ENDOCRINE SYSTEM

 The endocrine system consists of ductless glands, which secrete hormones. The hormones are directly poured into circulation without the help of a duct. Hormone is defined as the secretion of an endocrine gland, which is transported a site distant from its origin, where it produce its action. Hormone binds to specific receptors on various target tissues on which they act. The following are the endocrine glands present in the body.

    1. Pituitary gland.
    2. Thyroid gland.
    3. Parathyroid gland.
    4. Adrenal glands (Suprarenal gland).
    5. Pancreas.
    6. Sex glands (gonads).
    7. Thymus.
    8. Pineal gland.

Some hormones are produced by organs other than the organs mentioned above. These are:

  1. Erythropoietin: Secreted by kidney, stimulates the production of RBC by the bone marrow.
  2. Gastrin, secretin, chloecystokinin: Secreted by gastrointestinal tract, stimulates the secretion of gastric juice, pancreatic enzymes, and contraction of gallbladder respectively.
  3. Vitamin D: Considered a hormone produced by the skin, it stimulates the absorption of calcium from gastrointestinal tract.
  4. Prostaglandins: These are hormone-like substances produced by body cells help in temperature regulation, platelet aggregation, and contraction of uterus and secretion of acid in the stomach. 

PITUITARY GLAND (HYPOPHYSIS) 

The pituitary gland is situated at the base of brain in a hollow called sellaturica of sphenoid bone. It consists of two main lobes.

  1. Anterior lobe or adenohypophysis (Anterior pituitary).
  2. Posterior lobe or neurohypophysis (Posterior pituitary).

Both the lobes are embryonically derived from different structures i.e. anterior lobe is formed by upward growth from the pharynx and posterior lobe is formed by downward growth of nervous tissue from brain. Hypothalamus part of the brain lies in close proximity to the pituitary gland regulates the secretions of pituitary gland. These two lobes are connected by pars intermedia (which is a small intermediate lobe). 

Hormones of anterior pituitary: The anterior lobe of pituitary secretes the following hormones:

  1. Growth hormone (GH): Growth hormone is necessary for normal bone growth and development of the body.
  2. Thyroid stimulating hormone (TCH): thyroid stimulating hormone regulates the synthesis of thyroid hormone in the thyroid gland.
  3. Adrenocorticotrophic hormone (ACTH): Adrenocorticotrophic hormone stimulates the adrenal cortex to synthesize its hormones.
  4. Gonadotrophic hormones (Follicle stimulating hormone (FSH) and luteinizing hormone (LH)): In males FSH regulates sperm production and LH stimulates the interstitial cell of testes to produce testosterone. In females FSH and LH regulate menstrual cycle, production of eggs from ovaries.

Hormones of posterior pituitary: The posterior lobe of pituitary secretes two hormones.

  1. Oxytocin: It has got two functions.  a) Contraction of uterus during labor (delivery) and to bring about parturition (birth of baby).   b) Ejection of milk from the breast.
  2. Vasopressin (antidiuretic hormone ADH): Its functions are: a) Decreasing urine output by increasing tubular reabsorption in the kidney. b) Increasing blood pressure by constricting capillaries and arterioles. 

Pathological conditions of Pituitary gland: 

  • Acromegaly: enlargement of extremities caused by excess secretion of growth hormone after puberty. Etiology includes tumor (adenoma) of pituitary gland. This causes abnormal increase in the size of the bones of hands, feet, and jaw. Pituitary adenoma can be removed surgically. 
  • Gigantism: Abnormal overgrowth of the body due to excess growth of hormones by pituitary before puberty. Gigantism can be corrected by early diagnosis followed by resection or irradiation of pituitary gland. 
  • Dwarfism: Decreased of growth hormone. The effected children’s bones remains small and underdeveloped, but their mental function is normal. Treatment consists of administration growth hormone. 
  • Syndrome of inappropriate antidiuretic hormone: Increased secretion of antidiuretic hormone by posterior pituitary causes increased retention of water in the body. Etiological factors are tumor, drug reactions and head injury. 
  • Diabetes insipidus: Deficiency of antidiuretic hormone causes the kidney tubules to fail to hold back, water and salts. Symptoms included polyuria and polydipsia. Treatment includes synthetic preparation of ADH. 

THYROID GLAND 

The thyroid gland is situated in the lower part of neck on the thyroid cartilage. The thyroid gland contains two lobes, one on each side of the trachea. These two lobes are connected by an isthmus, which lies in front of the trachea.

Secretion of thyroid hormone: The thyroid gland synthesizes and secretes two hormones: Thyroxine (tetraiodothyronine T4) and triiodothyronine (T3). 

