The Circulatory

System Biology 20

The Circulatory

system

• The human circulatory system is designed

to transport blood throughout the body.

• Blood carries oxygen and nutrients to your

cells, carries waste products to elimination

sites, transports chemical messengers from

one part of the body to another, carries

immune cells to fight invaders, and

distributes heat throughout the body.

Blood Vessels

• Blood travels through a system of blood vessels

throughout the body.

• Arteries are blood vessels that carry blood away from

the heart.

• Veins are blood vessels that carry blood to the heart.

Arteries & Arterioles

• Arteries have thick, elastic walls to withstand the surge

of blood passing through them when the heart

contracts.

• Arteries stretch to accommodate this rush of blood

and is the pulse you feel after each heart contraction.

• Blood from arteries pass into smaller vessels called

arterioles.

Veins & Venules

• Venules empty into veins, which carry blood back to

the heart.

• Blood pressure is low in the veins, therefore skeletal

muscles and venous valves work together to move

blood back to the heart.

• When skeletal muscles contract, they squeeze blood

through the veins. When they relax, one-way venous

valves prevent the backflow of blood.

Capillaries

• Capillaries are tiny blood vessels, only one cell thick,

where fluid and gas exchange occurs between blood and

body cells.

• Oxygenated blood from arterioles enter capillary beds

where oxygen diffuses into the surrounding body cells.

Oxygenated blood appears deep red in colour.

• Deoxygenated blood leaves the capillary bed through

venules. Deoxygenated blood is purplish-blue in colour.

Capillary fluid

exchange

• Water is exchanged between the capillaries and the fluid

that occupies the spaces between cells, called extracellular

fluid (ECF).

• Water movement between capillaries and the ECF is

determined by osmotic pressure and fluid pressure.

• High fluid pressure at the arteriole end of a capillary bed

forces water out of the capillaries and into the ECF.

• Nutrients and minerals move with the water into the ECF

and large molecules, like proteins, and blood cells stay in

the capillaries.

• Osmosis is the movement of water from a region of

low solute concentration to a region of high solute

concentration.

• Since proteins are found in the blood but not in the

ECF, osmotic pressure draws water from the ECF into

the capillaries, bringing with it dissolved waste

materials.

• This equilibrium between fluid pressure and osmotic

pressure is important in maintaining levels of body

fluid.

• Normally a small amount of protein leaks from

capillaries into the ECF.

• Accumulation of protein in the ECF would reduce

osmotic pressure and tissues would swell.

• These proteins are removed from the ECF by another

system of vessels, called the lymphatic system.

• Lymph vessels are similar to veins and carry lymph

fluid to the right and left subclavian veins.

Complete

Questions 1-7 on

Circulatory

System

Assignment

Control of blood

flow

• The autonomic nervous system regulates the diameter of the arterioles.

• Nerve impulses can cause the smooth muscle in the arterioles to contract, reducing the diameter of the vessels and therefore decreasing blood flow to the tissues. This is called vasoconstriction.

• Vasodilation is the opposite process; smooth muscle relaxes, increasing blood flow to the tissues.

• Precapillary sphincters can also redirect flow of blood to needed areas.

Thermoregulation

• We are able to maintain a consistent body temperature

regardless of our surroundings. This is called

thermoregulation.

• When environmental temperature decreases, skin

blood vessels constrict, which decreases blood flow to

the skin thus minimizing heat loss.

• When environmental temperature increases, skin blood

vessels dilate, increasing blood flow to the skin.

Disorders

• Atherosclerosis is the accumulation of fat deposits on

the inner wall of the arteries. This can lead to a

hardening of the arteries, called arteriosclerosis.

• Hardening of the arteries causes high blood pressure

due to the narrowing of the arteries and loss of

elasticity.

• Because arteries are narrower, there is a greater chance

that they could become blocked, cutting off oxygen to

certain tissues (ie. heart attack).

• An aneurysm is a bulge that forms in the wall of a

weakened artery (often causes by atherosclerosis).

