steroid hormones pass through the plasma
membrane and act in a two step process.
• Once inside the cell, steroid hormones
bind to nuclear membrane receptors,
producing an activated hormone-receptor
complex.
• The activated hormone-receptor complex
binds to DNA and activates mRNA to
produce new proteins.
Endocrine-BIO 102 HANDOUT
5
• Nonsteroid hormones:
– Water soluble; derived from amino acid protein
building blocks
– Bind to receptors on target cell membranes and
converts an inactive molecule within the cell
into an active molecule. The activated
molecule produces a chemical which is called a
second messenger.
– Activate existing enzymes so that even a small
amount of hormone can produce a significant
cellular change
– Faster action than steroid hormones
Endocrine-BIO 102 HANDOUT
6
Homeostasis is generally maintained by a negative
feedback loop.
In a negative feedback loop involving a hormone,
the endocrine gland is the control center, the
hormone represents the pathway between the
control center and the effectors, the hormone’s
target cells, tissues, or organs.
• An endocrine system negative feedback loop is a stable,
self-adjusting mechanism for maintaining homeostasis of
the controlled variable.
Endocrine-BIO 102 HANDOUT
7
Hypothalamus and the Posterior Pituitary Gland
Hypothalamus
– plays an important role in the regulation of
homeostasis--monitors fluid and electrolyte balance,
temperature, and carbohydrate metabolism
– Is “the power behind the throne” -- the pituitary gland;
is physically connected to the pituitary by a thin strip
of tissue called the infidibulum
– produces hormones which stimulate the release of
most pituitary hormones
• Has specialized neuroendocrine cells which
function as nerve and endocrine cells; they
generate nerve impulses which release hormones
directly into the circulation; called the
neuroendocrine reflex
Endocrine-BIO 102 HANDOUT
8
– Hormones going to the posterior pituitary affect whole
body; these hormones are transported on the
hypothalamic neurons to the posterior pituitary;
• are actually neurosecretions
– Secretes tropic hormones to hypothalamic blood
vessels which delivers them to the anterior pituitary
– Interaction between the hypothalamus and
the pituitary demonstrates the relationship
between the endocrine and the nervous
systems
Endocrine-BIO 102 HANDOUT
9
• http://neuroscience.uth.tmc.edu/s4/chapter
02.html
• Fig 2.1=neurosecretion
• Fig 2.4, 2.5= ant pit secretion
Endocrine-BIO 102 HANDOUT
10
Pituitary Gland (also called hypophysis) is located
beneath the hypothalamus (and right behind the center
of the eyes) in a bony cavity at base of brain;
– Called the “master gland” because it secretes 8
different hormones which regulate many of the
other endocrine glands;
• Consists of 2 lobes: posterior and anterior
− Posterior pituitary lobe (neurohypophysis):
Neuroglial-like supporting cells and nerve fibers;
− Anterior pituitary lobe (adenohypophysis)
Glandular tissue
Endocrine-BIO 102 HANDOUT
11
Posterior pituitary:
– Connection to hypothalamus—may be considered an
extension of the hypothalamus; some hypothalamic
hormones are stored in posterior pituitary
– Hormones: nonsteroidal; made by neuroendocrine
cells
• Antidiuretic hormone (ADH): causes
reabsorption of water in kidneys, regulates water
balance in body
• Oxytocin: causes uterine contractions during labor
and milk ejection (milk let-down reflex)
– The neurons that make the hormones transport the
hormones down their axon to be released into the
blood
Endocrine-BIO 102 HANDOUT
12
Hypothalamus and the Anterior Pituitary Gland
• Anterior pituitary:
– Releasing and inhibiting hormones from the
hypothalamus travel to anterior pituitary through
the pituitary portal system--a special blood
supply that runs directly between the
hypothalamus and the anterior pituitary.
