BPCC/NSU Title III Cooperative Project
Circulatory System
The circulatory system consists of blood, blood vessels, & the heart.
Blood is composed of plasma, thrombocytes (platelets), erythrocytes (red blood cells or RBCs), & leukocytes (white blood cells or WBCs).
The picture below shows each of the components of blood as they appear under the microscope.
Plasma
Plasma is the fluid portion of blood & makes up around 55% of total blood volume. Plasma consists largely of water – around 90% depending on the specific location in the circulatory system. The remainder of plasma is composed largely of proteins (classes – albumins, globulins, & fibrinogen). Plasma also contains some dissolved oxygen & carbon dioxide, hormones, glucose, & some minerals & ions.
The main function of plasma is to transport various nutrients & wastes to their target organs.
Thrombocytes (Platelets)
Thrombocytes are fragments of another type of cell (megakaryocytes). They live for around 10 days, are smaller than RBCs, & make up less than 1% of total blood volume.
The main function of thrombocytes is to aid in blood clotting.
Erythrocytes (Red Blood Cells – RBCs)
RBCs transport oxygen from the lungs to the cells of the body where they pick up a small portion of carbon dioxide to transport back to the lungs. They make up around 45% of total blood volume.
RBCs are among the most specialized cells in the body. They have a biconcave shape, which increases surface area for gas exchange. They lack a nucleus, mitochondria, endoplasmic reticulum, or ribosomes. They live for around 120 days.
Leukocytes (White Blood Cells – WBCs)
WBCs help defend the body against invasion by pathogens & remove toxins, wastes, & abnormal or damaged cells. They are typically larger than RBCs, live for only a few days, & make up less than 1% of total blood volume.
WBCs are grouped into two classes: granulocytes & agranulocytes. Granulocytes have visible granules in their cytoplasm, while agranulocytes do not. Each type can typically be distinguished by its nucleus.
Granulocytes
Neutrophils (AKA polymorphonuclear leukocytes) are the most numerous type of WBC, making up anywhere from 50-75% of WBCs. They have a multi-lobed nucleus. Neutrophils specialize in attacking & digesting bacteria.
Eosinophils are fairly rare, making up only around 1-4% of WBCs. Eosinophils typically have a 2-lobed nucleus that resembles a U. Eosinophil levels increase during allergic reactions or parasitic infections.
Basophils are the least common leukocyte, making up less than 1% of all WBCs. Basophils typically have a 2-lobed nucleus that resembles an H. Basophils specialize in releasing chemicals that increase the inflammation response at an injury site.
Agranulocytes
Lymphocytes are the second most numerous leukocyte, making up around 20-30% of all WBCs. Lymphocytes typically have a large nucleus that fills most of the cytoplasm. Lymphocytes may attack foreign invaders directly or indirectly (by making antibodies that attack the invaders). Lymphocytes are also responsible for destroying abnormal body cells (&, thus, help prevent cancer).
Monocytes are moderately abundant & make up around 3-9% of all WBCs. Monocytes are the largest of the leukocytes & typically have an oval or kidney bean-shaped nucleus. Monocytes directly ingest foreign invaders.
The picture below shows each of the different types of leukocytes as they appear under the microscope. They appear in the following order: Neutrophil, Monocyte, Basophil, Lymphocyte, & Eosinophil.
Now that you've reviewed each of the types of leukocytes, complete the activities below.
Review each of the components of blood by matching them to their functions.
Blood vessels consist of arteries, arterioles, capillaries, venules, & veins. Blood flows through the blood vessels from the heart to arteries, arterioles, capillaries (where gas exchange occurs), venules, veins, & back to the heart.
Complete the activity below.
Artery & vein walls are composed of three main layers: the tunica interna (intima), tunica media, & tunica externa (adventitia). The tunica interna consists of simple squamous epithelial cells & the basement membrane (termed "endothelium"). The tunica media consists of loose connective (areolar) tissue & smooth muscle. The tunica externa consists of more connective tissue that contains many collagen & elastic fibers. The connective tissue helps anchor the blood vessel to surrounding organs.
