Endocrine system , Endocrine glands , Pituitary gland & Hormonal coordination in living organisms
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 :
- Regulate the plant growth .
- Organize the development of tissues .
- Regulate the formation of flowers , leaf falling and fruit ripeness and falling .
- 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 ) .
Hormonal coordination in man
The scientists were able to know the functions of hormones through :
- The study of symptoms that appear on the human or animal , due to the enlargement or removal of one of the endocrine glands .
- 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 :
- 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 .
- 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 .
- 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 .
Endocrine glands in man
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 .
- 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 ) .
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
- Thyrotropin : thyroid stimulating hormone ( TSH ) .
- Adrenocorticotropic hormone ( ACTH ) : affects on the function of the adrenal ( suprarenal ) cortex .
- Prolactin hormone : stimulates the milk secretion from the mammary glands .
- 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
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
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 ) .