Physiology Week 4

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Questions and Answers

Which factor is not associated with an increase in basal metabolic rate (BMR)?

Growth hormone levels

Increased muscle mass

Severe malnutrition (correct)

Higher thyroid hormone levels

Which of the following accurately reflects the relationship between age, sex, and BMR?

Older individuals generally have a higher BMR than younger individuals

BMR is not influenced by sex or age

Females typically have lower BMR due to differences in muscle mass (correct)

Males have consistently lower BMR than females regardless of age

What percentage of energy released by ATP hydrolysis is primarily converted to heat?

10%

50%

25%

33% (correct)

Which temperature range is typical for a healthy person at rest?

97 to 99.5°F Signup and view all the answers

Which statement about how the body produces heat is incorrect?

Friction at the surface level contributes most to heat production Signup and view all the answers

What physiological change indicates sympathetic nervous system stimulation in heart rate?

Heart rate greater than 90 beats per minute Signup and view all the answers

Which nerve is primarily responsible for inducing parasympathetic effects on heart function?

Vagus nerve Signup and view all the answers

Which neurotransmitter is associated with the sympathetic nervous system's effects on the heart?

Norepinephrine (NE) Signup and view all the answers

What does a diagnosis of bradycardia imply about heart rate?

Heart rate is slower than normal at rest Signup and view all the answers

Which specific receptor stimulation leads to increased contractile force in cardiac muscle?

Beta adrenergic receptors Signup and view all the answers

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

Activation of slow calcium channels Signup and view all the answers

How does the conduction velocity of Purkinje fibers compare to cardiac muscle fibers?

Faster than cardiac muscle fibers Signup and view all the answers

What is the difference between the absolute refractory period and the relative refractory period in cardiac muscle?

The relative refractory period can respond to strong stimuli Signup and view all the answers

Why is extracellular calcium concentration more significant for cardiac muscle contraction compared to skeletal muscle contraction?

Calcium influx occurs through t-tubules connected to extracellular space Signup and view all the answers

What mechanism initially causes vasoconstriction during exercise?

Release of adrenaline Signup and view all the answers

What is the role of potassium ions in the action potential of cardiac muscle?

They promote rapid repolarization Signup and view all the answers

Which factor significantly affects the duration of the cardiac cycle?

The heart rate of the individual Signup and view all the answers

What primarily differentiates action potential in cardiac muscle from that in skeletal muscle?

Involvement of slow calcium channels in cardiac muscle Signup and view all the answers

Which statement best describes the impact of increased heart rate on the cardiac cycle?

It results in less time for ventricular filling. Signup and view all the answers

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

To account for approximately 20% of ventricular filling. Signup and view all the answers

During the period of rapid filling of the ventricles, what primarily causes the AV valves to open?

Increased atrial pressure. Signup and view all the answers

Which of the following correctly explains isovolumetric contraction?

Requires a sufficient pressure build-up to allow ejection. Signup and view all the answers

What distinguishes the 'period of rapid ejection' from the 'period of slow ejection'?

Pressure is highest in the first third of systole during rapid ejection. Signup and view all the answers

How is ejection fraction calculated, and what is the normal value at rest for healthy individuals?

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

What is the difference in pressures between the right and left ventricles during systole?

Right ventricular pressure is only 1/6th that of the left. Signup and view all the answers

Which term describes the end diastolic pressure when the ventricle is filled, directly related to ventricular volume?

Preload Signup and view all the answers

What is the function of intercalated discs in cardiac muscle tissue?

They facilitate rapid communication between cardiac muscle cells. Signup and view all the answers

Which of the following best describes the role of papillary muscles in the heart?

They prevent bulging of valves towards the atria during contraction. Signup and view all the answers

How do semilunar valves differ from atrioventricular (AV) valves?

Semilunar valves are thicker and allow higher velocity blood flow. Signup and view all the answers

What is the pathway of blood flow in the heart starting from the vena cava?

Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Valve → Lungs → Pulmonary Vein → Left Atrium → Aortic Valve → Aorta. Signup and view all the answers

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

~15% Signup and view all the answers

Which statement accurately describes blood flow distribution to the coronary arteries during exercise?

