Navigate the Human Heart and Circulatory System
The heart and circulatory system of a human, as well as some other mammals, are complex. These large animals need to have a higher blood pressure to push the blood throughout their entire bodies. This need results in a two-circuit circulatory system, a system that has two distinct pathways:
One pathway is for pulmonary circulation, which first delivers deoxygenated blood to the lungs so it can become oxygenated and then delivers oxygenated blood back to the heart.
The other circuit is for systemic circulation, which carries oxygenated blood from the heart to the rest of the body and back.
The human heart has four chambers:
Two ventricles, muscular chambers that squeeze blood out of the heart and into the blood vessels. They reside at the bottom of the heart.
Two atria, muscular chambers that drain and then squeeze blood into the ventricles. They reside at the top of the heart.
Your heart is divided into halves because of your two-circuit circulatory system, so you have a left atrium and a left ventricle, as well as a right atrium and a right ventricle. Your heart’s right side pumps blood to your lungs, and its left side pumps blood to the rest of your body. Blood goes into both pathways with each and every pump.
Valves separate one chamber of the heart from another. Each valve consists of strong flaps of muscle tissue, called cusps or leaflets. When your heart is working properly, the valves open and close fully so blood can only flow in one direction through them.
Four valves separate the four chambers of your heart from one another and from the major blood vessels that are connected to it (see the following figure):
The right atrioventricular (AV) valve is located between the right atrium and the right ventricle. This valve is also referred to as the tricuspid valve because it has three flaps in its structure.
The pulmonary semilunar valve separates the right ventricle from the pulmonary artery. Semilunar means “half-moon” and refers to the valve’s shape.
The left atrioventricular (AV) valve is located between the left atrium and the left ventricle. This valve is also called the bicuspid valve because it has only two flaps in its structure.
The aortic semilunar valve separates the left ventricle from the aorta. Like the pulmonary semilunar valve, this valve has a half-moon shape.
For questions 1–8, use the terms that follow to label the valves and chambers of the human heart in the following figure.
a. Left AV valve
b. Right ventricle
c. Pulmonary semilunar valve
d. Right atrium
e. Left atrium
f. Aortic semilunar valve
g. Left ventricle
h. Right AV valve
The structures of the human heart and the flow of blood through them. The diagram shows the heart as if you are looking at a person’s chest.
The following is how the figure should be labeled:
e. Left atrium
a. Left AV valve
f. Aortic semilunar valve
g. Left ventricle
b. Right ventricle
h. Right AV valve
c. Pulmonary semilunar valve
d. Right atrium
Biology Glossary
anemia
A low number of red blood cells or low level of hemoglobin; may be caused by dietary deficiencies, metabolic disorders, hereditary conditions, or damaged bone marrow.
Biology Glossary
antigen
A foreign substance in the body that causes an immune response.
Biology Glossary
body mass index
The BMI is the result of a formula that uses your weight and height to determine whether you need to lose weight.
Biology Glossary
carbohydrates
Energy-packed compounds consisting of carbon, hydrogen, and oxygen that provide quick fuel for organisms.
Biology Glossary
cellulose
A form of carbohydrate that has a structural role in living organisms (animals and plants).
Biology Glossary
centrifuge
A machine that is used to separate blood cells and platelets from plasma.
Biology Glossary
chloroplasts
Plant cells that use energy from sunlight to create food.
Biology Glossary
cytoplasm
The fluid contained within animal cells. Also called plasma.
Biology Glossary
disaccharides
Carbohydrate molecules in which 2 monosaccharide molecules are joined together. Disaccharides consist of 6 to 14 carbon atoms.
Biology Glossary
DNA
Stands for deoxyribonucleic acid. Large molecules found in all living things that carry genetic information.
Biology Glossary
electron microscope
A high-powered, expensive device that uses beams of electrons to bring the finest details of cells into focus.
Biology Glossary
endocrine system
A system of glands that secrete different types of hormones that help regulate organisms.
Biology Glossary
endoplasmic reticulum
The ER is a series of canals that connects the nucleus of animal cells to the cytoplasm outside those cells.
Biology Glossary
equilibrium
The state of a chemical reaction in which the amounts on each side of the reaction have stabilized.
Biology Glossary
eukaryotes
Organisms — including plants and animals, as well as fungi, protozoa, and most algae — with cells that contain a nucleus and chromosomes.
Biology Glossary
Golgi apparatus
A component within cells that packages and distributes hormones, enzymes, and other cell products to other organelles or outside the cell.
Biology Glossary
hemoglobin
An iron-containing molecule in red blood cells that carries oxygen around the body.
Biology Glossary
heterotrophs
Animals — including herbivores, carnivores, and omnivores — that feed on other living organisms.
Biology Glossary
homeostasis
The processes used by the body to constantly achieve and maintain balance.
Biology Glossary
integument
The skin or outer surface of an animal. Small animals such as earthworms use integumentary exchange to exchange gases with the environment.
Biology Glossary
Krebs cycle
A method of describing the steps involved in the chemical process of respiration.
Biology Glossary
lipoproteins
Compounds such as HDL and LDL that carry cholesterol through the bloodstream; made from a fat (lipid) and a protein.
Biology Glossary
lysosomes
Specialized cellular organelles formed by the Golgi apparatus that help to “clean up” the cell by breaking down harmful cell products and removing dead organelles.
Biology Glossary
maceration
A process, such as chewing, that physically breaks down food into pieces.
Biology Glossary
matrix
The extracellular fluid in which animal cells float.
Biology Glossary
mitochondria
An organelle in animal cells that combines food with oxygen to supply energy to cells.
Biology Glossary
monosaccharides
Carbohydrate molecules in which simple sugars consist of three to seven carbon atoms.
Biology Glossary
nuclear membrane
A two-layer structure that separates the nucleus from the cytoplasm in animal cells.
Biology Glossary
organelles
Structures that float inside the fluid of cells; used during metabolic processes.
Biology Glossary
osmosis
A mechanism that moves water and nutrients into and throughout a plant.
Biology Glossary
peristalsis
The action of food being moved down the esophagus and through the entire digestive tract.
Biology Glossary
peroxisomes
Sacs of enzymes within animal cells that help protect the cell by breaking down accumulations of toxic products such as hydrogen peroxide.
Biology Glossary
photosynthesis
The biochemical process that plants use to acquire energy from the sun.
Biology Glossary
plasma membrane
The membrane that holds fluid within animal cells. Also called the cell membrane.
Biology Glossary
polysaccharides
Carbohydrate molecules that are formed by many long chains of monosaccharides.
Biology Glossary
prokaryotes
Organisms — such as bacteria and blue-green algae — with cells that do not contain a nucleus.
Biology Glossary
ribosomes
Components within cells that assist in making proteins from amino acids.
Biology Glossary
RNA
Stands for ribonucleic acid. In animals, works with DNA to produce proteins needed throughout the body.
Biology Glossary
ruminants
Mammals — such as cattle, sheep, and goats — that can break down and digest cellulose.
