What are the body's defenses? How do they differ from each other?

Hint: The defense mechanism in the case of organisms varies according to the various types of living habits and species of organisms. The defense mechanisms help the animals to safeguard themselves from outer harm or the attack of other organisms.

Complete answer:
A defense mechanism is caused by our immune system. Almost all the organs of the body play an important role in providing immunity. Immunity is the ability to defend against foreign cells, infectious agents, and abnormal cells in the body. Defense Mechanisms of the human body include the First line of defense, Second line of defense, and Third line of defense.
Defense Mechanisms of the human body include 3 mechanisms. They are
1st Line of defense – Block entry
2nd Line of Defence – Fight Local Infections
3rd Line of Defence – Combat Major Infections.
First-line defenses: This causes a block between the entry of substances from inside to outside and vice versa. Examples are: Skin acts as a physical or mechanical barrier.
Mucus produced by the mucous membranes lines the entrances of the body and it helps in trapping the foreign particles and moves them out of the body.
Saliva, Tears, and sweat possess some antibacterial properties and also prevent the entry of bacteria and other foreign particles into our body.
Gastric juice, vaginal secretions, and urine are acidic fluids that protect the entry of any foreign particles.
Second-line defense: Fight local infection with Inflammation Process. It begins as soon as the first line of defense fails. When the foreign particle enters the body by crossing the physical barrier it is engulfed in a section of the cell's membrane and forms a structure called a phagosome which fuses with lysosomes. Lysosomes contain a digestive enzyme that kills bacteria and results in inflammation. During the Inflammation process, histamines are released that cause redness, pain, swelling, and heat. Examples are Phagocytes.
Third-line of defense: The immune cells identify and destroy the pathogen. Cellular components of third-line defense include B cells and T cells. These cells play a major role in preventing the infection. Sometimes it may fail and cause disease which lasts for a lifetime.

Note:
The immunity response is of two types: Humoral (antibody-mediated response) - It defends against extracellular pathogens by binding to antigens and making them easier targets for phagocytes and complement proteins.
-Cell-mediated immune response - It defends against intracellular pathogens and cancer by binding to antigens and lyzing the infected cells or cancer cells.