CVS Flashcards
What is the function of the cvs?
Transport of O2 and substrates to cells
Transport of CO2 and metabolites from cells for excretion (e.g. to lungs, liver, kidneys)
02, C02 and glucose transport to the brain in
circulation is v important as the brain has no intrinsic glucose store
Transports hormones + defense mechansims to adapt our physiology in response to environmental changes
Controls thermoregulation via vasoconstriction/dilation in the cutaneous circulation.
What are benefits and limitations of diffusion?
The equation t ∝ x2 states that as diff distance ⇡, time taken for diffusion will increase exponentially
So diffusion is v efficient over distances of a few
micrometers, but way too slow over larger distances
Diffusion is still vital for exchange entre capillaries and tissues (shorter distance)
What is convective transport?
Substances transported over large distances use convective transport
Convection is the bulk flow transport of blood down a pa gradient created by the circulatory system.
During systole, blood is ejected into the aorta at high pa (~120mmHg)
As blood moves from aorta towards veins, its pa decreases.
This pa difference drives blood flow
How is the cvs a dual circulation?
The cvs is a dual circulation; parts are in parallel and series
In parallel: CO is split up- blood goes to different organs which safeguards O2 supply. So si hay problem in lower body circulation, upper is less likely to be affected
In series: liver receives fresh 02 blood from the hepatic artery and some slightly de02 blood from the spleen, stomach and intestines.
If the cvs is compromised the liver/kidneys receives aun mas de02 blood so can be especially affected.
Describe the fundamental relationships of the cvs
Heart Rate: n0 of beats per min
Stroke Volume (SV, ml): blood vol ejected from heart per beat
Cardiac Output (CO, ml/min): blood vol ejected from heart per min. It’s the same as blood flow (BF, ml/min).
BP (mmHg): Pressure of circulating BF on blood vessel walls
TPR: Resistance of blood vessels to BF
Arterial BP = CO x TPR
Blood flow = Arterial BP / TPR
How does the heart pump blood around the body?
Left ventricle ejects blood to body at high pa.
The svc and ivc pump de02 blood to the R atria, ⇡ Pa.
When atrial pa>ventricular pa, the tricuspid AV valves connecting the RA and RV open.Blood flows from atria to ventricles down the pa gradient
In ventricular systole, the ventricles contract, ⇡ pa. The RV pumps blood to the lungs via the pulmonary artery. The pulmonary SL valve opens.
O2 blood comes to the LA via the pulmonary vein and the mitral valve opens. Blood flows to the ventricles.
The LV pumps blood to the body via the aorta. The aortic SL valve opens and shuts due to pa
How is cardiac muscle different to skeletal and smooth?
The heart generates its own electrical activity which is converted into contraction. No need for nerve input (myogenic).
How is electrical activity conducted out the heart?
Pacemaker potentials are generated at the SAN in the RA. From the SAN, impulses are conducted across both atria to the AVN
At the AVN, impulse conduction is slowed down, allowing the ventricles to fill before contracting.
The impulse is then conducted down the Bundle of His to the apex of the heart
From the apex, the impulse is conducted up the ventricle walls along the Purkinje fibres. Purkinje fibres innervate ventricular tissue, causing bottom up contraction of the ventricles, ejecting blood into the aorta + pulmonary trunk
What Controls Cardiac Output?
Filling pressure: if blood volume ⇣, you often give a patient fluids to ⇡ venous return. Increased return of blood to the heart ⇡ SV and CO, important to maintain blood pressure and flow.
Afterload opposes CO.
Where does cardiac output go and how is this clinically important?
Generally cardiac output goes to organs which use up more oxygen. However we send lots more to the kidneys bc the kidneys filter blood and regulate bp.
Coronary & brain are relatively under perfused at rest. This create potential clinical problems e.g. MI, stroke triggered by relatively moderate fall in perfusion.
Describe the speed of blood in our circulatory system.
As cross sectional area increases, blood flow slows down. Capillaries have the largest cross-sectional area (bc hay tantos), so they have slowest blood flow – this allows time for gas exchange to occur.
As the blood goes from capillaries⇢venules⇢veins, cross-sectional area falls so blood flow speeds up. This helps drive blood flow back to the heart against gravity
Describe the histological structure of blood vessels
Blood vessel walls consist of 3 layers
The outer tunica adventitia. Main role: provide structural support to the vessel
The tunica media layer consists of circular smooth muscle and elastin. They allow elastic recoil and peristalsis of blood thru the vessel
The inner tunica intima is a single layer of endothelial cells. They detect changes in blood flow/composition, feeding back to the ns.
Different types of blood vessels can be classified by their function and properties – there are 4 major functional groups. Describe these groups
Elastic vessels: large arteries. They accommodate SV and use elastic recoil to allow continuous blood flow
Resistance vessels: arterioles. They control TPR through vasodilation/vasoconstriction, modulate BP and local blood flow
Capacitance vessels: Veins/venules. They act as a reservoir of blood.
Exchange vessels: capillaries. Responsible for nutrient delivery, removal of metabolic waste. Walls only 1 endothelial cell thick
What speeds up atrial conduction?
Intercalated discs and gap junctions between the myocytes speed up atrial conduction- this is so all cells in the atria contract simultaneously
