Bio 209 Ch 20B
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Define Cardiac Cycle
Events associated with a heartbeat
What are the events of a Cardiac Cycle
- 1. Atrial Systole
- 2. Ventricular Systole (Period of Isovolumetric Contraction)
- 3. Atrial Diastole
- 4. Ventricular Diastole
What is EDV?
End-Diastolic Volume: volume of blood at the end of disatolic systole
What occurs during Ventricular Systole?
- - Both ventricles contract
- - AV Valves close
- - Period of Isovolumetric Contraction
- - Opening of Semilunar Valve
- - Ejection of blood
What causes the AV Valves to close?
Back flow of blood
What is Isovolumetric Contraction?
Event in which ventricles contract and blood volume stays the same (because blood don't leave ventricles)
What is the importance of Isovolumetric Contraction?
It creates pressure within the ventricles, allowing blood to eject into the aorta and throughout the body
What causes the Semilunar Valves to open?
Higher pressure in L & R Ventricles than the Aorta & Pulmonary Trunk
Do both ventricles eject the same amount of blood?
What is ESV?
End-Systolic Volume: amount of blood remaining at the end of a Ventricular Systole
Define Stroke Volume
Volume ejected per beat by each ventricle (EDV - ESV)
Describe what occurs during Atrial Disatole
- 1. BP is lower in Atria than in Veins
- 2. Blood flows from Veins into Atria
- 3. Blood in Atria increases and BP increases
Describe what occurs in Ventricular Diastole
- 1. BP decreases in Ventricles
- 2. Blood flows back into Ventricles when Aortic pressure is higher than Ventricular pressure
- 3. Semilunar Valve closes when blood flows back
- 4. AV Valves open when Atrial pressure is higher than Ventricular pressure
- 5. Blood flows from Atria to Ventricles when AV Valves open
- 6. 3/4 of Ventricular filling occurs during Atrial Diastole
What causes the AV Valves to open? Close?
Open - Ventricular Pressure is LOWER than Atrial Pressure
Close - Ventricular Pressure is HIGHER than Atrial Pressure
What causes the Semilunar Valves to open? Close?
Open - L & R Ventricle pressures HIGHER than Aorta and Pulmonary Trunk pressure
Close - Back flow of blood from Aorta
How does increased HR affect the Relaxation Period?
Relaxation period decreases
How does increased HR affect blood flow through the Coronary Arteries?
Heart contracts more forcibly and requires more nutrients and oxygen
How does blockage of Coronary Arteries cause Angina?
If Coronary Arteries are blocked, blood flow during exercise may not be enough to supply cardiac muscle with enough Oxygen
What is Ausculation?
Listening to sounds within the body
What causes heart sounds?
Blood turbulance caused by closing of heart valves
What causes the first heart sound (lubb)?
Closure of AV Valves
What causes the second heart sound (dupp)?
Closure of Semilunar Valves
What is a Heart Murmur?
Abnormal heart sounds
Narrowing of the Mitral Valve
Backflow of blood from Ventricle into Atrium
What is Cardiac Output?
Volume of blood ejected from a ventricle each minute
Why does the heart rate increase as we exercise?
The demand for oxygen and nutrients increases, therefore heart rate increases
What is Stroke Volume?
Volume of blood ejected from one ventricle with each contraction (EDV - ESV)
Define Heart Rate (HR)
Heart beats per minute
What happens to the cardiac output if the stroke volume/heart rate increases?
What happens to the cardiac output if stroke volume/heart rate decreases?
What is Cardiac Reserve?
Difference between Cardiac Output at maximal exercise VS Cardiac output at rest (athletes have higher cardiac reserves)
What affects the cardiac output's: Preload, Contractility & Afterload?
- Preload: length of cardiac muscle fibers before contraction
- Contractility: force of ventricular contraction
- Afterload: pressure of blood in arteries
How does increasing Preload increase the length of cardiac muscle fibers?
Increasing cardiac fiber muscle length increases force of contraction
How does increasing the length of ventricular diastole and increasing venous return affect preload and therefore cardiac output?
Increasing length for ventricular diastole increases time for ventricular filling
Increasing venous return increases EDV
Define Positive Inotropic Agent
Agents that increases contractiliy
Define Negative Inotropic Agents
Agents that decreases contractility
Why does increased Afterload increase the work of the heart and EDV?
More blood is left in the ventricle after ventricular systole and EDV increases
How does a high EDV lead to congestive heart failure?
If EDV is large, cardiac muscle fibers are stretched beyond optimal length, which in turn can cause blood to back up into lungs or systemic veins, due to decreased ventricular contraction/increased EDV
What is Left Heart Failure?
Condition in which Left Ventricles does not pump blood efficiently and possibly lead to pulmonary edema because of back flow of blood
What is Right Heart Failure?
Condition in which Right Ventricle does not pump effectively and can lead to backflow of blood into systemic veins, leading to peripheral edema
How does the ANS affect HR?
Medulla Oblongata receives input from: limbic system, proprioceptors, chemoreceptors and baroreceptors
Sympathetic & Parasympathetic stimulation causes heart to increases & decrease
What are some hormones that affect HR?
Epinephrine, Norepinephrine, Thyroid Hormones
What kinds of Cations affect HR?
High levels of Na & K decreases HR
High levels of Ca increases HR
What are some factors that affect HR?
Age: HR decreases with age
Gender: females have slightly higher resting HR than males
Exercise: daily exercising may decrease resting HR
Temperature: heat (increases) & cold (decreases)
What is Tachycardia?
High resting HR
What is Bradycardia?
Low resting HR (less than 50 beats/min)
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