Endocrine System-

Endocrinology

Endocrinology is the science of endocrine glands, hormones and their effects. The term ‘endocrinology’ was given by Pende Thomas Addison is father of endocrinology.

Basically, a gland is an organ, tissue or cell of epithelial origin that secretes a chemical substance for performing a particular function. The glands are of three types: exocrine, endocrine and mixed.

Differences among exocrine, endocrine and mixed glands.

Exocrine gland

Endocrine gland

Mixed gland

It is provided with its own duct.

It is ductless gland.

It has both nature.

It generally secretes enzymes.

It always secretes hormones.

It secretes enzymes and hormones both.

Its secretion is carried to the target site through its own duct. e.g. salivary gland.

It secretion is carried to the target site through blood. e.g. pituitary gland.

Its nature is mixed e.g. pancreas.

HORMONE

1.These were initially mentioned as ‘fluid of internal environment’ (milieu interieur) by Claude Bernard (1855).

2.It was Starling who first of all used the term ‘hormone’ in 1905 with reference to secretin.

3.Secretin was the first hormone discovered in 1902 by Starling and Bayliss.

4.Huxley called hormone as Chemical messenger (also known as autocoids).

5.In general, the product of endocrine gland is called hormone but according to Starling & Bayliss “hormone is a chemical messenger, released from one group of cells and travel via blood stream to influence one or more different groups of cells”.

6.The hormones are small molecules of low molecular weight.

7.These are produced in very small quantity.

8.Hormones and absent in bacteria.

9.The tissue/organ influenced by a particular hormone is called its target.

10.Hyposecretion means less secretion while hypersecretion means more secretion of hormones than needed.

Nature of Hormones

1. Protein/Peptide:

For example hormones of hypothalamus, pituitary, pancreatic islets of Langerhans, gastro-intestinal mucosa, parathyroid and thymus glands.

Calcitonin (CT), relaxin and human chorionic gonadotropin (HCG) HORMONES.

2. Steroids :

Such hormones are either derived from cholesterol or resemble to that of cholesterol e.g. hormones of adrenal cortex, gonads and some hormones of placenta.

3. Amino acid derivatives :

Adrenal medullary hormones (E & NE) are derived from tyrosine amino acid. These are in fact catecholamines.

Pineal body hormone (=melatonin) is derived from tryptophan amino acid.

Thyroid hormones (T3 & T4) are in fact tyrosine (amino acid) based iodinated protein.

EMBRYONIC ORIGIN

Ectoderm

Mesoderm

Endoderm

Pituitary gland

Pineal body

Adrenal medulla

Adrenal cortex

Gonands (testis and ovary)

Kidney

Islets of Langerhans

Thyroid gland

Parathyroid gland

Thymus gland

Gastro-intestinal mucosa

Differences Between Hormones and Enzymes :

Character

Hormones

Enzymes

Nature

Protein/peptide, steroid, amino acid derivatives etc.

Always proteins

Secreted by

Endocrine glands

Exocrine glands

Molecular weight

Low

High

After action

Cannot re-participate, if once used.

Participate many times.

Functioning place

Other than the place of origin but always inside the cell.

Both at and other than the place of origin and both inside and outside the cell.

Similarities between Hormones and Enzymes:

1.Both are synthesized and secreted by the glands of body.

2.Both are easily soluble in water and are easily diffusible.

3.Both are needed in small quantity.

4.Both influence the metabolic activities.

5.Both are specific in nature.

MECHANISM OF HORMONE ACTION

The hormones first combine hormone receptors, located either inside the cells or on the cell surface. Accordingly, hormones are classified into two groups.

Group I : Hormones that bind to intracellular

receptors.

Group II : Hormones that ind to the cell surface receptors.

Group I : Hormones that bind intracellular receptors :

The receptors of thyroid hormones (T3 & T4) and steroid hormones are located inside the cell. The hormone and the receptors form a complex (=hormone receptor complex) that moves from the cytoplasm into the nucleus, where it attaches to a specific site on a chromosome.

The hormone receptor complex exerts an influence on gene activity at the site by promoting or suppressing transcription into RNA.

