THE ENDOCRINE

SYSTEM

Hormone - a specific messenger molecule synthesized and secreted

by a group of specialized cells called an endocrine gland. These glands

are ductless, which means that their secretions (hormones) are released directly into the bloodstream and travel to elsewhere in the body to

target organs, upon which they act

Collection of glands that

secrete chemical

messages we call hormones

hormones and glands-

foundation of the endocrine

system

Hormones are grouped into three classes based on their structure:

steroidspeptidesamines

steroid hormones including prostaglandins which function especially in a variety of female functions (aspirin inhibits synthesis of prostaglandins, some of which cause “cramps”) and the sex hormones all of which are lipids made from cholesterol,

amino acid derivatives (like epinephrine) which are derived from amino acids, especially tyrosine, and

peptide hormones (like insulin) which is the most numerous/diverse group of hormones.

STEROID HORMONEScrucial substances for the proper

function of the body; has a lipid nature

They mediate a wide variety of vital physiological functions ranging from anti-inflammatory agents to regulating events during pregnancy.

synthesized and secreted into the bloodstream by endocrine glands such as the adrenal cortex and the gonads

STEROIDS HORMONEScharacterized by the steroid nucleus

which is composed of three six member rings and one five member ring, ingeniously labeled A, B, C, and D respectively

Cholesterol- precursor for steroid hormonessterol which is a natural product

derived from the steroid nucleuscomponent of the cell membraneprecursor for bile acids (bile acids

aid in fat digestion), steroid hormones, and provitamin D (When irradiated by sunlight it changes to vitamin D3.

Glucocorticoidsoriginate in the adrenal cortex and

affect mainly metabolism in diverse ways; decrease inflammation and increase resistance to stress.

Mineralocorticoidsoriginate in adrenal cortex and

maintain salt and water balance.

Estrogensoriginate in the adrenal cortex and

gonads and primarily affect maturation and function of secondary sex organs (female sexual determination)

Androgensoriginate in the adrenal cortex and

gonads and primarily affect maturation and function of secondary sex organs (male sexual determination).

STEROIDS HORMONES

Progestinsoriginate from both ovaries and

placenta, and mediate menstrual cycle and maintain pregnancy

AMINO ACIDS HORMONESThyroid hormones - primarily derived

from the amino acid tyrosine with the incorporation of iodine atoms 

Catecholamines which include neurotransmitter hormones - epinephrine and nor epinephrine are also derivatives of the amino acid tyrosine 

Serotonin and melatonin are derived from the amino acid Tryptophan 

Histamine is derived from the amino acid Glutamic Acid. 

PEPTIDE HORMONESprotein hormonesvary considerably in size and can

be as short as a three amino acids chain or as large as a glycoprotein. Most of the peptide hormones are prohormones (i.e. precursors of the mature form of hormones)

1. Luteinizing Hormone and Follicle Stimulating Hormone: Both these hormones are secreted by the pituitary gland and have an action on the gonads. In females, these hormones bring about the maturation of the ovarian follicle and aid in secreting progesterone. While in males, these hormones stimulate the production of sperms and help in the production of the male hormone-testosterone. Further, these hormones also contribute in development of secondary sexual characteristics for both the sexes 

Prolactin: secreted by the pituitary, it works on the mammary glands and stimulates the release of breast milk from the breast tissue. 

ACTH (Adrenocorticotrophic Hormone): secreted by the pituitary gland, it stimulates the adrenal glands and regulates the production of glucocorticoids and the growth hormone which subsequently act on muscles, bones and the liver. 

Anti Diuretic Hormone (ADH): has essential functions of retaining fluid in the body.

Insulin: secreted by the pancreas, controlling blood sugar levels by aiding the absorption of glucose by the body cells.

Gastrin: secreted by the G- cells (located in the stomach and duodenum), gastrin facilitates the release of gastric juices by the parietal cells in the gastric mucosa and enhances gastro intestinal mobility. 

ENDOCRINE VS.NERVOUS SYSTEM

ENDOCRINE VS.NERVOUS The endocrine system acts with nervous system to

coordinate the body's activities. Both systems enable cells to communicate with others

by using chemical messengers. The endocrine system uses chemical messengers

called hormones that are transported by the circulatory system (blood). They act on target cells that may be anywhere in the body.

The endocrine system is slower than the nervous system because hormones must travel through the circulatory system to reach their target.

Target cells have receptors that are specific to the signaling molecules.   The binding of hormones to the receptors on or within the target cell produces a response by the target cell.

