Download Notes Chapter 51 Endocrine System

51 Endocrine System
1) Describe how hormones work with the feedback system to maintain homeostasis
a) The endocrine system consists of glands that transmit chemical messengers throughout
the body. These chemical messengers, called hormones, circulate in the bloodstream and
affect many types of body cells.
b) Types of Glands
c) Exocrine glands - secrete non-hormonal chemicals into ducts, which transport the
chemicals to specific locations inside and outside the body.
i) Examples: sweat glands, mucous glands, salivary glands, other digestive glands.
d) Endocrine glands - ductless glands that are located throughout the body. They secrete
hormones into the bloodstream through the fluid that surrounds their cells.
e) The body produces many hormones, and each hormone affects only specific cells, called
target cells.
i) Target cells have receptors that recognize and bind to specific hormones.
ii) Receptors are proteins that are located both inside the cytoplasm and on the surface of
a target cell.
iii) When a hormone binds to a receptor on its target cell, it triggers events that lead to
changes within the cell. .
f) Types of Hormones
i) Amino Acid-Based Hormones
(1) Because most amino acid-based hormones cannot diffuse passively across the
membranes of their target cells, a two-messenger system is commonly required for
the action of most of these hormones.
(2) Amino acid-based hormones identify their target cells by their attraction to
receptor proteins that are embedded in the target cell membrane.
(a) The hormone acts as a first messenger by binding to a specific receptor on the
surface of its target cell.
(i) This forms a hormone-receptor complex, which activates a second
messenger located inside the target cell.
(b) A second messenger relays and amplifies the hormone signal.
(i) In many cases, the hormone-receptor complex indirectly activates an
enzyme that converts molecules of ATP to cyclic AMP (c-AMP) inside the
cell.
(ii) Cyclic AMP acts as a second messenger by indirectly activating other
enzymes and proteins in the target cell.
(iii)
Thus, c-AMP initiates a chain of biochemical events that leads to
functional changes within the target cell.
ii) Steroid Hormones
(a) Steroid hormones do not act through cell surface receptors.
(i) Instead, they diffuse through the membranes of their target cells and bind to
receptors in the cytoplasm.
(ii) The newly formed hormone-receptor complexes cause the cells to activate
existing enzymes or to initiate synthesis of new enzymes or proteins.
(iii) Once bound to DNA, the hormone-receptor complex activates
transcription of mRNA.
(iv) By activating mRNA transcription, steroid hormones stimulate production
of new proteins, which cause changes in the target cell.
g) Prostaglandins
i) Prostaglandins, a group of hormone-like lipids, also regulate cell activities.
(1) Unlike hormones, prostaglandins are not produced by specific endocrine glands. ~
(2) Instead, these chemicals are produced in small quantities by many cells throughout
the body.
(3) Rather than being transported through the blood to distant regions of the body,
prostaglandins act locally.
(4) Their effects include relaxation of smooth muscles that line air passageways and
blood vessels, regulation of blood pressure, contraction of the intestinal walls and
the uterus, and stimulation of the body's inflammatory response to infection.
2) Distinguish between the endocrine glands and their functions.
a) Pituitary Gland - located at the base of the brain. Generally called the ''Master Gland" of
the endocrine system.
i) Two lobes - Posterior and Anterior. Regulated by the hypothalamus using
neurosecretory cells, which are stored in the pituitary.
(1) Posterior - produces oxytocin and Antiduretic hormone. Oxytocin is responsible
for uterine contraction. ADH helps regulate the concentration of solutes in the
blood my controlling the amount of water secreted by the kidneys.
(2) Anterior - secrete releasing hormones, which stimulate endocrine cells of the
anterior pituitary lobe to produce and secrete hormones. Other cells also produce
release inhibiting hormones, which prohibit production and secretion of anteriorpituitary hormones. Some cells produce Growth Hormone (GH), which controls
skeletal and muscular growth: while other cells secrete prolactin, which stimulates
the production of breast milk during lactation.
b) Thyroid Gland - located near the lower part of the larynx. The anterior pituitary releases
Thyroid Stimulating Hormone (TSH), which in turn causes the thyroid to release
thyroxine and triiodothyronine. These two hormones are derived from the same amino
acid and need iodine to be synthesized. They maintain normal heart rate, blood pressure,
and body temperature. The thyroid gland also releases calcitonin, which stimulates the
transfer of calcium ions from the blood to bone.
(1) Hyperthyroidism - over activity. Symptoms include weight loss, high blood
pressure, high heart rate, and high body temperature.
.
