The Valves

To pump blood effectively, the heart needs valves that ensure a predominantly one-way flow. There is a valve between each atrium and its ventricle and at the exit from each ventricle into its great artery (figs. 19.6 and 19.7). Each valve consists of two or three fibrous flaps of tissue called cusps, covered with endothelium.

11 trabecula = little beam + carne = flesh, meat

Aorta

Right pulmonary artery

Superior vena cava

Right pulmonary veins

11 trabecula = little beam + carne = flesh, meat

Aorta

Right pulmonary artery

Superior vena cava

Right pulmonary veins

Right Ventricle Anatomy

Pectinate muscles

Right AV-(tricuspid) valve

Chordae tendineae Trabeculae carneae Right ventricle

Inferior vena cava

Figure 19.6 Internal Anatomy of the Heart (anterior aspect).

Do the atrial pectinate muscles more nearly resemble the ventricular papillary muscles or the trabeculae carneae?

Right atrium Fossa ovalis

Pectinate muscles

Right AV-(tricuspid) valve

Chordae tendineae Trabeculae carneae Right ventricle

Inferior vena cava

Left pulmonary artery

Pulmonary trunk Pulmonary valve

Left pulmonary veins

Left atrium Aortic valve

Left AV (bicuspid) valve Left ventricle Papillary muscle Interventricular septum Myocardium

Epicardium i

Figure 19.6 Internal Anatomy of the Heart (anterior aspect).

Do the atrial pectinate muscles more nearly resemble the ventricular papillary muscles or the trabeculae carneae?

Saladin: Anatomy & I 19. The Circulatory System: I Text I I © The McGraw-Hill

Physiology: The Unity of The Heart Companies, 2003 Form and Function, Third Edition

722 Part Four Regulation and Maintenance

722 Part Four Regulation and Maintenance

Chordae Tendineae

Aortic valve

Left AV (bicuspid) valve

Right AV (tricuspid) (a) valve

Openings to coronary arteries

Aortic valve

Left AV (bicuspid) valve

Right AV (tricuspid) (a) valve

Chordae tendineae

Papillary muscle

Chordae tendineae

Papillary muscle

Chordae Tendineae

Figure 19.7 The Heart Valves. (a) Superior view of the heart with the atria removed; (b) papillary muscle and chordae tendineae seen from within the right ventricle. The upper ends of the chordae tendineae are attached to the cusps of the right AV valve.

The atrioventricular (AV) valves regulate the openings between the atria and ventricles. The right AV (tri-cuspid) valve has three cusps and the left AV (bicuspid) valve has two. The left AV valve is also known as the mitral (MY-trul) valve after its resemblance to a miter, the headdress of a catholic bishop. Stringlike chordae tendineae (COR-dee ten-DIN-ee-ee), reminiscent of the shroud lines of a parachute, connect the AV valve cusps to conical papillary muscles on the floor of the ventricle.

The semilunar12 valves (pulmonary and aortic valves) regulate the openings between the ventricles and the great arteries. The pulmonary valve controls the opening from the right ventricle into the pulmonary trunk, and the aortic valve controls the opening from the left ventricle into the aorta. Each has three cusps shaped somewhat like shirt pockets (see photograph on p. 715).

The opening and closing of heart valves is the result of pressure gradients between the "upstream" and "downstream" sides of the valve (fig. 19.8). When the ventricles are relaxed, the AV valve cusps hang down limply, both AV valves are open, and blood flows freely from the atria

12semi = half + lunar = like the moon into the ventricles. When the ventricles have filled with blood and begin to contract, their internal pressure rises and blood surges against the AV valves. This pushes their cusps together, seals the openings, and prevents blood from flowing back into the atria. The papillary muscles contract with the rest of the ventricular myocardium and tug on the chordae tendineae, which prevents the valves from bulging excessively (prolapsing) into the atria or turning inside out like windblown umbrellas (see insight 19.1). When rising "upstream" pressure in the ventricles exceeds the "downstream" blood pressure in the great arteries, the ventricular blood forces the semilunar valves open and blood is ejected from the heart. Then as the ventricles relax again and their pressure falls below that in the arteries, arterial blood briefly flows backward and fills the pocketlike cusps of the semilunar valves. The three cusps meet in the middle of the orifice and seal it, thereby preventing blood from reentering the heart.

_Think About It_

How would valvular stenosis (see insight 19.1) affect the amount of blood pumped into the aorta? How might this affect a person's physical stamina? Explain your reasoning.

Saladin: Anatomy & I 19. The Circulatory System: I Text I I © The McGraw-Hill

Physiology: The Unity of The Heart Companies, 2003 Form and Function, Third Edition

Chapter 19 The Circulatory System: The Heart 723

Operation Atrioventricular Valve

Figure 19.8 Operation of the Heart Valves. (a) The semilunar valves. When the pressure in the ventricle is greater than the pressure in the artery, the valve is forced open and blood is ejected. When ventricular pressure is lower than arterial pressure, arterial blood holds the valve closed. (b) The atrioventricular valves. When atrial pressure is greater than ventricular pressure, the valve opens and blood flows through. When ventricular pressure rises above atrial pressure, the blood in the ventricle pushes the valve cusps closed.

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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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Responses

  • SHISHAY
    How many chordae tendineae are in each ventricle?
    8 years ago
  • anita okkonen
    What is the function of the trabeculae carneae?
    8 years ago
  • zewdi
    When papillary muscles relax valves open?
    8 years ago

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