CFB L2 Flashcards
What is the cardiac cycle?
- Sequence of events during a single heart beat
- Consist of atrial and ventricular systole and diastole. Systole = contraction of chamber, diastole = relaxation of chamber
- 1/3 systole 2/3 diastole
- Atria + ventricles relax and contract alternately
- Blood is ejected from area of higher pressure ot area of lower pressure, from atria to ventricles, from ventricles to systemic + pulmonary blood vessels
What are the 3 phases of the cardiac cycle?
- Isovolumetric relaxation
- Ventricular filling
- Ventricular systole
Isovolumetric Relaxation
Early diastole
- Ventricles relax + therefore stretch, therefore, blood pressure in ventricles decreases
- Ventricular pressure < less than arterial pressure in aorta and pulmonary trunk
- Backflow of blood from aorta + pulmonary trunk into ventricles
- Forces the semi-lunar valves shut, this is because semi-lunar valves close inwards and the blood pushes them backwards
- Blood rebounds off closed valves, leading to blood volume to slightly increase at the valve, leading to slight increase aortic pressure - DICROTIC WAVE
- Closure of semi-lunar valves is followed by a short period of closure of all valves (SL, AV)
- Therefore, no change in residual volume of blood in ventricles (thats why called isovolumetric relaxation)
- As ventricular relaxation + stretching continues, ventricular pressure drops even more
- If ventricular pressure drops even further below arterial pressure + blood continues to fill up in atria, pressure over AV valves increases, valves open
NEXT PHASE - VENTRICULAR FILLING
AV VALVES - CLOSED
SL VALVES - CLOSED
Ventricular filling
Blood from atria flows through as soon as AV valves open into ventricles - from high to low pressure
3 stages:
- Rapid ventricular filling, passive filling
-75% of total filling volume - Diastasis
Slow ventricular filling, less blood ejected into ventricles
-5% of total filling volume
-Occurs when rapid ventricular filling slows down before atrial systole
These two stages occur while ALL chambers in diastole - therefore, relaxation period
- Atrial systole - Active filling
- Atria contract, therefore, blood in atria under even higher pressure
-Blood forces open AV valves, blood pushed through AV valves into ventricles from region of high to low pressure
End Diastolic Volume (EDV)
The total volume of blood in each ventricle after ventricular diastole
just before ventricular systole (contraction)
130ml in each ventricle
DIAGRAM SHOWING VENTRICULAR FILLING
You can see
-AV valves open
-SL valves shut
-Blood flow from atria to ventricles
Ventricular Systole
- Ventricular systole (ventricles contract), atrial diastole (atria relax)
- When ventricles contract, blood is pushed from apex to base, where the AV valves are
- Creating pressure at AV valves, forcing them shut
- All valves shut at this stage - SL, AV
- Isovolumetric contraction - equal residual volume of blood in both ventricles
- More ventricular systole occurs
- Eventually, pressure in left ventricle exceeds pressure in aorta, therefore, aortic semi-lunar valve is forced open, blood is ejected from left ventricle into aortic branch
- Simultaneously, eventually, pressure in right ventricle exceeds pressure in pulmonary trunk, this forces pulmonary semi-lunar valve open, blood is ejected from the right ventricle into pulmonary trunk
- Pressure in left ventricle 120 mm Hg, right ventricle 30 mm Hg
- THEN Ventricles relax, therefore expand, pressure in ventricles drops, isovolumetric relaxation starts again
Ventricular Ejection
ejection of blood from ventricles during ventricular systole while SL valves open
End systolic volume
Vol of blood in ventricles after ventricular systole
Stroke volume
Vol of blood ejected from each ventricle during 1 heart beat
SV = EDV - ESV (ml)
Ejection Fraction (EF)
fraction/% vol of blood ejected by ventricles in one ventricular systole (contraction)
Ef = SV/EDV x100
Diagram of ventricular systoloe
- SL valves open
- AV valves closed
- Direction of blood flow: blood flowing from right ventricle to pulmonary trunk, blood flowing from left ventricle to aorta/aortic branch
Cardiac output
Volume of blood pumped by the heart per min (ml/min)
Stroke vol (ml) x heart rate (b/m)
Not constant - depends on body’s oxygen demand
Factors affecting cardiac ouput
Factors affecting cardiac output include factors which increase stroke volume and heart rate, including vigorous exercise and carbon monoxide.
