Transcript The Endocrine System - SchoolWorld an Edline Solution

The Endocrine System
Endocrine System: Overview
• Endocrine system – the body’s second
great controlling system which influences
metabolic activities of cells by means of
hormones
• Endocrine glands – pituitary, thyroid,
parathyroid, adrenal, pineal, and thymus
• The pancreas and gonads produce both
hormones and exocrine products
Endocrine System: Overview
• The hypothalamus has
both neural functions and
releases hormones
• Other tissues and organs
that produce hormones –
adipose cells, pockets of
cells in the walls of the
small intestine, stomach,
kidneys, and heart
• Hormones are
substances secreted by
cells that act to regulate
the activity of other cells
in the body.
– Hormones affect all cells in
the body and are made and
secreted by endocrine
glands.
• Endocrine glands are
ductless organs that
secret hormones either
into the bloodstream or
the fluid around cells.
• The endocrine glands can be found
through out the body and are collectively
known as the endocrine system.
• Endocrine glands, such as the pancreas,
can also be exocrine glands.
– Exocrine glands secrete substances through
ducts to specific locations inside and outside
the body.
The Endocrine System
Types of Hormones
• Hormones can be grouped into two types based
on their structure. Hormones can either be
amino acid-based hormones or steroid
hormones.
– Amino acid based-hormones are made of amino
acids, either a single modified amino acid or a protein
made of 3-200 amino acids, and are water soluble.
– Steroid hormones are lipid hormones that the body
makes from cholesterol and are fat soluble.
• Similar to steroid hormones are thyroid hormones.
• Regardless of which type of hormone is being
activated, all hormones affect only their target
cells.
– Target cells are specific cells to which a hormone
travels to produce a specific effect.
– On the target cells are receptors. Receptors are
proteins that bind to specific signal molecules, such
as hormones, that cause a cell to respond.
• Amino acid-based hormones
– Amino acid-based hormones bind to receptor proteins
on the cell membrane and are called first
messengers.
– Second messengers are then activated. A second
messenger is a molecule that initiates changes
inside a cell in response to the binding of a specific
substance to a receptor on the outside of a cell.
• Changes to the cell through enzyme action then occur in a
cascade fashion.
• Steroid and Thyroid Hormones
– Steroid and thyroid hormones are similar because
they are both fat soluble.
– Because these hormones are fat soluble they can
pass through the cell membrane.
– Thus, these hormones can enter their target cells
and bind directly to receptor sites in the cytoplasm or
nucleus and directly activate enzymes.
• Two other types of chemical messengers that
are classified as hormones are neuropeptides
and prostaglandins.
– Neuropeptides are hormones secreted by the
nervous system and tend to affect many cells near the
nerve cells that release them.
– Prostaglandins are modified fatty acids that are
secreted by most cells and tend to accumulate in
areas where tissues are disturbed or injured.
Hypothalamus and Pituitary Gland
• Two organs, the hypothalamus and the
pituitary gland, control the initial release of
many hormones for the endocrine system.
– The hypothalamus is the area of the brain
that coordinates many activities of the
nervous and endocrine systems.
• The hypothalamus
secretes:
• 1. ADH = Antidiuretic
Hormone=stimulates
reabsorption of water in
the body.
• 2. Oxytocin- Used during
childbirth to bring on labor
contractions.
• The nerve cells in the hypothalamus that secrete
hormones are called neurosecretory cells.
– These cells secrete two types of hormones to the
pituitary gland.
• Releasing hormones stimulate the anterior pituitary to make
and secrete hormones.
• Release-inhibiting hormones inhibit production and secretion
of anterior-pituitary hormones.
Hypothalamus Video
The Pituitary Gland
• 1. Known as the
master gland.
Controls all other
glands.
• 2. It is stimulated by
hormones from the
hypothalamus to
target other glands.
