The Cardiovascular System Lectures 14 Flashcards
What does the mammalian cardiovascular system consist of?
Consists of the heart and circulatory system
What is the role of the cardiovascular system?
To supply every cell in the body with oxygen and nutrients
Where does deoxygenated blood enter the right atrium from?
From the inferior and superior vena cavae
Where does deoxygenated blood pass through?
Passes through the right AV valve and enters the right ventricle
Where is deoxygenated blood pumped into?
The pulmonary arteries through the pulmonary valve
Where is oxygenated blood returned from?
From the lungs to the left atrium
Where is oxygenated blood entered through?
Enters the left ventricle through the left AV valve
How is oxygenated blood pumped through?
Pumped by the left ventricle through the aortic valve into the systemic circulation
What does the CVS consist of?
Heart and blood vessels; arteries, arterioles, capillaries, venules and veins
What are the functions of the CVS?
-collect and transport O2 (from lungs) and nutrients (from gastrointestinal tract) to all cells of the body
-collect and transport CO2 (cells main metabolic by product) and other waste products
Excitation- contraction in the cardiac muscle;
What is cardiac action potential stimulated by?
-autorhythmic cells
*have an unstable resting membrane potential
*continuous depolarisation = produces pacemaker potentials that initiate APs
Excitation- contraction in the cardiac muscle;
Difference between cardiac muscle + skeletal muscle?
Cardiac muscle=
-heart either contracts as a unit or doesn’t contract at all
-acts as a functional synctium; since electrical activity can spread from one cell to the next
-absolute refractory period= 250ms; nearly as long as the contraction
Skeletal muscle=
-each muscle fibre is attached to a motor nerve and will only contract when that motor nerve is stimulated
-absolute refractory period= 1-2ms
What is the difference between non-contractile cells and contractile cells?
-non-contractile cells= auto rhythmic cells; comprise 1% of cardiac muscle fibres
-contractile cells= cardiac muscle cells; comprise 99% of cardiac muscle fibres
What are the electrical events in cardiac contractile muscle cells?
Changes in membrane potential and permeability of contractile cardiac muscle cells
Phases of the Cardiac muscle AP;
• Depolarization
• Voltage-gated Na+ channels cause rapid depolarisation (Na+ channels inactivation ends this phase)
• Plateau phase of AP
• Slow Ca2+ channels (slow channels) open
• Repolarisation
• Slow Ca2+ channels inactivate and K+ channels open
What happens during calcium induced calcium release?
-L-type Ca2+ channels in cell membrane= open in response to depolarisation caused by the opening of fast Na+ channels
-10-20% of Ca2+ enters here
-local influxes of Ca2+ triggers ryanodine receptors= causing opening of Ca2+ sensitive channels in the SR (called calcium induced calcium release; CICR)
What does the SA node generate?
-Generates action potentials that spread through the atria
-The atria then contracts
Where do the signals that are received from the pacemaker reach?
-reaches the AV node= which is then activated and fires
What are the action potentials transmitted through?
Transmitted through a set of modified muscle fibres
Where does the depolarisation spread from?
Spreads from the modified muscle fibres through the entire ventricle. The ventricles contract
What is the difference between sympathetic stimulation and parasympathetic stimulation?
Sympathetic= speeds up the heart rate
Parasympathetic= slows down the heart rate
What does the ECG consist of?
The ECG consists of the P wave (atrial depolarization),
QRS ventricular depolarization) and T wave (ventricular
repolarisation
SA node; activated and the atria contracts (P)
AV node; activated and the ventricles contract (QRS)
Ventricles repolarize and relax (T)
Heart sounds:
2 major heart sounds:
“Lub”- AV valve closes , its louder and longer,ventricular pressure is larger than atrial pressure i.e. beginning of ventricular systole
“Dub”- SL valve closes, its short and sharp, beginning of ventricular relaxation (diastole)
What are heart murmurs:
It’s result from turbulent blood flow due to valve malfunction
Types of heart murmurs: stenotic valve
It’s stiff narrowed valves which don’t open completely, blood is forced through a high pressure producing a whistle sound
Type of heart murmurs: insufficient/ incompetent valve
It’s valves that can’t close fully, backflow of blood causes turbulence and creates a swishing/gurgling sound
Rhythmic changes in the cardiac cycle:
Rhythmic changes in electrical activity results in a cycle of contraction and relaxation which causes pressure changes which controls blood flow through the heart
Blood flows down a pressure gradient through any available opening
Systole vs diastole:
Systole- is the period of the cardiac cycle when the ventricles or atria is contracting
Diastole- is the period of the cardiac cycle when the ventricles or atria are relaxing
Cardiac output (CO):
Cardiac output is amount of blood pumped out by each ventricle in one minute
Equation:
CO= Heart rate(HR) x stroke volume (SV)
SV is the volume pumped out by one ventricle with each beat (indicates the force of ventricular contraction)
Resting vs maximum CO:
Resting CO = 5L/min
Difference between resting and maximum CO is called cardiac reserve
Non athletic people= 20-25 L/min
Athletes= 35L/min
What is stroke volume (SV)?
