The urinary tract is one of the systems that our bodies use to get rid of waste products. The kidneys are the part of the urinary tract that makes urine (pee). Urine has salts, toxins, and water that need to be filtered out of the blood. After the kidneys make urine, it leaves the body using the rest of the urinary tract as a pathway.
What Are the Parts of the Urinary Tract?
People usually have two kidneys, but can live a normal, healthy life with just one. The kidneys are under the ribcage in the back, one on each side. Each adult kidney is about the size of a fist.
Each kidney has an outer layer called the cortex, which contains filtering units. The center part of the kidney, the medulla (pronounced: meh-DUH-luh), has fan-shaped structures called pyramids. These drain urine into cup-shaped tubes called calyxes (pronounced: KAY-luh-seez).
From the calyxes, pee travels out of the kidneys through the ureters (pronounced: YUR-uh-ters) to be stored in the bladder (a muscular sac in the lower belly). When a person urinates, the pee exits the bladder and goes out of the body through the urethra (pronounced: yoo-REE-thruh), another tube-like structure. The male urethra ends at the tip of the penis; the female urethra ends just above the vaginal opening.
What Do the Kidneys Do?
Kidneys have many jobs, from filtering blood and making pee to keeping bones healthy and making a hormone that controls the production of red blood cells.
The kidneys also help regulate blood pressure, the level of salts in the blood, and the acid-base balance (the pH) of the blood. All these jobs make the kidneys essential to keeping the body working as it should.
How Do the Kidneys and Urinary Tract Work?
Blood travels to each kidney through the renal artery. The artery enters the kidney at the hilus (pronounced: HY-luss), the indentation in middle of the kidney that gives it its bean shape. The artery then branches so blood can get to the nephrons (pronounced: NEH-fronz) — 1 million tiny filtering units in each kidney that remove the harmful substances from the blood.
Each of the nephrons contain a filter called the glomerulus (pronounced: gluh-MER-yuh-lus). The fluid that is filtered out from the blood then travels down a tiny tube-like structure called a tubule (pronounced: TOO-byool). The tubule adjusts the level of salts, water, and wastes that will leave the body in the urine. Filtered blood leaves the kidney through the renal vein and flows back to the heart.
Pee leaves the kidneys and travels through the ureters to the bladder. The bladder expands as it fills. When the bladder is full, nerve endings in its wall send messages to the brain. When a person needs to pee, the bladder walls tighten and a ring-like muscle that guards the exit from the bladder to the urethra, called the sphincter (pronounced: SFINK-tur), relaxes. This lets pee go into the urethra and out of the body.
What Can Help Keep the Kidneys and Urinary Tract Healthy?
To help keep your kidneys and urinary tract healthy:
- Get plenty of exercise.
- Eat a nutritious diet.
- Stay hydrated.
- For girls: Wipe from front to back after pooping so germs don't get into the urethra.
- Avoid bubble baths, sitting in the tub after shampoo has been used, and scented soaps. These can irritate the urethra.
- Wear cotton underwear.
- Promptly change out of wet bathing suits.
- Go for regular medical checkups.
- Talk to your doctor before taking any supplements or herbal treatments.
- Let the doctor know about any family history of kidney problems, diabetes, or high blood pressure.
- Let the doctor know if you have any swelling or puffiness, have pain with peeing, need to pee often, have foamy urine or blood in the urine, or are constipated.
Urethritis refers to inflammation of the urethra.
This can cause a range of symptoms, including:
- increased urge to urinate
- burning sensation while urinating
- releasing small amounts of urine at a time
- cloudy or foul-smelling urine
- blood in urine
- pelvic pain
Urethritis sometimes develops in response to a recent urinary procedure or placement of a catheter.
In other cases, it’s due to an infection. Bacteria can spread from the anus to the urethra, especially if you wipe back to front after going to the bathroom.
In addition, sexually transmitted infections (STIs) can cause urethritis. These include:
- gonorrhea
- chlamydia
- herpes simplex virus
If a surgery or catheter placement is causing urethritis, it usually resolves on its own over time. However, urethritis due to an infection requires treatment with antibiotics or antiviral medication.
Urethral stricture
Sometimes the urethra narrows or becomes blocked. This is known as urethral stricture. Males are more likely to develop urethral stricture because of their longer urethras, but it can affect females as well.
Symptoms of urethral stricture include:
- decreased urine flow
- pain while urinating
- blood in the urine
- abdominal pain
An injury often causes urethral stricture, such as an accident or surgery. Infections, including STIs, can also cause it.
Most cases are treatable with minor surgery to open up the urethra or remove a blockage.
Urethral cancer
Urethral cancer is one of the rarer types of cancer. It can rapidly spread to surrounding tissues in the bladder and vagina.
It may not cause any symptoms in its early stages. However, urethral cancer can eventually result in:
- blood in urine
- bleeding or discharge from the urethra
- increased need to urinate
- decreased urine flow
Experts aren’t sure about the exact cause of urethral cancer. There are several things that can increase someone’s risk of developing it, though. Risk factors include:
- older age
- history of bladder cancer
- chronic inflammation of the urethra, usually due to frequent UTIs or STIs
Treatment for urethral cancer includes surgery, chemotherapy, radiation, or a combination of all three.
Urethral syndrome
Urethral syndrome is a condition that causes symptoms similar to those of a UTI. However, there’s no underlying bacterial or viral infection.
