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Blood vascular system consists of (3, 5)
- Blood vessels (arteries, arterioles, capillaries, venuoles, veins)
functions of cardiovascular system (3)
- distribute and collect blood to and from organs and tissues.
- Distribution, Regulation, Protection
Blood functions in distribution (4)
- Supplies oxygen
- supplies nutrients
- removes waste and CO2
- transports hormones
Blood function in regulation (3)
- Regulates body temperature
- regulates pH
- Regulates blood volume to supply efficient circulation to cells, tissues, organs and systems
Blood functions in protection (2)
- prevents blood loss
- prevents infection with WBCs, complement and antibodies.
Placement of heart
- Dogs and cats ribs 3-7, horses ribs 2-6. Great vessels in base, apex points caudally, ventrally, a little left.
- (left) low P high A low M
- (right) High A low T
area around heart. Cranial, Middle (contains heart), caudal.
Which heart vessels have no valves?
Pulmonary veins or vena cavae. Contaction compresses to prevent backflow.
Sac around heart and layers of heart
- Pericardium: (out to in) fibrous, parietal serous, visceral serous (same as epicardium)
- Endocardium (continuous with tunica interna of great vessels)
What was wrong with Gertrude? Cow, arched back, grunting, "anxious expression", reluctant to move
Traumatic pericarditis. Nail or wire eaten, wanders from reticulum to pierce pericardium. Inflammation constricts, causing heart failure.
How do valves work?
Upon contraction, chordae tendinae becomes firm, papillary muscles contract and cusps are pulled open. Cannot pull the other way due to chordae tendinae, so one-way blood flow with no everting.
Higher pressure system in circulatory
Left system (pumps oxygenated blood from heart into aorta)
Layers of blood vessels
- Tunica interna (endothelium. Simple squamous. Some big vessels have sub-endothelium and basement membrane)
- Tunica media (smooth muscle controlled by sympathetic nervous system)
- Tunica externa (fibrous with collagen. Protect, anchor, hold lymph, nerves, vaso vasorium)
Capillaries only have
veins or arteries are bigger?
Lumen of veins is bigger, arteries have bigger walls, more smooth muscle and elastic tissue
who has more elastic tissue and smooth muscle?
Who has more endothelium?
Nobody--arteries, veins and capillaries are the same.
Who has higher pressure?
- Biggest vessels that carry oxygenated blood away from heart. Thicker and more elastic pressure maintains BP near the heart. Dampen BP changes. Elastic or conducting. Torturous. Smooth muscle and elastic tissue.
- Low compliance, high recoil
use resistance (muscle to regulate flow of blood) to make systemic blood pressure. Many have sphincter for adjustable resistance.
resistance and where it is greatest
arterioles use muscle to regulate blood flow, some with a sphincter.
- smallest vessels going from arteriole to venule. Only contain tunica intima, RBCs must go single-file, contain tiny pores or clefts to allow exchange.
- Continuous, Fenestrated or Sinusoid
- Move with diffusion or bulk flow
- Not high resistance due to branching.
in skin and muscle, uninterrupted, contain tight junctions and tiny pores.
oval pores between endothelial cells in capillaries that increase leakiness. Found in choroid plexus, ciliary process of eye, endocrine glands, kidney, small intestine.
HUGE fenestrations, large irregular lumens and holes in endothelial cells. No basement membrane makes them very leaky. Found in liver, bone marrow, lymphoid tissue, anterior pituitary and parathyroid.
- Simple: O2, CO2, glucose, amino acids, hormones
- Water: diffusion (osmosis), bulk flow (hydrostatic pressure)
- Filtration (outward flow)
- Reabsorption (from interstitial to capillaries)
vary in size, from capillaries to veins
- distensible, major reservoir vessels (capacitance). Thinner walls with less elastin and muscle than arteries. Large lumen, low-pressure system. 70% of blood volume in veins.
- Have small valves: one-way folds of interna to prevent backflow, squeezed by skeletal muscle around vein.
Where is blood flow slowest
what part of blood circulation has highest surface area
why does velocity of blood increase after capillaries
venules and veins have skeletal muscles pushing blood towards heart
vessel diameter is greatest in
veins, then arteries
cross-sectional area is greatest in
average blood pressure is greatest in
Velocity of blood flow is greatest in
arteries/arterioles, then veins. Lowest in capillaries
Where is most blood when resting
veins--70%. Large lumen, thin walls
Where do vena cavae drop blood
right side of heart
Which circulatory systems work in series
pulmonary and systemic, alternate.
