Heart Flashcards
What happens in a heart attack?
A myocardial infarction is caused when the blood supply to the heart is disrupted hence the muscle does not get a good enough blood supply and therefore dies. It consequently causes a loss of blood supply to the body.
(An infarct is dead or dying tissue resulting from a lack of oxygen and nutrients).
What are the functions of the cardiovascular system?
Delivery of oxygen and nutrients to cells, removal of CO2 and waste products from cells, temperature regulation, hydrodynamic device in sexual reproduction, communication between organs through transport of hormones.
What can cardiovascular circulation be split into?
Systemic = entire body and pulmonary = lungs
Whats the journey of blood in the body?
The aorta carries oxygenated blood from the heart to the systemic arteries, delivering it to cells and tissues around the body. Systemic veins then carry this deoxygenated blood back to the heart via the vena cava. The deoxygenated blood is then delivered to the lungs via the pulmonary trunk and arteries. At the lungs the blood is oxygenated and then transported back to the heart via the pulmonary vein.
Whats the composition of blood if allowed to separate?
55% plasma which contains water, ions, proteins, nutrients, hormones, metabolic waste, gases etc.
5% leucocytes and platelets known as the buffy coat
45% erythrocytes (hematocrit) responsible for oxygen transport.
At rest how is blood distributed around the body?
61% is in veins/venules of systemic circulation - this is a blood reservoir.
4% is in the heart, 20% in the kidneys and 24% in the abdominal organs.
From the heart, whats the order of blood vessels that the blood enters?
Arteries - arterioles - capillaries - venules - veins.
Whats the structure of the arteries and why?
The arteries contain a large lumen and a thick layer of smooth muscle and connective tissue. The thick layer of elastic smooth muscle acts as a pressure reservoir - the arteries are exposed to a lot of pressure from the heart pumping blood. At systole, when the blood is pumped into the arteries, the smooth muscle contracts hence absorbing pressure by stretching. Then at diastole, the muscle relaxes hence releasing the pressure by a passive recoil.
Without this mechanism blood would surge through the arteries and damage the capillaries.
Whats the structure of the arterioles and why?
Arterioles contain a thin muscular wall and a small lumen. Contraction of the smooth muscle regulates the diameter of the lumen. This determines the blood flow to organs and is a major determinant of mean arterial pressure.
Whats the structure of the capillaries and why?
Capillaries consist of just an endothelial cell wrapped round itself. The diameter of the capillaries allows just one erythrocyte at a time - this allows the exchange of nutrients, oxygen and waste accross the capillary wall, but not proteins. Intercellular clefts and fused vesicle channels in the endothelial cell assist the exchange. Exchange is also facilitated by the slow movement of blood and large surface area within the capillaries.
Whats the structure of the venules and veins and why?
Venules and veins contain thin walls, large diameter lumen and valves. The large diameter allows storage of a high volume of blood as a reservoir.
The return of blood to the heart in veins is facilitated by valves and skeletal muscle pumps. Movement causes the skeletal muscle surrounding the veins to contract hence squeezing the blood up, towards the heart. The closed valves stop the backflow of blood - in varicose veins, broken valves allow the blood to flow backwards under gravity.
Whats the structure of the heart?
Deoxygenated blood from body enters right atrium via vena cava, then enters right ventricle and goes to the lungs to be oxygenated. Oxygenated blood from the lungs then enters the left atrium then the left ventricle then gets transported around the body.
Right side supplies the lungs.
Left side supplies the body.
How do the right and left sides of the heart vary?
Although the atria and ventricles are the same size, the left side of the heart has thicker muscle to allow it to pump blood all over the body.
Wheres the right AV valve?
The tricuspid is on the vein entering the right atrium of the heart (vena cava). It is held in place by chordae tendinae attached to the papillary muscle. The chordae tendinae (heart strings) are fibrous cord of connective tissue.
Wheres the pulmonary semilunar valve?
The pulmonary semilunar valve is on the artery carrying blood to the lungs from the right ventricle.
How is atrium seperated?
By an interatrial septum.
How are the ventricles separated?
By an interventricular septum.
