B8 - Transport In Animals Flashcards
Open circulatory system
Transport medium pumped straight into the body cavity (hamocoel).
Pumped under low pressure
The transport medium directly contacts cells
It does not rely on diffusion as concentration gradients can not be maintained.
Closed circulatory system
Can be double (human) or single (fish)
Enclosed in blood vessels
Transport medium does not come into contact with cells and tissues.
Transport medium travels under pressure
Substances leave and enter the blood via diffusion
Similarities between open and closed circulatory systems
Liquid transport medium
Require a pumping mechanism
Can be described as a “mass transport system”
Artery structure
Narrow lumen
Lining called endothelium
Thick elastic layer
Thick smooth muscle layer
Tough outer layer (collagen)
Thin lining (endothelium)
Why do arteries have a narrow lumen
To keep the blood under high pressure while being pumped around the body
Why do arteries have a thick elastic layer
Elastic fibres allow arteries to withstand the force of the blood pumped and stretch to take a larger volume. The elastic fibres recoil and return to their original length. This helps to even out the surges of blood pumped from the heart to give a continuous flow.
Arterioles (structure and function)
Arterioles link the arteries and the capillaries. They have more smooth muscle and less elastin in their walls than arteries. They constrict or dilate to control the flow of blood into individual organs.
Vasoconstriction in arterioles
When the smooth muscle in the arteriole contracts it constricts the vessel and prevents blood flowing into a capillary bed. This is vasoconstriction.
Vasodilation in arterioles
When the smooth muscle in the wall of an arteriole relaxes, blood flows though into the capillary bed. This is vasodilation.
Capillaries (structure and function)
The capillaries are microscopic blood vessels that link the arterioles with the venules. The Lumen of a capillary is very small (10 micrometers). Substances are exchanged through the capillary walls between the tissue cell and the blood. Many substances pass out of the capillaries into the fluid surrounding the cells.
How capillaries are adapted for their role
The total cross-sectional area of he capillaries is always greater than the arteriole supplying them so the rate of blood flow falls. The relatively slow movement of blood through capillaries gives more time for exchange of materials by diffusion between the blood and the cells.
The walls are a single endothelial cell thick, giving a very thin layer for diffusion.
Where do arteries carry blood to
Arteries carry blood away from the heart to the tissues of the body. They carry oxygenated blood except in the pulmonary artery and (during pregnancy) the umbilical artery.
Where do veins carry blood to
Veins carry blood away from the cells of the body towards the heart. Except in the pulmonary vein and the umbilical vein.
Veins (structure and function)
Veins do not have a pulse
The blood pressure in the veins is very low compared with the pressure in the arteries.
Medium sized veins have valves to prevent the back flow of blood.
The walls contain lots of collage and little elastic fibre
Veins have a wide lumen
Thin lining called endothelium.
Why do veins have a wide lumen
Because blood in the veins is transported at low pressure.
Venules (structure and function)
Venules link the capillaries with the veins. They have very think walls and a little smooth muscle. Several venules join to form a vein.
How does deoxygenated blood return to the heart
The majority of the veins have one way valves at intervals that prevent backflow.
Many of the bigger veins run between active muscles in the body. When the muscles contract they squeeze the veins, forcing the blood toward the heart.
The breathing movements of the chest act as a pump. The pressure changes and the squeezing actions move blood in the veins of the chest and abdomen towards the heart.
What does the endothelium do
The endothelium is in both the veins and the arteries, it is a thin lining that ensures the blood flows easily.
What flows into the right atrium
Deoxygenated blood through the vena cava at relatively low pressure
How thick is the muscle in the atria
Thin muscular walls
What happens when blood enters the right atria
Slight pressure builds up until the atria-ventricular valve (the tricuspid valve) opens to let blood pass into the right ventricle. When the atrium and ventricle are filled with blood the atrium contracts, forcing the blood into the right ventricle. Tricuspid valve then closes, preventing blood backflow.
What do tendinous cords do
They make sure the valves are not turned inside out by the pressures exerted when the ventricle contracts.
What happens when the right ventricle contracts
It pumps deoxygenated blood through the semilunar valves into the pulmonary artery, which transports it to the capillary beds of the lungs. The semilunar valves prevent the back flow of blood into the heart.
What enters the left atrium
Oxygenated blood from the lungs enters the left atrium from the pulmonary vein.
What happens when oxygenated blood enters the heart
As pressure in the atrium builds the bicuspid valve opens between the left atrium and the left atrium and the left ventricle so the ventricle also fills with oxygenated blood. When both are full the atrium contracts, forcing all the oxygenated blood into the left ventricle. The left ventricle then contracts and pumps oxygenated blood through semilunar valves into the aorta and around the body. As the ventricle contracts the tricuspid valve closes, preventing any back flow.
Why is the muscular wall of the heart much thicker than that of the right
The left side has to produce sufficient force to overcome the resistance of the aorta and the arterial systems of the whole body and move the blood under pressure to all the extremities of the body.
