Anaemia or Anemia is defined as a decrease in the ability of the blood to carry oxygen due to (1) a decrease in the total number of erythrocytes, each having a normal quantity of hemoglobin, or (2) a diminished concentration of hemoglobin per erythrocyte, or (3) a combination of both. It decreases the oxygen-carrying capacity of the blood.

Causes of Anaemia:

• Dietary deficiencies of iron (iron-deficiency anaemia), vitamin B12, or folic acid
• Bone marrow failure due to toxic drugs or cancer
• Blood loss from the body (hemorrhage) due to severe injury leading to iron deficiency
• Inadequate secretion of erythropoietin in kidney disease
• Excessive destruction of erythrocytes (for example, sickle cell anaemia)

Symptoms of anaemia:

The symptoms include fatigue, weakness, pale or yellowish skin, irregular heartbeats, shortness of breath, headaches, dizziness, lightheadedness, chest pain, cold hands and feet.

Types of anemia:

Iron deficiency anemia. 

This most common type of anemia is caused by a shortage of iron in the body. Iron is very important in the production of haemoglobin which is an oxygen carrier. It is caused by blood loss, such as from heavy menstrual bleeding or severe injury, an ulcer, cancer and regular use of some pain relievers, which can cause inflammation of the stomach lining resulting in blood loss. The iron lost from the body must be replaced. Due to non-adequate iron in bone marrow, the body can’t produce enough hemoglobin for red blood cells. This type of anemia is observed in pregnant women.

Treatment of iron deficiency anaemia usually involves taking iron supplements and making changes in diet. This iron lost from the body must be replaced by the ingestion of iron-containing foods like meat, liver, shellfish, egg yolk, beans, nuts, and cereals.

Vitamin deficiency or pernicious anemia: 

Production of normal erythrocyte numbers requires an extremely small amount of a cobalt-containing molecule, vitamin B12 (also called cobalamin). It is required for the action of folic acid.  There are some people who consume enough B-12 aren’t able to absorb the vitamin. A diet lacking in these and other key nutrients can cause decreased red blood cell production. This leads to vitamin deficiency anemia. It is easy to treat with vitamin B12 shots (injections) given in a muscle periodically or pills.

Anemia of inflammation: 

Anemia of inflammation, also called anemia of chronic disease or ACD, is a type of anemia that affects people who have conditions that cause inflammation. Inflammation may prevent the body from using stored iron to make enough healthy red blood cells, leading to anemia.  Certain diseases like cancer, HIV/AIDS, rheumatoid arthritis, kidney disease, Crohn’s disease, and other acute or chronic inflammatory diseases can interfere with the production of red blood cells. It is the second most common type of anemia, after iron-deficiency anemia.

A health care professional may prescribe the erythropoiesis-stimulating agents (ESAs) epoetin alpha darbepoetin alpha to treat anemia related to CKD, chemotherapy treatments for cancer, or certain treatments for HIV.

Aplastic anemia:

Aplastic anemia occurs because of damage to stem cells inside the bone marrow. As a result, the bone marrow makes fewer red blood cells, white blood cells, and platelets. This rare, life-threatening anemia occurs when the bone marrow doesn’t produce enough red blood cells. Its causes include infections, certain medicines, autoimmune diseases and exposure to toxic chemicals.

Treatments may include medicines to suppress the immune system, blood transfusions, or a blood and bone marrow transplant.

Anemias associated with bone marrow disease:

Bone marrow disease (bone cancer), may be the result of a malignant tumor of the bone or cancer that has spread, or metastasized, from another area of the body to the bone. Bone cancer can destroy bone marrow tissue and the body’s ability to manufacture red blood cells, thereby causing anemia.  A variety of diseases, such as leukemia and myelofibrosis, can cause it by affecting blood production in the bone marrow. The effects of these types of cancer and cancer-like disorders vary from mild to life-threatening.

Supportive care is usually the first line of treatment for bone marrow disease anemia, and this care relieves symptoms but does not cure the disease. Supportive care includes blood transfusions, platelet transfusions, iron, and folic acid supplements, growth factor drugs such as epoetin alfa (Procrit), Following strict infection prevention procedures.

Hemolytic anemias:

Certain blood diseases increase red blood cell destruction. this type can be inherited or can develop it later in life.

Its main cause in the rapid destruction of RBCs. The life span of red blood cells is 120 days. Red blood cells develop in the bone marrow (hemopesis) are destroyed in the spleen (hemolysis). Thus red blood cells in the body are destroyed faster than bone marrow can replace them.

Treatments may include lifestyle changes, medicines, blood transfusions, blood and bone marrow transplants, or surgery to remove the spleen.

Sickle Cell Anaemia:

Sickle cell anemia is an inherited form (a genetic disorder) of hemolytic anemia. It is caused by a defective form of hemoglobin that forces red blood cells to assume an abnormal crescent (sickle) shape. These irregular blood cells die prematurely, resulting in a chronic shortage of red blood cells.

There’s no cure for most people for this disorder. But treatments can relieve pain and help prevent problems associated with the disease. Bone marrow transplant, also known as stem cell transplant, offers the only potential cure for it.

Science > Biology > Human Anatomy and Physiology > Cardiovascular System > Disorder Associated With RBCs Anaemia (Anemia)

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When a human blood sample is prevented from clotting and spun in a test tube (centrifuged), in a machine called a centrifuge, the blood separates into a   straw coloured liquid called plasma and a dark brown mass of blood cells. The lower layer consists of white blood cells, blood platelets, and red blood cells. Collectively, these are the formed elements, which make up about 45% of the total volume of whole blood; the percentage of blood attributed to red blood cells is called the hematocrit. The hematocrit is defined as the percentage of blood volume that is occupied by erythrocytes. The normal hematocrit is approximately 45 percent in men and 42 percent in women.

The upper layer is plasma, which contains a variety of inorganic and organic molecules dissolved or suspended in water. Plasma accounts for about 55% of the total volume of whole blood.

Composition of Plasma:

Plasma is the straw-coloured non-living, liquid part of blood. It makes up about 55 – 60% of blood volume and 5.5 % of body weight. Blood corpuscles and platelets are suspended in it. Blood without clotting factor is called serum. The characteristic straw color of plasma is due largely to a waste product of hemoglobin breakdown called bilirubin.

It is the liquid portion of blood, and about 92% of plasma is water. The remaining 8% of plasma is composed of various salts (ions) and organic molecules. The salts, which are dissolved in plasma, help maintain the pH of the blood. Small organic molecules such as glucose, amino acids, and urea are also dissolved in plasma. The large organic molecules in plasma include hormones and the plasma proteins.

Water:

Plasma is composed of about 90 to 92% water. Acts as a solvent and suspending medium for blood components.  

Plasma Proteins:

Plasma proteins or serum proteins constitute 6 to 8% of plasma. Important plasma-proteins are. The plasma proteins constitute, by weight, most of the plasma solutes. They can be classified, according to certain physical and chemical reactions, into three broad groups: the albumins and globulins, and fibrinogen, which function in blood clotting. Most plasma proteins are made in the liver. An exception is the antibodies produced by B lymphocytes, which function in immunity. Certain hormones are plasma proteins made by various glands.  It must be emphasized that the plasma proteins normally are not taken up by cells; cells use plasma amino acids, not plasma proteins, to make their own proteins. Plasma proteins must be viewed quite differently from most of the other organic constituents of plasma, which use the plasma as a medium for transport to and from cells. In contrast, most plasma proteins perform their functions in the plasma itself or in the interstitial fluid.