Wheres the left AV valve
The left atrioventricular valve is on the vein transporting blood from the lungs to the heart. It is also known as the bicuspid and is held in place by chordae tendinae, attached to pillary muscles.
Wheres the aortic semilar valve?
The aortic semilunar valve is within the aorta.
What are the layers of the heart?
The inner heart muscle is myocardium, its then a thin layer of epicardium then the pericardium.
Explain the cycle of blood flow around the body.
Oxygenated blood leaves the heart in the aorta to be transported in the body by arteries. The blood then enters arterioles, then capillaries - this is where gas nutrient and waste exchange occurs. The now deoxygenated blood then begins its journey back to the heart through the venules, then the veins. It then enters the heart in the vena cava into the right atrium. It then goes through the right AV valve into the right ventricle. Next it goes through the pulmonary semilunar valve into the pulmonary trunk on its way to the lungs. It goes through pulmonary arteries to the capillaries of the lungs where it is oxygenated. It then returns to the heart via the pulmonary veins entering the left atrium of the heart and through the left AV valve into the left ventricle. It then goes through the aortic semilunar valve into the aorta, restarting its cycle around the body.
Where does the blood supply to the heart come from?
The heart has an extensive network of blood vessels supplied with oxygenated blod via the coronary arteries. The coronary arteries branch off the aorta and split into right and left coronary arteries. Most deoxygenated blood drains back into the right atrium via a single vein (coronary sinus).
What can cause coronary arterial disease?
Drugs, surgery, blood clots (coronary thrombosis) and atherosclerosis (thickening of the coronary arteries hence less blood can get through).
Whats the treatment of coronary arterial disease?
Coronary arterial disease can be treated by balloon angioplasty - a procedure used to widen blocked or narrowed coronary arteries. This involves inserting a catheter into the artery then using a balloon to stretch the artery. It can also involve inserting a stent - a wire mesh tube which is left permanently to hold the blood vessel open so blood can flow more freely.
What are the meninges?
The meninges are tough finrosis membranes that surround the brain, below the skull. The meninges are the dura mater, arachnoid mater and pia mater. There is cerebrospinal fluid within the subarachnoid space (between the arachnoid and pia mater). A bacterial infection in the CSF is called meningitis - this causes increased pressure in the brain leading to seizures and loss of consciousness.
Where is the CSF produced?
CSF is produced by specialised epithelial cells called the choroid plexus of each ventricle.
Where does the CSF travel to?
The CSF flows through the ventricles into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. CSF flows through the subarachnoid space. CSF is absorbed into the dural venous sinuses cia the arachnoid villi.
CSF passes into veins via valves at the top of the skull - arachnoid villus.
Whats the purpose of CSF?
The brain is floating in CSF hence it cushions the brain against damage.
What affects the changes in circulation of CSF around the brain?
The circulation of CSF around the brain is driven by changes in circulation, respiration and posture.
Whats the blood brain barrier?
Blood vessels dive deep into the brain - the capillaries contain very tight juctions which are impermeable to many substances. This protects the brain, but does mean its more difficult to get drugs and proteins into the brain. The exception is lipophilic molecules like alcohol and anaesthetics.
Why does the brain require a constant blood supply?
The brain has no stored glycogen and therefore requires a constant supply of oxygen and glucose - damage would occur within minutes without this.
Would happens if the blood supply is cut off?
A loss of blood supply would cause death of neurons - this is what happens in a stroke.
What are the 2 major fluid compartments of the body?
Intracellular = 28L
Extracellular:
- Interstitial = 11L
- Plasma = 3L
Whats the function of the interstitial fluid?
The interstitial fluid acts as a reservoir that can supply or recieve fluid from the plasma.
Whats the characteristic of the capillary walls?
The capillary walls are highly permeable to water and most plasma solutes (not plasma proteins) allowing movement of molecules between the plasma and interstitial fluid.
Explain the process of filtration in the capillaries.
In the presence of a hydrostatic pressure, the capillary wall behaves like a porous filter, allowing protein free plasma to move by bulk flow from capillary plasma to interstitial fluid through water filled channels.
Explain the process of absorption in the capillaries.
The plasma proteins (colloids) are unable to move through capillary pores and have a low concentration in the interstitial fluid. This difference in protein concentration means the water concentration of plasma is slightly lower than interstitial fluid. This creates a colloidal osmotic pressure causing the flow of water from the interstitial fluid into the capillary.
