Excretory system

Cells produce nitrogenous materials, salts and carbon dioxide as by-products of metabolic breakdown of sugars, fats and proteins. If these toxic wastes accumulate in the body, they may cause damages. The process of removing the waste products from the body is called excretion. The organ system responsible for this excretion is known as excretory system. The excretory system removes non-solid wastes through sweat, urine and exhalation. The human excretory system consists of one pair of kidneys and associated structures, i.e. two ureters, a urinary bladder and urethra.

Human Kidney

The human body has two dark brown bean shaped kidneys in the abdominal region, one on either side of the vertebral column. The outer surface of kidney is convex while the inner surface is concave. The tube, which arises from each kidney and enters the urinary bladder, is called a ureter.lt transports urine from kidneys to urinary bladder. Urinary bladder is a muscular sac, which collects urine from both kidneys through ureters. From the urinary bladder the urine is released outside the body through a fine tube called urethra.

Internal Structure of Kidney

Internally, each kidney is divided into three region i.e. renal cortex, renal medulla and renal pelvis. Renal cortex is the outermost region. Renal medulla is the middle region and Renal pelvis is the inner area where urine is drained. The urine from renal pelvis moves into ureter.

Nephrons

Nephrons are the structural and functional units of the kidney. Each kidney has over one million nephrons. Each nephron has two parts. i.e. renal corpuscle and renal tubules.

Nephrons are the structural and functional units of the kidney. Each kidney has over one million nephrons. Each nephron has two parts. i.e. renal corpuscle and renal tubules.

Bowman's capsule is a cup shaped structure, enclosing the glomerulus. The tube like structure of the nephron connected to the Bowman's capsule at its tip is called the Renal Tubule. Urine is formed in these tubules. The renal tubule consists of three parts. The first coiled part of renal tubule is called proximal tubule. The next part is U-shaped and is called Loop of Henle. The third and last part of the renal tubule is again coiled and is called distal tubule. The distal tubules of many nephrons open in a collecting duct. Many collecting ducts join and drain the urine out of the nephrons into the Renal pelvis.

Role of Kidney

Blood carrying nitrogenous waste materials from the body is brought to the kidneys by incoming blood vessels called arterioles. Inside the kidneys, blood containing nitrogenous waste reaches the Glomerules. Here most of the excess water and waste materials filtered from the blood into the Bowman's capsule. The blood after losing waste material goes into the outgoing arteriole, which ultimately with many other arterioles forms the renal artery. The clean blood is brought back to the main circulatory system. The waste material and excess water pass into the renal tubule from the Bowman's capsule. From here, the waste material and excess water passes through the proximal tubule, the loop of Henle and finally through the distal tubule into the collecting duct in the form of urine. The urine then drains from the collecting tubules into the renal pelvis, which opens into the ureter from each kidney. From the ureter, the urine is passed to the urinary bladder. From here the urine is passed out of the body through the urethra.