• Fibrinogen and prothrombin: It constitutes 4% of the plasma proteins and required for blood clotting.
• Serum albumin: The albumins are the most abundant of the three plasma protein groups and are synthesized by the liver. It makes up 58% of the plasma proteins. They are partly responsible for blood viscosity, the regulation of water movement between tissues and blood and osmotic pressure; acts as a buffer; transports fatty acids,
  free bilirubin, and thyroid hormones.
• Globulins or Gamma globulins or Immunoglobins (Ig): It accounts for 38% of the plasma proteins. They act as antibodies and are associated with the defence mechanism of the body. They Transport lipids, carbohydrates, hormones, and ions like iron and copper; antibodies complement are involved in immunity

Inorganic Salts and Ions (Minerals):

They form 1-2 % of the plasma and includes electrolytes like Sodium, potassium, calcium, magnesium, chloride, iron, phosphate, hydrogen, hydroxide, bicarbonate. They are involved in osmosis, membrane potentials, and acid-base balance.

Dissolved Nutrients:

Glucose, lipids, vitamins, fatty acids, amino acids, and cholesterol. They act as sources of energy and basic “building blocks” of more complex molecules. Vitamins Promote enzyme activity.

Hormones and Enzymes:

Blood acts as the transport system for the transportation of regulatory substances called hormones secreted by different glands.  Thus plasma contains hormones and enzymes. Enzymes catalyze chemical reactions; hormones stimulate or inhibit many body functions.

Dissolved Gases:

Oxygen, It is necessary for aerobic respiration; terminal electron acceptor in an electron-transport chain, Carbon dioxide, a Waste product of aerobic respiration; as bicarbonate, helps buffer blood and nitrogen.

Excretory Substances:

Ammonia, urea, uric acid, creatine, and creatinine. Urea, uric acid, creatinine , and ammonia salts  are the breakdown products of protein metabolism; excreted by the kidneys. Bilirubin is the breakdown product of red blood cells; excreted as part of the bile from the liver into the intestine. Lactic acid is the end product of anaerobic respiration; converted to glucose by the liver.

Functions of Plasma:

Transport Nutrients:

Delivering nutrients to the body is a critical function of the circulatory system. Plasma of the blood is the carrier of all nutrients. After food is digested and assimilated, its component nutrients like carbohydrates, proteins, minerals, fats, and vitamins are absorbed into the bloodstream. Each of these nutrients is vital for healthy body function.

Transport of Waste Products:

The plasma collects metabolic waste products like urea, creatinine, and other chemical wastes and toxins and transports them to the liver, kidneys, skin, and lungs (excretory organs) for elimination from the body.

Transport of Hormones:

Hormones are chemical messengers produced by endocrine glands that affect distant organs. Hormones are released into the bloodstream through which they travel to target sites. The plasma collects the hormones from the endocrine glands and serves as the transportation connection between the glands and the organs or tissues.

Transport of Other Products:

Albumin transports the molecule bilirubin, a breakdown product of hemoglobin. Lipoproteins, whose protein portion is a globulin, transport cholesterol.

Body Temperature Regulation:

Plasma Picks up excess body heat from the deep-seated heat-producing organs and brings it to the skin to be excreted. If body temperature drops, surface blood vessels constrict(decrease in size) to conserve body heat. Thus it  helps in regulating the body temperature

Disease Protection and Healing:

There are three types of globulins, designated alpha, beta, and gamma globulins. The alpha and beta globulins, produced by the liver, bind to metal ions, to fat-soluble vitamins, and to lipids, forming the lipoproteins. Antibodies, which help fight infections by combining with antigens, are gamma globulins. The immunoglobins of plasma act as antibodies and attack the foreign intruder in the body. They neutralize these harmful foreign agents. Thus plasma is responsible for the immunity of the body.

Fibrinogen present in the plasma is responsible for clotting of blood which is important for stopping the blood flow from the wounds.

Maintain Haemostasis and Osmoregulation:

Plasma supplies water to different tissues at the same time and removes excess of water produced during metabolic activities. Thus it maintains water balance in the body. Osmotic pressure is a force caused by a difference in solute concentration on either side of a membrane. The plasma proteins, particularly the albumins, contribute to the osmotic pressure, which pulls water into the blood and helps keep it there.

Acid-Base Buffer:

Plasma proteins act as acid-base buffers and maintain blood pH within a range. Plasmaproteins are able to take up and release hydrogen ions; therefore, the plasma proteins help buffer the blood and keep its pH around 7.40.