Arteries contain a thin layer of elastic fibers between each of these layers. Between the tunica interna & media is the internal elastic lamina & between the tunica media & externa is the external elastic lamina.
The amount of smooth muscle & elastic fibers changes as the vessel moves further from the heart. Close to the heart, there is less smooth muscle & more elastic fibers. Further from the heart, there is more smooth muscle & less elastic fibers.
Both arteries & veins can be classified into three groups: Large, Medium, & Small. Large arteries are sometimes called elastic arteries & medium arteries are sometimes called muscular arteries.
The tunica media is typically the largest layer in arteries, whereas the tunica externa is typically the largest layer in veins.
The lumen (opening) is typically larger in veins than in arteries; however, the walls are typically thicker in arteries than in veins.
Medium veins contain valves that help prevent backflow of blood, while arteries do not contain valves.
In the systemic circuit (heart to the body & back), arteries carry oxygenated blood to the cells of the body, where oxygen will be dropped off & carbon dioxide will be picked up. This blood is often depicted as red in illustrations. Veins carry deoxygenated blood back to the heart. This blood is often depicted as blue in illustrations, but is not actually blue, but a deeper, darker red than arterial blood. Remember, blood is always red!
In the pulmonary circuit (heart to lungs & back), arteries carry deoxygenated blood to the lungs to pick up oxygen & release carbon dioxide. Veins carry oxygenated blood to the heart to be pumped to the body. Therefore, arteries & veins are not defined by what they carry, but by the structure of their walls.
Despite these differences, arteries always carry blood away from the heart, whereas veins always carry blood towards the heart.
Complete the activity below to review.
Capillaries are known as the exchange vessels as this is where oxygen & carbon dioxide are exchanged between the blood & either the cells of the body or the cells of the lungs. To aid in gas exchange, the walls of capillaries consist of the tunica interna only. There are three types of capillaries: Continuous, Fenestrated, & Sinusoid (Discontinuous).
Continuous capillaries form a continuous tube with very little passing through the walls, except very small molecules, such as glucose. These are found in skeletal muscle, fat, & the nervous system.
Fenestrated capillaries have numerous small holes in the walls allowing larger molecules to pass through. These are found in organs specialized for filtration or rapid absorption (kidneys, small intestines, endocrine glands).
Sinusoid capillaries have many holes and these holes are larger than those of fenestrated capillaries. Small & large molecules can pass through the holes. These capillaries follow the contours of the organs they are located in, such as the spleen, bone marrow, & liver.
Review the information above by completing the following activity.
Study the following pictures & locate the basic structures of the heart.
Review the structures & locate them on the images in the following activities.
The heart pumps blood throughout the body in two circuits.
The pulmonary circuit sends deoxygenated blood to the lungs to pick up oxygen & release carbon dioxide. Once the gases are exchanged in the capillaries of the lungs, oxygenated blood is sent back to the heart to be pumped to the rest of the body in the systemic circuit.
The systemic circuit pumps oxygenated blood to the cells of the body, where it will release the oxygen in the capillaries throughout the body & pick up carbon dioxide. The blood is then pumped back to the heart where it will enter the pulmonary circuit.
Review the picture below to see how blood flows through the heart. Red arrows indicate oxygenated blood, whereas blue arrows indicate deoxygenated blood. The structures listed on the arrows & between them indicate the order in which blood flows through each structure.
To review, complete the following activities below.
The coronary arteries branch off the aorta & supply oxygenated blood to the myocardium (muscular layer) of the heart. The coronary veins bring the deoxygenated blood back to the right atrium, where it enters the pulmonary circuit. The following pictures depict each of the major coronary blood vessels.
Review the structures & locate them on the images in the following activities.