– This allows minute quantities of hypothalamic
hormones to get to the anterior pituitary and not
be diluted in the systemic circulation
Endocrine-BIO 102 HANDOUT
13
Hypothalamus and the Anterior Pituitary Gland
– Hormones: nonsteroidal: these hormones are made in
the pituitary but released only upon hypothalamic
stimulation
• Adrenocorticotropic hormone (ACTH): stimulates
adrenal cortex
– Stimulates the adrenal cortex to release
glucocorticosteroids (steroid hormones involved
in stress related conditions and the metabolism
of glucose)
– TSH-Thyroid Stimulating Hormone
• Stimulates the thyroid gland to produce thyroid
hormone
Endocrine-BIO 102 HANDOUT
14
Hypothalamus and the Anterior Pituitary Gland
– Follicle stimulating hormone (FSH): induces
egg development and sperm development
– Luteinizing hormone (LH): promotes ovulation
and testosterone. These hormones are absent
until ages 10-13 years and their production
stimulates sexual maturation and development of
the secondary sexual characteristics
– Prolactin (PRL): stimulates the development of
mammary gland cells and production of milk
– Growth hormone (GH): widespread effects on
growth
Endocrine-BIO 102 HANDOUT
15
Pituitary Disorders
Endocrine disorders tend to be chronic conditions
of hypersecretion or hyposecretion
• Syndrome of inappropriate ADH secretion
(SIADH): hypersecretion of ADH, excessive
water retention so the body is out of balance—
symptoms: headache, vomiting
• Diabetes insipidus: hyposecretion of ADH,
inability to save water appropriately; frequent
urination
Endocrine-BIO 102 HANDOUT
16
Pituitary Disorders
• Gigantism: hypersecretion of growth hormone during
childhood and adolescence; usual cause is a tumor of
the anterior lobe of the pituitary. Person has relatively
normal body proportions
• Acromegaly: hypersecretion of growth hormone in
adulthood; overgrowth of hands, feet and face
• Both can cause headaches, poor vision, sinus
congestion, congestive heart failure, impotence, kidney
stones, weakness, arthritis and a shortened life span
• Pituitary dwarfism: hyposecretion of growth hormone
during childhood; immediate treatment with growth
hormone during childhood
Endocrine-BIO 102 HANDOUT
17
Pancreas: Endocrine Functions
Pancreas is both an endocrine gland and an
exocrine gland (secreting products into the
digestive tract)
Endocrine cells are located in the Islets of
Langerhans; clusters of cells throughout the
pancreas
• Hormones: nonsteroidal: all work to regulate
blood glucose (sugar)
– Glucagon: made by alpha cells; raises blood sugar
– Insulin: made by beta cells, lowers blood sugar
– Somatostatin: made by delta cells, inhibits secretion of
glucagon and insulin, regulates other hormones
Endocrine-BIO 102 HANDOUT
18
Disorders of the Endocrine System
Since the endocrine system is one of 2 primary
systems for controlling body functions, any
disruption can have a widespread effect
Diabetes mellitus: DM—poor control of blood
sugar inability to get glucose into cells.
• glucose stays in the circulatory system and
overwhelms the kidney’s ability to resorb the
sugar excreted in the urine.
• person also excretes a large amount of water
Endocrine-BIO 102 HANDOUT
19
– Person becomes dehydrated and very thirsty,
tired, has blurred vision, frequent infections,
slow healing cuts, tingling in feet and hands.
• When glucose can’t be metabolized correctly,
the body will metabolize fat and proteins. This
causes other problems—cardiovascular and
neural diseases, renal failure, blindness, and
potentially leg amputations.
Endocrine-BIO 102 HANDOUT
20
• There are 2 types of diabetes:
– Type I -caused by the failure of the pancreas
to secrete enough insulin possibly caused by
a virus that causes the immune system to
attack the beta cells of the pancreas
• Person is insulin dependent for the rest of
his/her life
Endocrine-BIO 102 HANDOUT
21
– Type II -thought to be insulin resistance—
cells fail to respond adequately to insulin
• Usually occurs in adults over 40 years
• Treatment: lifestyle changes
• Oral pills: drugs to stimulate the pancreas
to secrete more insulin; drugs that increase
the uptake of glucose by the liver and
muscle cells
• New: inhalable insulin
Endocrine-BIO 102 HANDOUT
22
Adrenal Glands
Adrenal glands are located just above the kidneys
– Have an outer layer—cortex
– an inner layer--medulla
• Adrenal cortex:
– Secretion: mediated through hypothalamuspituitary secretions
– Hormones: steroidal
Endocrine-BIO 102 HANDOUT
23
Adrenal Gland-Cortex
– Glucocorticoids: cortisol assists glucagon in
maintaining glucose levels during prolong fasting
by promoting using fats and amino acids (liver
can use amino acids to make glucose) AND
• Suppresses inflammation after infection or
injury
• Also secreted when we are under emotional
stress
– Mineralocorticoids: aldosterone--primarily
regulates minerals (sodium and potassium)
• Also helps maintain body water balance
Endocrine-BIO 102 HANDOUT
24
Adrenal Gland: Medulla
• Adrenal medulla: neuroendocrine organ
– when these are released into blood stream, function
as hormones; when work as neurotransmitters, are
nervous system transmitters
– Secretion: sympathetic nervous system
– Hormones: nonsteroidal:
• Epinephrine and norepinephrine: enhance
function of sympathetic nervous system (fightor-flight response)
• Play role in metabolism and controlling blood
pressure and heart activity
Endocrine-BIO 102 HANDOUT
25
Adrenal glands:
• Addison’s disease: failure of adrenal
cortex to secrete sufficient cortisol and
aldosterone
• Lack of cortisol decreases blood sugar levels
• Lack of aldosterone lowers blood sodium
levels
• Symptoms: fatigue, weakness, abdominal
pain, weight loss
• Treatment is medicine to replace hormones
Endocrine-BIO 102 HANDOUT
26
• Cushing’s syndrome: excessive cortisol
production causing
– Excessive production of glucose and retention
of salt and water.
– Blood sugar rises and muscle mass
decreases because protein is used to make
sugar.
– Some glucose is converted to fat but in
specific areas of the body—the face,
abdomen and back of the neck (a hump of fat
can be seen by the neck)
– Symptoms include weakness, fatigue, edema
and high blood pressure
Endocrine-BIO 102 HANDOUT
27
Thyroid Gland
Located below larynx at the front of the trachea.
