Hormones are chemical signals that are used for communication
between cells.Chemically, hormones are rather diverse group of
substances. They are derived from metabolism of amino acids,
polypeptide or cholesterol (steroid).
Hormones
Binding of a hormone to its receptor and activation of that
receptor is the initial in producing a hormone effect.Some hormones
act via second mesengers to alter activity of reexisting proteins
in target cells.Other hormones act by altering gene expression in
target cells to change the amount of a few key proteins.
The general mechanism of action of hormones with membrane
receptor
Illustration of coupling of membrane receptors to adenylate
cyclase by the Gs and Gi proteins.
Mechanism of action of hormones with intracellular receptors,
effects on gene expression, cell function might be altered.
Mechanism of action of aldosterone to increase sodium transport
across kidney tubule cells
Basic mechanisms of neural (a), endocrine (b) and neuroendocrine
(c)
Neural and vascular connections between the hypothalamus and the
anterior and posterior lobes of pituitary.
The Pituitary Hormones
The pituitary consist of two main lobes (anterior and posterior)The
hypothalamus serves to regulate secretion from both lobesThe
anterior pituitary secretes six different hormone into the general
circulation
The Pituitary Hormones
The posterior pituitary is a neuroendocrine gland; it secretes two
hormones and contains the terminals of neuroendocrine cells, in the
hypothalamusGH, affects skeletal growth, protein and carbohydrates
metabolismTSH, regulates thyroid hormone production. Thyroid
hormone regulate metabolism in most tissues in the body
Normal hand and acromegaly
The Thyroid Gland
Secretes /day
- T4 (thyroxine): 80 g
- T3 (triiodothyronine) 4 g
*
The Adrenal Glands
Consist of two distinct endocrine glands, different hormone
products.Cells of adrenal cortex produce steroid hormones,
predominantly cortisol and aldosterone. Cortisol affects metabolism
and generally results in the release of stored fuels. Aldosterone
acts on the kidneys and influences sodium and potassium balance in
the body.
The Adrenal Glands
The adrenal medulla functions as part of the sympathetic nervous
system and secretes primarily epinephrine. Epinephrine affects the
cardiovascular and pulmonary systems and a variety of metabolic
processes in the body.The net effect of the adrenal hormones
cortisol and epinephrine is to increase the bodys ability to
effectively respond to stress.
The Endocrine Pancreas
Produces insulin and glucagon, major roles in regulating fuel
homeostasis in both the fed and fasted statesInsulin is secreted
primarily in response to an increased blood glucose level. Glucagon
is secreted in response to a decreased v\blood glucose
level.Insulin directs the storage of excess nutrients in the form
of glycogen, triacylglycerols, and protein. The major tissue
targets of insulin are liver, muscle and adipose tissue.
The Endocrine Pancreas
Glucagon directs the movement of stored nutrients into the blood
stream. Liver is the primary physiological target of glucagon.In
the fed stated, the actions of insulin predominate in tissues, and
nutrients are stored. In the fasted state, the actions of glucagon
predominate, and stored nutrients are mobilized.Diabetes mellitus
occurs when there is a deficiency in insulin action as a result of
either an impairment in insulin secretion or an impairment in its
target tissues.
Pineal gland and Circadian rhythms
Secretes hormone melatoninMelatonin keep the bodys inherent
circadian rhythms in synchrony with the light-dark cycle.
Rhoades R, Pflanzer R. Human Physiology. 4th ed. Ganong WF. Review
of medical physiology. 22th ed.Sherwood L. Human Physiology, from
cells to system. 5 th ed.
