90. CCA Study Notes: Circulatory System, Cardiovascular and Lymphatic Systems

The Big Picture

The circulatory system moves important substances around the body. It carries oxygen and nutrients to cells and carries wastes away from them.

Two fluids move through this system: blood and lymph. The cardiovascular system includes blood, the heart, and blood vessels. The lymphatic system includes lymph, lymph nodes, lymph vessels, and other lymphatic structures.

Together, these two systems help keep body cells alive and functioning.

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Course Notes: Key Ideas You Need to Know

What Makes Up the Circulatory System?

The circulatory system transports substances to and from body cells. These substances include nutrients, oxygen, carbon dioxide, hormones, blood cells, and wastes.

Two fluids move through the circulatory system:

• Blood moves through the cardiovascular system.
• Lymph moves through the lymphatic system.

The cardiovascular and lymphatic systems together form the circulatory system.

The Cardiovascular System

The cardiovascular system includes:

• blood
• the heart
• blood vessels

The heart works as a pump. It sends blood through two separate circulation pathways.

Pulmonary Circulation

The right side of the heart pumps blood that has little oxygen to the lungs.

In the lungs, the blood receives oxygen. This pathway is called pulmonary circulation.

Systemic Circulation

The left side of the heart receives oxygen-rich blood from the lungs.

It then pumps this blood to the tissues and organs throughout the body. This pathway is called systemic circulation.

Main Functions of the Cardiovascular System

The cardiovascular system performs several important functions.

• Blood carries nutrients, oxygen, and other substances to body cells.
• During physical activity, increased blood flow helps meet higher energy demands in organs and muscles.
• Clotting cells and proteins travel to injured or bleeding areas to help stop bleeding and support healing.
• Blood removes waste products from cells.
• Blood and blood vessels help regulate body temperature.
• The cardiovascular system produces and carries white blood cells and antibodies ⓘ that defend against disease-causing microorganisms.

Blood Flow and Body Temperature

Blood carries heat produced by muscle activity to other parts of the body.

Blood vessels in the skin dilate ⓘ when the body needs cooling. They constrict ⓘ when the body needs to keep heat inside.

Blood

Blood contains blood cells and a liquid called plasma.

Blood is approximately:

• 55% plasma
• 45% cells

Plasma is approximately 90% water.

Plasma carries blood cells and other substances through the body. These substances include proteins, fats, carbohydrates, hormones, chemicals, and waste products.

Red Blood Cells

Red blood cells are called erythrocytes.

A substance called hemoglobin gives blood its red colour. Hemoglobin also carries oxygen.

As red blood cells move through capillaries in the lungs, hemoglobin picks up oxygen from inhaled air. When hemoglobin is saturated, or filled, with oxygen, blood appears bright red.

As blood reaches tissues and organs, hemoglobin releases oxygen to the cells. Blood with less oxygen changes from bright red to a bluish-red colour.

Cells release carbon dioxide as a waste product. Blood carries carbon dioxide back to the lungs, where the body releases it during ventilation.

Red Blood Cell Numbers and Life Span

The body contains about 25 trillion red blood cells.

A cubic millimetre of blood contains about 4.5 to 5 million red blood cells.

Red blood cells live for approximately 120 days. The liver and spleen destroy worn-out red blood cells.

Red bone marrow replaces them by producing about two million new red blood cells every second.

White Blood Cells

White blood cells are called leukocytes. They are colourless and protect the body against infection.

A cubic millimetre of blood contains about 5,000 to 10,000 white blood cells.

At the first sign of infection, white blood cells move to the infected area. They multiply rapidly and fight invading microorganisms.

The number of white blood cells increases during an infection.

Bone marrow produces white blood cells. They live for approximately 9 days.

Platelets

Platelets, also called thrombocytes, are necessary for blood clotting.

Bone marrow produces platelets.

A cubic millimetre of blood contains about 200,000 to 400,000 platelets.

A platelet lives for approximately 4 days.

The Heart

The heart is a hollow, muscular organ.

It lies in the middle to lower part of the chest cavity and tilts slightly toward the left side.

The Three Layers of the Heart

The heart has three layers.

