ENDOCRINE SYSTEM

RAVI P. AGRAHARI (Science & Technology)

Endocrine system is a system of isolated glands that pour their secretions directly into venous blood or lymph for passage to different body organs in order to control their functioning, metabolism, cell permeability, growth differentiation and stress condition.

A gland is a structure which secretes a specific chemical substance or substances. Like other communication networks, endocrine system contains transmitters, singles and receivers that are called, respectively hormone producing cells, hormones and receptors.

Nervous System Endocrine system

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Electrical and chemical transmission (never impulses and chemicals across synapses)

Rapid transmission and response

Often short term

Pathway is specific (through nerve cells)

Responses often very localized. eg. On muscle

Chemical transmission (hormones) through blood system

Slower transmission and relatively slow action (adrenaline an exception)

Often long term changes

Pathway is not specific (blood around whole body), target is specific.

Response may be widespread. eg. Growth.

Types of glands on the basis of presence or absence of ducts

1. Exocrine glands – Those which drain out their secretion duct. Eg. Liver, gastric glands, intestinal glands etc.

2. Endocrine glands (holocrine glands) – Those glands which lack which lack duct and discharge their secretion (mainly called hormones) directly into the blood stream. Due to absence of duct they are also called ductless gland.

3. Heterocrine glands – Those glands which have dual function due to possession of both exocrine as well as endocrine region. They secrete hormone in association with other substances for their respective function. Eg. ovary testes, pancreas.

Mechanisms controlling release of hormones

1. Presence of specific metabolite in the blood Eg. Excess glucose in the blood causes the release of insulin from the pancreas which lowers the blood glucose level.

2. Presence of another hormone in the blood Eg. Stimulation hormones released from the anterior pituitary gland cause the release of other hormones from other glands in the body.

3. Stimulation by neurons from the autonomic nervous systemEg. Adrenaline and noradrenaline are released from the cells of adrenal medulla by the arrival of nerve impulse in situations of anxiety, stress and danger.

Properties of hormones

The hormones have the following properties:

1. They have low molecular weight 2. They are soluble in water and blood 3. They have no cumulative effect 4. They can act in very low concentration 5. They are non-antigenic 6. They are organic catalysts 7. They may act slowly or quickly 8. Hormone controlled reactions are not reversible 9. Hormones are produced in inactive form called prohormones. . eg. Proinsulin→Insulin (active form) 10. It is also called messenger because it has effect at a site

different from the site different from the site where it is made.

Hormones 1. All hormones are synthesized in the animal body itself.2. Hormones are circulated in blood Completely used up in metabolism3. They may accelerate or retard the specific.4. Hormone controlled reactions are not reversible

Enzymes

1. All enzyme are proteins2. Enzyme are mostly used locally Catalyze metabolic reaction and are reusable.3. Enzyme speed up the reaction.4. Enzyme controlled reactions are reversible.

BIOCHEMICAL CLASSIFICATION OF HORMONE

1. Biogenic amines or phenolic or amino acid derivative -Thyroxine, adrenaline, noradrenaline

2. Proteinaceous or polypeptide - Hypothalamic hormones, ACTH, GH, vasopressin, oxytocin,parathormone, calcitonisn, MSH

3. Glycoproteinaceous - Thyrotropin, FSH, LH

4. Steroids - Sex hormones and adrenocorticoids.

5.Fatty acids - Prostaglandins.

hypothalamic – pituitary system

is a direct proof of coordination between the hormonal and nervous system. It regulates most of physiological activities of body and maintains

homeostasis inside the body.

Thyroid Gland Thyroxin

- It stimulates oxygen consumption by metabolic active tissues (except testes, uterus, lymph nodes, spleen, anterior pituitary) and increases metabolic rate.

- Helps to regulate tissue growth and development.

- It increases the oxidation of glucose in tissues.

- It increases the rate of metamorphosis in amphibians. In its absence or presence of thiourea (antithyroid substance), tadpoles remains in larva stage indefinitely.

- It maintains nervous and muscular tonus.

- It also has metabolic effects on protein synthesis and lipid metabolism. As metabolism is increased to meet the demand for substrate associated with the increase rate of O2 consumption. For this it increases glucose absorption (from GI tract), glycogenolysis, gluconeogenesis and glucose oxidation, lipolysis and protein synthesis and degradation.

Hyposecretion

CretinismDisorder of children and infants (called cretin). Hence called childhood hypothyroidism.Characterized by decreased TRH and TSH; dwarfism (stunted growth with peculiar infantile expressions), mental retardation; decreased BMR, blood pressure, heart rate, body temperature; delayed puberty; pigeon chest, protruding tongue etc.

MyxoedemaAlso called gull’s diseases Occurs in adults Characterized by puffy appearance due to subcutaneous accumulation of fat, low BMR, heart rate and body temperature, lack of alertness, retarded sexuality, growth etc.

