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Neurobiology, a branch of Biology Topics, investigates the structure and function of the nervous system.
What are the Excretory Organs in Animals and Humans?
We (human beings) eat food, drink water and breathe in air. When our body uses food, water and air, it produces some unwanted substances called waste materials (or just ‘wastes’). These waste materials are toxic (or poisonous) and hence they are harmful for our body. The waste materials must be removed from the body so that a person may stay healthy. The removal of waste materials produced in the cells of the living organisms is called excretion. The various waste materials produced in the cells of the human body are : Carbon dioxide, Urea and Sweat. The human body has many organs for the removal of various wastes from the body.
The organs for the removal of waste materials in the human body are : Lungs, Kidneys and Sweat glands. We will now describe how the various waste products are removed from the human body.
1. Carbon dioxide is produced as a waste product in our body cells during the process of respiration (when food is broken down to release energy). Carbon dioxide is removed from our body by the lungs during exhalation. Thus, our lungs act as the excretory organs for removing the waste product called ‘carbon dioxide from our body.
2. Sweat is a liquid waste of the body produced by sweat glands present in our skin. Sweat contains water, some salts and a little of urea. Sweat is removed from the body by sweat glands through the skin. We sweat a lot on a hot summer day. When sweat evaporates from our body, it takes the heat required for evaporation from our body. In this way, our body loses heat and makes us feel cool. Thus, sweating performs two functions :
- Sweating helps to remove excess water, some salts and a little of urea as liquid waste from the body, and
- Sweating helps to keep our body cool during hot summer days.
Sometimes in summer days, we see that white patches are formed on our clothes especially in areas like underarms. These white patches are formed by the the salts left on the clothes when the water present in sweat evaporates.
3. Urea is produced as a waste product by the decomposition of unused food proteins in the liver. Urea is removed from the blood by kidneys. In fact, kidneys are the main excretory organs in our body. Kidneys are part of an organ system called excretory system (or urinary system).
A major waste product of our body is urea. This urea goes into our blood and makes it dirty. Urea is a poisonous substance which must be removed. If the urea and other wastes are not removed from the blood of a person constantly, the person will soon die. Our kidneys remove urea, excess water and other unwanted salts from our blood. We will study this in the form of an excretory system.
Excretory System in Humans
Urea is a major waste product produced in our body. The urea and other unwanted salts dissolve in water in the body to form a yellowish liquid waste called urine. The excretory system collects the liquid wastes of tjre body (like urine) and helps get rid of them.
The excretory system of human beings consists of the following organs : two kidneys, two ureters, a bladder and a urethra (see Figure). The kidneys are bean-shaped organs towards the back of our body just above the waist (see Figure). Every person has two kidneys. The decomposition of unused food proteins in the liver produces urea as waste. This urea goes into blood. The blood in our body is constantly passing through our kidneys. The function of kidneys is to filter the blood to remove urea. This happens as follows : Each kidney contains thousands of tiny filters called ‘nephrons’. When the blood containing urea and other waste salts passes through nephrons in the kidneys, the nephrons filter the blood and remove urea and other unwanted salts from it.
The liquid left in the kidneys is a yellowish liquid called ‘urine’ which contains urea, other waste salts and excess water. The urine formed in kidneys goes into the bladder through the tubes called ureters. Urine is stored in the bladder (which is a kind of bag). Bladder is also called ‘urinary bladder’. The urine collected in bladder is passed out from the body at regular intervals through the opening at the end of a tube called urethra (see Figure 11). Urine is a yellowish liquid which consists of 2.5% urea, 2.5% other waste salts and 95% water. An adult human being normally passes out 1 to 1.8 litres of urine per day (24 hours).
Kidney Failure
The normal functioning of kidneys is essential for good health. Sometimes a persons kidneys may stop working due to infection or injury. When the kidneys do not work properly, they are not able to remove the waste product urea from the blood. Complete failure of kidneys leads to the accumulation of too much urea in the blood of a person. Urea is a toxic substance (or poisonous substance), so the accumulation of too much urea in the blood of a person can ultimately kill the person. A person having kidney failure cannot survive unless his blood is filtered periodically through kidney machine to remove urea (by a procedure called dialysis).
The procedure used for cleaning the blood of a person by separating the waste product urea from it is called dialysis. In the procedure called dialysis, the blood of a person having kidney failure is filtered regularly by using a kidney machine (or dialysis machine) to remove urea and other waste salts from it (see Figure). Since a kidney machine can do the work of damaged kidneys, therefore, kidney machine is sometimes also called artificial kidney’.
Thus, artificial kidney is a machine to remove urea and other waste salts from the blood of a person by filtering it. The best long term solution for kidney failure is, however, kidney transplant. In kidney transplant, the damaged kidney is removed and a matching kidney donated by a healthy person is ‘transplanted’ in its place by performing a surgical operation.
Excretion in Other Animals
The major excretory product in humans is urea. Other animals also excrete (or urinate) waste products from their body. The way in which waste products are excreted (or removed) from the body of the animal depends on the availability of water to it. The aquatic animals live in water. So, aquatic animals excrete cell waste in gaseous form (ammonia) which directly dissolves in water. For example, the fish excretes cell waste in gaseous form (ammonia) which directly dissolves in water. The land animals usually have less water available to them. The land animals such as birds, lizards, snakes and insects excrete a white coloured waste called uric acid in semi-solid form. We will now discuss the transport in plants.
Tissue
Before we learn the transport of substances in plants, we should know the meaning of the term ‘tissue’. A tissue is a group of similar cells which work together to perform a particular function. The arrangement of cells in a tissue depends on the function to be performed by the tissue. For example, if the function of tissue is to carry water from the roots of a plant to its leaves, then the tubular cells (tube-like cells) are arranged one over the other to form long tubes (or vessels).
Vascular Tissues
Those tissues which transport water, minerals and food to different parts of a plant, are called vascular tissues. There are two types of vascular tissues in a plant: xylem and phloem.
- The tissue which carries water and minerals from the roots to the leaves of a plant is called xylem.
- The tissue which carries food from the leaves to other parts of the plant is called phloem.
All the parts of a plant like roots, stems, branches and leaves contain vascular tissues called xylem and phloem. The xylem and phloem tissues are a kind of tubes made of tubular cells arranged end to end. The xylem tissue is made of dead xylem cells whereas phloem tissue is made of living phloem cells arranged one over the other. Keeping these points in mind, we will now describe the transport system in plants.