Circulatory System Chapter Notes | Basic Science for JSS 3 PDF Download

Introduction

The circulatory system is like a transport system in our body. It helps carry important things like food, oxygen, and waste materials to different parts of the body. In humans and animals, this system keeps us alive by moving blood, which carries oxygen and nutrients, and removes harmful waste like carbon dioxide. The heart, blood, and blood vessels work together in this system to keep our body healthy and working properly.

Human Circulatory System

Humans and animals need food and oxygen to stay alive. They also need to remove harmful things like carbon dioxide and waste from the body. The circulatory system is a transport system that moves food, oxygen, and waste in the body.

Fluids in Our Body

Our body contains three main types of fluids:

• Blood, which flows through the heart and circulates in the blood vessels, including arteries, veins, and capillaries, as part of the circulatory system.
• Tissue fluid, which fills the spaces between cells within various organs.
• Lymph, found in the lymphatic system, including lymph vessels and lymphoid organs such as the spleen and tonsils.

The Blood

Blood is a red-colored fluid made up of two main components:

• Plasma, which is the liquid portion, and
• Corpuscles, which are the cellular elements.

The corpuscles, or blood cells, are categorized into three types:

• Red Blood Cells (RBCs), also known as erythrocytes, are circular or biconcave disc-shaped cells. Mature RBCs do not have a nucleus. Their red color comes from haemoglobin, an iron-containing protein that functions as the carrier of oxygen in the body.
• White Blood Cells (WBCs), or leucocytes, are colorless due to the absence of haemoglobin. They are larger than RBCs and have a prominent oval or lobed nucleus. WBCs play a vital role in defending the body against infections and ensuring immunity. 
• They do this in two ways:
  (a) Some WBCs engulf and digest harmful germs.
  (b) Others produce antibodies, special chemicals that neutralize or destroy pathogens.
• Platelets, also known as thrombocytes, are small, round cell fragments and the smallest among the blood cells. Their key function is to assist in blood clotting, which helps stop bleeding and prevents harmful microbes from entering the bloodstream through wounds.

Functions of the Blood

• Blood transports nutrients absorbed from the small intestine to the liver, where they are either stored or used by the body.
• It delivers oxygen from the lungs to the body’s cells and carries carbon dioxide, a waste gas, from the cells back to the lungs for exhalation.
• It removes waste products from the body by transporting them to the kidneys for excretion.
• Blood helps maintain the water balance in body tissues.
• It regulates body temperature by spreading the heat generated in tissues to different parts of the body.
• Blood supports the immune system by destroying harmful microbes and protecting against infections.
• It helps prevent blood loss by forming clots at injury sites.

The Blood Vessels

Blood moves through long, tube-like vessels in the body called arteries, veins, and capillaries.

• Artery: An artery is a vessel that carries blood away from the heart to other body parts. It is thick, elastic, and muscular, and the blood in it flows with jerks because of the heart's pumping.
• Vein: A vein is a vessel that brings blood from the body organs back to the heart.  It has thin muscular walls with valves to stop the backflow of blood, and the blood flows smoothly without jerks.
• Capillary: Capillaries are tiny branches of an artery where the exchange of nutrients, waste, and gases happens between blood and body fluids.

Differences Between Arteries and Veins

Heart – The Pumping Organ

The heart is a strong, fist-sized organ, about 225-340 grams, located in the center of the chest cavity, slightly tilted to the left side. It is made of special muscles called cardiac muscles that contract and relax continuously without getting tired. The heart's main job is to pump blood and keep it circulating in the body.

Structure

• The heart has four chambers: two upper auricles (atria) and two lower ventricles.
• The auricles are called the receiving chambers because they receive blood from different body parts.
• The ventricles are called the distributing chambers because they pump blood into all body parts.
• A wall called the septum separates the heart into right and left parts, so blood in the right side does not mix with blood in the left side.

Blood Vessels of the Heart

The heart is connected to blood vessels to move blood in and out of the body.

• Vena Cava: The superior vena cava is a large vein that brings deoxygenated blood from the upper body, like the head and shoulders, to the right auricle. The inferior vena cava brings deoxygenated blood from the lower body, like the trunk and legs, to the right auricle.
• Pulmonary Veins: Pulmonary veins bring oxygenated blood from the lungs to the left auricle.
• Pulmonary Artery: The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs for oxygenation.
• Aorta: The aorta carries oxygenated blood from the left ventricle to all parts of the body through its branches.

Circulation of Blood

• Oxygen-rich blood from the lungs goes to the left auricle through the pulmonary veins.
• The left auricle contracts and pumps this blood into the left ventricle.
• At the same time, the left ventricle contracts and pushes the oxygenated blood into the aorta.
• The aorta sends this blood to all parts of the body through its branches.
• At the same time, deoxygenated blood from the body enters the right auricle through the vena cava.
• The right auricle contracts and sends this blood to the right ventricle.
• The right ventricle contracts and pushes the deoxygenated blood into the pulmonary artery.
• The pulmonary artery takes this blood to the lungs to get oxygenated.
• In the lungs, the blood gets oxygen, and the cycle repeats.
• This process is called double circulation because blood passes through the heart twice in one cycle.

Pulse and Heart Beat

• The heart's chambers have elastic walls that expand when blood enters them and contract to pump blood out.
• The auricles and ventricles contract and relax together in a rhythmic way, about 72 times per minute.
• This rhythmic contraction is called the heartbeat, which can be felt by pressing your finger on the wrist or heard using a stethoscope.
• The pulse is the rhythmic beating you feel in your wrist due to the heart pumping blood into the arteries.

