6.2 - The Blood System Flashcards
Explain how William Harvey contributed to our current understanding of circulation.
Previously it was thought that:
- Arteries and veins were separate networks
Harvey proposed that:
- Arteries and veins belonged to the SAME network
- Arteries pumped blood FROM the heart
- Veins returned blood TO the heart
Outline the structure and function of arteries.
Function: carry blood at HIGH pressure AWAY from the heart to body tissues.
Structure:
- THICK wall
- THIN lumen
- NO VALVES
- ELASTIC
Outline the structure and function of veins.
Function: carry blood at LOW pressure TOWARDS the heart.
Structure:
- THIN wall
- LARGE lumen
- HAS VALVES
- not very elasticy…
Outline the structure and function of capillaries.
Function: exchange materials between the cells in tissues and the blood. Blood flows through at LOW pressure and hence it is SLOW.
Structure:
- capillary walls are ONE CELL THICK
- they have a VERY SMALL diameter
Describe the network of arteries, veins and capillaries altogether!
- arteries stemming from the heart split into arterioles
- these arterioles split into capillaries. Blood flows at low pressure and it moves very slowly
- after material exchange has occurred (oxygen and nutrients INTO body tissue cells, waste products and carbon dioxide OUT of body tissue cells)
- capillaries then pool into venules, which will collect into larger veins.
Draw the heart, including relevant labels!
Nice! Good job!
Explain how blood flows through the heart and lungs.
- deoxygenated blood enters the right atrium through the vena cava (veins).
- it then flows through the atrioventricular valve, and enters the right ventricle.
- the right ventricle contracts and blood is pumped through the pulmonary valve into the pulmonary artery
- here, blood is pumped to the lungs where gas exchange occurs…
- now, the oxygenated blood enters the left atrium through the pulmonary veins
- blood flows through the atrioventricular valve and into the left ventricle
- under very high pressure, blood is pumped through the aortic valve into the aorta
- blood is pumped through to the body tissues and the cycle begins again!!
Describe the pressure changes in the left atrium, ventricle and aorta during one cardiac cycle.
Two events: contraction or SYSTOLE and relaxation or DIASTOLE.
SYSTOLE/contraction
- blood fills the left atrium, increasing the pressure in the atrium and forces blood to flow into the ventricles
- as ventricles contract, pressure in the ventricles exceeds the pressure in the atria, causing the atrioventricular valves to snap shut (FIRST HEART SOUND)
- pressure builds up in the ventricles, and when ventricular pressure exceeds pressure in the aorta, the aortic valve opens and blood is released into the aorta
DIASTOLE/relaxation
- as blood exits the ventricle and travels down the aorta, ventricular pressure falls
- when ventricular pressure drops below aortic pressure, the aortic valve closes (SECOND HEART SOUND)
- when the ventricular pressure drops below the pressure in the atrium, the atrioventricular valve opens and blood flows from the atria to the ventricle
How is a heart beat generated?
- the sinoatrial node acts as a PACEMAKER
- the SA node sends out an electrical impulse
- this impulse causes the atria to contract and stimulate another node, the atrioventricular node
- the atrioventricular node sends signals to a nerve bundle called the Bundle of His
- this stimulates the Purkinje fibres in the ventricular wall - LEADING TO VENTRICULAR CONTRACTION
How can the heart rate increase/decrease?
Nerve signalling: the nerves can release neurotransmitter chemicals.
- noradrenaline: increases heart rate
- acetylcholine: decreases heart rate
Hormonal signalling: hormones are chemical messengers released into the bloodstream.
- adrenaline: released from the adrenal glands and increases heart rate
Outline the risk factors for coronary heart disease.
- AGE: blood vessels become less flexible with age
- GENETICS
- OBESITY: places strain on the heart
- DISEASES: such as diabetes
- DIET: high cholesterol and saturated fats diet
- EXERCISE: lack of exercise increases risk
- SMOKING: nicotine raises blood pressure
Outline the consequences of coronary heart disease.
Atherosclerosis is the hardening and narrowing of the arteries due to excess cholesterol. If coronary arteries become blocked, the region of heart tissue will die. This can lead to heart attacks.
