The Cardio-Respiratory System – Blood Vessels

Pulmonary and Systemic circulation:

·       Pulmonary circulation: moves blood between the heart and the lungs. It transports deoxygenated blood to the lungs to absorb oxygen and release carbon dioxide. The oxygenated blood then flows back to the heart.

·       Systemic circulation: moves blood between the heart and the rest of the body. It carries oxygen and nutrients to the cells and picks up carbon dioxide and waste products. Systemic circulation carries oxygenated blood from the left ventricle, through the arteries, to the capillaries in the tissues of the body.

Primary roles of blood vessels:

There are 3 primary roles.

·       Transportation

-          We carry substances such as oxygen, nutrients, and hormones and CO2 and waste products.

-          Responsibility of our blood vessels to carry this blood flow around the body in order to transport the different substances.

·       Communication

-          To carry blood containing these substances to different areas of the body to allow communication.

·       Homeostasis

-          Trying to maintain equilibrium in the body.

-          Responsible for regulation

-          Two types of regulation I will focus on: Temperature regulation and blood pressure control.

Overall, the role of blood vessels is to ensure of rapid delivery of things such as oxygen and nutrients and to bring them close enough to the cells to allow diffusion to take place.

Types of blood vessels:

·       Arteries

-          Carry oxygenated blood away from the heart.

·       Arterioles

-          Arteries divide into smaller arteries and then arterioles. They branch from arteries and lead to capillaries. Important blood vessels that regulate blood pressure.

·       Capillaries

-          Blood vessels get even smaller and become capillaries. This is where diffusion takes place.

·       Venules

-          Allow blood to move from capillaries. Taking deoxygenated blood to the veins.

·       Veins

-          Deoxygenated blood back to the heart. Two major veins that come back to the heart: the superior vena cava and inferior vena cava.

-          General Structure of blood vessels

Table on the right gives a visual of the structure of the five blood vessels that I need to know and understand.

Ø  Diameter: distance between the wall on either side of the blood vessel.

Ø  Mean wall thickness: identifying how thick the wall in each blood vessel is.

Ø  Third column shows the different layers each blood vessel contains and the amount they have.

-          Difference in structure and why?

-         

Arteries: main role is to control and distribute blood.

Venous system: deliver blood back to heart. 65% of blood flow is contained within venous system.

Why the difference structure?

Blood vessels are structured in a certain way to be able to deliver a certain function in which we require it do within the body.

·       Artery: contain thick smooth muscle which keeps its structure and in place. The reason they have a large proportion of smooth muscle is because their primary role is to carry blood away from the heart. When blood comes out of heart it is under a large amount of high pressure. The smooth muscle layer allows it to withstand this pressure.

·       Veins: Has a thin wall which means it can’t keep its structure as well.

·       Capillaries: Really thin walls. This is because this where we have an exchange of substances, either between endothelial cells or through the endothelial cells.

-          Methods of exchange that happen at the capillary’s beds: diffusion, transcytosis, and bulk flow.

-          Diffusion: movement of gases (o2, Co2)

-          Transcytosis: larger lipid-insoluble molecules transported across vesicles

-          Bulk flow: mass movement of fluid. Pressure driven.

Different types of capillaries:

·       Continuous capillary: found mostly in skin and muscle. Their structure contains endothelial cells, that are tightly knitted together, that make up an uninterrupted lining.

·       Fenestrated capillary: found in kidneys, intestines, and endocrine organs. Still have tight junction between endothelial cells but within the lining there are large pores.

·       Discontinuous capillary: found in liver, bone marrow and spleen. Endothelial lining starts to get less tight junctions and has more gaps and holes. There are large intercellular clefts, very leaky capillaries.

Function of blood vessels:

·       Arteries –

-          Carrying blood away from the heart

-          Blood is pumped out the heart at high pressure.

-          Therefore, arteries experience high pressure and require thick walls to withstand the high pressure.

·       Veins

-          Carrying blood towards the heart

-          Blood is low pressure after going through other vessels.

-          Therefore, veins have thin walls and valves.

-          Valves stop blood from flowing backwards.

Different layers that make up blood vessels:

-          Lumen:

·       Transport area – where blood flows through a blood vessel

·       A hollow passageway where the blood flows

-          Tunica Intima

·       Inner most layer

·       Called endothelium.

·       Made up of thousands of endothelial cells.

·       Responsible for releasing nitric oxide. Nitric oxide responsible for vasodilation.

·       Arteries have endothelium, basement membrane and internal elastic lamina.

·       Veins have endothelium and basement membrane.

·       Capillaries have endothelium and internal elastic lamina (this is the only layer to a capillary)

-          Tunica Media

·       Middle layer

·       Where smooth muscle is contained

·       Arteries have smooth muscle and elastic lamina.

·       Veins just have smooth muscle.

·       Smooth muscle is much thicker in artery compared to veins.

-          Tunica Externa

·       Outer layer

·       Made up of primarily of collagen fibres.

·       Role is to protect and reinforce the blood vessel and anchor it to its surroundings.

·       Contained in both arteries and veins.

The structure of a blood vessel is related to it’s function.

-          Response to acute exercise

When we exercise there is an increase in muscle contraction and metabolic command

-          Blood flow responses during exercise

·       On average at rest, cardiac output is 5 litres per minute.

·       At high and intense exercise, cardiac output is around 25 litres per minute.

·       At rest, 20-25% of blood is going to stomach. When exercising it can be as low as 3-5%

·       At rest, 20% of blood is going to kidneys, when exercising this goes down to 2-4%

·       At rest, 15-20% of blood goes to the muscles, during exercise it can be as high as 80-85%

·       Our blood vessels can redistribute the direction of the blood to where it needs to be from areas it’s not as essential at that moment of time. From areas of low demand to areas of high demand.