Metabolism Week 4 Study Guide

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Questions and Answers

Which factor is least likely to contribute to an increase in basal metabolic rate (BMR)?

Chronic malnutrition (correct)

Elevated growth hormone levels

Fever

Increased muscle mass

How does the body primarily generate heat during physical activity?

Enhanced blood flow to muscles

Respiratory heat production

Heat from ATP hydrolysis (correct)

Increased heart rate

What is the approximate range of oral temperatures for a healthy person at rest?

98 to 100.4°F

95 to 98.6°F

97 to 99.5°F (correct)

96 to 99.5°F

Which hormone significantly contributes to the increase in metabolic rate among those with higher BMR?

Thyroxine Signup and view all the answers

Which of the following conditions is likely to decrease basal metabolic rate (BMR)?

Inadequate caloric intake Signup and view all the answers

What does tachycardia indicate in a resting heart rate context?

A faster than normal heart rate at rest Signup and view all the answers

Which neurotransmitter is released by the sympathetic nerves to increase heart rate and contractility?

Norepinephrine (NE) Signup and view all the answers

What part of the heart receives the parasympathetic supply from the vagus nerve?

SA node and AV junctional fibers Signup and view all the answers

How does the sympathetic nervous system increase the contractile force of cardiac muscle?

Via beta adrenergic receptor stimulation, enhancing calcium influx Signup and view all the answers

Which of the following statements about bradycardia is correct?

It represents a slower than normal heart rate at rest Signup and view all the answers

Which of the following correctly describes the flow of blood through the heart starting from the vena cava?

Vena cava → Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Valve (Semilunar) → Pulmonary Artery → Lungs → Pulmonary Vein → Left Atrium → Mitral Valve → Left Ventricle → Aortic Valve → Aorta Signup and view all the answers

What is a unique structural feature of cardiac muscle compared to skeletal muscle?

Cardiac muscle fibers are shorter and have intercalated discs. Signup and view all the answers

How do intercalated discs function within cardiac muscle tissue?

They facilitate the rapid diffusion of ions between cells for electrical conduction. Signup and view all the answers

What role do papillary muscles play in heart function?

They support the closure of the AV valves by preventing regurgitation. Signup and view all the answers

Which statement about the differences between AV valves and semilunar valves is accurate?

Semilunar valves have greater strength due to mechanical abrasion. Signup and view all the answers

How is blood distribution to the brain characterized during rest?

Blood flow to the brain remains constant in absolute volume. Signup and view all the answers

What percentage of total blood flow is directed to the coronary arteries at rest?

5% Signup and view all the answers

What happens to blood flow distribution to the kidneys during exercise?

It remains constant at 25%. Signup and view all the answers

What mechanism specifically prolongs depolarization in cardiac muscle during an action potential compared to skeletal muscle?

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

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

Faster than cardiac muscle fibers Signup and view all the answers

What is the state of the heart during the absolute refractory period?

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

Why is extracellular calcium concentration particularly critical for cardiac muscle contraction?

Cardiac muscle relies heavily on extracellular calcium compared to skeletal muscle. Signup and view all the answers

What differentiates the relative refractory period from the absolute refractory period in cardiac muscle?

The heart can contract with a strong stimulus during the relative period. Signup and view all the answers

How does vasoconstriction affect cardiac muscle performance during cold temperatures?

It can initially reduce blood flow to cardiac muscle. Signup and view all the answers

In terms of the cardiac cycle, what occurs with the duration of the action potential when heart rate increases?

Duration of action potential decreases significantly. Signup and view all the answers

What is the physiological significance of vasodilation during hot temperatures?

It facilitates heat elimination during exercise. Signup and view all the answers

What happens to diastole time with an increased heart rate?

It decreases Signup and view all the answers

What role does atrial contraction play in ventricular filling?

It accounts for approximately 20% of ventricular filling Signup and view all the answers

During the cardiac cycle, when does isovolumetric contraction occur?

Before the ejection period starts Signup and view all the answers

What is the ejection fraction, and what is its typical value at rest?

The fraction of end-diastolic volume ejected, normally 60% Signup and view all the answers

How do right and left ventricular pressures compare during systole?

Right ventricular pressures are about 1/6th that of the left Signup and view all the answers

Which mechanism causes the rapid filling period in the ventricles?

Increased atrial pressure pushes AV valves open Signup and view all the answers

What does preload refer to in the context of the cardiac cycle?

End diastolic pressure when the ventricle is filled Signup and view all the answers

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

Pressure is highest during the first third of systole Signup and view all the answers

What physiological consequence results from increased afterload on the ventricles?

Increased ATP consumption to generate contractile force Signup and view all the answers

How does the Frank-Starling mechanism primarily enhance cardiac output?

Through increased diastolic filling leading to greater stroke volume Signup and view all the answers

Which statement accurately describes the electrical conduction pathway in the heart?

The Sinoatrial node initiates the conduction and is the fastest Signup and view all the answers

Which intrinsic heart rate is associated with the Purkinje fibers?

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

What defines escape beats in the cardiac rhythm?

Impulses that originate from non-SA nodal tissue Signup and view all the answers

What is the significance of greater stretch in the heart according to the Frank-Starling law?

