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Urinary System. Exercises 40 and 41. Organs of the Urinary System. 2 kidneys Urinary bladder 2 ureters Urethra Primary function is to filter blood, and reabsorb water and needed substances back into blood. Remaining water and wastes are removed in urine.

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urinary system

Urinary System

Exercises 40 and 41

organs of the urinary system
Organs of the Urinary System
  • 2 kidneys
  • Urinary bladder
  • 2 ureters
  • Urethra
  • Primary function is to filter blood, and reabsorb water and needed substances back into blood. Remaining water and wastes are removed in urine.
Regulate blood volume and composition
  • Regulate blood pH
  • Regulate blood pressure
  • Contribute to metabolism
    • Calcitriol
    • Erythropoietin
    • Gluconeogenesis
location of kidneys
Location of kidneys
  • Between T12 and L3
  • Partially protected by 11th and 12th ribs
  • Right kidney is lower than left
  • Kidneys and ureters are retroperitoneal
  • Protected by three layers:
    • Renal capsule
    • Adipose capsule
    • Renal fascia
  • Renal hilum – ureter, blood and lymphatic vessels
  • Renal sinus
  • Renal cortex
  • Renal medulla
    • Renal pyramids
    • Renal papilla
  • Renal columns

Functional unit of kidney

Number constant from birth

Can function on 2/3 of one kidney

Forms the urine

duct system
Duct system
  • Minor calyces
  • Major calyces
  • Renal pelvis
  • Ureter
  • Urine is not changed after it leaves the collecting duct
Kidneys = 1% of body mass
  • Receive 15-30 % of blood flow
  • Blood supplied to kidney by renal artery
  • Afferent arteriole divides into ball shaped capillary network called the glomerulus.
  • Capillaries rejoin to form efferent arteriole, then peritubular capillaries
  • Vasa recta
functions of the nephron
Functions of the Nephron
  • Filtration
  • Tubular reabsorption
  • Tubular secretion
structure of a nephron
Structure of a nephron
  • Renal corpuscle
    • Glomerulus
    • Glomerular capsule or Bowman’s capsule
  • Renal tubule
    • Proximal convoluted tubule
    • Nephron loop or loop of Henle
    • Distal convoluted tubule
    • Collecting duct
bowman s capsule
Bowman’s capsule
  • Outer layer - simple squamous epithelium
  • Inner layer – modified simple squamous epi.
    • Cells called podocytes
    • Projections are pedicels
  • Endothelium of capillary and podocytes form the endothelial-capsular (filtration) membrane.
filtration membrane
Filtration membrane
  • Fenestrated endothelium – prevents the passage of cells
  • Basement membrane of glomerulus – prevents passage of large proteins
  • Slit membrane (between pedicels) – prevents the passage of medium sized proteins
Wall of renal tubules made up of single layer of epithelial cells and a basement membrane.
  • Proximal convoluted tubule – cells are cuboidal and have microvilli.
  • About 65 % of water and 100 % of some solutes are reabsorbed here.
renal physiology
Renal Physiology
  • Glomerular filtration – most substances easily filtered
  • Filtrate = 180 L/ day but urine = 1-2 L /day
  • Filter is thin
  • Glomerular capillaries are long
  • Capillary blood pressure is high

(afferent arteriole diameter > efferent arteriole)

Filtration fraction is the percentage of plasma that becomes filtrate, usually 16-20 %.
  • Glomerular Filtration Rate (GFR) is the amount of filtrate formed in both kidneys per minute; normally about 125 ml / min.
renal autoregulation
Renal autoregulation
  • JGA senses Na+, Cl- and water
  • When these ↓, JGA dilates afferent arteriole, ↑ blood pressure in glomerulus
hormonal regulation
Hormonal regulation
  • When BP ↓, JGA secretes renin which converts angiotensinogen to angiotensin I, angiotensin I is converted to angiotensin II in the lungs. Angiotensin II is a potent vasoconstrictor. It also stimulates the release of aldosterone, and stimulates the thirst center in the hypothalamus and release of ADH from the posterior pituitary gland.
tubular reabsorption
Tubular reabsorption
  • Volume of fluid that enters the proximal convoluted tubule in ½ an hour > total plasma volume.
  • Reabsorb water, glucose, amino acids, urea and ions, esp. Na+, Cl- and K+
  • Na+ diffuses into cells, but is actively pumped out into interstitial fluid
  • Promotes reabsorption of water
dct and collecting ducts
DCT and collecting ducts
  • By end of DCT 90 % of water and solutes reabsorbed.
  • Aldosterone causes principal cells to synthesize sodium pumps. Also causes potassium to be secreted into urine.
  • ADH stimulates cells to put water channels into membranes. ADH is responsible for facultative (responding to need) water reabsorption.
tubular secretion
Tubular secretion
  • Two main functions:
  • Secretion of substances to eliminate them from body – ions, nitrogen-containing waste (urea, creatinine) and certain drugs
  • Secretion of H+ helps to maintain blood pH
urinary bladder
Urinary bladder
  • Posterior to pubic symphysis
  • Stores urine prior to micturition
  • Trigone – between openings of ureters and internal urethral orifice – mucosa is firmly bound to muscularis.
  • Muscosa, submucosa, muscularis (detrusor muscle), and serous coat.
evaluation of kidney function
Evaluation of kidney function
  • Blood Urea Nitrogen (BUN) – urea is a breakdown product of proteins
    • Influenced by diet
  • Creatinine – end product of muscle metabolism
    • Normally constant
    • Can determine creatinine clearance
normal urine
Normal urine
  • Transparent yellow
  • Contains ions : Na+, Cl-, K+ ; nitrogenous wastes: ammonia, creatinine, urea and uric acid; and foreign chemicals: drugs, pesticides, food additives, etc.
  • Suspended solids in trace amounts: bacteria, blood cells, casts.
not normally present
Not normally present
  • Albumin
  • Glucose, Acetone– diabetes mellitus
  • Bile – liver disease, obstruction of bile ducts, hemolytic disease
  • pH 4.6 -8.0
specific gravity
Specific gravity
  • 1.001 -1.035
  • Damage to tubules , s.g. fixed at 1.010 = filtrate
  • Diabetes insipidus (lack of ADH) -
    • 1.003
  • Diabetes mellitus – “sugar diabetes”
    • 1.030 osmotic diuresis
  • Emesis or fever –
    • 1.040