Which areas have a portal system and what is it
- Where blood goes through two capillary beds
- kidney, liver, brain
which circulatory system is parallel
systemic. Sends blood to many areas at the same time, all happen together, parallel
Blood from GI goes first to
liver, to be filtered before systemic circulation. Portal system for max filtration/exchange
- aorta to celiac artery to hepatic artery to liver (capillary bed) to hepatic vein to caudal vena cava to heart.
- digestive tract arteries to capillary bed to hepatic portal vein to liver (capillary bed) to hepatic vein to caudal vena cava to heart.
- volume flowing through a given structure per unit time (mL/min)
- Blood flow = DP (change in pressure, pressure gradient)/resistance
- Resistance up, BF down; pressure up, BF up
- the pressure that blood exerts across the blood vessel wall
- force per unit area (mmHg)
- highest in aorta, lowest in right atrium
opposition to flow: generally encountered in the systemic circuit. peripheral resistance (PVR)
Mean circulatory filling pressure
pressure when heart stops. not zero because of recoil of blood (arteries)
Blood pressure changes through system
Highest in arteries, slows as friction uses up energy. How much depends on how much friction or resistance. Lowest in veins/vena cavae.
Sources of resistance
- Blood viscosity: (too many RBCs or dehydration raises viscosity, raises resistance, lowers flow. Hemorrhage/anemia causes opposite)
- Total blood vessel length: (longer vessel causes greater resistance)
- Blood vessel diameter: most important. Flow is inversly related to diameter (higher lumen size makes less resistance)
sphincter muscle causes contraction or dilation, allowing ateriole to adjust resistance. Arteriole walls are muscular.
Unidirectional flow of veins
- pumping action of skeletal muscle contraction
- one-way valves
- respiratory pump
What part of cardiac cycle has highest BP?
Left ventricular systole (~120)
pushback in arteries caused by thick, strong walls that accepts an increase in pressure and sustains BP during heart distole. Arteries are elastic.
what part of cardiac cycle has lowest BP
Cardiac cycle, starting with late distole
- AV valves are open, semilunar valves are closed.
- Atrial systole. Blood fills ventricles. End diastolic volume reached. Max blood in heart.
- Ventricle contracts. Increase of pressure, blood is pushed back towards atria. AV valves are closed.
- Isovolumic ventricular contraction.
- Pressure in ventricles is higher than aorta/pulmonary trunk, semilunar valves are pushed open. Blood rushes into aorta/pulmonary trunk. aortic pressure increases, ventricular pressure decreases, ventricle starts to relax.
- Ventricular pressure below aorta/pulmonary pressure, blood tries to backflow, semilunar valves close
- End systolic volume-minimum blood in heart. All valves closed.
- Isovolumic ventrical relaxation.
- blood is entering atria through non-gated pulmonary vein/vena cavae. Pressure in atria greater than pressure in ventricle pushes AV valves open. Late diastole.
2 ways to check BP
- arterial blood pressure (mmHg)
- central venous pressure (CVP)(cmH2O)--interthoracic vena cava
- 1 mmHg = 1.36 cm H2O (not on test)
- wave of pressure that travels through arterial walls when left ventricle ejects blood into aorta.
- Clinical indicator of the rate, regularity and strength of heartbeat.
Where to take pulse in dogs, cats, sheep, goats, horses, large animals
- dog/cat/sheep/goat: femoral artery (inguinal)
- horses: digital or facial arteries
- large animals: coccygeal artery (tail)
Herat sound one
close of AV valves. beginning of systole
Heart Sound 2
close of semilunar valves. End of ventricular systole
space between first and second heart sound.
End diastolic volume (EDV)
maximum blood in heart, when atria is in systole and ventricle is in diastole.
Isovolumic ventricular contraction
when all doors to ventricle are closed and max blood is inside (EDV)
End systolic volume (ESV)
minimum blood in heart, blood left after ventricle contracts in systole.
Isovolumic ventricular relaxation
when all doors to ventricle are closed and minimum blood is inside (ESV)
Cardiac output (CO)
- the quantity of blood pumped by the left ventricle into the aorta EACH MINUTE
- CO=SV x HR
- altering stroke volume or heart rate will alter cardiac output
Stroke Volume (SV)
- the quantity of blood pumped by the left ventricle into the aorta with EACH VENTRICULAR CONTRACTION
- CO=SV x HR
- SV = EDV - ESV
- altering stroke volume will alter cardiac output
Cardiac output equation
- CO = SV x HR
- Cardiac output = stroke volume x heart rate
Distribution of cardiac output between resting and exercising animal
- Brain stays the same, muscles increase, heart increases a little, gut/renal decreases.
