Module 1 - cardiovascular system Flashcards
How many circuits does the cardiovascular
system have?
Pulmonary and systemic
Which system has the highest pressure?
Systemic
How many chambers does the heart have?
Two atria & two ventricles
Which chamber is the most muscular?
Left ventricle
How many valves does the heart have?
2 x atrioventricular valves (tricuspid and bicuspid)
2 x semilunar valves (pulmonary and aortic)
Why are valves important?
To prevent backflow of blood
describe the functions of the cardiovascular system
TRANSPORT SYSTEM
* oxygen and nutrients to cells
* wastesincluding CO2
* hormones (endocrine)
HOMEOSTASIS
* body temperature by redistributing blood
* pH levels in blood & interstitial fluid
* blood volume/blood pressure
PROTECTION
* white blood cells (WBC) immune response
what are the major structures of the cardiovascular system?
- BLOOD: fluid connective tissue that is transported in the cardiovascular system
- HEART: muscular organ that pumps blood through blood vessels to all body parts
- BLOOD VESSELS:
- Arteries:
- Capillaries:
- Veins:
carry blood AWAY from the heart
exchange of gases, nutrients & waste products between blood & tissues
return blood TOWARD the heart
what is the septum of the heart?
dividing wall between the right and left sides of the heart.
what is the heart surrounded by?
pericardium
what is the pericardium and the various layers within the pericardium?
The pericardium:
* maintains the hearts position
* prevents heart from overfilling
* outer fibrous pericardium
* inner serous pericardium
* parietal layer of serous
pericardium
* visceral layer of serous
pericardium
The pericardial cavity is between
the 2 serous layers (fluid)
describe what the coronary arteries do and where they are
-are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle.
-The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ of the body.
-wrap around the entire heart.
Anatomical differences between the right and left ventricles
The left ventricle has thicker walls than the right because it needs to pump blood to most of the body while the right ventricle pumps blood only to the lungs.
where and how does blood enter the heart?
Deoxygenated venous blood from
the peripheral organs and tissues
enters the right atrium through the
superior and inferior vena cava
* This blood then enters the right
ventricle via the tricuspid valve
location of the tricuspid valve
the right side of the heart. Another
name right atrioventricular
valve.
location and function of the bicuspid valve
The left side of the heart. Another name mitral valve or left atrioventricular valve.
works better on the high-pressure side because, with only two sides to the valve, the muscles and ligaments are able to spring back from the high pressure on the left side of the heart.
describe the papillary muscles
located in the ventricles of the heart. They attach to the cusps of the atrioventricular valves (also known as the mitral and tricuspid valves) via the chordae tendineae and contract to prevent inversion or prolapse of these valves during ventricular contraction.
function and location of semilunar valves
(aortic and pulmonary valve): situated between the aorta and the left ventricle and between the pulmonary artery and the right ventricle. These valves permit blood to be forced into the arteries but prevent backflow from the arteries into the ventricles
do not have chordae tendineae that attach to papillary muscles
what is the direction of blood flow through the hear
unidirectional flow
-The blood MUST flow through each
circuit before returning to the heart.
what are the two circuits in the heart?
- systemic circulation (high pressure)
- pulmonary circulation (low pressure)
describe blood flow in the systemic circulation
blood flows in parallel through many different organs and tissues (i.e., it is ‘shared’ between these organs and tissues)
◼ High O2 in the arteries
◼ Low O2 in the veins
~84% of blood in body
describe blood flow in the pulmonary circulation
all the blood flows only through the lungs
◼ Low O2 in the arteries
◼ High O2 in the veins
~16% of blood in body
what are the components of the heart in order of blood flow
Atria -> Ventricles -> Arteries -> Arterioles -> Capillaries -> Venules ->
Veins
function of atria
receive blood returning to the heart from the veins (RA = deoxygenated, LA = oxygenated) Contraction fills ventricles
function of ventricles
their contraction generates the
pressure to drive the flow of blood (RV = pulmonary, LV = systemic)
function of arteries and arteries in the heart/ cardiovascular system
conduct blood to organs and tissues with little loss of pressure.
