Human Excretory System

The human excretory system functions to remove waste from the human body. This system consists of specialized structures and capillary networks that assist in the excretory process. The human excretory system includes the kidney and its functional unit, the nephron. The excretory activity of the kidney is modulated by specialized hormones that regulate the amount of absorption within the nephron.

Kidneys They are bean-shaped organs located on either side of the backbone at about the level of the stomach and liver. Blood enters the kidneys through renal arteries and leaves through renal veins. Tubes called ureters carry waste products from the kidneys to the urinary bladder for storage or for release.

The product of the kidneys is urine, a watery solution of waste products, salts, organic compounds, and two important nitrogen compounds: uric acid and urea. Uric acid results from nucleic acid decomposition, and urea results from amino acid breakdown in the liver. Both of these nitrogen products can be poisonous to the body and must be removed in the urine.

Nephron The functional and structural unit of the kidney is the nephron. The nephron produces urine and is the primary unit of homeostasis in the body. It is essentially a long tubule with a series of associated blood vessels. The upper end of the tubule is an enlarged cuplike structure called the Bowman's capsule. Within the Bowman's capsule is a coiled ball of capillaries known as glomerulus. Blood from the renal artery enters the glomerulus. The force of the blood pressure induces blood plasma to pass through the walls of the glomerulus, pass through the walls of the Bowman's capsule, and flow into the proximal tubule. Red blood cells and large proteins remain in the blood.

Salts, glucose, amino acids, and other useful compounds flow back through tubular cells into the blood by active transport. Once more, salts, water, and other useful materials flow back into the bloodstream. Homeostasis is achieved by this process: A selected amount of hydrogen, ammonium, sodium, chloride, and other ions maintain the delicate salt balance in the body.

The waste product made by the kidneys then begins to be moved towards the bladder. This waste fluid is referred to as urine. Urea, uric acid, salts, and other metabolic waste products are the main components of urine. The urine flows through the ureters toward the urinary bladder. When the bladder is full, the urine flows through the urethra to the exterior.

Fetal Pig Excretory System

Figure B

Figure A

Figure A pictures the ureter which transports waste between the kidney and bladder.

Figure B highlights the anatomy of the excretory system with respect to the reproductive organs of a female pig.

Figure C shows the renal artery and vein. The renal artery brings blood into the kidney which filters out urea and uric acid to produce urine. The renal vein carries the filtered blood out of the kidney and back into the circulatory system.

Figure C