REVIEW Flashcards
Syncitium
All of the muscle fibers contract as one (do not act individually)
Fibrous insulator
Surrounds AV valve openings between the atria and ventricles
- helps separate contractions, so atria goes before ventricles
How does blood come back through the venous system?
Enters thru superior/inferior vena cava (carries oxygen poor blood from the body —> right atrium –> tricuspid valve (AV valve) –> right ventricle–> pulmonary valve –> pulmonary artery (off to the lungs) –> pulmonary vein (empties oxygen rich blood) –> left atrium –> mitral valve (bicuspid, left AV) –> left ventricle –> aortic valve –> aorta –> body
Pulmonary artery
Only place where deoxygenated blood is
- also occurs in the placenta for a short period of time
Pulmonary vein
Carries oxygenated blood
What are the semilunar valves?
Aortic (left) and pulmonary (right) valves
- 3 cusps (resembles Mercedes logo)
What are the bicuspid valves?
Just the mitral valve!
- has 2 triangular flaps
What are the tricuspid valves?
Right AV valve
- 3 irregular flaps
Where is contraction actually happening during the action potential curve?
The peak/plateau
Ventricular muscle AP
- phase 0: fast Na channels open, then slow Ca channels
- phase 1: K channels open (tip of peak)
- phase 2: Ca channels open more (plateau)
- phase 3: K channels open more (end of peak)
- phase 4: resting membrane potential
What is the difference between conduction system and cardiomyocytes?
Conduction system has slow, leaky Ca channels that are not found in cardiac myocytes (just fast Na channels)
Systole
Muscle stimulated by action potential and contracting
Diastole
Muscle reestablishing Na/K/Ca gradient and is relaxing
EKG
P: atrial wave
QRS: ventricular complex
T: ventricular repolarization
Right atrial pressure
Is generally low! (located on the low pressure side)
- diastole: blood comes in from great veins, passes thru ventricles
- contraction does not change pressure much
- when valves bulge back during peak of compression is the area of highest pressure
Ventricular pressure
- diastole: raises pressure slightly
- systole: isovolumic metric pressure (volume is not changing, just pressure)
Ventricular pressure needs to be higher than ______ in order to eject blood into the aorta
Aortic pressure
Aortic pressure
Peaks with ejection peak
- systole: aorta stretches to accomodate increase in volume
- elastic muscle maintains pressure, does not go back to 0 until you reach diastole
Incisura
At the start of relaxation, aortic valve closes and blood runs backward in the aorta
Sounds of the heart
- S1: AV valves close (start of systole)
- S2: aortic/pulmonic valves close
- S3: hear if you have watery blood splashing
- S4: end of diastole when atria contract (not heard unless you have hypertension)
Ejection fraction
Amount of blood that comes out
- should be around 60%
- used to calculate cardiac output
Cardiac output
Stroke volume x heart rate
Frank-Starling mechanism
Within physiological limits, the heart pumps all the blood that comes to it without excessive damming in the veins
- extra stretch on cardiac myocytes makes actin and myosin filaments interdigitate to a more optimal degree for force generation
Does the Frank-Starling mechanism have a limit?
Yes!
- if you bring back more blood than max cardiac output, you get backflow of blood
If you _____ cardiac muscle, then it performs more efficiently and you have stronger contractions
Stretch
Pathway of heartbeat
Begins in SA node –> internodal pathway to AV node –> impulse delayed in AV node (allows atria to contract 1st) –> AV bundle takes impulse into ventricles –> left and right bundles of Purkinje fibers take impulses to all parts of ventricles
What is the slowest place in the conduction pathway?
