Medical Endocrinology / Introduction 2

Medical Endocrinology / Introduction 2

Medical Endocrinology / Introduction 2
Medical Endocrinology


Intercellular chemical signals
Intercellular chemical signals allow one cell to communicate with other cells. These signals coordinate and regulate the activities of most cells. Neurotransmitters and neuromodulators are intercellular chemical signals that play important roles in the function of the nervous system .
Hormones are intercellular chemical signals secreted by endocrine glands.
Autocrine chemical signals are released by cells and have a local effect on the same cell type from which the chemical signals are released. Examples include prostaglandin like chemicals released from smooth muscle cells and platelets in response to inflammation. These chemicals cause the relaxation of blood vessel smooth muscle cells and the aggregation of platelets. As a result, the blood vessels dilate and blood clots.
Paracrine chemical signals are released by cells and affect other cell types locally without being transported in the blood. For example, a peptide called somatostatin is released by cells in the pancreas and functions locally to inhibit the secretion of insulin from other cells of the pancreas .
Pheromones are chemical signals secreted into the environment that modify the behavior and the physiology of other individuals. For example, pheromones released in the urine of cats and dogs at certain times are olfactory signals that indicate fertility. Evidence supports the existence of pheromones produced by women that influence the length of menstrual cycles in other women.



Functional Classification of Intercellular Chemical Signals
Intercellular
Chemical
Signal Description Example
Autocrine Secreted by cells in a local area and influences the
activity of the same cell
type from which it was
secreted Prostaglandins
Paracrine Produced by a wide variety of tissues and secreted into tissue spaces; usually has
a localized effect on other
tissues Histamine , prostaglandins
Hormone Secreted into the blood by specialized cells; travels
some distance to target
tissues; influences specific
activities Thyroxine, insulin

Neurohormone Produced by neurons and functions like hormones Oxytocin, antidiuretic hormone

Neurotransmitter or neuromodulator



Produced by neurons and secreted into extracellular spaces by presynaptic nerve terminals; travels short distances; influences postsynaptic cells Acetylcholine, epinephrine
Pheromone Secreted into the environment; modifies physiology and behavior of other individuals Sex pheromones are released by humans and many other animals. They are released in the urine & other external secretions.Pheromones produced by women influence the length of the menstrual cycle of other women.

A hormone is a chemical messenger released by an endocrine gland into the circulation. Once released, a hormone travels in the bloodstream and affects only cells in the body that have receptors (binding sites) specific to it. Cells that respond to a particular hormone are called target cells for that hormone. Typically, a hormone is released in bursts from an endocrine gland in a pattern that often follows an inherent daily (diurnal) rhythm. The burst of hormone release can be increased or decreased above or below baseline level by various inputs to the gland. Inputs that affect hormone release involve:
(1) Stimulation by another hormone or neurotransmitter, or
(2) Stimulation caused by a decrease or increase in a certain ion or nutrient.
Examples of hormones that cause an increase or decrease in another hormone s release include all the hypothalamic hormones affecting the anterior pituitary.
Examples of neurotransmitters affecting a hormone s release include the release of insulin in response to epinephrine and norepinephrine stimulation. Ions that influence the release of a hormone include calcium ion s effect on parathyroid hormone, and sodium ion s effect on aldosterone.
Nutrients that affect the release of hormones include the amino acids that stimulate the release of insulin and growth hormone. Frequently, one endocrine gland is stimulated simultaneously by several different inputs.


Thank You
Prof. Dr. Sa ad Merza Alaraji