Functions of thyroid hormones: Maintains blood calcium level. It decrease blood calcium by level by stimulating osteogenesis. 

Pathological conditions of thyroid gland 

  • Goiter:  Diffuse enlargement of the thyroid usually two to three times in normal is called goiter. Based on the consistency it can be due to accumulation of glue like or gelatinous material-colloid goiter. Some times nodules develop as a result of hyperplasia of thyroid tissue-nodular or adenomatous goiter. Some times nodules develop as a result of hyperplasia of thyroid tissue-nodular or adenomatous goiter.
  • Hyperthyroidism: Decrease amount of circulating levels of thyroid hormones due to the under activity of thyroid gland. The most common form of this condition is known as Grave’s disease or thyrotoxicosis. The basal metabolic rate in the cells is increased. Clinical features include exophthalmos (protrusion of eyeballs), occurs as a result of excessive growth of extraocular muscles. Etiology is claimed to be immunological in origin but it is unclear. Treatment includes thyroidectomy, antithyroid drugs, and radioactive iodine.
  • Hypothyroidism: Decrease amount of circulating level of thyroid hormones due to the under activity of thyroid gland. Thyroidectomy, endemic goiter, destruction of gland by radiation will result in decrease amount of tissue in thyroid gland. The effects are weight again, intolerance of cold, mental sluggishness and constipation. Two types hypothyroidism are:
  • Myxedema:  Hypothyroidism in adulthood. In this condition practically no thyroid hormones is produced from the thyroid. This skin becomes dry and puffy because collection of gelatinous materials under the skin. In this condition blood lipoid levels also increase resulting in atherosclerosis. Thyroid hormone is given for recovery.
  • Cretinism:  Hypothyroidism during infancy and child-hood leads to lack of physical and mental growth resulting in dwarfness and mental debility. Treatment consists of administration of thyroid hormones.

I.Thyroid neoplasms: Thyroid neoplasm may be:

  1. An adenoma:  Slow growing without metastasis.
  2. Cacinoma: Histologically, they are three types
    1. a) Follicular spreads by lymphatics.
    2. b) Papillary spreads by blood stream.
    3. c) Medullary increased by calcitonin levels.

Treatment includes surgery and radiotherapy.  

PARATHYROID GLANDS 

The parathyroid glands are four in number. They are embedded on the posterior surface of the thyroid gland, two lying on each side.

Functions of parathyroid hormone: PTH increases the calcium level of plasma and extracellular fluid. This effects is produced by the following mechanisms:

  1. Mobilization of calcium of bone into the extracellular fluid.
  2. Increased reabsorption of calcium in the renal tubule.
  3. Increased absorption of calcium in the gastrointestinal tract. 

Pathological conditions of Parathyroid gland:

Hyperparathyroidism: Hyperparathyroidism results in increased calcium levels in the blood. Parathormone activates the osteoclasis resulting in increased bone resorption. Bone is decalcified and is susceptible to fractures. Kidney stones can also occur as a result of hypercalcemia. Etiology is parathyroid tumor, which is resected for the treatment of this condition.

  • Hypoparathyroidism: Commonest cause is damage to parathyroid glands during thyroid surgery hypocalcemia develops because of lack of parathormone. Decreased amount of calcium in the blood stream leads to muscle and nerve weakness with spasms of muscles, a condition called tetany.

ADRENAL (OR) SUPRARENAL GLANDS

The adrenal glands are two in number. One gland is situated on the top of each kidney. The adrenal gland can be divided into two parts, which are different in structure and functions.

They are:

  1. An inner medulla.
  2. An outer cortex.

Adrenal cortex: The adrenal cortex secretes three groups of hormones. The different layers of cortex secrete these hormones as follows:

  1. Zona glomerulosa secretes mineralocorticoids.
  2. Zona fasciculate secretes glucocorticoids.
  3. Zona reticularis secretes sex steroids.

Mineralocorticoids: The mineralocorticoids are aldosterone and desoxycorticosterone. They influence water and mineral metabolism. They help to maintain electrolyte and water balance of the body as follows:

  1. By increasing the reabsorption of sodium in the renal tubules.
  1. By promoting excretion of potassium. 

Glucocorticoids: The glucocorticoids are cortisol, cortisone and corticosterone. The glulcocorticoids influence carbohydrate metabolism. Their important functions are:

  1. Increase the synthesis of glycogen.
  2. Decrease the production of eosinophils and lymphocytes.
  3. Anti-inflammatory and anti-allergic effect.

Sex steroids:  They are androgens (in males) and estrogens (in females). These two hormones are similar to those produced by testes and ovaries. These two hormones influence growth and sex development.

