Functional organization of excretory organs in vertebrates and invertebrates

Priya sarda

ALL vertebrates have paired kidneys. Excretion is not the primary function of kidneys. Kidneys regulate body fluid levels as a primary duty, and remove wastes as a secondary one. Every living organism generates waste in its body and has a mechanism to expel it. In humans, the excretory system takes care of waste generation and elimination. It comprises of the following structures: 2 Kidneys 2 Ureters 1 Urinary bladder 1 Urethra Kidneys Kidneys are the main organ of the human excretory system. Also, every individual has a pair of kidneys. They are located one on each side of the spine at the level of the liver. Kidneys are divided into three regions. Namely, the renal cortex which is the outer layer. Next, the renal medulla which is the inner layer. And lastly, the renal pelvis which carries the urine from the kidney to the ureter. The nephron is the functional unit of a kidney. In fact, each kidney consists of millions of nephrons. They all function together to filter blood and expel waste products. It consists of the following parts: Bowman’s capsule– It is the first part of the nephron. It is a cup-shaped structure and receives the blood vessels. Glomerular filtration occurs here. The blood cells and proteins remain in the blood. Proximal Convoluted Tubule– The Bowman’s capsule extends downwards to form the proximal tubule. Water and reusable materials from the blood are now reabsorbed back into it. The loop of Henle– The proximal tubule leads to the formation of a u-shaped loop called the Loop of Henle. It has three parts: the descending limb, the u-shaped bend, and the ascending limb. It is in this area in which urine becomes concentrated as water is reabsorbed. The descending limb is permeable to water whereas the ascending limb is impermeable to it. Distal Convoluted Tubule– The Loop of Henle leads into the distal convoluted tubule. It is where the kidney hormones cause their effect. Collecting Duct– The Distal Convoluted Tubule of each nephron leads to the collecting ducts. The collecting ducts together form the renal pelvis. Through renal pelvis, the urine passes into the ureter and then into the bladder. Ureters There is one ureter that comes out of each kidney as an extension of the renal pelvis. It is a thin muscular tube that carries urine from the kidneys to the bladder. Urinary Bladder The bladder is a sac-like structure. And a smooth muscle layer lines it. It stores the urine until micturition. Furthermore, Micturition is the act of expelling urine from the body. The bladder receives urine from the ureters, one from each kidney. In addition, the level of placement of the bladder in the body differs in men and women. Urethra The urethra is a tube that arises from the urinary bladder. Its function is to expel the urine outside by micturition. In addition, it is shorter in females and longer in males. Furthermore, in males, it functions as a common path for sperms and urine. Also, sphincter guards the opening of the urethra. Aquatic invertebrates excrete ammonia by diffusion through the surface of their bodies, while terrestrial invertebrates, first convert ammonia to uric acid, which is then disposed. ... In unicellular organisms the process of excretion occurs through diffusion. Excretory Organs in Invertebrates: Contractile Vacuoles in Paramoecium Excretory System of Planeria (With Reference to Flame Cells) Excretion in Taenia Solium Excretion in Earthworm with Reference to Nephridia Excretion in Cockroach with reference to Malpighian Tubules Excretion in Prawn with Reference to Green Gland Excretion in Bivalve (Lamellidense) with Reference to Organ of Bojanus