Mammalian Cardiac Cycle Flashcards
Human Heart Review
- 4 chambered
- pumps blood through the lungs to acquire O2 + expel CO2
- each side has one atrium and one ventricle
- asymmetrical as a result of the distance blood must travel in the two circuits
- right side sends blood to the pulmonary (smaller side)
- left side send blood to the systemic
Atrioventricular (AV)
set of one-way valves that separate each atrium and ventricle to prevent blood backflow
Semilunar (SL)
set of valves that separate each ventricle from its associated artery
Path of Blood in the Mammalian Heart
- right atrium receives DO-blood from the systemic circuit from 2 large veins (superior + inferior vena cava)
- DO-blood passes to the right ventricle through the right AV - a flap of connective tissue that opens in only one direction to prevent blood backflow
- After it is filled, the right ventricle pumps blood through the pulmonary arteries, passing through the right SL to the lungs for re-oxygenation
- blood passes through the pulmonary arteries, the right SL CLOSE to prevent backflow into the right ventricle
- left atrium receives oxygenation blood from the lungs via pulmonary veins
- O-blood passes through the left AV to the left ventricle
- after it is filled, the LV pumps blood out through the aorta, taking O-blood to the organs and muscles, passing through the SL to do so
- once pumped out the LV into the aorta, the left SL closes to prevent backflow ingo the left ventricle
Cardiac Cycle
the coordination of the filling + operating of the heart of blood by electrical signals that cause the heart to contract (systole) + relax (diastole); four stages:
1. Cardiac diastole
2. Atrial systole
3. Ventricular systole
4. Cardiac diastole
Cardiac Diastole (STEP ONE)
pre-start of the cycle - all four chambers are relaxed
- allows blood to flow into the heart unimpeded as AV valves are open + SL valves are closed
- PRE CARDIAC CYCLE
Atrial Systole (STEP TWO)
the atria connect and push blood into the ventricles
- ventricles are still experiencing diastole
- AV valves are open to allow blood flow from the atria to ventricles
- SL valves are closed to prevent backflow into the ventricles into the arteries
Ventricular Systole (STEP THREE)
atria relax and ventricles contract to push blood out of the heart
- AV valves close to prevent backflow from ventricles to atria - creates the ‘lub’ sounds (first heart sound)
- SL valves open to allow blood to exit ventricles into the arteries
Cardiac Diastole (STEP FOUR)
heart enters CD in the final stage when both atria and ventricles are relaxed
- SL valves are closed and complete the cycle - creates the ‘dub’ sound (second heart sound)
Cardiomyocytes
specialized muscle cells whose coordination contraction cause the cardiac cycle
- properties between skeletal and smooth muscle
- striated like skeletal muscle
- pump rhythmically + involuntarily (without nervous system stimulation) like smooth muscle
Intercalated Discs
mediate the involuntary contraction of cardiomyocytes; spread membrane depolarization (contraction) from one cardomyo to the next
- contract autonomously if given enough nutrients and electrolytes
Cardiomyocyte Regulation
regulated by
- pacemaker cells
- cardiac action potentials
- AV node
Pacemaker Cells
responsible for initiating the cardiac cycle
- located at the sinoatrial (SA) node
- depolarize autonomously, creating a CARDIAC ACTION POTENTIAL
Sinoatrial (SA) Node
upper back wall of the right atrium just below where the superior vena cava joins the right atrium
Cardiac AP
specialized action potential/electrical pulse; spreads through the 2 atria via the intercalated discs that link the cardiomyocytes, causing the two atria to contract in unison
Atrioventricular (AV) Node
located between the right atrium + right ventricle; as the atria contract, the AP reaches this node which pauses the AP slightly before it spreads to the ventricle walls
- this pause allows the atria to empty completely into the ventricles before they contract to ump out the blood to the arteries
Ventricle Contraction
coordinated by a series of specialized structures that channel the AP through specific pathways within the ventricles
- AV node -> bundle of His -> left and right bundle branches -> Purkinje fibers -> ventricles contract
Electrocardiogram (ECG)
machine that can measure the electrical currents generated by the cardiac action potential
Cardiac Output
the volume of blood pumped by the heat in one minute
- heart rate: number of heart contractions per minute
- stroke volume: volume of blood pumped into the aorta per left ventricle contraction
Cardiac Output Formula
(heart rate) X (stroke volume)
Cardiac Output Factors
can be increased by any process that increases either heart rate or stoke volume
- increase heart rate from exercise
- increase stroke volume if the heart contracts with greater strength / blood circulation speeds up that causes more blood to enter the heart between contractions
Baroreceptors
type of mechanoreceptor that detects drops in blood pressure in the aorta; signal the brain stem, initiating an AUTOMATIC NERVOUS SYSTEM response:
- cardiac output increases due to increased stroke volume and heart rate
- arterioles constrict the capillary beds in non-critical tissues , diverting blood to more critical organs
- veins constrict, lowering the overall cross-sectional area of the circulatory system
