Explain the importance of intercellular communication and describe the mechanism involved.
Intercellular communication is important because it assist the nervous system to elongate
the long-term process of growth, development, or reproduction. The endocrine system
uses chemical messengers to relay information and instructions between cells. One of the
mechanisms involved in intercellular communication is know as direct communication
this communication is rare but is important when it occurs. This is when two cells of the
same type and the cells must be in extensive physical contact. The cells are so close they
function as one. The majority of the communication is known as paracrine
communication which is where the cell continuously exchanges chemical messages
between each other so they are in sink with one another.
Compare and contrast the modes of intercellular communication used by the endocrine and nervous systems and discuss the functional significance of the differences between the two systems.
The nervous system performs short term “crisis management” and the endocrine system
regulates long-term, ongoing metabolic processes. The endocrine system uses endocrine
communication which helps regulate hormones through the circulatory system and the
nervous system dose not have the capability to do this. Another significant difference is
synaptic communication, the nervous system uses this form of communication of neurons
to release neurotransmitter at a synapse very close to a target cell that bears the right
receptors. This form of communication allows the body to react quickly to situations to
escape from harm.
Explain the general mechanisms of hormonal action and identify which hormone types work through each mechanisms.
A hormone receptor is a protein molecule to which a particular molecule binds
strongly. Each cell has receptors for responding to several different hormones,
but cells in different tissues have different combinations of receptors. For every
cell, the presence or absence of a specific receptor determines the cells hormonal
sensitivities. Hormone receptors are located either on the cell membrane or inside the
cell. The mechanisms of hormonal action are that receptors for catecholamine's, peptide
hormones and eicosanoids are in the cell membrane of target cells. Thyroid and steroid
hormones cross the cell membrane and bind to receptors in the cytoplasm or nucleus,
activating or inactivating specific genes.
Describe the control of endocrine organs.
The endocrine organs are controlled by three mechanisms of the hypothalamic control.
One is the secretion of regulatory hormones to control activity of anterior lobe of
pituitary gland. Two the production of ADH and oxytocin. And finally is the control of
sympathetic output to adrenal medullae.
Explain the structural and functional relationship between the pituitary gland and the hypothalamus.
The pituitary gland releases nine important peptide hormones that all bind to the
membrane receptors and use cyclic-AMP as a second messenger. The pituitary gland
hangs inferior to the hypothalamus which all the anterior lobe of the pituitary gland to
help in the function of the hypophyseal portal system. By the hypothalamus secreting
specific regulatory hormones it controls the production of hormones in the anterior lobe.
This whole system works to secret hormones from the hypothalamus through the pituitary
gland in a network of capillaries that are connected. All this ensures that all the
hypothalamic hormones entering the portal vessels will reach the target cells in the
anterior lobe of the pituitary gland before entering general circulation.
Predict how alternations in hormone production, delivery, or reception by target tissues would affect its action and blood concentration levels.
Describe the factors that could determine a cells hormonal sensitivity.
Cells sensitivity is determined by two factors down-regulation and up-regulation. Down
regulation is a process in which the presence of a hormone triggers a decrease in the
number of hormone receptors. This process is when levels of particular hormones are
high, cells become less sensitive to it. Up-regulation is a process in which the absence of
a hormone triggers an increase in the number of hormone receptors. In this process the
levels of a particular hormone are low, cells become more sensitive to it.
Identify the hormones produced by the anterior and posterior lobes of the pituitary gland and specify the functions of those hormones.
The anterior lobe produces seven hormones:
Thyroid-stimulating hormone (TSH) targets the thyroid gland and triggers the release of
thyroid hormones. As circulation concentrations of thyroid hormones rise, the rate of
TRH and TSH production decline.
Adrenocorticotropic hormone (ACTH) stimulates the release of steroid hormones by the
adrenal cortex and targets cells that produce glucocorticoids.
Gonadotropins regulate the activities of the gonads.
Follicle-stimulating hormone (FSH) promotes follicle development in females and, in
combination with luteinizing hormone, stimulates the secretion if estrogen by ovarian
cells. In males, FSH stimulates sustentacular cells, specialized cells in the tubules where
Luteinizing hormone (LH) induces ovulation, the production of reproductive cell in
females. Also promotes the secretion, by the ovaries, of estrogen and the progestin, which
prepare the body for pregnancy. In male hormone is sometimes called interstitial cell-
stimulating hormone (ICSH), because it stimulates the production of sex hormones by the
interstitial cells of the testes.
Prolactin (PRL) works with other hormones to stimulate mammary gland development.
Growth hormone (GH) stimulates cell growth and replication by accelerating the rate of
The posterior lobe produces two hormones:
Antidiuretic hormone (ADH) is released in response to a variety of stimuli, most notably
a rise in the solute concentration in the blood or a fall in blood volume or blood pressure.