• Aneurysms in the brain can rupture and lead to a

stroke.

• When the one-way venous valves in veins begin to

degenerate, this can lead to pooling of blood causing

veins to become larger and begin to bulge. This is a

condition called varicose veins.

Pulmonary &

Systemic circulation

• There are two main pathways that blood takes in the

body.

• The pulmonary circuit is the system of blood vessels

that carry deoxygenated blood from the heart to the

lungs and oxygenated blood from the lungs back to the

heart.

• The systemic circuit is the system of blood vessels that

carries oxygenated blood to the tissues of the body and

deoxygenated blood from the tissues back to the heart.

Complete

questions

8 to 10

Blood vessels BLM

Anatomy of the

Heart

The Heart

• Humans have a four-chambered muscular heart that pumps

blood throughout the body.

• It is actually two parallel pumps separated by a muscular

wall, called the septum.

• The “pumps” are chambers with thick muscular walls

called ventricles.

• The right ventricle pumps deoxygenated blood to the lungs

via the pulmonary artery.

• The left ventricle pumps oxygenated blood to the body

tissues via the aorta (the largest artery in the body).

• The two chambers of the heart that receive blood are

called atria.

• The right atrium receives deoxygenated blood from the

systemic circuit.

• The left atrium receives oxygenated blood from the

pulmonary circuit.

• One-way valves, called atrioventricular (AV) valves, separate the atria from the ventricles. These valves prevent the backflow of blood into the atria when the ventricles contract.

• Semilunar valves separate the ventricles from the arteries and also prevent a backflow of blood.

• Coronary arteries supply the heart with oxygen and nutrients.

• Angina is a condition when too little oxygen reaches the heart, causing severe chest pain.

Anatomy of the

Heart

Angina #12

Heart Contraction

& Heart Rate

• Heart muscle is unique in that it can contract without

being stimulated by external nerves. This special kind

of muscle tissue is called myogenic.

• The heart rate is set by a region of tissue in the right

atrium called the sinoatrial (SA) node, which acts as

the heart’s pacemaker (~70 beats per minute).

• Nerve impulses generated by the SA node cause the

atria to contract and then pass through the

atrioventricular (AV) node to the ventricles.

• Nerve impulses from the AV node travel via two large

nerves, called Purkinje fibres, which run down the

septum and then branch up the walls of each ventricle,

causing them to contract.

• Heart rate can be influenced by your autonomic

nervous system, conducting nerve impulses from the

brain to the SA node.

• During times of stress, sympathetic nerves stimulate

the SA node and increase the heart rate.

• Tachycardia occurs when the heart rate exceeds 100

beats per minute.

• During times of relaxation, parasympathetic nerves

slow the heart rate down.

Bypass surgery video

#11-14

Electrocardiograms

Heart Sounds

• The lubb-dubb sound a heart makes is caused by the

closing of the heart valves.

• When the ventricles contract, the pressure forces the

AV valves shut producing the strong lubb sound. This

period of contraction is called systole.

• When the ventricles relax, the semilunar values close

producing the lighter dubb sound. This period of

relaxation is called diastole.

Cardiac Output

• Cardiac output is the amount of blood pumped from the

heart each minute. It is determined by two factors:

• Stroke volume

• Heart rate

• Stroke volume is the quantity of blood pumped with each

heart beat. The stronger the contraction, the greater the

stroke volume.

• Heart rate is the number of time a heart beats per minute.

• Therefore, cardiac output is calculated by multiplying

stroke volume by heart rate.

Blood Pressure

• Blood pressure is the force blood exerts on the walls of

the arteries and can be measured using a

sphygmomanometer.

• A cuff with an air bladder is wrapped around your arm

and inflated until blood flow is restricted.

• A stethoscope is placed just below the cuff and air is

slowly released until a sound can be heard.

• This first sound is blood entering the previously closed

artery and is caused by ventricular contraction. This is

called systolic blood pressure and is normally about

120 mmHg.