Pulmonary artery: Takes deoxygenated blood from the heart to the lungs
Aorta: carries oxygenated blood to
peripheral organs
function of arterioles
smallest arteries branch into arterioles. Control resistance to flow, thus, the distribution of flow to different organs and tissues.
function of capillaries
main site where substances are
exchanged between the blood and cell of the body.
function of venules
collect blood from the capillaries.
function of veins and veins in the heart/ cardiovascular system
return blood to the heart
Superior vena cava: return deoxygenated blood from the systemic circulation to the right atrium of the heart. It receives venous return from the upper half of the body
Inferior vena cava: return deoxygenated blood from the systemic circulation to the right atrium of the heart. It receives venous return from the lower half of the body
Pulmonary veins: Brings oxygenated blood from the lungs to the heart
blood flow through the heart
Deoxygenated venous blood
from the peripheral organs and
tissues enter the right atrium
through the superior and
inferior vena cava
This blood then enters the right
ventricle via the tricuspid valve
From the right ventricle blood is
pumped to the pulmonary artery
via the pulmonary valve to blood
vessels in the left and right lungs
Lungs remove Co2 and add O2 to
the blood
Oxygenated blood enters the left atrium via the pulmonary vein
Blood then enters the left ventricle
through the mitral valve (bicuspid valve)
Left ventricle ejects blood to the aorta via the aortic valve
Aorta distributes blood into
various organs in the body
explain the diastole and systole phases of the heart
Diastole and systole are two phases of the cardiac cycle. They occur as the heart beats, pumping blood through a system of blood vessels that carry blood to every part of the body.
Systole = when the heart contracts to pump blood out.
Diastole = when the heart relaxes after contraction (filling).
describe the cardiac cycle and events within each step of the cycle
the cycle of contraction and relaxation
Remember
❑ Blood always flows from a region of high pressure to a lower pressure.
❑ Heart valves are either open or shut depending on the relative pressures on either side of the valve.
a) atrial systole begins: (upper 2 chambers) atrial contraction forces a small amount of additional blood into relaxed ventricles (atrial systole + ventricular diastole)
b) atrial systole ends, atrial diastole begins
c) ventricular systole - 1st phase: ventricular contraction exerts enough pressure on the blood to close AV valves but not enough to open semilunar valves
d) ventricular systole - 2nd phase: as ventricular pressure rises and exceeds pressure in the arteries the semilunar valves open and blood is ejected into blood vessels
e) ventricular diastole - early: as ventricles relax, pressure in ventricles drops; blood flows back against cusps of semilunar valves and forces them closed. Blood flows into the relaxed atria
f) ventricular diastole - late: all chambers are relaxed. ventricles fill passively.
describe the heart sounds
the result blood turbulence
S1 - First heart sound “lub”: two bursts of vibrations (“turbulence”) due to sequential closure of Mitral and Tricuspid valves.
S2- Second heart sound “dub”: vibrations due to closure of aortic and pulmonary valves.
S3- Third heart sound: marks end of rapid filling phase. Due to “recoil” of blood from ventricular wall.
S4- Fourth heart sound: coincides with atrial contraction. Normally not heard. Indication of pathology involving strong atrial contraction.
define end-diastolic volume (EDV)
Volume of blood in the ventricle
during relaxation and prior to ventricular contraction
define end-systolic volume (ESV)
Volume of blood in the ventricle
after contraction
define stroke volume (SV)
Volume of blood pumped out of each ventricle during a single contraction (volume of blood pumped per heartbeat).