- Determined by resistance, so arterioles dilate or contract
Stroke volume equation
Stroke volume = end diastolic volume - end systolic volume
Factors that regulate stroke volume by increasing end diastolic volume
- Diastolic Filling Time
- The initial stretching of the cardiac myocytes prior to contraction (sarcomere length). More blood in stretches sarcomere. Less, no stretch.
- Measured by Left ventricular end diastolic pressure (LVEDP)
- changes end diastolic volume and therefore stroke volume and cardiac output
Left Ventricular end diastolic pressure
- The pressure exerted on the walls of the left ventricle at the end of diastole.
- means of measuring sarcomere length in the heart (to measure preload).
- Accepted as measurement of preload.
Effects of preload on EDV, SV
Preload increases, EDV increases, SV increases
Starling's Law of the Heart
- The more the heart is filled during diastole, the greater the volume of blood is pumped out.
- (higher volume of incoming blood stretches the vessels, causing a greater force of contraction)
- Increased preload or LVEDP=increased EDV = stretched muscle fibers = increased contractility = increased stroke volume = increased Cardiac output
- a measure of the ease with which the ventricular walls stretch to accommodate incoming blood during diastole
- Increase in compliance = increase in End diastolic volume = increase in stroke volume = increase in cardiac output
diastolic filling time
- The length of time available for ventricular filling during diastole. Increase increases end diastolic volume. (affected by heart rate).
- Increase filling time, increase stroke volume
Factors to decrease end systolic volume to increase stroke volume
- Empty the ventricles more completely during systole:
- pumping ability of a ventricle.
- Increased empties the ventricle more and decreases end systolic volume, increasing stroke volume without increasing end diastolic volume
- Sum of all forces opposing ventricular emptying during ventricular systole
- Dilation of arteries causes an decrease in afterload and an increase in stroke volume
- Contraction of arteries causes an increase in afterload and a decrease in stroke volume.
Peripheral vascular resistance (PVR)
the impedance to blood flow through the systemic arteries caused by constriction of the arterioles. (determined by arterioles)
Arterial blood pressure equation
- Arterial BP = CO x PVR
- Arterial Blood pressure = Cardiac output x Peripheral Vascular Resistance
Normal arterial BP determination and values
- take 5-6 recordings and average.
- Listen to artery, put a cuff on until you can't hear, release pressure, first time you hear is systolic
- Cat is high if over 160 mmHg
- Dog is high if over 170-189 mmHg
interconnected mass of fibers with many nuclei but no separate membranes. Atria and ventricles function as two separate syncytia separated by a fibrous band
Why do atria and ventricles go into systole and diastole separately?
Action potential has to go around fibrous band separating syncytia, then through very few gap junctions to give ventricles time to fill.
Why is the action potential so long in heart muscle?
Ca channels instead of Na makes longer depolarization period, then K channels open even more slowly. This provides a longer absolute refractory period and prevents tetany.
2 types of cells in cardiac action potential
- autorhythmic: do not have resting membrane potential, drift toward threshold on their own (SA node)
- Nonpacemaker: resting potential, long action potential due to calcium and slow potassium
Where do Ca ions come from to contract the heart?
Sarcoplasmic reticulum and extracellular fluid
drug that helps with heart failure. Slows down Ca removal from cytosol to increase heart contractions. Stops sodium potassium pump so Ca won't exit cell.
Cardiac conduction system
- generates rhythmic regular action potentials
- conducts action potentials through myocardium (organized, synchronized) for effective pumping
- made up of autoarrhythmic cells that can generate own action potential (pacemaker)
- path for electrical excitation.
parts of conduction system
- sinoatrial node
- atrioventricular node
- AV bundle or bundle of His
- Right and left bundle branches
- Purkinje Fibers
What happens if the SA node doesn't fire?
The AV node will take over. If that fails, the Purkinje fibers will fire, but slower. SA is just the fastest, so the others follow suit
Where is the pause in the conduction system in the heart?
AV node, where electrical stimulus is going around the fibrous band and squeezing through few gap junctions, giving the ventricles time to fill. This sets the rhythm.
- graphic recording of the electrical currents of the heart, measured on the surface of the body (NOT A MEASURE OF HEART FUNCTION)
- Major waves: PQRST
- Uses nodes.
What Lead do vets use in ECG?
