24.8 Urine Characteritistcs, Transport Storage, and Elimination

Typical urine composition

• 95% water

• 5% solutes

Solutes:

• salts (NA+, CI-, K+, Mg2+, Ca2+, SO42-, H2PO4-, Nh4+)

• nitrogenous wastes (urea, uric acid, creatinine)

• some hormones

• drugs

• small amounts of ketone bodies (a waste product of digesting fatty acids)

These substances are not completely reabsorbed, are secreted into tubular fluid or both.

Abnormal urine constituents:

• glucose

• ketones(acetone, acetoacetic acid, beta-hydroxybutyric acid)

• protein

• bile pigment

• erythrocytes

• hemoglobin (Hb)

• Leukocytes

• Nitrites

• Myoglobin

Glucose

Clinical Term: Glucosuria glycosuria

Possible Cause(s): Diabetes mellitus

Ketones (acetone, acetoacetic acid, beta-hydroxybuyric acid)

Clinical Term: Ketonuria

Possible Cause(s): Diabetes mellitus, starvation(anorexia), low-carbohydrate diet(Atkins, south beach), ketones produced as by products of fatty acid metabolism.

Protein(Trace amounts of protein 5-10 mg/dl are not clinically significant)

Clinical Term: Proteinuria

Possible Cause(s): Increased glomerular permeability caused by kidney trauma, heavy metals, bacterial toxins, exertion (running a marathon), hypertension, cold exposure, glomerular nephritis.

Bile pigment

Clinical Term: Bilrubinuria

Possible Cause(s): Liver pathology(hepatitis, cirrhosis) obstructed bile duct due to gallstones

Erythrocytes

Clinical Term: Hematuria

Possible Cause(s): Glomerular damage, kidney trauma, pathology along the urinary tract (as occurs with urinary tract stones), urinary tract infection, blood from menstrual flow

Hemoglobin (Hb)

Clinical Term: Hemoglobinuria

Possible Cause(s): Accelerated rate of erythrocyte destruction (hemolytic anemia, a transfusion reaction) burns, renal damage, contamination from menstrual flow

Leukocytes

Clinical Term: Pyruia

Possible Cause(s): Urinary tract infection, acute glomerulonephritis, contamination from female reproductive tract

Nitrites

Clinical Term: Nitrituria

Possible Cause(s): Urinary tract infection because bacteria convert nitrates (No3-) to nitrites (No2-)

Myoglobin

Clinical Term: Myoglobinuria

Possible Cause(s): Rhabdomyolysis (a condition where skeletal muscle breaks down; caused by excessive exercise and is an uncommon side effect of statins)

The average daily urine volume

1-2 L.

Variations occur due to:

• fluid intake

• blood pressure

• diet

• body temperature

• use of diuretics

• diabetes

• the amount of fluid excreted by other means (heavy sweating, vomiting)

A minimum of about ___ of urine per day is required to eliminate the wastes from the body.

0.5 L.

If crows below 0.4 L, wastes will accumulate in the blood.

Factors that DECREASE urine volume

• Increase in ADH

• Increase in aldosterone

• Decrease in ANP

• Decrease in fluid intake

• Decrease in blood pressure

• Increase in other fluid output (sweating, vomiting, diarrhea, hemorrhage)

Factors that INCREASE urine volume

• Decrease in ADH

• Decrease in aldosterone

• Increase in ANP

• Increase in fluid intake

• Increase in blood pressure

• Diabetes mellitus

• Diuretics (medications, alcohol)

The pH for urine typically ranges between

4.5 and 8.0

average value is: 6.0 which is slightly acidic.

the Ph of urine may be affected by

diet

decreases and becomes more acidic: consume proteins and wheat

Increases and become more basic: diet high in fruits and vegetables.

Other factors that influence urine pH

• metabolism (diabetes mellitus)

• bacterial infections.

Specific gravity

the density (g/mL) of a substance compared to the density of water (1g/mL)

The average specific gravity of urine

levels ranging from 1.003 to 1.035.

because solutes are components of urine

The average specific gravity of urine varies by

• time of day

• amount of food and liquids consumed

• amount of exercise

If you are well hydrated,

• urine output increases

• specific gravity values decrease

A specific gravity value below 1.010 indicates

relative hydration.

A specific gravity value above 1.020 indicates

relative dehydration

The color of urine ranges from

almost color to dark yellow

depends upon the concentration of pigment from urobilin

An increase volume of urine generally is

lighter in color

An decrease volume of urine generally is

darker in color.

Substances that change the color of urine

• beets

• certain vitamins

Things that increase the turbidity of the urine

• vaginal secretions

• excessive substances in urine (cellular material, protein)

• crystallization or precipitation of salts if collected and left standing bacteria.

Urinoid

term for typical smell of fresh urine.

Urine may develop an ammonia smell if allowed to stand because bacteria convert the nitrogen in urea into ammonia (NH3)/

Things that may alter the smell of urine

• asparagus

• certain other foods.

