Blood Vessels and Circulation

Objectives:1. Describe the structure and function of each of

the three types of blood vessels2. Compare and contrast each type of blood

vessel3. Explain the path that blood takes from the

heart

Quiz

1. What is a Erythrocyte?

2. What is the function of leukocytes?

3. Type A blood has what antibodies?

4. Which blood type is the universal recipient? (Don’t forget the +/-)

5. What component of blood initiates blood clotting?

How Does Blood Get Around?

• Vessel• A hallow tube that

circulates blood• An average adult has

~160 000 km of blood vessels

The need for a circulatory systemSimple organisms don’t require a circulatory

system…Unicellular organisms are in direct contact with their environment.

Multicellular organisms like Sponges don’t need a circulatory system because their body has only two layers so all their cells are very close to their environment. Also their body cavity has water containing oxygen and nutrients constantly circulating through it.

Increasing Body Size

Bigger organisms have cells that are not in contact with the external environment.

Cells can’t move around to get oxygen and nutrients.

Cells must be surrounded by fluid for gases, nutrients and wastes to be able to diffuse across.

The cells of complex multicellular animals are surrounded by tissue fluid.

Types of circulatory systems

Open circulatory system: blood and tissue fluid (hemolymph) is pumped into body cavities where it bathes all the cells.

Closed circulatory system: blood flows through vessels. Blood and tissue fluid is kept separate.

Three types of blood vessels

1. Arteries2. Capillaries3. Veins

•These blood vessels acting together are responsible for transporting or carrying blood to and from the heart, and to and from every cell in the body

•This network is a continuous and closed network

•Note: the arrow →represents the direction of blood flow through the blood vessels of the body

heart → arteries → arterioles → capillaries → venules → veins → heart ↓ ↑

O2 CO2

↓ ↑

cell

Function

• to carry blood away from the heart to the cells of the body

Structure

• thick, muscular walls

• can stretch slightly to

accommodate the

heart pumping blood

Gas content of Blood • blood carried by most arteries is rich in oxygen

(oxygenated)Colour of blood • bright redBlood is pushed by • blood in these vessels is pushed by the force of

contraction of the left ventricle of the heartBlood Pressure • these vessels are under high pressure due to

the force of contraction of the left ventricle

Clinical Usage • to measure a pulse that represents an estimation of

heart rate • to measure blood pressure

Note: the pulmonary arteries are the only arteries that carry deoxygenated blood (blood being pumped from the heart to the lungs)

Note: Blood pressure is greatest in the aorta, the largest artery of the body, and then decreases as it moves farther away from the heart

• are ‘small’ arteries• they link arteries with the capillaries

Function •Allow for the exchange of gases and the transfer of nutrients and waste products between cells and the blood; and they allow for the continuation of blood flow as they connect arterioles with venules.

•every cell in the body is within 50 micromillimetres of a capillary but only certain capillaries are open at any given time.

Structure

• narrow – only one blood cell at a time can flow through this vessel

• numerous – placed end to end they represent 6,300 square metres

• thin walls – composed of only a single layer cells. The walls are only one cell thick, allowing for maximum diffusion of gases, nutrients and waste products

Gas content of Blood

•blood carried by capillaries will contain O2 leaving the blood in the capillary and diffusing into the cells and CO2 entering the blood from the cell.

Colour of blood •red in arterial end and maroon in venous end Blood is pushed by •blood in these vessels is pushed by the residual or

left-over pressure of the force of contraction of the left ventricle of the heart

Blood Pressure • is very low in these vessels due to the large surface

area covered by capillaries, but not as low as the blood pressure in the veins

• are ‘small’ veins

• they contain deoxygenated blood collected from capillaries

• they connect or link capillaries to veins

Function •to carry or return blood back to the heartStructure •the walls of the veins are thinner than those

of the artery.•Veins contain valves that allow for one-

way flow of blood back to the heart. Valves prevent back flow of blood, counter balancing the affect of gravity

Gas content of Blood

• blood carried by most veins is rich in carbon dioxide (deoxygenated)

Note: the pulmonary veins are the only veins that carry oxygenated blood (back to the heart from the lungs)

Blood is pushed by

• blood in veins is squeezed back to the heart slowly, step by step, valve by valve. The return of blood is also aided by contraction of surrounding skeletal muscles

Blood Pressure • is negligible

Movement of blood • blood moves slowly and steadily through veins. There

are more veins than arteries and veins can expand more than arteries, thus they contain about 70% of total blood volume.

Clinical Usage • veins are used for injections, transfusions and

withdrawing blood. The reason for this is the fact that the walls of veins are relatively thin and therefore easily punctured, and the blood pressure is negligible so that blood will not rush out of the puncture

• Key Terms:–Arteries Arterioles–Veins Venules

• Valves

–Capillaries

• What is the function of each of these structures?

• The cardiovascular system is composed of two major components or organs, what are they?

i) a network of vessels – arteries, capillaries and veins

ii) a pump – the heart

• transporting or carrying blood to and from the heart, and to and from every cell in the body

Q) What is a clinical usage of Arteries???

A) to measure a pulse that represents an estimation of heart rate

A) to measure blood pressure

Q) What is a clinical usage of Veins???

A) used for injections, transfusions and withdrawing blood. The walls of veins are relatively thin and therefore easily punctured, and the blood pressure is negligible so that blood will not rush out of the puncture

Varicose Veins

A) Venules

B) Veins

C) Capillaries

D) Arteries

E) Arterioles

1) Drain blood from capillaries

2) Smallest blood vessels

3) May contain valves

4) Take blood to the heart

5) Sites for exchange of substances between blood and tissue fluid

6) Rate of blood flow is the lowest

Drain blood from capillaries

Smallest blood vessels

May contain valves

Take blood to the heart

Sites for exchange of substancesbetween blood and tissue fluid

Rate of blood flow is the lowest

A) Venules

B) Veins

C)Capillaries

Your Task

• Fill in the table comparing the structure and function of each of the types of blood vessels we discussed today.

• H/W: Read through pages 250-254• Answer questions 2-4 on page 253 and 1,

5-9 on page 255. These are potential test questions and we can discuss them tomorrow if enough people complete them.

Plenary

1. What are the three types of blood vessels?2. What is the function of veins, capillaries and

arteries?3. How are veins structured to help blood get

back to the heart?4. How are capillaries structured to do their job?5. State the path that blood takes from the

heart…what blood vessel does it pass through first?