L5-Adrenal medullary Hormones

catecholamine

a class of amines derived from the amino acid phenylalanine. that includes the neurotransmitters dopamine, norepinephrine, and epinephrine.

They act as neurotransmitters when released by the brain and nervous system.

They act as hormones when released into the blood by the adrenal gland

adrenaline (epinephrine)

secreted by the adrenal medulla; increases heart rate and blood pressure; allows more oxygen in the lungs; increases blood glucose levels; and causes vasodilation

adrenaline mechanism of action

acts as a non-selective direct agonist on alpha (α) and beta (β) adrenergic receptors via a G-protein-linked second messenger system.

Adrenergic receptors

-Alpha-1 (α₁) Receptors: increase intracellular Ca²⁺ and activate phospholipase

Location: Vascular smooth muscle, bladder, and liver.

Function: Arterial and venous vasoconstriction (increases blood pressure) and glycogenolysis;

-Alpha-2 (α₂) Receptors: decreases cAMP, opens potassium channels.

Location: nerve terminals, brainstem, platelets .......

Function: inhibition of norepinephrine release

Reduced sympathetic outflow. Platelet aggregation; inhibits lipolysis; inhibits insulin production

- Beta-1 (β₁) Receptors:

Location: Heart, juxtaglomerular cells of the kidneys

Function: Increased heart rate, increased renin secretion

-Beta-2 (β₂) Receptors:

Location: Bronchial smooth muscle, vascular smooth muscle, uterine smooth muscle, liver............

Function: Bronchodilation (relaxation of airway smooth muscle), vasodilation, relaxation of the uterus, glycogenolysis, and gluconeogenesis

-Beta-3 (β₃) Receptors:

Location: Adipose tissue (fat cells)..................................

Function: Stimulation of lipolysis.

regulation of adrenaline

1. Physical or psychological threats, fear, excitement, or extreme temperatures

2. The hypothalamus sends nerve signals through the autonomic nervous system down the spinal cord

3. Sympathetic nerve fibers release acetylcholine, which stimulates chromaffin cells (in the adrenal medulla) to rapidly secrete adrenaline

4. The pituitary gland releases adrenocorticotropic hormone (ACTH), prompting the adrenal cortex to produce cortisol, which helps upregulate the enzymes needed for adrenaline synthesis.

5. When the stressful event ends, the hypothalamus and sympathetic nervous system reduce nerve impulses to the adrenal medulla, stopping further adrenaline output.

Acetylcholine (ACh)

ACh binds to nicotinic receptors on chromaffin cells, signaling them to secrete adrenaline