It increases proportionately to supply the myocardium with more blood. Signup and view all the answers

What distinguishes cardiac muscle from skeletal muscle in terms of structure?

Cardiac muscle contains intercalated discs. Signup and view all the answers

What happens to blood flow to the GI tract during exercise?

It is substantially reduced to redistribute blood to more active muscles. Signup and view all the answers

What physiological effect does an increase in afterload have on the ventricles?

The ventricles require more ATP to pump blood. Signup and view all the answers

What is the primary function of the sinoatrial (SA) node in the cardiac conduction system?

To act as the fastest pacemaker setting the heart rhythm. Signup and view all the answers

Which statement best describes the relationship between atrial stretch and heart rate?

Increased atrial stretch stimulates greater autonomic nervous system activity, increasing heart rate. Signup and view all the answers

What aspect of the Frank-Starling mechanism explains the increase in stroke volume?

Greater amounts of blood lead to improved muscle elasticity and contractile force. Signup and view all the answers

Which component of the cardiac conduction system acts as a backup pacemaker?

Atrioventricular node Signup and view all the answers

During which situation are escape beats most likely to occur?

When the ventricles do not receive stimulation from the SA node. Signup and view all the answers

What condition is characterized by ectopic beats?

Contractions originating from fibers other than the SA node. Signup and view all the answers

What is the intrinsic heart rate when autonomic influences are absent?

15-40 beats per minute. Signup and view all the answers

Which mechanism primarily maintains the plateau phase in the action potential of cardiac muscle?

Activation of slow calcium channels and decreased potassium permeability Signup and view all the answers

What is the difference in conduction velocity between Purkinje fibers and cardiac muscle fibers?

Purkinje fibers conduct much faster than cardiac muscle fibers Signup and view all the answers

Which period in cardiac muscle is characterized by the inability to stimulate the heart to contract at all?

Absolute refractory period Signup and view all the answers

How does the requirement for extracellular calcium differ between cardiac muscle and skeletal muscle?

Cardiac muscle requires extracellular calcium to initiate contractions whereas skeletal muscle does not Signup and view all the answers

What describes the relative refractory period in cardiac muscle contraction?

It can only be stimulated by a strong signal Signup and view all the answers

Which aspect does NOT play a role in the duration of the cardiac cycle?

Vascular resistance Signup and view all the answers

Which statement correctly explains the role of vasoconstriction during exercise?

It prevents blood flow to the skin to maintain core temperature Signup and view all the answers

Which statement about the histological differences between cardiac and skeletal muscle is correct?

Cardiac muscle is involuntary and has branched fibers. Signup and view all the answers

What is the primary function of the chordae tendinae in the heart?

To prevent the AV valves from prolapsing during ventricular contraction. Signup and view all the answers

How do semilunar valves function compared to AV valves under pressure conditions?

Semilunar valves close passively when pressure in the arteries decreases. Signup and view all the answers

Which of the following correctly describes blood flow distribution to the skeletal muscles at rest compared to during exercise?

Skeletal muscle receives significantly increased blood flow during exercise. Signup and view all the answers

What distinguishes the role of intercalated discs in cardiac muscle compared to other muscle types?

They ensure rapid electrical conduction between cardiac muscle cells. Signup and view all the answers

What effect does an increase in afterload have on ventricular function?

It decreases the stroke volume due to increased resistance. Signup and view all the answers

Which factor contributes to the greater contractile force in the heart according to the Frank-Starling mechanism?

Greater amounts of blood result in increased stretch of cardiac muscle. Signup and view all the answers

What is the primary role of the atrioventricular (AV) node in the cardiac conduction system?

To slow down electrical signals between the atria and ventricles. Signup and view all the answers

Which statement correctly compares the intrinsic rhythmical rates of the cardiac conduction components?

The SA node generates impulses faster than the AV node and Purkinje fibers. Signup and view all the answers

What is an intrinsic heart rate, and how is it determined?

