Blood Components: A Biology Overview PDF

## Unit 6: The Circulatory System ### What is Blood? Blood is a specialized body fluid in the circulatory systems of humans and other vertebrates whose purpose is to deliver oxygen and nutrients to cells, while transporting carbon dioxide and metabolic wastes away from cells. While blood is mostly...

## Unit 6: The Circulatory System ### What is Blood? Blood is a specialized body fluid in the circulatory systems of humans and other vertebrates whose purpose is to deliver oxygen and nutrients to cells, while transporting carbon dioxide and metabolic wastes away from cells. While blood is mostly water, it contains many other dissolved substances, cells, and proteins necessary for transporting things efficiently. ### Components of Blood Blood can be divided into two main categories: the plasma and the formed elements. Each is composed of different materials: 1. **Plasma:** makes up 55% of total blood volume. - Water (90%) - Plasma proteins + hormones - Dissolved gases (CO2 + O2) - Nutrients (monomers like glucose) - Salts - Wastes 2. **Formed Elements:** make up 45% of total blood volume. | | | | :-------------- | :---------------------------------------------------------------------------------------------------- | | **Plasma** | - Water, proteins, nutrients, hormones, etc. | | **Buffy coat** | - White blood cells, platelets | | **Hematocrit** | - Red blood cells | ### Types of Blood Cells There are three main types of blood cells in the circulatory system. Each one has different physical attributes which make them well adapted to their respective purposes. We will explore all three types in detail here. 1. **Erythrocytes (also known as red blood cells)** - A red blood cell typically lives for about 120 days. - They are produced in the **red bone marrow**, which is a spongey tissue found in the center of many bones, such as the skull, ribs, vertebrae, and most long bones. - Red bone marrow produces **stem cells**, some of which will form the red blood cells. These stem cells are called **erythroblasts**. Erythroblasts will differentiate into **erythrocytes** before leaving the bone marrow and entering the blood stream. - About **5 million** are produced **every second**! - All red blood cells are **biconcave in shape** and do not have a **nucleus**. - They contain a protein called **hemoglobin**, which contains **iron** groups, giving blood its characteristic **red color**. - Hemoglobin picks up oxygen in the lungs and releases it in tissues. It also has an affinity for carbon dioxide and H+ in tissues and releases it at the lungs. - In one red blood cell, there are approximately **200,000,000 hemoglobin molecules**. - **Anemia = lack of iron.** - Red blood cells allow the blood to remain **liquid**, so the heart does not have to **work as hard**. If hemoglobin floated freely in the blood, it would be too thick, and the heart would have to **pump harder** to get oxygen around the body (increases blood pressure). - At the end of their lifespans, erythrocytes are destroyed in the **liver** and **spleen**. 2. **Leukocytes (also known as white blood cells)** - White blood cells are **larger** than red blood cells. They also stem from stem cells in the bone marrow (B cells) and can also originate in the **thymus gland** in the **lymphatic system** (T cells). - These cells have nuclei, but no definite shape. - White blood cells are less numerous than red blood cells and are outnumbered **700:1**! - Their main function is to fight against **infection**. Therefore, they are **immune system cells**. - There are several types of white blood cells: - **Neutrophils:** Kill bacteria, fungi, and foreign debris. - **Lymphocytes:** Protect against viral infections and produce antibodies. Most are found in the lymphatic system. - **Eosinophils:** Identify and destroy parasites and cancer cells. They also help your allergic response. - **Basophils:** Produce an allergic response. - **Monocytes:** Clean up damaged cells to prevent infection. - Many leukocytes are **phagocytic**, meaning they “eat” invaders and digest them in the cytoplasm using **lysosomes**. - Many produce **antibodies** which help **alert** other white blood cells of an infection. 