An indication that a person has diabete mellitus (smell of urine)

• urine smells fruity(like acetone) from the accelerated production of keto acids from fatty acid metabolism

Urinary tract

consists of:

• ureters

• urinary bladder

• urethra

Responsible for:

• transporting the urine produced in the kidneys

• storing the urine until the time and place are right for its elimination from the body

• transporting the urine from storage to the exterior of the body.

Ureters (definition)

• long, epithelial-lined fibromuscular tubes

• transport urine from the kidneys to the urinary bladder

• each tube in an adult averages about 25 centimeters (10 inches) in length and is retroperitoneal

• they originate from the renal pelvis as it exits the hilum of the kidney and then extend inferiorly to enter the posterlateral wall of the base of the urinary bladder.

• The wall of the ureter is composed of 3 concentric tunics. From innermost to outermost: mucosa, muscularis, adventitia)

• projects through the bladder wall obliquely.

• because of the projection, their walls are compressed as the bladder expands, decreasing the likelihood of urine refluxing into the ureters from the bladder when it is emptying.

• are intervated by the autonomic nervous system

• Sympathetic neurons extend from the T11-L2 segments of the spinal cord. Parasympathetic motor neurons are within the vagus nerve and pelvic splanchnic nerves.

• The vagus nerve (X) innervates the superior region of the ureter, and the pelvic spalanhnic nerves innervate the inferior region of the ureter.

• also are innervated by sensory neurons, which relay sensory input regarding ureter pain (T11-L2 dermatomes)

Mucosa (of ureters)

• formed by a transitional epithelium that is both distensible and impermeable to the passage of urine

• external to the transitional epithelium of the mucosa is the laminate propria, composed of a fairly thick layer of dense irregular connective tissue.

• In areas where the ureter is not filled with urine, the mucosa folds to fill the lumen.

The middle muscularis (of ureters)

• consists of an inner longitudinal and outer circular layer of smooth muscle cells.

• The presence of urine within the renal pelvis causes these muscle layers to contract rhythmically to propel the urine through the ureters into the urinary bladder.

adventitia (of ureters)

• composed of a dispersed array of collagen and elastic fibers within areolar connective tissue.

• Some exertions of the areolar connective tissue layer also anchor the ureter to the posterior abdominal wall.

Urinary bladder (definition)

• an expandable, muscular organ that serves as a reservoir for urine

• positioned immediately posterior to the pubic symphysis.

• (FEMALES) is anterinferior to the uterus and directly anterior to the vagina

• (MALES) is anterior to the rectum and superior to the prostate gland.

• is a retroperitoneal organ

• its superior surface is covered with the parietal peritoneum

• (EMPTY) exhibits an inverted pyramidal shape
  (FULL) distends superiorly until it assumes an oval shape.

Trigone

A posteroinferior triangular area of the urinary bladder wall

• Trigone is formed by imaginary lines connecting the 2 ureter openings and the uretheral opening.

• remains immobile as the urinary bladder fills and evacuates.

• It functions as a funnel to direct urine into the urethra as the bladder wall contracts to eliminate the stored urine.

• Because the ureters and urethra form the 3 points of this triangular region, inflections are more common within this area.

4 tunics that form the wall of the bladder:

• muscosa

• submucosa

• muscularis

• adventitia

Innermost mucosa of the bladder

• adjacent to the bladder lumen

• formed by a transitional epithelium, which accommodates the shape changes occurring with distention, and by a highly vascularized laminate propria (composed of areolar connective tissue) that supports the mucosa.

• mucosal folds allow for even greater dissension.

• Within the trigone region, the mucosa is smooth, thick, and lacking mucosal folds.

Submucosa of the bladder

• lies immediately external to the mucosa

• formed by dense irregular connective tissue that supports the urinary bladder wall.

muscularis of the bladder

formed by 3 layers of smooth muscle collectively called the detrusor muscle.

these smooth muscle exhibit such complex orientations that it is difficult to delineate individual layers in histology sections.

At the neck of the urinary bladder, an involuntary internal urethral sphincter is formed by the smooth muscle that encircles the urethral opening.

adventitia of the bladder

• outermost layer of areolar connective tissue

• covers the urinary bladder

• peritoneum covers only the superior surface of the urinary bladder.

Urethra (definiton)

• epithelial-lined fibromuscular tube that extends from the anteroinferior surface of the urinary bladder to the urethral opening.

• transports urine to the exterior of the body.

2 urethral sphincters restrict the release of urine until the pressure within the urinary bladder is

high enough and both involuntary and voluntary activities are activated to relate the urine.

Internal uretheral sphincter

• involuntary

• superior

• composed of smooth muscle

• surrounds the neck of the bladder

• controlled by the autonomic nervous system

external urethral sphincter

• inferior to the internal

• composed of skeletal muscle fibers within the urogenital triangle.

