Physiology of glands
Secretory processes in exocrine glands
Exocrine glands that produce mucus usually package their secretory granules initially as mucinogens which later form mucins that are released outside the cell. This phenomenon of packing for export is carried out by the agency of Golgi complex. Cells that produce enzymes and other protein substances usually produce zymogen granules, which are released outside the cell. The process of release of secretory granules differ from gland to gland and there are three major types.
1. Holocrine glands, which release their products by the disintegration of the whole cell. This occurs in goblet cells.
3. Eccrine (holocrine) glands. These cells release their stored products without damage to the cell. This is done by either by exocytosis or active transport across the cell membrane. All sweat glands in the body aside from the armpit and the genital region are eccrine glands.
There are large organ endocrine glands such as the adrenal gland or ovary and also single cell endocrine glands such as argentaffin cells of the gastrointestinal tact. These are also called APUD or gastroenteropancreatic endocrine cells. The modes of secretion of the endocrine cell glands can be utilized in their classification as follows
Secretory processes in endocrine cells
Synaptocrinia- secretion in this mode is made into synaptic cleft between one cell and another. This is the mode of secretion in the endocrine neurons of the posterior pituitary gland and also in olfactory and gustatory cells and many paraneurons.
Paracrinia. This is transfer of hormone from cell of secretion into intercellular spaces wider than a normal synaptic clefts, i.e. more than 200 nm. The secretion affects vicinal cells.
Endocrinia. This is the classical mode of secretion of large endocrine organs. Their secretion is passed into major blood vessels because they are ductless. Examples include ovary, testis, parathyroid gland.
Lymphocrinia. Hormonal secretion can be passed into lymphatic vessels
Ventriculocrinia. Hormonal secretions can be passed into the ventricles of the brain . A good example is the pinealocytic secretion into the 3rd ventricle of the brain
Two main processes must be present before a secretion can be said to be endocrine
There are three types of endocrine organs
There are four types of hormones
Peptides are the largest group of hormones. They may be neuropeptides, brain-gut peptides, APUD peptides, opioid peptides etc most of which are in neural tissues where they perform neuromodulation and single cell endocrine glands.
School of Medicine
Creator: Oluwole Ogunranti