Circulation of blood and structure of the heart Flashcards
(16 cards)
Why large organisms need a transport system?
- surface area to volume ratio is too low for exchange of materials through body surface alone → exchange surfaces
- transport between exchange surfaces and cells, exchange surfaces and the environment, different parts of the organism
- the lower the sa:v ratio, the more active the organism is, the greater is the need for a specialised system with a pump
Features of transport systems
- medium to carry materials
- form of mass transport
- closed system of tubular vessels to form a network
- a mechanism for moving the medium in vessels
- mechanism to maintain mass flow in one direction
- a mean of controlling the flow
→ mammals have a double circulatory system with a heart acting as a pump
Blood vessels
arteries - arterioles - capillaries - veins
structure of blood vessels, layers
tough outer layer - resists pressure change from within and outside
muscle layer - contracts to control blood flow
elastic layer - stretches and springs back to control blood pressure
thin inner lining (endothelium) - smooth to prevent friction and thin to allow diffusion
lumen - central cavity through which blood flows
Artery structure
- thick muscle layer compared to veins = controls volume of blood
- thick elastic layer compared to veins = stretches and recoils to maintain high pressure
- overall large thickness = resists bursting under pressure
- no valves - pressure is high so no back flow
Arteriole structure
- thicker muscle layer compared to arteries = controls blood flow into the capillaries
- larger lumen compared to arteries
- thinner elastic layer compared to arteries = blood pressure is lower
Vein structure
- thiner muscle layer
- thiner elastic layer = pressure too low for stretch and recoil action
- overall smaller thickness = no risk of bursting
- valves = prevent back flow when muscles contract
Capillary structure
- only endothelium = one-cell thick, short diffusion distances
- numerous and highly branched = larger SA for diffusion
- narrow diameter = closer to cells
- narrow lumen = RBCs squeezed flat so they’re closer to cells, reducing diffusion distances
- spaces between the lining cells - allow WBCs to escape to deal with infections
Tissue fluid formation - ultrafiltration, reabsorption, drainage
Ultrafiltration, arterial end
1. Blood is pumped through arteries, arterioles, capillaries, blood vessels get narrower
2. So high hydrostatic pressure in the capillaries
3. → Tissue fluid forced out of the capillaries into the surrounding tissue
Reabsorption, venous end
1. Hydrostatic pressure in the capillary decreases as tissue fluid moves out
2. So low hydrostatic pressure in the capillaries
3. Blood plasma has a lower water potential than tissue fluid due to proteins and cells left behind
4. → Tissue fluid moves back into the capillaries by osmosis and due to difference in hydrostatic pressure
Drainage, lymphatic system
1. Remaining tissue fluid enters lymphatic system - vessels are dead ends to allow flow in one direction only
2. Lymph fluid is moved by hydrostatic pressure and contraction of body muscles
3. Joins the circulatory system close to the heart
Cardiac cycle -
Cardiac cycle - a continuous series of events which make up a single heartbeat
cardiac consists of three phases:
Diastole - relaxation of the heart
Atrial systole - contraction of the atria
Ventricular systole - contraction of the ventricles
Diastole - relaxation of the heart
- Blood returns from vena cava and pulmonary vein, atria fill
- Pressure in the atria rises, opening the atrioventricular valves
- Muscular walls of both atria and ventricles are relaxed
- Pressure in the ventricles is reduced, so semi-lunar valves close
Atrial systole - contraction of the atria
- Muscle of the atria walls contract
- The remaining blood is forced into the ventricles
- Muscle of the ventricle walls are relaxed
Ventricular systole - contraction of the ventricles
- Muscle of the ventricles walls contract
- Blood pressure in the ventricles increases, forcing the atrioventricular valves to close to prevent back flow of blood
- Pressure in the ventricles rises further forcing the semi-lunar valves to open
- Blood leaves the heart through pulmonary artery and aorta
Cardiac output -
Cardiac output - volume of blood pumped by one ventricle of the heart in one minute.
cardiac output = stroke volume * heart rate
How the cardiac cycle is controlled?
- Wave of electrical activity spreads out from the sinoatrial node
- Wave spreads across both atria, causing them to contract, and reaches the atrioventricular node
- Atrioventricular node passes the wave between the ventricles along the bundle of His, after a short delay, and releases it at the apex, causing the ventricles to contract
- sinoatrial node - in the wall of the right atrium
- atrioventricular node - between the atria
- atrioventricular septum prevents the wave crossing to the ventricles in stage 1