ENDOCRINE VS.NERVOUS SYSTEM

1.SIMILARITIES A. both maintain homeostasis

B. both secrete chemicals- such as:  1. Nervous System: secretes

neurotransmitters 2. Endocrine System: secretes hormones

DIFFERENCES

• A nerve travels very fast around the body however a hormone travels very slowly around the body.• Hormones are produced by glands and nerves are produced by the nervous system.

• Nerves die out very quickly whereas hormones live longer.• Hormones travel around the body as chemicals but nerves travel by electrical impulses.• Hormones are regenerated but nerves are not.• Hormones have slow effects but last longer.• Nerves have fast effects but don’t last long

The effects of the endocrine system are widespread in the body while the nervous system has a localised effect

CONCLUSION

, the body often combines the speed of the nervous system with the specificity of the endocrine system to create the neuroendocrine system. Neuroendocrine cells receive neurally transmitted information and release hormones in response which is carried via blood the the target cells. The neuroendocrine system is mainly organised by the hypothalamus.

SYNTHESIS, STORAGE AND SECRETION OF

HORMONES

Starting Material/Origin

Processes

Where Does It Go?

Cholesterol Precursor Molecules

Biochemical Reaction Series

Processed in Endoplasmic Reticulum

and Golgi Bodies

Direct into the Bloodstream

Stored in Secretory Granules until Needed

Target and NatureNucleus/Stimulate or

inhibit protein synthesis

Membrane proteins/amplified

responses

Steroid HormonesHormones Non-Steroid Hormones

MECHANISMS OF HORMONE ACTION

Endocrine Glands

Bloodstream

Receptor Cells

Hormones

Target Tissueor Cell

Basic Hormone Pathway

Action of Steroid Hormones

New proteins

Bloodstream

Steroid

Cell membrane

Cytoplasm

Cell receptor

Nucleus

mRNA

Ribosomes

Action of Non-Steroid Hormones

GTP

ATP AMPActivates

many enzymes in

the cytoplasm

Hormone

Plasma membrane

Receptor molecule

G-protein

Adenylate cyclase

ENDOCRINE SYSTEMS AND FEEDBACK CYCLES (RESPONSE)

Imagine your body as a house with a thermostat. When the weather gets cold, the thermostat is turned to heat up, but when the weather is hot the air conditioning is turned on.

The same is true with the endocrine system, when there is an imbalance, the endocrine glands will control and maintain homeostasis.

Increase in blood pressure and

heart rate

Cate-cholamines

Adrenal Medulla

Stress

THE ENDOCRINE GLANDS

PITUITARY GLAND AND

HYPOTHALAMUS

PITUITARY GLANDa tiny organ, the size of a pea,

found at the base of the brain. As the master gland of the body, it produces and secretes many hormones that travel throughout the body, directing certain processes stimulating other glands to produce different types of hormones. 

Also called hypophysis.

ANTERIOR PITUITARYthe front portion of the pituitary, also called adenohypophysis

ANTERIOR PITUITARY HORMONES

HORMONE Secretory cell type

Target ACTION

Follicle-Stimulating Hormone (FSH)

Gonadotrope Ovaries and testes

Stimulates production of eggs and sperms/ regulates reproductive functioning

Luteinizing Hormone (LH)

Gonadotrope Ovaries and testes

Stimulates ovaries and testes; prepare uterus for implantation of fertilized egg

Thyroid Stimulating Hormone (TSH)

Thyrotrope Thyroid gland

Stimulates the synthesis and release of thyroxin from the thyroid gland

adrenocorticotropic hormone(ACTH)

Corticotrope Adrenal gland(cortex

)

Stimulates release of some hormones from adrenal cortex

Growth Hormone (GH)

Somatotrope Liver and adipose tissue

Stimulates protein synthesis and growth in cells

Prolactin Lactotrope Mammary glands

Stimulates milk production

Melanocyte-stimulating

hormone(MSH)

Stimulates the melanocytes of the skin, increasing their production of the skin pigment melanin.

POSTERIOR PITUITARY

the back portion of the pituitary, also called neurohypophysis

Posterior pituitary Hormone

Hormones Secretory cell type Action

Antidiuretic hormone(ADH)

Kidneys and arterioles

Stimulates contractions of uterus during birth; releases milk in nursing mothers/ water retention and increased blood pressure

Oxytocin Uterus and mammary glands

Uterine contraction and lactation

ABNORMALITIES OF PITUITARY GLAND

PITUITARY GLAND

• this gland secretes the maximum number of hormones in the human body that regulate growth and development.

DIABETES INSIPIDUS• caused due to insufficient secretion of vasopressin secreted by the posterior pituitary gland. • a condition characterized by excessive thirst and excretion of large amounts of severely diluted urine.