AV node! It pierces fibrous insulator to get signal into ventricles
- AV bundle is second slowest
- Purkinje fibers are the fastest (have to go the farthest in the shortest amount of time)
Conduction system
Regular, spontaneous action potentials (depolarization)
- SA node is the fastest (leakiest) to fire
- AV node next fastest to fire
- Purkinje fibers third fastest to fire
Conductance
Speed at which action potential is passed to the next cell
- Purkinje fiber is the fastest
- SA node/internodal pathways: medium speed
- AV bundles: medium slow
- AV node: slowest
Rhythmical discharge of sinus nodal fiber
Na leak causes resting potential to slowly increase to -40 (threshold) –> slow Ca channels open –> K channels open more –> after peak, it hits the sinus nodal fiber –> goes back to -50
SA node never goes as low as ______
Ventricular muscle fiber (will be at -80 due to specialized cells)
PR interval
Atrial depolarization
QT interval
Ventricular depolarization
Ventricular repolarization does not occur until ___
End of T wave
Lead 1
(-) right arm, (+) left arm
- looking at heart form the top down (0.5 mV)
Lead 2
(-) right arm, (+) left leg
- looking at heart from right side (1.2 mV)
Lead 3
(-) left arm, (+) left leg
- looking at heart from left side (0.7 mV)
First degree heart block
Incomplete block, AV node is slow to respond
Seen as a long space betwen P wave and QRS complex (prolonged PR interval)
PR interval cannot be longer than?
The RR input (the space between 2 heart beats)
Second degree heart block
- PR interval increases
- atria beat faster than ventricles (dissociated)
Mobitz type 1 and 2
Associated with incomplete second degree block
- type 1: PR gets longer with each beat until a beat is dropped
- type 2: some impulses pass thru the AV node and some do not = dropped beats
Horses have a mild _______ at rest
Second degree block
Third degree complete block
Total block thru the AV node or AV bundle
- P waves are completely dissociated from QRST complexes (AV dissociation)
- ventricles escape and AV nodal rhythm ensues
Normal rates of discharge
- sinus node: 70-80/min
- AV node: 40-60/min
- Purkinje: 15-40/min
Premature atrial contractions
PR interval is shortened if ectopic foci originating the beat are near the AV node –> impulse travels thru the AV node and back toward the sinus node = discharge of sinus node
- early contraction does not allow heart to fill with blood = low stroke volume and a weak radial pulse
Premature ventricular contractions
QRS is prolonged because impulse is conducted thru muscle, which has slow conduction
- QRS voltage is high because one side deoplarizes ahead of the other
- T wave is inverted due to slow conduction = area to first depolarize is also first to repolarize (opposite of normal)
Paroxysmal
Series of rapid heart beats that suddenly start and stop
- P wave is inverted if origin is near AV node
- occurs by re-entrant pathways
Atrial flutter
Single large impulse wave travels around atria in one direction
- atria contracts at 200-350/min
- AV node will not pass signal until 0.35 sec elapses after the previous signal
- atria may beat 2 or 3 times as rapidly as the ventricle
Atrial fibrillation
Mostly occurs without ventricular fibrillation
- causes by atrial enlargement due to AV valve dysfunction, results in long pathway of conduction which is favorable for circus movements
- decreased ventricular pumping
- irregular, fast HR due to irregular arrival of cardiac impulse at the AV node
Ventricular fibrillation
Circus movements occur when pathway is too long (dilated heart), if conduction velocity is decreased, if refractory period is shortened
- some parts of ventricles contract, others relax and little blood flows out of the heart (caused by electrical shock or cardiac ischemia)
Components of the circulation
- Venous side: 60%
- Arterial side: 20%
- Pulmonary: 10%
Arterioles
Control site for blood flow
- major resistance site of the circulation
The _____ have the largest total cross-sectional area of the circulation
Capillaries!!