• The six hormones of the adenohypophysis:
– Are abbreviated as GH, TSH, ACTH, FSH, LH, and
PRL
– Regulate the activity of other endocrine glands
• In addition, pro-opiomelanocortin (POMC):
– Has been isolated from the pituitary
– Is enzymatically split into ACTH, opiates, and MSH
Growth Hormone (GH)
• Produced by
somatotropic cells of the
anterior lobe that:
– Stimulate most cells, but
target bone and skeletal
muscle
– Promote protein synthesis
and encourage the use of
fats for fuel
• Most effects are mediated
indirectly by
somatomedins
Acromegaly
• Widening of bones
Pituitary Video
Thyroid Stimulating Hormone
(Thyrotropin)
• Tropic hormone that stimulates the normal
development and secretory activity of the
thyroid gland
• Triggered by hypothalamic peptide
thyrotropin-releasing hormone (TRH)
• Rising blood levels of thyroid hormones
act on the pituitary and hypothalamus to
block the release of TSH
Adrenocorticotropic Hormone
(Corticotropin)
• Stimulates the adrenal cortex to release
corticosteroids
• Triggered by hypothalamic corticotropinreleasing hormone (CRH) in a daily rhythm
• Internal and external factors such as fever,
hypoglycemia, and stressors can trigger
the release of CRH
Gonadotropins
• Gonadotropins – follicle-stimulating hormone
(FSH) and luteinizing hormone (LH)
–
–
–
–
Regulate the function of the ovaries and testes
FSH stimulates gamete (egg or sperm) production
Absent from the blood in prepubertal boys and girls
Triggered by the hypothalamic gonadotropin-releasing
hormone (GnRH) during and after puberty
Functions of Gonadotropins
In females
– LH works with FSH to cause maturation of the
ovarian follicle
– LH works alone to trigger ovulation (expulsion
of the egg from the follicle)
– LH promotes synthesis and release of
estrogens and progesterone
Functions of Gonadotropins
In males
– LH stimulates interstitial cells of the testes to
produce testosterone
– LH is also referred to as interstitial cellstimulating hormone (ICSH)
Prolactin (PRL)
• In females, stimulates milk production by the
breasts
• Triggered by the hypothalamic prolactinreleasing hormone (PRH)
• Inhibited by prolactin-inhibiting hormone (PIH)
• Blood levels rise toward the end of pregnancy
• Suckling stimulates PRH release and
encourages continued milk production
The Posterior Pituitary and
Hypothalamic Hormones
• Posterior pituitary – made of axons of
hypothalamic neurons, stores antidiuretic
hormone (ADH) and oxytocin
• ADH and oxytocin are synthesized in the
hypothalamus
• ADH influences water balance
• Oxytocin stimulates smooth muscle contraction
in breasts and uterus
• Both use PIP-calcium second-messenger
mechanism
Oxytocin
• Oxytocin is a strong stimulant of uterine
contraction
• Regulated by a positive feedback
mechanism to oxytocin in the blood
• This leads to increased intensity of uterine
contractions, ending in birth
• Oxytocin triggers milk ejection (“letdown”
reflex) in women producing milk
Antidiuretic Hormone (ADH)
• ADH helps to avoid dehydration or water overload
– Prevents urine formation
• Osmoreceptors monitor the solute concentration of the
blood
• With high solutes, ADH is synthesized and released,
thus preserving water
• With low solutes, ADH is not released, thus causing
water loss from the body
• Alcohol inhibits ADH release and causes copious urine
output
• The tropic hormones that are released are:
– Thyroid-stimulating hormone (TSH)
– Adrenocorticotropic hormone (ACTH)
– Follicle-stimulating hormone (FSH)
– Luteinizing hormone (LH)
• 3. It secretes:
– A.
– B.
– C.
– D.
– E.
GH= Growth Hormone
ACTH= Adrenocorticotrophic Hormone
FSH= Follicle Stimulating Hormone
LH=Luteinizing Hormone
TSH=Thyroid Stimulating Hormone
The Thyroid Gland
• The thyroid gland is
located near the larynx
and helps maintain a
normal heart rate, blood
pressure, and body
temperature by
increasing or decreasing
cellular metabolic rates.
• It secretes thyroxine.
• The thyroid gland is also
important for
development.
Thyroid Gland
• The largest endocrine gland,
located in the anterior neck,
consists of two lateral lobes
connected by a median tissue
mass called the isthmus
• Composed of follicles that
produce the glycoprotein
thyroglobulin
• Colloid (thyroglobulin + iodine)
fills the lumen of the follicles
and is the precursor of thyroid
hormone
• Other endocrine cells, the
parafollicular cells, produce the
hormone calcitonin
Thyroid Hormone
• Thyroid hormone – the body’s major
metabolic hormone
• Consists of two closely related iodinecontaining compounds
– T4 – thyroxine; has two tyrosine molecules
plus four bound iodine atoms
– T3 – triiodothyronine; has two tyrosines with
three bound iodine atoms
Effects of Thyroid Hormone
• TH is concerned with:
– Glucose oxidation
– Increasing metabolic rate
– Heat production
• TH plays a role in:
–
–
–
–
Maintaining blood pressure
Regulating tissue growth
Developing skeletal and nervous systems
Maturation and reproductive capabilities
Goiter
• Abnormal thyroid activity can result in
hypothyroidism or hyperthyroidism.
