Content Summary:
This chapter focused on the heart, the cardiac cycle, cardiac output, blood vessels, blood flow and blood pressure. The heart has four chambers, the right and left atria receive blood from the venous system and the right and left ventricles pump blood into the arterial system. Venous refers to veins and arterial refers to arteries. Blood is pumped from the right atria and ventricle into the lungs where gas exchange occurs and the blood receives oxygen and carbon dioxide is diffused out. This is pulmonary circulation. The oxygen rich blood returns to the left atria and ventricle where it is pumped into the aorta and transported to the rest of the organ systems. This is systemic circulation. Returning blood to the right atria and right ventricle contains a high carbon dioxide concentration and the process starts over again.

Summary #1:
The cardiac cycle has a repeating pattern of contraction and relaxation. Contraction, known as systole, occurs when the right and left atria almost simultaneously contract after filling with blood. Contraction of the right and left ventricles occurs seconds later. Blood is filling the ventricles before atrial contraction starts, and finishes just as the atria begin contracting. Contraction of the ventricles ejects blood contained within them. Relaxation of the ventricles is called diastole. The contraction and relaxation of the ventricles produces sound which can be heard using a stethoscope, and are called heart sounds. Abnormal heart sounds which are produced by abnormal patterns of blood flow are called murmurs. These can be congenital or the result of rheumatic fever.

Summary #2
Arteries have a thick muscular wall that is composed of three layers: 1) the tunica externa, composed of connective tissue, is the outermost layer, 2) the tunica media, composed mostly of smooth muscle, is the middle layer, and 3) tunica interna is the inner layer and is composed of three parts: 1) the endothelium, a simple squamous epithelium that lines the lumina of all blood vessels, 2) the basement membrane, composed of a layer of glycoproteins, that lies over some connective tissue fibers, and 3) elastin, a layer of elastic fibers that form an internal elastic lamina. Arteries are perfect for transporting blood because their thick walls can withstand the high pressure when blood is ejected from the heart. The elastin within arteries allows them to expand and contract as needed. Some small arteries and arterioles have only smooth muscle walls they are less elastic. Arterioles aas needed. Some small arteries and arterioles have only smooth muscle walls and they are less elastic. Arterioles can vasoconstrict and vasodilate.


Summary #3
Atherosclerosis is a process of the arteries hardening and causes about 50% of the deaths in the United States, Europe and Japan. Plaque causes an obstruction (atheroma) in the artery because of an abnormal accumulation of lipids. The atheroma protrudes into the lumen of the artery and causes a reduction in blood flow. This reduction can cause damage to organs which can be life threatening. Atheromas are attributed to smoking, hypertension, high blood cholesterol and diabetes. Fatty streaks (aggregations of lipid filled macrophages and lymphocytes within the tunica interna) can be seen in the lumen of arteries as early as 10 to 14 years of age.


Anything having to do with the heart interests me as many of the medical happenings in my family have centered around heart functions. My father-in-law had open heart surgery in October 1980, a month after my son was born. Prior to this, he had suffered a heart attack and heart arrhythmia. An episode of arrhythmia would have been fatal, but he fell and the jolt jump started his heart back into a steady rhythm. In 1980, open heart surgery was more of a major surgery than it is now. He spent quite some time in the hospital, and I can remember seeing him after surgery. His appearance was ashen, almost as if he had died. Thankfully the medical profession has had major advancements in this surgery. My father suffered from many blockages in vessels to his heart that were opened via angioplasties. He made two trips to Abbott Hospital in Minneapolis via helicopter due to heart vessel blockage. One of those times he was thought to have had a heart attack. The difference from his first angioplasty and his last were huge. He was awake for his last one and was able to be mobile much sooner. Again, medical advancements have come far. My husband suffered from a fatal heart attack, with no prior warning. Due to these experiences, my children and I are more aware of the intricacies of the heart and how we can protect it. Exercise, a low fat and low sodium diet, and managing stress are things we are very aware of.

On a profession note, I can better help my heart disease patients by awareness and knowledge of how the heart functions, as well as the limitations that heart disease can put on the body. It would be my job to help them work toward independent ADL as much as possible. Teaching health management and maintenance in this area would also be beneficial to my patients.

Essential Questions:
The three most important variables that affect blood pressure (BP) are:
  • Stroke Volume determined by blood volume
    • Stroke volume (SV) is the amount of blood leaving the ventricles in one contraction
    • SV is determined by the blood volume. Blood volume increases, then SV increases.
    • Blood volume increases central venous pressure, which increases right atrial pressure, right ventricular end-diastolic pressure
    • When the body is under stress, the nervous system makes the heart pump harder and SV increases
    • Blood volume can also be regulated by the kidneys
  • Total peripheral resistance
    • The ability of vessels to control their diameter
    • Results from vasoconstriction and vasodilation that affects blood flow and determines arterial blood pressure
    • Blood traveling in narrow vessels incur more resistance than blood traveling in wider vessels
    • Impediment to vessel diameter can influence resistance
  • Cardiac Rate
    • The rate at which the heart beats, measured in beats per minute (BPM)
    • When heart rate increases, generally BP rises.
    • When heart rate decreases, generally BP decreases
    • The nervous system, hormones, disease and medications can affect heart rate

Two reflexes that help maintain BP within limits are:
  • Barorecepteors
    • Stretch receptors within the aortic arch and carotid sinuses
      • When BP increases above normal, the walls of the aortic arch and carotid sinuses stretch and produce an increased frequency in AP
      • When BP decreases below normal, the walls of the aortic arch and carotid sinuses constrict and produce a decreased frequency in AP
  • Atrial stretch receptors
    • Activated by increased venous return to the heart
      • Stimulates reflex tachycardia because of increased sympathetic nerve activity
      • Inhibits ADH release which causes excretion of large amounts of urine that directly lowers blood volume
      • Promotes increased secretion of ANP which lowers blood volume through increased excretion of urine

References: Human Physiology by Stuart Ira Fox,