Urinary System

• Urinary System

  Functions: Excretion, Ridding waste, Filtering blood, Forming urine, Stabilizing electrolytes, Maintaining blood pressure, Vitamin D
• Urinary System

  • Composed of kidneys and urinary tract: Kidneys, Ureters, Bladder, Urethra

  
• Urinary System development

  Mesoderms develops into kidneys during 3rd to 8th week of fetal development

  
• Urinary System


  Works with the cardiovascular system
• Kidneys


  • Both kidneys are retroperitoneal (behind perineum), Right kidney slightly inferior due to position of liver, Left kidney placed between T12-L3, Protected somewhat by last ribs

  
• Kidneys


  Filters blood to remove metabolic waste and eliminates it through urine
• Kidneys' homeostatic processes


  Regulates fluid and electrolyte balance through osmolarity, Regulates acid-bases and blood pH, Maintains blood pressure by controlling blood volume

  
• Kidneys

  • Constricts/dilates blood vessels, Secretes enzyme renin, Regulates erythropoiesis (RBC) by releasing hormone erythropoietin, Helps with glomerulus to eliminate waste and returning vital molecules, Regulates blood glucose, Detoxifies substances, Excretes, Activates vitamin D
• Kidneys' blood supply

  Receives 20-25% of cardiac blood output, Abdominal Aorta → Renal Artery → Segmental Arteries → Interlobar Artery → Arcuate Artery → Cortical Radiate Artery → Afferent Arteriole → Glomerulus → Efferent Arteriole → Peritubular Capillaries → Peritubular Venules → Cortical Radiate Vein → Interlobar Vein → Renal Vein → Inferior Vena Cava

  
• Kidneys' nerve supply

  Carries sympathetic flow by decreasing blood to maintain pressure, where blood will go to other organs for fight-or-flight, Regulates blood flow

  
• Kidney anatomy

  • Protected by 3 outer connective tissue layers: Renal Fascia, Adipose Capsule, Renal Capsule

  
• Renal Hilum/Hilus

  Medial and Indented surface, Obtains the calyces, renal pelvis, Where the renal artery, vein, lymphatics, nerves, and ureter extends from

  
• Kidney internal regions

  • Renal Cortex, Renal Columns, Renal Medulla, Renal Pyramids, Renal Pelvis

  
• Nephrons


  The functional unit of kidney, Responsible for urine formation and maintaining body's internal balance through filtering, reabsorption, and secretion of molecules

  
• Nephron types

  • Cortical Nephrons, Juxtamedullary Nephrons
• Renal Corpuscle

  Filters blood through Glomerulus and Glomerular/Bowman's Capsule, Filtrate exits the glomerulus to capsular space, into the renal tubule lumen

  
• Renal Tubule

  Receives filtrate to be further altered in 3 regions: Proximal Tubule, Nephron Loop/Loop of Henle, Distal Tubule
• Juxtaglomerular Apparatus (JGA)


  • Macula Densa, Granular/Juxtaglomerular Cells, Extraglomerular Mesangial Cells
• Collecting System

  Series of ducts with its own structural and functioning tubules, Second to last in receiving filtrate to reabsorb water and excretes in the form of urine either concentrated or diluted
• Filtration

  Occurs in the glomerulus of nephron, 60x a day, Filters substances based on size but does not filter some effectively and some need ATP, Macromolecules are not filtered, Smaller molecules are filtered
• After blood filtration, the efferent arteriole carries the blood out, containing both filtered & unfiltered components still
• Filtrate

  Fluid substances successfully filtered becomes filtrate that is organized to be sent to their right destination
• Urine formation

  1. Filtration in glomerulus of nephron

  2. Reabsorption in renal tubule and collecting duct

  3. Secretion in renal tubule and collecting duct

  
• Filtration

  • Occurs in the glomerulus of nephron, 60x a day
  • Filter refers to substances being selectively separated from blood and passed into the tubule for further processing
  • Blood pressure forces it out of blood
  • Where urine formation begins by the filtration of blood plasma fluid, entering from the afferent arteriole/renal artery
  • Filters its substances based on size but does not filter some effectively and some need ATP
  • Macromolecules are not filtered (RBC, proteins)
  • Smaller molecules are filtered (water, electrolytes, acids, bases, organics, metabolic wastes)
  • After blood filtration, the efferent arteriole carries the blood out, containing both filtered & unfiltered components still
• Filtrate

  • Fluid substances successfully filtered becomes filtrate that is organized to be sent to their right destinations
  • The useful, dissolved substances such as water, amino acids, glucose, nutrients are typically directed into the capsular space, to the tubule but gets reabsorbed in accordance to homeostasis
  • Some nitrogenous wastes are filtered as well such as urea, creatine, uric acid but remains in the tubule
  • The useless, waste substances may enter the tubule directly or may also be actively secreted from the peritubular capillaries connected to the efferent arteriole for elimination
• Glomerular filtration barrier

