HUMAN CIRCULATORY SYSTEM CHAPTER 8 - CBSE BIOLOGY CLASS-VII
* Circulatory System: This system is concerned with the circulation of body fluids to distribute various substances to various body parts. The circulatory system is also known as the cardiovascular system.
HUMAN CIRCULATORY SYSTEM CHAPTER 8 - CBSE BIOLOGY CLASS-VII
You have learnt earlier that all organisms need food, water and oxygen
for survival. They need to transport all these to various parts of their
body. Further, animals need to transport wastes to parts from where they
can be removed. Have you wondered how all this is achieved? Look at
Fig. 11.1. Do you see the heart and the blood vessels? They function to
transport substances and together form the circulatory system. In this
chapter, you shall learn about transport of substances in animals and
What happens when you get a cut on your body? Blood flows out.
But what is blood? Blood is the fluid which flows in blood vessels. It
transports substances like digested food from the small intestine to
the other parts of the body. It carries oxygen from the lungs to the
cells of the body. It also transports waste for removal from the body.
How does the blood carry various substances? Blood is composed of
a fluid, called plasma in which different types of cells are suspended.
The circulatory system is made up of blood vessels that carry blood
away from and towards the heart. Arteries carry blood away from
the heart and veins carry blood back to the heart. The circulatory
system carries oxygen, nutrients, and hormones to cells, and removes
waste products, like carbon dioxide.
What Are the Parts of the Circulatory System?
Two pathways come from the heart:
The pulmonary circulation is a short loop from the heart to the lungs
and back again.
The systemic circulation carries blood from the heart to all the other
parts of the body and back again.
* It is an organ system that allows blood to circulate and transport
nutrients (such as electrolytes and amino acids), oxygen, carbon
dioxide, hormones, and blood cells. These are circulated to and from
cells in the body to nourish it.
•The most important function of
the circulatory system is
transporting oxygen throughout
•The other vital functions of the
human circulatory system are as
It helps in sustaining all the
It transports blood, nutrients,
oxygen, carbon dioxide and
hormones throughout the body.
It protects cells from pathogens.It
acts as an interface for cell-to-cell
The substances present in the
blood helps repair the damaged
*Human Heart: Heart is a muscular organ; which is composed of
cardiac muscles. It is so small that it can fit inside and adult’s fist.
The heart is a pumping organ which pumps the blood.
* The heart has four chambers — two on top and two on bottom:The
two bottom chambers are the right ventricle and the left ventricle.
These pump blood out of the heart. A wall called inter ventricular
septum is between the two ventricles. The two top chambers are the
right atrium and the left atrium. They receive the blood entering the
heart. A wall called inter arterial septum is between the atria.
* Contraction of cardiac muscles is called systole. The relaxation of
cardiac muscles is called diastole.
* Arteries: These are thick-walled blood vessels which carry
oxygenated blood from the heart to different organs. Pulmonary
arteries are exceptions because they carry deoxygenated blood from
the heart to lungs; where oxygenation of blood takes place.
* Veins: These are thin-walled blood vessels which carry
deoxygenated blood from different organs to the heart. Pulmonary
veins are exceptions because they carry oxygenated blood from lungs
to the heart. Valves are present in veins to prevent back flow of
* Capillaries deliver nutrients and oxygen to tissues and remove the
by products of cellular reactions, such as carbon dioxide and water.
With the exception of the lungs, where the opposite is true,
capillaries bring oxygenated blood, blood-carrying oxygen, to organs
and carry away deoxygenated blood, blood with the oxygen
Blood is a body fluid in humans and other animals that delivers
necessary substances such as nutrients and oxygen to the cells and
transports metabolic waste products away from those same cells. In
vertebrates, it is composed of blood cells suspended in blood plasma.
Your blood is made up of liquid and solids. The liquid part, called
plasma, is made of water, salts, and protein. Over half of your blood
is plasma. The solid part of your blood contains red blood cells,
white blood cells, and platelets. Red blood cells (RBC) deliver oxygen
from your lungs to your tissues and organs.
* Red Blood Cells (RBCs): These are of red color because of the
presence of hemoglobin which is a pigment. Hemoglobin readily
combines with oxygen and carbon dioxide. The transport of oxygen
happens through hemoglobin. Some part of carbon dioxide is also
transported through hemoglobin.
* White Blood cells: these also called leukocytes, White Blood cells
play an important role on the immune system. These cells help fight
infections by attacking bacteria, viruses, and germs that invade the
* Platelets: Platelets are responsible for blood coagulation. Blood
coagulation is a defense mechanism which prevents excess loss of
blood; in case of an injury.
* Lymphatic System: The human circulatory system consists of
another body fluid called lymph. It is also known as tissue fluid. It is
produced by the lymphatic system which comprises a network of
interconnected organs, nodes and ducts.
* Lymph is a colorless fluid consisting of salts, proteins, water, etc.
which transport and circulates digested food and absorbed fat to
inter cellular spaces in the tissues. Unlike the circulatory system,
lymph is not pumped; instead, it passively flows through a network
* Double Circulation: The way blood flows in the human body is
unique, and it is quite efficient too. The blood circulates through the
heart twice; hence, it is called double circulation.
* Other animals like fish have single circulation, where blood
completes a circuit through the entire animal only once.
* The main advantage of double circulation is that every tissue in the
body has a steady supply of oxygenated blood, and it does not get
mixed with the deoxygenated blood.
* Open circulatory system: In open circulatory system, the blood
vessels open into spaces and not into capillaries, so that blood comes
in direct contact with tissues.
* Whereas in closed circulatory system, blood flows through
capillaries connected by arteries and veins.