Blood Flashcards
What did William Harvey discover and how?
Discovered systematic blood circulation.
He demonstrates the blood flow in unidirectional with vavles preventing its backflow. The rate of flow through the major vessels is far too high for blood to be consumed in the organs. He predicted the presence of fine vessels in the tissues linking arteries to veins.
What is double circulation?
The blood passes through the heart twice for each complete circuit of the body. The heart is a double pump. It delivers blood under different pressures separately to the two circulations.
Arteries
Carry blood at high blood pressure away from the heart
Veins
Carry blood at low pressure to the heart
Capillaries
Very fine vessels, carry blood through tissues for exchange of materials between tissue and blood
Describe the structure of arteries
- High blood pressure
- thick wall
- three wall layers (tunica externa, media, and intima)
- large amounts of muscle and elastic fibres
- narrow lumen
- no valves
- large diameter of vessel
Describe the structure of vein
- low blood pressure
- thin wall
- three wall layers
- small amounts of muscle and elastic fibres
- wide lumen
-valves present - larger diameter of vessel than artery
Describe the structure of capillaries
-low pressure
-extremely thin walls
- one wall
- no muscle and elastic fibre
- very narrow lumen
- no valves
- very small diammeter
Why do arteries have thick walls and what is the purpose of the three walls?
To withstand the high blood pressure and prevent bursting
Tunica externa: made of collagen and gives strength
Tunica media: many muscle fibres and elastic fibres which help to pump blood
What are muscle fibres needed for and how?
Help to maintain the blood pressure between pump cycles- regulate the blood pressure by controlling the diameter of the lumen.
What are elastic fibres needed for and how?
Allow artery wall to stretch and recoil and also help maintain the blood pressure between cycles.
Why do capillaries have pores?
To allow plasma and tissue fluid to leak out and for phagocytes to squeeze out
Vasoconstriction
Narrowing of vessels
Vasodilation
Dilation of vessles
Describe vasoconstriction
When the temp drops, arterioles in the skin constrict. Shunt vessels which connect an artery to a vein, dilate providing an alternative path for blood. Thus blood bypasses the capillaries near the skin surface. Thus less blood flows to the skin capillaries so less heat is lost
