Regulation of stroke volume: 3 factors: preload amount of stretch of ventricular wall. How much return of blood we get into heart: contractility force of contraction of ventricles, after load pressure contracting ventricles must produce to overcome pressure & move blood through aorta. Regulation of heart rate: several factors: ans, hormones, ions, age, gender, physical tness, temperature. Cardiac accelerator nerves increase stroke volume sympathetic nerves . Increases hr go to coronary blood vessels and many cardiac cells of heart. Vagus nerve parasympathetic decrease hr releases acetylcholine: both nerves innervate both sa & av nodes (mostly at sa node) Rbcs, wbcs, and platelets: plasma is made up of water (91. 5%), proteins (7%), other solutes (1. 5%, blood. Lymphoid stem-cell branch forms many wbcs. Red blood cells also known as erythrocytes contain hemoglobin thats used to carry o2 to all cells: each hemoglobin molecule contains an iron ion which allows each molecule to bind.