A look at cardiovascular disorders

For about cardiovascular disorders, although people are living longer than ever before, they’re increasingly living with chronic conditions or the effects of acute ones. Of these conditions, cardiovascular disorders head the list. In the United States, over 80 million people suffer from some form of cardiovascular disorder, and many of them suffer from a combination of disorders. Year after year, the number of affected patients continues to rise.

Because of this upward trend, you’ll be dealing with cardiovascular patients more often. To provide effective care for these patients, you need a clear understanding of cardiovascular anatomy and physiology, assessment techniques, diagnostic tests, and treatments as well as cardiovascular disorders.

Anatomy and physiology

Focus Topic: Cardiovascular disorders

The cardiovascular system delivers oxygenated blood to tissues and removes waste products. The heart, controlled by the autonomic nervous system, pumps blood to all organs and tissues of the body. Arteries and veins (the vascular system) carry blood throughout the body, keep the heart filled with blood, and maintain blood pressure. Let’s look at each part of this critical system.

Cardiovascular disorders: Heart

The heart is a hollow, muscular organ about the size of a closed fist. Located between the lungs in the mediastinum, it’s about 5n (12.5 cm) long and 31/2n (9 cm) in diameter at its widest point. It weighs between 8.8 and 10 oz (250 to 285 g).

Where’s your heart?

The heart spans the area from the second to the fifth intercostal space. The right border of the heart lines up with the right border of the sternum. The left border lines up with the left mid-clavicular line. The exact position of the heart may vary slightly with each patient. Leading into and out of the heart are the great vessels:

  • inferior vena cava
  • superior vena cava
  • aorta
  • pulmonary artery
  • four pulmonary veins.

Cardiovascular disorders: Slip and slide

A thin sac called the pericardium protects the heart. It has an inner, or visceral, layer that forms the epicardium and an outer, or parietal, layer. The space between the two layers contains 10 to 30 ml of serous (pericardial) fluid which prevents friction between the layers as the heart pumps.

Cardiovascular disorders: Chamber made

The heart has four chambers — two atria and two ventricles — separated by a cardiac septum. The upper atria have thin walls and serve as reservoirs for blood. They also boost the amount of blood moving into the lower ventricles, which fill primarily by gravity. (See Inside the heart.)

Blood pathways

Blood moves to and from the heart through specific pathways. Deoxygenated venous blood returns to the right atrium through three vessels:

  1. superior vena cava — returning blood from the upper body
  2. inferior vena cava — returning blood from the lower body
  3. coronary sinus — returning blood from the heart muscle

Inside the heart

The heart’s internal structure consists of the pericardium, 3 layers of the heart wall, 4 chambers, and 4 valves.

 

Cardiovascular disorders

 

Get some fresh air

Blood in the right atrium empties into the right ventricle and is then ejected through the pulmonic valve into the pulmonary artery when the ventricle contracts. The blood then travels to the lungs to be oxygenated.

Share the wealth

From the lungs, blood travels to the left atrium through the pulmonary veins. The left atrium empties the blood into the left ventricle, which then pumps the blood through the aortic valve into the aorta and throughout the body with each contraction. Because the left ventricle pumps blood against a much higher pressure than the right ventricle, its wall is three times thicker.

Valves

Valves in the heart keep blood flowing in only one direction through the heart. Think of the valves as traffic cops at the entrances to one-way streets, preventing blood from traveling the wrong way despite great pressure to do so. Healthy valves open and close as a result of pressure changes within the four heart chambers.

Matching sets

The heart has two sets of valves:

  1. atrioventricular (between atria and ventricles) — tricuspid valve on the heart’s right side and mitral (bicuspid) valve on its left
  2. semilunar — pulmonary valve (between the right ventricle and pulmonary artery) and aortic valve (between the left ventricle and aorta).

On the cusp

Each valve has cusps (leaflets), which are anchored to the heart wall by cords of fibrous tissue (chordae tendineae). The cusps of the valves act to maintain tight closure. The tricuspid valve has three cusps, the mitral valve has two cusps, and each of the semilunar valves has three cusps.