Equation
SV is the volume of blood pumped out by one ventricle with each beat (indicates the force of ventricular contraction)
SV represents the difference between end diastolic volume (EDV) and end systolic volume (ESV)
SV= EDV-ESV
What factors affect Stroke volume (SV)?
Preload
Contractility
Afterload
Preload:
It’s the degree of stretch of the heart muscle - can produce dramatic increases in contractile force
Intrinsic property of the cardiac muscle
Most important is venous return is an increase in venous return e.g.exercise increases EDV
Contractility:
Contractility is the contractile strength achieved at a given muscle length, independent of muscle stretch and EDV
Increased sympathetic stimulation increases Contractility of heart
E.g. mechanism by which no adrenaline influences heart Contractility
After load:
After load is the back pressure exerted by arterial blood- must be overcome for the ventricles to eject blood
In a healthy individual it is not a major determinant
Becomes more important in those with hypertension
How these factors affect SV?
Preload - increased EDV therefore increase in SV
Contractility- decreased ESV therefore increase in SV
Afterload- increased ESV therefore decrease in SV
Regulation of heart rate:
Autonomic nervous system
Sympathetic stimulation (NA & Adr) increased HR
Parasympathetic decreased HR
Chemical regulation
Hormones: Adr, cortisol, thyroxine - all increased HR
Ions: decreased [Ca2+]o and increased [K+]o - both decreased HR
Other factors include age, gender, exercise and body temperature
Coronary arteries:
Branch from aorta just beyond aortic valve
Most arteriole flow occurs during diastole
Blood flow normally adjusted to meet oxygen requirements
Cardiovascular disease (CVD):
Most common cause of death in the UK; includes diseases of the heart and circulation including:
coronary heart disease (angina and heart attack)
stroke
Occurs due to atherosclerosis: coronary arteries become narrowed by a gradual build-up of fatty material within their walls (atheroma).
Angina – the pain resulting when coronary arteries cannot deliver enough oxygen containing blood to the heart muscle, particularly at times when there is more demand
If atheroma becomes unstable, a piece may break off and lead to a blood clot forming.
Myocardial infarction (MI) - occurs if the blood clot blocks the coronary artery
Stroke - may occur if the blood supply to part of the brain is cut off
What is vasodilation?
Widening of blood. Occurs when smooth muscles (located in walls of arteries or large veins) relax which allows blood vessels to become more open.
When blood vessels dilation the blood flow to the tissue is increased.
Circulating Adrenalin acts on B2 receptors which causes vasodilation
E.g. skeletal muscle; the adrenaline acts on B2 receptors causing vasodilation and increased blood flow
What is vasoconstriction?
It is the narrowing of the blood vessels by contraction of circular smooth muscle in their walls. When blood vessels constrict, blood flow is slowed or blocked.
Vasomotor fibres of sympathetic nervous system releases noradrenalin (NA) which acts on α1 receptors to cause vasoconstriction
E.g. gastrointestinal tract; the noradrenaline acts on the a1 receptors to cause vasoconstriction
What is haemodynamics?
It means the movement of blood.
Blood flows down a pressure gradient (ΔP); this is the perfusion pressure.
Perfusion is the passage of blood through the circulatory system
Also depends upon resistance offered by the blood & blood vessels i.e., the peripheral resistance
The relationship between blood flow, perfusion pressure (P) & total peripheral resistance (TPR) is described:
BLOOD FLOW = ΔP / TPR
Total peripheral resistance (TPR)
TPR is the sum of all frictional forces that oppose blood flow.
Factors that affect TPR include:
length of the system
radius of blood vessel
viscosity of the blood a measurement of the thickness and stickiness of a person’sblood
TPR (and thus blood flow) is most sensitive to changes in blood vessel radius (r).
Blood flow is proportional to r4 – Poiseuille’s Law so TPR is proportional to 1/r4
Relationship between radius and flow
See slide 9 on lecture 16 CVS 3
Blood pressure in various blood vessels of the systematic circulation
See slide 10 on lecture 16 CVS 3
Maintaining blood pressure:
This is important to make sure adequate flow to all organs
The blood pressure varies directly with; cardiac output(CO), peripheral resistance and blood volume
Homeostatic mechanisms operate to ensure blood pressure is maintained
Baroreceptors:
See slide 13- 17 on lecture 16 CVS 3
What is normal blood pressure?
Healthy adult - systolic pressure usually < 140 mmHg & diastolic pressure < 90 mmHg
Systolic: the pressure exerted by the blood on the blood vessel walls during contraction of the ventricle
Diastolic: the pressure exerted by the blood on the blood vessel walls during relaxation of the ventricle
Affected by age, gender, body size & disease
Both pressures tend to be lower in young adults & children.
Hypertension is persistently raised BP above 140/90mmHg on 3 consecutive occasions
Mean arterial blood pressure (MAP)?
The mean pressure is time weighted average of arterial pressure over entire cardiac cycle
MAP= Diastolic BP + 1/3 (systolic BP- diastolic BP)
The relationship of Blood flow velocity and total cross sectional area in blood vessels:
The velocity of blood flow is lowest (i.e. slowest) in the capillaries due to the larger cross sectional area.
This is necessary for exchange of materials
Blood flow velocity is inversely proportional to the cross sectional area
