Endocrine System Communication

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

sperm differentiate.

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

protein synthesis.

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

hormones are:

• 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

losses.

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

digestive tract.

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

sparked.

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

progesterone.

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

complementary, results

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

patterns.

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

Reference page:

S.Schaffer. Chapter 18. The endocrine system. Retrieved January 20, 2008 from

http://www.harford.edu/faculty/SSchaeffer/Endocrine%20Outline.doc

Martini. Chapter 18. The endocrine system. Retrieved January 20, 2008 from

http://www.miramar.sdccd.cc.ca.us/faculty/kpetti/Bio160/Martini7DetailLectOutlines/18-Detailed_Lect_Out_LO.pdf.pdf