Urinary System

Organs of the Urinary System

• Kidneys - remove substances from the blood (filters blood)

• ureters - transport urine from kidneys to bladder (muscular tubes)

• urinary bladder - urine storage

• urethra - conveys urine outside

Function of the Urinary SYstem

• regulate aspects of homeostasis

  • water balance and electrolytes

  • acid-base balance in the blood

  • blood pressure (with the enzyme renin)

  • red blood cell production (with the hormone erythropoietin)

  • activation of vitamin D

• Elimination of waste products

  • nitrogenous wastes, toxins, drugs

• if urine has…

  • glucose→ diabetes

  • blood→ damaged tissue

  • proteins→ damaged kidneys

Location of the Kidneys

• Against the dorsal body wall

• In retroperitoneal cavity

• at the level of T12 to L3 (spine)

• The right kidney is slightly lower because of the liver

• Lateral side is convex, medial is concave, kidneys sit in a depression called renal sinus (indentation)

• Attached to the ureters, renal blood vessels, and nerves enter at renal hilus (opening w/ blood vessels)

• Atop each kidney is an adrenal gland (produces cortisol)

Urinary Bladder

• smooth, collapsible, muscular sac

• temporarily stores urine

• Holds 1L of urine

• bladder can stretch

• Trigone—three openings

  • two from the ureters

  • one to the urethra

Urinary Bladder wall

• Three layers of smooth muscle (called detrusor muscle)

• Walls are thick and folded in an empty bladder (2-3 inches)

• Bladder can expand significantly without increasing internal pressure (more than 5 inches and more than 1L of urine)

Urethra

• thin-walled tube that carries urine from the bladder to the outside of the body by peristalsis

• Release of urine is controlled by two sphincters

  • internal urethral sphincter (involuntary)

  • external urethral sphincter (voluntary)

Urethra Gender Differences

• Length

  • females - 3-4cm (1 inch)

  • males - 20cm (8 inches)

• Location

  • females - along wall of the vagina

  • Males - through the prostate and penis

• Function

  • females - only carries urine

  • Males - carries urine and is a passageway for sperm cells

UTI (Urinary Tract Infections)

• An infection in any part of the urinary system, the kidneys, bladder, or urethra

• Urinary tract infections are more common in women. They usually occur in the bladder or urethra, but more serious infections involve the kidney

• A bladder infection may cause pelvic pain, increased urge to urinate, pain with urination, and blood in the urine. A kidney infection may cause back pain, nausea, vomiting, and fever

• Women are at greater risk of developing a UTI than men are

• Common treatment is with antibiotics

Regions of the kidney

• Renal cortex—outer region

  • contains many cells that produce urine

• Renal medulla—inside the cortex

• Renal pelvis—inner collecting tube

  • collects urine produced by pyramids

• Renal capsule—protects kidney

• Medullary pyramids—triangular regions of tissue in the medulla

• Renal columns—extensions of cortex-like material inward

• Calyces—cup-shaped structures that funnel urine towards the renal pelvis

Nephrons

• The structural and functional units of the kidneys

• Responsible for forming urine

• Each kidney has over 1 million nephrons

• Main structures of the nephrons

  • Glomerulus

  • Renal tubule

    • made of 3 parts

Renal Tubule

• About 3cm long

• Proximal convoluted tubule (PCT)

• Loop of Henle

• Distal convoluted tubule (DCT)

Urine Formation Processes

• glomerular filtration

• tubular reabsorption

• tubular secretion

Filtration

• nonselective passive transport

• filtrate is collected in the glomerular capsule and leaves via the renal tubule

• The glomerulus is the site of blood filtration where it filters water and other substances from the bloodstream into the Bowman’s capsule. As blood flows through the glomerulus, blood pressure pushes water and solutes from the capillaries into the capsule through a filtration membrane.

  • The filtration membrane keeps blood cells and large proteins in the bloodstream

  • Blood cells cannot pass out to the capillaries

    • blood should not be in urine

Reabsorption

• The peritubular capillaries reabsorb several materials by moving nutrients and water back into the blood stream

  • Some water

  • glucose

  • amino acids

  • ions

• Some reabsorption is passive, most is active

• Most reabsorption occurs in the proximal convoluted tubule (PCT)

• Materials that are not reabsorbed

  • nitrogenous waste products (this is what should be in your urine)

    • urea

    • uric acid

    • creatinine

      • Chemicals created through the breakdown of proteins

  • Excess water

Secretion — Reabsorption in reverse

• Some materials move from the peritubular capillaries into the renal tubules

  • hydrogen and potassium ions

  • Creatinine

  • Drugs

• Materials left in the renal tubule move toward the ureter

• Waste ions and hydrogen ions are secreted from the blood to complete the formation of urine

• Secretion primarily happens in the proximal convoluted tubule but also in smaller amounts in the DCT or distal convoluted tubule and collecting duct.

