1. Biology 12 Chapter 16 Urinary System and Excretion

2. 16.1 The Urinary System Kidneys Primary organs of excretion =
The Kidneys are bean-shaped organs located on either side of the vertebral column just below the diaphragm, surrounded by adipose (fat) tissue.
Kidneys function to produce urine via nephrons

3. Excretion Removal of metabolic wastes from the body
Don’t confuse with:
Defecation (elimination of feces from the digestive system)
Secretion (releasing substances via exocytosis from a cell)

4. Organs of the Urinary System
Renal artery
(red)
Kidney
Renal vein
(blue)
Ureter
Urinary bladder
Urethra
Figure 16.1 p. 304 of Mader textbook

5. Kidneys, Renal Artery, Renal Vein
Renal Artery- originates from the aorta, brings oxygenated blood to the kidney
Renal Vein- Takes deoxygenated blood away from the kidney to the inferior vena cava

6. Ureters
Muscular tubes that conduct urine from the kidneys to the bladder
Peristaltic contractions cause urine to enter the bladder in spurts

7. Urinary Bladder Hollow muscular organ which temporarily stores urine
The mucosal wall of the bladder has folds called rugae that disappear as the bladder expands
Where the ureter enters the bladder there are valves to prevent backflow
Where the urethra exits the bladder there are sphincters to control emptying

8. Urethra
Small duct that transports urine from the urinary bladder to the external opening of the body
Males vs Females
Longer in males
Surrounded by the prostate gland in males
Connected to reproductive system in males

9. Outline the Path of Urine
I) Kidneys produce urine
II) Ureters transport urine
III) Urinary bladder stores
urine
IV) Urethra passes urine to
the outside
Figure 16.1 p. 304 of Mader textbook

10. Functions of the Urinary System
4 main ways that the kidneys contribute to maintaining homeostasis:
Excretion of metabolic wastes (urea)
Maintenance of water-salt balance
Maintenance of acid-base balance
Secretion of hormones

11. Urination/Micturition
Bladder fills (250 ml)
Stretch receptors send nerve impulses to spinal cord
Cause urinary bladder to contract and sphincter to relax
Urination
Figure 16.2 p. 305 of Mader textbook

12. Internal Anatomy of the Kidney
Renal blood vessels and ureter enter on concave side
Many branches of the renal artery and renal vein reach inside the kidney
Figure 16.3 Mader Text

13. Path of blood in the nephron
Each nephron has its own blood supply:
Aorta
Renal artery
Afferent arteriole
Glomerulus
Efferent arteriole
Peritubular capillary network
Venule
Renal Vein
Inferior Vena Cava

14. Figure 16.5 Mader Textbook

15. Renal Artery- brings oxygenate blood to the kidney containing:
water
nitrogenous wastes
salts
nutrients
Renal Vein- brings deoxygenated blood away from the kidney containing:
most water
required salts

16. Three Regions of the Kidney
Figure 16.3 Mader Text

17. 1. Renal Cortex
Outer granulated layer that dips down between the renal medulla

18. 2. Renal Medulla
Has a radially striated conical layer = renal pyramids

19. 3. Renal Pelvis
Inner cavity continuous with the ureter

20. Anatomy of a Nephron What is a nephron? Functional unit of the kidney
Also called renal/kidney tubules
> 1 million nephrons/kidney
Each nephron has its own blood supply

21. Anatomy of the Kidney and Excretion
Chapter 16.2

22. Process of Urine Formation
Glomerular Filtration
Tubular Reabsorption
Tubular Secretion
Efferent arteriole
Afferent arteriole
Proximal Convoluted Tubule
Distal Convoluted tubule
Glomerulus (Bowman’s Capsule)
Water (descending limb)
Salt (ascending limb)
Reabsorption
of Water
Loop of Henle
Collecting Duct

23. Looking at the Parts of a Nephron

24. I) Bowman’s (glomerular) capsule
Cup-like structure that contains the glomerulus

25. II) Glomerulus Knot of capillaries inside the glomerular capsule
Located in
renal cortex

26. III) Proximal Convoluted Tubule (PCT)
“Proximal” = near the glomerular capsule
Lined with cuboidal epithelial cells with inner brush border (microvilli)
Located in renal cortex
What’s the purpose of microvilli?
Increase surface area for reabsorption

27. IV) Loop of Henle Also known as loop of the nephron
Proximal convoluted tubule narrows, forms a u-shaped turn
Composed of simple squamous epithelium
Dips down into the renal medulla

28. V) Distal Convoluted Tubule
Composed of cuboidal epithelial cells
Numerous mitochondria/ no brush border
Not specialized for reabsorption
Specialized to move molecules from blood into the tubule
Located in renal cortex

29. VI) Collecting Duct
Distal convoluted tubules of several nephrons enter one collecting duct
Many collecting ducts carry urine to the renal pelvis
Located in the renal medulla
Give renal pyramids their lined appearance

30. Urine Formation An overview of the steps
I) Glomerular filtration
(Pressure Filtration)
II) Tubular Reabsorption
(Selective Reabsorption)
III) Tubular Secretion
(Tubular Excretion)