• Overproduction of thyroid hormones is called
hyperthyroidism and can have symptoms that
vary from overactivity to high body temperature.
• A deficiency in a thyroid hormone is known as
hypothyroidism and can have symptoms that
vary from weight gain to retardation.
Thyroid Video
Parathyroid Glands
• Tiny glands embedded in
the posterior aspect of
the thyroid
• Cells are arranged in
cords containing oxyphil
and chief cells
• Chief (principal) cells
secrete PTH
• PTH (parathormone)
regulates calcium
balance in the blood
Effects of Parathyroid Hormone
• PTH release increases
Ca2+ in the blood as it:
– Stimulates osteoclasts to
digest bone matrix
– Enhances the reabsorption
of Ca2+ and the secretion of
phosphate by the kidneys
– Increases absorption of
Ca2+ by intestinal mucosal
cells
• Rising Ca2+ in the blood
inhibits PTH release
• Parathyroid Gland
– The parathyroid glands is
made up of four glands
embedded in the two
thyroid glands.
• These glands secrete the
parathyroid hormone,
(calcitonin) which
stimulates the transfer of
calcium ions from the
bones to the blood.
Calcitonin
• Calcitonin targets the skeleton, where it:
– Inhibits osteoclast activity (and thus bone
resorption) and release of calcium from the
bone matrix
– Stimulates calcium uptake and incorporation
into the bone matrix
• Regulated by a humoral (calcium ion
concentration in the blood) negative
feedback mechanism
Parathyroid Video
The Adrenal Gland
• Humans have an adrenal
gland located above each
kidney. Each adrenal gland
has an inner core, the medulla,
and an outer core, also called
the cortex.
• The medulla and the cortex
function as separate endocrine
glands.
– The medulla is controlled by
the nervous system, and the
cortex is controlled by the
anterior pituitary.
Adrenal Cortex
Mineralocorticoids
• Regulate the electrolyte concentrations of
extracellular fluids
• Aldosterone – most important
mineralocorticoid
– Maintains Na+ balance by reducing excretion
of sodium from the body
– Stimulates reabsorption of Na+ by the kidneys
Mineralocorticoids
• Aldosterone secretion
is stimulated by:
– Rising blood levels of
K+
– Low blood Na+
– Decreasing blood
volume or pressure
Glucocorticoids (Cortisol)
• Help the body resist stress by:
– Keeping blood sugar levels relatively constant
– Maintaining blood volume and preventing
water shift into tissue
• Cortisol provokes:
– Gluconeogenesis (formation of glucose from
noncarbohydrates)
– Rises in blood glucose, fatty acids, and amino
acids
Excessive Levels of
Glucocorticoids
• Excessive levels of glucocorticoids:
– Depress cartilage and bone formation
– Inhibit inflammation
– Depress the immune system
– Promote changes in cardiovascular, neural,
and gastrointestinal function
Adrenal Video
Cushing’s Syndrome -11month old
baby
Cushing’s Syndrome
• Adrenal Medulla
– The adrenal medulla secretes the hormones that
stimulate a “flight-or-fight” response to a stress.
– In this response, the hormones epinephrine, also
called adrenaline, and norepinephrine are released.
• These hormones increases heart rate, blood pressure, blood
glucose levels, and blood flow into the heart and lungs so the
body can respond to the initial stress.
• Adrenal Cortex
– In the presence of some stresses the pituitary
gland will secrete the adrenocorticotropic
hormone (ACTH).
– This hormone stimulates the adrenal cortex to
produce the hormone cortisol.
• Cortisol promotes the production of glucose from
proteins to help cells make usable energy.