Cardiac cycle

Contractions of the heart occur in a rhythm — the cardiac cycle — and are regulated by impulses that normally begin at the sinoatrial (SA) node, the heart’s pacemaker. The impulses are conducted from there throughout the heart. Impulses from the autonomic nervous system affect the SA node and alter its firing rate to meet the body’s needs. The cardiac cycle consists of two phases: diastole and systole.

Just relax… then, kick!

During diastole, the heart relaxes and fills with blood and the heart muscle receives its own supply of blood from the coronary arteries. The mitral and tricuspid valves are open, and the aortic and pulmonic valves are closed. Diastole has three phases:

  1. isovolumetric relaxation — when ventricular pressure drops below the pressure in the aorta and the pulmonary artery, allowing blood to back up toward the ventricles and causing the aortic and pulmonic valves to snap shut, leading to the second heart sound (S2) and atrial filling (the beginning of the cardiac cycle)
  2. ventricular filling (passive) — when 70% of the blood in the atria drains into the ventricles by gravity, which may cause vibrations heard as the third heart sound (S3)
  3. atrial contraction (active), also called atrial kick — when the remaining 30% of blood is pumped into the ventricles, which may cause the fourth heart sound (S4).

Outward bound

During systole, ventricular contraction sends blood on its outward journey. Systole has two phases:

  1. isovolumetric contraction — when pressure within the ventricles rises (because of atrial kick) causing the mitral and tricuspid valves to snap closed, which makes the first heart sound (S1)
  2. ventricular ejection — when ventricular pressure rises above the pressure in the aorta and pulmonary artery, causing the aortic and pulmonic valves to open and blood to eject into the pulmonary artery and out to the lungs and into the aorta and out to the rest of the body.

Cardiovascular disorders: Vascular system

The vascular system consists of a network of arteries, arterioles, capillaries, venules, and veins. This network is constantly filled with about 5 L of blood. The vascular system delivers oxygen, nutrients, and other substances to the body’s cells and removes the waste products of cellular metabolism. (See A close look at the arteries, and A close look at the veins.)

 

A close look at the arteries

This illustration shows the major arteries of the body.

 

Cardiovascular disorders

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A close look at the veins

This illustration shows the major veins of the body.

 

Cardiovascular disorders

 

Arteries

Arteries carry blood away from the heart. Nearly all arteries carry oxygen-rich blood from the heart throughout the rest of the body. The only exception is the pulmonary artery, which carries oxygen-depleted blood from the right ventricle to the lungs.

Tough stuff

Arteries have thick walls because they transport blood under high pressure. Arterial walls contain a tough, elastic layer to help propel blood through the arterial system.

Pulse is pressure

Arterial pulses are pressure waves of blood generated by the pumping action of the heart. All vessels in the arterial system have pulsations, but you can only feel the pulsations where an artery lies near the skin. You can palpate for these peripheral pulses: temporal, carotid, brachial, radial, ulnar, femoral, popliteal, posterior tibial, and dorsalis pedis. The location of pulse points varies between individuals. Older adults may have diminished peripheral pulses.

Capillaries, arterioles, and venules

The exchange of fluid, nutrients, and metabolic wastes between blood and cells occurs in the capillaries. The exchange can occur because capillaries are thin-walled and highly permeable. At any given moment, the capillaries contain about 5% of the circulating blood volume. They’re connected to arteries and veins through intermediary vessels called arterioles and venules, respectively.

Veins

Veins carry blood toward the heart. Nearly all veins carry oxygen-depleted blood, with the sole exception of the pulmonary vein, which carries oxygenated blood from the lungs to the left atrium. Veins serve as a large reservoir for circulating blood.

Feeling flexible

Veins have thinner, more pliable walls than arteries. That pliability allows veins to accommodate variations in blood volume. Veins contain valves at periodic intervals to prevent blood from flowing backward.

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