It's the rate of the heart when autonomic influence is absent. Signup and view all the answers

What is the primary effect of increased heart rate on diastolic time?

Decreased time in diastole Signup and view all the answers

How much of ventricular filling is attributed to atrial contraction?

20% Signup and view all the answers

Which statement best describes isovolumetric contraction?

Both AV and semilunar valves are closed Signup and view all the answers

What is the nature of pressure in the right ventricle during systole compared to the left ventricle?

Half the pressure Signup and view all the answers

During which part of systole is blood pressure the highest?

First third of systole Signup and view all the answers

What is the typical ejection fraction at rest in healthy individuals?

60% Signup and view all the answers

Which statement correctly differentiates preload from afterload?

Preload is associated with end diastolic pressure Signup and view all the answers

What primarily causes the rapid filling of the ventricles?

Increased atrial pressure Signup and view all the answers

What distinguishes the period of slow ejection from the period of rapid ejection?

Lower ejection velocity Signup and view all the answers

How are left ventricular and aortic pressures related during the cardiac cycle?

Left ventricular pressure must exceed aortic pressure for ejection Signup and view all the answers

What function do the intercalated discs serve in cardiac muscle tissue?

They allow for communication between cells through rapid diffusion of ions. Signup and view all the answers

Which statement accurately contrasts the properties of AV valves and semilunar valves?

Semilunar valves operate passively under high arterial pressure without the need for chordae tendinae. Signup and view all the answers

During rest, which percentage of total blood flow is typically distributed to skeletal muscle?

25% Signup and view all the answers

Which accurately describes the role of papillary muscles in the heart?

They prevent the regurgitation of blood into the atria during ventricular contraction. Signup and view all the answers

What distinguishes cardiac muscle from skeletal muscle in terms of structural features?

Cardiac muscle has intercalated discs, while skeletal muscle does not. Signup and view all the answers

What is the primary mechanism that prolongs depolarization during the action potential of cardiac muscle?

Opening of L-type calcium channels Signup and view all the answers

Which of the following best describes the relationship between heart rate and the duration of the action potential in cardiac muscle?

Increased heart rate shortens action potentials Signup and view all the answers

What characterizes the absolute refractory period in cardiac muscle contraction?

The heart cannot be stimulated at all Signup and view all the answers

How does the conduction velocity of cardiac muscle fibers compare to that of Purkinje fibers?

Purkinje fibers conduct much faster than cardiac muscle fibers Signup and view all the answers

Why is extracellular calcium concentration vital for cardiac muscle contraction?

Calcium from extracellular fluid triggers contraction Signup and view all the answers

What typically distinguishes the relative refractory period from the absolute refractory period in cardiac muscles?

The heart can be stimulated only by strong signals during the relative period Signup and view all the answers

What physiological change occurs initially during exercise concerning vasoconstriction?

Initial vasoconstriction followed by vasodilation Signup and view all the answers

What physiological consequence does increased afterload have on ventricular performance?

Increased workload resulting in higher ATP demands Signup and view all the answers

Which component of the cardiac conduction system has the slowest intrinsic rhythmical rate?

Atrioventricular (AV) node Signup and view all the answers

Which statement accurately reflects the Frank-Starling mechanism's role in stroke volume?

Greater blood volume in the heart leads to increased contractile force due to optimal actin-myosin overlap Signup and view all the answers

What defines the intrinsic heart rate, and which statement is accurate regarding it?

It reflects the natural beating rate without autonomic influence, approximately 100 beats per minute Signup and view all the answers

Which feature of ectopic beats distinguishes them from escape beats?

They are generated by non-SA node sites independent of the normal conduction pathway Signup and view all the answers

How does increased heart rate affect the time spent in diastole?

Decreases the duration of diastole Signup and view all the answers

What percentage of ventricular filling is attributed to the atrial contraction?

20% Signup and view all the answers

What primarily initiates the period of rapid filling of the ventricles?

Increased atrial pressure Signup and view all the answers

What is the primary function of isovolumetric contraction?

To generate enough pressure to overcome the aortic pressure Signup and view all the answers

Which phase of ejection yields the highest pressure in the left ventricle?

