Adrenal medulla hormones produced

ADRENAL MEDULLA HORMONES. Adrenaline (epinephrine) and its immediate biological precursor noradrenaline (norepinephrine, levartei-nol) are the principal hormones of the adult adrenal medulla. See Fig.l. Some of the physiological effects produced by adrenaline arc contraction of the dilator muscle of the pupil of the eye (mydriasis), relaxation of the smooth muscle of the bronchi constriction of most small blood vessels dilation of some blood vessels, notably those in skeletal muscle increase in heart rate and force of ventricular conlraction relaxation of the smooth muscle of the intestinal tract and either contraction or relaxation, or both, of uterine smooth muscle. Electrical stimulation of appropriate sympathetic (adrenergic) nerves can produce all the aforementioned effects with exception of vasodilation in skeletal muscle. 

Endorphin is a 31-amino-acid polypeptide released together with ACTH. When introduced into the third ventricle of the brain, it produces dramatic behavioral changes, but when injected systemically, it does not. Thus, the function of circulating 3-endorphin remains unclear. The CNS and gastrointestinal effects of the hormone are probably produced by that secreted locally. Circulating 8-endorphin may act in conjunction with enkephalins released by the adrenal medulla to produce stress analgesia. 

The adrenal medulla synthesizes two catecholamine hormones, adrenaline (epinephrine) and noradrenaline (norepinephrine) (Figure 1.8). The ultimate biosynthetic precursor of both is the amino acid tyrosine. Subsequent to their synthesis, these hormones are stored in intracellular vesicles, and are released via exocytosis upon stimulation of the producer cells by neurons of the sympathetic nervous system. The catecholamine hormones induce their characteristic biological effects by binding to one of two classes of receptors, the a- and )S-adrenergic receptors. These receptors respond differently (often oppositely) to the catecholamines. 

Q3 Which hormones are produced by the adrenal medulla and what is the function of the medulla ... 

Epinephrine and norepinephrine, hormones called catecholamines, are released from the adrenal medulla during exercise. Epinephrine and, to a lesser extent, norepinephrine stimulate effects in muscles and the liver similar to those produced by glucagon. Epinephrine activates adenylate cyclase, resulting in such events as the breakdown of glycogen and fatty acids. 

The organization of the endocrine system can best be described in relation to the central nervous system. Three levels of endocrine tissues can be distinguished on the basis of their association with the central nervous system (Figure 30-12). The first level consists of those that are (or were) derived from nerve cells these include the hypothalamus, adrenal medulla, thyroid C-cell, and gastrointestinal enterochromaffin cells. The hypothalamus and adrenal medulla still retain their neural connections and can therefore be regarded as endocrine extensions of the nervous system. The C-cell and the gut cells, however, are APUD cells and lack neural connections. These four tissues produce hormonal peptides or amines having, like neurotransmitters, rapid-onset, short-term effects. 

The adrenal glands produce a variety of hormones. Adrenaline and noradrenaline are secreted from the adrenal medulla in response to sympathetic stimulation. 

The adrenal medulla produces the sympathetic hormones (e.g., epinephrine). 

The adrenal medulla forms part of the sympathetic nervous system and is the primary site for the production of the catecholamines—epinephrine (adrenaline) and norepinephrine (noradrenaline), which are primary hormones (also called biogenic amines). The cells of the medulla are arranged in lobules and the medulla contains chromaffin cells, which are modified postganglionic cells of the sympathetic nervous system. The medulla produces catecholamines from tyrosine and their structures contain catechol and amine groups (Figure 10.3.3). 

In Topic 41, we considered in general terms the way in which hormones act as chemical messengers, transmitting information from one tissue to another. In this topic, we are going to look at three of the most important hormones and the way in which they control how we handle major foodstuffs in three major tissues muscle, liver and adipose tissue (which, between them, make up a high percentage of total body mass). The three hormones are insulin, glucagon and adrenaline, two of them produced by the pancreas and the third, as its name implies, by the adrenal medulla. Their effects, explained below, are summarised in Table 43.1. 

Intracellular metabolic activity may be modulated in response to extracellular conditions by hormones. Hormones are substances which act as chemical messengers between cells in different locations to alter the activity of the recipient cell. Three classes of hormones have been identified protein (polypeptide) hormones, steroid hormones and tyrosine-derivative hormones of which there are two distinct groups, the catecholamines and the thyroid hormones. The catecholamine hormones (adrenaline and noradrenaline) are produced by and secreted from the adrenal medulla. The thyroid hormones (thyroxine and triiodothyronine) are elaborated by and secreted from the thyroid gland. 

Q1 Each adrenal gland is composed of an outer cortex and an inner medulla. The cortex consists of three layers where several steroid hormones, synthesized from cholesterol, are produced and secreted. The outer layer of the cortex, the zona glomerulosa, produces the mineralocorticoid aldosterone. The zona fasciculata lies under this layer and, together with the inner layer, the zona reticularis, secretes glucocorticoids, mainly cortisol, corticosterone and androgens. 

Tissues that produce hormones include the hypothalamus, anterior and posterior pituitary, adrenal cortex and medulla, gonads, thyroid and parathyroid glands, heart, brain, cells of the gastrointestinal tract, and the pancreas. 

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