Preload and Afterload also have an effect.
Preload
The amount the ventricles are streatched at end of diastole - more blood = more stretch
Afterload
The resistance needed by LEFT ventricle to overcome the force which opens the aortic semi lunar valve and allows blood to flow through into aorta and enter systemic circulation
Cardiac Reserve
Difference between resting cardiac output and maximum heart capacity
In people who have severe heart failure, they have no cardiac reserve
healthy adults: 4x5 cardiac output
How does blood circulate in the human body?
Blood in human body circulates in the cardiovascualr system (CVS) through 2 circulations:
- Systemic circulation
- Pulmonary circulation
Breifly describe systemic circulation
GREATER CIRCULATION (because higher pressure)x
Starts at the left ventricle and ends at the right atrium.
Oxygenated blood is pumped from left ventricle to all body tissues
At body tissues, blood loses its oxygen + becomes deoyxgenated - gains CO2
This deoxygenated blood then returns to the heart via right atrium
State the 3 compartments of systemic circulation
- Arterial system
- Venous System
- Capillaries
What is the main vessel of the arterial system in systemic circulation
Aorta
What are the 3 divisions of the aorta?
- Ascending aorta
- Aortic arch
- Descending aorta
Describe the structure of the ascending aorta
The aorta leaves the left ventricle as the ascending aorta
Just above the aortic valve, ascending aorta branches into smaller vessels; aortic sinuses
These give rise to left and right coronary arteries
These further branch to supply the heart
Describe the structure of the aortic arch
Has 3 branches (arteries):
- Brachiocephalic, branches into right subclavian and right common carotid - supplies right side of head, chest wall, neck, right arm
- Common Carotid - supplies left side of head, chest wall, neck, left arm
- Subclavian - supplies left side of head, chest wall, neck, left arm
Describe the structure of the descending aorta
Branches into
- Thoracic aorta
- Abdominal aorta
State the general function of the descending aorta
Supply:
- Pelvic organs
- Abdomen (Abdominal organs)
- Chest (thoracic organs)
Describe the structure and function of the thoracic aorta
To supply the chest / thoracic area
Branches into
- Subcostal artery
- Intercostal artery
- Inferior bronchiol artery
- Superioir bronchiol artery
Describe the structure and function of the abdominal aorta
To supply abdominal organs + pelivic organs
- Left common iliac artery
- Right common illiac artery
Function of capillaries in systemic circulation
Connect arterial + venous systems
by creating microcirculation system
What is the main vessel in the venous system
Vena cava
Describe the struture of the vena cava
Superior Vena Cava
Inferior Vena Cava
Superior Vena Cava
Drains venous blood of head, neck, upper limbs, chest to heart
Inferior Vena Cava
Drains venous blood from abdominal organs, pelvic organs, lower limbs to heart
State the function of the coronary sinus
Drains venous blood from walls of heart to right atrium
Briefly describe pulmonary circulation
LESSER CIRCULATION (because low pressure)
Starts at right ventricle, ends at left atrium.
Deoxygenated blood pumped from right ventricle to lungs via pulmonary artery
Pulmonary arteries branch into pulmonary capillaries in the lungs, this is where gas exhange occurs of O2 and CO2 between blood + air in alveoli
Pulmonary capillaries then branch into pulmonary veins which transport bloood back to the heart (left atrium)
Blood then flows from left atrium to left ventricle, ready for systemic circulation to occur
Diagram of pulmonary circulation
- look at the vessels involved (pulmonary artery, pulmonary veins, pulmonary capillaries)
- direction of blood flow (right ventricle to left atrium)
-alveoli
Summary of systemic circulation
Left ventricle
Aorta
Systemic arteries
Systemic capillaries
Systemic veins
SVC
IVC
Right atrium
Summary of pulmonary circulation
Right ventricle
Pulmonary trunk
Pulmonary artery
Pulmonary capillaries
Pulmonary veins
Left atrium
Explain one full circulation of blood in the CVS
1 full circulation consists of both circulations, systemic and pulmonary.
These circulations are in series. Blood flows through one and then the other.
This increases efficiency of respiration
Due to the circulation being in series, the volume of blood pumed by both ventricles needs to be equal - pulmonary blood flow must equal systemic blood flow
This is achieved by Frank Starling mechanism