Stroke volume = End diastolic volume (EDV) – end-systolic volume (ESV)
define cardiac output
- Volume of blood pumped by each ventricle per minute
- Indicates blood flow through peripheral tissues
Cardiac output (CO) = Heart rate (beats/min) x stroke volume (ml/beat)
define preload
= amount of stretch during diastole (diastole = when the heart is relaxing)
* More stretch of the cardiac muscle = greater force of the cardiac contraction
* Primary determinant of preload = left ventricular end diastolic volume (EDV)
* Greater the EDV, greater the cardiac contraction
define afterload
= amount of resistance the heart must overcome when ejecting blood
The main determinant of afterload is resistance in the blood vessels
explain venous return
= The volume of blood returning back to the heart each minute
– Increased venous return increases EDV
– Causes heart muscle to stretch (increased preload due to increased
EDV)
– As cardiac muscle stretches, the next contraction will be stronger
describe the Frank-Starling Law
intrinsic property of cardiac tissue
The greater the end-diastolic volume, the greater the force of contraction during systole (within limits!)
Stretching the cardiac muscle cells produces a more optimum overlap between thick & thin filaments, leading to a stronger contraction
what 2 things increase stroke volume
Frank-starling law and increased sympathetic activity
ways that stroke volume is increased through intrinsic and extrinsic controls
intrinsic controls
increased venous return = increased EDV = increased strength of cardiac contraction = increased stroke volume
extrinsic controls
increased sympathetic activity (and epinephrine) = increased venous return AND = increased strength of cardiac contraction
what are the factors that influence cardiac output?
increased venous return (FS law) = increased EDV = greater cardiac contraction = greater stroke volume
increased sympathetic activity = increased venous return + cardiac contractility = increased stroke volume
increased sympathetic activity = increased HR
parasympathetic = decreased HR = decreased cardiac output
what are the two cell types of cardiac muscle cells (cardiomyocytes)
- contractile:
Almost all of the cardiac cells are contractile cardiac muscle cells (pumping activity). - non-contractile/ autorhythmic: pacemaker cells
Pacemaker cells can spontaneously depolarize (auto-rhythmicity and
intrinsic conduction system) (no neural input is required). Transplanted hearts – can cut all neural input but it still beats
what is the composition of contractile cells?
Contractile cells are composed of many tubular myofibrils.
Mitochondria account for 25-35%of volume of cardiac cells
* Most of the remaining volume is occupied by myofibrils composed of typical sarcomeres
what are myofibrils?
contractile units and repeating sections of sarcomeres that are
contractile units with actin (thin filaments) and myosin (thick filaments)
what is the intercalated disk?
The junction between cardiac cells
explain the contraction of cardiac muscles
Heart cells are electronically joined
together by gap junctions. pacemaker cells can not only initiate their own depolarization but also that of the rest of the heart
- Gap junctions tie cardiac muscle cells together to form a functional unit. Allows the wave of depolarization to travel from cell to
cell across the heart. (Acts as a single big motor unit) - Contraction of all cardiac myocytes
ensures effective pumping by the
heart
explain excitation-contraction coupling in the cardiac muscle
- The process whereby an electrical stimulus is converted to a mechanical response.
- Action potentials triggered by pacemaker cells (electrical stimulus) initiate cardiac contraction (mechanical response).
Action potential travels down T tubules; causes sarcoplasmic reticulum (SR) to release Ca2+
– Ca2+ leads to binding of actin and myosin filaments leading to contraction of the cardiomyocyte.
what are the three criteria must the heart meet for the spread of excitation
- Each heart chamber must pump as a unit
- Atria should contract together; ventricles should contract together
- Atrial excitation & contraction must complete before ventricular contraction
Describe the spread of excitation through the heart
The sinoatrial node in the right atrium is the primary pacemaker of the heart. Atrioventricular node delays impulse spread. Atrioventricular bundle conducts the impulse to the interventricular septum. AV bundle splits into L & R bundles. Connect with Purkinje fibres in the apex – contraction spreads through L & R ventricles.
another explanation:
Action potential spreads through the heart > this induces calcium release in the heart> calcium is required for actin-myosin binding in cardiac contractile cells > actin-myosin binding leads to contraction of the cell.
describe the electrical conduction system of the heart
Sinoatrial (SA) Node: The process starts in the right atrium with the SA node, often referred to as the heart’s natural pacemaker. The SA node initiates an electrical signal, which causes the atria to contract. This signal spreads across both the right and left atria, causing them to contract and push blood into the ventricles.
