Lecture 11: The Urinary System

Question 1

what is urine

Answer 1

-clear, sterile liquid, different substnaces
-95% water and 5% solutes
-concentration dpends on: osmotic movement of H2O across walls or tubules and collecting ducts

Question 2

what are the nitrogenous wastes (solutes found in urine)

Answer 2

-urea: from amino acid breakdown; largest solute component
-uric acid: from nucleic acid metabolism
-creatinine: from metabolite of creatine phosphate

Question 3

what are some other normal solutes foundin urine

Answer 3

-Na+, K+, PO43–, and SO42–, Ca2+, Mg2+ and HCO3–
-abnormally high concentrations of any constituent, or abnormal componenets such as blood proteins, WBCs, and bile pigments, may indicate pathology

Question 4

what are some abnormal urinary constituents (components)

Answer 4

albumin, glucose, RBCs, ketone bodies, bilirubin, urobilinogen, casts, microbes

Question 5

What is glucose (in urine)

Answer 5

Presence of glucose in urine-glucosuria (gloo-kö-SOO-ré-a)-usually indicates diabetes mellitus. Occasionally caused by stress, which can cause excessive epinephrine secretion. Epinephrine stimulates breakdown of glycogen and liberation of glucose from liver.

Question 6

What are RBCs (in urine)

Answer 6

Presence of red blood cells in urine-hematuria (hem-a-TOO-re-a)— generally indicates pathological condition. One
cause is acute intlammation or urinary organs due to disease or irritation trom kidney stones. Other causes: tumors, trauma, kidney disease, contamination of sample by menstrual blood.

Question 7

What are ketone bodies (in urine)

Answer 7

High levels of ketone bodies in urine-ketonuria (ke-to-NOO-re-a) —may indicate diabetes mellitus, anorexia,
sorvation, or too lucie carDon vorate in dier

Question 8

What is bilirubin (in urine)

Answer 8

When red blood cells are destroyed by macrophages, the globin portion of hemoglobin is split off and heme is converted to biliverdin. Most biliverdin is converted to bilirubin, which gives bile its major pigmentation. Above-normal level of bilirubin in urine is called bilirubinuria

Question 9

What is urobilinogen (in urine)

Answer 9

Presence of urobilinogen (breakdown product of hemoglobin) in urine is called urobilinogenuria (‘-rö-bi-lin’ -o-je-NOO-re-a). Trace amounts are normal, but elevated urobilinogen may be due to hemolytic or pernicious anemia, infectious hepatitis, biliary obstruction, jaundice, cirrhosis, congestive heart failure, or infectious mononucleosis.

Question 10

What are casts (in urine)

Answer 10

Casts are tiny masses of material that have hardened and assumed shape of lumen of tubule in which they formed, from which they are flushed when filtrate builds up behind them. Casts are named after cells or substances that compose them or based on appearance (for example, white blood cell casts, red blood cell casts, and epithelial cell casts that contain cells from walls of tubules).

Question 11

What are microbes (in urine)

Answer 11

Number and type of bacteria vary with specific urinary tract infections. One of the most common is E. coli. Most common fungus is yeast Candida albicans, cause of vaginitis. Most frequent protozoan is Trichomonas vaginalis, cause of vaginitis in females and urethritis in males.

Question 12

what are the 4 different normal physical characteristics of urine

Answer 12

1. colour and transparency
2. odor
3. pH
4. specific gravity

Question 13

what is normal colour and trnasparency of urine

Answer 13

-clear/transparent
-cloudy may indicate urinary stract infection
-pale to deep yellow from urochome: pigment from hemoglobin breakdown, yellow colour deepends with increased concentration
-abnormal colour: (pink, brown, smoky) can be cause by certain foods, bile pigments, blood, drugs

Question 14

what is normal odor of urine

Answer 14

-slightly aromatic when fresh
-develops ammonia odor upon standing: bacteria metabolize urea
-may be altered by some drugs or vegetables
-disease may alter smell: pts with diabetes may have acetone smell to urine

Question 15

what is the normal pH or urine

Answer 15

-Urine is slightly acidic (~pH 6, with range of 4.5 to 8.0)
-Acidic diet (protein, whole wheat) can cause drop in pH
-Alkaline diet (vegetarian), prolonged vomiting, or UTIs can cause
an increase in pH

