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Adrenal Glands - Anatomy & Physiology (view source)
Revision as of 16:22, 11 September 2008
, 16:22, 11 September 2008→'''Adrenal Medulla'''
==='''Adrenal Medulla'''===
==='''Adrenal Medulla'''===
The adrenal medulla converts the amino acid to '''catecholamines'''. This group of hormones contain '''epinephrine''' and '''norepinephrine'''. All of the bodie's circulating epinephrine is produced by the adrenal medulla, where as norepinephrine comes from both the medulla and postganglionic sympathetic neurons.
'''Synthesis, secretion and metabolism'''
Tyrosine is firstly converted to dihydroxyphenylalanine by tyrosine hydroxylase. This is the rate-limiting step. Dihydroxyphenylalanine is then coverted into dopamine, then into norepinephrine and finally into epinephrine. They are stored in secretory vesicles and are released by exocytosis. They are metabolised in the liver and kidney and their half-lives are only 1-3 minutes. Some unmetablised catecholamines are excreted in the urine.
'''Regulation of synthesis and secretion'''
They are released in response to stress by the firing of preganglionic sypathetic nerve fibres in the adrenal medulla. This causes release of acetylcholine, thus depolarizing the cell membrane. An action potential is generated and an influx of calcium ions results in the exocytosis of the catecholamine vesicles.
'''Adrenergic Receptors'''
The catecholamines bind to two types of receptor proteins in cell membranes to elicit a response; these are alpha and beta receptors. The following is a table of where the receptors are located in the body and their effects when stimulated.
<TABLE CELLPADDING="3" CELLSPACING="3" >
<TR>
<TD BGCOLOR="#C1f0f6"><center>'''Target Tissue'''</center></TD>
<TD BGCOLOR="#C1f0f6"><center>'''Receptor Type'''</center></TD>
<TD BGCOLOR="#C1f0f6"><center>'''Responses'''</center></TD>
</TR>
<TR>
<TD><center>Eye</center></TD>
<TD><center>alpha-1</center></TD>
<TD><center>radial muscle contraction</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>Pancreas</center></TD>
<TD BGCOLOR="#C1f0f6"><center>alpha-2</center></TD>
<TD BGCOLOR="#C1f0f6"><center>decreased insulin secretion</center></TD>
</TR>
<TR>
<TD><center>Cardiovascular system</center></TD>
<TD><center>alpha-2</center></TD>
<TD><center>vasoconstriction</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>urinary bladder</center></TD>
<TD BGCOLOR="#C1f0f6"><center>alpha-2</center></TD>
<TD BGCOLOR="#C1f0f6"><center>sphincter contraction</center></TD>
<TR>
<TD><center>uterus</center></TD>
<TD><center>alpha-2</center></TD>
<TD><center>contraction</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>male sex organs</center></TD>
<TD BGCOLOR="#C1f0f6"><center>alpha-2</center></TD>
<TD BGCOLOR="#C1f0f6"><center>ejaculation, detumescence</center></TD>
<TR>
<TD><center>central nervous system</center></TD>
<TD><center>alpha-2</center></TD>
<TD><center>stimulation</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>skin</center></TD>
<TD BGCOLOR="#C1f0f6"><center>alpha-2</center></TD>
<TD BGCOLOR="#C1f0f6"><center>piloerection, sweat production</center></TD>
<TR>
<TD><center>cardiovascular system</center></TD>
<TD><center>beta-1</center></TD>
<TD><center>increased heart rate, increased contractility, increased conduction velocity</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>renin secretion</center></TD>
<TD BGCOLOR="#C1f0f6"><center>beta-1</center></TD>
<TD BGCOLOR="#C1f0f6"><center>stimulation</center></TD>
<TR>
<TD><center>liver</center></TD>
<TD><center>beta-2</center></TD>
<TD><center>glycogenolysis, lipolysis, gluconeogenesis</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>adipose tissue</center></TD>
<TD BGCOLOR="#C1f0f6"><center>beta-2</center></TD>
<TD BGCOLOR="#C1f0f6"><center>lipolysis</center></TD>
<TR>
<TD><center>skeletal muscle</center></TD>
<TD><center>beta-2</center></TD>
<TD><center>glycogenolysis</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>pancreas</center></TD>
<TD BGCOLOR="#C1f0f6"><center>beta-2</center></TD>
<TD BGCOLOR="#C1f0f6"><center>increased insulin secretion</center></TD>
<TR>
<TD><center>cardiovascular system</center></TD>
<TD><center>beta-2</center></TD>
<TD><center>vasodilation in skeletal muscle arterioles, coronary arteries and all veins</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>bronchial muscles</center></TD>
<TD BGCOLOR="#C1f0f6"><center>beta-2</center></TD>
<TD BGCOLOR="#C1f0f6"><center>relaxation</center></TD>
<TR>
<TD><center>gastrointestinal tract</center></TD>
<TD><center>beta-2</center></TD>
<TD><center>relaxation</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>urinary bladder</center></TD>
<TD BGCOLOR="#C1f0f6"><center>beta-2</center></TD>
<TD BGCOLOR="#C1f0f6"><center>detrusor relaxation</center></TD>
<TR>
<TD><center>uterus</center></TD>
<TD><center>beta-2</center></TD>
<TD><center>relaxation</center></TD>
</TR>
<TR>
<TD BGCOLOR="#C1f0f6"><center>male sex organs</center></TD>
<TD BGCOLOR="#C1f0f6"><center>beta-2</center></TD>
<TD BGCOLOR="#C1f0f6"><center>erection?</center></TD>
<TR>
<TD><center>eye</center></TD>
<TD><center>beta-2</center></TD>
<TD><center>ciliary muscle relaxation</center></TD>
</TR></TABLE>
==Histology of the Adrenal Glands==
==Histology of the Adrenal Glands==