1. Pericardium: The outer layer. This thin sac surrounds the heart and forms a fluid-filled space called the pericardial space. The fluid is called pericardial fluid.
2. Myocardium: The thick, muscular middle layer.
3. Endocardium: The inner membrane that lines the heart chambers.

The Four Chambers of the Heart

The heart has two upper chambers and two lower chambers.

Atria

The upper chambers are called atria. One upper chamber is an atrium.

The atria receive blood.

• The right atrium receives blood from body tissues.
• The left atrium receives blood from the lungs.

Ventricles

The lower chambers are called ventricles.

The ventricles pump blood out of the heart.

• The right ventricle pumps blood to the lungs through pulmonary circulation.
• The left ventricle pumps blood throughout the body through systemic circulation.

Heart Valves

Heart valves keep blood moving in one direction.

Valves prevent blood from flowing backward from the ventricles into the atria.

The heart has four valves:

1. Tricuspid valve: Between the right atrium and right ventricle.
2. Mitral valve, or bicuspid valve: Between the left atrium and left ventricle.
3. Pulmonary valve: Between the pulmonary artery and right ventricle.
4. Aortic valve: Between the aorta and left ventricle.

Diastole and Systole

Heart action has two phases.

Diastole is the resting phase. During diastole, the heart chambers fill with blood.

Systole is the working phase. During systole, the heart contracts and pumps blood into the major arteries leaving the heart.

Heart Rate and Pulse

Heart rate means the rate at which the heart beats.

Several factors influence heart rate.

• Larger body size generally goes with a slower heart rate.
• Men generally have slower heart rates than women.
• Heart rate generally slows with age.
• Disease affects heart rate.
• Fever affects heart rate.
• Exercise affects heart rate.
• Some medications affect heart rate.

The pulse provides a way to measure heart rate.

Blood Vessels

Blood travels to tissues and cells through blood vessels.

Blood vessels differ in size, structure, and function. Major types include:

• arteries
• arterioles
• capillaries
• veins
• venules

Arteries Carry Blood Away From the Heart

Arteries carry blood away from the heart.

Systemic Arteries

Systemic arteries carry blood from the heart toward vessels that supply body tissues.

The aorta is the largest systemic artery. It leaves the heart directly from the left ventricle.

The aorta branches into other arteries. These arteries carry oxygen-rich blood throughout the body and continue branching into smaller vessels.

Pulmonary Arteries

Pulmonary arteries carry blood from the heart toward the lungs, where gas exchange takes place.

The pulmonary trunk is the largest pulmonary artery. It leaves the right ventricle.

The pulmonary trunk divides into:

• the right pulmonary artery, which goes to the right lung
• the left pulmonary artery, which goes to the left lung

Arterioles and Capillaries

An arteriole is the smallest branch of an artery.

Arterioles connect with capillaries.

Capillaries are tiny, thin-walled blood vessels. They form the exchange area between the bloodstream and body cells.

Nutrients, oxygen, and other substances move from capillaries into cells.

Waste products, including carbon dioxide, move from cells into the bloodstream.

Veins Return Blood to the Heart

Veins carry blood back to the heart.

Systemic Veins

Systemic veins collect blood from vessels that drain capillaries in body tissues.

Pulmonary Veins

Pulmonary veins carry blood from the lungs back to the heart after gas exchange takes place.

Venules and the Venae Cavae

Venules are microscopic and form the smallest type of veins.

Venules drain blood from capillaries. They join larger branches of systemic veins.

Near the heart, systemic veins form two main veins.

1. Inferior vena cava: Drains blood from lower areas of the body, including abdominal structures and the legs.
2. Superior vena cava: Drains blood from upper areas of the body, including the head, neck, and arms.

Both veins empty into the right atrium.

Blood in these systemic veins appears dark bluish-red because it contains little oxygen.

Blood Flow Through the Cardiovascular System

Blood follows an organized path through the heart, lungs, and body.