Followed by venules, small veins, etc
Characteristics of blood flow
Usually flows in streamlines with each layer of blood remaining the same distance from the wall = laminar flow
- results in higher velocity in the center of the vessel, creating a parabolic profile
Volume-pressure relationships in circulation
Any given change in volume within the arterial tree results in larger increases in blood pressure than in veins
- when veins are constricted, large quantities of blood are transferred to the heart = increased cardiac output
Stroke volume
Increases in stroke volume increase pulse pressure, conversely decreases in stroke volume decrease pulse pressure
Arterial compliance
Decreases in compliance increases pulse pressure, and increases in compliance decrease pulse pressure
Capillary hydrostatic pressure
Force fluid outward thru the capillary membrane
Interstitial fluid pressure
Opposes filtration when valve is positive
Plasma colloid osmotic pressure
Opposes filtration causing osmosis of water inward thru the membrane
Interstitial fluid colloid pressure
Promotes filtration by causing osmosis of fluid outward thru the membrane
MIcrocirculation
Important in transport of nutrients to tissues
- site of waste product removal
- over 10 billion capillaries with surface area of 500-700 square meters perform function of solute and fluid exchange
- large sphincters over metarterioles to squeeze blood down
Net starling forces in capillaries
Net filtration pressure of 0.3 mmHg, which causes a net filtration rate of 2 ml/min for the entire body
- more fluid tends to leave capillaries into tissues than is returned
Acute control of local blood flow
Increases in tissue metabolism lead to increases in blood flow
Decreases in oxygen availability to tissues increases tissue blood flow
2 theories: vasodialtor and oxygen lack (demand)
Vasodilator theory
Increase tissue metabolism –> increase release of vasodilators –> decrease arteriole resistance –> increase blood flow
Vasodilators
CO2, lactic acid, adenosine, ADP compounds, histamine, K ions, H ions
- compounds diffuse to where sphincters are located causing them to relax and increase blood flow
Oxygen lack (demand) theory
Increased tissue metabolism or decreased oxygen delivery to tissues –> decreased tissue oxygen concentration –> decreased arteriole resistance –> increased blood flow
Sympathetic innervation of blood vessels
Innervate all vessels except capillaries, precapillary sphincters, and some metarterioles
- innervation of small arteries/arterioles allow sympathetic nerves to increase vascular resistance
Parasympathetic nervous system
Important in control of heart rate via vagus nerve
There is more sympathetic innervation on the _____
Venous side
- important because this is where most residual volume is located to increase cardiac output
Vasomotor center
VMC transmits impulses downward thru the cord to almost all blood vessels
- located bilaterally in the reticular substance of the medulla and the lower third of the pons
- composed of the vasoconstrictor area, vasodilator area, and sensory area
Anatomy of baroreceptors
Spray type nerve endings located in the walls of the carotid bifurcation called the carotid sinus and in the walls of the aortic arch
Signals from carotid sinus
Transmitted by Hering’s nerve to the glossopharyngeal nerves and then to the nucleus tractus solitarius of the medulla
Signals from the arch of the aorta
Transmitted thru the vagus into the NTS
Chemoreceptors
Chemosensitive cells sensitive to oxygen lack, CO2 excess, or H ion excess
- located in carotid bodies near the carotid bifurcation and on the arch of the aorta
- activation = excitation of the VMC
- not stimulated until pressure falls below 80 mmHg
Chemoreceptor activation
Decreased O2, increased CO2, or decreased pH –> chemoreceptors –> VMC –> increase sympathetic activity –> increase blood pressure
Effect of ECFV on arterial pressure
Increased ECFV –> increased blood volume –> increased mean circulatory filling pressure –> increased venous return of blood to the heart –> increased CO –> could stimulate increased arterial pressure directly, OR –> autoregulation –> increased total peripheral resistance
Where is renin made?
Renin is synthesized and stored in modified smooth muscle cells (juxtaglomerular cells) in afferent arterioles of the kidney
Renin is released in response to _____
Fall in arterial pressure
- acts on a plasma globulin called angiotensinogen to form angiotensin 1
A1
Converted to A2 by a converting enzyme (ACE) located in endothelial cells in the pulmonary circulation
Renin-Angiotensin System
Decreased arterial pressure –> renin –> renin substrate (angiotensinogen) –> angiotensin 1 –> converting enzyme (lung) –> angiotensin 2 –> renal retention of Na and H2O, vasoconstriction = increased arterial pressure, OR A2 is inactivated by agniotensinase
Sympathetic regulation of the circulation (exercise)
Brain and coronary has little effect - skin is dialated by temp - constriction of splanchnic and renal - non exercised muscle is constricted = increased leg flow during exercise *vasodilation overcomes sympathetic*
Coronary flow
225 ml/min
- epicardial vessels: can see on the outside of the heart
- subendocardial vessles: located on endocardial surface, interdigitae, is under the most pressure
Right and left coronary arteries
Come off the base of the aorta
- epicardial vessels wrap around the heart to supply the muscle
Changes in subendocardial coronary flow during the cardiac cycle
Subendocardial decreases drastically during systole, followed by rapid increase and hyperincrease at the start of diastole that evens out back to normal
- area under the most pressure!
