Excretion definition– It is the process of eliminating toxic metabolic wastes like uric acid, urea, and salts from the body. Kidneys are used for excretion in the Human body excretory system and other higher cellular organisms excretory systems. At the same time, lower cellular organisms and unicellular organisms use nephridia and diffusion for excretion.

1. Kidneys-They are essential life-sustaining organs that perform multiple functions to maintain the chemical balance and keep it clean. Waste products excreted by kidneys are urea and creatinine. The kidneys act as very active filters for clearing the body of toxic substances and restoring vitamins, amino acids, vitamins,  hormones,  glucose, and other indispensable elements into the bloodstream. 
2. Skin-  Sweating is a necessary bodily function as it helps in the thermoregulation of the body. Sweat glands allow the escape of excess water molecules along with waste salts. Sweat glands discharge fluids that will reduce your body temperature in cases of excessive heat. Sebum is the excess oil excreted from the skin through sebaceous glands.
3. Lungs- They are the respiratory organs in human beings. The pulmonary artery carries impure blood to the lungs from the heart. The alveolar cells of the lungs help in the exchange of oxygen with carbon dioxide to provide the former to the bodily tissues. Lungs excrete carbon dioxide out of the body.

Carbon from carbon dioxide and inorganic carbon can be joined into natural particles; this interaction is called carbon fixation, and the carbon in natural atoms is otherwise called fixed carbon. The fixed carbon that is consolidated into sugars during photosynthesis can be utilised to construct different sorts of natural atoms required by cells.

1. Renal tubule– It starts with Bowman’s capsule and is made up of distal convoluted tubule, proximal convoluted tubule, and Henle’s loop.Kidney
   it is an excretory organ in the human anatomy. They act as excretory organs. Moreover, they also maintain the balance of mineral ions and water in human beings. According to the autonomy of the kidneys, it can be separated into two regions, i.e., the internal region and external region.
   The inner region– It comprises of two zones: 

• • Renal cortex: The renal cortex has a random organisation of nephrons, tiny tubules that act as the kidney’s basic filtration units.

• • Renal medulla: The renal medulla comprises cone-shaped tissue pieces that stretch to the body’s pelvic region. 

The external region: It is built up of a thick layer of fat that functions as a shock absorber.
Nephrons
They are the basic microscopic filtration units of the kidney. Furthermore, they play a critical role in the process of urine formation taking place in the kidney. The first step in the formation of urine is Ultra-filtration. In this step, the nephrons filter waste minerals and water but preserve red blood cells, large molecules, and proteins. A single nephron can be divided into two parts- a renal tubule and a renal corpuscle.
As the renal tubule progresses, it leads away from Bowman’s capsule to become an extremely coiled structure that forms the proximal convoluted tubule. The renal tubule also forms a hairpin loop known as the loop of Henle or Henle’s loop. This loop has a descending and ascending limb—the latter resumes in the distal convoluted tubule form.
This distal convoluted tubule further opens up into a collecting duct structure, which moves into the kidney’s internal region, specifically the renal medulla.

1. • Renal corpuscle- It is composed of clusters of tangled and tiny blood capillaries called Bowman’s capsule and glomerulus.
     The glomerulus is also known as the filtration unit. It consists of a cluster of blood capillaries which is made up of afferent arterioles. The blood cells from this region are moved away by efferent arterioles.
   • Bowman’s capsule- It is a cup-like structure that encloses the glomerulus.
2. Ureter
   The ureter is a thin pair of muscular tubular structure from each kidney and extends to the renal pelvis. They join to form one tube which opens in the urinary bladder. The function of the ureter is to carry urine from the kidney to the bladder.
3. Urinary Bladder
   It is a muscular sac-like arrangement at the lower half of the abdomen receiving urine through ureters. The bladder also stores urine until the process of micturition (the action of urinating) is carried out.
4. Urethra
   It is a tube that emerges from the urinary bladder and aids in expelling toxic urine out of the human body. In males, the urethra acts as the common path for urine and sperms. Sphincter muscles safeguard the opening. In females, it connects to the vagina.

1. Where are the columns of Bertin located?
   Columns of Bertin are located in the kidney.
2. What causes the yellow colour of urine?
   Urochrome causes the yellow colour of urine.
3. What kind of cells line the body and neck of the nephron?
   Ciliated and cuboidal epithelial line the body and neck of the nephron
4. Define osmoregulation
   The process by which kidneys maintain an organic balance between dissolved materials and water is called osmoregulation.