Disorders Related with Blood Plasma:

Oedema or Edema:

Oedema is swelling that occurs when too much fluid becomes trapped in the tissues of the body, particularly the skin. It most often occurs in the skin, especially on the hands, arms, ankles, legs, and feet. However, it can also affect the muscles, bowels, lungs, eyes, and brain. It usually starts slowly, but the onset can be sudden.

In case of a person suffering from protein deficiency, a fall in plasma protein leads to escape of excess volume of water from the blood to tissues. Due to excess of fluid of fluid in tissues causes swelling of feet. The state is called oedema.  The condition mainly occurs in older adults and women who are pregnant. Symptoms include skin that retains a dimple after being pressed for a few seconds,  puffiness of the ankles, face, or eyes, higher pulse rate and high blood pressure.

Diuretics are a type of medication. They help get rid of excess fluid by increasing the rate of urine production by the kidneys.

Cholesterol:

Cholesterol is present in plasma. Cholesterol has a tendency to deposit on the walls of blood vessels leading to a condition called atherosclerosis. The liver is responsible for producing and clearing cholesterol in the body.

Dietary cholesterol increases plasma total cholesterol concentrations in humans. There is a relationship between increased plasma cholesterol concentrations and cardiovascular disease risk. Dietary guidelines have consistently recommended to such person limiting food sources of cholesterol. Potential sources of dietary cholesterol are limited to animal foods; eggs, dairy products, and meat.

LDL (low-density lipoprotein) cholesterol is also called “bad” cholesterol. LDL can build up on the walls of arteries and increase the chances of getting heart disease. HDL (high-density lipoprotein) cholesterol is also called “good” cholesterol. HDL protects against heart disease by taking the bad cholesterol out of the blood and keeping it from building up in arteries. Along with cholesterol, triglycerides form plasma lipids. Excess triglycerides in plasma have been linked to the occurrence of coronary artery disease in some people.

Everyone over the age of 20 should get their cholesterol levels checked at least once every 5 years by a test called “Lipid profile”. Everyone over the age of 40 should get their cholesterol levels checked at least once a year.

Lifestyle changes such as exercising and eating a healthy diet are the first line of defence against high cholesterol. The choice of medication for high cholesterol depends on individual risk factors, age,  current health and possible side effects. Common choices include Statins, Bile-acid-binding resins, Cholesterol absorption inhibitors, Injectable medications. The choice of medication for high triglycerides is Fibrates, Niacin, Omega-3 fatty acid supplements.

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Science > Biology > Human Anatomy and Physiology > Cardiovascular System > Composition of Blood: Blood Plasma

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In the Cardiovascular system, the ‘‘heart’’ (cardi) pumps the blood in a ‘‘little circle’’ (circul), which travels through ‘‘little vessels’’ (vascul). In human, the transportation is done through blood circulatory system and lymphatic system. Thus two fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the Cardiovascular System. The lymph, lymph nodes and lymph vessels form the Lymphatic System. Human blood circulatory system has three main components. A fluid (blood), tubing (arteries, veins and capillaries) and a pump (the heart).

Study of blood is called haematology. It is a fluid connective tissue. It is bright red, slightly alkaline, salty viscous fluid heavier than water.

The Constituent of the Blood:

In this article, we shall only take an overview of the composition. In the next article, each constituent is discussed in detail.

When a human blood sample is prevented from clotting and spun in a test tube (centrifuged), in a machine called a centrifuge, the blood separates into a   straw coloured liquid called plasma and a dark brown mass of blood cells. The lower layer consists of white blood cells, blood platelets, and red blood cells. Collectively, these are the formed elements, which make up about 45% of the total volume of whole blood; the percentage of blood attributed to red blood cells is called the hematocrit. The hematocrit is defined as the percentage of blood volume that is occupied by erythrocytes. The normal hematocrit is approximately 45 percent in men and 42 percent in women.

The upper layer is plasma, which contains a variety of inorganic and organic molecules dissolved or suspended in water. Plasma accounts for about 55% of the total volume of whole blood.

