The urinary system
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The Urinary System. Function. Remove nitrogenous wastes Maintain electrolyte, acid-base, and fluid balance of blood Homeostatic organ Acts as blood filter Release hormones: calcitriol & erythropoietin. Kidneys as Filters. Diuretic- loose water; coffee, alcohol

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  • Remove nitrogenous wastes

  • Maintain electrolyte, acid-base, and fluid balance of blood

  • Homeostatic organ

  • Acts as blood filter

  • Release hormones: calcitriol & erythropoietin

Kidneys as filters
Kidneys as Filters

  • Diuretic- loose water; coffee, alcohol

  • Antidiuretic- retain water; ADH

  • Aldosterone- sodium & water reabsorption, and K+ excretion

  • GFR= 180 liters (50 gal) of blood/day

  • 178-179 liters are reabsorbed back into blood

  • Excrete a protein free filtrate

Organs of the urinary system
Organs of the Urinary System



urinary bladder


A Kidney

Blood and waste enter through renal artery

Filtered blood leaves through renal vein

Excess water and toxic waste leaves through ureter as urine

Nitrogenous wastes
Nitrogenous Wastes


Amino acids



Uric Acid



Kidney anatomy
Kidney Anatomy



renal cortex

renal medulla

renal pelvis

renal pyramids

renal capsule

Each kidney contains over 1 million nephrons and thousands of collecting ducts

renal cortex

renal medulla




Collecting duct

Loop of Henle

DCT of collecting ducts



Collecting duct

Peritubular capillaries

Loop of Henle

To renal pelvis

Glomerular filtration
Glomerular Filtration of collecting ducts

efferent arteriole

afferent arteriole


Bowman’s capsule

Filters blood; proteins can’t pass through

Composition of glomerular filtrate
Composition of Glomerular Filtrate of collecting ducts

  • Water

  • Small Soluble Organic Molecules

  • Mineral Ions

Proximal convoluted tubule
Proximal Convoluted Tubule of collecting ducts

Reabsorbs: water, glucose, amino acids, and sodium.

  • 65% of Na+ is reabsorbed

  • 65% of H2O is reabsorbed

  • 90% of filtered bicarbonate (HCO3-)

  • 50% of Cl- and K+

Loop of henle
Loop of Henle of collecting ducts

Creates a gradient of increasing sodium ion concentration towards the end of the loop within the interstitial fluid of the renal pyramid.

  • 25% Na+ is reabsorbed in the loop

  • 15% water is reabsorbed in the loop

  • 40% K is reabsorbed in the loop

Distal convoluted tubule
Distal Convoluted Tubule of collecting ducts

Under the influence of the hormone aldosterone, reabsorbs sodium and secretes potassium. Also regulates pH by secreting hydrogen ion when pH of the plasma is low.

  • only 10% of the filtered NaCl and 20% of water remains

Collecting duct
Collecting Duct of collecting ducts

Allows for the osmotic reabsorption of water.

ADH (antidiuretic hormone)- makes collecting ducts more permeable to water-- produce concentrated urine

Urine of collecting ducts

  • Water- 95%

  • Nitrogenous waste:

    • urea

    • uric acid

    • creatinine

  • Ions:

    • sodium

    • potassium

    • sulfate

    • phosphate

From the original 1800 g NaCl, only 10 g appears in the urine

Urinary bladder
Urinary Bladder of collecting ducts


internal sphincters


external sphincters

Diuresis (Micturition) of collecting ducts

When bladder fills with 200 ml of urine, stretch receptors transmit impulses to the CNS and produce a reflex contraction of the bladder (PNS)

When is incontinence normal?

Urinalysis of collecting ducts

Why do doctors ask for a urine sample?       

  • characteristics:

  • smell- ammonia-like

  • pH- 4.5-8, ave 6.0

  • specific gravity– more than 1.0; ~1.001-1.030

  • color- affected by what we eat: salty foods, vitamins

Odor of collecting ducts

odor- normal is ammonia-like

diabetes mellitus- smells fruity or acetone like due to elevated ketone levels

diabetes insupidus- yucky


Color of collecting ducts

Color- pigment is urochrome

Yellow color due to metabolic breakdown of hemoglobin (by bile or bile pigments)

Beets or rhubarb- might give a urine pink or smoky color

Vitamins- vitamin C- bright yellow

Infection- cloudy

Specific Gravity of collecting ducts

Water: s.g. = 1g/liter;

Urine: s.g. ~ 1.001 to 1.030

Whenurine has high s.g.; form kidney stones

Diabetes insipidus- urine has low s.g.; drinks excessive water; injury or tumor in pituitary

pH of collecting ducts-range 4.5-8 ave 6.0

vegetarian diet-urine is alkaline

protein rich and wheat diet-urine is acidic

Normal Constitutes of Urine of collecting ducts

Normal Constitutes of Urine of collecting ducts

Abnormal Constitutes of Urine of collecting ducts

  • Glucose

  • Indicative of:

  • Excessive carbohydrate intake

  • Stress

  • Diabetes mellitus

Abnormal Constitutes of Urine of collecting ducts


Abnormal Constitutes of Urine of collecting ducts

  • Ketone

  • RBC

  • Hemoglobin

  • Bile

  • WBC

  • Casts

INQUIRY of collecting ducts

  • List several functions of the kidneys.

  • What does the glomerulus do?

  • What are several constitutes you should not find in urine?

  • What is specific gravity?

  • What two hormones effect fluid volume and sodium concentration in the urine?

  • Where are the pyramids located in the kidney?

  • What vessel directs blood into the glomerulus?

  • Where does most selective reabsorption occur in the nephron?

Moment of Zen of collecting ducts