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Urinary System
Kidneys are the main organs of the urinary system that filter around 200 liters of blood and purify it through excreting excessive water, toxins, electrolytes and metabolic wastes that assist in maintaining body’s fluid equilibrium. The other components of the urinary system are ureters, urethra and urinary bladder (Marieb & Hoehn, 2003).
The urinary system can be differentiated into main four parts, kidney, bladder, ureters, and urethra. Kidneys are secured by the tri-layered arrangement that includes an outer renal fascia composed of fibrous connective tissues, a middle perirenal fat capsule to provide defense against any physical wrench and the inmost fibrous capsule to shield infections. The kidney is divided into the granular renal cortex and renal medulla. The medulla contains renal pyramids. The tiny functional units of the urinary system are nephron and there are one million nephrons in one kidney. There are certain microscopic structures in a nephron that play the essential part in excretory mechanisms including Glomerulus capsule, Bowman capsule, Henle’s loop, proximal and distal convoluted tubules, collecting ducts and ascending limb of a medullary segment (Figure 1) (Marieb & Hoehn, 2003).
The minute segments of nephron are responsible for specific functions that mutually accomplish the excretory procedure. Firstly, blood enters the glomerulus through the juxtamedullary apparatus where a network of capillaries sieves the blood across Bowman capsule (Arnould-Taylor, 1998). The porous filtration membrane of Bowman capsule filters water and solutes through channeling the flowing molecules from the blood. Later ward, this filtrate travels through the proximal tubule which is accountable for re-absorption of glucose as well as other solutes. Glomerulus pushes filtered blood towards renal pyramids via efferent glomerular arterioles (Marieb & Hoehn, 2003).
Figure 1: Structure of Nephron (Marieb & Hoehn, 2003)
Kidneys send the filterate to 10 to 12 inches long ureters that carry it to the bladder. An ureterovesical valve of ureter inhibits the backflow of urine. The urinary bladder is composed of extremely flexible muscles that enable it to endure 600 to 800 ml. of urine at a time. The urethra is the last organ that eliminates the urine out of the body (Marieb & Hoehn, 2003).
Physiology of Urinary system
Kidneys are the main site of blood filtration, metabolic waste excretion, and urine formation. Kidneys help in maintaining the acid-base equilibrium through eliminating the excessive electrolytes. In the microscopic structures of nephrons, the filtration and reabsorption of water and various elements occur. Through these incidences, kidneys regulate the blood pressure with the help of certain Sodium-potassium-chloride exchangers and transporters. Any anomaly at any site of nephron can result in water retention causing edema, glaucoma, and certain cardiac problems. The urine formation can be divided into three phases: filtration inside glomerulus, reabsorption at the proximal tubule and finally the tubular secretion. High efficiency and larger surface area of glomerulus create a stimulating hydrostatic pressure that acts as a mechanical filter. Molecules with less than 3 mm diameter easily filtered through the glomerulus membrane. Tubular reabsorption is a transepithelial procedure that starts from the proximal tubules and reabsorbed nutrients blend into the blood via transcellular or paracellular course (Marieb & Hoehn, 2003). Electrochemical gradient and Na+-K+-ATPase pump induce the reabsorption and transportation of potassium-sodium ions, and water, at the different sites (Arnould-Taylor, 1998). Tubular secretion eliminates drug metabolites, as well as certain undesirable substances, such as unnecessary K+. Thus, urinary system maintains body homeostasis, blood pH, and blood pressure (Marieb & Hoehn, 2003).
References
Marieb, E. N., & Hoehn, K. N. (2003). The urinary system.
Human Anatomy and Physiology.
Arnould-Taylor, W. (1998). A textbook of anatomy and physiology.
Nelson Thornes.