Simple goitre Occurs due to deficiency of iodine, hence less thyroxine productionAlso called endemic goitre because it occurs in northern hilly areas where soils and ground water is deficient of iodine Characterized by enlarged thyroid gland which brings about a swelling in the neck region.

Hashimoto’s disease Also called autommunea thyroiditsis thyroiditis due to sensitization of their own thyroid proteins called thyroglobuliiiin.It occurs in middle aged females. Characterized by the iodine deficiency and atrophy of the thyroid gland due to antibodies produced in response to thyroid antigens. Hence it is known as wuicide of thyroid gland. Discovered by Japanese surgeon Hakaru Hashimoto.

Hypersecretion

Grave’s diseaseOver activity of gland produces a swelling in the necl region called as goitre. Also called exophthalmic goitre as the eyes appear as if they are coming out of their sockets

Characterized by enlarged thyroid gland; increased BMR, heart rate, pulse rate, cardiac output, body temperature; protrution of eyes or exophthalmia; physical and mental restlessness, insomnia and nervouseness etc.

Parathoid glandParatharmone

Regulate calcium and phosphate level in blood Increases the rate of calcium absorption from intestine in children to elevate blood level of calciumRetards bone dissolution (osteoclastic action) and stimulates excretion of calcium in urine It affects the growth of bones, membrane permeability, nerve functioning and the muscular activity of body.

Hyposecretion : Causes : parathyroid tetany Since calcium is reqired for blood clotting, nerve and mucle functioning, so low level of calcium (parathoromone) lead tetany Characterized by decreased serum Ca and increased serum phosphate and decreased urinary phosphate muscle spasm, twitching, contraction of muscles of face, hands, feets etc., and increase deneuroexcitation.

Hypersecretion : Causes : osteitis fibrosa cystica Osteitis fibrosa cystica means normal bones is replaced by cysts and fibrous tissues Destruction of bone starts (osteoporosis) Increased level of calcium is deposited in various parts of body to bring about calcification of soft tissues Produces stones in kidneys and ureters causing renal insufficiency.

What are the Adrenal Glands?

• The adrenal glands are endocrine glands that produce hormones. A hormone is a chemical messenger. Each hormone influences specific organs or tissues, thus regulating a certain body process.

• The adrenal glands are shaped like a boomerang and located on top of each kidney. The adrenal glands are about the size of the end of your thumb.

• The adrenal glands produce hormones that affect almost every system in your body. When the adrenal glands fail to work properly, serious diseases and disorders can develop.

• One of the hormones that the adrenal glands secretes is called adrenaline. Adrenaline produces a sudden and remarkable burst of energy.

Outer and Inner layer

The adrenal glands consists of two portions: the inner core (medulla) and the outer layer (cortex).

• The inner core of the adrenal gland produces hormones called catecholamines. The 2 most important catecholamines are: adrenaline and noradrenaline. Physical and emotional stress usually trigger their release. When secreted into the bloodstream, adrenaline and noradrenaline increase heart rate and blood pressure. Adrenaline often produces a sudden and remarkable burst of energy.

• The outer layer of the adrenal gland produces hormones called corticosteroids. There are three types of corticosteroids.

Sex Hormones.– Male androgens and female estrogens.– They affect sexual development and reproduction.– Sex hormones are also produced in larger amounts in the testicles and ovaries.

Glucocorticoids– Hormones that aid in the conversion of starchy foods into glycogen.– An important glucocorticoid is cortisol. Cortisol helps regulate the immune

system, helps maintain proper blood pressure and blood volume, and helps the body deal with physical stress.

Mineralocorticoids– Control the body's content of the minerals sodium and potassium

Adrenaline1. Amine hormone 2. Secreted by adrenal medulla on stimulation by sympathethic nervous system for meeting an emergency or stress condition, like injury, pain, fear, accident, grief, fall in blood pressure etc. hence called emergency hormone.3. It increases blood pressure, BMR4. Acts as vasodilator 5. Increases respiration rate 6. Increases sugar level in blood by stimulating gycogenolysis in liver and skeletal muscles 7. Slows down peristalsis 8. Lipolysis in adipose tissue to increase level of fatty acids in blood.9. Hyper secretion of adrenaline causes hypertension, high level of sugar in the blood and urine, high metabolic rate, nervousness

and sweating etc

Nor-adrenaline

1. Amino hormone

2. More or less it resembles adrenaline in its biological effects excepts that it operates during normal state, exercise

3. It has lesser effect on cardiac activity and produces greater constriction of vessels in muscles (i.e. it is tonus hormone for circulatory system)

Thymus Gland

Thymus is a pyramidal shaped lymphoid organ situated in front of the heart in the upper part of sternum. Thymus is active in young ones but gradually becomes inconspicuous after sexual maturity. Hence the decline and disappearance of this gland by the middle age is the primary cause of ageing.

