Urine is transported by the ureters, stored in the bladder, and eliminated through the urethra, aided by the micturition reflex (18-5)

Urinary Bladder

A hollow, muscular organ that stores urine prior to urination. Its size varies depending on how distended it is. A full urinary bladder can contain as much as a liter or urine.

Ureters

A pair of muscular tubes that conduct urine from the kidneys to the urinary bladder. Each ureter begins at the funnel-shaped renal pelvis. It ends at the posterior wall of the bladder without entering the peritoneal cavity.

Trigone

A triangular area within the urinary bladder. This area is bounded by the ureteral openings and the entrance to the urethra. The urethral entrance lies at the apex of this triangle at the most inferior point in the bladder. The area surrounding the urethral entrance is called the neck of the urinary bladder.

Wall of the Ureter

Contains three layers, an inner transitional epithelium, a middle layer of longitudinal and circular bands of smooth muscle, and an outer connective tissue layer continuous with the renal capsule.

Micturition Reflex

Coordinates the process of urination, or micturition. As the bladder fills with urine, stretch receptors in the wall of the urinary bladder are stimulated. Afferent sensory fibers in the pelvic nerves carry the resulting impulses to the sacral spinal cord.

Urethra

Extends from the neck of the urinary bladder to the exterior of the body. In males, the urethra extends to the external opening, or external urethral orifice, at the tip of the penis. In females, the urethra is very short and extends from the bladder to the exterior.

External Urethral Sphincter

In both sexes, as the urethra passes through the muscular floor of the pelvic cavity, a circular band of skeletal muscle forms the ________. This sphincter consists of skeletal muscle fibers. Its contractions are under voluntary control.

Urinary Bladder Location

Lies in the pelvic cavity. Only its superior surface is covered by a layer of peritoneum. Held in position by peritoneal folds that extend to the umbilicus, and by bands of connective tissue attached to the pelvic and pubic bones. In males, the base of the urinary bladder lies between the rectum and the pubic symphysis. In females, the urinary bladder sits inferior to the uterus and anterior to the vagina.

Transitional Epithelium

Lines the urinary bladder. This stratified epithelium is continuous with the renal pelvis and the ureters. It can tolerate a considerable amount of stretching.

Urinary Tract Infections

Result when bacteria or yeasts colonize the urinary tract. The intestinal bacterium escherichia coli is most commonly involved. Women are particularly susceptible to UTIs because the external urethral orifice is so close to the vagina and anus.

Ureteral Openings

Slit-like rather than rounded. This shape prevents the backflow of urine into the ureters or kidneys when the urinary bladder contracts.

Calculi (Kidney Stones)

Solids made of calcium deposits, magnesium salts, or crystals or uric acid may form within the kidney, ureters, or urinary bladder. These obstruct the flow of urine but may also reduce or prevent filtration in the affected kidney.

Detrusor Muscle

The bladder wall consists of inner and outer layers of longitudinal smooth muscle with a circular layer between the two. Together, these layers form the powerful _____ of the bladder. Contraction of this muscle compresses the urinary bladder and expels its contents into the urethra.

Incontinence

The inability to control urination voluntarily. Infants lack voluntary control over urination because the necessary corticospinal connections have yet to be established.

Micturition Reflex (2)

The increased level of activity in the fibers 1) brings parasympathetic motor neurons in the sacral spinal cord close to threshold and 2) stimulates interneurons that relay sensations to the thalamus, and then, by projection fibers to the cerebral cortex. As a result, you become aware of the fluid pressure within the urinary bladder.

Internal Urethral Sphincter

The smooth muscle of this ______ provides involuntary control over the discharge of urine from the bladder.