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Chapter 43

Review of Hemodynamics

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Review of Hemodynamics Overview of the circulatory system

Delivery of oxygen, nutrients, hormones, electrolytes, and other essentials to the cells

Removal of carbon dioxide, metabolic wastes, and other detritus from cells

Two major divisions• Pulmonary circulation and systemic circulation

Regulation of cardiac output Regulation of arterial pressure (AP)

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Overview of the Circulatory System

Components of the circulatory system Arteries Arterioles Capillaries Venules Veins

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Overview of the Circulatory System

Distribution of blood 9% in the pulmonary circulation 7% in the heart 84% in the systemic circulation

What makes blood flow? Force that drives flow is greater than resistance

How does blood get back to the heart?

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Fig. 43–1. Distribution of blood in the circulatory system.

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Fig. 43–2. Forces that promote and impede flow of blood.

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Fig. 43–3. Distribution of pressure within the systemic circulation.

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Regulation of Cardiac Output Determinants of cardiac output

Average adult, 5 L/min Cardiac output = Heart rate × Stroke volume Heart rate

• Controlled by the autonomic nervous system Stroke volume

• Myocardial contractility• Cardiac afterload• Cardiac preload

Preload• End-diastolic volume or end-diastolic pressure

Afterload• Arterial pressure the left ventricle must overcome to eject blood

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Regulation of Cardiac Output Control of stroke volume by venous return

Starling’s law of the heart Factors that determine venous return

• Systemic filling pressure• Auxiliary muscle pumps• Resistance to flow between peripheral vessels and the

right atrium• Right atrial pressure

Starling’s law and maintenance of systemic-pulmonary balance

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Fig. 43–4. Venous valves and the auxiliary venous “pump.”

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Fig. 43–5. The Starling relationship between myocardial fiber lengthand contractile force.

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Fig. 43–6. Systemic-pulmonary imbalance that develops when the output of the left and right ventricles is not identical.

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Regulation of Arterial Pressure Overview of control system

AP = Peripheral resistance × Cardiac output Arterial pressure is regulated by:

• Autonomic nervous system (ANS)• Renin-angiotensin system• Kidneys

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Regulation of Arterial Pressure Steady-state control by the ANS

Regulates AP by adjusting cardiac output (CO) and peripheral resistance

Rapid control by the ANS: the baroreceptor reflex Constriction of nearly all arterioles Constriction of veins Acceleration of heart rate

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Regulation of Arterial Pressure Renin-angiotensin-aldosterone system

Constriction of arterioles and veins (angiotensin II) Retention of water by the kidney (aldosterone)

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Regulation of Arterial Pressure Renal retention of water Postural hypotension (orthostatic

hypotension) Natriuretic peptides

Protect the cardiovascular system in the event of volume overload

Three principal members• Atrial natriuretic peptide (ANP)• B (brain)-natriuretic peptide (BNP)• C-natriuretic peptide (CNP)