Question 16

what is the specific gravity of normal urine

Answer 16

-Ratio of mass of substance to mass of equal volume of water
(specific gravity of H2O = 1)
-Ranges from 1.001 to 1.035

Question 17

where does urine trnasportation, storage, and elimination take place

Answer 17

takes place in urinary tract
-ureters
-urinary bladder
-urethra

Question 18

what are the ureters

Answer 18

-Paired muscular tubes
-Connect kidneys to urinary bladder
-Begin at renal pelvis and pass over psoas major
-Penetrate posterior wall of urinary bladder at oblique angle
-Ureteric orifices: slit-like rather than rounded, which Prevents backflow of urine when urinary bladder
contracts

Question 19

describe the three layers of the ureter wall

Answer 19

1. Inner mucosa – transitional epithelium and lamina propria
2. Middle muscularis – longitudinal and circular bands of smooth muscle
3. Outer Adventitia (CT layer) – continuous with fibrous capsule and peritoneum

Question 20

what is the peristaltic actions of smooth muscles in the urinary system

Answer 20

~ every 30 seconds
-Begin at renal pelvis
-Sweep along ureter
-Forcing urine toward urinary bladder
-Rate of peristalsis adjusted to rate of urine formation

Question 21

describe the anatomy of the urinary bladder

Answer 21

-Muscular sac for temporary storage of urine
-On pelvic floor posterior to pubic symphysis
-Males: prostate inferior to bladder neck
-Females: anterior to vagina and uterus
-Has openings for ureters and urethra
-Trigone: Smooth triangular area outlined by openings for ureters and urethra, Infections tend to persist in this region

Question 22

describe the layers of the urinary bladder

Answer 22

1. Mucosa: transitional epithelial mucosa
2. Muscular layer: thick detrusor muscle which contains three layers of smooth muscle: Inner and outer longitudinal layers with circular middle layer
3. Fibrous adventitia, except on superior surface where it is covered by peritoneum

Question 23

what is the urine storage capacity

Answer 23

the bladder:
-Collapses when empty and rugae appear
-Expands and rises superiorly during filling without significant rise in internal pressure
-Moderately full bladder is ~12 cm long and can hold ~ 500 ml (1 pint)
-Can hold twice that amount if necessary but can burst if overdistended

Question 24

what is the urethra and what does its epithelium consist of

Answer 24

-Muscular tube that drains urinary bladder
Epithelium – consists of:
-Mostly pseudostratified columnar epithelium, except:
-Transitional epithelium (urothelium) near bladder
-Stratified squamous epithelium near external urethral orifice

Question 25

describe the two sphincters of the urethra

Answer 25

1. internal urethral sphincter: involuntarily controls opening and closing of urethra
2. external urethral sphincter: in deep muscles of perineum (voluntarily controls opening and closing of urethra

Question 26

what does the male urethra carry and what are its regions

Answer 26

-Carries semen and urine; ~ 20 cm long
Three Regions:
1. Prostatic urethra (2.5 cm): within prostate
2. Membranous urethra – intermediate part (2 cm): passes through urogenital diaphragm from prostate to beginning of penis
3. Spongy urethra (15 cm): passes through penis; opens via external urethral orifice

Question 27

describe the female urethra

Answer 27

-3–4 cm; tightly bound to anterior vaginal wall; carries urine
-External urethral orifice: anterior to vaginal opening; posterior to clitoris

Question 28

what is the comparison between the male and femlae urethra

Answer 28

-it is 5x longer in males than females
-it is dividied into three segments in males but is only one short tube in females
-the urethra is a common duct for the urinary and reproductive system in males. these two system are entirely seperate in females

Question 29

what is micturition (urination or voiding)

Answer 29

-Discharge of urine involves voluntary and involuntary muscle contractions
-Stretch receptors trigger a spinal reflex, which we learn to control in childhood
-Urethra carries urine from the internal urethral orifice to the exterior of the body

Question 30

describe micturition in infants

Answer 30

-Lack voluntary control over urination
-Necessary corticospinal connections are not yet established

Question 31

what is incontinence

Answer 31

-Inability to control urination voluntarily
-May be caused by trauma to internal or external urethral sphincter

Question 32

describe the urine voiding reflex

Answer 32

-Involves spinal reflexes and pontine micturition center
-When bladder contains about 200 mL of urine, urge to urinate appears
-Stretch receptors send impulses to pontine micturition center (PMC), initiating sacral spinal reflexes: detrusor contracts, internal & externa; urethral sphincters relax