Hormone of thymus gland

THYOMSINE

- Polypeptide hormone secreted by reticular epithelial cells.- Lymphocyte formation - Promotes immunocompetence in young T-lymphocytes - Accelerates cell division - Attainment of sexual maturity- Produces antibodies to keep the young ones immune to some diseases and allergies.- Hypersecretion may lead to Myasthenia gravis, characterized by abnormal neuromuscular excitation.

Pancreas

Type of cells Hormones

1. α cell - Glucagons 2. β cell - Insulin 3. γ cell - Gastrin 4. δ cell - Somatostatin 5. f cell - Pancreatic polypeptides

Insulin

As a regulator of carbohydrate metabolism it stimulates glyco-genesis (conversion to glycogen) in muscles and liver and maintains normal glucose level in the blood i.e. 80-120 mg per 100 ml of blood.

It increases the rate of protein and fat synthesis and acts as an anabolic hormone

It reduces the breakdown of fats and proteins

It increases the uptake of sugar n various tissues, there by lowering the blood sugar level.

Glucagons

Glucagon has opposite effect to that of insulin. It’s secreted wherever there is decreased level of plasma glucose.

It promotes glycogenolysis or conversion of glycogen to glucose.

It is also responsible for gluconeogenesis (formation of glucose) and deamination of amino acids.

Hypersecretion : Glycosuria

Diabetes mellitus

- Occurs due to either deficient insulin production or due to failure of cells to take up insulin from blood.- It is characterized by

Hyperglycemia – High level of blood glucose (300-1200 mg/100 ml)

Polyuria – Excessive urination due to increase in water content of urine Polydipsia – Excessive thirst Glycosuria – glucose in urine Polyphagia – excessive eating

- Increased oxidation of fats produces increased amount of ketone bodies in body - Loss of weight and tiredness - Dehydration, reduced healing power due to which injuries may result in gangrenes, blurred vision etc.

Hypoglycemia - hunger, sweating, irritability double vision

Diabitis Mellitus

If you have diabetes, the amount of blood glucose is too high - a condition called hyperglycemia. This happens for one of two main reasons:

The body is producing no insulin - this is Diabetes Type- 1

The cells do not respond correctly to the insulin - this is Diabetes Type- 2 Diabetes mellitus are of two types – type I diabetes and type II diabetes.

What is type 1 diabetes?

In Type 1 Diabetes, the person's own body has destroyed the insulin-producing beta cells in the pancreas. When your own body destroys good stuff in your body it has what is called anautoimmune disease. Diabetes Type 1 is known as an autoimmune disease. 

Quite simply - a person with Diabetes Type 1 does not produce insulin. In the majority of cases this type of diabetes appears before the patient is 40 years old. That is why this type of diabetes is also known as Juvenile Diabetes or Childhood Diabetes. Diabetes Type 1 onset can appear after the age of 40, but it is extremely rare. About 15 per cent of all diabetes patients have Type 1. 

People with Type 1 have to take insulin regularly in order to stay alive. 

Whether a person is fat, thin, fit or unfit, makes no difference to his or her risk of developing Type 1. In the case of Diabetes Type 2, much of its onset is the result of bodyweight, fitness and lifestyle. The vast majority of people who develop Type 1 are not overweight, and are otherwise healthy during onset. You cannot reverse or prevent Type 1 by doing lots of exercise or eating carefully. Quite simply, the Diabetes Type 1 patient has lost his/her beta cells. The beta cells are in the pancreas; they produce insulin.

What is type 2 diabetes?

• Person with Diabetes Type 2 has one of two problems, and sometimes both:

1. Not enough insulin is being produced. 2. The insulin is not working properly - this is known as insulin resistance.

• The vast majority of patients who develop Type 2 did so because they were overweight and unfit, and had been overweight and unfit for some time. This type of diabetes tends to appear later on in life. However, there have been more and more cases of people in their 20s developing Type 2, but it is still relatively uncommon. 

Approximately 85% of all diabetes patients have Type 2. 

Insulin resistance

The body produces insulin, but its insulin sensitivity is undermined and does not work as it should do - glucose in not entering the body's cells properly. Consequently, blood sugar levels rise, and the cells are not getting their required nutrients for energy and growth. 

Diabetes Mellitus Vs. Diabetes insipidus

Diabetes Mellitus is mainly caused by deficiency of insulin due to either destruction of Istet of Langerhans present in the pancreas or any autoimmune cause. Here there is increased blood sugar level and sugar starts to appear to come with urine. It even becomes fatal when sugar level increases very much.

Diabetes insipidus is caused by defect in secretion of vasopressin (Antidiuretic Harmone) which is secreted from pituitary gland present in hypothalamus. Its function is to reabsorb water from distal tubules in the kidney and due to this it control the concentration of urine. But its deficiency causes increased water excretion through urine even in low intake of water.

