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| Internal urethral orifice | |
|---|---|
 Male urinary bladder | |
 The interior of bladder. | |
| Details | |
| Identifiers | |
| Latin | ostium urethrae internum |
| TA98 | A08.3.01.028F A08.3.01.027M |
| TA2 | 3424 |
| FMA | 85264 |
| Anatomical terminology | |
The internal urethral orifice is the opening of the urinary bladder into the urethra. [1]
It is usually somewhat crescent-shaped.[ citation needed ]
It is formed by the neck of the urinary bladder. It opens at the apex/inferior angle of the trigone of the bladder, some 2-3 cm anteromedial to either ureteral orifice. [1]
The mucous membrane immediately posterior to it presents a slight elevation in males - the uvula vesicae - caused by the middle lobe of the prostate.[ citation needed ]
The urethra is the tube that connects the mammalian urinary bladder to the urinary meatus. In placental mammals, the urethra transports urine through the penis or vulva during urination and semen through the penis during ejaculation.
The bladder is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In placental mammals, urine enters the bladder via the ureters and exits via the urethra. In humans, the bladder is a distensible organ that sits on the pelvic floor. The typical adult human bladder will hold between 300 and 500 ml before the urge to empty occurs, but can hold considerably more.
The prostate is both an accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found in all male mammals. It differs between species anatomically, chemically, and physiologically. Anatomically, the prostate is found below the bladder, with the urethra passing through it. It is described in gross anatomy as consisting of lobes and in microanatomy by zone. It is surrounded by an elastic, fibromuscular capsule and contains glandular tissue, as well as connective tissue.
The human urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites, and regulate blood pH. The urinary tract is the body's drainage system for the eventual removal of urine. The kidneys have an extensive blood supply via the renal arteries which leave the kidneys via the renal vein. Each kidney consists of functional units called nephrons. Following filtration of blood and further processing, wastes exit the kidney via the ureters, tubes made of smooth muscle fibres that propel urine towards the urinary bladder, where it is stored and subsequently expelled through the urethra during urination. The female and male urinary system are very similar, differing only in the length of the urethra.
Urination is the release of urine from the bladder to the outside of the body. Urine is released from the urethra through the penis or vulva in placental mammals and through the cloaca in other vertebrates. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, or, rarely, emiction, and known colloquially by various names including peeing, weeing, pissing, and euphemistically going number one. The process of urination is under voluntary control in healthy humans and other animals, but may occur as a reflex in infants, some elderly individuals, and those with neurological injury. It is normal for adult humans to urinate up to seven times during the day.
Urinary incontinence (UI), also known as involuntary urination, is any uncontrolled leakage of urine. It is a common and distressing problem, which may have a large impact on quality of life. It has been identified as an important issue in geriatric health care. The term enuresis is often used to refer to urinary incontinence primarily in children, such as nocturnal enuresis. UI is an example of a stigmatized medical condition, which creates barriers to successful management and makes the problem worse. People may be too embarrassed to seek medical help, and attempt to self-manage the symptom in secrecy from others.
The ureters are tubes composed of smooth muscle that transport urine from the kidneys to the urinary bladder. In an adult human, the ureters typically measure 20 to 30 centimeters in length and about 3 to 4 millimeters in diameter. They are lined with urothelial cells, a form of transitional epithelium, and feature an extra layer of smooth muscle in the lower third to aid in peristalsis. The ureters can be affected by a number of diseases, including urinary tract infections and kidney stone. Stenosis is when a ureter is narrowed, due to for example chronic inflammation. Congenital abnormalities that affect the ureters can include the development of two ureters on the same side or abnormally placed ureters. Additionally, reflux of urine from the bladder back up the ureters is a condition commonly seen in children.
The seminal vesicles are a pair of convoluted tubular accessory glands that lie behind the urinary bladder of male mammals. They secrete fluid that partly composes the semen.
The corpus spongiosum is the mass of spongy tissue surrounding the male urethra within the penis. It is also called the corpus cavernosum urethrae in older texts.
A ureterocele is a congenital abnormality found in the ureter. In this condition the distal ureter balloons at its opening into the bladder, forming a sac-like pouch. It is most often associated with a duplicated collection system, where two ureters drain their respective kidney instead of one. Simple ureterocele, where the condition involves only a single ureter, represents only twenty percent of cases.
The trigone is a smooth triangular region of the internal urinary bladder formed by the two ureteric orifices and the internal urethral meatus.
Stress incontinence, also known as stress urinary incontinence (SUI) or effort incontinence is a form of urinary incontinence. It is due to inadequate closure of the bladder outlet by the urethral sphincter.
The deep perineal pouch is the anatomic space enclosed in part by the perineum and located superior to the perineal membrane.
The spongy urethra is the longest part of the male urethra, and is contained in the corpus spongiosum of the penis.
The membranous urethra or intermediate part of male urethra is the shortest, least dilatable, and, with the exception of the urinary meatus, the narrowest part of the urethra. It extends from the apex of the prostate proximally to the bulb of urethra distally. It measures some 12 mm in length. It traverses the pelvic floor. It is surrounded by the external urethral sphincter, which is in turn envelopped by the superior fascia of the urogenital diaphragm.
The urethral crest is an anatomical feature present in the urinary system of both males and females.
The navicular fossa is a short dilated portion of the male urethra within the glans penis just proximal to the external urethral meatus. The roof of the fossa is especially dilated, forming a lacuna; medical instruments being inserted into the male urethra should initially be directed towards the floor of the fossa so as not to get snagged at the fossa. It is one of three dilations of the male urethra.
The urinary meatus, also known as the external urethral orifice, is the opening where urine exits the male and female urethra. It is where semen also exits the male urethra. The meatus has varying degrees of sensitivity to touch.
The urethral sphincters are two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are either the male or female external urethral sphincter and the internal urethral sphincter. When either of these muscles contracts, the urethra is sealed shut.
The internal urethral sphincter is a urethral sphincter muscle which constricts the internal urethral orifice. It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle, but anatomically and functionally fully independent from it. It is composed of smooth muscle, so it is under the control of the autonomic nervous system, specifically the sympathetic nervous system.
This article incorporates text in the public domain from page 1232 of the 20th edition of Gray's Anatomy (1918)
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