1. The Internal Environment
Chapter 32

2. Impacts, Issues Video
Truth in a Test Tube

3. Physicians routinely test:
sugar level, pH, protein content
Urine tests give information about:
kidneys
hydration
pregnancy
certain cancers
Athletes take urine tests to screen for prohibited drugs
Urine tells potential employers if you’ve been taking “street drugs” such as marijuana, cocaine, and Ecstasy

4. Animal Fluids
Interstitial fluid lies between cells and other tissue components
Blood transports substances by way of the circulatory system
Interstitial fluid and blood make up the extracellular fluid

5. Maintaining Extracellular Fluid
Urinary system keeps volume and composition of extracellular fluid within tolerable ranges
It interacts with the following systems:
Digestive
Respiratory
Circulatory

6. Controlling Water Gain & Loss
Water and solute balance

7. Key functions of most excretory systems
Filtration
Filtering of body fluids
Reabsorption
Reclaiming valuable solutes
Secretion
Adding nonessential solutes and wastes from the body fluids to the filtrate
Excretion
Releasing processed filtrate containing nitrogenous wastes from the body

8. Filtration Capillary Filtrate Excretory tubule Reabsorption Secretion
Figure Key steps of excretory system function: an overview
Secretion
Urine
Excretion 8

9. Components of Urinary System
Pair of kidneys
Pair of ureters
Urinary bladder
Urethra

10. Function of Kidneys Filter the following from the blood: Water
Mineral ions
Wastes from the blood
Adjust filtrate concentration and return most to blood
Remaining water and solutes in filtrate constitute urine

11. Urinary Excretion Urine flows from each kidney to a ureter
Ureters deliver urine to bladder
Contraction of the smooth muscle of the bladder forces urine out of the body into the urethra
Skeletal muscle surrounds urethra
allows voluntary control of urination

12. Structure of Kidney Renal capsule surrounds kidney Two regions
Outer renal cortex
Inner renal medulla
Renal pelvis collects urine and funnels it to ureter

13. Structure of Kidney
Human kidney

14. Nephron Functional unit of the kidney
Each consists of a renal tubule and associated capillaries
Bowman’s capsule (red)
collecting duct
distal tubule
proximal tubule
loop of Henle

15. Nephron
Urine formation

16. Urine Formation Hormone action Filtration Tubular secretion Tubular
reabsorption
Excretion

17. Structure of the glomerulus
Urine Formation
Structure of the glomerulus

18. Leaky Glomerular Capillaries
Glomerular capillaries have large pores
Fluid leaks from glomerular capillaries into kidney tubules
Renal corpuscle
(Bowman’s capsule + glomerular capillaries)

19. Reabsorption and secretion

20. Tubular Reabsorption
Ions move from the filtrate in tubule lumen into the interstitial fluid
Sodium ions are actively pumped out of the proximal tubule into the interstitial fluid
Chloride ions follow
they are passively transported

21. Tubular Reabsorption Ion flow creates an osmotic gradient
it is saltier outside the tubule than inside
Water flows down the osmotic gradient, from the tubule lumen into the interstitial fluid
Peritubular capillaries pick up the water and ions from the interstitial fluid

22. Tubular Reabsorption
Tubular reabsorption

23. Tubular Reabsorption interstitial fluid filtrate in tubule Na+ Na+ Na+
Cl-
Na+
Na+
Na+
H2O
peritubular capillary
sodium pump

24. Tubular Secretion The opposite of reabsorption
Molecules are transported out of the peritubular capillaries, through tubule cells, and into the filtrate
Eliminates H+ ions, metabolites, and toxins

25. BOWMAN’S CAPSULE
The capillaries and specialized cells of Bowman’s capsule
permeable to water and small solutes but not blood cells or large molecules
filtrate produced there contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules

26. Animation: Bowman’s Capsule
Right click slide / Select play

27. PROXIMAL TUBULE Proximal tubule
Reabsorption of ions, water, and nutrients takes place in the proximal tubule
Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries
Some toxic materials are actively secreted into the filtrate

28. LOOP of HENLE Descending limb of the loop of Henle
Reabsorption of water continues through channels formed by aquaporin proteins
Movement is driven by the high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrate
filtrate becomes increasingly concentrated all along its journey down the descending limb

29. LOOP of HENLE Ascending limb of the loop of Henle
has a transport epithelium that lacks water channels
salt but not water is able to move from the tubule into the interstitial fluid
filtrate becomes increasingly dilute as it moves up to the cortex

30. Animation: Loop of Henle
Right click slide / Select play

31. DISTAL TUBULE Distal tubule
regulates the K+ and NaCl concentrations of body fluids
controlled movement of ions contributes to pH regulation

32. COLLECTING DUCT Collecting duct
carries filtrate through the medulla to the renal pelvis
Most of the water and nearly all sugars, amino acids, vitamins, and other nutrients are reabsorbed into the blood

33. Animation: Collecting Duct
Right click slide / Select play

34. Hormone Effects ADH Acts on collecting ducts
Makes walls more permeable to water
Urine more concentrated
Aldosterone
Stimulates reabsorption of sodium

35. Thirst Osmoreceptors detect changes
Activate thirst center in hypothalamus and ADH-secreting cells
Angiotensin II acts on brain to promote thirst and ADH secretion

36. Animation: Effect of ADH
Right click slide / Select play

37. Variation in Urinary Systems
Structure of vertebrate urinary systems varies in details
Adapted to particular habitats
Freshwater fish must deal with continuous influx of water by osmosis
Marine fish must deal with continuous loss of water

38. Land animals have mechanisms to prevent dehydration
body coverings that help reduce water loss
drink water and eat moist foods, and they produce water metabolically

39. Length of Loop of Henle
Longer loop of Henle allows an organism to produce a very steep osmotic gradient
Allows reabsorption of more water than a shorter loop

40. NITROGENOUS WASTES
The type and quantity of an animal’s waste products may greatly affect its water balance
Among the most significant wastes are nitrogenous breakdown products of proteins and nucleic acids
Some animals convert toxic ammonia (NH3) to less toxic compounds prior to excretion

41. Ammonia excretion is most common in aquatic organisms
Vertebrates excrete urea
a conversion product of ammonia, which is much less toxic
Insects, land snails, and many reptiles including birds excrete uric acid as a semisolid paste
less toxic than ammonia and generates very little water loss, but it is energetically more expensive to produce than urea