Adrenaline directly affects the

Explanation

Adrenaline directly affects the SA node.The SA node, also known as the sinoatrial node, is the natural pacemaker of the heart. It is responsible for generating the electrical impulses that cause the heart to beat. Adrenaline increases the heart rate by binding to beta-adrenergic receptors on the SA node. This binding activates the adenylate cyclase enzyme, which leads to an increase in cAMP levels. cAMP is a second messenger that activates a number of proteins, including protein kinase A. Protein kinase A phosphorylates a number of proteins in the SA node, which ultimately leads to an increase in the heart rate. The other options are not directly affected by adrenaline: The dorsal root of the spinal cord contains sensory neurons that transmit signals from the periphery to the central nervous system. Adrenaline can indirectly affect the dorsal root of the spinal cord by increasing the firing rate of sensory neurons. B cells of Langerhans are pancreatic islet cells that produce insulin. Adrenaline can indirectly affect B cells of Langerhans by increasing the release of insulin from the pancreas. Epithelial cells of the stomach are responsible for secreting acid and other digestive enzymes. Adrenaline can indirectly affect epithelial cells of the stomach by decreasing the secretion of acid and other digestive enzymes.