A rise in the solute concentration stimulates specialized hypothalamic neurons.
Oxytocin (OT) stimulates smooth muscles contraction in the wall of the uterus, promoting
labor and delivery. After delivery this hormones stimulates the contraction of
myoepithelial cells around the secretory alveoli and the ducts of the mammary gland,
promoting the ejection of milk.
Discussion the results of abnormal levels of pituitary hormones
Abnormal levels of pituitary hormones can have a cast and complex impact on the
growth, fertility, and function on the human body via the effect of the hormones on their
target organs. Diseases anywhere from asthma to growth problems can occur.
Identify the hormones produced by the thyroid gland, specify the functions of those hormones, and discuss the causes and results of abnormal levels of thyroid hormones.
The thyroid gland produces thyroglobulin, tyrosine, and thyroxine. The functions of these
- Thyroid hormones enter target cells by means of an energy dependent transport system and they affect almost every cell in the body.
- Thyroid hormones bound to cytoplasmic receptors are held in storage until
intracellular levels of thyroid hormone decline. Thyroid hormones bound to
mitochondria increase ATP production. Thyroid hormones bound to receptors in
the nucleus activates genes that control energy utilization.
- The calorigenic effect: the cell consumes more energy resulting in increased heat generation.
- In growing children, thyroid hormones are essential to normal development of the skeletal, muscular, and nervous systems.
- The thyroid gland is primarily responsible for a strong, immediate, and short-lived increase in the rate of cellular metabolism.
- The major factor controlling the rate of thyroid hormone release is the concentration of TSH in the circulating blood.
The causes of abnormal levels of thyroid hormones can create an iodide deficiency
because in the U.S. we consume more than they daily amount needed. Thyroid hormone
production declines, regardless of the circulating levels of TSH.
Describe the functions of the parathyroid hormones, and the effects of abnormal functions of each hormone.
Parathyroid hormone has four major effects:
1. It stimulates osteoclasts, accelerating mineral turnover and the release of
Ca2+ from bone.
2. It inhibits osteoblasts, reducing the rate of calcium deposition in bone.
3. It enhances the reabsorption of Ca2+ at the kidneys, reducing urinary
4. It stimulates the formation and secretion of calcitriol at the kidneys. The
effects of calcitriol complement or enhance those of PTH, but one major
effect of calcitriol is the enhancement of Ca2+ and PO43- absorption by the
The parathyroid glands, aided by calcitriol, are the primary regulators of blood
calcium I levels in healthy adults. When the parathyroid calcium levels become abnormal
there are two disorders that can occur. Hypoparathyroidism the gland secretes low
calcium concentrations in body fluid. Hyperparathyroidism is when calcium
concentrations become abnormally high.
Identify the hormones produced by the adrenal cortex and medulla and specify the functions of each hormone
The adrenal cortex secrets the hormones adrenocortical, mineralocorticoids,
glucocorticoids and androgens. The adrenocortical steroids or corticosteroids are vital: if
the adrenal glands are destroyed or removed, the individual will die unless corticosteroids
are administered. Mineralocorticoids increase renal reabsorption of Na+ and water which
accelerates urinary loss of potassium. Glucocorticoids release amino acids from skeletal
muscles and lipids from adipose tissue; promote liver formation of glucose and glycogen;
promotes peripheral utilization of lipids; anti-inflammatory effects. Androgens are not
important in men; encourages bone growth, muscle growth, and blood formation in
children and women. The adrenal medulla secrets epinephrine and norepinephrine. These
hormones increase cardiac activity, blood pressure, glycogen breakdown, blood glucose
levels; releases lipids by adipose tissue. Also this is where the fight or flight syndrome is
Discuss the results of abnormal levels of adrenal hormone production
When the adrenal hormone becomes abnormal it produces several different disorders.
The first is hypoaldosteronism; the zona glomerulosa fails to produce enough
aldosterone, generally either as an early sign of adrenal insufficiency or because the
kidneys are not releasing adequate amounts of rein. A rare but serious disorder can occur
called Addison's disease which results from inadequate stimulations of the zona
fasciculata by the pituitary hormone ACTH or, more commonly, from the inability of the
adrenal cells to synthesize the necessary hormones, generally from adrenal cell loss
caused by autoimmune problems. Another disease is Cushing's disease which results
from overproduction of glucocorticoids. There is another aspect of abnormal production
of adrenal hormones that affects men and women's sexual characteristics called
adrenogenital syndrome. In women, this condition leads to the gradual development of
male secondary sex characteristics, including body and facial hair patters. In male to
causes an increase of estrogen resulting in larger breast tissue or other female secondary
sex characteristics. Last but not least there is a disorder of the adrenal medulla called
pheochromocytoma which is an overproduction of epinephrine that causes a tumor that
produces catecholamines in massive quantities.
