Human Physiology Week 4 - Cardiovascular Study Guide

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Questions and Answers

What is the primary role of intercalated discs in cardiac muscle?

To facilitate rapid communication between cells (correct)

To provide structural support to the muscle fibers

To prevent regurgitation during contractions

To increase the tensile strength of the muscle

Which statement accurately compares the function of semilunar valves to AV valves?

Both types of valves require chordae tendinae for function

AV valves prevent regurgitation through passive mechanisms

Semilunar valves are thin to allow for greater flexibility

Semilunar valves function without the need for chordae tendinae (correct)

During rest, what percentage of blood flow is distributed to the brain?

35%

15% (correct)

25%

Which characteristic distinguishes cardiac muscle from skeletal muscle?

Cardiac muscle has intercalated discs Signup and view all the answers

What happens to blood flow to the skin during exercise in response to temperature changes?

It decreases initially due to vasoconstriction Signup and view all the answers

What primarily causes the plateau in the action potential of cardiac muscle?

Decreased outflow of potassium ions Signup and view all the answers

Which statement about the refractory periods in cardiac muscle is true?

The absolute refractory period prevents any contraction Signup and view all the answers

What accurately describes the relationship between heart rate and duration of cardiac cycle?

Increased heart rate results in reduced systole time Signup and view all the answers

Which factor is relevant for cardiac muscle contraction that differs from skeletal muscle contraction?

Extracellular calcium plays a vital role Signup and view all the answers

What is the ejection fraction formula, and what is its normal resting value?

(EDV - ESV) / EDV; 60% Signup and view all the answers

During the cardiac cycle, when does isovolumetric contraction occur?

Before the period of ejection begins Signup and view all the answers

Which of these factors increases ventricular filling during the cardiac cycle?

Decreased heart rate Signup and view all the answers

What distinguishes the intrinsic rates of the SA node, AV node, and Purkinje fibers?

SA node sets the rhythm for the heart Signup and view all the answers

What is the primary role of atrial contraction in the cardiac cycle?

It provides the majority of ventricular filling Signup and view all the answers

What occurs during the period of rapid ejection of blood from the heart?

Pressure is greatest in the first third of systole Signup and view all the answers

Study Notes

Cardiac Anatomy and Function

Blood travels from the vena cava, through the right atrium, then through the tricuspid valve into the right ventricle.
The blood then travels through the pulmonary valve into the pulmonary artery and into the lungs.
From the lungs, the oxygenated blood enters the pulmonary veins, then the left atrium, then through the mitral valve into the left ventricle.
Lastly, the blood travels through the aortic valve into the aorta.
Cardiac muscle is striated like skeletal muscle, but additionally has intercalated discs and a syncytial arrangement.
Intercalated discs allow for rapid diffusion of ions, enabling communication between cells.
Papillary muscles are attached to AV valves through chordae tendinae, which prevent bulging towards the atria and regurgitation.
Semilunar valves are stronger and built for faster velocity and higher pressures than AV valves.
AV valves function through chordae tendinae, while semilunar valves function passively based on pressure fluctuations.

Blood Flow Distribution at Rest

At rest, approximately 15% of blood flows to the brain, 5% to coronary arteries, 25% to kidneys, 25% to the GI tract, 25% to skeletal muscle, and 5% to the skin.
The relative percentage to the brain decreases during exercise, while the percentage of blood to the coronary arteries remains constant.
Blood flow to the kidneys is critical for adjusting vascular resistance at rest and during exercise.
Blood flow to the GI tract decreases significantly during exercise.
Skeletal muscle receives the largest increase in blood flow during exercise, as working muscles require more oxygen.
Skin blood flow varies depending on temperature: vasoconstriction occurs in cold temperatures and initially during exercise, while vasodilation occurs during hot temperatures and to eliminate heat during exercise.