Period of rapid ejection Signup and view all the answers

What does the ejection fraction represent?

The fraction of end-diastolic volume that is ejected Signup and view all the answers

What is the typical pressure difference between the right and left ventricles during systole?

Right pressures are one-sixth of the left Signup and view all the answers

Which concept describes the pressure during the initial filling phase of the ventricle?

Preload Signup and view all the answers

During what phase does the greatest blood volume flow out of the heart occur?

Rapid ejection Signup and view all the answers

Which of the following best describes the physiological significance of atrial pressure during the cardiac cycle?

Increased atrial pressure facilitates opening of the AV valves Signup and view all the answers

Study Notes

Basal Metabolic Rate (BMR)

BMR is the minimum amount of energy your body needs to function at rest.
Muscle mass increases BMR because it requires more energy to maintain.
Hormones like growth hormone, testosterone, and thyroxine increase metabolic rate.
Fever increases BMR.
Sleep decreases BMR.
Malnutrition decreases BMR as the body becomes more efficient.
Females and older individuals generally have lower BMR due to differences in muscle mass, body fat, and sex hormone levels.

Heat Production in the Body

Approximately one-third of the energy released from ATP hydrolysis is converted to heat.
Friction at the microscopic level contributes to heat production such as blood flow and movement within the musculoskeletal system.

Oral Temperature Ranges

Resting oral temperature ranges from 97 to 99.5 degrees Fahrenheit.
During exercise, oral temperature can rise between 101 and 104 degrees Fahrenheit.
In cold conditions, oral temperature can decrease.
Rectal temperature is typically higher than oral temperature.

Cardiac Anatomy and Function

Blood flows through the heart in the following order: Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Valve → Pulmonary Artery → Lungs → Pulmonary Vein → Left Atrium → Mitral Valve → Left Ventricle → Aortic Valve → Aorta
Cardiac muscle, like skeletal muscle, is striated due to the presence of actin and myosin however cardiac muscle has intercalated discs and a syncytial arrangement
Intercalated discs allow for rapid diffusion of ions between cardiac muscle cells, facilitating electrical conduction
Papillary muscles attach to the atrioventricular (AV) valves via chordae tendinae, preventing valve prolapse and regurgitation into the atria
Semilunar valves (pulmonary and aortic) are thicker and stronger than AV valves, with faster blood flow and more mechanical abrasion
Semilunar valves function passively due to high pressure in arteries, not requiring chordae tendinae for closure

Blood Flow Distribution at Rest

Approximately 15% of blood flow is directed to the brain at rest; this percentage decreases during exercise, but absolute volume remains constant
Coronary arteries receive about 5% of blood flow, increasing proportionally during exercise to meet the increased metabolic demands of the working myocardium.
Kidneys receive 25% of blood flow at rest making it a key site for adjusting vascular resistance
The GI tract also receives 25% of blood flow at rest, significantly reduced during exercise
Skeletal muscle receives 25% of blood flow at rest, dramatically increasing during exercise with working muscles receiving the greatest flow
Skin receives 5% of blood flow, varying based on body temperature.
Vasoconstriction occurs in cold temperatures, initially during exercise, and during hot temperatures to eliminate heat
Vasodilation occurs during hot temperatures and during exercise for heat elimination

Cardiac Muscle Contractility

The action potential plateau in cardiac muscle is a slower calcium influx from L-type calcium channels, allowing greater inflow of Na+ and Ca2+ compared to skeletal muscle, where only Na+ channels are involved
The slower calcium channels contribute to the prolonged depolarization and plateau in the action potential of cardiac muscle
The plateau is also sustained by decreased permeability for potassium ions, preventing rapid repolarization
Purkinje fibers conduct electrical signals much faster than cardiac muscle fibers, enabling quick and efficient spread of the conduction signal through the heart
The absolute refractory period represents a time when the heart cannot be stimulated to contract, while the relative refractory period allows contraction only to a strong stimulus
Extracellular calcium is crucial for cardiac muscle contraction due to the direct connection of t-tubules to the extracellular space, providing a source of calcium for contraction