Atrioventricular (AV) Node: The electrical signal then reaches the AV node, which is located in the lower part of the right atrium near the ventricles. The AV node is like a ‘gatekeeper’ – it slows down the electrical signal before it enters the ventricles. This slight delay allows the atria to fully empty their contents into the ventricles before ventricular contraction (systole) begins.
Bundle of His/ AV bundle: From the AV node, the electrical signal travels down a pathway called the Bundle of His. This bundle divides into right and left bundle branches along the interventricular septum, which separates the right and left ventricles.
Purkinje Fibers: The bundle branches then divide into thin, wire-like structures called Purkinje fibers. These fibers distribute the electrical signal throughout the ventricles, causing them to contract and pump blood – to the lungs from the right ventricle, and to the rest of the body from the left ventricle.
in terms of the regulation of heart rate, describe the impacts of Sympathetic stimulation
of SA node
Noradrenaline (adrenaline)
Increases rate of closure of K+
channels and inward leak of Na+
(and Ca2+)
Faster rate of “slow” depolarisation
Threshold reached earlier
Heart rate increases
in terms of the regulation of heart rate, describe the impacts of parasympathetic stimulation
of SA node
Acetylcholine (vagus nerve)
Hyperpolarises SA node cells
Decreases rate of closure of K+ channels and inward leak of Na+ (and Ca2+)
Slower rate of “slow” depolarisation
Takes longer to reach threshold
Heart rate decreases
what are the blood vessels in the body and what do they do
- Arteries: carry blood AWAY from the heart (mostly oxygenated, not always!)
- Capillaries: exchange of gases, nutrients & waste products between blood & tissues
- Veins: return blood TOWARD the heart (mostly de-oxygenated, not always!)
Compare the walls of arteries, capillaries & veins
*Arteries & veins have similar 3 layers but they vary in relative thickness
* Arteries have a smaller lumen to a comparable-sized vein
*Arteries have a muscular wall, veins have scant smooth muscle
*Arteries contain elastic lamellae
Capillaries only have tunica intima
because arteries are designed to withstand higher pressures than veins
Summarise blood vessel structure and function
- Arteries carry blood away from the heart.
- Arterioles distribute blood to capillary beds.
- Capillaries exchange gas, nutrients and waste between blood and tissues.
- Venules receive blood from capillaries.
- Veins return blood towards the heart.
- Arteries, arterioles, veins and venules have Tunica intima, Tunica media, Tunica externa.
- Capillaries only have tunica intima. Arteries & veins have similar 3 layers but they vary in relative thickness
- Arteries have a smaller lumen to a comparable sized vein
*Arteries have a muscular wall, veins have scant smooth muscle - Arteries contain elastic lamellae and their structure reflects their function.
Arteries are designed to withstand higher pressures than veins
describe the structure and function of capillaries
- Link arteries with veins
- Microscopic (<10µm diameter, 1mm long)
The exchange of materials between the blood and body can only occur
at the level of capillaries
true or false small & medium veins contain valves
true, because blood only flows in the direction of the heart
summarise pulmonary circulation
2 arteries, 4 veins
low pressure pump
*Right ventricle pumps into
*Pulmonary trunk
*1 left & 1 right pulmonary
artery carry oxygen-poor
(deoxygenated) blood to each
lung
*2 left & 2 right pulmonary veins
from each lung carries oxygen rich
(oxygenated) blood to the left
atrium
summarise systemic circulation
All systemic arteries branch from
the aorta
DEEP VEINS:
* Usually accompany the arteries and share similar names
* Some exceptions
SUPERFICIAL VEINS:
* Located just below the skin
The body can shunt blood between the deep & superficial veins for body temperature control
Systemic blood leaves the heart through 1 artery. Returns via 3 systemic veins to the right atrium
Superior vena cava:
Receives blood from the body superior to the diaphragm (except the lungs)
Inferior vena cava:
Receives most of the blood from the body inferior to the diaphragm
Coronary sinus:
Receives blood from the heart
Describe the three components of blood
55% plasma = H20 + proteins (fibrinogen) + other
1% “buffy coat” = leukocytes + platelets
44% erythrocytes
What is the function of
blood vessels?
