3.1.2 - Transport in Animals Flashcards
Why do multicellular animals need a transport system?
As they get larger their surface area to volume ratio decreases so diffusion is no longer sufficient to provide for their needs and metabolic rate.
What are open circulatory systems?
- Found in insects and arthropods
- The transport medium haemolymph is pumped directly into the open body cavity and there are very few transport vessels
- Haemolymph is pumped at low pressure and transports food and nitrogenous waste but not gases
What are closed circulatory systems?
- Found in all vertebrates such as fish and mammals and some invertebrates
- The transport medium blood is pumped from the heart through vessels
- Blood transports oxygen and carbon dioxide
What are single circulatory systems?
- The blood passes through the heart once per cycle
- Found in fish
- The blood is pumped by the heart through the gills to the body and back to the heart
What are double circulatory systems?
- The blood passes through the heart twice per cycle
- Found in birds and most mammals
- One circuit of blood vessels carries blood from the heart to the lungs for gas exchange
- The second circuit of blood vessels carries blood from the heart to the rest of the body to deliver oxygen and nutrients and to collect waste
What is the function of arteries?
Carry blood away from the heart
What is the structure of arteries?
- No valves
- Thicker walls than veins to help maintain blood pressure
- Collagen outer layer to provide structural support
- Thicker elastic layer than veins to help maintain blood pressure. The walls can stretch and recoil in response to the heart beat
- Thicker smooth muscle layer than veins so that constriction and dilation can occur to control the volume of blood
What are arterioles?
Connectors between arteries and capillaries
What is the structure of arterioles?
- No valves
- Thinner walls than arteries as pressure is slightly lower
- Thinner collagen layer than arteries
- Thinner elastic layer than arteries as pressure is lower
- Thicker smooth muscle layer than arteries to help restrict blood flow into capillaries
What is the function of capillaries?
Responsible for the exchange of oxygen, nutrients, and waste products between the blood and the cells
What is the structure of capillaries?
- No valves
- No smooth muscular wall
- No elastic layer
- No collagen layer
- One cell thick consisting of only a lining layer which provides a short diffusion distance for exchanging materials between the blood and cells
What are venules?
Connectors between capillaries and veins
What is the structure of venules?
- Have valves
- A thin layer of smooth muscle
- No elastic layer
- No collagen layer
- Very thin wall
What is the function of veins?
Carry blood to the heart
What is the structure of veins?
- Have valves
- Relatively thin smooth muscle layer so it cannot control the blood flow
- Relatively thinner than arteries as pressure is much lower
- Contains lots of collagen
- Thin walls as the pressure is much lower than arteries so there is low risk of the vessel bursting. The thinness means the vessels are easily flattened which helps the flow of blood up to the heart
What is hydrostatic pressure?
The pressure from fluid on the walls of the capillary usually forcing plasma out of the circulatory system
What is oncotic pressure?
Osmotic pressure from proteins in the blood plasma that draws water into the circulatory system
How is tissue fluid formed in the plasma?
At the arterial end there is high hydrostatic pressure due to the smaller diameter as the blood enters from the arterioles to the capillaries. This means there is a net flow of fluid out of the capillary to form tissue fluid
How is tissue fluid reabsorbed?
At the venous end there is low hydrostatic pressure due to the loss of liquid at the arterial end. This means there is a net flow of fluid back into the capillary by osmosis
What happens to the remaining fluid which isn’t reabsorbed?
It is absorbed into the lymphatic system and called lymph. It eventually drains back into the bloodstream near the heart
What is the composition of blood?
- Contains plasma with dissolved glucose, amino acids, mineral ions, hormones and large proteins
- Contains red blood cells, platelets and white blood cells
- Erythrocytes carry oxygen, carbon dioxide and antigens