ACROMEGALYis caused due to an overproduction of growth hormone.

ACROMEGALY

cheekbones are obviousforehead bulgejaw is enlarged facial lines prominentforehead and overlying skin is thickened

PROLACTINOMAis a tumor that causes increased secretion of prolactin.

can be observe in males and females

SEX HORMONE DISORDERS

pituitary gland secretes various sex hormones, thus altered secretion of these affects the sexual development or regulation of sexual characteristics.

HYPOTHALAMUS

the "hypo-thalamus" (literally, the under-thalamus)

FUNCTIONSMaintains homeostasis links the nervous system to the endocrine

system via the pituitary glandresponsible for certain metabolic

processes and other activities of the autonomic nervous system. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, micturition (urination), and sexual arousal.

controls body temperature, hunger, thirst, fatigue, sleep, and circadian cycles.

synthesizes and secretes certain neurohormones, often called hypothalamic-releasing hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones.

RELEASING HORMONES SECRETED BY THE HYPOTHALAMUS :

Thyrotropin-releasing hormone (TRH),Corticotropin-releasing hormone (CRH),Gonadotropin-releasing hormone

(GnRH),Growth hormone-releasing hormone

(GHRH),

Thyrotropin-releasing hormone (TRH)stimulates the release of thyroid-

stimulating hormone and prolactin by the anterior pituitary.

Corticotropin-releasing hormone (CRH) involved in the stress response. Its

main function is the stimulation of the pituitary synthesis of ACTH.

Gonadotropin-releasing hormone (GnRH)responsible for the release of follicle-

stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary.

Growth hormone-releasing hormone (GHRH)

releasing hormone for growth hormone.

INHIBITORY HORMONESomatostatin

Inhibit the release of growth hormone (GH) and thyroid-stimulating hormone (TSH)]

Dopamine inhibit the release of prolactin from the

anterior lobe of the pituitary.

PINEAL GLAND

Photosensitive organ in the brain; also called epiphysis

Like a petite pine cone

It maintains the body’s natural rhythms likewaking up and falling asleepAlso responsiblefor the completevisual map of theeye

Hormones Secreted

In the absence of light, the pineal gland secretes melatonin which can influence the secretions of the gonadsand influence in sexual activity.

In winter the hamster’s sexual activity is suppressed because melatonin levels are high due to long nights;

THYROID GLAND

THYROID GLAND

is at the base of the neck in the front of trachea or windpipe.

Main hormone: thyroxine triiodothyronine Calcitonin

THYROXINE TETRA IODOTHYRONINE

(T4) 

is the major hormone secreted by the follicular cells of the thyroid gland. With 99.95% of the secreted T4 being protein bound, principally to thyroxine binding globulin (TBG), to a lesser extent thyroxine binding pre albumin (TBPA) and albumin.

TRI IODOTHYRONINE (T3)

is 3 4 times more potent than T4. Only 15% of the total normal T3 concentration is directly secreted by the follicular cells. With 99.5% of the secreted T3 being bound to the same proteins as T4.

CALCITONIN

is secreted by the C cells of the thyroid gland. Its function is totally unrelated to the other thyroid hormones, since it's involved in calcium homoeostasis.

COMMON THYROID PROBLEMS

concerning the production of hormone (too much, or too little)

due to increased growth of the thyroid, causing compression of important neck structures or simply appearing as a mass in the neck

the formation of nodules or lumps within the thyroid which are worrisome for the presence of thyroid cancer

THYROID GOITER

is a dramatic enlargement of the thyroid gland.

 common among women

the most common cause for goiter is iodine deficiency

THYROID CANCER

is a thyroid neoplasm that is malignant.

It can be treated with radioactive iodine or surgical resection of the thyroid gland.

Chemotherapy or radiotherapy may also be used

HYPERTHYROIDISM overactive tissue within

the thyroid gland causing an overproduction of thyroid hormones (thyroxine or "T4" and/or triiodothyronine or "T3"). 

 thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood.

PARATHYROID GLAND

Parathyroid gland are endocrine glands usually in four numbers.

It is located at the front of the neck close to the tips of thyroid lobes

Hormone Secreted

Parathyroid Hormone

• Function regulates the levels of calcium,

phosphorus, and magnesium. Essential for bone mineralization.

DISORDERS OF PARATHYROID GLAND

Hypoparathyroidism

Hyperparathyroidism

Hypoparathyroidism

Inadequate production of parathyroid hormone

Disease characterized by low blood calcium level due to diminished or absent of parathyroid hormone production or absence of parathyroid glands.

