Excretion is a life process which is as important as nutrition. In animals including humans, as a part of metabolism, many waste products are produced. Animals excrete them in different forms such as urine, sweat, feces, and tears. Among these, the usual form of excreta, urine, is produced and discarded from our body as fluid. The process of urination is called micturition. This article will briefly describe the process of micturition.
Elimination of toxic and waste products from the body is called excretion. Many waste products are excreted from the human body in the form of urine. Micturition is the mode of excretion of urine from the body. As we know, complex organisms such as animals including humans have a specialized system of excretion called excretory system.
A human excretory system consists of a pair of kidneys and ureters, a urinary bladder, and a urethra. The kidneys play a major role in the process of urine formation and its excretion. Urine formation takes place in three phases namely glomerular filtration, reabsorption and secretion.
Kidneys have a structural unit called nephron where the blood is filtered. Capillaries in kidneys filter the blood and the essential substances like glucose, amino acids, salts, and the required amount of water are reabsorbed and the pureblood is then circulated back to different parts of the body. While the nitrogenous and other waste products and excess water will be converted into urine. Urine thus formed will be passed to urinary bladder via ureters. The urinary bladder is under the control of the central nervous system (CNS). Thus urinary bladder will store the urine until the CNS signals it.
The process of micturition initiates when the brain signals urinary bladder to contract. This happens on a feedback mechanism i.e. when the urinary bladder is full and starts to stretch. The receptors of the urinary bladder send a signal to the CNS, in response to this CNS sends a signal that stimulates the contraction of the urinary bladder. Through the urinary opening at urethra, we excrete urine. This is called micturition and the neural mechanism is called the micturition reflex.
On an average, a normal adult excretes 1 to 1.5 L of urine per day. Normal human urine is light yellow fluid majorly consisting of 95 percent water and 5 percent solid wastes. It is slightly acidic with a pH close to 6. Many endocrinal disorders can be diagnosed through urine analysis. For example, if a patient suffers from diabetes, presences of glucose and ketone bodies can be detected in his/her urine. Thus it is a major clinical diagnostic element.
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