The URINARY System

Excretion is the body’s removal of waste products from cellular metabolism.

Whole-body examples:- lungs excrete CO2- skin excretes salts

Main excretory pathway is the urinary system

Carbohydrates ‐‐‐‐‐‐‐‐‐ > CO2 + H20

Lipids ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ > CO2 + H20

Proteins ‐‐‐‐‐> Amino Acids ‐‐‐‐‐‐‐ > NH2

Harmless

CellularBreakdown Products

Toxic

NH2  ‐‐‐‐‐‐‐‐>   Urea Harmless

Conversionin all cells

Food Type

Does urea = urine ??

NO

“Average” Urine:  95% Water …………… 5% Solids

Solids in 1 day of Urine (~ 1500 mL)

Urea 30 gramsSalts 20 gCreatine 1‐2 gAmmonia 1‐2 gUric Acid 1 g

Urine is sterile until the urethra

Bacteria live on epithelial lining of the urethra

Muscles in the Urinary System ??  

Bladder filling and emptying are muscular events !!

Urine movement is unrelated to gravity.

Ureter walls contain smooth muscle

Wavelike contractions known as peristalsis

Once every 10‐15 sec a contraction shoots urine into the bladder

Possible to fill your bladder upside down.

Urine Formation

“Source” of urine ??

BLOOD

Blood flow to organs of a 70 kg man at rest

Skin 0.08Brain 0.5Heart 0.8Liver 0.9Kidneys 4.0

Blood FlowOrgan                   (L/kg/min)

Filters blood … modifies filtrate … creates urine

Modifies final water content

Directional Terms

Proximal & Distal

Afferent & Efferent

Ascending & Descending

NextSlide

Pre‐Urine

Blood filtrate passes through holes in capillary wall

Filtration of molecules in the Glomerulus

Water 18 YesUrea 60 YesSucrose 342  YesSmall Protein 15,000 SomeLarge Protein 70,000 NoBlood Cells ‐ No

Pass intoSubstance                        Weight            Pre‐urine?

Conclusion:  Anything smallish enters pre‐urine

Problem:  Nutrients & Building Blocks are small

Solution:  Re‐claim valuable molecules

Pre‐Urine                                                        Final Urine

Diuresis

Anti‐diuresis

Bladder Fills                                                  Urge to Urinate

200‐400 mL … walls stretch … brain awareness

Toddlers?

Urinary Bladder tolerates

STRETCHING

600-800 mL storage

QUESTION: Type of lining epithelium??

STRETCHable Epithelium

Stretched Transitional Epithelium(Bladder Full)

(Bladder Empty

FETUS

Back intoBlood 

Daily BALANCE ……. Why?

CONSUMING SEAWATER:  WHALE vs HUMAN

Sea Water      UrineConsumed ProducedmL mM mL mM

___________________________________Human      1000        535         1350      400

Whale       1000        535           650      820___________________________________