Biochemical and physiological structures of the heart

Question 1

What are the components of the heart wall?

Answer 1

• epicardium: smooth outer surface of the heart
• myocardium: middle layer composed of cardiac muscle cells, responsible for heart contraction, thickness varies
• endocardium: smooth inner surface of heart chambers which also covers heart valves, thin endothelial layer over connective tissue, lowers resistance

Question 2

Describe cardiac myocytes

Answer 2

• elongated branching cells
• abundant mitochondria for energy supply (25-50% of fibre by mass)
• sarcolemma: plasma membrane which creates transverse tubules (T-tubules)
• T-tubules: invaginations of sarcolemma, from cell surface to SR, coordinated muscle contraction
• sarcoplasmic reticulum: smooth ER, surround myofibrils, store for calcium
• contractile elements arranged into sarcomeres and myofibrils (myofibrils vary in diameter and branch extensively, skeletal muscle uniform), interspersed with numerous mitochondria

Question 3

What is the excitation-contraction coupling?

Answer 3

• action potential enters from adjacent cell