Adrenal Medulla
• Made up of chromaffin cells that secrete
epinephrine and norepinephrine
• Secretion of these hormones causes:
– Blood glucose levels to rise
– Blood vessels to constrict
– The heart to beat faster
– Blood to be diverted to the brain, heart, and
skeletal muscle
Adrenal Medulla
• Epinephrine is the more potent stimulator
of the heart and metabolic activities
• Norepinephrine is more influential on
peripheral vasoconstriction and blood
pressure
The Gonads
• Gonads are the gamete-producing organs that
also produce a group of steroid sex hormones.
– Gonads, ovaries in females and the testes in males,
are regulated by sex hormones, which begin
production at puberty.
• Puberty is the adolescent stage during which
the sex organs mature and secondary sex
characteristics appear.
• The production of sex hormones is stimulated by
the release of two hormones by the pituitary.
– The first hormone is luteinizing hormone (LH). This
hormone stimulates ovulation and the release of
progesterone in females and the release of androgens,
such as testosterone, in males.
– The second hormone is follicle-stimulating hormone
(FSH). This hormone stimulates the growth and maturation
of the ovarian follicles in females and
sperm production in males.
Gonadocorticoids (Sex Hormones)
• Most gonadocorticoids secreted are androgens
(male sex hormones), and the most important
one is testosterone
• Androgens contribute to:
– The onset of puberty
– The appearance of secondary sex characteristics
– Sex drive in females
• Androgens can be converted into estrogens
after menopause
Gonads: Female
• Paired ovaries in the abdominopelvic
cavity produce estrogens and
progesterone
• They are responsible for:
– Maturation of the reproductive organs
– Appearance of secondary sexual
characteristics
– Breast development and cyclic changes in the
uterine mucosa
Gonads: Male
• Testes located in an extra-abdominal sac
(scrotum) produce testosterone
• Testosterone:
– Initiates maturation of male reproductive
organs
– Causes appearance of secondary sexual
characteristics and sex drive
– Is necessary for sperm production
– Maintains sex organs in their functional state
The Gonad Video
The Pancreas
• The pancreas contains both exocrine and
endocrine cells. The endocrine cells are called
islets of Langerhans.
• These cells secrete hormones that regulate the
level of sugar in the blood. The hormone insulin
is one of the hormones produced.
– Insulin lowers the blood sugar level by stimulating
body cells to store glucose or use it for energy.
• A condition called diabetes mellitus occurs when cells
are unable to obtain glucose from the blood. This results
in a high glucose level in the blood
• There are two types of diabetes: Type I and Type II.
– Type I occurs when immune cells attack and destroy the islet of
Langerhans cells.
– Type II occurs when cells don’t have sufficient insulin levels or
when the organism’s cells have become less responsive.
• A condition called hypoglycemia occurs
when excessive insulin is stored and not
properly delivered to body cells.
• This leads to a lowered blood glucose
concentration, which can cause such
symptoms as overactivity and dizziness.
Pancreas
• A triangular gland, which has both exocrine and
endocrine cells, located behind the stomach
• Acinar cells produce an enzyme-rich juice used
for digestion (exocrine product)
• Pancreatic islets (islets of Langerhans) produce
hormones (endocrine products)
• The islets contain two major cell types:
– Alpha () cells that produce glucagon
– Beta () cells that produce insulin
Glucagon
• A 29-amino-acid polypeptide hormone that
is a potent hyperglycemic agent
• Its major target is the liver, where it
promotes:
– Glycogenolysis – the breakdown of glycogen
to glucose
– Gluconeogenesis – synthesis of glucose from
lactic acid and noncarbohydrates
– Release of glucose to the blood from liver
cells
Insulin
• A 51-amino-acid protein
consisting of two amino acid
chains linked by disulfide
bonds
• Synthesized as part of
proinsulin and then excised by
enzymes, releasing functional
insulin
• Insulin:
– Lowers blood glucose levels
– Enhances transport of glucose
into body cells
– Counters metabolic activity
that would enhance blood
glucose levels
Diabetes Mellitus (DM)
• Results from hyposecretion or hypoactivity of
insulin
• The three cardinal signs of DM are:
– Polyuria – huge urine output
– Polydipsia – excessive thirst
– Polyphagia – excessive hunger and food
consumption
• Hyperinsulinism – excessive insulin secretion,
resulting in hypoglycemia
Pancreas Video
Other Glands
• There are several other glands in the endocrine
system, including thymus gland, the pineal gland
and the parathyroid glands.
