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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
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.
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