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Circulatory System
- the circulatory system is the transport system for the body
- it moves blood to all cells of the body
- the blood carries nutrients, oxygen, and wastes among other things
Heart
- the job of the heart is to pump blood to all parts of the body
- the blood travels through blood vessels
- it is really a double pump:
- the right side pumps blood to the lungs
- the left side pumps blood to the rest of the body
- each side is divided into two chambers:
- smaller, upper chambers called the left and right atrium
- larger, lower chambers called the left and right ventricle
- the atria receive blood coming to the heart and pump it to the ventricles
- the ventricles are much stronger as they must pump blood to all parts of the body
- when the atria fill with blood they contract, pushing blood into the ventricles
- when the ventricles fill with blood they contract, pushing blood to other parts of the body
Heart Valves
- valves are strong flaps of tissue that act as a one-way door
- when a chamber contracts, the valves close to prevent blood from flowing backward
- e.g., blood can pass easily from the left atrium into the left ventricle but it cannot flow back
- the valves between atria and ventricles are called AV valves
- the valves between ventricles and blood vessels are called semilunar valves
- when the ventricles contract, the AV valves close to prevent blood flowing back into the atria
Heartbeat
- the pumping rhythm of the heart is called the heartbeat
- the sound of the heartbeat is made by the valves closing
- the first sound of the beat is caused by the AV valves closing
- the second sound is caused by the semilunar valves closing
Blood Vessels
The circulatory system has three kinds of blood vessels:
1. Arteries
- carry blood away from the heart
- they have thick, muscular walls
- when the heart beats, it forces blood into the arteries
- the elastic arteries stretch when they fill with blood
- you can feel this as your pulse
- blood pressure is the force of blood pushing against the walls of the arteries
2. Veins
- carry blood back to the heart
- they have thinner walls than the arteries and are less muscular
- the blood in veins is at lower pressure so they do not need to be as strong
- this low pressure makes it difficult for blood to get back to the heart
- as skeletal muscles push against veins, blood is squeezed out an helped
back to the heart
- veins have valves that prevent blood from flowing backward
3. Capillaries
- these are the smallest blood vessels that connect the branches of arteries and veins
- they have very thin walls so materials can move into and out of them easily
- everything carried by the blood is exchanged with body cells through the walls of
capillaries
- nutrients and oxygen move from the blood to body cells
- carbon dioxide and other wastes move from body cells into the blood
Circulation
- the circulatory system is divided into two main loops
1. Pulmonary circulation
- this is the path of blood between the heart and the lungs
- blood from the body has little oxygen in it and carries carbon dioxide, a waste product
from cells
- it enters the right atrium and is pumped to the right ventricle
- the right ventricle pumps blood through the pulmonary artery to the lungs
- in the lungs the blood releases carbon dioxide and picks up oxygen
- the blood returns to the heart through the pulmonary veins and enters the left atrium
2. Systemic circulation
- this is the path of blood between the heart and the rest of the body
- from the left atrium blood is pumped to the left ventricle
- the left ventricle is the strongest of the four chambers because it must pump blood
throughout the entire body
- from the left ventricle blood enters the aorta, the largest artery in the body
- the aorta branches into smaller and smaller arteries to reach all parts of the body
- blood returning from the body enters the right atrium
- some major arteries are:
Blood
- the average person has about 5 L of blood
- the liquid part of blood is called plasma
- plasma is about 90% water
- it carries dissolved vitamins, minerals, digested nutrients, wastes, and hormones
- floating in the plasma are the blood cells
Red blood cells (RBC)
- RBC carry oxygen in the blood
- the red color comes from hemoglobin, the protein that carries oxygen
- hemoglobin contains iron and this is why iron is an important part of the
diet
- blood that carries oxygen is bright red while blood with little oxygen is
dark red
- YOUR BLOOD IS NEVER BLUE!
White blood cells (WBC)
- you have about 1 WBC for every 1000 RBC
- these cells are part of the immune system which defends you from disease
- imagine you cut yourself and it becomes infected by bacteria
- WBC are attracted to the infection and start to kill the bacteria
- the infected area turns red and often produces pus
- the pus is composed of dead WBC, bacteria and other dead cells
- some WBC can squeeze out of blood vessels to attack bacteria by engulfing them
- other WBC produce antibodies to fight bacteria and viruses
Platelets
- these tiny cells form blood clots to prevent bleeding
- if you cut yourself, the injured cells send out a chemical signal that causes
platelets to release chemicals that form a clot
- the clot is made of protein fibers that form a mesh to trap RBC
Blood Groups
- there are four main types of blood: A, B, AB, and O
- blood type depends on the presence or absence of certain protein markers on the surface of
RBC
- these markers are antigens that can make people produce antibodies if they do not have the
markers
- it is important for doctors to know your blood type if you require a transfusion
- if you get the wrong type, your immune system can produce antibodies against it and the
blood would form clumps
- these clumps can block blood vessels and kill you
Diseases of the Circulatory System
- Heart disease is the leading cause of death in North America
- there are several common disorders of the circulatory system:
Heart murmur
- caused by a damaged valve which does not close properly
- blood flows back through the valve and causes a swishing sound
High Blood Pressure
- blood pressure is recorded as two different numbers and expressed as a fraction
- the top number is the pressure when the ventricles are contracting - when the heart
pumps
- the bottom number is the pressure when the ventricles are relaxed
- a blood pressure of 120/80 is normal
- high blood pressure is dangerous because it puts extra strain on the heart
- high blood pressure can be caused by different things:
- genetics (family history)
- a high salt diet
- narrowing arteries from a high fat diet. Cholesterol can deposit on the walls of an
artery, making it narrower. It is more difficult for blood to move through the narrow
artery so the heart must work harder.
Heart Attack
- the heart is made of living muscle cells and they need blood to survive
- if an artery carrying blood to the heart is narrowed, the flow of blood through that
artery is limited
- that part of the heart does not receive enough blood dies
- this is a heart attack
Blood Disorders
Anemia
- this is the most common blood disorder
- in this disorder, the blood cannot carry enough oxygen
- it can be caused if there are not enough RBC
- it can also be caused if there is a shortage of iron because iron is needed
for hemoglobin to carry oxygen
- the symptoms are being tired, pale, and feeling cold
- it can be treated by taking vitamin B12, folic acid, or eating foods high in iron
Leukemia
- leukemia is a type of cancer that affects the blood
- it is caused when the body produces too many WBC
- these WBC are immature and unable to perform their function
- they also interfere with the production of RBC
- the symptoms often include anemia, internal bleeding, and infections
- it is treated by chemotherapy, radiation, or a bone marrow transplant