Biology: Body Fluids and Circulation (Part-1)

White Blood Cells :

>> have a life span of 3-4 days

>> granulocytes include neutrophils, eosinophils and basophils

>> agranulocytes include lymphocytes and monocytes

>> neutrophils have a polymorphic nucleus and have phagocytic ability

>> basophils are involved in inflammatory reactions as they secrete histamine, serotonin

>> eosinophils are involved in an allergic reaction

Blood platelets or thrombocytes are involved in the clotting of blood. They are formed from the megakaryocyte cells of bone marrow.

Blood Groups

The ABO blood grouping system categorizes blood into four main types: A, B, AB, and O. These classifications are based on the presence or absence of specific antigens on the surface of red blood cells (RBCs). The two primary surface antigens are labeled as A and B. Blood type A has antigen A on its RBCs, blood type B has antigen B, blood type AB has both antigens A and B, and blood type O has neither antigen A nor B.

This system is crucial for determining blood compatibility for transfusions and plays a significant role in medical procedures and treatments.

Rhomboid Classification

The Rh factor, named after the Rhesus monkeys in which it was first discovered, is an antigen found on the surface of red blood cells (RBCs). Individuals with this antigen are considered Rh-positive, while those without it are Rh-negative. If an Rh-negative person receives Rh-positive blood, their body may produce antibodies against the Rh antigen, leading to potential complications in future transfusions.

During pregnancy, an Rh-negative mother carrying an Rh-positive fetus can develop antibodies against the Rh antigen if the blood mixes during childbirth. This can result in a condition known as erythroblastosis fetalis, where the mother’s antibodies attack the fetus’s RBCs, leading to anemia and jaundice in the newborn.

To prevent this, Rh-negative mothers are typically given injections of anti-Rh antibodies after the birth of their first child carrying an Rh-positive blood type. This helps prevent the development of Rh antibodies and reduces the risk of complications in subsequent pregnancies.

Functions Of Blood :

Coagulation of Blood

Blood clotting, also known as blood coagulation, is a natural process that occurs in response to injury or trauma to prevent excessive blood loss. When a person is injured, a clot forms at the site of the injury, which appears as a reddish-brown scab over time. This clot, medically known as a fibrin clot, is composed of a network of fibrils, which are threads formed from fibrinogen, a protein in the blood plasma.

When activated by the enzyme thrombin, fibrinogen is converted into fibrin, which forms the structural framework of the clot. Platelets release certain substances that help initiate and promote the clotting process. Calcium ions play a crucial role in blood coagulation, aiding in the activation of various clotting factors. Overall, blood clotting is essential for wound healing and preventing excessive blood loss in the body.

Lymph :

Lymph is another important fluid found in the body, alongside blood. As blood circulates through blood capillaries in tissues, some water and water-soluble compounds leak into the interstitial spaces. This fluid, known as tissue fluid or interstitial fluid, fills the spaces between cells and tissues.

The lymphatic system consists of a network of tubes that collect this interstitial fluid and transport it back to the main veins. This fluid collected by the lymphatic system is called lymph. Lymph contains various components, including lymphocytes, which are a type of white blood cell crucial for the immune system’s functioning.

Overall, the lymphatic system plays a vital role in maintaining fluid balance in the body and supporting the immune system’s functions by transporting lymphocytes and other immune cells.

Pathways of Circulation

The circulatory systems in animals can be broadly categorized into two types: the open circulatory system and the closed circulatory system. In an open circulatory system, blood flows through lacunae and sinuses, bathing the organs directly. This type of circulation is commonly found in invertebrates like molluscs and arthropods.

On the other hand, vertebrates, including humans, have a closed circulatory system where blood flows within vessels, such as arteries, veins, and capillaries. The heart, a muscular pumping organ, plays a central role in this system.

In fishes, the heart typically consists of two chambers: one atrium and one ventricle. Amphibians, except for crocodiles, have three-chambered hearts, while birds, reptiles, and mammals, including humans, have four-chambered hearts. These four chambers include two atria and two ventricles, allowing for efficient separation of oxygen-rich and oxygen-poor blood.

Circulatory System of the Human Body

The human circulatory system is comprised of the heart, blood vessels, and blood itself. The heart, a mesodermal organ, is situated in the thoracic cavity between the lungs. It is protected by a double membrane called the pericardium, which surrounds the pericardial fluid. The heart consists of four chambers: two atria and two ventricles. These chambers are separated by walls called septa.