- ‘Vascular highways’ that transport blood around
the body to meet demands:
– Oxygen delivery
– Nutrient delivery
– Waste removal
– Chemical messenger delivery (e.g. hormones)
– Maintain body temperature
Distribution of blood
around the body
- Parallel arrangement of vessels from the aorta ensures fresh blood to all organs
- Blood flow to each organ can be changed independently
the rate at which blood flows
through the circulatory system is
dependent on…
– The pressure gradient (ΔP)
– The resistance to blood flow (R)
F = ΔP/R
The heart has to generate enough
pressure to overcome resistance to
blood flow
what is the pressure gradient?
The difference in pressure between the two ends of a vessel, not the
absolute pressures within the vessel determines flow rate
Resistance to blood flow is due to 3
factors….
– blood viscosity (η) – direct proportional
– vessel length (L)– direct proportional
– vessel radius (r) – inversely proportional
The most important of these is
radius (r)
Double the radius = increase blood flow by 16 times!
describe blood viscosity
Viscosity is the resistance to flow caused by interactions among
molecules and suspended materials in a liquid. Liquids with low viscosity, such as water (viscosity 1.0), flow at low pressures.
Under normal conditions, the viscosity of blood remains stable.
Anemia, polycythemia, and other disorders that affect the hematocrit also change blood viscosity, and thus peripheral resistance.
describe turbulence
High flow rates, irregular surfaces, and sudden changes in vessel
luminal diameter upset the smooth flow of blood, creating eddies and swirls. This phenomenon, called turbulence, increases resistance and slows blood flow.
* Turbulence normally occurs when blood flows between the atria
and the ventricles, and between the ventricles and the aortic and
pulmonary trunks. It also develops in large arteries, such as the aorta, when cardiac output and arterial flow rates are very high.
* However, turbulence seldom occurs in smaller vessels unless
their walls are damaged
describe Poiseuille’s law
The precise relationship between flow, pressure, and resistance
Flow rate = (π/8) ΔP r4/ηL
Where P=Pressure; r= radius; viscosity= η and L= length.
describe arteries as a pressure reservoir
- Elastin allows arteries to expand like a balloon & temporarily hold excess blood
- When the heart is in diastole, stretched arterial walls recoil & exert pressure on blood, ensuring continued flow even when heart is relaxed & not pumping
how do arterioles regulate blood flow to issues?
Vascular smooth muscles can contract or relax:
Contraction → vasoconstriction
Relaxation → vasodilation
intrinsic controls
- control entirely within tissue or organ
- uses paracrine or properties of muscle tissue
extrinsic controls
- control from outside the tissue or organ
- uses nerves or hormones
How is diffusion maximized in capillaries?
Minimal distance
* Single layer of endothelial cells
* Thin wall (1 μm) & small diameter (7 μm)
* Proximity to cells
Capillaries: sites of exchange
Maximal surface area
* High numbers (10-40 billion) =600m2
Maximal time
* Velocity is slow due to extensive
branching
Permeability
* Molecules pass between or
through endothelial cells
how do capillaries control blood flow?
