There is a triangular area, called the trigone , formed by three openings in the floor of the urinary bladder. Two of the openings are from the ureters and form the base of the trigone. Small flaps of mucosa cover these openings and act as valves that allow urine to enter the bladder but prevent it from backing up from the bladder into the ureters.
The third opening, at the apex of the trigone, is the opening into the urethra. This processed liquid is stored until a convenient time for excretion. All structures involved in the transport and storage of the urine are large enough to be visible to the naked eye. This transport and storage system not only stores the waste, but it protects the tissues from damage due to the wide range of pH and osmolarity of the urine, prevents infection by foreign organisms, and for the male, provides reproductive functions.
The urethra transports urine from the bladder to the outside of the body for disposal. The urethra is the only urologic organ that shows any significant anatomic difference between males and females; all other urine transport structures are identical. Figure 1. The urethra transports urine from the bladder to the outside of the body. This image shows a a female urethra and b a male urethra.
The urethra tracks posterior and inferior to the pubic symphysis see Figure 1. In both males and females, the proximal urethra is lined by transitional epithelium, whereas the terminal portion is a nonkeratinized, stratified squamous epithelium.
In the male, pseudostratified columnar epithelium lines the urethra between these two cell types. Voiding is regulated by an involuntary autonomic nervous system-controlled internal urinary sphincter , consisting of smooth muscle and voluntary skeletal muscle that forms the external urinary sphincter below it.
The external urethral orifice is embedded in the anterior vaginal wall inferior to the clitoris, superior to the vaginal opening introitus , and medial to the labia minora. Its short length, about 4 cm, is less of a barrier to fecal bacteria than the longer male urethra and the best explanation for the greater incidence of UTI in women. Voluntary control of the external urethral sphincter is a function of the pudendal nerve.
It arises in the sacral region of the spinal cord, traveling via the S2—S4 nerves of the sacral plexus. The male urethra passes through the prostate gland immediately inferior to the bladder before passing below the pubic symphysis see Figure 1b. The length of the male urethra varies between men but averages 20 cm in length.
It is divided into four regions: the preprostatic urethra, the prostatic urethra, the membranous urethra, and the spongy or penile urethra. The preprostatic urethra is very short and incorporated into the bladder wall. The prostatic urethra passes through the prostate gland.
During sexual intercourse, it receives sperm via the ejaculatory ducts and secretions from the seminal vesicles. The mucus neutralizes the usually acidic environment and lubricates the urethra, decreasing the resistance to ejaculation.
The membranous urethra passes through the deep muscles of the perineum, where it is invested by the overlying urethral sphincters. Give It Up for the Kidneys. The Three Steps of Urine Formation. Urine Storage and Elimination. Common Diseases and Disorders. When you select "Subscribe" you will start receiving our email newsletter. Use the links at the bottom of any email to manage the type of emails you receive or to unsubscribe. See our privacy policy for additional details.
Learn Site. Kidneys Filter Blood at the Top of the Urinary System The kidneys are bean-shaped organs situated on the back of the abdominal wall, behind the peritoneum. The Ureters Move Urine from the Kidneys to the Bladder Urine drains from the renal pelvis of each kidney into the ureters. The Female Urethra Is Shorter Than the Male Urethra Urine produced in the kidneys passes through the ureters, collects in the bladder, and is then excreted through the urethra.
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:. Urine Transport, Storage, and Elimination. Overview of Urine Transport, Storage, and Elimination The urinary organs include the kidneys, ureters, bladder, and urethra.
Learning Objectives Outline the process of urine transport, storage, and elimination. Key Takeaways Key Points Urine collects from the nephrons and flows into the ureters. The ureters use smooth muscle contractions to facilitate the flow of urine. The urinary bladder is a hollow, muscular, and elastic organ that stores urine.
Urine exits the bladder and the body through the urethra. The kidneys, ureters, bladder, and urethra make up the urinary tract, the pathway through which urine flows and is eliminated from the body.
Key Terms ureter : These are two long, narrow ducts that carry urine from the kidneys to the urinary bladder. Urine enters the bladder via the ureters and exits via the urethra. Ureters The ureters are two tubes that drain urine from each of the kidneys into the bladder. Learning Objectives Describe the role of ureters in the urinary system and their structure. Key Takeaways Key Points The ureter contains transitional epithelium and an additional smooth muscle layer in the more distal one-third to assist with peristalsis.
The ureters are usually 25—30 cm 10—12 in long and 3—4 mm in diameter. Muscles in the walls of the ureters send the urine in small spurts into the bladder. Kidney stones are a common disease of the ureter, in which a stone made of minerals obstructs the ureter.
The ureter has a few points of constriction where kidney stones are more commonly found. Key Terms transitional epithelial tissues : Epithelial tissues that can change between columnar and squamous forms that are found in the ureters and the cervix. Ureter Pathology Kidney stones and cancer are common diseases of the ureter. Urinary Bladder The urinary bladder is a hollow, muscular, and distendible or elastic organ that sits on the pelvic floor. Learning Objectives Summarize the features and function of the urinary bladder.
Key Takeaways Key Points The bladder is made of transitional epithelium and has a trigone. A normal bladder empties completely upon a complete discharge, otherwise it is a sign that its elasticity is compromised.
When the bladder becomes half full, stretch receptors send nerve impulses to the spinal cord, which then sends a reflex nerve impulse back to the sphincter muscular valve at the neck of the bladder, causing it to relax and allow the flow of urine into the urethra. The internal urethral sphincter is involuntary and the external sphincter is voluntary.
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