3.4b The Circulatory System - Blood Vessels and Tissue Fluid

What is the lymphatic system?

A system of vessels throughout the body which start in the tissues and rejoin the veins.

What do arteries do? What do they need to be adapted for?

Arteries transport blood directly from the heart to the respiring tissues of the body. Because the blood is leaving the heart it has a high pressure.The arteries must be able to cope with this high pressure and also maintain it so the blood reaches the extremities.

Which vessels have a layered structure? How are they different from each other?

Arteries, arterioles and veins all have a similar structure where the lumen is surrounded by layers.

What do arterioles do?

Arterioles are basically smaller arteries which link the arteries and capillaries. They basically control the blood flow from the arteries by lowering the speed and pressure when it enters the capillaries so it doesn't make the capillaries burst.

Name the four main types of blood vessel

Artery, arteriole, capillary, vein

Where does tissue fluid return to the capillaries?

At the venous end of the capillaries, when the capillaries become veins

Why does tissue fluid move back into the capillaries from the tissues?

Because the blood in the venous end of the capillaries has not only a very low pressure but also a very low water potential. Tissue fluid moves in readily down a pressure and water gradient.

Why does blood slow down as it goes through capillaries?

Because they are so narrow and delicate it must slow down. This also increases the time for exchange to occur.

What is the special function of capillaries?

Capillaries are an exchange surface, not a transport vessel. They are the site where materials like oxygen move out of the blood and into the tissues.

How is tissue fluid formed?

Hydrostatic pressure forces tissue fluid to leave the blood in the capillaries; it then diffuses out oft eh capillaries.

What creates hydrostatic pressure and where?

Hydrostatic pressure is the pressure of the blood in the arterioles, originally from the heart.

What two pressures keep the lymph flowing in the lymph vessels?

Hydrostatic pressure of the tissue fluid, and the contraction of the body muscles which flattens the lymph vessels.

What is tissue fluid actually made of?

It is a watery fluid made of the smallest parts of the blood - the blood plasma with the suspended glucose, amino acids, ions, fatty acids, oxygen

What is the lining layer like? Why?

It is very thin, made of epithelial cells. This means it has a short diffusion distance and it also has a smooth layer.

Give ways large surface areas are achieved in capillaries.

Numerous and highly branched, very tiny

What kind of materials do capillaries exchange?

Oxygen, glucose, amino acids, fatty acids, ions, carbon dioxide.

Why are there gaps in the lining cells of capillaries?

So white blood cells can escape the blood and enter the tissues to deal with infections there.

Describe the blood vessels the blood passes through from when it leaves the heart through the aorta.

The blood leaves the heart through the aorta and passes into the arteries, where it travels at a high blood pressure to the respiratory tissues oft he body. Here it will flow into the smaller arterioles where the blood pressure is controlled before it enters the tiny capillaries. Exchange of materials happens here. it will then leave the capillaries and enter the veins to flow back to the heart, now at a low pressure.

What is the elastic layer for?

The elastic layer can stretch and spring back in a recoil action, This helps to maintain blood pressure and the smooth pressure surges that keep the blood moving.

What is ultrafiltration?

The filtration of tissue fluid and the materials in it out of the blood, under high pressure including hydrostatic pressure.

What does not leave the blood in tissue fluid? Why doesn't it?

The larger molecules of the blood are too big to pass the membranes of the capillaries so they are not in tissue fluid. These include white and red blood cells, platelets and proteins.

What is the muscle layer for?

The muscle tissue in the muscle layer can contract and expand to constrict and control the flow of blood.

How do valves work in the veins and why?

The pocket valves are cusp shaped. Blood should flow from the convex to the concave side. When the blood pools within the cusps (on the wrong side) they press closely together to prevent the blood flowing backwards.

Why don't arteries need valves?

The pressure in the arteries is always high as it comes from the heart and also as they have such thick muscle and elastic. Therefore blood generally always flows in the correct direction.

What is the tough outer layer for?

The tough fibrous other layer protects the vessel and resists it bursting under pressure both from the blood inside and the fluid outside.

Give three ways short diffusion distances are achieved in capillaries.

The walls are very thin epithelial tissues. The capillaries are narrow so blood cells must be flattened against the walls. Numerous and highly branched so no cells is far from a capillary.

What is tissue fluid carrying when it re-enters the circulatory system?

The waste materials of the cell including carbon dioxide.

Describe the structure of arteries.

They have an overall very thick wall which is needed to resist the high pressure so they don't burst. They have a thick muscle layer as this needs to constrict and dilate the artery to control blood flow. They have a thick elastic layer to maintain the high blood pressure by the recoil action. They have no valves.

What is the structure of veins like?

Thinner overall wall, thinner muscle, thinner elastic as the pressure and speed are low; there is little chance of bursting. Pocket valves at regular intervals to prevent backflow of blood due to low pressure.

Describe the movement of tissue fluid in terms of hydrostatic pressure.

Tissue fluid always moves from a place of higher hydrostatic pressure, to one of lower pressure.

Name the two ways tissue fluid can return to the circulatory system.

Tissue fluid can return directly into the capillaries and go back to the heart in the veins, or it can enter the lymphatic system and return to the heart by the lymph vessels which eventually join the veins.

What does tissue fluid do?

Tissue fluid is the immediate environment which bathes all cells. It provides a constant environment for cells to live in and is the final place where exchange happens. The materials that need to move from the blood to the cells are within the tissue fluid.

Describe the movement of tissue fluid in terms of water potential.

Tissue fluid will move from a place with a higher water potential to one with a lower water potential by osmosis.

Name the layers.

Tough fibrous outer layer Muscle layer Elastic layer Thin epithelial lining layer Lumen

What resists the hydrostatic pressure?

Two forces resist the hydrostatic pressure forcing tissue fluid out of the blood: - the hydrostatic pressure of the fluid already outside the capillaries - the fact that blood has a low water potential so normally fluid would move into it

What do veins do? how do they need to be adapted?

Veins transport blood at a lower pressure and speed back towards the heart to receive another pump. They don't need adaptations to cope with pressure but they do need to be adapted to ensure blood flows in the correct direction.

How does the lymphatic system rejoin the circulatory system?

Via two ducts which join the veins closer to the heart.

How is the lymphatic system related to absorption of lipids?

When chylomicrons move out of the epithelial cells of the ileum, they enter lacteals which are lymph vessels in the villi.

What is the structure of arterioles like?

they have a thicker muscle wall to be able to constrict the blood flow. They have thinner elastic as the pressure is lower.