Urinary System Learning Objectives

Describe the location and structural features of the kidney.

• Smooth, reddish-brown, bean-shaped

• Enclosed in fibrous capsule surrounded by fat

• Located between 12th thoracic vertebrae and 3rd lumbar vertebrae

• Retroperitoneal (behind the abdominopelvic cavity)

• Left kidney is slightly higher than right kidney

• Two main sections are the renal cortex and renal medulla

  • Within these sections are renal pyramids, renal columns

Describe the structure of the nephron.

• Two main structures are the renal tubules and renal corpuscle.

  • Renal tubules -- contains proximal and distal convoluted tubules and nephron loop (aka: Loop of Henle)

  • Renal corpuscle — contains glomerulus and glomerular capsule (aka: Bowman’s capsule)

    • Glomerulus is a bunch of small capillaries

Identify and describe the major functions responsible for the production of urine.

1. Glomerular filtration

• Filters cells and proteins out of blood plasma using hydrostatic pressure (passive process)

• Regulated by intrinsic controls (renal autoregulation) and extrinsic controls (nervous and endocrine systems) to control GFR (glomerular filtration rate)

2. Tubular reabsorption

• Moves certain substances from tubular fluid into blood, within the peritubular capillary

  • From there, it reabsorbs all amino acids and glucose, most of water, and electrolytes as needed

• Leftover products not reabsorbed become urine

3. Tubular secretion

• Moves certain substances from blood in peritubular capillary to tubular fluid (opposite of tubular reabsorption)

• Important for substance disposal, eliminating unwanted substances, removing excess potassium, and controlling blood pH

Describe how antidiuretic hormone and aldosterone influence volume and concentration of urine.

ADH and aldosterone — causes increase in water reabsorption, effectively decreasing urine output and making it more concentrated

List and describe the factors that influence filtration pressure.

Glomerular hydrostatic pressure

• Blood pressure in glomerulus that pushes water and sodium out of the blood

• Pushes fluid outward, increasing filtration

Glomerular capsule colloid osmotic pressure

• Filtration membranes block proteins from entering

• Draws water toward area with higher solute concentration

Surface area available for filtration

• Larger filtration surface provides more area for fluid movement and therefore less pressure

Describe the structure and functions of ureters, urinary bladder, and urethra.

Ureters

• ~30 cm of 3 layered walls (mucous, muscular, and fibrous layers)

• Transport urine from kidney to urinary bladder

Urinary bladder

• Hollow and muscular organ

• Has trigone at bottom with opening at each of its angles

• Has rugae to allow stretching

• Has 4 layers of walls (mucous, submucous, muscular, serous)

• Stores urine and forces it into urethra

Urethra

• Carries urine from bladder to outside body

• Men: ~8 in. (spread across 4 sections)

• Women: ~1.5 in.

Differentiate between contents of different substances in plasma and in urine.

Plasma — water, proteins, glucose, amino acids, uric acid, creatinine

Urine — water, trace amino acids, urea, uric acid, creatinine

Describe the normal characteristics and composition of urine.

• Contains water, urea, uric acid, trace amino acids and electrolytes

• Yellow, slightly acidic

• Generally not much odor unless sitting for a while (then smells like ammonia)

• Specific gravity 1.001-1.035

List the most important waste products excreted by kidneys.

Urine (more specifically, urea, uric acid, creatinine, electrolytes)

Describe the micturition reflex center.

• In the spinal cord

• Sends parasympathetic motor impulses to detrusor muscle

  • Makes detrusor muscle contract as part of 3rd step of micturition