Path of Blood FlowScenario:• 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 deactivatedQuestion:• How did it get there?
Simplified Path of Blood Flow bodyright leftheart heart lungs
Review QuestionTell whether the following statement is true or false.The pulmonary circulation moves blood through the left side of the heart.
False AnswerRationale: 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 Basics of Cell Firing• Cells begin with a negative charge: resting membrane potential• Stimulus causes some Na+ channels to open Threshold• Na+ diffuses in, making potential the cell more positive Resting membrane potential Stimulus
The Basics of Cell Firing (cont.)• At threshold potential, Action more Na+ channels open potential• Na+ rushes in, making the cell very positive: Threshold depolarization potential• Action potential: the cell responds (e.g., by Resting contracting) membrane potential Stimulus
The Basics of Cell Firing (cont.)• K+ channels open Action potential• K+ diffuses out, making the cell negative again: Threshold repolarization potential• Na+/K+ ATPase removes the Na+ from Resting the cell and pumps membrane the K+ back in potential Stimulus
Cardiac Muscle Firing• Cells begin with a negative charge: resting membrane potential• Calcium leak lets Ca2+ Threshold diffuse in, making the cell potential more positive Resting membrane potential Calcium leak
Cardiac Muscle Firing (cont.)• At threshold potential, Action more Na+ channels potential open• Na+ rushes in, making Threshold potential the cell very positive: depolarization Resting• Action potential: the membrane cell responds (e.g., by potential Calcium contracting) leak
Cardiac Muscle Firing (cont.)• K+ channels open Action• K+ diffuses out, making potential PLATEAU the cell negative again, but Ca2+ channels are Threshold still allowing Ca2+ to potential enter• The cell remains positive: plateau Calcium leak
Cardiac Muscle Firing (cont.)• During plateau, the muscle Action contracts potential PLATEAU strongly Threshold• Then the Ca2+ potential channels shut and it repolarizes Calcium leak
QuestionWhich ion channels allow cardiac muscle to fire without a stimulus?b. Na+c. K+d. Ca2+e. Cl-
a. Ca2+ AnswerRationale: 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).
Heart ContractionHow 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 relaxed• 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
QuestionWhich of the following statements is true about ventricular systole?b. Atria contractc. Ventricles contractd. AV valves are opene. Semilunar valves are closed
Answera. Ventricles contractRationale: 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 CycleDiscussion:• Arrange these steps in the proper order: – Ventricles relax – First heart sound – Systole – Semilunar valves open – Diastole – AV valves close – AV valves open – Semilunar valves close – Ventricles contract – Second heart sound
Pressure, Resistance, Flow• Fluid flow through a vessel depends on: – The pressure difference between ends of the vessel º Pressure pushes the fluid through º Pressure keeps the vessel from collapsing – The vessel’s resistance to fluid flow º Small vessels have more resistance º More viscous fluids have greater resistance
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
DiscussionHow will each of these factors affect arteriole size and peripheral resistance?• Lactic acid • Low PO2• Cold • Histamine• Endothelin • Heat• NO • Adenosine
Blood Pressure BP = CO x PRBlood pressure = cardiac output × peripheral resistance
QuestionTell whether the following statement is true or false.In patients with hypertension (high blood pressure), peripheral resistance is increased.
True AnswerRationale: 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).