Cardiac Cycle

Increased heart rate shortens the action potential plateau, decreases the duration of systole and diastole, and increases the ratio of systole to diastole
During the cardiac cycle, ventricular volume increases during diastole, atrial pressure increases during atrial contraction, aortic pressure increases during ventricular ejection, and ventricular pressure increases during systole
Atrial contraction contributes to ventricular filling by pumping blood into the ventricles before ventricular contraction
The period of rapid filling of ventricles is driven by increased atrial pressure pushing blood through the open AV valves into the low-pressure ventricles
Isovolumetric contraction occurs before ejection because sufficient pressure must be generated to overcome the pressure in the aorta and pulmonary artery
The period of rapid ejection is characterized by higher pressure and a greater ejection fraction than the period of slow ejection
Ejection fraction is calculated as the ratio of stroke volume (EDV-ESV) to end diastolic volume (EDV) and is normally around 60% at rest
The right ventricle generates pressures about 1/6th of the left ventricle during systole
Preload refers to the end diastolic pressure, representing ventricular tension prior to contraction and reflecting filling pressure
Afterload refers to the resistance to blood flow in the aorta, effectively the pressure that the ventricle must overcome to eject blood; it is represented by the aortic diastolic pressure
The Frank-Starling mechanism asserts that greater ventricular filling leads to greater contractile force and stroke volume, which is attributed to increased elastic energy and more optimal actin-myosin overlap

Conductive System of the Heart

The electrical impulse travels through the heart in the following sequence: Sinoatrial (SA) Node → Internodal Pathways → Atrioventricular (AV) Node → Atrioventricular Bundle → Bundle Branches → Ventricular Muscle
The SA node has the highest intrinsic rate of 70-80 beats per minute, followed by the AV node at 40-60 bpm, and the Purkinje fibers of the ventricles at 15-40 bpm
Ectopic beats originate from sites other than the SA node, while escape beats occur when the ventricle contracts independently due to a slower supraventricular impulse rate
The intrinsic heart rate, the rate in the absence of autonomic nervous system influence, is approximately 70-90 beats per minute
Sympathetic stimulation increases heart rate, while parasympathetic stimulation decreases heart rate

Autonomic Regulation of Heart Rate and Impulses

Sympathetic nerves innervate all parts of the heart, releasing norepinephrine (NE) to increase SA node discharge, conduction rate, and contractile force
Parasympathetic nerves predominantly supply the SA node and AV junctional fibers, releasing acetylcholine (ACh) to slow down the conduction process and decrease heart rate
The sympathetic nervous system increases contractile force through stimulation of beta-adrenergic receptors leading to
increased intracellular calcium levels

Heart Rate Terminology

Tachycardia is a faster than normal resting heart rate, while bradycardia is a slower than normal resting heart rate
These terms are descriptive, and their presence does not always indicate pathology

Cardiovascular System: Blood Flow

Blood Flow Path: Blood enters the heart through the vena cava into the right atrium. It then passes through the tricuspid valve into the right ventricle. From there, it is pumped through the pulmonary valve into the pulmonary artery and flows to the lungs. After oxygenation, the blood returns to the heart via the pulmonary veins to the left atrium. Through the mitral valve, it enters the left ventricle and is then pumped through the aortic valve into the aorta.
Cardiac Muscle vs Skeletal Muscle: Both types of muscle are striated due to the presence of actin and myosin, but they differ in structure and function. Cardiac muscle possesses intercalated discs that allow for communication and rapid diffusion of ions between cells. Cardiac muscle also has a syncytial arrangement, meaning that the cells connect and function as a unit.
Intercalated Discs Function: These structures allow for the rapid conduction of electrical signals throughout the heart, ensuring coordinated contraction.
Papillary Muscles & Chordae Tendinae: These structures work together to prevent the atrioventricular (AV) valves from buldging back into the atria during ventricular contraction, preventing regurgitation.
AV & Semilunar Valve Function: AV valves are thin and regulate blood flow between the atria and ventricles. Semilunar valves are stronger and handle the higher velocity blood flow in the arteries. They function passively, opening and closing based on pressure gradients.

