Blood vessels and their functions

Artery structure related to function

The function of arteries is to transport blood rapidly under high pressure from the heart to the tissues.

Vein structure related to function

Veins transport blood slowly, under low pressure, from the capillaries in tissues to the heart.

The outward pressure is opposed by two forces:

-Hydrostatic pressure of the tissue fluid outside the capillaries, which resist outward movement of liquid. -The lower water potential of the blood, due to the plasma proteins that causes water to move back into the blood within capillaries.

The contents of the lymphatic system is moved by;

-Hydrostatic pressure of the tissue fluid that has left the capillaries. -Contraction of the body muscle that squeeze the lymph vessels to ensure that the fluid inside them moves away from the tissues in the direction of the heart.

Return of tissue fluid to the circulatory system process:

-Loss of tissue fluid from capillaries reduces the hydrostatic pressure inside them. -By the time the blood has reached the end of the capillary, the pressure is lower than on the outside. -Tissue fluid is forced back into the capillary by higher hydrostatic pressure outside them. -Also, the plasma has lost water, meaning that it has a lower water potential than tissue fluid. -As a result, water leaves the tissue by osmosis down a water potential gradient.

The structure of arteries is adapted to its function (part 2)

-The elastic layer is relatively thick compared to veins- because its important that blood pressure in it is kept high if blood is to reach all parts of the body. The elastic wall stretches at each heart beat and springs back when the heart relaxes, which helps to maintain high pressure and smooth pressure surges created by the beating of the heart.

The structure of arteriole is adapted to its function

-The muscle layer is relatively thicker than in arteries -The contraction allows constriction of the lumen of the artetriole. This restricts the flow of blood and so control its movement into capillaries. -The elastic layer is relatively thinner than in arteries-because blood pressure is lower.

The structure of veins is adapted to its function

-The muscle layer is relatively thin-because they cant control the flow of blood, instead takes it away from tissues. -The elastic layer is relatively thin-as the low pressure of blood wont cause them to burst. -The overall thickness of the wall is small-no need for a thick wall as there is no risk of bursting. -There are valves at intervals throughout- to stop backflow.

The structure of arteries is adapted to its function (part 1)

-The muscle layer is thick -This means smaller ones can be constricted and dilated in order to control the volume of blood pass through it. -The overall thickness of the wall is great- also resists the vessel bursting under pressure. -There are no valves- because blood is under constant high pressure due to heart pumping blood, therefore tends not to flow backwards.

The structure of capillary is adapted to its function

-The walls consist mostly of lining layer- which is thin for rapid diffusion. -Numerous and highly branched-providing large surface area. -Lumen is so narrow-so that blood cells are squished for reduced diffusion distance. -Have a narrow diameter-so that no cell is far away. -Space between the lining cells-allow white blood cells to escape in order to deal with infections.

Types of blood vessels

Arteries (carry blood away from the heart and into arterioles), arterioles (are smaller arteries that control blood from arteries to capillaries), capillaries (are tiny vessels that link arterioles to veins) and veins (carry blood from capillaries back to the heart).

Formation of tissue fluid

It is formed from blood plasma. The composition of blood plasma is controlled by various homeostatic systems, which provides a mostly constant environment for the cells it surrounds.

Lymphatic system

Its a system of vessels that begin in the tissue. Initially the resemble capillaries (but they have dead ends), but they gradually merge into larger vessels that form a network throughout the body. These vessels drain their contents back into the bloodstream by two ducts that join veins close to the heart.

Capillary structure related to function

Its to exchange metabolic materials between the blood and cells of the body. The flow is much slower.

Return of tissue fluid to the circulatory system

Once tissue fluid has exchanged metabolic materials with the cells it bathes, its returned to the circulatory system. Most tissue fluid returns to the blood plasma directly by the capillaries, but not all can. The remainder is carried back to the lymphatic system.

Movement of tissue fluid

Pumping by the heart creates a pressure (hydrostatic pressure) at the arterial end of the capillaries. This pressure causes tissue fluid to move out of the blood plasma. The combined effect of all these forces create ab overall pressure that pushes tissue fluid out of the capillaries. Its only enough pressure to force small molecules out of the capillaries, leaving proteins in the blood. This type of filtration under pressure is called ultrafiltration.

Arteriole structure related to function

They carry blood under lower pressure than artery from artiers to capillaries. They also control the flow of blood between the two.

Tissue fluid

Tissue fluid is the means by which materials are exchanged between blood and cells and it bathes all the cells of the body.

Arteries, arterioles and veins basic structure ( from the outside inwards)

Tough fibrous outer layer (resists pressure changes from both within and outside), muscle layer (can contract and so control flow of blood), elastic layer (helps maintain blood pressure by stretching and recoiling), thin inner lining ((endothelium) is smooth to reduce friction and thin to allow diffusion) and lumen (central cavity of the blood vessel through which blood flows).