Circulation Overview and Human Heart Anatomy

Circulation Overview

• Vertebrates have a closed cardiovascular system.
• Atria receive blood, ventricles pump it out through vessels.
• Arteries carry blood away from the heart.
• Arterioles are smaller arteries.
• Capillaries exchange materials with tissue fluid.
• Veins return blood to the heart.
• Venules are smaller veins.

Human Heart

• Fist-sized, cone-shaped, muscular organ.
• Myocardium is largely cardiac tissue.
• Lies within a sac called the pericardium.
• Four chambers: two atria and two ventricles (upper and lower).
• Septum separates the left and right halves.
• Atrioventricular valves (tricuspid and bicuspid) regulate blood flow between atria and ventricles.
• Semilunar valves (pulmonary and aortic) regulate blood flow out of the ventricles.
• The right side of the heart pumps blood to the lungs (pulmonary circuit).
• The left side of the heart pumps blood to the body (systemic circuit).
• Oxygen-poor blood and oxygen-rich blood never mix.

Heartbeat

• Systole: Heart chamber contraction.
• Diastole: Heart chamber relaxation.
• Pulse: Wave effect in arterial walls caused by aortic expansion and recoil during ventricular contraction.
• Conducting system: Sinoatrial node (SA node) sets the pace; Atrioventricular node (AV node); Branches of the AV bundle and Purkinje fibers send electrical impulses to coordinate heart contractions.
• Electrocardiogram (ECG): Records electrical changes in the myocardium during a cardiac cycle.
• P wave indicates atrial contraction.

Vascular Pathways

• Human cardiovascular system has two main pathways:
• Pulmonary circuit: Carries oxygen-poor blood to the lungs and returns oxygen-rich blood to the heart.
• Systemic circuit: Carries oxygen-rich blood from the heart to the rest of the body, and returns oxygen poor blood to the heart.

Blood Pressure

• Systolic pressure: Pressure during ventricular contraction.
• Diastolic pressure: Pressure during ventricular relaxation.
• Measured with a sphygmomanometer on the brachial artery.
• Normal blood pressure is expressed as systolic/diastolic.

Blood

• Blood is a transport medium.
• Plasma: Liquid portion of blood, containing various molecules (nutrients, wastes, salts, proteins).
• Plasma proteins maintain osmotic pressure and are involved in clotting.
• Red blood cells: Carry oxygen; Lack a nucleus at maturity; Contain hemoglobin.
• White blood cells: Larger than red blood cells; Contain a nucleus; Important in inflammatory response and fighting infection.
• Platelets are involved in blood clotting.

Cardiovascular Disorders

• Hypertension: High blood pressure.
• Atherosclerosis: Fatty material accumulation in artery linings.
• Stroke: Cranial arteriole burst or blockage.
• Heart attack (Myocardial infarction): Coronary artery blockage.