What is diabetes insipidus?

Diabetes insipidus (DI) is a rare disease that causes frequent urination. The large volume of urine is diluted, mostly water. To make up for lost water, a person with DI may feel the need to drink large amounts and is likely to urinate frequently, even at night, which can disrupt sleep and, on occasion, cause bedwetting. Because of the excretion of abnormally large volumes of dilute urine, people with DI may quickly become dehydrated if they do not drink enough water. Children with DI may be irritable or listless and may have fever, vomiting, or diarrhea. Milder forms of DI can be managed by drinking enough water, usually between 2 and 2.5 liters a day. DI severe enough to endanger a person's health is rare.

GONADS

The main function of the gonad is to produce gametes which are mixed glands i.e. they are both exocrine and

endocrine in function. Secretion of both gonadal hormones are stimulated by GTH of pituitary.

MALE GONAD – TESTES

Testes is situated in the scrotum of male. Endocrine part of testis is formed of group of cells called interstitial cells

or leydig cells. These cells secrete male sex hormone androgen.

Androgens

Four types of androgen are testosterone, androsterone, epiandrosterone and dehydroepiandrosterone.The principle androgen is testosterone and it is known to be asculanization hormone.

Testosterone, a steroid hormone, is responsible for the growth and development of male secondary sex organs (like epididymis, seminal vesicle etc.) and male secondary characteristic (like beard, moustaches etc.)It stimulates spermatogenesis and erythropoiesis.

Eunochoidism is a hormone disorder due to non-secretion of testosterone in a genetically male individual.(1) This condition retards growth of genitalia, muscles and bones, as well as the development of sexual characteristics. It leads to following changes in the body.(2) Their genitals are of chills size and have under development of secondary male sex organs like prostrate and seminal vesicles.(3) Failure of testis to produce sperms (4) Failure of the development of male sex characters like beard, moustaches, and deepening of voice.

FEMALE GONAD – OVARY

Just like testes, the ovaries are cryptogenic as well endocrine in function. Ovaries lies in the abdominal cavity. It secretes 3 types of female hormones – estrogen, progesterone and relaxin.  Estrogen

Estrogen, group of steroid hormone is mainly secreted by follicular epithelial cells of membrane granulosa of graafian follicles (a mature follicle). Secretion of estrogen is stimulated by LH of anterior lobe of pituitary gland. It includes estradiol, estriol, and estrone. Principle estrogen is estradiol. It stimulates the growth and development of female secondary sex organs and female secondary sexual characteristics. It decreases the secretion of FSH and increases the secretion of LH during menstrual cycle. During pregnancy, estradiol is secreted by placenta.

Progesterone

Progesterone is a steroid hormone secreted by corpus luteum. Small amount of progesterone is also secreted by adrenal cortex and placenta. Progesterone is responsible for the maintenance of pregnancy, hence called as pregnancy hormone. Hyposecretion of progesterone results in abortion. It is also called antiabortion hormone. During pregnancy progesterone helps in attaching embryo to uterine wall, development of placenta and growth of secretary alveoli in mammary glands. It has negative feedback effects on FSH and LH secretion. Maintains secretary activity of the uterus during the luteal phase. Progesterone is thermogenic and is probably responsible for the rise in basal body temperature at the time of ovulation.

Relaxin

It is a proteinaceous hormone, secreted by corpus albicans (which is formed from the corpus luteum at the end of gestation period).

It softens the pubis symphysis to help in parturition (child birth) in rats and guinea pig. In humans, this role is played by estrogens and progesterone.

VITAMIND D3 is produces in the skin under the

influence of sunlight. Final hydroxylation and activation occurs in the kidney, and activity which is stimulated by PTH. The primary function of 1, 25-dihydroxy vitamin D3,

also called calcitroil, is the stimulation of intestinal absorption of calcium and phosphate. Osteomalacia and rickets occur as defective minerlization of bones, because of vitamin D deficiency. This contrasts wit osteoporosis, where there is reduction in bone mass as a whole, rather than just the mineral content.

Pheromones

Pheromones constitutes an environmental factor. Organisms as ancient as bacteria and slime moulds produce a chemical substance that on its release into the environment influences the behaviorural and physiological action of other member of the same species. Hence pheromones are chemicals used for communication amongst individuals of the same species. Also known as ectohormones/sex attratants etc. Pheromones invoke a specific response in other membranes like recognition, warning and attraction.

Types of pheromones

Sex pheromone- Bombykol (silkworm), Queen substance (honey bee), Civertone (cat), Muskkone (muskdeer)Aggregation pheromones – Geradiol (honey bee)Alarm pheromone – Danger signals Marking pheromones – Mark the territory in wild animals

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