Question 33

describe the urine storage reflex

Answer 33

I-nvolves spinal reflexes and pontine storage center
-Afferent impulses from stretch receptors in urinary bladder stimulate
sympathetic outflow: inhibiting contraction of detrusor & Stimulating contraction of internal urethral sphincter
-pontine storage center inhibits urination by: decreasing parasympathetic activity, and contracting external urethral sphincter

Question 34

what is the formation of dilute or concentrated urine

Answer 34

-Medullary osmotic gradient can now be used to form
dilute or concentrated urine
-Without gradient, would not be able to raise urine concentration > 300 mOsm, to conserve water
-Overhydration produces large volume of dilute urine
-ADH production decreases; urine falls ~100 mOsm
-If aldosterone (not shown) present, DCT and collecting duct cells remove Na+ and other ions are removed → H2O dilute to ~50 mOsm

Question 35

describe the formation of dilute urine

Answer 35

-Glomerular filtrate and blood have same osmolarity at 300 mOsm/L
-But tubular osmolarity changes due to medullary conc. gradient

-When dilute urine is formed, osmolarity in the tubule:
* Increases in the descending limb
* Decreases in the ascending limb
* Decreases more in the collecting duct

-Thick Ascending Limb: Symporters actively resorb Na+, K+, Cl–, Low water permeability, Solutes leave & water stays in tubule

-Collecting Duct: Low water permeability in absence of ADH

Question 36

what causes the formation of concentrated urine

Answer 36

-Dehydration produces small volume of concentrated urine
-Maximal ADH is released; urine rises to ~1200 mOsm
-Severe dehydration: 99% water reabsorbed and returns to the blood
-Movement of H2O also carries urea into the medulla, contributing to its osmolarity

Question 37

describe the formation of concentrated urine

Answer 37

-juxtamedullary nephrons with long loops
-Osmotic gradient is created by the countercurrent multiplier
-Solutes pumped out of ascending limb, but water stays in tubule
-Medulla osmolarity is increased
-In presence of ADH, collecting ducts become very permeable to
water
-Tubular fluid there becomes very concentrated

Question 38

what are diuretics

Answer 38

-Chemicals that enhance urinary output:
-ADH inhibitors, such as alcohol
-Na+ reabsorption inhibitors (and resultant H2O reabsorption), such as caffeine or drugs for hypertension or edema

-Loop diuretics inhibit medullary gradient formation
-Osmotic diuretics: substance not reabsorbed, so water remains in urine; for example, in diabetic patient, high glucose concentration pulls water from body

Question 39

what are urinary tract infections (UITs)- causes

Answer 39

-improper toilet habits: wiping bacl to front after defecation, short urethra of females can allow fecal bacteria to easily enter urethra
-most UTIs occur in sexually active women: 40% of women get urinary tract infections. intercourse drives bacteria from vagina and external genital region toward bladder; use of spermicides magnifies problem

Question 40

what is urethritis

Answer 40

inflammation of urethra

Question 41

what is cysitis

Answer 41

inflammation of bladder

Question 42

what is trigonitis

Answer 42

inflammation of trigone
-symptoms: painful urination, pelvic pain, blood in urine, urgent need to urinate
-causes:
a) hormonal imbalances, estrogen and progesterone may play a role in the cellular changes that occur with pseudomembranous trigonitis
b) prolong use of catheter irritates the floor
c) recurrent UTIs

Question 43

what is anuria

Answer 43

abnormally low urinary output (less than 50ml/day)
-may indicate that glomerular blood pressure is too low to cause filtration
-renal failure and anuria can also result from situations in which nephrons ston functioning
-examples: acute nephritis, transfusion reactions, and cursh injuries

Question 44

describe the effects of aging on the urinary system

Answer 44

Age-related changes:
-Nephrolithiasis (formation of calculi)
-Decrease in number of functional nephrons
-Reduction in GFR
-Reduced sensitivity to ADH

-Problems with urinary reflexes:
-External sphincter loses muscle tone
-Control of urination can be lost due to a stroke, Alzheimer’s disease, and other CNS problems
-In males, urinary retention may develop

Question 45

Beta oxidation and the urinary system

Answer 45

The kidney is a highly metabolic organ and requires a large amount of ATP to maintain its filtration-reabsorption function, and mitochondrial fatty acid β-oxidation serves as the main source of energy to meet its functional needs