BIO 355: Heart Structure and Flow

The Heart - The heart beats over 100,000 times per day - Located behind the sternum slightly to the left - The human heart has 4 chambers - 2 atria – top part of the heart - Pump blood to the ventricles - 2 ventricles – bottom part of the heart - Left – pumps blood to the body - Right – pumps blood to the lungs Structure of the Heart - The heart is composed mostly of myocardium – (Heart muscle cells) - Surrounded by a pericardium membrane - A septum divides left and right Cardiac Muscle versus Skeletal Muscle - Both are striated - Myocardia are smaller and have single nucleus per fiber - Have intercalated disks - Gap junctions provide electrical connection - T-tubes are larger and branched - Sarcoplasmic reticulum is smaller - Mitochondria occupy one-third of cell volume. Lots of aerobic respiration Semilunar Valves

- Aortic and pulmonary valves - Valves open when pressure in ventricle exceeds pressure in arteries - As ventricles relax, some backflow permitted but blood fills valve cusps closing them Tightly Atrioventricular Valves - Left AV also called Bicuspid or Mitral - Right AV also called Tricuspid - Valves open when pressure in the ventricle exceeds pressure in the aorta - When the filled ventricle contracts, chordae tendinease pull the valve to keep it From prolapsing