Mechanisms of Contraction Because of the close junction of cardiac muscle cells, they contract in unison. The nervous system adjusts rate and strength. Blood Pressure in the Cardiovascular System Blood pressure drops along the way due to energy loss from resistance. Arterial Blood Pressure Arteries conduct blood away from the heart. Resistance at Arterioles Arteries branch into smaller arterioles, which offer greater resistance to flow and thus cause a drop in blood pressure.
Arterioles serve as control points where adjustments can be made in blood volume distribution.
Neural and endocrine signals cause changes in arteriole diameter by stimulating the muscle cells in the walls. The medulla oblongata of the brain monitors signals from various arteries to determine the rate of heartbeat and any changes needed in vessel diameters. Hormones such as epinephrine and angiotensin also assist. The nervous system and endocrine system also control the allocation of more or less blood to different body regions at different times. Sympathetic and parasympathetic nerves make adjustments in heart rate and vessel diameter to meet tissue needs.