The urethra is a muscular tube that connects the bladder with the outside of the body and removes urine from the body. The urethra is a tube that connects the urinary bladder to the genitals for the removal of fluids from the body.
The external urethral sphincter is a striated muscle that allows voluntary control over urination by controlling the flow of urine from the bladder into the urethra. In females, the urethra is shorter relative to males, and emerges above the vaginal opening. Its lining is composed primarily of non-keratinized stratified squamous epithelium that becomes transitional near the bladder. The urethra consists of three layers of tissues:. The urethral sphincter separates the bladder from the urethra.
Somatic conscious innervation of the external urethral sphincter is supplied by the pudendal nerve, which allows the sphincter to open and close. As the urethra is shorter in females relative to males, they are more vulnerable to bacterial urinary tract infections.
In males, the urethra travels through the penis and carries semen as well as urine. Semen does not flow through the bladder or the rest of the urinary tract, instead it is a fluid made of sperm cells and other fluids that passes through a few different glands from the testes to the urethra through the vas deferens.
Micturition is the ejection of urine from the urinary bladder through the urethra to the outside of the body. Micturition, also known as urination, is the ejection of urine from the urinary bladder through the urethra to the outside of the body.
In healthy humans the process of urination is under voluntary control. In infants, elderly individuals, and those with neurological injury, urination may occur as an involuntary reflex. Physiologically, micturition involves the coordination of the central, autonomic, and somatic nervous systems.
The brain centers that regulate urination include the pontine micturition center, the periaqueductal gray, and the cerebral cortex, which cause both involuntary and voluntary control over micturition. In males, urine is ejected through the penis, and in females through the urethral opening. Due to sexual dimorphism, and the positions where the urethra ends, males and females often use different techniques for urination. Micturition consists of two phases:.
Location of urethral orifice in females : Location of the external urethral orifice in adult females. The muscles controlling micturition are controlled by the autonomic and somatic nervous systems, which open the two sphincters during the voiding phase of micturition.
During the storage phase the internal urethral sphincter is tense and the detrusor muscle is relaxed by sympathetic stimulation. During the voiding phase of micturition, parasympathetic stimulation causes the internal urethral sphincter to relax.
The external urethral sphincter sphincter urethrae is under somatic control and is consciously relaxed and thus opened during micturition. Many males prefer to urinate standing. In females, the urethra opens straight into the vulva. Because of this, the urine often does not exit at a distance from the body and is therefore seen as harder to control.
The state of the micturition reflex system is dependent on both a conscious signal from the brain and the firing rate of sensory stretch fibers from the bladder and urethra.
At low bladder volumes, the afferent firing of the stretch receptors is low, and results in relaxation of the bladder. At high bladder volumes, the afferent firing of the stretch receptors increases, and causes a conscious sensation of urinary urge.
This urge becomes stronger as the bladder becomes more full. The micturition reflex causes bladder contraction during voiding, through a neural pathway. This reflex may lead to involuntary micturition in individuals that may not be able to feel the sensation of urinary urge, due to the firing of the stretch receptors themselves.
In addition to the kidneys, the liver, skin, and lungs also have important roles in the excretion of waste from the body. Besides the renal system, many other organs and body systems are directly involved in the excretion of waste products. These other systems are responsible for the elimination of the waste products of the metabolism, as well as other liquid and gaseous wastes, but also provide other critical functions.
The lungs : The lungs are responsible for the removal of gaseous waste from the body. Similar to renal clearance, these other organs have a clearance rate of their own, and also forms a part of total body clearance.
The skin, lungs, and liver are the main waste removal organs outside of the non-renal system; however, their ability to remove wastes is generally less than that of the renal system. The liver has many vital functions, including a role in digestion, protein synthesis, and nutrient and vitamin storage. The liver also plays an important function in the management of body waste.
It acts as a detoxification system for the body, processing and neutralizing drugs and toxins. The liver is involved in the breakdown and recycling of red blood cells, including the removal of bilirubin from the body by secreting it into the bile, which then functions as a fat emulsifier in the digestive system.
Additionally, the liver is involved in the removal of toxic ammonia from the body by converting it to non-toxic urea, which is then excreted by the kidneys and put into urine during tubular secretion.
Skin has sweat glands that secrete a fluid waste called perspiration. Perspiration, or sweat, is a fluid consisting primarily of water, as well as various dissolved solid wastes, that is excreted by the sweat glands. The sweat glands remove a bit of excess water and salts, and also serve the function of cooling the body during thermoregulation.
The lungs are responsible for the removal of gaseous waste from the body. Carbon dioxide is a toxic byproduct of cellular respiration. The lungs remove carbon dioxide from the bloodstream during ventilation, exchanging it for oxygen. This function is essentially important for regulating blood pH, since blood acidity is directly related to the concentration of carbon dioxide dissolved in carbonic acid in the blood stream.
Excreting more carbon dioxide waste will reduce the acidity of blood. Privacy Policy. Skip to main content. Urinary System. Search for:. Sometimes the ureters can become blocked or injured.
This can block the flow of urine to the bladder. If urine stands still or backs up the ureter, you may get a urinary tract infections. Doctors diagnose problems with the ureters using different tests.
These include urine tests, x-rays, and examination of the ureter with a scope called a cystoscope. Treatment depends on the cause of the problem. It may include medicines and, in severe cases, surgery. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. Urea is carried in the bloodstream to the kidneys, where it is removed along with water and other wastes in the form of urine.
Other important functions of the kidneys include blood pressure regulation and the production of erythropoietin, which controls red blood cell production in the bone marrow. Kidneys also regulate the acid-base balance and conserve fluids.
Two kidneys. This pair of purplish-brown organs is located below the ribs toward the middle of the back. Their function is to:. The kidneys remove urea from the blood through tiny filtering units called nephrons.
Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.
Two ureters. These narrow tubes carry urine from the kidneys to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine downward, away from the kidneys.
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