16 - Urin: Structure, Function, and Micturition

What are the organs of the urinary system?

2 kidneys

2 ureters (kidney -> bladder)

1 bladder

1 urethra

Where are all of the organs of the urinary system located in relation to the peritoneum?

Located behind the peritoneal lining of the abdomen, therefore, they are all RETROPERITONEAL organs

Which major branch of the aorta supplies the urinary system?

Abdominal aorta

What organs are located on the top of the kidneys?

Adrenal glands

What organs do the gonadal arteries supply?

Reproductive organs (ovaries/testes)

What are the 8 functions of the kidneys?

1. Excrete waste, mostly nitrogenous wastes (urea, creatinine, uric acid, bilirubin->urobilin, toxins, drugs)

2. Regulating blood ionic composition/electrolyte levels

3. Regulating blood pH (retention/excretion of H+ and HCO3)

4. Regulating blood volume (retention/excretion of water)

5. Regulating blood pressure (RAA pathway via juxtaglomerular cells->renin)

6. Maintaining blood osmolarity (conc of solutes in water)

7. Producing hormones (calcitriol -> vit. D, erythropoietin -> rbc prod)

8. Regulating blood glucose (via gluconeogenesis, converting amino acids into glucose)

What are the three layers of tissue surrounding the kidney?

KIDNEY

1. Renal capsule

2. Perirenal fat capsule

3. Renal fascia

OUTSIDE

What is the role of the renal capsule of the kidney?

Consists of collagen

Prevents the kidneys from blowing up due to blood pressure increases

What is the role of the perirenal fat capsule of the kidney?

Consists of adipose tissue

Provides cushioning of the kidney from external forces

What is the role of the renal fascia of the kidney?

Consists of connective tissue

Anchors the kidney to external organs

What would happen to the kidneys if the perirenal fat capsule of the kidney was lost?

Would result in drooping of the kidney, which could result in a kink (bending) of the ureter, resulting in filtrates not being able to exit the kidney

What are the two regions of the kidneys?

Outer cortex

Inner medulla

What structures of the kidneys are part of the inner medulla?

Consists of...

Renal pyramids, large pyramid shaped ducts in the medulla

Renal papilla, tip of the renal pyramid that points towards the renal hilum

Renal columns, separates the renal pyramids

What are nephrons of the kidneys?

The basic functional unit of the kidney, performs filtration

Describe the path of urine flow from the collecting duct of the kidneys to the ureter

Collecting duct -> Papillary duct -> Minor calyx -> Major calyx -> Renal pelvis -> Ureter -> Urinary bladder

What structure marks the turning point of "filtrate" being called "urine"?

The papillary duct, last chance to converse water

What structure are kidney stones most likely to form in?

The renal pelvis, VERY BIG, then becomes very small in the ureter

Where are 3 locations along the urinary system where kidney stones are most likely to be lodged?

1. Ureteropelvic joint -> between ureter and pelvis, where the ureter narrows after exiting the renal pelvis

2. Crossing of iliopsoas muscle -> can be lodged between the muscle in the ureter

3. Ureterovesical junction -> right before ureter enters the bladder, usually the opening is closed

How do kidney stones form?

Occurs when urine is supersaturated with salts and changes to pH occur (usually from calcium salts, uric acid, struvite, or cystine), allowing for precipitates to form

What are two treatments of large kidney stones?

Nephrolithotomy -> surgery

Lithotripsy -> using sound waves to break it down

What is the major risk factor for kidney stones?

Low fluid intake

What is hydronephrosis?

Blockage of the ureters, resulting in an expansion of the renal pelvis

What is hydroureter?

Blockage of the ureters, resulting in an expansion of the ureters

What are the three layers of the muscular tubes of the ureter? What differences exist between the urinary tubes and the GI tubes?

1. Mucosa (consists of urothelium + lamina propria) NO SUBMUCOSA

2. Muscularis (consists of inner longitudinal muscle and outer circular muscle) SWAPPED

3. Adventitia

What force drives urine in the ureters towards the bladder?

Peristaltic contractions by the muscularis of the ureter wall

What prevents urinary reflux from the bladder to the ureters?

A physiological valve, formed by the ureter entering the bladder (ureterovesical junction) at an oblique angle, which results in the walls of the bladder collapsing behind the urine as it heads towards the bladder

What deformity in the ureter would cause urinary reflux?

If the ureters enter the bladder at a straight angle

Where is the bladder located in males?

Anterior to the rectum and superior to the prostate, when full, it extends beyond the tip of the pubic bone

What is the purpose of the bladder?

Stores urine for micturition

What are the three segments of the urethra in males?

prostatic urethra -> Prostate

Pelvic floor muscles (also forms external sphincter) -> membranous urethra

Penile/spongy urethra -> Penis

Where is the bladder located in females?

Anterior to the vagina and inferior to the uterus, when full, it extends beyond the tip of the pubic bone

Is the urethra longer in males or females?

Longer in males

When would a urinary catheter be used in the hospital?

Surgery

Urinary retention or obstruction

Measurement of urinary output (Ins and Outs)

Immobilization for trauma or surgery

What is the significance of differences in urinary anatomy between males and females in relation to catheterization?

In males, there are a lot of twists and turns in the urethra ,as well as being longer in general, which means it may be harder to insert a catheter (can damage membranous urethra, enlargement of prostate), whereas in females, the urethra is a straight shot to the bladder, making it easier to insert a catheter

What is the most common complication of using a urinary catheter?

Contact of catheter with skin near urethra may cause UTIs since many bacteria grow in that area (ex: ecoli, close to anus)

Introduction of these bacteria in the bladder can cause inflammation, aka cystitis

What is a cystitis infection in the urinary system?

Inflammation of the bladder, commonly through the introduction of e.coli

What is a pyelonephritis infection in the urinary system

Inflammation of the kidneys caused by an ascending UTI (commonly e.coli), which can lead to sepsis, shock, and acute renal failure

More common in females due to having a shorter urethra, and the urethra being in close proximity to the anus (contact with e.coli)

What tissue "covers" the bladder superiorly?

The peritoneum, which serves the maintain the bladder's position in the pelvis

What kind of epithelium is the bladder wall lined with? What is the significance of this?

Lined by transitional epithelium, that forms a rugae when empty (switches from cuboidal to flat shape with urine)

Allows for greater storage of urine

What kind of muscle is found on the wall of the bladder?

Involuntary smooth muscle, aka detrusor muscle, which pushes urine into the urethra

What is the bladder trigone?

A section of the bladder bordered by the openings of both of the ureters and the opening of the urethra

Muscles in this area will contract to prevent urinary reflux to reenter the bladder during micturition

What two urethral sphincters are present in the bladder?

Internal urethral sphincter -> Involuntary control/smooth muscle (prevents sperm from entering the bladder in males)

External urethral sphincter -> Voluntary control/skeletal muscle (conscious control of micturition)

What is the micturition reflex?

1. Urine fills the bladder, which is detected by stretch receptors

2. These stretch receptors send signals to the sacral spinal cord

3a. An autonomic parasympathetic reflex is initiated via visceral efferents , which contracts the detrusor muscle, pushing urine into the urethra, and causes the internal urethral sphincter in males to relax

3b. Conscious awareness of "the urge" is sent through the sacral spinal cord, which can initiate the external urethral sphincter to contract or relax

4. If both internal urethral sphincter and external urethral sphincter relax, micturition occurs