• voluntary

• controlled by the somatic nervous system (frontal lobe of the cerebral cortex)

• the muscle children learn to control when they become toilet trained

• male and female urethera differ in length and morphology.

Female Urethra

• function is to transport urine from the urinary bladder to exterior of the body.

• lumen is lined by transitional epithelium (near its junction within the bladder) and then by nonkeratinized stratified squamous epithelium along most of its length.

• approximately 4 centimeters (1.6 inches) long.

• opens to the outside of the body at the external urethral orifice located in the perineum.

Male urethra

• functions in both urinary & reproductive functions because in saves as a passageway for both urine and semen.

• approximately 19 centimeters (7.5 inches) long

• partitioned into 3 segments: prostatic urethra, membranous urehtra, spongy urethra

prostatic urethra (in male urethra)

• approximately 3.5 centimeters (1.5 inches) in length

• most dilatable portion of the urethra

• extends through the prostate gland immediately inferior to the bladder, where multiple small prostatic ducts enter it.

• lined by a transitional epithelium

• 2 smooth muscle bundles surround the mucosa: an internal longitudinal bundle & external circular bundle.

• external circular muscle bundles are a continuation of the thickened, circular region of the internal urethral sphincter at the bladder outlet.

membranous urethra (in male urethra)

• shortest and least dilatable portion of the male urethra.

• extends from the inferior surface of the prostate gland

• surrounded by skeletal muscle fibers that from the external urethral sphincter of the urinary bladder.

• epithelium is often either stratified columnar or pseudostratified columnar

spongy urethra (in male urethra)

• longest part of the male urethra at approximately 15 centimeters long (about 6 inches)

• encased within a cylinder of erectile tissue in the penis called corpus spongiosum and it extends to the external urethral orifce.

• proximal part is lined by a pseudostratified columnar epithelium

• distal part has stratified squamous epithelial lining.

Micturition

the expulsion of urine from the bladder.

2 reflexes associated:

• storage reflex

• micturition reflex

reflexes are regulated by the sympathetic and parasympathetic divisions of the autonomic nervous system.

(for micturition)Innervation by the parasympathetic division is from the

micturition center located in the pons and extends from the spinal cord segments S2-S4 in the pelvic splanchnic nerves to the detrusor muscle of the urinary bladder and internal urethral sphincter.

the pelvis splanchnic nerves cause

contraction of the detractor muscle and relaxation of the internal urethral sphincter so that urine can be expelled.

the parasympathetic division stimulates

micturition

The external urethral sphincter is innervated by

the somatic nerves system via the pudendal nerve (S2-S4 spinal cord)

the pudendal nerve voluntarily contracts this sphincter to prevent urination.

Storage Reflex

Vary motor output conducted by sympathetic axons cause smooth muscle cells of the

• detrusor muscle of the urinary bladder wall to relax, which allows the bladder to accommodate the urine

• the internal urethral sphincter to contract, so that urine is retained within the bladder,

• The skeletal muscle of the external urethral sphincter is also continuously stimulated by motor output along the pudendal nerve so it remains contract.

Micturition Reflex

• When the volume of urine retained within the urinary bladder reaches approximately 200 to 300 mL, the bladder becomes distended to a degree that stretch receptors in the bladder wall are activated.

• These stretch receptors (a type of mechanoreceptor) initiate sensory input through visceral sensory neurons to stimulate the micturition center within the pons.

• The micturition center alters motor output relayed down the spinal cord and through the pelvic splanchnic nerves (which are parasympathetic nerves).

• Parasympathetic stimulation causes the smooth muscle cells composing the detrusor muscle to contract and the internal urethral sphincter to relax. In infants, urination occurs at this point because they lack voluntary control of the external urethral sphincter.

• The sensation of having to urinate is relayed along sensory pathways to the cerebral cortex.

An indviduals’s conscious decision to urinate is due to

altering signals relayed from the cerebral cortex through the spinal cord and along the pudendal nerve to cause the relaxation of the external urethral sphincter.

Expulsion or urine is facilitated by the voluntary contraction of muscles in the abdominal wall and breathing muscles as part of the Valsava maneuver.

Upon emptying of the urniary bladder (all but about 10 mL) the detrusor muscle relaxes, and the neurons of the micturition reflex center are inactivated, while those of the storage reflex are activated.

If an individual does not urinate at the time of the 1st micturition reflex,

the detrusor muscle relaxes as a consequence of the stress-relaxation response of smooth muscle (see section 10.10d). The urinary bladder continues to fillwith urine, and the micturition reflex is initiated again after another 200-300 mL of urine is added. This cycle continues until there is between 500 mL and 600 mL. At this point, urination occurs without conscious control.

Additionally, an individual may choose to empty the urinary bladder prior to the initiation of the micturition reflex by contracting the abdominal muscles as part of the Valsalva maneuver, which compresses the bladder. This compression of the bladder stimulates stretch receptors within the bladder wall and the micturition reflex is initiated.