(2) Hypothyroidism - under activity. Symptoms include lethargy, weight gain, and low
heart rate and body temperature, cretinism (form of mental retardation), and goiter
(a swelling of the thyroid gland because of lack of iodine).
c) Adrenal Gland -located above each kidney. The medulla and the cortex function as
separate endocrine glands.
i) Adrenal Medulla - produces epinephrine and norepinephrine. These hormones are
responsible for the body's "fight-or-flight" response. When stressed, the medulla
secretes epinephrine into the blood stream. This causes the liver to breakdown
glycogen, which will be used for extra energy. The pupils enlarge, heart rate increases,
and more blood circulates to the muscles, brain, and heart.
ii) Adrenal cortex - responds to adrenocorticotropic hormone (ACTH), which is secreted
by the pituitary. This secretion stimulates the cortex to secrete cortisol, which
regulates metabolism of carbohydrates and proteins, and aldosterone, which helps
maintain the salt-to-water balance in the body.
d) Gonads - the ovaries and testes. They secrete the sex hormones, which causes body
changes around puberty. Puberty is when the secondary sex characteristics start to appear.
i) Females - the anterior pituitary secretes lutenizing hormone (LH) and folliclestimulating hormone (FSH). These stimulate the secretion of estrogen and
progesterone by the ovaries. These hormones cause the monthly release of the egg in
preparation for pregnancy. Estrogen is also responsible for the secondary sex
characteristics in females.
ii) Males - LH stimulates the testes to secrete androgens (ex. Testosterone). This causes
the appearance of the secondary sex characteristics. Along with FSH, testosterone also
stimulates the production of sperm.
e) Pancreas - contains endocrine cells called the Islets of Langerhans. These cells secrete 2
amino-acid based hormones that regulate the level of sugar in the blood. Insulin lowers
the blood sugar level by causing cells to absorb the glucose. Glucagon stimulates the
release of glucose into the bloodstream by the liver cells.
i) Diabetes mellitus - a condition of abnormally high blood glucose concentration.
(1) Type I - severe childhood disorder in which the Islet cells die. Treated by daily
injections of insulin into the blood. Sometimes treated with an Islet transplant.
(2) Type II - usually occurs after 40 and is less severe. Caused by insufficient insulin
production or unresponsive target cell receptors. Usually hereditary and can be
controlled with diet and exercise. This condition can cause hypoglycemia, a
disorder in which glucose is store~ rather than used by the body cells. This can
cause lethargy, dizziness, nervousness, and in extreme cases, death.
f) Thymus - located beneath the sternum and between the lungs. Consists of T -cells, which
playa role in the immune response. It secretes and amino-acid based hormone called
thymosin, which stimulates the formation of T-cells.
g) Pineal Gland - Located near the base of the brain. Secretes the hormone melatonin. This
hormone regulates the sleep-wake cycle.
h) Parathyroid Glands - embedded in the back of the thyroid gland, two in each lobe.
Secretes parathyroid hormone, which increases the concentration of calcium ions in the
blood. .
i) Digestive organs - endocrine cells of the stomach secrete gastrin, a hormone that
stimulates other stomach cells to release digestive enzymes and HCI.
i) Endocrine cells of the small intestine secretes secretin, a hormone that stimulates the
release of various digestive fluids from the pancreas and bile from the liver.
3) Explain Feedback Mechanisms
a) The last step in a series of events controls the first step
b) Homeostasis
i) Controlled by the endocrine system. For example, insulin and glucagon work together
to maintain a balanced blood glucose level. These hormones are considered
antagonistic hormones because their actions have opposite effects.
ii) Most hormone systems use negative feedback, in which the release of an initial
hormone stimulates release and production of other hormones or substances that
subsequently inhibit further release of the initial hormone.
iii) In positive feedback, release of an initial hormone stimulate production of other
hormones, which stimulate further release of the initial hormone.
Chapter 51 Endocrine System
 Endocrine glands produce and secrete hormones that affect distant target cells.
 Amino acid–based hormones bind to receptors on their target cells, activating a second messenger.
 Steroid hormones diffuse through the membranes of their target cells and bind to cytoplasmic
receptors.
 Prostaglandins are hormone-like lipids that affect nearby cells.
 The hypothalamus links the nervous system to the endocrine system by regulating the pituitary
gland.
 Releasing hormones and release-inhibiting hormones secreted by the hypothalamus regulate the
anterior-pituitary hormones.
 The thyroid gland secretes hormones that regulate metabolism.
 The adrenal glands help regulate metabolism and the body’s responses to stress and danger.
 The gonads secrete sex hormones that are responsible for body changes that begin at puberty.
 The islets of Langerhans of the pancreas secrete hormones that regulate the blood glucose level.
 Other endocrine glands include the thymus gland, the pineal gland, the parathyroid glands, and
endocrine cells of the digestive system.
 Feedback mechanisms help maintain homeostasis.
 In negative feedback, the final step in a series inhibits the first step.
Vocabulary List
Adrenal gland
Amino acid–based
hormone
Antagonistic
hormones
Endocrine gland
Endocrine system
Exocrine gland
Feedback
mechanism
First messenger
Gonads
Hormone
Hormone-receptor
complex
Hyperthyroidism
Hypoglycemia
Hypothyroidism
Insulin
Melatonin
Negative feedback
Neurosecretory cell
Parathyroid gland
Pineal gland
Pituitary gland
Positive feedback
Prostaglandin
Receptor
Second messenger
Sex hormones
Steroid hormone
Target cell