Regulation of adrenocortical secretion. The secretion of various hormones in the adrenal cortex is controlled by adrenocorticotrophic hormone (i.e. ACTH of anterior pituitary). 

Adrenal medulla: The adrenal medulla secretes adrenaline and noradrenaline. These two substances are also liberated from sympathetic nerves.

Action of adrenaline and noradrenaline:

  1. Vasoconstriction and rise in blood pressure.
  2. Dilatation of the pupil.
  3. Erection of the hair due to contraction of erector pili muscles (of hair follicles).
  4. Increase heart rate.

Pathological conditions of adrenal gland:

  • Cushing’s syndrome: It is defined as symptoms and signs associated with prolonged elevation of corticosteroids. Obesity, moonface, decreased skin thickness, hyperglycemia, hypokalemia, osteoporosis, hyperkalemia, and hypertension result with increased cortisol in the blood. Etiology may be may be excess of secretion of ACTH from pituitary (Cushin’s disease) or a tumor adrenal cortex. 
  • Addison’s disease: Decreased level of mineralocorticoids and glucocorticoids results in hypoglycemia, (decreased in glucocorticoids), hyponatremia  (deficiency of mineralocorticoids), weakness, weight loss and pigmentation of skin because of increased MSH are the symptoms of this condition. Treatment consists of cortisone administration and intake of salts. 
  • Pheochromocytoma: Tumor of the adrenal medulla. The tumor cells produce increased levels of epinephrine and norepinephrine. Symptoms are hypertension, palpitation, headache, sweating, anxiety and flushing of face. Treatment includes surgery to remove the tumor and hypertensive drugs.

PANCREAS

The pancreas lies on the posterior abdominal wall in front of abdominal aorta and lumbar vertebrae. It extends between the C- shaped curvature of duodenum and the spleen. The pancreas contains a head, body and tail.

Structure: The bulk of pancreas contains exocrine cells called acini. These acini secrete the pancreatic juice which is digestive in function. In between the acini, there some endocrine cells called islets of langerhains.

Islets of Langorhans: The islets are present more in the tail portion of pancreas. The islets constitute to the extend of 1% of the net weight of the pancreas. There are 1-2 million islets in the pancreas. The islets contain two types of cells.

  1. Alpha cells, which secrete glucagons.
  2. Beta cells, which secrete insulin.

Glucagon: It is a hormone secreted by the alpha cells of islets of Langerhans. It maintains blood glucose levels by

  1. Increasing glycogen synthesis but preventing glycogen breakdown in the liver.
  2.  Preventing fresh synthesis of glucose (gluconeogenesis).
  3. Promoting the conversion of glucose into fat in the adipose tissue. 

Insulin 

It is secreted by β-cells of pancreas functions of insulin are:

  1. Sugar are passed from the blood into the cells of the body; thus decreasing blood glucose level.
  2. Stimulates the conversion of glucose to glycogen.

Pathological conditions of Pancreas: 

  • Hyperinsulinism: Tumor of the pancreas (benign adenoma or carcinoma) or over dosage of insulin results in decreased amount of glucose in the blood as result of increased insulin secretion. Insulin draws out sugar from the blood stream in to the cells. Fainting, convulsions, loss of consciousness can occur with diseased glucose in the blood. 
  • Diabetes mellitus: Increased blood glucose level due to deficiency of insulin. There are two major types of diabetes mellitus.

Type I diabetes: Also known as insulin-dependent diabetes mellitus (DDM). This usually occurs in children. It involves destruction of Beta cells of pancreas with complete deficiency of insulin in the blood.

Type II diabetes: It is also known as non-insulin diabetes mellitus (NIDDM). It occurs in patients who are older and obsess. In this condition, the islets are not completely destroyed but there is relative deficiency of insulin. Treatment includes insulin and oral hypoglycemics. Diabetes is associated with complications which include ketoacidosis (fats are metabolized lading to accumulation of ketones and coma). Long-term complications are because of destruction of blood vessels resulting in diabetic retinopathy nephropathy and neuropathy.

SEX GLANDS (GONADS): 

The sex glands are: 

  1. Ovaries in the female, which secrete estrogen and progesterone.
  2. Testes in male, which secrete androgens.

Estrogen: It is the female sex hormone secreted by the ovaries. Its functions are:

  1. Regulation of menstrual cycle.
  2. Development of secondary sex characters.

The secretion of estrogen is controlled by follicle stimulating hormone (FSH) of anterior pituitary.