If the body fails to regulate fluid compartments, whats the consequence?
Oedema - an abnormal accumulation of fluid in the interstitial fluid.
How can heart failure lead to oedema?
Heart failure causes increased venous pressure which reduces blood flow out of the capillaries, the increased capillary hydrostatic pressure causes excess filtration and accumulation of interstitial fluid.
Whats osmosis?
Osmosis is the net diffusion of water accross a selectively permeable membrane from a region of high water concentration to low water concentration. (low particle concentration to high particle concentration).
How is the total number of particles in a solution measured?
In terms of osmoles - 1 osmole = 1 mole of solute particles in 1L.
How is equilibrium reached accross a cell membrane for both a fully permeable and semi permeable membrane?
With a fully permeable membrane, both water and solute molecules will diffuse accross the membrane until equilibrium is reached - concentrations are balanced.
With a selectively permeable membrane, only water can diffuse hence it will move until equilibrium is reached - this will result in equal concentrations but different volumes.
Whats the permeability of cell membranes?
Cellular membranes are permeable to water but impermeable to solutes. Osmosis determines distribution of water - osmotic pressure is the pressure required to prevent osmosis.
How is the balance of ions maintained between fluid compartments?
There are differential levels of cations and anions in intracellular and extracellular compartments - the balance is maintained by active transport.
Whats the concentration of the intracellular and extracellular fluid?
300mM - the extracellular fluid is isotonic.
Why does the concentration of the extracellular media affect the cell size?
If there is a difference in concentration between extracellular and intracellular fluid, fluid will rapidly transfer accross cell membranes to establish osmotic equilibrium. If extracellular > 300mM - its hypertonic and cell will shrink.
If extracellular < 300mM - its hypotonic and cell will swell.
Whats colloidal osmotic pressure?
The concentration of plasma proteins is much higher in the capillaries then the interstitial fluid - this exerts a colloidal osmotic pressure, drawing water back into the plasma.
Whats hydrostatic pressure?
Hydrostatic pressure is the force exerted by the blood upon the capillary walls - it drives blood from plasma to interstitial fluid. Pressure drops as blood moves through the capillaries.
Whats the net filtration pressure (NFP)?
The overall movement accross the capillary membrane is determined by the capillary net filtration pressure.
How does NFP vary along the capillary?
In the arterial end of the capillary, hydrostatic pressure = 35, it therefore dominates and NFP = 10 meaning there is net filtration out of the capillary.
In the venous end of the capillary, hydrostatic pressure = 15, the colloidal osmotic pressure therefore dominates and NFP = -10 hence there is net filtration into the capillary.
The lymph system is a parallel vascular system - whats its two major functions?
Draining fluid from the tissues and returning it to the cardiovascular system.
Maintenance of the immune system.
Explain how the drainage of the lymphatic system works.
8L of fluid a day passes from the blood into the interstitial area, surrounding cells in tissues. Excess fluid passes into lymph capillaries through lymph nodes before passing back to the bloodstream at the neck (largest is thoracic duct that drains into subclavian vein).
Lymph vessels contain valves and fluid is forced along by action of muscles and breathing. Larger lymph vessels are surrounded by smooth muscle that contract spontaneously and are driven by pacemaker cells.
Explain the role of the lymphatic system in immunity.
Lymph fluid contains white immune blood cells (lymphocytes, macrophages and dendritic cells).
The lymph system collects antigens (proteins produced by pathogens) - antigens are recognised by beta lymphocytes in lymph nodes leading to activation of immunity. Beta cells proliferate to produce antibodies - lymph nodes also contain multiple other immune cells.
How can heart failure lead to oedema?
Heart failure can lead to excessive water retention in the kidneys. This causes increased arteriolar resistance and high venous pressure which increases filtration and therefore leads to excess interstitial fluid.
What else can cause oedema?
A reduction in plasma proteins decreases colloidal osmotic pressure hence increasing the volume of interstitial fluid causing oedema. This can be caused by:
- loss of proteins in urine due to kidney failure.
- loss of proteins in burns.
- malnutrition.