• linked to the parathyroid gland. Both help
regulate calcium balance.
Thyroid gland helps control metabolism.
• Secretion: mediated through hypothalamus–
pituitary secretions
• Steroidal hormones:
– Thyroxine (T4) and Triiodothyronine (T3):
both regulate production of ATP from
glucose, affect metabolic rate
Endocrine-BIO 102 HANDOUT
28
Thyroid Gland
Iodine deficiency causes decrease in production of
thyroid hormones
• This causes goiter which is a result of the failure of the
feedback inhibition of production of TRH and TSH.
– Hypothalamus secretes thyrotropin releasing hormone (TRH)
which stimulates your pituitary to release TSH.
– TSH stimulates the thyroid to make thyroid hormones.
– TSH causes increase in size of thyroid gland as a result of the
gland trying to produce more hormones which it can’t do
because of lack of iodine
• Calcitonin: decreases rate of bone resorption
– lowers blood calcium levels by stimulating the intake of
calcium by bone and increasing bone mass
• Especially important for bone development
Endocrine-BIO 102 HANDOUT
29
Disorders of the Endocrine System
Thyroid:
– Hyperthyroidism: overactive thyroid gland;
hyperactivity, nervousness, agitation and
weight loss
• Graves’ disease: an autoimmune disease
in which the person’s antibodies stimulate
the thyroid to produce too much thyroxine.
Accompanied by protruding eyes (called
exopthalmos, caused by fluid accumulation
behind the eyes)
Endocrine-BIO 102 HANDOUT
30
Disorders of the Endocrine System
Thyroid:
– Hypothyroidism: underactive thyroid gland
slows body growth, changes brain
development, delays the onset of puberty
• Children: cretinism—mental retardation and
stunted growth
• Adults: myxedema—swelling under the
skin, lethargy, weight gain, low body
temperature
Endocrine-BIO 102 HANDOUT
31
Parathyroid Glands
Located in the back of the thyroid gland
• Hormone: parathyroid hormone (PTH),
nonsteroidal:
– Removes calcium and phosphate from bone
– Increases absorption of calcium by the
digestive tract
– Increases retention by the kidneys of calcium
and excretion of phosphate
• PTH increases the calcium concentration in the
blood and is secreted in response to lowered
blood calcium levels
Endocrine-BIO 102 HANDOUT
32
Reproductive Hormones
The gonads (testes and ovaries) are responsible for the
production of sperm and eggs and production of the sex
hormones.
The testes, located in the scrotum, produce androgens, the
male sex hormone.
• Hormone: in males: the androgen testosterone
(steroidal):
– Functions:
• Regulates development and normal functioning of
sperm, male reproductive organs, male sex drive
• Development of male secondary sex
characteristics and bone and muscle growth at
puberty
Endocrine-BIO 102 HANDOUT
33
Ovaries
• Hormones (steroidal) and functions:
– Estrogen: initiates development of secondary
sex characteristics, regulates menstrual cycle
– Progesterone: regulates menstrual cycle
Endocrine-BIO 102 HANDOUT
34
Other Hormone Sources
• Thymus: thymosin and thymopoietin, assist
maturation of T lymphocytes (non-steroidal hormone)
• Pineal gland: melatonin
– Receives input from the eyes; melatonin secretion is
higher in the dark; important in synchronizing the
body’s rhythms to the daily light/dark cycle (Circadian
cycle or rhythm)
• Heart: atrial natriuretic hormone (ANH) (nonsteroidal hormone); secreted by the atria to help
regulate blood pressure by increasing the rate at
which sodium and water are excreted in urine thus
decreasing blood volume
Endocrine-BIO 102 HANDOUT
35
Other Hormone Sources
• Digestive system: gastrin, secretin,
cholecystokinin; they stimulate activities of the
stomach, pancreas and gallbladder
• Kidney: Erythropoietin stimulates RBC
production
– Renin stimulates aldosterone secretion and
constricts blood vessels
Endocrine-BIO 102 HANDOUT
36
Other Chemical Messengers
Function in ways similar to hormones but aren’t
secreted directly into the bloodstream.
– Actions of these are primarily local
– Actions short because they are either quickly
destroyed or reabsorbed by the cells that produced
them
• Histamine: inflammation
– Mast cells release into local interstitial fluid in
response to tissue injury or allergen presence
• Histamine increases local mucus secretion, dilates
blood vessels and increases the leakiness of
capillaries
Endocrine-BIO 102 HANDOUT
37
• Prostaglandins: local control of blood flow;
– Can constrict or dilate blood vessels depending on
what is needed; contribute to the inflammatory
response; involved in blood clotting at injury site
• Nitric oxide: multiple functions
– Regulates local blood flow, regulating smooth muscle
contraction in the digestive tract; fights bacteria,
interferes with clotting mechanisms
• Growth factors: local acting to modify development
of specific tissues; influence when a cell will divide
Endocrine-BIO 102 HANDOUT
38