CST - Introduction to the Circulatory System Lesson
Introduction to the Circulatory System
Most of the cells in the human body are not in direct contact with the external environment. he circulatory system acts as a transport service for these cells. Two fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the circulatory system. The lymph, lymph nodes, and lymph vessels form the lymphatic system.
What is Blood?
Blood is the body's internal transportation medium. Pumped by the heart, blood travels through a network of vessels carrying materials such as oxygen, nutrients, hormones, and waste products to and from each of the hundred trillion cells in the human body.
The average adult has approximately 5 L of blood in their body. Blood is a type of connective tissue that contains both dissolved substances and specialized cells. This tissue performs many important functions within the body, including:
- Supplying oxygen to tissues
- Supplying nutrients such as glucose, amino acids, and fatty acid
- Removing waste such as carbon dioxide, urea, and lactic acid
- Immunological functions, including circulating white blood cells and detecting foreign material by antibodies
- Coagulation, which is one part of the body's self-repair mechanism
- Messenger functions, including the transport of hormones and the signaling of tissue damage
- Regulation of body pH
- Regulation of core body temperature
- Hydraulic functions (penis and clitoris)
Blood Components
Whole blood is made of four major components: plasma, erythrocytes, leukocytes, and thrombocytes. These components can be separated using a centrifuge, where a tube of blood is spun and the heaviest components will move towards the bottom of the tube (see the picture above).
Plasma
About 55% of blood is blood plasma. Plasma is blood's liquid medium, made of 90% water. The other 10% is composed of various dissolved substances such as gases, salts, nutrients, enzymes, hormones, waste products, and proteins.
The largest group of solutes in plasma consists of three proteins:
- Albumin - produced by the liver; functions to maintain the osmotic balance between the blood and tissue fluids and to assist in the transport of various materials such as bilirubin and fatty acids
- Globulins - function to transport various substances in the blood; gamma globulins assist the body's immune system
- Clotting proteins - produced mainly in the liver; functions to create blood clots to slow the loss of blood in response to tissue damage
Erythrocytes
Around 45% of whole blood consists of erythrocytes. Erythrocytes, also known as red blood cells or RBCs, function to transport oxygen in the bloodstream.
Sickle cell disorder is an autosomal recessive disorder that affects the structure and function of hemoglobin. The change in the structure of hemoglobin causes a sickling effect to red blood cells. Sickle cell disorder can cause anemia, shortness of breath, fatigue, repeated infections, and periodic episodes of pain due to the stiff and inflexible sickle cells getting stuck in small vessels. Some people have mild symptoms, while others have more serious complications.
Leukocytes
Less than 1% of whole blood consists of leukocytes. Leukocytes, also known as white blood cells or WBCs, function to attack foreign substances or organisms.
Leukemia is a cancer of the white blood cells that causes bone marrow to produce abnormal white blood cells. These abnormal cells crowd out healthy blood cells, preventing their normal functions. Leukemia can develop quickly or slowly. Children most often develop the acute type that grows rapidly. Treatments include chemotherapy, radiation, and stem cell transplantation.
Human immunodeficiency virus (HIV) is a virus that attacks the body's immune system (specifically T cells). Over time, the virus can destroy so many of these cells that the body is unable to fight off infections and diseases causing acquired immunodeficiency syndrome (AIDS). No effective cure for HIV currently exists, but the virus can be controlled with proper medical care.
Platelets
Less than 1% of whole blood consists of thrombocytes. Thrombocytes, also known as platelets, are membrane-bound cell fragments. Platelets are produced from stem cells in the bone marrow. Around 100,000,000,000 platelets are produced each day in the average healthy adult, with an average lifespan of just 5 to 10 days.
Platelets function in the formation of blood clots (also known as coagulation) when a vessel is damaged to prevent further loss of blood. The sticky surface of platelets allows them to accumulate at the damage site to form a clot.
If the platelet numbers are too high, blood clots (thrombosis) can form. Blood clots can obstruct blood vessels and cause strokes, heart attacks, pulmonary embolisms, or the blockage of blood vessels to other parts of the body. If the platelet levels are too low, excessive bleeding can occur.
Platelets also secrete clotting factors to facilitate the coagulation process by attracting more platelets. Hemophilia is a sex-linked, recessive disorder that is caused by a lack of certain clotting factors. This rare bleeding disorder causes you to bleed excessively even after a minor injury or even in the absence of injury.
Blood Groups
If a person loses an excessive amount of blood due to injury or surgery, a transfusion may be needed. Blood transfusion is the process of receiving blood intravenously. When the procedure was first performed, whole blood was used; however, now only components of blood such as RBC, WBC plasma, clotting factors, and platelets, are transfused.
Doctors quickly discovered that people had different types of blood or blood groups due to the presence of glycoproteins called antigens on the surface of RBCs.
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