HUMAN EXCRETORY SYSTEM
In human beings excretion of waste materials take place through a well developed system of organs called urinary system. The urinary system of human beings consists of: two kidneys, two ureters, a urinary bladder and a urethra.
In human beings a pair of kidneys is present in the abdomen. The kidneys are dark red, bean shaped organs. Each kidney is 10 – 13 cm. long and 2.5 to 4 cm. wide. The function of kidney is to remove the waste materials present in the blood in the form of yellowish liquid called urine. As shown in Fig. 14ach kidney is covered by a layer of fibrous tissue called renal capsule. The renal capsule protects the kidneys from injuries and infection. Internally the kidney is divisible into two parts: outer renal cortex and inner renal medulla. The renal cortex is dark red while the renal medulla is light in colour. The medulla is divided into a number of conical areas called pyramids.
Each kidney is made up of about ten lakh excretory units called nephrons. We shall discuss the structure of nephron later on.
Ureters are two narrow tubes which carry urine from kidneys to the urinary bladder.
Urinary bladder is a hollow, pear shaped bag. The function of urinary bladder is to store urine temporarily.
Urethra is a muscular tube, through which the urine collected in the urinary bladder is passes out of the body.
Functions of kidneys
- Kidneys remove the nitrogenous wastes such as urea from the blood.
- Kidneys also remove excess of water from the body.
- Kidneys maintain the proper pH of blood by removing excess of acids and bases from the blood.
- Kidneys maintain the proper balance of concentration of salts in the blood.
- Kidneys also remove other toxic substances from the blood.
Test Your Understanding and Answer These Questions:
- What is urethra?
- Name the excretory unit of a kidney.
- Where is urine carried through the ureters?
- Explain excretory system of human beings.
- State the vital functions of the human kidney.
- How many nephrons are present in each kidney?
- Draw and label the parts of the human excretory system.
- Explain internal structure of kidney by drawing a well labeled diagram.
- How many kidneys are present in human beings? Where are these situated in human body?