  • Fenestrated Glomerular Capillary Endothelial Cells (pores prevent blood cells, platelets, proteins from exiting)
  • Basal Lamina (made of collagen fibers that's negatively charged for repel)
  • Podocytes (visceral layer, have finger-like projections called pedicals that forms its slits, wrapping over the capillary, allows the pass of small substances through the slits to capsular space)
• Reabsorption

  1. Occurs in the renal tubule and collecting duct

  2. Most of the filtrate's useful components of water, nutrients, glucose, ions enters in the renal tubule lumen to be modified by being reabsorbed into the bloodstream

  3. Diffuses into a peritubular capillary network that merges into venules, forming the renal vein eventually being returned to circulation

  
• Secretion

  1. Occurs in the renal tubule and collecting duct

  2. Added/missed; useless, waste, and excess components such as salts, urochrome (urine color), urea, creatine, drugs are secreted from the peritubular capillaries for elimination & maintaining balance in body

  3. Diffuses into the renal tubule to be excreted through urine

  
• Urine composition

  • Water
  • Sodium
  • Potassium
  • Chloride
  • Hydrogen
  • Phosphate
  • Metabolic Waste
  • Urea
  • Uric Acid
  • Creatinine
  • Ammonia
  • Bicarbonate
  • Calcium
  • Magnesium
• 1. 2 L of urine is excreted
• Urinalysis


  • A tool that analyzes urine to detect abnormalities
  • Urine color should typically be yellow from the pigment called urochrome to breakdown hemoglobin
  • Darker urine is due to being concentrated with less water
  • Lighter urine is due to being diluted with more water
  • Urine should be translucent, not cloudy (infection or high protein)
  • Fresh urine should have a mild odor, strong odors can be due to diseases, foods, infections
  • pH level should be slightly acidic; 6.0-8.0
  • Gravity depends on amount of solutes to water greater than 1.0, normal range of diluted is 1.001, concentrated is 1.035
• Urine abnormalities

  • Albuminara (presence of albumin, damage to glomerulus where large proteins passes through)
  • Glucosuria (presence of glucose, should be 100% reabsorbed in bloodstream, due to diabetes, excess amounts, renal impairment)
  • Hematuria (presence of RBC, damage from stones, tumors, trauma, sickle disease, infection)
  • Pyuria (presence of WBC)
  • Ketonuria (high ketone bodies, due to fasting, starvation, anorexia, diabetes, little carbohydrates in diet)
  • Bilirubinuria (greater level of bilirubin)
  • Urobilinogenuria (presence of Urobilinogen of hemoglobin breakdown, due to anemia, hepatitis, jaundice, cirrhosis, heart failure)
  • Proteinuria (presence of high proteins, due to high protein intake, kidney stones, dehydration, intense exercise, preeclampsia)
  • Nitrituria (presence of nitrites, due to bacterial infection, UTI)
  • Casts
  • Microbes (bacterial infections such as yeast, vaginitis)
• Renal clearance

  • Rate of kidneys removing substance in blood through urine
  • Substances should be completely filtered, not reabsorbed nor secreted
  • Creatine is one example, remained elevated blood levels indicate kidney impairment, no clearance, filtering

  
• Urinary tract

  1. Ureters (functions to transport urine from renal pelvis through peristalsis, hydrostatic pressure, gravity, begins at 2nd lumbar, behind peritoneum, 3 layers: adventitia, muscularis, mucosa)

  2. Urinary bladder (hollow, disposable organ that functions for expansion and storing urine, held in position by parietal peritoneum, flap opens to allow filling of urine, deflates when empty, inflates into pear-shaped when full, holds 400-800 mL, 3 layers: adventitia, detrusor muscle, mucosa)

  3. Urethra (small opening for the function of draining urine out of the body, surrounded by internal sphincter that only opens when urine passes, external sphincter formed by levator ani muscle that is under voluntary control for urination)

  
• Micturition


  1. Elimination of urine in body through combinations of involuntary and voluntary muscle contractions

  2. When bladder is full, stretch receptors signals are sent to CNS to trigger the reflex of urination

  3. Controlled by the parasympathetic system (stimulates the detrusor muscle to contract and internal sphincter to relax)

  4. Centers in pons

  5. Brain cortex responds to allow external sphincter to also relax
• Kidneys weigh approximately 140 g (about half a pound) each.
• Each kidney is about 10 cm long, 5 cm wide, and 3 cm thick.
• The kidneys are located retroperitonally in the upper part of the posterior abdominal wall.
• The kidneys lie on either side of the vertebral column between T12 and L3.
• The right kidney lies slightly lower than the left because it must accommodate the liver.