31. Figure 15.9, p.85 Polar Bear Book

32. I) Glomerular Filtration (pressure filtration)
Divides blood (filtration)
due to the glomerular blood pressure
Filterable Blood Components
Non-filterable Blood Components
Water
Nitrogenous wastes
Nutrients
Salts (ions)
Formed elements (blood cells and platelets)
Plasma proteins

33. I) Glomerular Filtration Continued
Blood pressure forces small molecules (glucose) and ions (salt) to move from the glomerulus  Bowman’s capsule
= Glomerular Filtrate
contains small molecules
in approx. same
concentration as plasma
Figure 16.5 Mader Text

34. II) Tubular Reabsorption (Selective reabsorption)
Molecules move from the convoluted tubules (nephron) to the peritubular capillaries (blood) both actively and passively
Reabsorbed Filtrate Components
Non-Reabsorbed Filtrate Components
Most Water
Nutrients
Required salts (ions)
Some water
Much nitrogenous waste
Excess salt (ions)

35. II) Tubular Reabsorption Continued A) Active Reabsorption
PCT cells adapted for active reabsorption:
-microvilli
-mitochondria
-carrier proteins
Na+ (65% PCT)
Glucose normally reabsorbed completely (if maximum rate of transport exceeded, glucose appears in the urine)

36. II) Tubular Reabsorption Continued B) Passive Reabsorption
Cl- follows Na+ passively
Reabsorption of salt (NaCl) = Osmolarity of blood compared to filtrate
= Water enters blood

37. III) Tubular Secretion (Tubular excretion)
Second addition of wastes from blood (peritubular capillaries) to tubular fluid (DCT) via active transport
Hydrogen ions
Potassium ions
Creatinine
Ammonia
Antibiotics (penicillin)

38. Final Urine Composition
In the end, urine contains…
Substances that have undergone glomerular filtration but have not been reabsorbed
Substances that have undergone tubular secretion

39. Summary of Urine Formation
Name
Process
Molecules
Glomerular Filtration
Blood pressure forces small molecules from glomerulus into Bowman’s capsule = glomerular filtrate
Water, salts, nutrients, wastes
Tubular reabsorption
Molecules are actively and passively reabsorbed from the convoluted tubules into the peritubular capillary network
Water, nutrients,
salt
Tubular secretion
Certain molecules actively secreted from blood into convoluted tubules
H+and K+ ions, creatinine, penicillin

40. 16.3 Regulatory Functions of the Kidney
The excretion of concentrated urine (more so than blood) depends on: 1. reabsorption of salt 2. establishment of a solute gradient 3. reabsorption of water Note: reabsorption means into the tissue of the kidneys and into the bloodstream

41. 1. Reabsorption of Salt
Main salt ions: Na+ (sodium), K+ (potassium), Mg 2+ (magnesium), HCO3- (bicarbonate)
99% of salt is reabsorbed
proximal tubule
ascending loop
The distal convoluted tubule (DCT)
Aldosterone controls reabsorption of Na+ in the DCT
Reabsorption of Na+ causes the reabsorption of water (osmosis)
Causes increased blood volume and pressure, which causes Atrial Natriuretic Hormone (ANH) to be released from the heart
ANH inhibits the production of Aldosterone

42. Regulation of Blood Sodium Levels
Homeostasis
Low Blood Na+
High Blood Na+
Heart secretes ANH
ANH in blood
Kidneys excrete Na+ and H20 in urine
Kidney secretes Renin
Adrenal Gland secretes Aldosterone
Kidney reabsorbs Na+ and H20

43. 2. Establish an Osmotic Gradient
Urea leaks from collecting duct  [salts] in the inner medulla = concentration gradient
H2O is reabsorbed 1st, concentrating the salts inside the loop. Ascending loops is impermeable to H2O, salts actively transported out
H2O is passively re-absorbed again in the collecting ducts

44. 3. Reabsorption of Water
H2O diffuses out of the descending limb due to the concentration gradient
Renal cortex has lower [solutes] than the inner medulla  greater osmosis in inner medulla and less in the renal cortex
Antidiuretic Hormone (ADH)- from the pituitary in the brain, increases the amount of reabsorption from the collecting ducts ( blood volume and pressure)

45. NaCl
H2O
NaCl
H2O
H2O
H2O
NaCl
H2O
H2O
urea

46. Diuretics Diuretics= chemicals that increase the flow of urine
Consuming alcohol = inhibits the secretion of ADH (antidiuretic hormone
Caffeine = increases glomerular filtration and decreases tubular reabsorption of Na+

47. Maintaining Acid-Base Balance
Alkalosis= blood pH above 7.4
Acidosis= blood pH below 7.4
Normal pH of blood ~7.4  important to maintain this so that enzymes function properly
Blood= buffer (takes up excess H+ ions or OH- ions) to keep pH constant

48. Maintaining Acid-Base Balance Cont’
Respiration can help maintain blood pH  increased breathing rids the body of excess H+ ions
Kidneys can rid the body of a wide range of acidic and basic substances (slower acting, but biggest effect)
Blood acidic  H+ secreted, HCO3- reabsorbed
Blood basic  H+ not secreted, HCO3- not reabsorbed