3. **Thrombocytes (also known as platelets)** - Platelets are produced from stem cells in the bone marrow. They are very small and are composed of **broken fragments** of larger cells. You produce about **2 billion a day**! - They play an important role in **blood clotting**—without them, you would not be able to stop bleeding, and you would **lose** too much blood. - Platelets will **clump** at the site of the bleed and partially close it. Then the platelets and the injured tissue release an **enzyme** to further the clotting process. - In addition to platelets, there are many other chemical compounds necessary to initiate blood clotting. If even one is missing, it would have dire consequences. - **Hemophilia = inability to clot blood**. ### Blood Clotting Cascade - When a blood vessel is damaged (i.e., **by a cut**), platelets flowing in the bloodstream begin **clumping** at the damaged area. This partially **closes** the "leak." - Platelets and damaged cells release a substance called **thromboplastin**. - Now in the bloodstream, **thromboplastin** converts a blood protein called **prothrombin**, which is produced by the **liver**. Prothrombin is an **activator protein** and contains **potassium (K)**. - **Prothrombin** is converted into a new, active substance called **thrombin** (by thromboplastin). - **Thrombin** is an **enzyme** that converts another blood protein called **fibrinogen** (also made by the **liver**) into an active protein called **fibrin** (clot). - **Fibrin is sticky** and forms a mesh-like **network** over the leak. Blood cells and more platelets get **trapped** and form the **clot**, which stops the flow of blood out of the vessel. Now the vessel can begin **repairs**. - The **fibrin clot** is only **temporarily present**: as soon as the blood vessel repair is initiated, a new enzyme called **plasmin** destroys the network (**fibrinolysis**). ### Blood Types Blood types refer to the category of **antibodies** carried in the blood **plasma** as well as the **antigen proteins** on the outside of blood cells. Antigens are the identifiers on cells that antibodies **bind to**. Once an antibody binds to an antigen, an **immune response** is triggered. Antibodies help **flag pathogens** as foreign so immune cells can **dispose** of them. There are four main blood types: **A, B, AB, and O**. Each type is named for the **antigens** on the cells, as well as the **antibodies** present in the plasma. - **Blood type A cells** have **A antigens** on them, but the plasma contains **Antibody B**. - **Blood type B cells** have **B antigens** on them, but the plasma contains **Antibody A**. - **Blood type AB cells** have **both A and B antigens** on them, while the plasma contains **no antibodies**. - **Blood type O cells** have **no antigens** on them, while the plasma contains **Antibodies A and B**. ### How do we find our blood type? Blood typing is done on a plate or card where drops of blood are placed in special categories. Each category is mixed with an **antibody serum**. Lab technicians look for **agglutination** (clumping of the blood) to determine which blood type the sample is. Agglutination occurs when antibodies bind to antigens, causing a **close mesh** to form. We observe this mesh as **clump**. - If you have blood type A, clumping will appear in the **Anti-A field**. - If you have blood type B, clumping will appear in the **Anti-B field**. - If you have blood type AB, clumping will appear in the **Anti-A** and **Anti-B field.** - If you have blood type O, **no clumps will appear**. If a person receives blood from a donor with a different blood type than they have, the antibodies in the donor blood will **attack** the antigens on the recipient's cells, or vice versa. This causes **agglutination**, which blocks blood flow by clotting the blood. This is **fatal**. ### Rhesus Factor There is an extra antigen protein called **Antigen D**, or **Rhesus factor**, on red blood cells. Blood can either be **Rhesus positive (Rh+)** or **Rhesus negative (Rh-)**, depending on the presence or absence of Rhesus Factor. People with **negative-type blood** do not have Antigen D on their cells, so these cells will not be attacked by **D antibodies** in the blood. These individuals make great **blood donors** because the risk of immune response is lowered in the recipient. O negative individuals are known as the **universal donors**, while AB positive individuals are **universal recipients**. If an expecting mother is **Rh-** while the father is **Rh+**, there is a chance that the baby will be born **Rh+**. In this case, the mother's antibody D may attack the baby's cells, which contain Antigen D. This destroys the baby's **Rh+ blood cells**, which can severely harm it. Usually, the first pregnancy is not a problem, as it only alerts the mother's immune system, but a response is not stimulated. If a second pregnancy were to occur, then the mother's immune system attacks the baby. **Prenatal testing** is done to monitor blood types and to ensure the safety of both the mother and the baby. If a pregnancy does occur, a medicine called **RhoGAM** can be injected into the mother to **eliminating** antibody D.