Characteristics of Human blood:

Study of blood is called haematology. Blood is a fluid connective tissue. It is bright red, slightly alkaline (pH 7.3 to 7.5), salty viscous fluid heavier than water. the pH of blood is more in arteries than that in veins. The viscosity of blood is 5 to 6 times that of water. An adult has a blood volume of approximately 5.5 litres. It forms 6 to 10 % of the body weight. Blood is the only tissue that exists in both the liquid and solid state simultaneously.

Volume of Blood and Different Constituents:

The volume of blood in an average-sized person is approximately 5.5 L. Now hematocrit is 45 percent of the total volume,

Then, Erythrocyte volume = 0.45 x 5.5 L = 2.5 L

Since the volume occupied by the leukocytes and platelets is normally considered negligible, the plasma volume equals the difference between blood volume and erythrocyte volume; therefore, in our average person

Plasma volume = 5.5 L – 2.5 L = 3.0 L

Plasma:

The plasma consists of 90 to 92% water and 8% to 10% proteins, salts, hormones, enzymes, waste products and other various chemicals. Most of the solute part about 7% is proteins. These include antibodies that help to protect the body from diseases, fibrinogen that helps the blood to clot. The waste product includes urea and carbon dioxide. Hormones are the chemical messenger, which help to coordinate different body functions.

Plasma obtained from blood donation may be converted to a powdered form for storage. During the transfusion, it is dissolved in sterile distilled water and can be administered at once. This method saved the lives of many during World war.

Red Blood Cells (RBCs): 

They are also called erythrocyte. They are produced inside the bone marrow. They have a lifespan of about 100 to 120 days after which they are destroyed by the liver. They are the most common type of blood cell (5.1 to 5.8 million per cubic mm). They are non-nucleated, small in size, round and biconvex in shape. They are able to fold and bend as they are forced through the smallest blood vessels.

The strong red colour of blood is due to the large number of RBCs. Red blood cells contain haemoglobin which gives them their red colour and enables them to carry oxygen from lungs to different parts of the body. They also carry carbon dioxide from different parts of the body to the lungs. Their main function is to carry oxygen from the lungs to the tissues.

White blood cells (WBCs):

They are also called leucocytes. Many white cells are made in the bone marrow. Their lifespan is 3 to 4 days. They are colourless and they have a nucleus. WBCs are larger than red cells but they are lesser in number. (About 5000-7000 per cubic millimetre of blood). They are further classified as lymphocytes and phagocytes. The nucleus of each type has a characteristic shape. When they travel in the blood they are more or less spherical, but they flatten and continuously change their shape along the inside walls of the blood vessels.

WBC’s rid the body of pathogens in the process called phagocytosis. In this process, the WBC surrounds, engulfs and “eats” the invading pathogen.

Platelets : 

Platelets are also called thrombocytes. They are made in the bone marrow and have a lifespan of 8-14 days. They are much smaller than red cells. One cubic millimetre of blood contains about a quarter of million platelets. Their function is to help the blood clot. Clotting prevents loss of blood from wounds.

Observing Blood Under Microscope:

• Clean the skin of your finger with a swab of cotton dipped in ethanol. With a sterile needle prick your finger so that a drop of blood comes out.
• Place the drop of blood at one end of a microscope slide. With another slide spread the blood over the surface to form a smear. Let it dry and then examine it under a microscope. We can observe red blood corpuscles.
• Now cover the smear with Leishman’s stain and leave it for five minutes. Then wash the stain off with tap water gently. Let the slide dry and then examine it under the microscope again. Now, we can observe white blood corpuscles.

Functions of Human blood:

Transportation:

The blood moves from the heart to all the various organs, where exchange with tissues takes place across thin capillary walls. Blood collects oxygen from the lungs and nutrients from the digestive tract and transports these to the tissues. It delivers enzymes and chemical messengers to cells and tissues. Various organs and tissues secrete hormones into the blood, and blood transports these to other organs and tissues, where they serve as signals that influence cellular metabolism. It delivers water, vitamins and minerals to cells. It carries carbon dioxide from cells, tissues and carries it to lungs for disposal. It carries waste materials like urea and other chemical wastes and carries them to the liver and kidneys for disposal. It carries antibodies from place to place in the body. It carries vitamins and enzymes.