Progesterone: It is also a female sex hormone secreted by the ovary. Its functions are:

  1. Maturation and development of uterus and breast.
  2. Preparation of the uterus to receive the fertilized ovum.

Androgens: They are male sex hormones secreted by the interstitial cells of the testes. The most important androgen is testosterone. The important functions of androgens are:

  1. Stimulation of spermatogenesis.
  2. Growth of penis, scrotum, and prostate.
  3. Development of secondary sex characters.

The secretion of androgen is controlled by luteinising (LH) of anterior pituitary. 

Laboratory tests and clinical procedures: 

  1. Serum and urine tests: these test measure hormones and other substances (glucose, electrolytes) in blood and urine, indicating endocrine function.
  2. Thyroid function test: This test measures the levels of T4, T3  and TSH in blood stream.
  1. Glucose tolerance test: In this test fasting blood sugar levels and blood sugar levels after 30 minutes, 60 minutes 1 hour and  2 hours after ingestion of glucose are measured. 
  1. Blood sugar level: Blood sugar levels are used to diagnose the diabetes mellitus and response to oral hypoglycemia agents  various types are:  a) Fasting blood sugar: Blood sugar levels after

overnight fasting or early morning samples. b)  Post prandial blood sugar: Blood sugar levels after

lunch. c)  Random blood sugar: Blood sugar levels at any time  not related to intake of food.

 d) Thyroid scan: A radioactive substance is administered and localizes in thyroid gland the gland then visualized with a scanner to detect tumors or nodules. e) Glycosylated hemoglobin: The glucose bound to

hemoglobin is estimated this i.e. expected to be more reliable in diagnosis of diabetes mellitus.

DRUGS USED IN ENDOCRINAL DISORDERS 

ANTITHYROID DRUGS 

Propithiouracil, Methimazole, Carbimazole

Thiocyanates (-SCN). Percholorates (-CIO4), Nitrates (-NO3)

Iodine, Iodides of Na and K, organic iodide.

Radioactive iodine (131 I, 125 I, 123 I).

PREPARATIONS OF INSULIN 

Regular (soluble) Insulin

Prompt insulin Zinc Suspension or

Lente (Ultra: Semi: 7:3)

Neutral protamine Hagedorn

(NPH) or Isophane Insulin

Extended insulin Zinc suspension

(Crystalione) or Ultralente

Protamine Zinc Insulin (PZI)

ORAL HYPOGLYCAEMIC DRUGS 

Tolbutamide                                    Gilbenclamide

Chlorpropamide                              (Gllyburide)

Acetohexamide                               Glipizide

Tolazamide                                     Cliclazide

Phenformin

Metformin.

SYSTEMIC CORTICOSTEROIDS 

Glucocorticoids

Hydrocortisone (cortisol)

Cortisone

Prednisolone

Methylprednosolone

Triamcinolone

Paramethasone

Dexamethasone

Betamethasone

MINERALOCORTICOIDS 

Desoxycorticosteroneacetate (DOCA)

Fludrocortisone

Aldosterone

ANDROGENS 

Testosterone, dihydrotesterone, dehydroepiandrosterone

Methyltesterone, fluoxymesterone.

ANTIANDROGENS 

Danazol

Cyproterone acetate

Flutamide

ESTROGENS 

Estradiol

Ethinylestradiol, Mest ranol

Diethylstilbestrol (sttilbesterol)

Hexestrol, dienestrol

PROGESTINS

Progesterone

Hydroxyprogesterone acetate

Megestrol acetate

Dydrogesterone

Hydroxyprogesterone caproate

Chlomadinone acetate

Ethindrone (norethisterone)

Norethynodrel

Ethynodiol diacetate

Lynesterenol (ethinylestrenol)

Alylestrenol

Levonorgestrel

ABBREVIATIONS

ACTH         : Adrenocorticotropic hormone

ADH          : Antidiuretic hormone (vasopression)

BMR          : Basal metabolic rate (an indicator of thyroid function)

DI             : Diabetes insipidus

DM            : Diabetes mellitus

FBS           : Fasting blood sugar

FSH           : Follicle-stimulating hormone

GH            : Growth hormone

GTT           : Glucose tolerance test

Hgh           : Human growth hormone

ICSH         : Interstitial cell-stimulating hormone

IDDM         : Insulin-dependent diabetes mellitus

K              : Potassium

LH             : Luteinizing hormone

MSH          : Melanocyte-stimulating hormone

Na            : Sodium

NIDDM       : Non-insulin-dependent diabetes

PRL           : Prolactin

PTH           : Parathyroid hormone (parathormone)

RIA           : Radioimmunoassay

SIADH       : syndrome of inappropriate ADH

T3             : Triiodothyronine

T4             : Thyroxin

TFT           : Thyroid function test

TSH           : Thyroid-stimulating hormone