Group II : Hormones that bind to cell surface receptors :

The protein and peptide hormones bind receptor sites on the plasma membrane. This causes the activation of an enzyme adenyl cyclase, located in plasma membrane, which transforms ATP into cAMP (=cyclic adenosine monophosphate).

The cAMP initiates a series of enzyme catalyzed reactions called an enzyme cascade within cells that influence the activity of genes in the nucleus.

Calcium ions act as third messengers.

Such hormones are called first messengers and cAMP as second messenger.

The role of cAMP as a second messenger was described by Sutherland & others (1971) and they called it also a “director of foreign affairs”.

1. HYPOTHALAMO-HYPOPHYSIAL SYSTEM

Pituitary is now known as hypophysis, which is connected with hypothalamus through a hypophysial stalk. Almost all the secretions of hypophysis are under the control of hypothalamus. Due to this inseparable functional relationship between the two, endocrinologies of both are studied together under a separated system called hypothalamo-hypophysial system.

This system is supplied with pure blood through circle of Willis while impure blood is collected through hypothalamo-hypophysial portal vein.

Hypothalamo-hypophysial system

=endocrine hypothalamus + hypophysis

A. PITUITARY (=HYPOPHYSIS)

The term ‘Pituitary’ was given by Vesalius, as initially it was believed that it is concerned with the secretion of mucus (phlegm) to lubricate the nasal passage. After the establishment of its true function, it is renamed as hypophysis (i.e. undergrowth) because of its location below the brain as an undergrowth Hypophysis is smallest endocrine gland, found in a depression called sella tursica of sphenoid bone of skull.

Sella turcica is located in basisphenoid of parietal segment of skull

Entire pituitary is originated from embryonic ectoderm, which arises from two different sources i.e. adenohypohysis from Rathke's pouch and neurohypohysis from neural ectoderm.

This endocrine gland is physiologically divided as following:

I. Adenohypophysis a) Pars distalis

(anterior pituitary) b) Pars tuberalis

c) pars intermedia=

Intermediate lobe

II. Neurohypophysis a) Pars nervosa

(posterior pituitary) b) Infundibulum

c) Median eminence

Adenohypohysis (pars distalis) is composed of following cell types :

Cell Type

Nature

Hormone

1.Corticotroph

Basophil

ACTH

2. Thyrotroph

Basophil

TSH

3.Gonadotroph

Basophil

FSH & LH

4. Lactotroph

Acidophil

PRL

5.Somatotroph

Acidophil

GH

I. Hormones of Adenohypophysis :

The anterior pituitary secretes following seven protein/peptide hormones-

1. TSH (Thyroid stimulating hormone):

Controls the secretion of thyroid hormones.

2.ACTH (Adreno-cortico tropic hormone): stimulates secretion of adrenal cortical hormones mainly glucocorticoids.

3.STH or GH (somatotropic hormone or growth hormone or somatotroipin):

It does not function through a target area but causes the growth of almost all tissues of the body including muscles and bones.

It stimulates cellular growth, multiplication and diferentiation. The GH is more effective along with thyroxine.

It increases protein synthesis (but protein synthesis is retarded by cortisol).

3. FSH (Follice stimulating hormone = gametokinetic factor):

To stimulate the growth and maturation of ovarian follicles in females.

To stimulate the spermatogenesis in seminiferous tubules in males, as it stimulates the Sertoli cells that causes spermiogenesis i.e. formation of sperms from spermatids.

To intiate the spermatogenesis, both FSH and testosterone are necessary.

4. LH (Luteinzing hormone):

To stimulate ovulation and transformation of Graafian follicle into corpus luteum in females.

To stimulate interstitial cell of Leydig for androgen secretion, hence the name ICSH (interstitial cells stimulating hormone).

Synergism is a phenomenon in which some hormones work together to control a process e.g. FSH and LH. The FSH and LH are collectively known as gonadotropic hormones.

5. PRL=LTH=MTH (Prolactin or lactogenic or luteotropic or mamotropic hormone):

This is called hormone of maternity because it:

Stimulates the growth and development of mammary glands during pregnancy.

Stimulates lactogenesis i.e. milk producing and secretion.