1. The inferior and superior venae cavae carry blood high in carbon dioxide and low in oxygen into the right atrium.
2. Blood moves from the right atrium through the tricuspid valve into the right ventricle.
3. The right ventricle pumps blood through the pulmonary semi-lunar valve into the right and left pulmonary arteries and toward the lungs.
4. In the lungs, oxygen moves into the capillary blood, while carbon dioxide moves from the blood into the lungs for removal.
5. Oxygen-rich blood returns from the lungs through the right and left pulmonary veins and enters the left atrium.
6. Blood moves through the mitral, or bicuspid, valve into the left ventricle.
7. The left ventricle pumps blood into the aorta.
8. Arteries branch into arterioles, which carry blood toward tissues. Capillaries bring blood to cells.
9. Cells receive oxygen and nutrients from capillaries and give carbon dioxide and waste products to the blood.
10. Capillaries connect with venules.
11. Venules carry blood containing carbon dioxide and waste products.
12. Venules join to form veins.
13. Veins return blood to the heart and into the right atrium.

The Lymphatic System

The lymphatic system includes:

• lymphoid organs
• lymph nodes
• lymph ducts
• lymphatic tissue
• lymph capillaries
• lymph vessels

As blood moves through capillaries, some plasma leaks into spaces between cells.

About 85% of this fluid returns to the blood capillaries.

The remaining 15% drains into nearby lymphatic capillaries. This fluid is called lymph.

Lymph consists mainly of:

• water
• electrolytes
• waste from metabolizing cells
• some protein

Lymphatic capillaries empty into larger lymph vessels.

How Lymph Moves

Lymphatic vessels run throughout the body beside veins.

Lymph travels through larger and larger vessels until it reaches lymph ducts.

The lymph ducts empty into the subclavian veins, which lie below the collarbone.

The heart pumps blood, but lymph relies on other movements.

Lymph moves through:

• skeletal muscle contractions
• chest movement during respiration
• smooth muscle contractions

Lymphoid Organs

Lymphoid organs include:

• lymph nodes
• tonsils
• the thymus gland
• the spleen

Lymph Nodes

Lymph nodes are small, pea-shaped patches of lymphatic tissue.

Different groups drain lymph from different body areas.

• Cervical lymph nodes: Drain and filter lymph from the head and neck.
• Axillary lymph nodes: Drain and cleanse lymph from the upper extremities, shoulders, and breasts.
• Inguinal lymph nodes: Lie in the groin and drain and cleanse lymph from the lower extremities and external genitalia.

Tonsils

The tonsils are located in the throat.

They filter tissue fluid contaminated by pathogens entering through the nose, mouth, or both.

Thymus Gland

The thymus gland is located in the thoracic cavity.

It plays an important role in immune system development before birth and during the first few months after birth.

After puberty, the thymus shrinks but remains active. It secretes a hormone that helps the immune system.

Spleen

The spleen filters blood instead of lymph.

It cleans the blood and destroys microorganisms.

The spleen also produces disease-preventing cells, including lymphocytes and macrophages.

Three Main Functions of the Lymphatic System

The lymphatic system has three main functions.

1. Fluid balance: It keeps fluid balanced between blood and body tissues. This balance is called fluid homeostasis.
2. Immune defence: It transports white blood cells to and from lymph nodes and helps defend the body against bacteria and other intruders.
3. Fat absorption: It helps the digestive system absorb fats and fat-soluble nutrients.

Immunity means protection against a disease or condition.

Effects of Aging on the Lymphatic and Immune Systems

The immune system becomes less effective as people age.

Macrophages Work More Slowly

Macrophages ingest bacteria and other foreign cells.

With aging, macrophages destroy bacteria, cancer cells, and other antigens ⓘ more slowly.

This slower action is given as one possible reason cancer occurs more often in older people.

Distinguishing Self From Non-Self Becomes Harder

The immune system becomes less able to identify foreign antigens and distinguish them from the body’s own cells.

As a result, autoimmune disorders ⓘ become more common.

Fewer White Blood Cells Respond to New Antigens

Older people have fewer white blood cells available to respond to new antigens.

When they meet a new antigen, the body has more difficulty remembering it and defending against it.

Protein Production Changes

As people age, their bodies do not make the type of proteins needed to fight bacterial infections.

Antibodies Attach Less Effectively

Antibodies become less able to attach to antigens.

This change is described as one possible partial explanation for why pneumonia, influenza, infective endocarditis, and tetanus occur more often in older people and lead to death more often.

These immune changes also provide one possible partial explanation for reduced vaccine effectiveness in older people and the importance of booster shots when boosters are available.