SymptomsTingling of lips and musclesMuscle cramps ( leads to muscle spasm)Brittle handsDry hairCataract formation ( not uncommon)

TreatmentRestoration of calcium associated

minerals in the body

Hyperparathyroidism

Disease associated with an excessive amount of parathyroid hormone.

Hyperparathyroidism can be caused by idiopathic enlargement of one or more of the glands, by parathyroid adenoma or in response to an abnormally low calcium level in the blood.

Symptomsfatigue, back pain, joint pain, fractures of

long bones, decreased height, increased urine output, increased thirst, epigastric pain, loss of appetite, nausea, muscular weakness, depression, personality changes, stupor and possibly coma, itching of the skin, cataracts, clay colored stools, nail abnormalities, diarrhea, or bone pain and tenderness

o PreventionoEarly detection of vitamin D deficiency

THYMUS GLAND

LocationBehind the breast bone, between the

two lungs.

Hormones SecretedThymosines – may induce the

formation and early development of T-lymphocytes which is integral for the immune system. Children with immunodeficiency diseases showed significant improvement when provided with thymosine.

ADRENAL GLANDS

ADRENAL GLAND (EMERGENCY GLAND)

are two small glands that are located superior to each kidney.

encased in a connective tissue capsule that is usually partially buried in an island of fat.The adrenal glands lie beneath the peritoneum (that is, they are "retroperitoneal").

it has two distinctive components namely:

Adrenal medulla (inner part)Adrenal cortex (bark or the outer part)

ADRENAL MEDULLA

The medulla consists of many large columnar cells called "chromaffin cells.

These synthesize and secrete catecholamines. The principal hormone released from the

adrenal medulla is epinephrine or adrenalin and the norepinephrine.

Epinephrine and norepinephrine are released in response to stimulation by the sympathetic nervous system which becomes most active when a person is excited or physically active.

Stress and low blood glucose levels can increased the sympathetic stimulation of adrenal medulla.

SOME MAJOR EFFECTS OF THE HORMONES RELEASED BY ADRENAL MEDULLA ARE:

Increases release of glucose from the liver, fatty acids from the fat stores

Increase heart rate Increase blood flow to skeletal muscles and

the heart Increased in metabolic rate in skeletal and

cardiac muscle as well nervous tissues. Rate and depth of breathing increased. Force of muscular contraction improves. Decrease functions of visceral organ

Responses to hormones from the adrenal medulla reinforce the effect of

the sympathetic division of the autonomic nervous system. Thus the adrenal medulla and the sympathetic

division function together to prepare the body for physical activity and to help to

cope with the stressful situation, to produce “fight-or-flight” response and to

produce many of the responses to stress.

ADRENAL CORTEX the outer part of adrenal gland The adrenal cortex consists of three

concentric zones of steroid-synthesizing cells: glomerulosa, fasiculata and reticularis.

it produce three major groups of steroid hormones:

1. Mineralocorticoids 2. Glucocorticoids 3. sex hormone

MINERALOCORTICOIDS known also as aldosterone it is produced by the outermost adrenal

cortex cell layer it regulates mineral (or salt) content of the

blood, particularly the concentrations of sodium and potassium ions.

their target is the kidney tubules that selectively reabsorb the minerals or allow them to be flushed out of the body in the urine.

it helps to regulate both water and electrolyte balance in the body fluids.

GLUCOCORTICOIDS

it helps to regulate blood nutrient levels in the body

it produce major hormone called cortisol Cortisol increases the breakdown of protein

and fat and increases their conversion to forms that can be used as energy sources of the body.

it reduces the inflammatory and immune responses by decreasing edema, and they reduce pain by inhibiting some pain-causing molecules called prostaglandins.

SEX HORMONE (ANDROGENS) both male and female sex hormones are

produced by the adrenal cortex throughout life in relatively small amounts.

androgen have the ability to stimulate the development of male sexual characteristics

in females the adrenal androgens influence the female sex drive.

if secretion is high, it result exaggerated male characteristics develop in both males and females but this condition is most apparent in females and in males before puberty.

DISEASES/DISORDER/ABNORMALITIES IN ADRENAL

GLAND

Adrenal insufficiency- is a condition in which the adrenal glands, located above the kidneys, do not produce adequate amounts of steroid hormones (chemicals produced by the body that regulate organ function), primarily cortisol, but may also include impaired aldosterone production (a mineralcorticoid) which regulates sodium, potassium and water retention. Craving for salt or salty foods due to the urinary losses of sodium is common.