Protection:

The blood defends the body against invasion by pathogens (microscopic infectious agents, such as bacteria and viruses) in several ways. Certain blood cells are capable of engulfing and destroying pathogens, and others produce and secrete antibodies into the blood. White blood corpuscles  (WBC) fight against disease-causing germs that harm the body.

It prevents the loss of blood after an injury by clotting. Blood helps in the repair process after a cut or other injury. Without blood clotting, we could
bleed to death even from a small cut.

Regulation:

Blood Picks up excess body heat and brings it to the skin to be excreted. The sweat is formed on the skin. Which is evaporated and heat required for it is taken from the body. Hence the body cools down. It controls the amount of water in the body. The salts and plasma proteins in blood act to keep the
liquid content of blood high. In this way, blood plays a role in helping to maintain its own water-salt balance. It also helps to regulate the amount of chemical substance in the tissues of the body. Due to the presence of buffers in the blood, it also helps to regulate body pH and keep it relatively constant.

Blood Donation:

Anybody who is healthy weighs over 50 kg and is between the age of 18 years and 65 years can donate blood. An adult has a blood volume of approximately 5 litres. A donor may give up to half a litre of blood at one time. This is quickly replaced by the body.

Many donors give blood regularly. It is immediately mixed with a chemical which prevents it from clotting and also provides food for the living cells. The blood is then stored in a refrigerator until it is required. Similarly, sodium citrate is added to it to avoid coagulation. The place where the blood is stored is called a blood bank.

Blood groups:

Human blood group is determined by the antigens present on the surface of RBC’s.  Blood groups are inherited and do not change throughout life. Human blood is classified into 4 main groups: A, B, AB and O. Each can be either Rhesus + ve or Rhesus – ve, giving  8 groups in all. Blood grouping is the identification of the antigens in a blood sample. This system is called ABO system.

An individual’s RBC’s may carry an A antigen, a B antigen, both A and B antigens, or no antigen at all. These antigen patterns are called blood types A, B, AB and O, respectively. Type AB is known as a universal recipient, meaning that they can receive any type of blood, while O is the universal donor, meaning they can donate blood to anyone

Blood transfusion:   

Blood transfusion is the transfer of blood that is taken from one person, into the bloodstream of another person. The person who gives blood is called the donor. The person who receives blood is called the recipient. When there is a loss of blood suddenly due to an accident, or because of the bursting of a blood vessel, there is a danger that not enough blood will be left to maintain the circulation. In such a case, the patient may lose consciousness due to low blood pressure and hence less supply of oxygen to tissues. Losing blood is called haemorrhage. To restore the blood volume and to provide more red cells, a blood transfusion is carried out.

Before doing blood transfusion the compatibility between the groups of the donor and the recipient should be checked. If the blood of the donor is not compatible with the blood of the patient, the red cells in the patient’s blood will stick together. This may lead to death.

Clotting of Blood:

Human blood contains heparin and antithrombins as anticoagulants, it prevents the blood to clot inside the blood vessels. As soon as blood vessel ruptures, bleeding starts. The conversion of liquid blood into semisolid jelly is called blood coagulation or blood clotting. Platelets adhere to the site of the wound and release clotting factors known as prothrombin. Prothrombin is inactive. At the site of rupture the platelets and injured tissues release thromboplastin which initiates the formation of enzyme prothrombinase.  In the presence of Ca, ions prothrombinase converts inactive prothrombin to active thrombin. Thrombin converts soluble fibrinogen into fibrin. The fibrin forms a net to enmesh platelets blood cells and plasma to form a clot.

