chapter 17 control of cardiovascular function essentials of pathophysiology
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CHAPTER 17
CONTROL OF CARDIOVASCULAR FUNCTION
Essentials of Pathophysiology
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.
PRE LECTURE QUIZ (TRUE/FALSE)
F
T
T
F
F
_______________ 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.
PRE LECTURE QUIZ
Diastolic
Fibrillation
output
Tricuspid
veins
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
right heart
lungs
left heart
body
HEART ANATOMY
Lungs
QUESTION
True or False.The pulmonary circulation moves blood
through the left side of the heart.
ANSWER
FalseRationale: 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.)
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
Action potential
THE BASICS OF CELL FIRING (CONT.)
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
Action potential
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.)
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
Action 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
Threshold potential
PLATEAU
Action potential
Calcium leak
CARDIAC MUSCLE FIRING (CONT.) During
plateau, the muscle contracts strongly
Then the Ca2+ channels shut and it repolarizes
Threshold potential
PLATEAUAction potential
Calcium leak
QUESTION
Which ion channels allow cardiac muscle to fire without a stimulus?
a. Na+
b. K+
c. Ca2+
d. Cl-
ANSWER
c. 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
Systole
What happens in isovolumetric contraction?
QUESTION
Which of the following statements is true about ventricular systole?
a. Atria contractb. Ventricles contractc. AV valves are opend. Semilunar valves are closed
ANSWER
b. 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 CYCLE
Discussion: Arrange these steps in the proper order:
8– Ventricles relax 4– First heart sound1– Systole 5– Semilunar valves open10–Diastole 3– AV valves close9– AV valves open 6– Semilunar valves
close2– Ventricles contract 7– 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 throughº Pressure keeps the vessel from collapsing
The vessel’s resistance (R) to fluid flowº Small vessels have more resistanceº 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
BP = CO x PRBlood 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
TrueRationale: 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
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