Module 3.2 - Transport in Animals Flashcards
What factors affect the need for a transport system?
- Size
- SA:vol ratio
- Level of metabolic activity
How does size affect the need for a transport system?
- Cells further from surface, diffusion pathway increases
- Diffusion rate reduced + diffusion too slow to supply all requirements
- Outer layers of cells use up all supplies so less would reach cells deep in body
How does surface area to volume ratio affect the need for a transport system?
-Larger organisms have larger SA:vol ratio so each g of SA has smaller body surface for exchange
How does level of metabolic activity affect the need for a transport system?
- Animals get energy from food for movement
- Releasing energy from food by aerobic respiration requires oxygen
- In animal is active, cells need good supplies of nutrients to supply energy for movement
- Animals that keep themselves warm need even more energy
What are the features of a good transport system?
-Fluid/medium to carry nutrients, oxygen + wastes around body (blood)
-Pump to create pressure to push fluid around body (heart)
-Exchange surfaces that enable substances to enter blood + leave again where needed (capillaries)
For efficiency:
> Tubes/vessels to carry blood by mass flow
> 2 circuits: one to pick up oxygen (pulmonary) + one to deliver oxygen to respiring tissues (systemic)
What is the route of blood through a single circulatory system (e.g. fish)?
heart –> gills –> body –> heart
What is the route of blood through a double circulatory circuit (e.g. mammals)?
heart –> body –> heart –> lungs –> heart
What are the disadvantages of a single circulatory system?
- Blood pressure drops as blood passes through tiny capillaries of gills
- Blood has low pressure as it flows towards body - won’t flow very quickly
- Rate at which O2 + nutrients delivered to respiring tissues + CO2 + urea is removed is limited
What are the advantages of a double circulatory system in mammals?
- Blood pressure mustn’t be too high in pulmonary circulation as may damage lung capillaries
- Heart can increase pressure of blood after passing through lungs, so blood is under higher pressure as it flows to body + flows more quickly
- Systemic circulation can carry blood at higher pressure than pulmonary circulation
Give an example of an animal with an open circulatory system.
Insects
How do substances get around animals with open circulatory systems?
- Movement helps to circulate blood, when stationary blood stops moving so transport stops
- Insects: muscular pumping organ similar to heart just under dorsal of body. Blood enters heart through pores (ostia) which pumps towards head by peristalsis. At front end of heart blood pours into body cavity. Can continue at rest but movement may affect circulation
- Larger insects (e.g. locusts): -Open ended tubes attached to heart. Direct blood towards active parts of body e.g. leg + wing muscles
What are the disadvantages of an open circulatory system?
- Blood pressure low + blood flow is slow
- Circulation of blood may be affected by body movements or lack of
What are the advantages of a closed circulatory system with tissue fluid to supply cells with the necessary substances?
- Higher pressure so blood flows quicker
- More rapid delivery of oxygen + nutrients
- More rapid removal of CO2 + other wastes
- Transport is independent of body movements
What is the blood in the arteries like?
-High pressure so arterial wall has to be thick
Describe the structure of arteries.
-Narrow lumen to maintain high pressure
-Thick wall to withstand high pressure. 3 layers:
> Inner layer: thing layer of elastic tissue allowing stretch + recoil to help maintain blood pressure
> Middle layer: thick layer of smooth muscle
> Outer layer: relatively thick layer of collagen + elastic tissue, providing strength to withstand high pressure + recoil to maintain pressure
Where are arterioles found?
Between arteries and capillaries - distribute blood from the artery to the capillary
Describe the structure of arterioles.
- Arteriole walls contain smooth muscle that contracts to constrict diameter of arteriole to increase resistance to decrease rate of flow of blood
- Constriction of arteriole wall can be used to divert flow of blood to regions of body demanding more oxygen
Describe the structure of capillaries.
- Very narrow lumen: diameter about same as RBC (7μm) so RBCs squeezed against walls of capillary as they pass along it, reducing diffusion path of oxygen to tissues. Also increases resistance so reduces rate of flow
- Walls consist of a single layer of flattened endothelial cells reducing diffusion distance for materials being exchanged
- Walls are leaky allowing blood plasma + dissolved substances to leave the blood
Where are venules found?
Between capillaries and veins - collect blood from capillary bed + lead into veins
Describe the structure of venules.
- Wall consists of a think layer of muscle + elastic tissue outside endothelium
- Thin outer layer of collagen
Describe the structure of veins.
- Relatively large lumen to decrease resistance to ease flow of blood
- Walls; thinner layers of collage, smooth muscle + elastic tissue than artery walls. Don’t need to stretch + recoil + are not actively constricted to reduce blood flow
- Valves: help blood flow back to heart + prevent it flowing in opposite direction
- Walls are thin so vein can be flattened by action of surrounding skeletal muscle. Contraction of surrounding skeletal muscle applies pressure to blood forcing blood to move along in a direction determined by valves
How does tissue fluid form?
- At arteriole end of capillaries blood is under high hydrostatic pressure due to heart’s contractions
- This pressure pushes blood fluid (plasma) out of capillaries through gaps between cells of capillary wall. This happens as the hydrostatic pressure is higher than the oncotic pressure
- Plasma + dissolved substances leave the blood
- RBCs, platelets + most WBCs are too large to leave so stay in capillary
- Tissue fluid surrounds cells for exchange to occur
How is tissue fluid drained?
- Some returns to capillaries: low hydrostatic pressure at venule end + oncotic pressure now high due to plasma proteins in the blood, fluid moves back into blood carrying dissolved wastes down a pressure gradient
- Rest leaves through lymphatic system
How does fluid from tissue fluid reenter the blood through the lymphatic system?
- Pores allow fluid to leave tissue fluid + enter lymph vessels
- Removes large proteins + neutrophils from tissue fluid to reenter blood
- Lymph vessels drain lymph into large vessels which eventually rejoin blood system in the chest (via subclavian vein)