Life Processes in Living Organisms
Transportation of Water and Minerals in Plants (Group B)
Excretion and Its Importance
Excretory system consists of groups of organs that are responsible for excreting waste materials such as, harmful chemicals and other impurities from the body. The major excretory organ is kidney. However, there are some other organs also that perform the function of excretion.
Let us understand the function of the following organs as excretory organs.
Respiration is a necessary process that provides energy for cellular activities. During respiration, carbon dioxide gets accumulated in the cells, from where it diffuses into the bloodstream and is finally transported to the lungs. From lungs, this carbon dioxide leaves the body every time we exhale.
Liver helps in the excretion of various unneeded substances in the body. It converts toxic ammonia into urea, a harmless fluid, by the process of deamination. This urea is then filtered by the kidney into urine. It does not directly eliminate excretory substances.
Skin also acts as an excretory organ. It possesses glands, namely, sweat glands and sebaceous glands. Sweat is a watery fluid that consists of metabolic wastes like water, sodium chloride, lactic acid, amino acids, urea, glucose, etc. Besides excreting metabolic wastes from the body, sweat also has a cooling effect on the body. On the other hand, sebaceous glands help in excretion of sebum which consists of lipids, fatty acids, etc.
How the other kinds of waste materials removed from the body? Is there a particular organ system that functions to remove waste materials from the body?
The organ system that performs the function of excretion is known as the excretory system. The excretory system removes the waste materials present in the blood.
Which organs are involved in this process? What mechanism is required for filtering blood?
The primary components of the excretory system are the kidneys, the ureter, the urinary bladder, and the urethra.
When blood reaches the kidneys, useful substances are absorbed back into blood, while the waste materials are dissolved in water and removed from the body in the form of urine.
The urine enters a long tube-like structure called the ureter. The ureter then passes the urine into the urinary bladder, which stores it until it is passed out of the body. Urine is passed out of the body through a muscular tube-like structure called the urethra.
Waste materials are also removed from the body through sweat. During sweating, water and salts are removed from the body.
Do you know which organs make up the nervous system?
The nervous system is made up of the brain, spinal chord, and nerve cells or neurons.
Let us first study about the structure of the functional units of the nervous system i.e., the neurons.
Structure of a neuron
The three main parts of a neuron are the axon, dendrite, and cell body. The axon conducts messages away from the cell body. The dendrite receives information from the next cell and conducts it towards the cell body. The cell body contains the nucleus, mitochondria, and other organelles. It is mainly concerned with maintenance and growth of the cell.
Arrangement of neurons
Neurons are arranged end to end, forming a chain. This helps in the continuous transmission of impulses. Each neuron receives an impulse through its dendrite and transmits it to the next neuron in a sequence through its axon.
Neurons are not connected. Synapse or a small gap occurs between the axon of one neuron and dendron of the next neuron.
A synapse in the muscle fibre is also known as neuromuscular junction. Let us discuss the working of a synapse in detail.
A nerve is a collection of nerve fibres (or axons) enclosed in a tubular medullary sheath. This sheath acts as an insulation and prevents mixing of impulses in the adjacent fibres.
Types of neurons
Neurons are of three types.
How does a nerve impulse travel?
The dendrite end of the neuron collects information and triggers a chemical reaction, which results in an electric impulse. This impulse is transmitted from the dendrite to the cell body and then to the axon. From the axon, the impulse travels to its end, where the electrical impulse sets off the release of some more chemicals. These chemicals cross the synapse and start a similar electrical impulse in the dendrite of the next neuron. In this way, impulses are transmitted from one neuron to another to finally reach the brain.
Under normal conditions, the outer side of the nerve fibre consists of positive charge as more Na+ ions are present outside axon membrane. The neuron is then said to be in polarised …
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