BRAINCAKEHormonal Control of the Heart
Heart rate is also affected by the hormone adrenaline. Adrenaline is secreted by the adrenal medulla (the inner part of the adrenal glands, which sit above the kidneys) when the sympathetic nervous system stimulates it during stress, fear, excitement or exercise.
Adrenaline travels in the blood plasma to all parts of the body, but only affects target cells that have adrenaline receptors on their cell surface membrane. It acts as a first messenger and does not enter the cell. When it binds to its receptor, it activates the enzyme adenylyl cyclase, which converts ATP into cyclic AMP (cAMP). cAMP acts as a second messenger inside the cell and triggers the cell's response.
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Key terms in this lesson
- second messenger
- A chemical inside a cell that relays a signal from a receptor at the cell surface to target molecules within the cell.
More in Homeostasis
- Controlling the Heart Rate
- Nervous Control of the Heart
- Baroreceptors
- Chemoreceptors
- Additional Responses
- Protein Homeostasis in the Liver
- Osmoregulation
- Osmoregulation in Mammals
All 41 lessons in Homeostasis · All Edexcel A-level Biology topics