Changes in epicardial flow during the cardiac cycle
Slight decrease at the beginning of systole, but quickly recovers by diastole
Immediate depressed pumping ability caused by acute moderate heart failure
- reduced cardiac output
- back up of venous return
- activates reflexes baroreceptor + chemoreceptor
- if severe: CNS ischemic response
Immediate compensation caused by acute moderate heart failure
- reflexes stimulate sympathetic response
- remaining normal cardiac muscle pumps harder
- maximum by 30 sec post- insult
Chronic responses to cardiac failure
- renal Na and H2O retention
- cardiac recovery (repair of muscle)
- ANP (atrial natriuretic peptide) = extra Na secreation
ANP
- normal C.O.
- RAP (right atrial pressure increased)
- resting HR increased
- air hunger/exercise intolerance
- weight gain from fluid retention
- reduced cardiac reserve
Progressive shock
Occurs 30 min after hemorrhage, will recover if given a transfusion around 60 min post-insult
Irreversible shock
Occurs during progressive stage if transfusion is not given
- happens 60-90 min post-insult
In fetal circulation ______ is higher than ______
Right atrial pressure; left atrial pressure
Ductus arteriosus
Shunt from pulmonary artery to aorta; also right to left shunt
Foramen ovale
Shunt from right to left atrium
- oval hole in the septum
- blood with highest O2 content to left ventricle to supply carotid and brain
- flow across about 1/2 cardiac output (300 ml/min/kg)
What are the 2 bypasses for the lungs in the fetal heart?
Foramen ovale and ductus arteriosus
What is the 2nd place in the arterial system that carries unoxygenated blood?
Umbilical arteries
1st heart sound (S1)
Lub
- AV valves close (mitral and tricuspid)
- lounder than S2
- low pitch
2nd heart sound
Dup
- aortic and pulmonary valves close
3rd heart sound
- low pitch
- caused by inrushing of blood into ventricles
4th heart sound
- atrial contraction late in diastole
- hard to hear with stethoscope, except in hypertensive patients with a thick left ventricle
Heart sounds heard on the left side of the body
PAM
- pulmonary, aortic, mitral
Heart sounds heard on the right side of the body
Tricuspid valve
You want to listen for ____ and ____ when grading murmurs
Timming - systolic/pan or holo - diastolic/ pan or holo - continuous - crescendo-decrescendo Loudness - grade 1-5 scale, or 1-6 scale
Grading murmurs
- point of maximal intensity (where the murmur is heard the loudest
- cardiac thrill
- low viscosity murmur due to anemia
- acquired vs congenital
Causes of murmurs
- stenosis: narrowing
- insufficiency: not sealing, leaky (regurgitation)
Congenital murmurs
Failure of heart formation during gestation
- patent ductus arteriosus
- interventricular septal defect
- interatrial septal defect
- tetralogy of fallot (have all 4)
Blood tissue barriers
Depend on structure of endothelial wall
- highly fenestrated: many compounds pass (liver)
- specific filtration (kidney glomerulus)
- very tight junctions: limited passage, only small molecules (brain)
What molecules pass thru the BBB?
- O2, CO2, Na, etc
- NO: proteins, drugs
- must pass thru pinocytotic vesicles
Cerebrospinal fluid flow
Choroid plexus in lateral ventircles –> foramen of Monro to 3rd ventricle –> aqueduct of Sylvius –> 4th ventricle –> foraminal of Magendie and Luschka –> subarachnoid space over brain and spinal cord –> reabsorption into venous sinus blood via arachnoid villi