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Science > Biology > Human Anatomy and Physiology > Cardiovascular System > The blood, an Overview

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In living things, many substances such as food, gases, minerals salts, hormones and waste products have to be transported from one part of the body to another. Plants and animals have a system of transporting substances throughout their body. In animals (vertebrates), blood is the medium of transport. In small animals (lower animals) such as protozoa and Flatworms, Diffusion of gases takes place through their body surface. Due to their smaller size, they lack a special system for the transport of other materials such as oxygen for existence. Higher animals have higher metabolic activity, hence higher animals require an efficient and speedy supply of nutrients and oxygen for their tissues at the same time they require efficient and speedy disposal of respiratory products, nitrogen products. Hence such animals have developed a special fluid called blood in them and conducting system called circulatory system consisting of heart, vessels etc. This system is also called a vascular system. The circulatory system has two functional components viz. a) blood vascular system and b) lymph vascular system.

Functions of the Circulatory System

Transport of oxygen:

The main function of the circulatory system is supplying oxygen to the different parts of the body. Every cell requires oxygen for their survival. Particularly the brain cells are the most sensitive and begin to die in as little as 3 minutes if deprived of oxygen. During inhalation, air enters the lungs and oxygen is absorbed through the air sacs (alveoli) into the bloodstream. Oxygen combines with the haemoglobin of RBCs to form oxyhaemoglobin. This oxygen-rich blood is pumped through the heart into the arterial circulation. In the capillaries, unstable oxyhaemoglobin breaks down into haemoglobin and oxygen. The separated oxygen diffuses out of the blood into the cells of the body’s organs and tissues where it is utilized for metabolic activities.

Transportation of Carbon dioxide:

Carbon dioxide is a waste product produced by cells during its metabolic activities. A small amount of carbon dioxide combines with haemoglobin to for carbamino-haemoglobin. Some carbon dioxide dissolves in blood plasma.  The absorbed carbon dioxide in the blood is transported to the lungs through the venous circulation. When this oxygen-poor blood reaches the lungs, carbon dioxide diffuses through the air sacs (alveoli) and is then exhaled.

Transport of Nutrients:

Delivering nutrients to the body is another critical function of the cardiovascular system. After food is digested and assimilated, its component nutrients like carbohydrates, proteins, minerals, fats, and vitamins are absorbed into the bloodstream. Each of these nutrients is vital for healthy body function. Carbohydrates are a direct source of energy for the body while proteins (amino acids) are building blocks of new cells. Thus circulatory system supply nutrients wherever it is required. Like oxygen, nutrients diffuse from the bloodstream into body cells via the capillaries.

Transport of Waste Products:

The circulatory system collects metabolic waste products like urea and other chemical wastes and toxins and transports them to the liver, kidneys, skin, and lungs (excretory organs) for elimination from the body.

Transport of Hormones:

Hormones are chemical messengers produced by endocrine glands that affect distant organs. Hormones are released into the bloodstream through which they travel to target sites. Thus the cardiovascular system serves as the transportation connection between the endocrine glands and the organs or tissues. For example, Pituitary gland situated near the brain produces hormones which control other endocrine glands such as the thyroid, ovaries and testes and growth. Similarly, pancreas situated near liver produce hormone insulin which is required for maintaining blood sugar level throughout the body. The circulatory system delivers these hormones to the site of use of that hormone.

Body Temperature Regulation:

Blood Picks up excess body heat and brings it to the skin to be excreted. The sweat is formed on the skin. Which is evaporated and heat required for it is taken from the body. Hence the body cools down. Optimal function of the human body occurs within a relatively narrow temperature range, which is tightly regulated. If body temperature begins to rise, blood vessels close to the body surface dilate (increasing in size). This allows the body to get rid of an excess of heat through the skin. If body temperature drops, surface blood vessels constrict (decrease in size) to conserve body heat. Thus the cardiovascular system works in concert with the body’s sweating mechanism  to regulate the body temperature

Disease Protection and Healing:

The circulatory system serves as the path for disease-fighting cells and proteins, and messengers of the immune system. WBC’s rid the body of pathogens (invading germs) in the process called phagocytosis. In this process, the WBCs surround, engulf and “eats” the invading pathogen. Thus they fight against the pathogens. On entry of germs, antibodies are produced in the blood and a chemical alarm signal is created that travel through the bloodstream, which subsequently transports antibodies to the site of the infection. The circulatory system also carries chemical messengers that attract cells to heal tissues that have been damaged due to injury or disease. It helps in clotting to heal the wound.

