The basic functional unit of our body are cells. They form the basic living breathing portion of our body. There are more than a trillion cells in our body. The cells group together based on structure and function into tissue, the tissue in turn make up the organs and various organs linked together to performing essential function form the organ systems.
There are 11 systems in the body, You might understand the human body better if I compare it to other structures you might be familiar with let’s say a city or a village.
The integumentary system:
Imagine a city or town from our history lessons, you are bound to imagine a city wall armed with guards with big gates which allow only essential goods and people inside. That is what the integumentary system is. skin and its appendages which form the largest organ of our body is the integumentary system. It function as a barrier to the outside environment and protects your body from various physical agents including microbes.
The muscular system & The skeletal system
This is like the buildings, constructions and the builders of the city. They give structure to the city and give support for the entire population of the city and the builders are capable of moving the city by expanding it or reconstructing it. Likewise the musculoskeletal system gives support to the body and and all its organs and protect the vital organs from physical damage and the muscles move the body.
The digestive system
The digestive system takes in the food we eat and breaks it down into smaller particles and simpler molecules that is absorbed into our system and finally expels the undigested food out. Think of your grocer, supermarket chain or restaurants which provide the food for the residents of the city. The digestive tract including the oesophagus, stomach, small intestine, large intestine, rectum extends from the mouth to the anus and works along with many glands and organs such as pancreas and the liver for effective absorption of nutrients while protecting against pathogens.
The respiratory system
The respiratory system absorbs the oxygen from the air we breathe in, hands it over to the circulatory system and the oxygen is used by every living cell in our body to burn up the food molecules (mostly glucose absorbed by the digestive system)to provide energy for the survival. It also expels out carbon dioxide which is a byproduct of the energy metabolism out of the body as we let out our breath. I can compare this to greenery in a city or as gas pipeline for cooking.
The circulatory system
The circulatory system is the highways and roads of our body. The heart pumps blood through the blood vessels throughout the body and through the lungs. It functions as a means of transport for cells involved in transport of oxygen, cells for defence mechanisms and clotting as well as molecules dissolved in the blood like nutrients and carbon dioxide.
The immune system
The immune system is like police force or the army. It works against pathogens and other foreign substance entering the body. Most of the symptoms of disease processes are the body’s immune system fighting against potential pathogens or cells which are deemed foreign by your own system.
The nervous system
Every human society has a government to oversee the well being of its citizens. The nervous system controls the executive function of the body it includes the central nervous system which includes the Brain and the spinal cord while the peripheral nervous system includes all the nerves and sensory terminals. The nervous system is a very complex system. We lack conscious control of majority of our body function most of our essential function like breathing, heart beat, digestion are all directly taken care of by the nervous system. The main function of the brain is to receive data from the sensory organs, analyse it, store the data and execute a function or respond accordingly. This is a very simplified explanation. The brain can do lots more than that, every brain is a supercomputer on its own. The AI technology being developed are nowhere near the complexity of a human brain.
The endocrine system
The endocrine gland is also an executive level system which is mainly involved with the metabolism of the body along with growth and development also sexual function and procreation. It is not under the direct control of the nervous system but can be influenced by the same. I think as a comparison the civil services might work in this case. This system includes the pituitary gland, thyroid gland, the parathyroids, certain cells in the pancreas, the adrenal glands and the gonads.
The renal system
The renal system is responsible for fluid and electrolyte balance in the body. It maintains the pH of the blood and also eliminated all the waste products produced by the various cells of the body. It can be thought of as the waste management system of the human body. The renal system consists of the two kidneys and the various pathways by which urine is eliminated including the ureters, the bladder and the urethra.
The reproductive system
When the population of a city becomes large the people either open up more land for use or shift to other areas to settle down likewise the reproductive system deals with the procreation of the human species. It comprises of the gonads and also endocrine control over the system.