3.2 - Transport in animals Flashcards
Why do multicellular organisms require transport systems?
High metabolic demands
- Diffusion over long distances not fast enough
Small SA:V ratio
- Not enough surface available to absorb sufficient amount of
substances
Hormones and enzymes needed in different region to where they’re made
Waste products need to be removed from cells and transported to excretory organs
Describe the differences between an open and closed circulatory system
Open:
- Few transport vessels
- Haemolymph instead of blood - Doesn’t carry oxygen or carbon dioxide
- Haemolymph pumped straight from heart into body cavity at low pressure - Comes into direct contact with cells
- e.g. insects
Closed:
- Blood enclosed in blood vessels (e.g. veins, arteries)
- Does not come into direct contact with cells of body
- Heart pumps blood through vessels under high pressure
- Substances leave and enter blood by diffusion
- Blood flow can be diverted
- e.g. mammals
Describe the differences between a single and double circulatory system
Single:
- Blood passes through the heart once for each circuit of the body
- Passes through two sets of capillaries
- Oxygen and carbon dioxide exchanged in the first
- Nutrients and gasses exchanged with cells in the second
- e.g. fish
Double
- Blood flows twice through the heart for every once around the body
- Pulmonary circulation (heart - lungs - heart)
- Systemic circulation (heart - body - heart)
- e.g. mammals
Describe the structure and function of arteries
Structure:
- Three layers in their walls
- Thick smooth muscle and elastic fibre walls to withstand high pressures
- Narrow lumen to maintain high pressure
Function:
- Carry blood at high pressure from the ventricles of the heart to tissues of body
Describe the structure and function of veins
Structure:
- Three layers in their walls
- Thin smooth muscle and elastic fibre walls allows them to be pressed flat by muscles to carry blood under low pressure
- Valves to prevent backflow of blood
- Wide lumen for slow flowing blood
Function:
- Carry blood at low pressure
from the tissues of body to the atria of the heart
Describe the structure and function of capillaries
Structure:
- Single layer of endothelium
- Very narrow lumen
- Permeable walls
Function:
- Carry blood through tissues
- Exchange of materials between cells in the tissue and the blood in the capillary
What is the role of elastic fibres?
- Composed of elastin
- Can stretch and recoil - make vessel walls flexible
What is the role of smooth muscle?
Contracts and relaxes - changes size of lumen
What is the role of collagen?
Provides structural support for vessels
Why do artery walls require elastic fibres?
- Withstand force of blood pumped out of heart
- Stretch to take large volume of blood
- Recoil evens out surges of blood pumped from heart
Describe and explain how the wall of an artery is adapted both to withstand and maintain high hydrostatic pressure
To withstand pressure:
- Wall is thick and contains collagen - Provides strength
To maintain pressure:
- Thick layer of elastic fibres - Cause recoil to return to original size
- Thick layer of smooth muscle - Narrows lumen
Why is the lining of arteries smooth?
Allow blood to flow easily
What links arteries and capillaries?
Arterioles
How does the structure of arterioles differ to that of arteries?
- Arterioles have more smooth muscle, less elastic fibre
- Muscle can control blood flow to organs
- Smaller lumen
What is the function of capillaries?
Exchange of substances
How are capillaries adapted to their function?
- Large surface area for diffusion
- Narrow lumen - red blood cells pass through one at a time - Slows blood down to give more time for exchange
- Walls are one endothelial thick - Short diffusion pathway
What links capillaries to veins?
Venules
Describe the structure of venules
- Very thin walls with little smooth muscle - allows blood to flow into veins
- Do not have valves so cannot control blood flow
How are veins adapted to their function?
- Valves prevent backflow of blood
- Run between muscles - Contractions squeeze veins, forcing blood towards heart
- Smooth endothelial lining to allow blood to flow easily
Why do veins require valves?
- Blood under much lower pressure than in arteries
- No pumping from heart and little elastic recoil in veins - Blood might flow backwards as it moves towards heart against gravity
- Valves prevent backflow - open as blood flows towards heart and close if it flows in
opposite direction
Why do arteries require thicker walls than veins?
Blood flows at higher pressure through arteries
List the components of the blood
- Red blood cells - transports oxygen
- White blood cells - engulf and destroy pathogens
- Plasma - liquid that transports all other components of the blood
- Proteins - maintain osmotic potential of the blood
- Platelets - involved in blood clotting
What substances are transported by the blood?
- Oxygen to respiring cells
- Carbon dioxide away from respiring cells
- Digested food e.g. glucose, amino acids
- Nitrogenous waste e.g. urea
- Hormones
- Antibodies
- Platelets
Define tissue fluid
The fluid forced out of blood into surrounding space around cells
What is the role of tissue fluid?
- Deliver oxygen to respiring cells
- Remove carbon dioxide from respiring cells
- Deliver amino acids, glucose, hormones to cells
What feature of capillaries allows tissue fluid to form?
Small gaps between epithelial cells
Which components of the blood cannot be forced out of capillaries?
- Red blood cells
- Most white blood cells
- Plasma proteins
- All other substances dissolved in plasma can pass through gaps
Define hydrostatic pressure
- The pressure from heart beat
- Forces liquid out through gaps between cells of capillary linings
Define oncotic pressure
Tendency of water to move from a region of high water potential to a region of low water potential
Explain how hydrostatic and oncotic pressure affect the movement of fluids into and out of
capillaries
- Hydrostatic pressure forces liquid out of capillaries
- Hydrostatic pressure (4.6kPa) higher than oncotic pressure (-3.3KPa) at arterial end of
capillary - Water forced out of capillary and forms tissue fluid
- As blood moves along capillary more fluid moves out
- Hydrostatic pressure decreases
- By venous end of capillaries hydrostatic pressure falls to 2.3kPa
- Oncotic pressure remains at -3.3kPa throughout
- Plasma proteins too large to leave capillary so water potential remains constant
- Water moves back into capillary by osmosis at venous end
- Around 90% of tissue fluid moves back into capillaries
Define lymph
10 % of tissue fluid that does not return to capillaries
Describe the lymph system
- Lymph vessels
- Valves prevent backflow
- Lymph nodes - contain lots of lymphocytes
Where does lymph return to the blood?
Subclavian veins