Blood Flow Distribution

Organ Blood Flow at Rest:
- Brain: 15%
- Coronary Arteries: 5%
- Kidneys: 25%
- GI Tract: 25%
- Skeletal Muscle: 25%
- Skin: 5%

Cardiac Muscle Contractility

Cardiac Action Potential Plateau: Caused mainly by the activation of slow calcium channels (L-type calcium channels) and decreased permeability to potassium ions.
Slow Calcium Channels: Their activation in cardiac muscle prolongs depolarization, creating the plateau in the action potential. This is unlike skeletal muscle.
Purkinje Fiber Conduction: Purkinje fibers conduct electrical signals much faster than cardiac muscle fibers, ensuring efficient spread of the signal throughout the heart.
Refractory Periods:
- Absolute: The heart cannot be stimulated to contract regardless of the strength of the signal.
- Relative: The heart cannot be excited by a normal signal but can be stimulated by an especially strong signal.
Extracellular Calcium & Contraction: Contraction in cardiac muscle depends on calcium influx from the extracellular fluid, unlike skeletal muscle where calcium is primarily released from the sarcoplasmic reticulum.

Cardiac Cycle

Heart Rate & Cardiac Cycle Duration: Increasing heart rate decreases the duration of the action potential plateau, resulting in a shorter systole and diastole. It also reduces the relative filling time.
Cardiac Cycle Events:
- Ventricular Filling: Begins with passive filling followed by atrial contraction.
- Isovolumetric Contraction: Muscle contracts but no blood is ejected, pressure builds up to overcome aortic pressure.
- Ejection: Rapid ejection occurs during the first third of systole, followed by slower ejection.
Ejection Fraction: The percentage of blood ejected from the ventricle during each contraction, calculated as (EDV-ESV)/EDV, with a normal resting value of 60%.
Ventricular Pressures: The pressure in the right ventricle is much lower than the left during systole.
Preload & Afterload:
- Preload: End diastolic pressure when the ventricle is filled, reflecting the degree of tension at the start of contraction.
- Afterload: Pressure in the aorta (resistance in circulation), which the ventricle must overcome to eject blood.
Frank-Starling Mechanism: The heart's ability to increase stroke volume in response to increased preload, due to greater stretch and elastic energy, and increased contractile strength.

Cardiac Conduction System

Conduction Pathway: Electrical impulse originates at the SA node and travels through the internodal pathways to the AV node. It then progresses through the AV bundle, bundle branches, and lastly to the ventricular muscle, ensuring coordinated contraction.

Automaticity

Intrinsic Rhythm Rates:
- SA Node: 70-80 beats/minute
- AV Node: 40-60 beats/minute
- Purkinje Fibers: 15-40 beats/minute
Ectopic Beats: Originate from sites outside the SA node.
Escape Beats: Occur when the ventricle is not stimulated by impulses from the SA node and takes over the pacemaking role because of the intrinsic rate in the ventricle.
Intrinsic Heart Rate: (~70-90 bpm) Represents the heart rate in the absence of autonomic nervous system influence.

Autonomic Regulation

Sympathetic & Parasympathetic Distribution:
- Sympathetic: Innervate all parts of the heart.
- Parasympathetic: Primarily target the SA node and AV junctional fibers.
Parasympathetic Nerve: Vagus nerve.
Neurotransmitters:
- Sympathetic: Epinephrine (adrenaline) and norepinephrine.
- Parasympathetic: Acetylcholine.
Sympathetic Influence on Contractility: Increases contractile force through beta-adrenergic receptor stimulation, leading to increased calcium influx.

Heart Rate Terminology

Tachycardia: Faster than normal resting heart rate.
Bradycardia: Slower than normal resting heart rate.
Note: These terms merely describe heart rate and do not necessarily indicate pathology.

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Explore the fascinating concepts of Basal Metabolic Rate (BMR) and heat production in the human body. This quiz covers factors affecting BMR, the role of hormones, and normal oral temperature ranges during different states. Test your understanding of physiological processes essential for maintaining body function.