Endocrine system , Endocrine glands , Pituitary gland & Hormonal coordination in living organisms

Endocrine system

Endocrine system is the second system after the nervous system that controls the body functions , So , all the body functions are under the nervous and hormonl control , Endocrine glands are ductless glands that secrete their hormones directly into the blood stream with very small amounts to perform their functions .


They are organic chemical substances that synthesized inside the endocrine glands and secreted directly into the blood which transports them to another organ , where they affect on the functions , growth and source of nutrition of this organ .

Hormones are secreted in a small define amounts to perform their functions perfectly , where any increase or decrease in the amount of secretion of any hormone leads to a disturnance in the function of body organs and results in pathological changes and sympotons that are characteristic for each hormone , Most of the effects of hormones are in the form of stimulation , where it stimulates organs or other glands .

Hormones in plants ( Auxins )

Plants have no special glands to secrete hormones as in animals , but the hormones of plants ( auxins ) are secreted by special plant cells , Boyson Jensen in 1913 was considered as the first scientist who referred to the auxins ( plant hormones ) and explained their role in phototropism of a growing point ( stem ) .

He proved that the tip of coleoptile ( receptor site ) secretes a chemical substance “indole acetic acid” which is transmitted to the responding site ( the site of curvature ) , causing its bend .

Auxins are chemical substances that secreted from the tips of coleoptiles and buds and affect on the functions of other parts of the plant , They are secreted from the tips of coleoptiles and buds , because the plant has no special glands to secrete auxins , Auxins affect on the functions of different parts of the plant , where they :

  1. Regulate the plant growth .
  2. Organize the development of tissues .
  3. Regulate the formation of flowers , leaf falling and fruit ripeness and falling .
  4. Affect on the functions of all plant tissues .

Discovery of animals hormones

Cloud Bernar : He studied the liver functions in 1855 , He considered the stored sugar inside the liver as its internal secretion and the bile as its external secretion .

Starling : In 1905 , He found that the pancreas secretes the pancreatic juice directly after the arrival of food from the stomach to the duodenum , even after the cutting of nerve supply between the pancreas and the other organs .

He concluded that there must be a non nervous stimulation , He discovered that the mucous membrane that lines the duodenum secretes a certain chemical substances ( chemical messages ) which pass into the blood stream to stimulate the pancreas to secrete its pancreatic juice , He named these chemical messages by hormones ( a Greek word which means activators ) .

Scientific studies : By the help of recent scientific studies , the scientists were able to know the endocrine glands in the human body and the hormones of each gland .

Hormonal coordination in man  

The scientists were able to know the functions of hormones through :

  1. The study of symptoms that appear on the human or animal , due to the enlargement or removal of one of the endocrine glands .
  2. The study of the chemical structure of endocrine gland extracts and their effects on the different vital activities .
Characteristics of hormones

Hormones are organic substances , where some of them are made up of complex proteins and others are made up of simple components such as amino acids or steroids ( lipid derivatives ) , Hormones are secreted in very small amounts that estimated by micrograms ( 1/1000 milligram ) .

Hormones perform the following important functions :

  • Keep the balance of the internal environment of the body ( Homeostasis ) .
  • Body growth .
  • Sexual maturity .
  • Metabolism ( Utilization of food through anabolism and catabolism processes ) .
  • Human behaviour , emotional and intellectual development .
Types of glands in man 

There are three types of glands that present in human body which are :

  1. Exocrine glands : Glands with external secretions that consist of a secretory part in addition to a duct or a system of ducts which carries the secretions either to a cavity inside the body such as the salivary glands and other digestive glands or outside the body such as the sweat glands .
  2. Endocrine glands : They are ductless glands with internal secretions that secrete their hormones directly into the blood stream , such as pituitary gland , thyroid gland and adrenal gland .
  3. Mixed glands : They are glands that gather between the exocrine and endocrine glands , where they consist of a duct glandular part and another ductless glandular part , such as pancreas .

The human body contains a group of endocrine glands which are distributed in different places in the body and each of them has its own secretion that contains one hormone or a group of hormones :

Endocrine glands in man

Endocrine system

Endocrine system

Pituitary gland :

  • Adenohypophysis part secretes growth hormone ( GH ) and pituitary tropic hormones ( Thyroid stimulating hormone ( TSH ) , Adrenocorticotropic hormone ( ACTH ) , Gonadotropic hormones FSH and LH , Prolactin ) .
  • Neurohypophysis part secretes Antidiuretic hormone ( ADH ) and Oxytocin hormone .