- Pre-capillary sphincters are smooth
muscle cells that spiral capillaries:
sensitive to local metabolic factors - If metabolic activity increases,
sphincters relax → increase flow - If metabolic activity decreases,
sphincters contract → flow is
bypassed
function of venules
- Blood flows from capillaries into venules
- These converge to form veins that exit the organ
- They have little tone or resistance
- Communicate with arterioles, chemically, to match inflow & outflow
function of veins
Return blood toward the heart
- Large radius
- Low resistance
- Less smooth muscle with little myogenic tone
- Less elastin so little recoil
Highly compliant → huge storage
capacity therefore called capacitance vessels
what is Mean Arterial Blood Pressure and what determines it
driving force for the flow of blood through organs and tissues.
◼ Mean arterial blood pressure is determined by two factors:
1) The Cardiac Output (CO), and
2) The Total Peripheral Resistance (TPR)
MAP = CO X TPR
– Pulse pressure phases out
near end of arterial tree
– Flow is non pulsatile with a
steady MAP pressure
* Heart spends more time in
diastole, so not just a simple
average of diastole and systole
what is Total Peripheral Resistance?
The sum of the resistance of all of the blood vessels.
◼ Mainly determined by the arterioles.
- changes in TPR are mainly brought about by changes in the state of constriction or dilation of arterioles.
describe systemic blood pressure
- Pumping action of heart generates blood flow
- Pressure results when flow is opposed by resistance
- Systemic pressure is highest in aorta and declines throughout pathway
– Steepest drop occurs in arterioles
what are the 2 factors that determine arterial blood pressure?
- Elasticity (compliance or
distensibility) of arteries
close to heart - Volume of blood forced into
them at any time
Blood pressure near
heart is pulsatile
– Rises and falls with each
heartbeat
explain Systolic pressure
pressure exerted in aorta during ventricular contraction
– Left ventricle pumps blood into
aorta, imparting kinetic energy
that stretches aorta
– Averages 120 mm Hg in normal
adult
explain diastolic pressure
lowest level of aortic pressure when the heart is at rest
explain pulse pressure
difference between systolic and diastolic pressure
what is your pulse?
throbbing of arteries due to
difference in pulse pressures, which
can be felt under skin
how do you measure blood pressure?
Systemic arterial BP is measured indirectly by auscultatory methods using a sphygmomanometer
1. Wrap cuff around arm superior
to elbow
2. Increase pressure in the cuff until it
exceeds systolic pressure in brachial artery
3. Pressure is released slowly, and the examiner listens for sounds of Korotkoff with a stethoscope (details later)
Systolic pressure:
normally less than 120 mm Hg
– Pressure when sounds first occur as blood starts to spurt through artery
Diastolic pressure:
normally less than 80 mm Hg
– Pressure when sounds disappear because artery no longer constricted; blood flowing freely
what the factors that affect regulation of blood pressure?
– Short-term regulation: neural controls
– Short-term regulation: hormonal controls
– Long-term regulation: renal controls
what are the 2 neural mechanisms that control peripheral resistance?
- MAP is maintained by altering blood vessel diameter,
which alters resistance
* Example: If blood volume drops, all vessels constrict
(except those to heart and brain) - Can alter blood distribution to organs in response to
specific demands
what is the short-term neural controls of MAP?
Baroreceptor reflex
Cardiovascular center of medulla
what is the main long-term control of MAP?
regulation of blood volume
what is the role of the Baroreceptor Reflex?
◼ Provides for rapid adjustment of mean arterial blood pressure in the event of sudden disturbances.
◼ very quickly (within several seconds to minutes) compensate for any sudden changes in blood pressure.
- Carotid sinuses
– Monitor blood flow to the brain - Aortic arch
– Monitor blood flow to the systemic circulation
The rate of action potential firing is proportional to arterial pressure
- if pressure rises the rate of baroreceptor firing increases
- if pressure falls rate of baroreceptor firing decreases
-> Sends information to the medullary cardiovascular center
what is the role of the cardiovascular control center?
Located in the medulla oblongata
– Receives sensory info about blood pressure (baroreceptors)
– Regulates sympathetic & parasympathetic activity to heart and vessels
