Mass Transport in Animals

• Mass flow is the bulk movement of liquids (and gases) due to a pressure difference
• Closed systems (liquid within tubes) are more efficient than open systems
• The lower the surface are to volume ratio of an organism the greater the need for a specialised transport system.
• Mammals have a double circulatory system (blood passes twice through the heart for each complete circuit of the body)
• Double circulatory systems have blood moving at a higher pressure compared to a single circulatory system.
• Double circulatory systems keep deoxygenated and oxygenated blood separate
• The heart is made up from cardiac muscle and pumps blood around the body
• The vena cava is the main vein returning blood to the right atrium
• The pulmonary artery takes the blood from the right ventricle to the lungs
• The pulmonary vein returns the blood from the lungs to the left atrium (oxygenated)
• The Aorta is the main artery taking blood from the heart to the organs
• The coronary arteries branch from the aorta and take blood to the muscle of the heart
• The livers function is to absorb food molecules
• The Hepatic artery takes blood from the aorta to the liver
• The Hepatic vein takes blood from the liver to the vena cava
• The Hepatic Portal Vein takes blood from the intestines to the liver (contains absorbed food molecules)
• The kidney is responsible for excretion of nitrogenous waste and for osmoregulation
• The Renal artery and vein takes blood to and from the kidney
• Arteries have a outer coat of connective tissue (collagen fibres), a thick layer of muscle and elastic tissue and a small lumen.
• A vein has a outer coat of connective tissue(collagen fibres), a thin layer of muscle and elastic tissue and a large lumen.
• The blood enters the artery at a relatively high pressure the moves down the pressure gradient to the arteriole then the capillaries then the venule and then to the vein where it has a relatively low pressure
• Arteries have a inner endothelial layer that is once cell thick (endothelial cells) that is smooth to reduce friction
• arteries have a large amount of elastic protein fibres that allows the wall to stretch preventing the blood pressure firm rising too high
• Arteries have a muscle layer (smooth) that contracts constricting helping to reduce the volume of blood passing through
• The outer layer of arteries and veins are made out of fibrous proteins and gives strength and support to the walls helping it to resist damage caused by high pressure
• Arterioles have a thinner elastic layer but a thicker muscle layer than arteries. They can also relax the muscle to dilate the vessel to allow for more blood flow.
• Capillaries only have an endothelial layer
• capillaries have a a small diameter and a high cross sectional area but there are a large number of capillaries
• Veins have similar structure to arteries but have a thin muscle/elastic layer and they also contain valves to control blood flow instead
• In arteries there is a high fluctuation of pressure (pulsa)
• Capillaries are very thin in order to increase the rate of diffusion
• Capillaries also have wall spaces (gaps in the walls) to allow for a rapid formation of tissue fluid
• Tissue fluid is made out of water,oxygen,glucose,amino acids and plasma
• The hydrostatic pressure in the capillaries is greater than the tissue fluid so therefore there is a net movement of fluid out of the capillaries
• The water potential of the blood is lower than the tissue fluids water potential
• The difference in water potential causes the tissue fluid to be forced back into the capillaries further along the capillaries once the hydrostatic pressure has decreased
• the blood starts of in the capillaries with a high hydrostatic pressure and it decreases as the blood moves along the capillaries
• The hydrostatic pressure causes plasma to leave the capillaries
• More liquid leaves the capillaries than enters them therefore the fluid drains into the lymphatic vessels
• The lymphatic vessels merge together forming a network in the body that eventually empty back into the blood stream in veins (in the neck region)