In pigeon, prolaction stimulates the epithelial cells of crop in both males and females to secrete "pigeon's milk" for the nourishment of newly hatched infants.

6. MSH (Melanocyte stimulating hormone=intermedin):

It is secreted by intermediate lobe.

This is a vestigial hormone in mammals with uncertain function in human.

In amphibians and reptiles, controls the colour change, as it stimulates the synthesis and dispersion of melanin pigments.

The MSH works against melatonin and makes the skin colour dark.

TSH, FSH and LH are glycoprotein hormones.

II. Hormones of Neurohypophysis :

Herring bodies (accumulations of stored neurosecretory substances) and pituicytes (supporting cells) are found in posterior pituitary.

The posterior pituitary secretes following two hormones, which are collectively known as pituitrins:

(a) Vesopresin = pitressin = ADH

(b) Oxytocin = pitocin

It was Du Vigneaud (1953) who determined their molecular structures.

Each of these two hormones, is made up of nine amino acids.

These two neurohypophysial hormones are in fact synthesized in hypothalamic supraoptic and paraventricular nuclei and then transpoted to the posterior pituitary gland.

(a) Vasopressin :

To stimulate muscles of blood vessel for vasoconstriction hence increases blood pressure.

To increase the rate of water reabsorption from glomerular fitrate in kidney; to check the diuresis (excess water in urine), hence vasopressin is also called antidiuretic hormone (ADH).

Thus, vasopressin regulates the kidney's retention of water and if it is missing, the kidneys cannot retain water.

(b) Oxytocin:

To stimulate / deliver/eject the milk from mammary glands during suckling hence called milk ejection hormone.

To stimulate labour pain / uterine contraction for the delivery of baby hence called birth hormone.

Differences between prolactin and oxytocin:

Prolactin

Oxytocin

Secreted by anterior pituitary.

Secreted by posterior pituitary.

Activates the growth and development of mammary glands during pregnancy.

Stimulates labour pain or uterine contraction for the delivery of baby.

Stimulates lactogenesis i.e. milk production and secretion.

Stimulates ejection of milk from mammary gland.

Diseases: Hypo-and Hyperpituitarism

1. Diabetes insipidus :

It occurs because of hyposecretion of vasopression (=ADH) which causes diuresis (=excretion of diluted urine in excess.).

The urine of the patient becomes insipid (=tasteless), colourless and diluted. The sufferer feels intermittent urination at short intervals and thirst.

2. Dwarfism (midget):

It is a disease occurs due to less secretion of GH during childhood, characterized by retarded skeletal growth and other organs.

With the result, body length remains short but they are mentally normal.

3. Gigantism:

It occurs because of more secretion of GH during childhood. This is characterized by overgrowth of skeleton hence body becomes giant.

4. Acromegaly:

It is a disease caused by hypersecretion of GH after adolscence/during adulthood, characterized by enlargement of long bones and membraneous bones.

The whole body becomes asymmetrical with gorilla-like appearance.

5. Simmond's disease :

It occurs in adults due to degeneration of anterior pituitary.

B. ENDOCRINE HYPOTHALAMUS

Almost all the secretions of hypophysis (=pituitary) are under the control of hypothalamus. The hypothalamus controls the anterior pituitary secretions by its releasing and inhibiting hormone/factors. The secretion of posterior pituitary is controlled by nerve signals originating in hypothalamus and terminating into former.

Some important releasing and inhibiting hormones/factors are as following:

Adenohypophysial Hormones

Controlled by hypothalamic

1. TSH (=thyrotropin)

TRH

2. ACTH (=corticotropin)

CRH

3. GH (=Somatotropin)

GHRH & GHIH

4.FSH & LH (=gonadotropin)

GnRH & GnIH

5. PRL (=prolactin)

PRF & PIF

6. MSH (=melanotropin)

MSH-RH & MSH-IH

Role of Endocrine Hypothalamus as a master of master gland.

Since pituitary controls the functioning of major endocrine glands such as thyroid, adrenal cortex, gonads etc., hence its is called master gland or chief executive of endocrine system or leader of endocrine orchestra.

