Excretion is a process of filtering the unwanted substances from the body. Those substances are Carbon dioxide which excreted by lungs, Heat result of working metabolic excreted from the surface of the body (i.e. skin) and urine excreted by kidneys through bladder.

Role of Kidneys in Urinating Process: A pair of kidneys consist of millions of functional and blood in clearing wastes in very evident.The ureters (a duct) of both the kidneys drains into urinary bladder through urethra while empties by external urethral orifice. The job of the kidneys are to filter the unneeded and unwanted liquids from the blood. This lagged form consists of a toxin called nitrogen or urea.

Parts of a Kidney: 1 Cortex (outer layer) contains Nephron
2 Medulla (Inner part) reabsorbs the nutriens into blood.

After passing through the the kidneys, Urine keeps stored in bladder until the relaxing muscular.








http://www.marymount.k12.ny.us/maryn...ml/excretf.htm
http://en.wikipedia.org/wiki/Excretion
http://www.answers.com/library/World...Body-cid-28027

structure of nephron



these are easy pics to show the internal structure of kidney.
regards

Kidney

The kidney is part of the urinary tract, which filters waste and maintains fluid and ion balance in the body. The bean-shaped organ is in the abdominal cavity, held in place by connective tissue, the fibrous renal capsule, and cushioned by fatty tissue, the perinephric fat. Humans normally have two kidneys, but they can survive with one if healthy.

Basic Renal Structures

The kidney is fed by the renal artery, which enters the renal medulla through the hilus, the concave portion of the kidney. Within the kidney, the artery branches into smaller blood vessels. The renal medulla is the inner portion of the kidney; the renal cortex is the smooth outer portion with projections called cortical columns. The medulla and cortex are connected by the renal tubules, drainage canals that carry the wastes removed from the blood.
The basic building blocks of the kidney are the nephrons, which consist of intricate webs of blood vessels and drainage canals. Wastes and excess ions or water are filtered from the blood, which is regulated by endocrine hormones that target the kidneys. The nephrons form units called renal pyramids, sections of cone-shaped tissue. The apices of the pyramids point inward to the medulla, which contains 10-20 pyramids.
The renal tubules are made of the proximal tubule, loop of Henle, and distal convoluted tubule. Other structures within the cortex are cortical collecting ducts and corpuscles, the initial filtering component of the nephron. Corpuscles are made up of the glomerulus and Bowman's capsule. The portion of the tubules in the medulla is the loop of Henle.
The renal calyces are structures where urine drains from the nephron into the ureters, drainage canals leading to the bladder.

Basic Physiology

As mentioned above, the initial filtering component of the nephron is the corpuscle, which is in the cortex. Ultrafiltration also occurs in the cortex, in the cortical collecting ducts at the final portion of the nephron. These two mechanisms occur in the renal cortex because of the presence of the blood vessels in this region of the kidney: The glomerulus is a capillary extension fed by the renal circulation with very high pressure. This pressure pushes water and other material (such as sugars and salt) into the space outside the blood vessel, the interstitium, which is protected by the Bowman's capsule. The filtered fluid then proceeds to the renal tubule, which carries it to the collecting ducts.
Parts of the tubule further filter the fluid and maintain the body's ion and fluid balance by reabsorbing some solutes. The proximal tubule reabsorbs water, salts, glucose, and amino acids. The loop of Henle, also known as the nephron loop, turns to pass back into the cortex from the medulla and concentrates salts in the interstitium. The distal convoluted tubule is the distal portion of the renal tubule; it has cells specialized in active transport and is involved in maintaining the pH of the urine and blood.
Fluid filtered and concentrated by the corpuscle and tubule enters the collecting tubule. The ducts become permeable or impermeable to water in order to either concentrate or dilute the urine depending on the body's needs. Lower portions of the collecting ducts are also permeable to urea, the nitrogen-containing component of urine.
Consistent muscular contractions, called peristalsis, force the fluid through the renal calyx into the funnel-like renal pelvis. It is here that urine leaves the kidneys, having started as an assortment of water and solutes in the blood