Valves within the heart ensure that blood flows in the correct direction. The tricuspid valve guards the opening between the right atrium and the right ventricle, while the mitral valve, or bicuspid valve, protects the opening between the left atrium and the left ventricle. Semilunar valves are located at the exits of the right and left ventricles into the pulmonary artery and aorta, respectively.

Composed of cardiac muscle, the heart contracts rhythmically to pump blood throughout the body. Specialized nodal tissue, including the sinoatrial (SA) node and atrioventricular (AV) node, coordinates this rhythmic contraction. The SA node, situated in the right atrium, acts as the heart’s natural pacemaker, generating electrical impulses. These impulses travel through the AV node and along the atrioventricular bundle and Purkinje fibers, causing the heart muscle to contract and pump blood effectively.

COMPARISON BETWEEN OPEN CIRCULATORY SYSTEM AND CLOSED CIRCULATORY SYSTEM

Blood Vessels :

The tissue of blood arteries is divided into three layers :-

• The inner layer of the Tunica intima surrounds the blood as it circulates through your body. It keeps toxins out of your blood, maintains blood pressure, and avoids blood clots. It maintains a healthy blood flow
• Elastic fibres in the intermediate layer keep your blood flowing in a single path. The media also aids in the expansion and contraction of arteries
• Nerves and small veins are found in the outer layer of adventitia. It helps remove waste and transports oxygen and nutrients from your blood to your cells. It also gives blood vessels structure and stability

Types of Blood Vessels

There are three types of blood vessels: – 

Arteries

• These muscular blood vessels transport oxygen-rich blood from your heart to the rest of your body. They can withstand a lot of strain and pressure from your blood flow, but they can’t carry much blood. Only around 10% to 15% of your body’s blood flows through your arteries at any given moment
  Arteries are blood vessels that carry oxygenated blood from the heart to the rest of the body. They’re tough on the surface, but they feature a smooth layer of epithelial cells on the inside that allows blood to flow easily. In arteries, there is a strong, muscular middle layer that aids in the pumping of blood throughout the body
• Arteries branch into arterioles, which are smaller vessels. Arterioles and arteries are both extremely flexible. They grow or shrink in size to help keep your blood pressure in check
  The arteries (red) deliver oxygen and nutrients from your heart to your body’s tissues. The veins (blue) are in charge of returning exhausted oxygenated blood to the heart. The aorta, the main artery leaving the guts, is where arteries begin.
• They are liable for transporting oxygen-rich blood from the guts to all or any of the body’s tissues. As they carry blood far away from the guts , they branch multiple times and become smaller and smaller

Capillaries

• Capillaries have thin walls and are tiny blood vessels. The blood’s oxygen and nutrients can pass through the walls and into the organs and tissues. Waste materials are also removed away from your tissues by capillaries. Oxygen and nutrients are exchanged for carbon dioxide and waste in capillaries.
  Small, thin blood vessels that connect the arteries and veins are referred to as capillaries. The tissue cells’ thin walls allow oxygen, nutrients, carbon dioxide, and waste materials to undergo
• The arteries and veins are connected by capillaries. The arteries transport oxygen-rich blood to the capillaries, where the oxygen and carbon dioxide are exchanged. The waste-rich blood is subsequently delivered to the veins, where it is transported back to the lungs and heart

Veins

• Unlike arteries, veins do not have to transport highly pressured blood, but they must transport enormous volumes of deoxygenated blood back to your heart. They can manage huge volumes and low pressure thanks to their thin, less elastic walls. The valves in most veins open and close. Blood flow is controlled by valves, which keep blood flowing in one direction. Your veins contain about 75% of your blood
• The blood is returned to the guts via veins. They resemble arteries, although they are not as powerful or thick. Veins, unlike arteries, have valves that ensure blood only travels in a method. (Arteries don’t need valves since the heart’s pressure is so high that blood can only flow in a method.) Valves also assist blood in returning to the guts against gravity
• Venules: Veins start off as small veins called venules and get larger as they move closer to your heart. Capillaries supply blood to venules. These are blood vessels that take oxygen-poor blood back to the guts. Veins become larger and bigger as they meet up with to the guts. The superior vein is the large vein that brings blood from the top and arms to the guts, and therefore the inferior vein brings blood from the abdomen and legs into the heart
• The vast system of blood vessels including arteries, veins, and capillaries is over 60,000 miles long which is long enough to travel round the world quite twice.
  Blood flows continuously through your body’s blood vessels. Your heart is the pump that creates it all possible.