3.2.6 The Circulation of Blood and The Structure Of The Mammalian Heart Flashcards Preview

A-level Biology Oxford AQA > 3.2.6 The Circulation of Blood and The Structure Of The Mammalian Heart > Flashcards

Flashcards in 3.2.6 The Circulation of Blood and The Structure Of The Mammalian Heart Deck (65)
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What is the function of the circulatory system?

Transports raw materials from specialised exchange organs to body cells


Describe the 2 circuits the circulatory system consists of

  • 1 takes blood from heart to lungs, then back to heart
  • Other loop takes blood around the rest of the body


What the function of a vein?

Take blood back to heart under low pressure


Describe the structure of a vein 4x

  • Large lumen
  • Very little elastic or muscle tissue = thin walls
  • Contain valves to prevent blood flowing backwards
  • Blood flow is helped by contraction of body muscles surrounding veins


What is the function of arteries?

Carry oxygenated blood from heart to rest of body


Describe the structure of arteries 2x

  • Walls = thick, smooth muscular & have elastic tissue
  • Endothelium (inner lining) is folded


What does the walls of the arteries do and what does this help to do? (3)

  • Stretches under high pressure
  • Recoils under low pressure
  • Helps to maintain blood pressure


Arteries divide into smaller vessels called _____



What is the function of arterioles?

Control blood flow from arteries to capillaries


Describe how arterioles control blood flow

  • Muscles contracts & arterioles narrow to restrict blood flow to capillaries or relax to allow full blood flow


Arterioles branch into _____



What is the function of capillaries?

Exchange substances between blood and body tissues


Name 4 adaptations of capillaries for efficient diffusion

  1. Found near cells in exchange tissues = short diffusion pathway
  2. Walls = single layer of endothelium cells = shortens diffusion pathway
  3. Large no. of capillaries & highly branched = increase SA for exchange
  4. Narrow lumen so RBCs are squeezed flat against capillary
    • Reduces diffusion distance


What are capillary beds?

Network of capillaries in tissue


Capillaries have ___ between lining (endothelial) cells



Why do capillaries have gaps between lining (endothelial) cells?

  • They act as a sieve - controlling which molecules can leave the capillaries
  • Allows WBCs to escape 


What is tissue fluid?

Fluid that surrounds cells 


What is tissue fluid made from?

Small molecules that leave blood plasma (e.g. oxygen, water and nutrients)


Why doesn't tissue fluid contain RBCs or big proteins?

∵ they're too large to be pushed out through capillary walls


What do cells do with tissue fluid?

They take in oxygen and nutrients from tissue fluid & release metabolic waste into it


In capillary bed, substances move out of capillaries into tissue fluid, by ____ _____

pressure filtration


Describe how substances move out of capillaries into tissue fluid by pressure filtration

  1. At start/arterial end of capillary bed: hydrostatic (liquid) pressure inside capillaries > hydrostatic pressure in tissue fluid
  2. Difference in hydrostatic pressure = pressure forces water/fluid + small molecules out of capillaries & into spaces around cells, forming tissue fluid
  3. Loss of water/fluid = hydrostatic pressure reduces in capillaries ∴ hydrostatic pressure is lower at venule end
  4. + there's increasing conc. of plasma proteins ∴ Ψw at venule end is lower than Ψw in tissue fluid 
  5. Some water re-enters capillaries from tissue fluid at venule end by osmosis


If asked about a particular end of the capillary, what do you need to do?

Compare hydrostatic pressure and osmotic pressure


Explain how fluid leaves the capillary at the arterial end

Hydrostatic pressure is greater than osmotic effect which forces molecules/fluid out


What within the bloodstream can affect the water potential?



If water moves out of the capillary, what happens to the water potential?

The water potential in the capillary will go down

(Proteins within bloodstream can affect the water potential)


Water potential of blood plasma is more negative at venule end of the capillary than at arteriole end of capillary. Explain why. (2)

  • Water has left the capillaries
  • Proteins (in blood) are too large to leave capillary
    • Increasing conc. of blood proteins & thus water potential ↓


What happens to excess tissue fluid?

It's drained into lymphatic system


What is swelling essentially?

Swelling → excess tissue fluid


Describe the lymphatic system

  • Network of tubes that acts like a drain
  • Have a dead end

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