Blood Pressure

• Blood pressure is the pressure exerted by the blood on the walls of the arteries while flowing through them.
• The instrument used to find out blood pressure is called a sphygmomanometer.
• The normal level of blood pressure in a healthy person is around 120/80 mm Hg.
• A rise in blood pressure above 140/90 mm Hg is known as hypertension (high blood pressure).
• Blood pressure below the normal is called hypotension (low blood pressure).

Cardiac Arrest

• A cardiac arrest happens when the heart suddenly stops beating.
• It can happen to anyone, even healthy people, not just those with heart problems.
• Some people who look healthy can have a high chance of cardiac arrest because of hidden heart issues.
• Both men and women can have a cardiac arrest.
• Things that increase the chance of cardiac arrest are smoking, not eating healthy, not exercising, and being overweight.
• If a cardiac arrest happens, call an ambulance or doctor immediately.
• Chest compression, which means pressing on the chest, can help the person until the doctor arrives.
• Doing chest compression can improve the chances of the person surviving by keeping blood flowing in the body.

Causes of a Cardiac Arrest

• Cardiac arrest is mostly caused by heart problems.
• Not eating healthy, not exercising, smoking, and being overweight are big reasons for cardiac arrest.
• High blood pressure, heart failure, and heart attacks can also cause a cardiac arrest.
• Some people can have a cardiac arrest because of quick or uneven heartbeats, which doctors call ventricular fibrillation.
• The chance of surviving a cardiac arrest is better if the person gets help quickly.

Difference Between a Cardiac Arrest and a Heart Attack

• A cardiac arrest happens when the heart suddenly stops beating.
• A heart attack happens when blood flow to the heart is blocked, often because of a clot in the blood vessels.
• In a heart attack, the heart keeps beating, but in a cardiac arrest, the heart stops completely.
• A heart attack can sometimes lead to a cardiac arrest if the heart stops due to the blockage.
• Both are dangerous, but they are not the same thing.

Preventing a Cardiac Arrest

• Eat healthy foods to keep your heart strong.
• Do regular exercise to make your heart work better.
• Do not smoke because it is bad for your heart.
• Stay active and keep your body fit and healthy.
• Keep your weight normal, because being overweight is bad for the heart.

Blood Groups

• A scientist named Karl Landsteiner found different types of blood groups in humans in the year 1900.
• Humans have two main types of proteins on their blood cells called antigens: antigen A and antigen B.
• Based on these antigens, there are four blood groups: A, B, AB, and O.
• If a person’s blood has antigen A, their blood group is A.
• If a person’s blood has antigen B, their blood group is B.
• If a person’s blood has both antigens A and B, their blood group is AB.
• If a person’s blood has neither antigen A nor B, their blood group is O.

Keeping the Heart Healthy

• Eating healthy food is very important to protect your heart from diseases.
• Exercise regularly because it helps your heart grow strong and healthy.
• Being very overweight is a big problem because it can cause heart diseases, especially heart attacks.
• Playing games is a good way to stay active and happy.
• Walk regularly, cycle, and jog to keep your body fit and healthy.
• Do not eat too many oily and fried foods because they are bad for your heart.
• Eat healthy foods like vegetables and fruits because they are good for your heart.
• Do not eat too many sugary foods because they can cause obesity, which is bad for your heart.
• Do not eat too many grains, oats, or cereals because they can also cause obesity if you eat too much.
• Obesity means being very overweight, and it can cause heart problems.

Tissue Fluid and Lymph

1. Tissue Fluid (or Intercellular Fluid)

• Blood flows in the tiny blood vessels called capillaries.
• Some part of the blood plasma (the liquid part of blood) and white blood cells “leak out” through the walls of these capillaries.
• This fluid that leaks out is called tissue fluid or intercellular fluid because it is found between the cells.
• The tissue fluid gives oxygen, food, and other important things to the cells.
• It also takes away waste like carbon dioxide from the cells and puts it back into the blood.

2. Lymph and Lymphatic System

• Some of the tissue fluid may be taken back into tiny vessels called lymph vessels.
• These lymph vessels are part of the lymphatic system.
• The fluid inside these lymph vessels is called lymph.
• Lymph is a clear fluid that flows in the lymph vessels and goes back into the blood.

Lymph

• The main job of lymph vessels is to take extra fluid from the tissues and send it back to the blood.
• Lymph vessels also carry white blood cells, which help fight infections in the body.
• Lymph vessels are found all over the body, except in the brain and spinal cord.

Composition of Lymph

Lymph has two main parts:

• Only lymphocytes (a type of white blood cell) and no other blood cells like red blood cells or platelets.
• No red blood cells because lymph is a clear fluid, not red like blood.

Lymph also has:

• Nutrients like proteins, fats, carbohydrates, and enzymes, but only about 1% of these.
• Oxygen to give to the tissues where blood does not reach directly.
• Waste products like carbon dioxide that are taken away from the tissues.
• Tissue fluid and metabolites (waste products) that are carried from the tissues to the blood.
• Fats from the intestine that are absorbed through special lymph vessels called lacteals in the intestinal wall.

Functions of Lymph

• Lymph takes extra fluid from the tissues and puts it back into the blood.
• It carries white blood cells (lymphocytes) to fight infections and protect the body.
• Lymph helps remove bacteria and other harmful things from the tissues.
• It carries fats from the intestine to the blood because these fats cannot go directly into the blood.
• Lymph also helps in healing wounds by bringing white blood cells to the injured area.

Differences Between Blood and Lymph

Blood and lymph are different in many ways. Here are the differences: