“Excretion is a process of removal of metabolic waste”
Excretory organs are the organ through which metabolic waste removes.
Excretion in human:
In human excretion is done by kidney. In human excretion system consist of a pair of kidney, a pair of ureters, one urinary bladder and one urethra.
Kidney is located in the abdominal cavity on either side of the vertebral column just beneath the diaphragm. Each kidney is surrounded by peritoneum membrane which attach the kidney with the abdominal wall. The outer margin of kidney is convex and the inner is concave. Concave margin posses a notch called hilum. Internal part of kidney is divided into two parts cortex and medulla. The kidneys are highly vascular (contain a lot of blood vessels) and are divided into three main regions: renal cortex, renal medulla (middle region which acts as a collecting chamber), and renal pelvis.
Renal Capsule: It is the outermost membrane of the kidney. It is thin and tough. Cortex: It is the outer region of the kidney and consist of about one million blood filtering nephrons. Medulla: It is the inner region of the kidney contains renal pyramids. The pyramids empty into the calyx. Calyx: An extension of the renal pelvis. It delivers urine from the pyramids to the renal pelvis.
Renal Pelvis: It collects urine from the nephrons, and deliver it to the upper end of the ureter. Ureter: collects filtrate and urine from renal pelvis and takes it to the bladder for urination. Renal Artery: Bringing waste-filled blood into the kidney for filtering in the nephrons; the renal artery is further subdivided into several branches inside the kidney. Each minute, the kidneys receive 20% of the blood pumped by the heart. Renal Vein: Removes the filtered blood from the kidneys to the inferior vena cava.
Function of Kidney:
It purifies the blood.
It excretes harmful and other toxic substance from the body.
It controls blood pressure.
It maintains the amount of mineral salts in the blood.
Each kidney is connected with a thin, muscular tube called ureter. Ureter is a tube which connects the kidney with the urinary bladder. It carries urine or other excretory products from the kidney to the urinary bladder.
A small sac like structure is present at the posterior part of abdominal cavity. According to the quantity of urine it changes its shape and size.
Nephron is the structural as well as the functional unit of kidney. Half portion of nephron is situated in the cortex and other half is in the medulla. It consists of two parts:
(A) Bowman’s Capsule: The closed end of of the nephron comprises a cup shaped structure called Bowman’s capsule, which contains a bunch of blood capillaries known as glomerulus. Urine is filtered by the semipermeable walls of glomerulus. The blood flows very fast from afferent arterioles into glomerulus which increase it’s pressure to 70 mm-Hg. Since opposite pressure is 50 mm-Hg therefore effective filtration pressure of glomerulus is (70-50) “20 mm-Hg”. Due to this blood containing urea, uric acid, glucose, salt and other materials are filtered and come into the Bowman’s capsule. Rate of filtration in a normal adult is about 125ml per minute. About 1.5 litres urine is passed out daily.
(B) Secretory Tubular Part: It is the coiled posterior part of bowman’s capsule. It has three parts-
(1) Proximal convoluted tubule.
(2) “U” shaped Henle’s loop situated in the medulla.
(3) Distal convoluted tubule opens in a collecting tubule of kidney.