THE EXCRETORY SYSTEM

                         Just as how we thrown away the waste materials from our homes, our body to has a system to remove the waste. The system is called the excretory system. The excretory system consists  of  a pair of kidneys , ureters, the urinary bladder, a urethra. The main organs of the excretory system are the kidneys. There are two reddish brown bean shaped organs located on each side of the lower abdomen. Each kidney of an adult human measures 10-12 cm in length,5-7cm in width, 2-3cm in thickness with an average weight of 120-170 g . Towards the centre of the inner concave surface of the kidney is a notch called hilum through which ureter , blood vessels and nerves enter.    The kidneys filter the blood. They help to get rid of waste in the form of urine.  The urine is carried by tubes called ureters to the urinary bladder. The urinary bladder stores the urine. When the bladder is full, the urine is passed out through the urethra. In this way the excretory system removes the wastes from the body.

                    A detailed anatomy of the kidney showed here. The longitudinal section of the kidney shows the location of the renal cortex, renal medulla, the renal pyramids and the renal pelvis.

The outer layer of kidney is a tough capsule. Inside the kidney, there are two zones. An outer cortex  and inner medulla. The medulla is divided into a few conical masses projecting into the calyces. These conical masses are known as medullary pyramids. The cortex extends in between the medullary pyramids as renal columns called columns of bertini.

           Each kidney has nearly one million complex tubular structures called nephrons. Nephrons are the functional units and they are also known as kidney tubule.

              Observe the placement of the nephrons in the enlarged renal nerve. Seen here is the anatomy of nephron.

             The main parts of nephrons are the bowman’s capsule, the glomerulus, the proximal  convoluted tubule, the distal convoluted tubule and the loop of Henle.

              Glomerulus is a tuft of capillaries formed by the afferent arteriole. Blood from the glomerulus is carried away by an efferent arteriole.  The renal tubule begins with a double walled cup- like structure called bowman’s capsule . The bowman’s capsule encloses  the glomerulus.                   Glomerulus along with  bowman’s  capsule is called the malpighian body or renal corpuscle.(figure 4). The tubule continues further to form a highly coiled network called proximal convoluted tubule(PCT).A hairpin shaped Henle’s loop is the next part of the tubule which has a descending and an ascending limb. The ascending limb continues as another highly coiled tubular region called distal convoluted tubule(DCT). The DCTs of many nephrons open into a straight tube called collecting duct.

              The efferent arteriole emergingfrom the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries. Aminute vessel of this network runsparallel to the Henle’s loop forming a ‘U’ shaped vasa recta.

              The structure of human excretory system, the kidneys and the nephrons can be observed here.