Ch18 pt2

Blood Circulation in the Heart

Overview of Blood Flow

• Blood circulation begins with deoxygenated blood entering the heart.

• Blood returns to the heart via the superior vena cava and inferior vena cava.

• This blood flows into the right atrium.

Transition from Right Atrium to Right Ventricle

• Tricuspid Valve: Divides the right atrium and right ventricle (three cusps).

• Through the tricuspid valve, blood enters the right ventricle.

• Papillary Muscles: Contract to pull on chordae tendineae during ventricular contraction.

• Trabeculae Carneae: Muscular ridges in the right ventricle's wall, contributing to its structure.

Pulmonary Circulation

• Blood moves from the right ventricle through the pulmonary valve into the pulmonary trunk.

• Blood travels to the lungs for oxygenation.

• Inside the lungs, alveoli are tiny air sacs where gas exchange occurs:

  • Oxygen diffuses into blood.

  • Carbon dioxide diffuses from blood into alveoli.

Oxygenated Blood Returns to the Heart

• Pulmonary Veins: Oxygenated blood returns to the heart from the lungs.

• Blood enters the left atrium from:

  • Left pulmonary veins

  • Right pulmonary veins

• Changes from low to high oxygen content.

Transition from Left Atrium to Left Ventricle

• Blood flows from the left atrium to the left ventricle through the mitral valve (also called bicuspid valve, two cusps).

• From the left ventricle, blood passes through the aortic valve into the aorta.

Systemic Circulation

• The aorta branches into various arteries that deliver oxygenated blood throughout the body:

  • Brachiocephalic artery

  • Common carotid arteries

  • Left subclavian artery

• Blood travels via arteries → arterioles → capillaries.

  • Capillaries are sites for nutrient and gas exchange:

    • Oxygen delivered to tissues.

    • Carbon dioxide picked up from tissues.

Return of Deoxygenated Blood

• Deoxygenated blood returns via venules, then to medium-sized veins and larger veins.

• Blood collects in the superior and inferior vena cava to return to the heart.

Heart Anatomy and Function

Heart Structure

• Connection Sites: The fossa ovalis connects the pulmonary trunk to other blood vessels (closure occurs after birth).

• The coronary sinus is a vein on the posterior side draining blood from the heart.

Myocardium Layers

• Epicardium: Outermost layer surrounding the heart.

• Myocardium: Muscular layer of the heart responsible for pumping blood.

• Endocardium: Inner lining of the heart chambers.

Heart Valves

• Four main valves ensure unidirectional blood flow:

  • Atrioventricular Valves:

    • Tricuspid Valve (right side)

    • Mitral/Bicuspid Valve (left side)

  • Semilunar Valves:

    • Pulmonary Valve (between right ventricle and pulmonary trunk)

    • Aortic Valve (between left ventricle and aorta)

Valves Function

• Valves Prevent Backflow: When ventricles contract, AV valves close, preventing blood from returning to atria.

• Chordae Tendineae: Fibrous cords connecting AV valves to papillary muscles, keeping valves closed during ventricular contraction.

• Semilunar Valves: Open to allow blood from ventricles to aorta and pulmonary trunk, and close to prevent backflow into ventricles.

Heart Sounds and Conditions

• Heart Sounds:

  • First sound (lub) due to closure of the AV valves.

  • Second sound (dub) due to closure of the semilunar valves.

Valve Disorders

• Incompetent Valves: Blood leaks back; must be replaced or repaired to restore function.

• Stenosis: Narrowing of valve opening, increasing heart workload.