Human Excretion and Kidney Physiology

Each human kidney contains approximately one million nephrons, which are the functional units responsible for blood filtration.

The primary nitrogenous waste product in human beings is urea, which is produced in the liver and excreted by the kidneys.

Hemodialysis is a medical procedure used to filter waste products from the blood when the kidneys are unable to perform this function, effectively acting as an artificial kidney.

The urinary bladder is a muscular sac that stores urine until it is ready to be voided from the body through the urethra.

If kidneys fail, toxic wastes accumulate, blood composition is disrupted, and if left untreated, this leads to systemic failure and death.

Human kidneys are characteristically bean-shaped organs located in the abdominal cavity.

Primary urine (filtrate) is converted into final urine through the selective reabsorption of water, glucose, and ions in the renal tubules.

Antidiuretic hormone (ADH), also known as vasopressin, increases the permeability of the collecting ducts and distal tubules to water. This promotes water reabsorption back into the bloodstream, concentrating the urine.

After blood is filtered in the Bowman's capsule, the resulting glomerular filtrate passes into the renal tubule (proximal convoluted tubule, loop of Henle, and distal convoluted tubule) for selective reabsorption.

The glomerulus, located inside the Bowman's capsule, acts as a high-pressure filter. It forces water and small solutes out of the blood to form the filtrate.

The renal artery branches off the aorta and delivers oxygenated, waste-rich blood to the kidneys for filtration.

Urea is a nitrogenous waste product that is not reabsorbed by the nephron tubules; instead, it remains in the filtrate to be excreted as urine. Glucose and amino acids are typically reabsorbed back into the blood.

Blood plasma is the yellow liquid component of blood, in which the blood cells in whole blood, are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid (all body fluid outside of cells). It is mostly water (93% by volume) and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide. It transports urea.

The contractile vacuole is known as the kidney of the protozoans. Its function is to pump out excess water from the cytoplasm of amoeba. They are most prominent and active in freshwater amoebae as marine amoebae are closer to isotonicity with seawater than freshwater.

It is a V shaped segment of the nephron located in the renal medulla. It consists of two straight parallel limbs: a descending limb which is a continuation of the PCT and enters into the renal medulla and an ascending limb which reenters the renal cortex and joins the DCT.