Composition and Mechanism of Urine Formation-2

Characteristics of Urine

• Color: Typically, urine is a clear liquid with a faint golden or amber hue. Urochrome, also known as urobilin, is a bile pigment that gives bile its yellow hue. Foods like beets, vitamin supplements (B group), specific medications, or bleeding somewhere along the urinary tract can all affect the color of the urine.
• Odor: Fresh urine has a faint aroma. However, if it is left to stand, the bacterial metabolism of its urea solutes causes it to smell like ammonia.
• pH: 4.5 to 7.5, depending on how many foods are acidic and how many are basic.
• Specific gravity: 1.010 to 1.030, which will be higher during a fever, after excessive perspiration, or when fluid intake is decreased.
• Chemical Composition: At least 95% of urine is water; the remaining portion is made up of metabolic waste products and electrolytes that were present in excess in the blood. These include sodium, chloride, creatinine, urea, and uric acid ions. Take note that urine typically contains no glucose.

Accessory Structures of the Urinary System

Although accessory structures are needed to move, store, and ultimately eliminate urine from the body after it is formed in the kidney. The two ureters, urinary bladder, and urethra are these organs.

Ureters

Each kidney is connected to a small tube called the ureter. From the renal pelvis to the bladder, they carry urine. The ureters range in diameter from 1 mm to 10 mm and are between 25 and 30 cm long. Beginning at L2, each ureter descends behind the peritoneum to the base of the bladder in the pelvic cavity. At the kidney, it is thin, and it becomes wider near the bladder. Peristaltic waves of contraction are capable of being produced by the ureters, which transport urine from the kidney to the bladder.

The wall of the ureter is composed of three layers:

• Tunica Mucosa: The transitional epithelium is present in the inner lining.
• Tunica Muscularis: Fibers of smooth muscle make up the middle layer.
• Tunica Adventitia: The outermost layer of connective tissue in areoli.

Normal constriction of ureters

The ureters typically have three constrictions:

• At the point where the renal pelvis and ureters converge.
• Where the pelvic inlet's brim and ureters meet.
• When they are passing through the urine bladder's wall.

Potentially, ureteric stones could obstruct these constricted areas.

Functions of the Ureters:

• Urine travels through the ureters from the kidneys to the bladder.
• Urine is pushed toward the bladder by them.

Blood Supply of the Ureters

The renal arteries constantly give rise to arterial branches that enter the abdominal area of the ureter, but the testicular or ovarian arteries less frequently give rise to such branches. With ureteric branches emerging from the internal iliac, common iliac, and ovarian arteries, the vascular supply to the pelvic regions of the ureters varies.

The renal and gonadal (testicular or ovarian) veins are the recipients of veins that drain the abdominal portion of the ureters. In general, the venous drainage from the pelvic portions of the ureters drains to veins with names that correspond to the arterial supply.

Nerve Supply of the Ureter

The renal, abdominal aortic, and superior hypogastric plexuses are the sources of the nerves that line the abdominal portion of the ureters. Inferior hypogastric nerve is the nerve of the ureter's pelvic portion.

Urinary Bladder

The hollow, muscular organ known as the urinary bladder is responsible for collecting urine from the ureters and storing it until excretion. It is situated behind the pubic bone on the floor of the pelvic cavity. In a female, it is anterior to the vagina and uterus, while in a man, it is anterior to the rectum. Externally, the bladder has an apex, a body, a fundus, and a neck when it is empty, giving it a slightly tetrahedral shape. The superior, two inferolateral, and posterior surfaces of the bladder are most easily seen when looking at an empty, contracted bladder that has been removed from a cadaver. At this point, the bladder resembles a boat.

When the bladder is empty, the apex of the bladder faces the superior margin of the pubic symphysis. The moderately convex posterior wall, which is the fundus of the bladder, is located opposite the apex. Between the apex and the fundus, the bladder's body makes up the majority of the organ. The bladder's neck is where the fundus and inferolateral surfaces meet.

It typically stores 300 to 400 ml of urine, but it has the potential to double that volume. There are three layers making up the bladder's wall:

• Tunica mucosa: Epithelium in transition lines the innermost layer.
• Tunica muscularis: Three layers of smooth muscle make up the middle layer. The term "detrusor muscles" refers to all of these.
• Tunica adventitia: Only the upper and lateral surfaces of the bladder are covered by the outer layer, which is derived from the peritoneum.

The trigone is a triangle-shaped region that is defined by the opening of the ureters and urethra in the bladder cavity. The smooth muscle in the bladder wall organizes into spiral, longitudinal, and circular bundles at the point where the urethra exits the organ. These bundles contract to stop the bladder from emptying too soon. The internal urethral sphincter is a sphincter made up of these bundles. The external urethral sphincter is formed by a circular sphincter of voluntary skeletal muscle that extends from there along the middle membranous portion of the urethra.

Organs Associated with the Urinary Bladder

In the male and female, the associated organs with the bladder are different.

In females:

• Anteriorly: The symphysis pubis.
• Posteriorly: The uterus.
• Superiorly: The peritoneal folds and the small intestine.
• Inferiorly: The muscle that makes up the pelvic floor and the urethra.

In males:

• Anteriorly: The symphysis pubis.
• Posteriorly: The seminal vesicles and the rectum.
• Superiorly: The peritoneal folds and the small intestine.
• Inferiorly: The prostate gland and the urethra.

Functions of the Urinary Bladder:

• Urine storage is the bladder's primary job.
• Urine cannot backflow from the bladder into the ureters because of the thickened smooth muscle layer in the bladder.
• Urine is easily expelled from the body with the aid of the bladder.

Blood supply of the Urinary Bladder

The internal iliac arteries have branches that supply the bladder's main arteries. Anterosuperior portions of the bladder are supplied by the superior vesical arteries. The fundus and neck of the bladder are supplied by the inferior vesical arteries in males. Small branches from the vaginal arteries travel to the bladder's posteroinferior regions in females, where they take the place of the inferior vesical arteries.

The internal iliac veins, which are tributaries of the bladder's blood vessels, correspond to the arteries. The prostatic venous plexus and vesical venous plexus in men are continuous.

Urethra

When urinating, pee travels from the urinary bladder to the outside of the body through the urethra, a tiny tube with a thin wall. The urethra is different in length and function between the sexes. It is just approximately 4 cm long in females and is located exactly posterior to the symphasis pubic. The urethra in males is around 20 cm long and travels via the penis. It opens in females between the vagina and the clitoris. In both sexes, the urethra empties into the external urethral opening. It is located posterior to the clitoris and anterior to the vagina in females. It opens at the tip of the penis in males (glans penis).

In males, it is divided into three regions:

• The prostatic urethra: The prostate gland is traversed by the first 2.5 cm.
• The membranous urethra: It extends from the prostate gland to the start of the penis for about 2 cm, passing through the pelvic wall.
• The penile urethra: It is about 15 cm long and passes through the penis. It releases semen during an ejaculation in males.

The urethra has both internal and exterior sphincters. The external sphincter, with the exception of during infancy, is voluntary while the internal sphincter is involuntary. Two layers make up the urethral wall:

• The inner layer: A stratified squamous epithelium in the lower section and a mucous membrane lining in the upper part.
• The muscle layer: A layer of muscle made up of striated muscle in the external sphincter and smooth muscle in the interior sphincter.

Functions of the Urethra

• It serves as a conduit for the bladder to release pee.
• During ejaculation, it releases semen in males.