Thyroid gland : secretes Thyroxine hormone and calcitonin hormone .

Parathyroid gland : secretes parathormone hormone .

Adrenal gland :

  • Cortex : Glucocorticoids ( Cortisone hormone , Corticosterone hormone ) , Mineralocorticoids ( Aldosterone hormone ) , Sex hormones .
  • Medulla : Adrenaline hormone and Noradrenaline hormone .

Pancreas ( Islets of Langerhans ) : Alpha cells ( Glucagon hormone ) , Beta cells ( Insulin hormone ) .

Sex glands : Testis ( Testosterone hormone , Androsterne hormone ) , Ovary ( Oestrogen hormone , Progesterone hormone ) .

Gastrointestinal glands : Stomach ( Gastrin hormone ) , Small intestine ( Secretin hormone , Cholecystokinin hormone ) . 

Pituitary gland

It is considered as the master gland , because it controls the endocrine system through the hormones that secreted by it and affects on the functions and secretions of the most endocrine glands , It is located beneath the brain and connected with the hypothalamus .

The pituitary gland consists of two parts which are :

  • Adenohypophysis part : consists of the anterior and middle lobes .
  • Neurohypophysis part : consists of the poterior lobe and a part of the brain called the infundibulum ( a stalk connects the pituitary gland with the brain ) .

Hormones of the Adenohypophysis part

Growth hormone ( GH )

It controls the metabolism especially the protein synthesis , accordingly it controls the physical growth of the body , The hypersecretion or hyposecretion of this hormone causes a disease that depends on the age of the patient :

During childhood : Hypersecretion causes gigantism , Hyposecretion causes dwarfism .

In adults : Hypersecretion causes acromegaly case that is characterized by the increasing of bone growth at the extremities ( enlarged hands , feet and fingers ) and enlargement of face bones .

Pituitary tropic hormones

A group of hormones that affect on the activity and secretion of some of the other endocrine glands and includes :

  1. Thyrotropin : thyroid stimulating hormone ( TSH ) .
  2. Adrenocorticotropic hormone ( ACTH ) : affects on the function of the adrenal ( suprarenal ) cortex .
  3. Prolactin hormone : stimulates the milk secretion from the mammary glands .
  4. Gonadotropic hormones : affect on the functions of gonads ( ovaries in females and testes in males ) which include the following :

Follicle stimulating hormone ( FSH ) : It stimulates the growth of the ovarian follicles and formation of Graafian follicles in female , It helps in the formation of seminiferous tubules and spermatozoa in male .

Luteinizing hormone ( LH ) : It stimulates the formation of corpus luteum in female , It responsible for the formation and secretion of the interstitial cells in testis in male , The hormones ( FSH ) and ( LH ) are important for the individual sexual maturity .

Hormones of the neurohypophysis part

The hormones of neurohypophysis part are secreted from the nerve cells that present in the hypothalamus of the brain which are called the neuro-secretory cells .

Neuro-secretory cells are nerve cells that present in the hypothalamus region of brain and secrete the hormones of the neurohypophysis part of pituitary gland , where these hormones reach the posterior lobe of pituitary gland .

These secreted hormones reach the posterior lobe of the pituitary gland through the infundibulum and they include the following hormones :

Antidiuretic hormone ( Vasopressin hormone ) ADH

This hormone increases the reabsorption of water from the kidney nephrons and decreases the amount of urine excreted and it increases the blood pressure .

Oxytocin hormone

There is a direct relation between this hormone and regulation of uterine contractions , where it increases them strongly during delivery ( labour ) , so , gynecologists use this hormone to accelerate the birth of the baby by stimulating strong contractions of the uterine muscles , It stimulates the release of milk from mammary glands after the delivery process as a response to the lactation ( milk letting hormone ) .

Endocrine glands and the most important pituitary glands in the human body

Thyroid gland , Diseases of thyroid gland & Function of Parathyroid glands

Adrenal ( suprarenal ) glands , Pancreas & Sex glands ( Gonads )

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