The Heart

Transportation In Human Beings

In humans, transportation of oxygen nutrients, hormone and other substances to tissue, CO₂ to the lungs and waste products to the kidneys is carried out by a well-defined Circulatory System. In lower organisms material is transported by diffusion.
Circulatory System:
It comprises of the heart, blood vessels, blood, lymphatic vessels, lymph, which together serve to transport materials, throughout the body.
Components of the circulatory system in higher animals are –

1. Blood
2. Pumping organ- ‘Heart’
3. System of blood vessels for distribution and collection of blood – consisting of arteries, veins and capillaries.

1. Blood Corpuscles:

1. Red Blood Corpuscles (RBC) or Erythrocytes :
   These are minute, circular biconcave discs having no nucleus. They look red due to the presence of red coloured pigment, haemoglobin. Red blood cells have life span about 120 days. They are produced in bone marrow number is 4.5 – 5.5 millon/cu.mm.
   Function:
   Haemoglobin transports oxygen from lungs to body tissues.
2.  WBC or White Blood Cells or Corpuscles:
   These are large, nucleated colourless cells and are less numerous than erythrocytes. There are about 5000 W.B.C per mili litre of blood. They move actively and protect the body against disease-causing microorganisms by destroying them.
   
   WBC are mainly of two Type W.B.C.
   
3. Blood Platelets:
   Platelets are rounded, colourless, biconvex and non-nucleated blood- cells, which help in the coagulation of blood they are called thrombocytes. Whenever you have a cut on your body, blood comes out. The bleeding is stopped after sometime by the blood platelets present in the blood. Blood platelets are colourless, irregularly shaped, and much smaller than the RBCs.

2. Blood Vessels
Blood flows through our body in a complex system of tubes called blood vessels. There are three types of blood vessels: arteries, capillaries, and veins. Capillaries are the thinnest of the blood vessels and connect arteries to veins. Differences between arteries and veins are listed Table.

Capillaries are thin-walled blood vessels and form a network of extremely tiny blood vessels between arteries and veins. The walls of the capillaries are so thin that diffusion of gases and chemical substances takes place very easily.

3. The Heart
The heart is a four-chambered muscular organ that pumps blood into the blood vessels. The pressure that this pumping generates is enough for the blood vessels to carry this blood to all parts of the body. The heart is able to do so by the rhythmic contractions and relaxations of its muscles. These are known as the heart beats. A normal heart beats about 60 to 80 times per minute. We can hear our heart beat with the help of an instrument called a stethoscope.

As the heart beats and forces blood through our body, we would feel a throbbing sensation at any point where an artery comes close to the surface of your skin, such as the wrist, neck, or upper arm. This throbbing sensation is called the pulse. Counting your pulse rate is a simple way to estimate how fast your heart is beating.

The four chambers of the heart are (i) the right auricle (ii) the left auricle, (iii) the right ventricle, and (iv) the left ventricle. The right auricle opens into the right ventricle and the left auricle into the left ventricle.

Activity
Aim: To measure your pulse
Method:
1. Feel your pulse by placing the index and middle finger over the underside of the opposite wrist, below the base of the thumb.
2. Do not use your thumb because it has its own pulse that you may feel.
3. Count the beats for 30 seconds, then double the result to get the number of beats per minute.