Hypothalamus secretes releasing hormones that work upon anterior pituitary.

Since, master gland is controlled by hypothalamus hence hypothalamus is called supermaster gland or master of the master gland or supreme commander of endocrine regulation.

2. PINEAL BODY

1.It is also known as epiphysis cerebri, hanging from roof of diencephalon (=epithalamus).

2.This is a small, about the size of a pea and is shapen- like a pine cone (hence it name).

3.It is the last endocrine gland discoered in human body in 1958.

4.Pineal body is composed of many branched glandular cells called pinealocytes and neuroglial cells (supporting tissue).

5.In some lower verterate such as Sphenodon (=tuatara), it exists as third eye (but crocodiles lack the pineal glands).

6.Pineal body secretes melatonin hormone, which is derived from tryptophan amino acid.

7.In mammals it does receive nerve impulse from the eyes by way of optic tract and influences sexual behaviour according to light.

Darkness stimulates pineal secretion whereas light condition inhibits.

8.The pineal gland and melatonin are involved in daily cycles called circadian rhythms.

9.In human, pineal gland starts degenerating after the age of 10 years due to the deposition of brain sand (granules of calcium salts).

10.In lower vertebrates, melatonin stimulates chromatophores and acts antagonistically to MSH to make the skin colour light.

3. GASTRO-INTESTINAL MUCOSA

The localized area of gastro-intestinal tract, secretes certain peptide hormones, which are collectively known as gastro-intestinal hormones. Important of them are :

1. Gastrin :

It is secreted by G-cells of pyloric gland of stomach.

It stimulates gastric glands to secrete gastric juice including HCI.

2. Enterogasterone:

It is secreted by duodenal mucosa.

It retards the secretion of gastric juice including HCI.

3. Cholecystokinin-Pancreozymin (CCK-Pz):

Initially, it was believed that both are two different hormones but now it has been established that it is a single hormone.

It is secreted by duodenal and jejunal mucosa.

The CCK-Pz stimulates contraction of gall bladder for releasing bile into duodenum.

It stimulates enzyme secretion in pancreatic juice.

4. Sacretin :

(a)The first hormone to be discovered was secretin by Starling and Bayliss in 1902.

(b)It i secreted by duodenal and jejunal mucosa.

(c)Secretin is made of 27 amino acids, hence resembles to that of glucagon (29 amino acids).

(d)It stimulates fluid portion of pancreatic juice secretion (but not enzyme), rich in bicarbonates.

5. Enterocrinin:

It is secreted by intestinal mucosa including ileum.

It stimulates intestinal juice secretion (fluid and enzymes).

6. Duocrinin:

It is secreted by intestinal mucosa.

It stimulates mucus secretion from Brunner's glands.

7. Vilikinin:

It is secreted by mucosa of intestinal villi.

It stimulates, movements o the intestinal villi hence accelerates intestinal absorption.

4. THYMUS GLAND

1.It is a bilobed, pyramidal, lymphoid gland located in chest cavity behind the sternum.

2.Thymus grows maximum upto the age of puberty and then its gradual degeneration starts. In adult, finally it becomes inconspicuous.

3.Thymus has hassalls corpuscles, which act as phagocytes.

4.According to 'Immunity Theory of Ageing' decline and disappearance of thymus by late middle age is the basic cause of ageing.

The science of ageing is called Gerantology.

5.This is a gland, which is associated with AIDS (as the HIV attacks helper T-cells or T4 cells).

6.Thymus gland secretes a proteinaceous hormone called thymosin with following important functions:

To set up lymphocyte producing machinery.

To provide a basis for antibody production.

7. Gluco-corticoids impart adverse effects on thymus gland.

5. KIDNEY : RENIN

1.Renin is an enzyme synthesized in juxtaglomerular cells of kidney.

2.In is secreted when arterial pressure falls.

Students must note that renin is essentially an enzyme and not a hormone.

3. Renin converts angiotensinogen (=a plasma protein) into angiotensin I, which is then converted into peptide one called angiotensin-II by a converting enzyme is lungs.

Angiotensinogen

renin

Angiotensin I

converting enzyme

Angiotensin II (hormone)

4. The hormone angistensin II-

acts as vasoconstrictor i.e. to constrict the blood vessels.

Stimulates aldosterone secretion by zona glomerulosa of adrenal cortex. The aldosterone increases salt and water reabsorption by kidney tubules. With the result, arterial pressure is normalized.

Renin is also an enzyme secreted in mammalian stomach. This enzyme is activated by HCl. It changes soluble milk protein (=casein) into insoluble curd protein (=calcium paracaseinate).

6. THYROID GLAND

1.It is H shaped/like a shield (thyros=shield), hence the name thyroid.

2.It is the largest endocrine gland.

3.In human, it lies just below the Adam's apple in front of neck, immediately behind the larynx. It consists of two lobes, lie one on either side of trachea. Both lobes are interconnected by a thin isthmus.

4.The unit of thyroid gland is called thyroid follicle, which has a lumen surrounded by single layered cuboidal epithelium.

This lumen is filled with a jelly-like colloid substance that has mainly thyroglobulin.

5.Thyroglobulin is the inactive storage form of thyroid hormones secreted by follicular cells.

Thyroid is unique in having the only extra-cellular storage of hormone within the gland.

6.In lower Chordates, thyroid is absent but its homologous structure called endostyle is found in them for the same purpose.

7.Thyroglobulin (=tyrosine based iodinated protein) gives rise following two hormones :

Tri-iodothyronine (T3)

Tetra-iodothyronine (T4) or thyroxine.

8. Thyroid hormones (T3 & T4) are iodinated tyrosine, where iodine is approximately 65%.

Functions of thyroxine :

Active component of thyroid was isolated by Kendall (1915) who gave it the name 'thyroxine.' Herrington and Barger (1927) worked out its molecular structure. Gudernatsch (1912) told the need to thyroid substance in the metamorphosis of amphibian tadpole.

Thyroxine performs following important functions:

It stimulates differentiation of tissues.

It controls the metamorphosis of amphibian tadpole. Removal of thyroid from larva prevents the metamorphosis while injection of iodine VT4 will make fast the rate of metamorphosis.

T4 influences general metabolism and controls the BMR.

It enhances oxidative metabolism and increases energy production, hence called calorienic hormone.

Thyroxine increases glucose absorption, glucose utilization, glycogenolysis, gluconeogenesis, deamination, protein synthesis, heart beat rate and body temperature.

Thyroxine increases glucose absorption, glucose utilization, glycogenolysis, gluconeogenesis, deamination, protein synthesis, heart eat rate and body temperature.

Thryoid hormone secretion is under the control of thyrotropin (TSH) i.e. thyroid stimulating hormone, secreted by anterior pituitary.

Diseases :

I. Hypothyroldism :

Cretinism

Myxedema (Gull's disease)

Hashimoto's disease

Simple goitre

II. Hyperthyroidism :

Exophthalmic goitre

Grave's disease

Plummer's disease

1. Cretinism:

It occurs during childhood due to hyposecretion of thyrosine. The sufferer is called cretin or thyroid dwarf.

It may be either congenital (due to genetic defect in gland) or endemic (due to iodine deficiency).

Body parts unproportionate with low BMR and retarded physical, mental, sexual and skeletal development.

2. Myuxedema (=Gull's disease) :

It occurs in adulthood because of less secretion of T4.

Bagginess below the eyes.

Puffy appearance due to accumulation of fat in subcutaneous tissues because of low metabolic rate.

Muscular, gastric and nervous weakness with poor memory.

3. Hashimoto's disease :

During acute hypothyroidism, certain drugs are introduced to promote gland activity but sometimes its acute less secretion and drug introduced begin to act like an antigen, against which antibodies are produced.

These antibodies start to destroy thyroid cells hence this disease is also known as autoimmune thyroiditis or suicide of thyroid.

4. Simple goitre :

It occurs because of iodine deficiency and characterized by enlargement of thyroid.

Due to hyposecretion of thyroxine, TSH stimulates thyroid to secrete hormones hence gland grows in size to cope the situation. But iodine deficiency does not permit more T4 synthesis hence TSH secretion remains continue. With the result, gland enlarges many times.