Describe the functions of the hormones produced by the pineal gland.
It contains pinealocytes, which synthesize the hormone melatonin. The suggested
functions of the pineal gland is that it inhibits reproductive functions, protects against
damage by free radicals, and sets circadian rhythms.
Identify the hormones produced by the pancreas and specify the functions of those hormones.
The pancreas contains both exocrine and endocrine cells. Cells of the endocrine
pancreas form clusters called pancreatic islets (islets of Langerhans). The pancreatic islets
release insulin and glucagons. Insulin is released when blood glucose levels rise, and it
stimulates glucose transport into and utilization by, peripheral tissues. Glucagon is
released when blood glucose levels decline, and it stimulates glycogen breakdown,
glucose synthesis and fatty acid release.
Discuss the results of abnormal levels of pancreatic hormone production.
When the pancreatic hormones produce abnormal levels of insulin and glucose it causes
an individual to be diabetic. Diabetes mellitus is characterized by glucose concentration
that is high enough to overwhelm the reabsorption capabilities of the kidneys. Glucose
appears in the urine, and urine production generally becomes excessive.
Describe the functions of the hormones produced by the kidneys, heart, thymus, testes, ovaries, and adipose tissue.
Control of the heart, kidneys, thymus, gonads, and adipose tissue. The kidneys release
erythropoietin and calcitriol into the red bone marrow, intestinal lining, bone and
kidneys. All of the hormones releases are to stimulate red blood cell production and
calcium and phosphate absorption and it also stimulates calcium ions from bone; inhibits
PTH secretion. The heart controls the hormones natriuretic that targets the kidneys,
hypothalamus and adrenal gland. These hormones increase water and salt loss at
kidneys; decrease thirst; and suppress secretion of ADH and aldosterone. The adipose
tissue contain two hormones that support to different functions, first is leptin which
targets the hypothalamus for suppression of appetite; permissive effects on GnRH and
gonadotropin synthesis. Second is resistin that targets cell throughout the body that
suppresses insulin response. Last but not least are the gonads with the hormones
androgens, inhibin, estrogen and progestin. All these hormones are targeted by the
pituitary glands to support the reproductive organs in males and females.
In males the interstitial cells of the testes produce androgens. Testosterone is the most
important sex hormone in males. Sustentacular cells in the testes support the
differentiation and physical maturation of sperm. Under FSH stimulation, these cells
secrete the hormone inhibin, which inhibits the secretion of FSH at the anterior lobe.
The female body develops oocytes in the follicles; follicle cells produce estrogens,
especially estradiol. After ovulation, the remaining follicle cells reorganize into a corpus
luteum. Those cells release a mixture of estrogens and progestin's, especially
Explain how hormones interact to produce coordinated physiological responses.
Hormones interact to produce coordinated physiological responses in four ways:
1. antagonistic (opposing) effects
2. synergistic (additive) effects
3. permissive effects, in which one hormone is necessary for another to
produce its effect
4. integrative effects, in which hormones produce different, but
Identify the hormones that are especially important to normal growth, and discuss their roles.
There are several hormones that are important for normal growth: GH, insulin, PTH,
calcitriol, reproductive and thyroid hormones. The circulation concentrations of these
hormones are regulated independently. Changes produce unique individual growth
Growth Hormone (GH): effects are most apparent in children where GH supports
muscular and skeletal development. In adults GH assists in the maintenance of
normal blood glucose concentrations and in the mobilization of lipid reserves.
Thyroid hormones: if these hormones are absent during fetal development or for
the first year after birth, the nervous system will fail to develop normally and
mental retardation will result. If T4 concentrations decline before puberty, normal
skeletal development will not continue.
Insulin: without insulin the passage of glucose and amino acids across cell
membranes will be drastically reduced or eliminated.
Parathyroid Hormone (PTH) and Calcitriol: promote the absorption of calcium
salts for subsequent deposition in bone. Without adequate levels of both
hormones, bones will be weak and flexible.
Reproductive Hormones: the sex hormones (androgens in males, estrogens in
females) stimulate cell growth and differentiation in their target tissues.
Differential growth induced by each hormone accounts for gender-related
differences in skeletal proportions and secondary sex characteristics.
Define the general adaptation syndrome.
Any condition that threatens homeostasis is a stress.
Our bodies respond to a variety of stress-causing factors through the general
adaptation syndrome (GAS), or stress response.
The GAS can be divided into three phases:
- the alarm phase
- the resistance phase
- the exhaustion phase
S.Schaffer. Chapter 18. The endocrine system. Retrieved January 20, 2008 from
Martini. Chapter 18. The endocrine system. Retrieved January 20, 2008 from
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