It increases elastic energy for stronger contractions Signup and view all the answers

What distinguishes the intrinsic rhythm of the heart when affected by the autonomic nervous system?

It allows the heart to beat at a rate unaffected by external stimuli Signup and view all the answers

What is the primary role of a higher diastolic blood pressure in relation to afterload?

It signifies increased work requirement for the ventricles Signup and view all the answers

Study Notes

Metabolism Overview

Basal Metabolic Rate (BMR) represents the minimum energy required for the body to function at rest.
Influencing factors of BMR include muscle mass, hormones, fever, sleep, nutrition, sex, and age.

Factors Influencing BMR

Muscle Mass: More muscle leads to a higher BMR due to increased energy requirements for maintenance.
Hormones: Growth hormone, testosterone, and thyroxine enhance metabolic rate.
Fever: Increases metabolic rate as the body works to fight off illness.
Sleep: Decreases metabolic rate, reflecting reduced energy needs during rest.
Malnutrition: Reduces BMR, as the body becomes more efficient in energy use.
Sex and Age:
- Females and older individuals typically have a lower BMR.
- Key factors include differences in muscle mass, adipose tissue, and hormonal variations across sex and age.

Heat Production in the Body

Approximately one-third of energy from ATP hydrolysis is converted to heat.
Microscopic friction from blood flow and musculoskeletal movements also generates heat.

Temperature Ranges for Healthy Individuals

Oral Temperature:
- Rest: Approximately 97 to 99.5°F
- Exercise: Approximately 101 to 104°F
- Cold Conditions: Specific temperatures not provided.
Rectal temperature generally reflects core body temperature and is typically higher than oral measurements.

General Cardiac Anatomy and Function

Blood flow sequence: vena cava → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary artery → lungs → pulmonary vein → left atrium → mitral valve → left ventricle → aortic valve → aorta.
Cardiac muscle features intercalated discs, allowing rapid ionic communication, unlike skeletal muscle.
Papillary muscles and chordae tendinae prevent AV valves from bulging into atria, ensuring unidirectional blood flow.
AV valves are thinner, while semilunar valves are sturdier and allow faster blood flow due to less mechanical abrasion.

Blood Flow Distribution at Rest

~15% of blood flows to the brain, decreasing during exercise.
~5% goes to coronary arteries, increasing proportionally during exercise to meet myocardial needs.
~25% is directed to kidneys, crucial for vascular resistance adjustment.
~25% reaches the GI tract, significantly reduced during physical activity.
~25% supplies skeletal muscle, greatly increasing during exercise.
~5% to skin, varying with temperature; vasoconstriction in cold, initial exercise, and vasodilation in heat.

Cardiac Muscle Contractility

Action potential plateau in cardiac muscle differs due to L-type calcium channels and reduced potassium permeability.
Purkinje fibers conduct signals faster than cardiac muscle fibers, facilitating rapid contraction throughout the heart.
Absolute refractory period means no contraction stimulation is possible, while relative refractory period allows stimulation by strong signals.
Extracellular calcium plays a more significant role in cardiac contraction compared to skeletal muscle, which relies on sarcoplasmic reticulum.

Cardiac Cycle

Increased heart rate results in shorter action potentials, decreased systole and diastole durations, and less filling time.
Atrial contraction accounts for ~20% of ventricular filling with increased pressure facilitating rapid ventricular filling.
Isovolumetric contraction occurs to build pressure for overcoming aortic and pulmonary artery resistance.
Ejection fraction (EDV-ESV)/EDV is typically around 60%, indicating efficiency.
Right ventricular pressure is significantly lower than left ventricular pressure during systole (1/6th).
Preload reflects end-diastolic pressure, while afterload is the pressure against which the ventricles must contract.
Frank-Starling mechanism indicates that greater blood volume enhances contractile strength and stroke volume.

Conductive System Anatomy

Electrical conduction pathway: SA node → internodal pathways → AV node → AV bundle → branches into smaller Purkinje fibers → ventricular muscle.

Automaticity

SA node (70-80 bpm) is the primary pacemaker, followed by AV node (40-60 bpm) and Purkinje fibers (15-40 bpm).
Ectopic beats arise from outside the SA node, and escape beats occur when the ventricle independently contracts due to lack of stimulus.
Intrinsic heart rate is 70-90 bpm without autonomic influence.

Autonomic Regulation

Sympathetic nerves innervate all heart regions; parasympathetic nerves primarily influence the SA node and AV junction.
Vagus nerve facilitates parasympathetic activities.
Sympathetic neurotransmitter norepinephrine increases heart rate and contractility, while parasympathetic acetylcholine decreases it.

Heart Rate Terminology

Tachycardia denotes a resting heart rate faster than normal; not to be confused with exercise-induced increases.
Bradycardia indicates a resting heart rate slower than normal.
Tachycardia and bradycardia are descriptive terms; they may or may not signify underlying health issues.

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Description

This study guide focuses on metabolism, specifically the concept of basal metabolic rate (BMR). It discusses the minimum energy required for survival, factors influencing BMR, and the effects of muscle mass and hormones on metabolic rate.