5. Exophthalmic goitre:

It occurs because of more secretion of thyroxine due to origin of tumor etc. in thyroid.

This is characterized by protrusion of eyeball with staring look due to deposition of fat and mucus in eye orbit, followed by enlargement of gland.

6. Grave's disease :

It is the further condition of exophthalmic goitre in which thyroid enlarges uniformly.

7. Plummer's disease:

In this condition, enlarged thyroid becomes nodulated.

7. PARATHYROID GLAND (PTG)

In human, the PTG are two pairs, partially or completely embedded in dorsal surface of the lobes of thyroids.

The PTG is mainly composed of so called chief cells or principal cells. Sometimes, oxyphil cells may also be present.

The chief cells secrete only one hormone variously known as parathyroid hormone (=PTH) or parathormone or Collip's hormone.

This hormone was first discovered and purified by Collip (1925).

Potts gave the molecular structure of PTH, which is a polypeptide of 84 amino acids.

Functions of PTH :-

It plays a key role in calcium and phosphate metabolism.

It stimulates absorption and re-absorption of calcium by the gut and kidney tubules respectively.

PTH increases calcium level in ECF .

It promotes the excretion of phosphate with urine.

This hormone keeps the muscles in active state.

This hormone keeps the muscles in active state.

The PTH causes remodeling of bones by increasing osteoblast (=bone forming cell) and removes additional parts of newly formed bones by increasing osteoclast (=bone eating cell) activity.

Calcitonin (=CT) and its functions :

This hormone is secreted by parafolicular (=C-cells) of thyroid gland. This is a peptide of 32 amino acids. The function of CT is antagonistic to that of PTH.

Vitamin 'D' and its functions :

Vitamin D3 (=cholecalciferol) is synthesized in human skin. For biological activity, it is converted into 1, 25-dihydroxycholecalciferol, which is steroid hormonal form of vitamin D.

Vit D3 or cholecalciferol (Skin)

25 (OH) D3 (Liver)

1, 25-(OH)2 D3 (Kidney)

This hormone along with PTH, controls the mineralization of bone.

PTH (mainly), CT and 1, 25-(OH)2D3 are involved in the regulation of calcium and phosphate metabolism.

Diseases :-

1. Hypoparathyroidism :-

The PTH is essential to life. The deficiency of PTH causes a severe disease called tetany. It is characterized by hypocalcemia (=decreased calcium level) and hyper-excitability of neuromuscular system that finally causes death.

2. Hyperparathyroidism :-

More secretion of PTH causes hypercalcemia (=increased calcium level) and osteoporosis (=bone becomes soft, weak, distorted and fragile).

Students must know that vitamin 'D' is a hormone also.

8.ISLETS OF LANGERHANS

Pancreas is a mixed gland as it includes both exocrine as well as endocrine parts. The endocrine part is called pancreatic islets of Langerhans, in the honour of its discoverer Langerhans.

These islets may contain following types of cells :

Cells

Hormones

-cells

Glucagon

cells

Insulin

ss-cells

Somatostatin

pp-cells

pancreatic polypeptide

Insulin and its function :-

1.Insulin is secreted by cells, which can be destroyed by using alloxan compounds.

2.Banting and best (1922) prepared the extract of insulin.

3.In 1953-54, Frederick Sanger determined the molecular structure of bovine insulin, for which he was awarded with Nobel Prize (1958). He received 2nd Nobel Prize in 1980 on his work on chemical structure of gene.

4.Tsan synthesized human insulin while Abel prepared the crystal of insulin.

5.Insulin is a dimer of A and B chains with 21 and 30 amino acids respectively. Both chains are interconnected by disulfide bond.

6.Insulin is the first protein synthesized in laboratory through genetic engineering / recombinant DNA technology.

7.The insulin plays a key role in carbohydrate metabolism with following important functions :

To stimulate the conversion of glucose into glycogen both in liver and muscles. This process is called glycogenesis.

To stimulate the lipogenesis i.e. synthesis of fat in hepatic and adipose tissues.

To promote the rate of protein synthesis (protein synthesis is also stimulated by growth hormone and thyrosine but retarded by cortisol).

