Describe the pump system in the human heart.
Two separate pumps lying side by side.
Pump on left deals with oxygenated blood from lungs.
Pump on right deals with deoxygenated blood from body.
Each pump has two chambers-
The atrium and the ventricle
Describe the structure and function of the atrium.
Thin walled and elastic- stretches as it collects blood.
Only has to pump blood a short distance to ventricles and therefore only has a thin muscular wall.
Describe the structure and function of the ventricle.
Much thicker muscular wall than atria because it has to pump blood further
- Left ventricle thicker than right because has to create enough pressure to pump blood around whole body whereas right only has to pump it to the lungs.
Why does blood return to the heart after being oxygenated by the lungs?
So the pressure can increase before it's distributed to the rest of body.
Speed up blood flow to rest of body.
What do the atrioventricular valves do and describe the two different ones.
Prevent backflow of blood into the atria when the ventricles contract.
Left atrioventricular (BICUSPID) valve has two cup shaped flaps.
Right atrioventricular (TRICUSPID) valve has three cup shaped flaps.
What are pulmonary vessels?
Vessels connecting the heart to the lungs
Describe the Aorta.
Connected to the left ventricle carries oxygenated blood to all parts of the body except lungs.
Describe the Vena Cava.
Connected to the right atrium and brings deoxygenated blood back from the tissues of the body.
Describe the pulmonary artery.
Connected to the right ventricle and carries DEoxygenated blood to the lungs, where its O2 is replenished and CO2 removed.
Describe the pulmonary vein.
Connected to the left atrium and brings oxygenated blood back from lungs.
How is the heart muscle supplied with oxygen?
Supplied by its own blood vessels, called CORONARY ARTERIES.
Branch off aorta shortly after it leaves the heart.
Blockage of theses arteries lead to myocardial infarction (heart attack) because area of heart muscle is deprived of oxygen so therefore dies.
RELAXATION- Blood returns to ATRIA through PULMONARY VEIN(lungs) and the VENA CAVA (body).
As ATRIA fill, pressure in them rises, pushing open ATRIOVENTRICULAR VALVES and allowing blood to pass into VENTRICLES.
Walls of ATRIA and VENTRICLES are relaxed at this stage.
Relaxation of VENTRICLE wall reduces pressure within VENTRICLE which causes pressure to be lower than in AORTA and PULMONARY ARTERY so SEMI LUNAR VALVES close.
Describe atrial systole.
Muscle of atrial wall contracts, forcing remaining blood that they contain into the ventricles.
Blood only pushed v. short distance so muscular walls of atria are v. thin.
Describe ventricular systole.
(SHORT DELAY AFTER ATRIAL SYSTOLE TO ALLOW VENTRICLES TO FILL WITH BLOOD)
Ventricle walls contract simultaneously.
This increases the blood pressure within them, forcing atrioventricular valves shut and preventing backflow of blood.
With AV valves closed, pressure rises further, forcing open the semi-lunar valves and pushing blood into pulmonary artery and aorta.
Ventricle walls much thicker than those of atria because have to pump blood further.
Left ventricle thicker than right.
How is blood flow controlled?
Mainly controlled by the pressure created by the heart muscle.
Blood moves from an area of higher pressure to an area of lower pressure.
However also controlled by valves- prevent unwanted backflow.
How are valves designed to control blood flow?
Open whenever difference in blood pressure either side of them favours the movement of blood in the required direction.
When pressure differences are reversed the valves are designed to close.
Describe how atrioventricular valves prevent backflow of blood.
When ventricles contract, ventricular pressure exceeds atrial pressure.
Closure of AV valves ensures that blood moves to the aorta and pulmonary artery.
Describe how semi lunar valves prevent backflow of blood.
Prevent backflow of blood into ventricles when recoil action of the elastic walls of these vessels creates a greater pressure in the vessels than in the ventricles.
Describe the design of valves.
Made up of a number of flaps of tough, but flexible, fibrous tissue, which are cusp shaped.
When pressure is greater on convex side rather on concave side, they move apart to let blood pass between the cusps.
When pressure is greater on concave side than convex side, blood collects within the "bowl" of the cusps.
Pushes them together to form a tight fit.
To prevent inversion, the valves have string like tendons that are attached to pillars of muscle in the ventricle wall.