• As the cuff continues to deflate, the sound will

disappear. This is the point of ventricular relaxation,

called diastolic blood pressure and is normally about

80 mmHg.

#18

Complete Questions 15-18

Heart Anatomy BLM

Flow of Blood

through the heart

BLM

The Lymphatic System

• Some protein escapes the capillaries causing a reduction of osmotic pressure (water would be retained by the tissues).

• The lymphatic system drains the proteins from the ECF and returns them to the circulatory system.

• Lymph, similar to blood plasma, travels in low pressure vessels similar to veins (have valves to prevent backflow and smooth muscles help move lymph).

• Lymph is returned to the circulatory system by the right and left subclavian veins.

• Lymph nodes are enlargements of the lymph system

that filter out bacteria via lymphocytes (white blood

cells).

• Lymphocytes (wbc) are stored in the lymph nodes and

are important in the production of antibodies.

Lymphoid Organs

• Red bone marrow is where all blood cells are made.

• Bone marrow contains stem cells that can differentiate

into a variety of different types of blood cells

depending on the needs of the body.

• Blood cells enter the circulatory system via sinuses.

Spleen & Thymus

• The spleen is richly supplied with sinuses and is a

storage organ of red blood cells (released in response

to low blood pressure, or low blood oxygen levels).

• The thymus is the site of T-cell maturation (T-

lymphocytes) whose job is to protect the body from

foreign proteins.

Homework

• Why does low concentration of plasma protein cause

edema?

• What are lymph vessels and how are they related to the

circulatory system?

• What is lymph? How is lymph transported in the body?

• Why are lymphocytes important to the immune

system?

• What is the importance of the spleen?

Response of the Circulatory

System to Exercise

Exercise is a form of stress on the body.

What nervous system controls our body when we are under stress?

(hint.. It is involuntary)

Our body produces the hormone adrenaline, which stimulates the

release of more red blood cells to aid in oxygen delivery. Increase

heart rate provides for faster oxygen transport, and increased

breathing rate ensures that the blood contains higher levels of

oxygen. Your heart is working harder to pump blood, which

increases the blood pressure, specifically the systolic pressure.

Systolic

Diastolic

1. The chamber of the heart that receives blood directly

from the pulmonary vein is:

a. The right atrium

b. The left atrium

c. The left ventricle

d. The aorta

B

2. Your pulse can be taken in a(n)

a. Artery

b. Capillary

c. Venule

d. Arteriole

A

3. The blood vessels through which nutrients and wastes diffuse the blood and cells of the body are the

a. Veins

b. Arteries

c. Capillaries

d. Pulmonary Blood Vessels

C

4. Heart sounds are produced by which structures

a. The right and left ventricles

b. The left ventricle and the atrioventricular valve

c. The left ventricle and the vena cava

d. The atrioventricular valve and the semi-lunar valve

(in pulmonary vein)

D

5. Blood vessels that contain oxygenated blood are

a. The vena cava and pulmonary vein

b. The aorta and pulmonary vein

c. The aorta and pulmonary artery

d. The vena cava and pulmonary artery

B

6. True or False. The left side of the heart is thicker than

the right side. Explain your answer

True- the left side of the heart transports blood to the rest

of your body which requires more muscle to travel longer

distances

7. What is atherosclerosis?

a. Heart attack

b. Fat accumulated on your heart

c. Bulge formed in a weakened blood vessel

d. Fat deposit on the walls of your arteries

D

8. Cardiac Output is measured by:

a. Stroke volume x heart rate

b. Heart rate + blood pressure

c. Stroke volume x cardiac output

d. Heart rate x Total volume of blood

A

9. Which of the following describes a vein?

a. It has thin walls with valves and it carries blood to the heart

b. It has thick walls with valves and it carries blood under pressure

c. It has thin walls and carries oxygenated blood away from the heart

d. It has a very thin wall with valves and it carries blood under pressure

A