Living body is made up of all the basic functions that help in their survival and proper functioning. Plants take in minerals and carbon dioxide, giving some useful product and thus excreting all the unused substances or excess substances in the soil. Likewise, human body is remarkably made with all the systems that help in their survival. Digestive, respiratory, reproductive, circulatory, integument, nervous, excretory and many more of other systems functions in human body making is perfect for their survival and growth. All these systems work in well coordinated manner so as to give the proper output. Likewise, excretion is also the major function of human body to eliminate all the waste product from the body. In the process of excretion, urine and faeces are expelled out from the body. On one hand, faeces are excreted after digestion of food, passing from large intestine to the anus whereas urine has quite a different pathway for regulation and excretion.
In case of urine, kidneys play a main role for its excretion. Along with kidney, many more organs like ureter, urinary bladder and urethra also help in the process of excretion of urine from the body.
Ureter: these are the paired tubes that run from left and right side of the vertebral column. The muscular force along with hydrostatic pressure and gravity push urine to the urinary bladder. These are retroperital organ that curve medially and pass obliquely through the wall of urinary bladder.
Urinary bladder: these are sac like organ that stores urine, it is located inferior to the pelvis and once the urine is passed to the urinary bladder or the maximum capacity for urine storage is reached, it receives signal from the brain thus passing the stored urine to the urethra.
Urethra: it is a tube that passes urine to the exterior of the body. The position of urethra in male and female varies. In case of female, it lies superior to vaginal opening and inferior to clitoris whereas in male it ends at the end of penis. Urine when reaches the urethra is guided by two sphincter, internal and external sphincters. In case of internal sphincter, it opens when need to urinate is reached and external sphincter opens to pass the urine outside of the body. Internal sphincter in involuntary but external sphincter is voluntary.
We all know that kidney has several functions, like that of regulation of blood pressure, blood pH, blood volume and many more, and among these excretion of urine is one of its important function performed by the kidneys. Kidneys are a paired, bean shaped, retroperital organ located between the peritoneum and posterior wall of the abdomen. The level of both the kidneys are different, among the two, the right kidney is slightly lowered than the left kidney because the space above the right kidney is occupied by the liver. If we see the external morphology of the kidney, it can be clearly noticed that the concave part has a centre portion and near that portion is renal hilum from where emerges ureter, blood vessels, lymphatic vessels and nerves. Kidney is surrounded by three layers, at the internal portion is the renal capsule that serves as the barrier and maintains the shape of the kidney. On the middle side lies the adipose capsule that also protects and maintains the shape of the kidney. Finally, at the external portion lies the renal fascia that anchors it to the surrounding structure to the abdominal wall. If we view the interior portion of the kidney it is again divided into two parts, renal cortex and renal medulla. Renal medulla lies interior to the renal cortex and the renal cortex consist of many renal pyramids. Thus, renal cortex and renal pyramid are altogether called parenchyma. This parenchyma has many functional unit of kidney called nephron. Urine is drained into large ducts called papillary ducts that again drain into major and minor calyces. Then the urine is drained into renal pelvis and finally through the ureter it reaches urinary bladder.
Flow chart for the blood supply of the
Nephron as we know is the functional unit of kidneys. This functional unit has two main parts, renal corpuscle and renal tubule. In case of renal corpuscle only the blood plasma is filtered whereas in the renal tubule filtered fluid passes. Renal corpuscle is again divided into two compartments, Bowman’s capsule and glomerulus, whereas renal tubule is divided into three main sections: proximal convoluted tubule, loop of Henle and distal convoluted tubule. Renal corpuscle and DCT and PCT all lies within the renal cortex whereas loop of Henle extends up to renal medulla and return back to renal cortex. Now, finally urine from DCT empties into papillary duct and further compartments. In this process, loop of Henle connects PCT and DCT, thus its first part inserts into renal medulla hence called descending limb of loop of Henle, whereas when it makes a hairpin turn and enters back into renal cortex it is called ascending limb of loop of Henle. Nephrons are also of two types, cortical nephron and juxamedullary nephron. On one hand, in cortical nephron renal corpuscle lies in the outer portion of renal cortex whereas in juxamedullary nephron, it lies to the inner side. The loop of Henle of cortical nephron receives its blood supply from peritubular capillaries whereas in juxamedullary, the loop of Henle receives blood supply from two parts, one is the peritubular capillaries and other is the vasa recta.
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Now, coming to the physiological process, urine production and excretion is not a simple and easy process, in fact combination of many steps finally leads to the end process. Among them 3 basic steps are involved: glomerular filtration, tubular reabsorbtion and tubular secretion. In case of glomerular filtration, water and solutes present in blood plasma move from glomerular capillaries to glomerular capsule then to renal tubule. Now, water and solutes are reabsorbed when the fluid flows through the collecting duct. At the same time during the flow through vase recta and peritubular capillaries, solutes are returned to the blood and finally in tubular secretion, all the waste materials are removed from the blood. Most of the solutes that are drained in renal pelvis get excreted with urine. After the urine is produced from the body, now it has to be excreted, thus for this it is transported through the ureter to the urinary bladder. Urinary bladder stores urine, until it gets signal from the brain, the signal from brain results for relaxation of the urethral sphincter and hence urge to urinate.
Therefore, this way, with this entire complex pathway, urine is finally excreted from the body. Excretion of unused product is important for living body, whether it’s human or the animals, because if the wastes are not expelled out; they get accumulated within the body creating several complications and making life hard for the survival. Therefore, it is necessary to hydrate the body and keep all the organs and system in proper state. Generally, people suffer from kidney problems but avoidance of any bad habits and adequate supply of water to the body can help stay away from any kind of diseases and uninvited problems.
Hence, our organs are our greatest assets, so we must be careful enough to keep them in proper condition so as to lead a healthy life.