Since, insulin lowers the blood glucose level hence it is a hypoglycemic factor.

Glucagon and its functions :-

1.Glucagon is secreted by -cells, which can be destroyed by using cobalt chloride.

2.It was discovered and named as glucagon by Kimball and Murlin (1923).

3.Glucagon is a single straight peptide of 29 amino acids, mostly similar to that of secretin (27 amino acids).

4.Glucagon is antagonistic to that of insulin, with following important functions:

To promote the glycogenolysis i.e. breakdown of glycogen into glucose.

To stimulate the breakdown of fat (=lipolysis).

To stimulate the gluconeogenesis i.e. synthesis of glucose from fat and amino acids.

Since, glucagon raises the blood glucose level, hence it is a hyperglycemic factor.

Somatostatin and its functions :

Besides the islets of Langerhans, somatostatin is secreted by hypothalamus also. This is a peptide of 14 amino acids. It was discovered by Guillemin (1977).

It is known to inhibit the secretion of both GH and insulin. It means, it is a growth hormone inhibiting hormone (GHIH).

Diseases :

I. Hypoinsulinism : Less secretion of insulin causes a severe disease called diabetes mellitus, characterized by excretion of sugar with urine.

Differences between D. mellitus & D. insipidus

Diabetes mellitus

Diabetes insipidus

Caused by hyposecretion of insulin.

Caused by hyposecretiion of vasopresin.

Glucose is excreted with urine.

Large quantity of diluted urine is excreted (diuresis).

The urine becomes sweety (=mellitus).

Urine becomes tasteless (=insipid).

Diabetes mellitus includes:

(a)Hyperglycemia : raised blood glucose level.

(b)Glycosuria: means appearance of glucose with urine.

II. Hyperinsullinism: More secretion of insulin causes hypoglycemia i.e. decreased blood glucose level.

Continued excess secretion of insulin in blood causes unconsciousness and the patient may die. This is called insulin shock.

9. ADRENAL (=SUPRARENAL) GLAND

Mammalian adrenals are located at the top of two metanephric kidneys. These glands were discovered by Eustachius in 1563. Adrenal gland is embryologically, structurally and functionally divided into :

Division

Origin

Hormone

1. Outer cortex

Mesoderm

steriod

2. Inner medulla

ectoderm

catecholamine

A. ADRENAL CORTEX

Adrenal cortex secretes about 50 steroid hormones. These are synthesized from precursor cholesterol. The cortex is made of 3-layers:

Layer

Cells in

Secrete

1. Outer Zona glomerulosa

Whorls

Mineralocorticoids

2. Middle zona fasciculata

Columns

Glucocorticoids

3. Inner zona reticularis

Network fashion

Sex steroids

1. Mineralocorticoids (Aldosterone):

Aldosterone is the chief mineralo-corticoids, secreted by zona glomerulosa.

This is a life saving or salt retaining hormone with following important functions:

To stimulate the absorption and reabsorption of sodium (and water) by gut and kidney tubules respectively.

To stimulate the excretion of potassium by kidney tubules .

Controlled mainly by renin-angiotensin pathway.

Hypomineralocorticoidism: Addison's disease-discoered by Thomas Addison (father of endocrinology), occurs basically because of les secretion of aldosterone.

Hypermineralocorticoidism:conn's disease- discovered by Conn, occurs because of more secretion of aldosterone.

2. Gluco-corticoids (Cortisol):

Cortisol is the chief gluco-corticoids, secreted by zona fasciculata.

It acts as an anti-inflammatory hormone, as it regulates the activity of WBCs by decreasing their migration.

Cortisol is an immuno-suppressive agent because it supresses antibody production / immune reaction. (its injection is given during organ transplantation).

it is used for the treatment of allergy.

It induces adverse effect upon thymus and other lymphoid organs.

Controlled by ACTH (=adrenocortico tropic hormone), secreted by anterior pituitary.

Hyperglucocorticoidism: Cushing's disease: discovered by Cushing, occurs because of more secretion of cortisol. It is characterized by red moon face and buffalo hump.