Maintain Haemostasis and Osmoregulation:

Homeostasis is a property of cells, tissues, and organisms that allows the maintenance and regulation of the stability and constancy needed to function properly. Homeostasis is a healthy state that is maintained by the constant adjustment of biochemical and physiological pathways. Humans’ internal body temperature, the blood sugar level, blood pressure are all maintained through homeostasis. The circulatory system plays an important role in it. The maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations is called osmoregulation. The osmotic pressure and concentrations are maintained by the circulatory system.

Types of Circulatory Systems

Higher organisms have higher metabolic activity, hence higher animals require an efficient and speedy supply of nutrients and oxygen for their tissues at the same time they require efficient and speedy disposal of respiratory products, nitrogen products. Hence such animals have developed a special fluid called blood in them and conducting system called circulatory system consisting of heart, vessels etc. This system is also called a vascular system. The circulatory system has two functional components viz. a) blood vascular system and b) lymph vascular system.

The blood vascular system is of two types a) Open circulation and  b) Closed circulation

Open Circulatory System:

Open circulatory systems are the more basic type of circulatory system. In this circulatory system, the blood is not contained within an enclosed circuit of vessels. Blood (haemolymph) flows from the heart through open-ended vessels and, when it reaches the end of the vessels, The haemolymph enters into an open cavity called a haemocoel. The haemolymph mixes with interstitial fluid and moves around the haemocoel, thus bathing the internal organs and tissues. Haemolymph flows directly over the tissues delivering nutrients and in some cases, gases such as oxygen. Then the haemolymph freely flows back into vessels that direct the blood back to the heart.

The heart is simply an aorta or other blood vessels, and the haemolymph is pulsed throughout the body by muscle contractions. There are no arteries or major veins to pump the haemolymph, so blood pressure is very low and the volume of haemolymph is relatively high.

Examples: arthropods which include insects, spiders, prawns and most molluscs.

Characteristics of Open Circulatory System:

• Blood flows through large open spaces called lacunae and sinuses.
• No capillary system so tissues are in direct contact with haemolymph.
• Exchange of nutrients and gases takes place directly between haemolymph and tissue.
• The volume of haemolymph flowing through tissues cannot be controlled as hemolymph is flowing through open spaces.
• haemolymph flow is very slow. The blood pressure is very low
• Found in higher invertebrates like most arthropods such as prawns, cockroach etc. and in some molluscs.

Closed Circulatory System:

William Harvey (1578-1657)  discovered and published the first accurate description of the human circulatory system, based on his many years of experiments and observations as a scientist and physician. The humans have closed circulatory system. Unlike an open circulatory system, a closed circulatory system is more structured and controlled. The blood of a closed system always flows inside vessels. These vessels make up the vessel system of the body and can be found throughout the entire body.

Characteristics of Closed Circulatory System:

• Blood flows through a closed system i.e. heart and blood vessels.
• Capillary system present so blood is not in direct contact with tissues.
• Nutrients and gases pass through the walls of capillaries to tissue fluid which is then taken up by the tissues.
• Blood flow is controlled by contraction and relaxation of muscles of blood vessels.
• Blood flow is rapid here.
• Found in some molluscs, annelids and all vertebrates.

Importance of Human Circulatory System:

Most of the cells in the human body are not in direct contact with the external environment, so rely on the circulatory system to act as a transport service for them. Two fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the Cardiovascular System. The lymph, lymph nodes and lymph vessels form the Lymphatic System. The Cardiovascular System and the Lymphatic System collectively make up the Circulatory System. The system in which blood is circulated throughout the body is called the circulatory system.

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Science > Biology > Human Anatomy and Physiology > Cardiovascular System > Circulatory System and its Function

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