• The secreted ions combine with the remaining filtrate and become urine.

• The urine flows out of the nephron tubule into a collecting duct

• It passes out of the kidney through the renal pelvis, into the ureter, and down to the bladder.

Characteristics of urine used for Medical Diagnosis

• colored somewhat yellow due to the pigment of urochrome (from the destruction of hemoglobin—RBCs) and solutes

  • When RBCs die, they release a substance called bilirubin, which is then converted into uroschrome by gut bacteria to give its yellow color

• sterile (no bacteria)

• slightly aromatic

  • if you have diabetes, urine will smell fruity

• Normal pH of around 6 (varies 4.5-8)

• Specific density of 1.001 to 1.035 since 95% of urine is water

• The typical urine volume for an adult is between 750-2000 mL a day

• Solutes normally found in urine

  • sodium and potassium ions

  • chloride ions

  • small amounts of other ions, hormones, metabolites, and pigments

  • urea (waste product from liver breaking down proteins)

  • uric acid

  • creatinine

• Solutes NOT normally found in urine

  • glucose (diabetes)

  • Blood proteins (pregnancy, HBP)

  • Red blood cells (bleeding—trauma, kidney stones)

  • Hemoglobin (anemia)

  • White blood cells (pus) (UTI)

  • Bile (liver disease, hepatitis)
    

Pregnancy Tests

• urine may also contain other chemicals that can be detected that are produced by the placenta

• hormones present in a pregnant woman are detectable in urine

Micturition (voiding)

• The act of emptying the bladder

• The detrusor muscle in the bladder wall contracts, causing the internal urethral sphincter to relax and allow urine to flow out.

• Activation is from an impulse sent to the spinal cord and then back via the pelvic splanchnic nerves

• The external urethral sphincter controlled by the pudendal nerve is the muscle that voluntarily controls the flow of urine by relaxing to allow urination.

  • Both sphincter muscles must open to allow voiding

Maintaining water balance

• normal amount of water in the human body

  • Young adult females—50%

  • Young adult males—60%

  • Babies—75%

  • Old Age—45%

• Water is necessary for many body functions and levels must be maintained

• Water intake must equal water output

• Sources for water intake

  • ingested foods and fluids

  • water produced from metabolic processes

• Sources for water output

  • Vaporization out of the lungs

  • lost in perspiration

  • leaves the body in the feces

  • urine production

• Coffee dehydrates or gets rid of water (diuretic)

• Dilute urine is produced if water intake is excessive

• Less urine (concentrated/darker) is produced if large amounts of water are lost

• Proper concentrations of various electrolytes must be present

Developmental Aspects of the Urinary System

• Control of the voluntary urethral sphincter does not start until age 18 month (around 2 years old)

  • longer for males

• Urinary infections are the only common problems before old age

Aging and the Urinary system

• There is a progressive decline in urinary function

• The bladder shrinks with aging

• Urinary retention is common in males

  • frequent urinations even during the night.

Main function of urinary system

The main functions of the urinary system are to filter waste products from the blood, produce urine, remove excess water and salts from the body, maintain electrolyte balance, regulate blood pressure, and contribute to the body's overall fluid balance by excreting waste products like urea through urine.

Retroperitoneally meaning

"Retroperitoneally" means "behind the peritoneum," referring to a position in the abdomen located posterior to the peritoneal cavity, the lining of the abdominal cavity; essentially, situated behind the abdominal lining.

Hormone that regulates formation of urine

• The hormone that regulates the formation of urine is Antidiuretic Hormone (ADH), also known as vasopressin

  • it is produced in the hypothalamus and released by the posterior pituitary gland.

• ADH primarily controls the amount of water reabsorbed by the kidneys, thus regulating the concentration and volume of urine produced.

• When ADH levels are high, more water is reabsorbed, leading to less urine production, and vice versa.