Topic 1 - Heart and Circulation Flashcards
Define mass flow
The transport of substances in bulk from one part of an organism to another
Why can larger organisms not rely only on diffusion
Low surface area to volume ratio
Mass transport allows organisms to overcome:
The limitations of diffusion
Main function of exchange surfaces?
To establish and maintain differences in conc and pressure
Two examples of mass flow systems
Xylem and phloem in a plant
Name 4 features of a mass flow system
- A system of vessels to carry substances
- A means of making sure substances are moving in right direction
- A means of maintaining conc gradient so that substances move fast enough to meet organisms needs
- Suitable transport medium
2 types of circulatory system
Closed - mammals
Summary of open circulation
- Simple heart pumps blood into cavities surrounding insects organs
- Substances diffuse in/out of cells directly into blood
- Heart relaxes, blood is drawn back into heart though small calves along length of heart
Closed circulatory systems are generally for…
Larger animals that are more active
Critical structural difference between open and closed circulation
Closed: blood is enclosed in tubes (arteries, veins, capillaries)
Main advantage of closed system
Blood is forced along narrow channels, creating higher blood pressure
Why is higher blood pressure better
Blood travels faster so more efficient at delivering substances around the body
What type of circulatory system do fish have
Single
What’s the main feature of single circulation
Blood only flows through heart once for each circulation
3 steps of single circulation
- Heart pumps deoxygenated blood to gills
- Gas exchange takes place as blood passes through gills (large SA)
- Blood leaves gills, oxygenates body, returns to heart
Describe simply double circulation
1) right ventricle pumps deoxygenated blood to lungs to be oxygenated
2) blood returns to heart, pumped a second time from left ventricle to rest of body
Advantages of double circulation
- blood can be pumped at power pressure to lungs, reducing risk of vessel damage
- blood returning from lungs gets an extra boost, speeding circulation around the body
Two types circulation in humans:
Pulmonary circulation- low pressure, from heart to lungs, (40mmHg)
Systemic circulation- high pressure, carries blood from heart to body and back, (120mmHg)
Structure of capillaries
Smaller diameter means RBCs have to flex to pass though, slows down so more time for diffusion
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Endothelium is permeable to water and dissolved substances
-
Small pores in walls
Structure of arteries near the heart
Middle layer is composed of elastic fibres, allowing them to dilate then elastically recoil
Structure of arteries further from the heart
Supplied with neurones that can stimulate vasodilation/constriction
Structure of arterioles
Smallest type of arteries, consist of endothelium with a few muscle fibres wrapped around them
Structure of veins
Much less muscle and elastic fibres in middle layer, so wall is thinner - Diameter of lumen is greater - Valves to prevent back-flow
How do skeletal muscles help to circulate blood?
Venous return
Contract, squeezing veins, create higher pressure in vein
What coronary arteries
Can not get from 4 chambers directly
Cardiac cycle =
One complete sequence of contraction and relaxation
2 main stages of cardiac cycle
Diastole: heart relaxes, fills with blood
What happens in atrial systole
Atria contract - This pushes blood into ventricles - Opens atrio-ventricular valves
What happens in ventricular systole
Ventricles contract - Atria relax - A/V valves close - Blood enters aorta and pulmonary vein, opening semi-lunar valves
What happens in ventricular diastole
Ventricles relax - Semi-lunar valves close - Pressure in ventricles fall so blood flows into them from atria - A/V valves open
What is cardiac diastole
When both atria and ventricles are relaxed at the same time
What artery takes blood from heart to body at high pressure
Aorta
How is the left ventricle structural adapted for us function
Has thicker more muscular walls
What is the function of atrioventricular valves?
Stop backflow when ventricles contract
Where are semi-lunar valves found?
Aorta
What’s the function of semi lunar valves
Stop blood flowing back into the heart
Four structural features of an artery
Elastic tissue - Thick muscle layer - Lumen - Folded endothelium
4 features of a vein
Large lumen - Think muscle wall - Valves - Endothelium
What are capillaries for?
Metabolic exchange- substances are exchanged between cells and capillaries
Contraction is…
Systole
Relaxation is of the heart is…
Diastole
