Cardiology Flashcards
(28 cards)
Name the 3 layers of the pericardium
From inside to outside
1. Epicardium
2. Parietal pericardium
3. Fibrous pericardium
Pericardial space between epicardium and parietal pericardium
How does cardiac muscle function as a syncytium?
Intercalated discs (gap junctions) between cells to allow ion flow
Describe the ion movement in a cardiac action potential. How does this differ in a pacemaker cell (SAN)?
Cardiac action potential:
1. Opening of fast voltage gated Na+ channels depolarises membrane. These then close and membrane starts to repolarise as K+ leaves cell
2. By this time slow L-type Ca2+ channels have opened - influx of Ca into cell = plateau
3. Closure of L type Ca2+ channels and efflux of K+ via K+ channels depolarises membrane
SAN has funny current - slow leak Na+ channels which depolarise membrane to threshold so have spontaneous excitability
Where does the cardiac muscle get its calcium from to contract?
Small amount comes from cardiac muscle sarcoplasmic reticulum but much less than skeletal muscle - SR less developed
Relies mostly on extracellular calcium - T tubules in cardiac membrane have Ca channels in them - influx of Ca which activates ryanodine receptors in SR - more Ca released
After a cardiac action potential and contraction, how are normal concentrations of calcium restored within the cell?
- Use of SERCA2 pump (sarcoplasmic reticulum CA-ATPase pump) to pump Ca back into SR
- Use of Ca/Na pump to pump Ca out of membrane and Na in
- Na then has to go back out to restore normal membrane potential - use of NA/K ATPase pump
What is isovolumic contraction?
First part of ventricular contraction in systole where pressure is increasing inside ventricles but semilunar valves not yet open -> volume of ventricles does not change
What is the difference in location of where nerve fibres act on heart - parasympathetic vs sympathetic nerve fibres?
Parasympathetic nerve fibres mainly act on SAN and AVN to slow speed of conduction - don’t affect muscle therefore force of contraction not affected.
Whereas sympathetic affect both nodes and muscle
Which duct do the lymphatics from the left upper body and total lower body empty into?
And which vessels does this empty into?
Thoracic duct
Empties into junction between Left internal jugular vein and left subclavian vein
Which duct to the lymphatics from the right upper body empty into?
Which vessels does this empty into?
Right lymph duct (smaller than thoracic duct)
This then empties into junction between right internal jugular vein and right subclavian vein
What forces act on a capillary?
Starlings forces
1. Hydrostatic pressure of fluid inside capillary
2. Hydrostatic pressure of fluid in interstitium
3. Oncotic pressure in capillary
4. Oncotic pressure in interstitial
Describe the contents of the interstitium (3 parts)
- Collagen fibres
- Proteoglycan matrix
- Free fluid in rivulets/vesicles
What law determines blood flow through vessels?
Ohm’s law
Flow = pressure difference / resistance
How do you calculate Reynolds number and what does this tell you?
Reynold’s number = how likely blood flow is to be turbulent
Re = (velocity x diameter x density)/viscosity
Where does most resistance occur within the circulation?
Arterioles
What does Poiselle’s law tell us about and what is the equation?
Poiselle’s law = measure of conductance in a blood vessel (flow)
Flow = (Pi x pressure gradient x radius to power of 4)/8 x viscosity x length
What is the law of Laplace?
Tension on a vessel/heart = pressure difference x (radius/wall thickness)
Therefore if experiencing increased tension then wall thickness increases
How is a metaarteriole different to a normal arteriole and where is it?
This is the final arteriole before capillaries
Rather than continuous smooth muscle it has rings of smooth muscle instead
Pre capillary sphincter = final ring of smooth muscle before the capillary
What is vasomotion in the capillary?
Start stop movement of blood due to the smooth muscle rings of the metaarteriole and pre-capillary sphincter
What are 3 ways that substances can travel across the capillary membrane?
- Diffusion of molecules through endothelial cell - lipid soluble molecules eg O2 and CO2
- Intercellular movement through slit pores/intercellular clefts for water soluble substances. NB size dependent - big things can’t go through, although tissue dependent (eg liver has big intercellular clefts)
- Plasmalemmal vesicles/caveolae in endothelial cells which perform endocytosis and transcytosis across the endothelial cell for macromolecules
What causes the lymphatic pump?
Capillary lymphatic pump - anchoring filaments pull on lymphatic capillary wall the excess fluid enters the tissue to allow fluid to flow in. Then pressure causes these to close like valves and push lymph up
Lymphatics also have actomyosin filaments to allow pumping
External pressure - muscles, vessels beating nearby, external tissue compression (eg compression socks), moving
What triggers nitric oxide production? What is it produced from and where? What is production catalysed by?
Triggered by shear stress
Produced in endothelial cell from L-arginine and O2 -> makes NO + L-citrulline
Catalysed by endothelial derived nitrous oxide synthase
How does NO cause vasodilation?
NO produced in endothelial cells and diffuses into blood vessel
Activates guanylate cyclase
Guanylate cyclase catalyses cGTP to cGMP conversion (cGMP protein kinase also produced)
cGMP causes vascular smooth muscle vasodilation
How is bradykinin made and what triggers its production?
Tissue damage triggers production -> activates kallikrein enzyme which cleaves alpha-globulins to kallidin.
Kallidin then converted to bradykinin by tissue enzymes.
What does bradykinin do?
Powerful arteriolar dilator and increases vascular permeability
Also enhances neurotransmitter release from sympathetic nerves, but does not directly act on them