What is cardiac output?
Th volume of blood pumped by one ventricle of the heart in one minute.
CARDIAC OUTPUT= Heart rate x Stroke volume
Heart rate- rate at which heart beats
Stroke volume- volume of blood pumped out at each beat.
When contraction is initiated from within the muscle itself, rather than nervous impulses from outside.
Describe how the cardiac cycle is controlled.
Cardiac muscle is myogenic.
Within wall of right atrium is a distinct group of cells- SINOATRIAL NODE (SAN).
It is from here that the initial stimulus for contraction originates.
SAN has a basic rhythm of stimulation that determines the beat of the heart. (Often referred to as pacemaker).
Sequence of events-
-Wave of electrical activity spreads out from SAN across both atria--> CONTRACT
-Layer of non-conductive tissue (AV septum) prevents waves crossing to ventricles.
-Wave of electrical activity allowed to pass through another group of cells call ATRIOVENTRICULAR NODE (AVN), which lies between atria.
-AVN, after a short delay, conveys a wave of activity between ventricles along a group of muscle fibres called the bundle of His.
-Bundle of His conducts wave through AV septum to base of ventricles, where bundle branches into smaller fibres.
-Wave released from fibres, causing ventricles to contract quickly at the same time, from apex of heart upwards.
Describe an atheroma.
A fatty deposit that forms within the wall of an artery. Begins as fatty streaks (accumulations of white blood cells that have taken up low-density lipoproteins).
These streaks enlarge to form irregular patch, or atheromatous plaque.
Atheromatous plaques occur most commonly in larger arteries.
Made up of deposits of cholesterol, fibres and dead muscle cells.
Bulge into lumen of the artery, causing it to narrow (blood flow reduced).
Atheromas increase risk of thrombosis and aneurysm.
If an atheroma breaks through lining of the blood vessel, it forms a rough surface that interrupts the otherwise smooth flow of blood.
MAY RESULT IN A BLOOD CLOT OR THROMBUS.
Thrombus may block the blood vessel, reducing or preventing the supply of blood to tissues beyond it.
Region of tissue deprived of blood usually dies as a result of the lack of oxygen and glucose and other nutrients.
Sometimes thrombus is carried from its place of origin and lodges in, and blocks another artery. EMBOLUS
Describe an aneurysm.
Atheromas that lead to the formation of a thrombus also weaken the artery walls.
Weakened points swell to form a balloon-like, blood filled structure called an ANEURYSM.
Aneurysms frequently burst, leading to haemorrhage and therefore loss of blood to the region of the body served by that artery.
A brain aneurysm is known as a cerebrovascular accident, or stroke.
Describe a myocardial infarction.
Lack of oxygen to muscle in heart as result of a blockage in the coronary artery.
If blockage occurs close to the junction of the coronary artery and aorta, the heart will stop beating because blood supply will be completely cut off.
If blockage further along coronary artery, symptoms will be milder- smaller area of muscle will suffer O2 deprivation.
What are the risk factor associated with coronary heart disease?
SMOKING- CO combines easily but irreversibly with haemoglobin in red blood cells to form carboxyhaemoglobin.
REDUCES O2 carry capacity of blood.
Heart must work harder to supply enough blood. Increased blood pressure.
-Nicotine stimulates production of the hormone adrenaline, which increases heart rate and raises blood pressure.
Also makes platelets more "sticky" which leads to higher risk of thrombosis.
HIGH BLOOD PRESSURE- Genes, excessive prolonged stress, diet, lack of exercise all increase the risk of high blood pressure.
High pressure in arteries means heart must work harder to pump blood into arteries.
More likely to develop aneurysm.
Walls of arteries become thickened to resist high pressure and may harden, restricting blood flow.
BLOOD CHOLESTEROL- Carried in the plasma as tiny spheres of lipoproteins.
High-density lipoproteins (HDLs) remove cholesterol from tissues and transport to liver for excretion. Protect against CHD.
Low-density lipoproteins (LDLs) transport cholesterol from liver to tissues, including artery walls, where they infiltrate, leading to atheroma.
DIET- HIGH SALT- ^BP HIGH
SAT. FAT- ^ LDL levels and hence blood cholesterol levels.
ANTIOXIDANTS and fibre- reduce risk of CHD
Structure of heart