Cardiac Muscle Contractility

Cardiac muscle differs from skeletal muscle in its action potential due to the activation of L-type calcium channels that prolong depolarization and create a plateau in the action potential.
Decreased permeability for potassium ions also plays a role in prolonging the action potential in cardiac muscle.
Purkinje fibers have much faster conduction of signals than cardiac muscle fibers, enabling rapid spread of the conduction signal throughout the heart.
The absolute refractory period is when the heart cannot be stimulated to contract at all, while the relative refractory period is when it can be stimulated by an especially strong signal.
Cardiac muscle contraction relies heavily on extracellular calcium concentration as the calcium used is derived from the extracellular fluid, unlike skeletal muscle where it comes from the sarcoplasmic reticulum.

Cardiac Cycle

A faster heart rate results in:
- a shorter action potential plateau
- decreased time in systole
- decreased time in diastole
- an increased ratio of systole to diastole
During the cardiac cycle, ventricular volume, atrial pressure, aortic pressure, and left ventricular pressure change in a specific pattern correlated with the electrocardiogram and phonocardiogram.
Atria contract slightly before ventricles to pump blood into the ventricles before contraction, accounting for approximately 20% of ventricular filling.
The period of rapid filling of the ventricles is caused by increased atrial pressure pushing AV valves open and allowing blood to flow into the low-pressure ventricles.
Isovolumetric contraction occurs before ejection as sufficient pressure needs to be built up in the ventricles to overcome the pressure in the aorta and pulmonary artery.
During the period of rapid ejection, more blood is ejected out of the heart due to higher pressure in the first third of systole.
The period of slow ejection occurs during the remaining two-thirds of systole.
Ejection fraction is the fraction of EDV ejected ((EDV-ESV)/EDV) and the normal value at rest is 60%.
Right ventricle pressures are only 1/6th that of the left ventricles during systole.
Preload is the end diastolic pressure when the ventricle is filled, representing the tension at the beginning of contraction.
Afterload is the pressure in the aorta, representing the resistance the ventricle must overcome to eject blood. A higher afterload requires the ventricles to work harder.
The Frank-Starling mechanism is driven by two key factors:
- Greater blood volume in the heart leads to greater contractile force and stroke volume.
- Greater stretch causes greater elastic energy and contractile strength.

Conduction System of the Heart

The electrical conduction pathway travels from the SA node, through the internodal pathways and inter-atrial fibers, to the AV node, then through the AV bundle, bundle branches, and finally to the ventricular muscle.

Automaticity (Self-Excitation)

The intrinsic rhythmical rates are:
- SA node: 70-80/min
- AV node: 40-60/min
- Purkinje fibers: 15-40/min
Ectopic beats originate from non-SA node sources.
Escape beats occur when the ventricle has not received a stimulus from the SA node, resulting in a slower heart rate.
Intrinsic heart rate is the rate at which the heart beats without autonomic nervous system influence, approximately 70 to 90 beats per minute.
A heart rate faster than 90 indicates sympathetic stimulation, while a heart rate slower than 70 indicates parasympathetic stimulation.

Autonomic Regulation of Heart Rhythmicity and Impulse Conduction

The sympathetic nervous system innervates all parts of the heart, while the parasympathetic nervous system innervates the SA node, AV junctional fibers, and to a lesser extent, the atria.
The vagus nerve supplies parasympathetic function to the heart.
Sympathetic nerves release norepinephrine, which increases SA node discharge, conduction rate, and contractile force.
Parasympathetic nerves release acetylcholine, which slows down the action potential process.
Sympathetic stimulation increases contractile force by binding to beta-adrenergic receptors, leading to an increase in calcium ions.

Heart Rate Terminology

Tachycardia is a faster than normal heart rate at rest.
Bradycardia is a slower than normal heart rate at rest.
Both tachycardia and bradycardia may or may not indicate underlying pathology and are not diagnoses themselves.

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Description

Test your knowledge on the intricacies of cardiac anatomy and physiology. This quiz covers the pathway of blood flow through the heart and the characteristics of cardiac muscle and valves. Dive deep into the structure and function of the heart to enhance your understanding of human biology.