• Thymus Gland
– The thymus gland is located beneath the sternum and
plays a role in the development of the immune system
by secreting thymosin.
• This amino acid-based hormone stimulates formation of T
cells.
Thymus
• Lobulated gland located deep to the
sternum in the thorax
• Major hormonal products are
thymopoietins and thymosins
• These hormones are essential for the
development of the T lymphocytes (T
cells) of the immune system
Thymus Video
• Pineal Gland
– The pineal gland is
located near the base
of the brain and helps
regulate sleep patterns
by secreting
melatonin.
Pineal Gland
• Small gland hanging from the roof of the
third ventricle of the brain
• Secretory product is melatonin
• Melatonin is involved with:
– Day/night cycles
– Physiological processes that show rhythmic
variations (body temperature, sleep, appetite)
Pineal Gland Video
• Digestive Cells
– Some of the digestive organs also act as endocrine
cells by secreting a variety of hormones that control
digestive processes. Two hormones that are secreted
are gastrin and secretin.
• Gastrin is released by the stomach when food is eaten.
• Secretin is released by the small intestine and helps
stimulates the release of various digestive fluids from the
pancreas.
Other Hormone-Producing
Structures
• Heart – produces atrial natriuretic peptide (ANP),
which reduces blood pressure, blood volume,
and blood sodium concentration
• Gastrointestinal tract – enteroendocrine cells
release local-acting digestive hormones
• Placenta – releases hormones that influence the
course of pregnancy
Other Hormone-Producing
Structures
• Kidneys – secrete erythropoietin, which
signals the production of red blood cells
• Skin – produces cholecalciferol, the
precursor of vitamin D
• Adipose tissue – releases leptin, which is
involved in the sensation of satiety, and
stimulates increased energy expenditure
• The endocrine system plays an important role in
the maintenance of a stable internal
environment, or homeostasis.
• Maintenance of homeostasis is controlled by
feedback mechanisms. A feedback mechanism
is one in which the last step in a series of events
controls the first.
• Feedback mechanisms can be either negative or
positive.
• Negative Feedback
– When the final step in
a series of events
inhibits the initial
signal in the series it is
called negative
feedback.
– An example of
negative feedback is
the regulation of
thyroid hormones.
Negative Feedback
Positive Feedback
Positive feedback occurs when
the release of an initial hormone
stimulates release or production of
other hormones or substances.
An example of positive feedback is
the stimulation and increase in
luteinizing hormone by estrogen.
• Antagonistic Hormones
– Antagonistic hormones work together in
pairs to regulate the levels of critical
substances.
– Example: Both glucagon and insulin regulate
blood sugar levels.
Quiz
1.What are the chemical messengers of the
endocrine system called?
A. neurons
B. hormones
C. blood cells
D. carbohydrates
• Answer
• D. Hormones
2.
X and Y are hormones. X stimulates
the secretion of Y, which exerts negative
feedback on the cells that secrete X.
Suppose the level of Y decreases. What
should happen immediately afterwards?
F. Less X is secreted.
G. More X is secreted.
H. Secretion of Y stops.
J. Secretion of X stops.
• Answer
• G. More X is secreted
3.Endocrine glands
A. function only after puberty.
B. function only before puberty.
C. release products through ducts.
D. release products into the bloodstream.
• Answer
• D. Release products into the bloodstream
4. What happens after food
is eaten?
F. Blood glucose levels
increase.
G. Blood glucose levels
decrease.
H. Blood glucose levels
remain the same.
J. Blood glucose levels
decrease then increase.
• Answer
• F. Blood glucose increases
5. Which hormones are
primarily responsible for
the changes in blood
glucose levels about 2
hours after food is eaten?
A. insulin
B. estrogen and
progesterone
C. epinephrine and
norepinephrine
D. aldosterone and
parathyroid hormones
• Answer
• A. insulin
6.Neurotransmitters : nervous system ::
hormones :
F. feedback system
G. endocrine system
H. circulatory system
J. respiratory system
• Answer
• G. Endocrine system
7. Thyroid stimulating hormone (TSH) is a
hormone that stimulates the release of the
thyroid hormones from the thyroid gland. At
what time would you expect thyroid
hormone levels to be at their lowest?
A. 0 hours
B. 4 hours
C. 8 hours
D. 12 hours
• Answer
• D. 12 hours