Chapter 17 Control of Cardiovascular Function Essentials of Pathophysiology Chapter 17 Control of Cardiovascular Function

PRE LECTURE QUIZ (TRUE/FALSE) The left side of the heart pumps blood to the lungs.  The venous side of the circulation contains a larger portion of the blood volume than the arterial side.  The rate of blood flow through a vessel is affected by pressure, resistance, and vessel radius.  The loose-fitting sac that surrounds the heart is called the myocardium.  The rhythmic impulse of the cardiac conduction system is generated at the AV node and is known as the pacemaker of the heart. F T

PRE LECTURE QUIZ Diastolic Fibrillation output Tricuspid veins   _______________ is the result of disorganized electrical activity in the atrium or the ventricle. Cardiac _______________ is the amount of blood the heart pumps each minute and is defined by the formula SV × HR. The _______________ are thin-walled, distensible, and collapsible vessels that are capable of enlarging and storing large quantities of blood. The ______________ period of the cardiac cycle is marked by ventricular relaxation and filling. The heart valve that controls the direction of blood flow from the right atrium to the right ventricle is called the _________________ valve.

Path of Blood Flow Scenario: You inject a medication into the client’s arm Within a few minutes, some of that drug has reached the client’s liver and is being deactivated Question: How did it get there?

Simplified Path of Blood Flow body left right heart heart lungs

Heart Anatomy Lungs

Question True or False. The pulmonary circulation moves blood through the left side of the heart.

Answer False Rationale: The right side of the heart pumps blood to the lungs through the pulmonary arteries, where gas exchange takes place. The left side of the heart is considered systemic circulation because blood is pumped to all body tissues.

The Heart Layers

The Basics of Cell Firing Cells begin with a negative charge: resting membrane potential Stimulus causes some Na+ channels to open Na+ diffuses in, making the cell more positive (less Negative) Threshold potential Resting membrane potential Stimulus

The Basics of Cell Firing (cont.) Action potential At threshold potential, more Na+ channels open Na+ rushes in, making the cell very positive: depolarization Action potential: the cell responds (e.g., by contracting) Threshold potential Resting membrane potential Stimulus

The Basics of Cell Firing (cont.) Action potential K+ channels open K+ diffuses out, making the cell negative again: repolarization Na+/K+ ATPase removes the Na+ from the cell and pumps the K+ back in Threshold potential Resting membrane potential Stimulus

Cardiac Muscle Firing Cells begin with a negative charge: resting membrane potential Calcium leak lets Ca2+ diffuse in, making the cell more positive Threshold potential Resting membrane potential Calcium leak

Cardiac Muscle Firing (cont.) Action potential At threshold potential, more Na+ channels open Na+ rushes in, making the cell very positive: depolarization Action potential: the cell responds (e.g., by contracting) Threshold potential Resting membrane potential Calcium leak

Cardiac Muscle Firing (cont.) K+ channels open K+ diffuses out, making the cell negative again, but Ca2+ channels are still allowing Ca2+ to enter The cell remains positive: plateau Action potential PLATEAU Threshold potential Calcium leak

Cardiac Muscle Firing (cont.) During plateau, the muscle contracts strongly Then the Ca2+ channels shut and it repolarizes Action potential PLATEAU Threshold potential Calcium leak

Question Which ion channels allow cardiac muscle to fire without a stimulus? Na+ K+ Ca2+ Cl-

Answer Ca2+ Rationale: In the SA and AV nodes, resting cardiac muscle cells have open Ca2+ channels. This allows Ca2+ to leak into the cells, making them more positive (the cells reach threshold this way without the need for a stimulus).

The Cell Passes the Impulse to Its Neighbors Desmosomes link cells tightly together Gap junctions pass the electrical signal to the next cells

Heart Contraction How would each of the following affect heart contraction: A calcium channel blocker An Na+ channel blocker A drug that opened Na+ channels A drug that opened K+ channels

Cardiac Cycle—Diastole Ventricles relax Blood entering atria Blood flows through AV valves into ventricles Semilunar valves are closed

Cardiac Cycle—Systole Ventricles contract Blood pushes against AV valves and they shut Blood pushes through semilunar valves into aorta and pulmonary trunk

What happens in isovolumetric contraction? Systole What happens in isovolumetric contraction?

Question Which of the following statements is true about ventricular systole? Atria contract Ventricles contract AV valves are open Semilunar valves are closed

Answer Ventricles contract Rationale: During ventricular systole, the ventricles contract. Because blood is being forced from the ventricles, semilunar valves must be open and AV valves closed. The atria are in diastole (relaxation) during ventricular systole.

Cardiac Cycle Discussion: Arrange these steps in the proper order: 8– Ventricles relax 4– First heart sound 1– Systole 5– Semilunar valves open 10–Diastole 3– AV valves close 9– AV valves open 6– Semilunar valves close 2– Ventricles contract 7– Second heart sound

Pressure, Resistance, Flow Fluid flow through a vessel depends on: The pressure difference between ends of the vessel Pressure pushes the fluid through Pressure keeps the vessel from collapsing The vessel’s resistance (R) to fluid flow Small vessels have more resistance More viscous fluids have greater resistance ΔP = Pin - Pout Flow, F= ΔP ÷ R

Pressure, Resistance, Flow of Blood Blood flow through a vessel depends on: Heart creating pressure difference between ends of the vessel Heart pushing the blood through Blood pressure keeping the vessels open The vessel’s resistance to fluid flow Constricting arterioles increasing resistance Increased hematocrit increasing resistance

Discussion How will each of these factors affect arteriole size and peripheral resistance? Lactic acid • Low PO2 Cold • Histamine Endothelin • Heat NO • Adenosine

Blood pressure = cardiac output × peripheral resistance BP = CO x PR Blood pressure = cardiac output × peripheral resistance How is this related to F=P/R ?

Question Tell whether the following statement is true or false. In patients with hypertension (high blood pressure), peripheral resistance is increased. (Hint: P= F x R )

Answer True Rationale: In hypertension, blood vessels are constricted/narrowed. Smaller vessels increase resistance (it’s harder to push the same amount of fluid/blood through a tube that has become smaller).

Forces Moving Fluid In and Out of Capillaries Higher Pressure from artery Lower Pressure of the veins

Lymph Vessels Carry Tissue Fluid Back to the Veins Interstitial fluid not recaptured in the capillaries enters the lymphatic system and ultimately reenters the blood at the subclavian vein