Chemical coordination the body includes endocrine glands, their hormones and their mode of action. The chemical coordination is performed by a system known as the endocrine system (Human endocrine System).
Glands (Human Endocrine System)
A gland is an organ which synthesizes some substances and secretes them at various locations e.g., sweat glands secrete sweat, endocrine gland secretes hormones like growth hormone, etc.
Types of glands
In vertebrates, glands may be classified on the basis of presence or absence of ducts. These are called exocrine and endocrine glands.
Difference between Exocrine and Endocrine Glands
| Exocrine Glands | Endocrine Glands |
| These are glands with ducts | These are ductless glands or glands of internal Secretions |
| The secretions of these glands are carried by ducts to a particular organ for some metabolic activities, e.g., salivary glands, liver, etc | These glands have no ducts and their secretions (hormones) get absorbed into the immediate surrounding blood circulation to reach the target (specific) organs to initiate a particular metabolic change, e.g., thyroid, parathyroid, adrenals, etc. |
Hormones
These are the non-nutrient chemical made up of amino acid derivatives, peptides and steroids etc., that are secreted by endocrine glands in response to change in external or internal environment. They act as intercellular messengers that regulate the biological processes in organisms and are produced in trace amounts. Ernest H starling coined the term hormone in 1905.
The first hormone was discovered by the English physiologist William M bayliss and Ernest H starling in 1903.
Characteristics of Hormones
- Hormone releases directly into the blood and circulates in the body for performing regulatory functions.
- It is always released out in very small amount
- It regulates various functions in the body like growth and development, behavioral characters, sexual characters, reproductive activities, metabolic activities etc.
- It also helps in maintaining body balance.
The human endocrine system includes the endocrine glands and hormones produced by diffused tissues or cells located in different parts of the body.
It includes the following organs for the purpose of secretion
Endocrine Glands Thyroid, parathyroid, adrenal, pituitary, thymus, and pineal.
Mixed Glands Pancreas
Other Structures include hypothalamus, skin, gastrointestinal mucosa, heart, kidneys, gonads (ovaries in woman and testes in men), placenta and liver.
Types of Pituitary Glands
| Gland | Hormone | Type | Action |
| Posterior | Oxytocin Antidiuretic hormone | Peptide | Initiate labor and milk ejection |
| Antidiuretic hormone | Peptide | Stimulates water resorption by kidneys | |
| Anterior | Growth hormone | Protein | Stimulates body growth |
| Prolactin | Protein | Promotes lactation | |
| Follicle-stimulating homorne | Glycoprotein | Stimulates follicle maturation and production of estrogen | |
| Luteinising hormone | Glycoprotein | Triggers ovulation and production of estrogen and progesterone by ovary | |
| Adrenocorticotropic hormone | Peptide | Promotes release of glucocorticoid and androgens from adrenal cortex | |
| Thyroid-stimulating hormone | Glycoprotein | Stimulates release of T3 and T4 | |
| Thyroid gland | T3 (Triiodothyronine) | Amine | Increase metabolism, blood pressure and regulates tissue growth |
| T4 (Thyroxine) | Amine | Increase metabolism, blood pressure and regulates tissue growth | |
| Calcitonin | Peptide | Childhood regulation of blood calcium levels through uptake by bone | |
| Parathyroid | hormone | Peptide | Increse blood calcium levels through action on bone, kidneys, and intestine |
| Pancreas | Insulin | Protein | Reduces blood sugar levels by regulating cell uptake |
| Glucagon | Protein | Increases blood sugar levels |
Types of Adrenal Glands
| Gland | Hormone | Type | Action |
| Adrenal medulla | Epinephrine | Amine | Short-term stress response: increased blood sugar levels, vasoconstriction, increased heart rate and blood divination |
| Norepinephrine | Amine | Short-term stress response increased blood glucose levels; blood volume maintenance and immune suppression | |
| Adrenal cortex | Glucocorticoids | Steroid | Long-term stress response; Increased blood glucose levels, blood volume maintenance, immune and suppression |
| Mineralocorticoids | Steroid | Long term stress response, blood volume and pressure maintenance, sodium and water retention by kidneys | |
| Pineal gland | Melatonin | Amine | Circadian Timing |
| Thymus | Thymosis | Peptide | Development of T-lymphocytes |
Types of Gonads
| Gland | Hormone | Type | Action |
| Testes | Androgens | Steroid | Reproduction maturation and sperm production |
| Ovaries | Estrogens | Steroid | Reproduction maturation and regulation of menstrual cycle |
| Progesterone | Steroid | Regulation of menstrual cycle |
- The study of endocrine glands and hormones secreted by them is called endocrinology.
- The first hormone to be discovered was secretin but the first hormone to be isolated was insulin by Banting and McLeod
- Hypothalamus is considered as supreme commander of human endocrine system
- Pituitary gland was considered as master gland of the body but today it is considered as Orchestra of Human endocrine system
- The pituitary gland is the smallest endocrine gland in the human body.
- Thyroid gland is the largest endocrine gland in the human body
Disorders of Human Endocrine System
- Dwarfism. It occurs due to deficiency of Growth Hormone (GH) secretions during childhood. Growth of long bones and body stop prematurely making person dwarf.
- GIgantism It occurs when large quantities of growth hormone is secreted during childhood resulting in person with abnormal height and very long bones.
- Acromegaly If an acidophilic tumor occurs causing high GH secretion after adolescence, it results in acromegaly in which jaws and limbs become abnormally large bu the body do not attain giant structure.
- Cretinism It is caused due to the hyposecretion of thyroid hormone in infants. This leads to slow heart beat, lower blood pressure, low body temperature, stunted growth, mental retartdation, retarded sexual development.
- Addison’s disease It is caused by deficiency of mineralocorticoids and glucocorticoids
- Cushing’s Syndrome It is caused by excess of cortisol which may result in high blood sugar, obesity, rise in blood volume and pressure.
- Aldosteronism It is caused by dexcessive production of aldosterone from adrenal contical tumours.
- Adrenal virilism It is the appearance of male characters in female, which result in beard, moustaches, etc. It is caused due to excessive production of male sex corticoids (androgen) in females.
- Gynecomastia It is the development of enlarged mammary glands (breasts) in males due to excessive secretion of female sex hormones (estrogen) in males.
- Precocious Puberty It is early maturation of ovaries and testes with the production of ova before the age of 9 years in girls or sperms before 10 years in boys, called sexual pseudo precocity.
- Eunuchoidism It is a disorder which affects males due to failure of testosterone secretion. A eunuch has under developed and non-functional secondary sex organs lacks external or accessory sex characters and does not produce sperms.