3.2 Exchange in animals Flashcards
What happens in a single circulatory system?
The blood passes through the heart once during one complete circuit of the body
What happens in a double circulatory system?
the blood passes through the heart twice during one complete circuit of the body
What is a closed circulatory system?
blood is pumped around the body and is always contained within a network of blood vessels
—> vertebrates and invertebrates
What is an open circulatory system?
blood is not contained within blood vessels but is pumped directly into body cavities
—> arthropods and molluscs
Explain the features of the circulatory system in insects
- The dorsal vessel is the main blood vessel
- The tubular heart in the abdomen pumps haemolymph into the dorsal vessel
- The dorsal vessel delivers the haemolymph into the haemocoel (body cavity)
What do arteries do?
transport blood away from the heart (usually at high pressure) to tissues
What do arterioles do?
arteries branch into narrower blood vessels called arterioles which transport blood into capillaries
What do veins do?
transport blood to the heart (usually at low pressure)
What do venules do?
these are narrower blood vessels transport blood from the capillaries to the veins
What is the structure of arteries?
Tunica externa: collagen shell to prevent the vessel bursting
Tunica media: Thick layer of smooth muscle and elastic fibres
Tunica intima: an endothelial layer, a layer of connective tissue and a layer of elastic fibres
—> smooth to reduce friction for smooth blood flow
What is the structure of arterioles?
Thin muscle layer which can contract, to direct blood to areas which need it
Connects arteries to capillaries
What is the structure of veins?
- Thinner tunica media as they don’t withstand high pressures
- Contains valves to prevent the backflow of blood
- Larger lumen helps to ensure that blood returns to the heart at an adequate speed
What is the structure of venules?
- Connect the capillaries to the veins
They have few or no elastic fibres and a large lumen
As the blood is at low pressure after passing through the capillaries there is no need for a muscular layer
What is the function of capillaries?
allows substances to leave the blood to reach the body’s tissues
They can form networks called capillary beds which are very important exchange surfaces within the circulatory system
What is the structure of capillaries?
Very small diameter: Forces blood to travel slowly to allow more diffusion
Walls one cell thick: Reduces diffusion distance
Pores: allows blood plasma to leak out and form tissue fluid
What is hydrostatic pressure?
The pressure exerted by a fluid, e.g. blood
What is oncotic pressure?
The osmotic pressure exerted by plasma proteins within a blood vessel
Plasma proteins lower the water potential within the blood vessel, causing water to move into the blood vessel by osmosis
How is tissue fluid formed?
As blood passes through capillaries some plasma leaks out through gaps in the walls of the capillary to surround the cells of the body
This results in the formation of tissue fluid
What is the composition of tissue fluid?
Very similar to plasma - yet contains fewer proteins, as these are too large to fit through the gaps in the capillary walls
What happens at the arterial end?
- blood is at the arterial end of a capillary the hydrostatic pressure is great enough to force fluid out of the capillary
- Proteins remain in the blood as they are too large to fit out of pores in the capillary
- this creates a water potential gradient, between the capillary and tissue fluid
- the hydrostatic pressure is greater than the osmotic pressure so the net movement of water is out of the capillaries into the tissue fluid
What happens at the venous end?
- the hydrostatic pressure within the capillary is reduced due to increased distance from the heart and the slowing of blood flow as it passes through the capillaries
- same WP gradient as at the arterial end
- the oncotic pressure is greater than the hydrostatic pressure and water begins to flow back into the capillary from the tissue fluid
—> 90% fluid lost is returned
—> 10% which remains is tissue fluid
What happens if blood pressure is high?
The pressure at the arterial end is even greater
This pushes more fluid out of the capillary and fluid begins to accumulate around the tissues. This is called oedema
How is lymph formed?
- Some tissue fluid enters lymph vessels
- These have larger pores and allow large molecules to pass through
- Plasma proteins return to the blood via lymph capillaries
What is the heart found inside of?
Pericardium - thin membrane attached to the diaphragm which keeps the heart in place
Which blood vessels bring deoxygenated blood to the heart?
Superior and inferior Vena Cava
Arrives at right atrium
Which blood vessels take deoxygenated blood from the heart to the lungs?
Pulmonary artery
Which blood vessel brings oxygenated blood from the lungs to the heart?
Pulmonary vein
Arrives at left atrium