3. Sex steroids:

Androgen (=male hormone) and estrogen (=female hormone) are the sex steroids secreted by zona reticularis. These are mainly associated with :

Sex differentiation.

Development of sex glands.

Secondary sexual characters.

Diseases :

Gynaecomastia

Virilism

It occurs in males due to more secretion of female hormones.

It occurs in females due to more secretion of male hormones.

It is characterized by the development of certain female characters in males such as breast.

It is the development of certain male characters in females such as beard.

B. ADRENAL MEDULLA

1. It is associated with sympathetic ANS, hence both are collectively known as sympatho-adrenal system.

2. Adrenal medulla is composed of chromaffin cells, which secrete following two catecholamine hormones:

Adrenaline or epinephrine (E)

Nor-adrenaline or nor-epinephrine (NE)

3. Abel gave the term epinephrine while Aldrich gave its molecular structure.

4. Important effects are as following.

To stimulate heart beat and arterial pressure

To increase breathing rate.

To cause vasoconstriction i.e. constriction of blood vessels.

To increase BMR.

To increase blood glucose level by stimulating glycogenolysis.

When a person suffers from marked fall in BP, it is advisable to give adrenaline.

Role of epinephrine (=E) as an emergency hormone:

W.B. Cannon appropriately called epinephrine as an emergency hormone because during emotional conditions and emergency such as fear, danger, anger, mental tension, emotional upsets, stress, intense pain etc. 'E' is secreted in excess just to prepare the body within seconds for alarm reaction.

This is often known as general adaptation syndrome (GAS), in which concerned person either boldly faces the emergency or escapes somehow from it. That is why 'E' is called 3F (fight, fright & flight) hormone.

Adrenal gland as wisdom of body:

The adrenal gland controls:

salt metabolism

sugar metabolism

sex differentiation

stress reaction / energy

Hence it is essential for proper development, existence and welfare o body and gland it therefore known as 4 'S' gland or wisdom of the body.

Vasopressin, angiotensin II and epinephrine hormones cause vasoconstriction.

Guru Gyan

1. Huxley called hormones as chemical messenger.

2. Hormones are also called as autocoids.

3. First hormone discovered by Bayliss and Starling was scretin.

4. Father of endocrinology – Thomas Addison, a British physician, (1793 – 1860). Addison's disease caused by deficiency of mineralocortiocoids has been named after him.

5. Herring bodies are the bodies which store neurosecretory substance basically formed in hypothalamus.

6. Cells present in posterior pituitary gland are called pituicytes or neuroglial cells. These have no secretary role.

7. Crystalline insulin was prepared by Abel (1926). Now animal based and DNA recombinant insulin named as Humulin is produced of which the latter is better.

8. Glucagon was discovered by Kimball and Murlin (1923).

9. Islet of Langerhans was discovered by Langerhans (1869).

10. Thyroid disorders are more frequent in females than in males.

11. Endostyles of lower chordates like Herdmania, Amphioxus is homologous to thyroid gland.

12. BMR of a normal adult man and woman is 40 cal/m2 respectively.

13. T3 is more active (3 to 4 times) than T4, but T4 is produced in greater quantity than T3.

14. The name thyroid was introduced by Thomas Wharton (1956). Wharton duct of the parotid gland is named after him.

15. PTH or Parathormone is important in bone development.

16. Melatonin is synthesized by serotonin (formed from Amino acid Tryptophan).

17. The surgical removal of testes is called castration or orchidectomy, (vs. ovariectomy – ovaries).

18. Castrated human male are called eunuch or neuter or oxen (instead of bulls) in case of cattle.

19. Pheochromocytomas is due to tumors of chromaffin cells of adrenal medulla.

20. Kinin and bradykinins are polypeptides that cause contraction of smooth muscles and dilation of blood vessels.

21. Local hormones (also called tissue hormones/parahormone/paracrine) do not pass into blood but diffuses to the target and work upon adjacent tissue. Eg. acetylcholine, bradykinin.

22. Temporary endocrine glands – corpus luteum and placenta.

23. Receeding endocrine gland – thymus.

24. A deer produces seven different types of pheromones al from different sites and with different functions.

25. Low blood pressure stimulates the rennin-angiotensin pathway.