- Lead II. Right arm is negative (white)
- Left leg is positive (Red)
- Left arm is the ground. (black)
- Placed at joints (elbow and stifle)
- Toward the + (left leg) means + (up) (P, R)
- Away from the + means - (Q, S)
- Opposite of depolarization.
- Toward +(Left leg) means - (down)
- Away from + means + (up) (usu T wave, sometimes not)
atrial depolarization, positive, towards left leg
- Ventricular depolarization
- Q, tiny negative (sometimes missing)
- R, huge positive
- S, tiny negative
- repolarization of ventricles
- can be positive (usually) or negative.
To read ECG
- Rate, Rhythm, Axis, P wave morphology, PR interval, QRS complex morphology
- ST segment morphology
- T wave morphology
- Use graph boxes. Can't diagnose just from ECG.
Relationship between ECG waves and systole/diastole
- Waves precede/cause contraction.
- P before atrial systole
- QRS before ventricular systole.
- The ability to spontaneously initiate a depolarization, triggering an action potential
- All (autorhythmic) conduction fibers CAN, but only SA node exhibits automaticity
- SA node is faster, so it sets the heartrate
Who are the latent pacemakers
AV node and His-Purkinje system. Would set heart rate if SA failed
Autonomic nerve supply to heart
- Brain stem (medulla) regulates.
- Sympathetic, norepinephrine, stimulate ventricles. Increase force of contraction.
- Parasympathetic, vagus, acetylcholine, can decrease but doesn't affect force of contraction.
Cardiac arrhythmias (dysrhythmias)
- deviations from the norm: cardiac rate or rhythm, site of origin of cardiac impulse, sequence of activation of atria and ventricles.
- Comes from abnormalities in impulse initiation OR impulse conduction
- regular sinus (SA) rhythm that is slow.
- Don't treat without seeing lethargy/collapse. Then give atropine (decrease the parasympathetic)
- Caused by elevated vagus or decreased sympathetic, hypothermic, hypothyroid, sick sinus syndrome, vagus due to other systemic disease (respiratory, neurologic, ocular, GI, urinary)
- regular sinus (SA) rhythm at a fast rate.
- treat problem not symptoms
- caused by stress (ups sympathetic), hyperthyroid, fever, hypervolemia, compressed heart (tamponade), heart failure, drugs that increase the SA (catecholamines).
- failure of the SA node to discharge for a short period of time.
- Causes pause between complexes of ECG. Missing beat.
- heart rate is interrupted by escape beat or resumption of sinus.
- Possible fainting or weakness
Arrhythmia from impulse initiation
- impulse initiation from abnormal or ectopic impulse (some part of heart not SA node signaling contraction). Are described by site of origin (atrial, junctional, supraventricular, ventricular)
- characterized by timing (premature or escape)
abnormal premature arrhythmias in groups of three or more.
Supraventricular (atrial or junctional) premature complex
- arrhythmia where early arrhythmia is initiated from above the AV node, either in atrium or AV junction (just above node).
- QRS complex normal but premature
- p wave can be weird.
- Not always very obvious
Ventricular premature complex (VPC)
- depolarization coming from a site within ventricular myocardium.
- complex is wide, bizarre and early. P wave not associated
three or more ventricular premature depolarizations conseculatively
atrioventricular (AV) block
- alteration of impulse conduction from atria to ventricles. Something is stopping/slowing
- Three degrees of AV block
First degree AV block
- Something is slowing electrical impulse from atria to ventricles.
- Conduction time is increased.
- Increased inerval between P and R on ECG
Second degree AV block
- intermittent conduction. Occasional impulses fail to make it from atria to ventricles. Atrial contraction is not followed by ventricular contraction.
- May be at regular intervals or random
- 2 types (Type 1 and type 2)
Second degree AV block type 1
- Intermittant conduction between atria and ventricles.
- Increasing delays in each cycle of ECG before an omission.
Second degree AV block type 2
- Intermittant conduction between atria and ventricles.
- No pattern. Random.
Third degree AV block
- Complete heart block. No impulses are conducted from atria to ventricles.
- Lack of synchronization between P-wave and QRS complex.
What was wrong with Molly? 11yr spayed whippet. Respiratory distress, thick white mucous, choking cough, tired, losing weight, abnormal lung sounds, left systolic murmur
Degenerative mitral disease or mitral regurgitation. Mitral valve is thickened and no longer closing properly, so blood is flowing backward. Left heart failure. Pulmonary edema. Management (treat respiratory signs).