The main symptom of urethral syndrome is chronic pain in the pelvis and urinary tract. In some cases, the pain is constant. In others, certain things, including exercise, allergies, or exposure to irritants, can trigger it.
Other common symptoms include an increased need to urinate and pain while urinating.
Exercise or physical therapy programs may be helpful in treating urethral syndrome. Avoiding scented soaps, perfumes, or bath oils may also help.
For urethral syndrome linked to allergies or food sensitivities, eliminating the following may relieve symptoms:
- spicy foods
- acidic foods
- alcohol
- caffeine
Urethral caruncle
A urethral caruncle is a benign mass found in the urethra, usually occurring after menopause. It usually doesn’t cause any symptoms. However, some people might notice pain when urinating or bleeding from the urethra.
Experts aren’t sure what causes it, but low estrogen levels might be involved.
Large urethral caruncles can be surgically removed. Otherwise, topical anti-inflammatories or estrogen creams can help.
The posterior male urethra forms from the urogenital sinus (see the image below). This sinus derives from the endoderm-derived cloaca, which is separated from the anorectal canal by the growth of the urorectal septum in the fourth week of gestation. The spongy urethra is formed after the seventh week by tubularization of the urethral folds along the urethral groove under the influence of dihydrotestosterone. The most distal portion of the urethra is likely formed by invagination of an epithelial tag at the distal end of the genital tubercle. [1]
Embryologic development of pendulous urethra.
The male urethra originates at the bladder neck and terminates at the urethral meatus on the glans penis. It is roughly 15-25 cm long in the adult and forms an "S" curve when viewed from a median sagittal plane in an upright, flaccid position (see the image below). The male urethra is often divided into 3 segments on the basis of its investing structures: prostatic urethra, membranous urethra, and spongy (or penile) urethra.
Male urethra and its segments.
Other systems for naming the parts of the urethra have been described. The urethra can be separated simply into anterior and posterior urethra. The spongy urethra can be subdivided into fossa navicularis, pendulous urethra, and bulbous (bulbar) urethra. Finally, the bladder neck, or preprostatic urethra, can be classified as a distinct part of the urethra (see the image below).
Posterior wall of urethra.
The prostatic urethra is the portion of the urethra that traverses the prostate. It originates in the region of the bladder neck, courses roughly 2.5 cm inferiorly, and terminates at the membranous urethra. It lies in a retropubic location and is bordered superiorly by the bladder and supported inferiorly by the sphincter urethrae externus muscle and the perineal membrane (formerly called the urogenital diaphragm). It is invested in the prostate, a glandular and fibrostromal organ that secretes seminal fluids and has clinical relevance.
The urethra runs through the prostate eccentrically, with most of the prostatic tissue in a posterior and inferior location. The prostatic urethra is surrounded by an inner circular layer and an outer longitudinal layer of smooth muscle. The urethra forms an angle of roughly 45º (range, 0-90º) at the midpoint of the prostatic urethra. The segment proximal to this location is surrounded by the involuntary internal sphincter. It is also the area most commonly affected by benign prostatic hyperplasia (BPH).
The posterior wall of the prostatic urethra contains the urethral crest, which is bordered laterally by prostatic sinuses, into which the prostatic glands drain. The most prominent aspect of this crest is the seminal colliculus, or verumontanum, where the paired ejaculatory ducts and the opening of the prostatic utricle (a small midline paramesonephric duct remnant) meet the lumen of the urethra. The seminal colliculus has no functional significance but is a crucial landmark in urethroscopy and transurethral surgery.
The shortest and least distensible portion of the urethra is the membranous urethra. This region spans from the apex of the prostate to the bulb of the penis. It is invested in the external urethral sphincter muscle and the perineal membrane.
The external sphincter is related anteriorly to the dorsal venous complex and is connected to the puboprostatic ligaments and the suspensory ligament of the penis. The external urethral sphincter muscle and the perineal membrane fix the urethra firmly to the ischial rami and inferior pubic rami, rendering this portion of the urethra susceptible to disruption with pelvic fracture.
The spongy urethra is the region that spans the corpus spongiosum of the penis. It is divided into the pendulous urethra and the bulbous (or bulbar) urethra. The pendulous urethra is invested in the corpus spongiosum of the penis in the pendulous portion of the penis. The urethra is located concentrically within the corpus spongiosum.
In the distal urethra lies the fossa navicularis, a small dilation of the urethra just proximal to the urethral meatus. The meatus is a slitlike orifice with its long axis in a midline sagittal plane. The urethral meatus is slightly ventral to the tip of the penis. The bulbous urethra is invested in the bulb of the penis, the portion of corpus spongiosum that lies between the split corpora cavernosa in the superficial perineal space.
Bulbourethral (Cowper) glands, a male homologue of the greater vestibular (Bartholin) glands, originate in the external urethral sphincter muscle but terminate in ducts that empty into the bulbous urethra. The spongy urethra lies closer to the dorsum of the penis in the bulb.
The prostatic urethra is supplied by the inferior vesical artery, which branches to penetrate the prostate and the bladder neck in superolateral positions. The bulbourethral artery supplies the membranous and bulbar urethra, whereas the pendulous urethra is supplied by the deep penile artery, a branch of the internal pudendal artery. In general, venous drainage mirrors the arterial supply. The prostatic and membranous urethra drain to the obturator and internal iliac nodes.
Lymphatic drainage from the spongy urethra drains to the deep and superficial inguinal nodes. [2]