An adrenal crisis often occurs if the body is subjected to stress, such as an accident, injury, surgery, or severe infection; death may quickly follow

Addison’s disease - is caused by the failure to produce adequate levels of cortisol. This can be caused by a disorder of the adrenal glands, autoimmune disorder. The disorder causes the body’s immune system to gradually destroy the adrenal cortex.

Cushing’s syndrome is the result of the excessive production of corticosteroids by the adrenal glands. An overproduction of corticotrophin, the hormone that controls the adrenal gland by the pituitary gland, which stimulates the adrenal glands to produce the corticosteroids, could be of one cause. It also can be in excessive cortisol levels in the blood which may be the result of a tumor of the pituitary glands, adrenal glands or from tumors or cancer arising elsewhere in the body.

It results in moon face, bufallo hump.

Phaeochromocytoma, a benign tumor neuroblatoma, malignant tumor. Symptoms results from the release of large amounts of epinephrine and norepinephrine and include hypertension, sweating, nervousness, pallor and tachycardia.

PANCREAS

located close to the stomach in the abdominal cavity

the best hidden endocrine gland in the body is the pancreatic islets.

in pancreas there is exocrine part (enzyme producing) –which acts as part of digestive system.

it secretes two important hormones namely:1. Insulin 2. Glucagon

INSULIN it is released from the beta cells primarily in

response to the elevated blood glucose levels and increased parasympathetic stimulation that is associated with digestion of a meal.

increased blood levels of certain amino acids also stimulate insulin secretion.

the major target cells of insulin are the liver adipose tissue,muscles ant area of hypothalamus that controls appetite called satiety center.(fulfillment of hunger).

GLUCAGON is released from the alpha cells when blood

glucose levels are low. the primary organ target is the liver, which

stimulates to break down stored glycogen to glucose and to release the glucose in the blood.

ABNORMALITIES OF PANCREAS• Pancreatitis – inflammation of pancreas.

• Acute pancreatitis - a rapid-onset inflammation of the pancreas, most frequently caused by alcoholism or gallstones.

• Chronic pancreatitis - a long-standing inflammation of the pancreas.

• Diabetes mellitus- is a group of metabolic diseases in which a person has high blood sugar.• Type 1 diabetes- results from the body's failure to

produce insulin, and presently requires the person to inject insulin.

• Type 2 diabetes- results from insulin resistance, a condition in which cells fail to use insulin properly.

• Gestational diabetes - is when pregnant women, who have never had diabetes before, have a high blood glucose level during pregnancy.

Exocrine pancreatic insufficiency – inability to properly digest food due to lack of digestive enzymes made by the pancreas.

Cystic fibrosis - hereditary disease that affects the entire body, causing progressive disability and early death.

Pseudocysts - a circumscribed collection of fluid rich in amylase and other pancreatic enzymes, blood and necrotic tissue, typically located in the lesser sac.

Hemosuccus pancreaticus - is a rare cause of hemorrhage in the gastrointestinal tract.

OTHER CHEMICAL MESSENGERS Interferon - are proteins released when a cell has been

attacked by a virus. They cause neighboring cells to produce antiviral proteins. Once activated, these proteins destroy the virus. Interferon Type I –

Interferon-alpha (leukocyte interferon) is produced by virus-infected leukocytes, etc.

Interferon-beta (fibroblast interferon) is produced by virus- infected fibroblasts, or virus-infected epithelial cells, etc

Interferon Type IIInterferon-gamma  (immune

interferon) is produced by certain activated T-cells and NK cells.

Prostaglandins - are fatty acids that behave in many ways like hormones. They are produced by most cells in the body and act on neighboring cells.Functions of Prostaglandins:

1. Activation of the inflammatory response, production of pain, and fever.

2. Blood clots form when a blood vessel is damaged.

3. Certain prostaglandins are involved with the induction of labor and other reproductive processes.

4. Prostaglandins are involved in several other organs such as the gastrointestinal tract (inhibit acid synthesis and increase secretion of protective mucus), increase blood flow in kidneys, and leukotrienes promote constriction of bronchi associated with asthma.

Pheromones - are chemical signals that travel between organisms rather than between cells within an organism. Pheromones are used to mark territory, signal prospective mates, and communicate. The presence of a human sex attractant/pheromone has not been established conclusively.

By 2005, the scientific literature recognized four classes of pheromones:

1. Human sex-attractant pheromones 2. Mother-infant recognition pheromones3. Menstrual synchrony pheromones in women4. Territorial marking animal pheromones

GONADS

Androgens including testosterone – sperm maturation and development of sexual traits

Estrogens – egg maturation and development of sexual traits

Progesterone – uterine lining and breast development

TESTIS

OVARIES