1. Biology 212 Anatomy & Physiology I
Renal or Urinary System

2. Renal (Urinary) System
Primary function: Maintains homeostasis by regulating concentrations of both water and solutes in the blood.
Disposes of metabolic wastes
excess water
excess ions
toxins
while retaining proper amount of water
proper concentrations of ions
nutrients
anything else needed in blood

3. Renal (Urinary) System
Primary function: Maintains homeostasis by regulating concentrations of both water and solutes in the blood.
Disposes of metabolic wastes
excess water
excess ions
toxins
while retaining proper amounts of water
proper concentrations of ions
nutrients
anything else needed in blood
Secondary function: Regulates blood pressure within
normal range (homeostasis)

4. Organs of Renal System

5. Kidney
Located high in abdominal cavity
Posterior to peritoneum
Liver pushes right kidney
more inferiorly
Mass ~ 150g
Size ~ 12 cm x 6 cm x 3 cm

6. Kidney
Located high in abdominal cavity
Posterior to peritoneum
Liver pushes right kidney
more inferiorly
Mass ~ 150g
Size ~ 12 cm x 6 cm x 3 cm
Lateral surface convex
Medial surface concave with
hilus where renal artery,
renal vein, ureter connect

7. Kidney
Capsule: External covering
of dense irregular connective
tissue
Cortex: Outer solid region
Medulla: Inner solid region
8 to 12 cone-shaped masses
(apex toward hilus) called renal pyramids,
separated by renal columns
Pelvis: Hollow medial region, extensions = calyces
Connects medially with ureter

9. Kidney:
Each renal artery (direct branch of aorta) divides into lobar or segmental arteries, which divide into interlobar arteries, then arcuate arteries (between cortex & medulla), which give off interlobular arteries (Saladin calls these “cortical radiate arteries”) into the cortex.

10. In the cortex, interlobular arteries (called “cortical radiate” arteries in Saladin) send blood through afferent arterioles into groups of capillaries called glomeruli.
This is where filtration will occur to begin formation of urine (more on that in a moment).

11. In the cortex, interlobular arteries (called “cortical radiate” arteries in Saladin) send blood through afferent arterioles into groups of capillaries called glomeruli.
This is where filtration will occur to begin formation of urine (more on that in a moment).
From a glomerulus, blood flows out an efferent arteriole to another set of capillaries called peritubular capillaries which surround the tubules (more in a moment) where urine is forming.

12. Each renal artery divides into
lobar/segmental arteries,
interlobar arteries,
arcuate arteries,
interlobular arteries,
afferent arterioles,
glomeruli,
efferent arterioles,
peritubular capillaries
Blood then flows into interlobular veins or
arcuate veins,
interlobar veins, and
lobar veins to reach the renal vein which carries it to the inferior vena cava.

13. Let’s go back to the glomerulus:
Consists of a group of interconnected capillaries.
As blood flows through these capillaries, plasma (the liquid
part of blood) is filtered out
and flows though a series of
tubes to form urine.
This series of tubes is called
a nephron.

14. Distal Convoluted Tubule
Glomerular (Bowman’s) Capsule
Proximal Convoluted Tubule
Collecting Duct
Loop of Henle

15. Each kidney contains ~ 1,000,000 nephrons
Pattern of nephrons creates pattern of cortex and medulla:
Cortex consists primarily of convoluted tubules which twist many directions.
Medulla consists primarily of loops of Henle & collecting ducts all oriented in the same direction

16. Functions of nephrons:

17. Thus:
Primary function of renal system: Maintains homeostasis by regulating concentrations of both water and solutes in the blood.
Disposes of metabolic wastes
excess water
excess ions
toxins
while retaining proper amount of water
proper concentrations of ions
nutrients
anything else needed in blood

18. Two types of “pressure” are involved in these processes of filtration, reabsorption, and secretion.
1) Hydrostatic pressure = weight of water or blood pressure
2) Osmotic pressure caused by different concentrations of solutes on different sides of a membrane. This can cause movement of both solutes and water
(please review diffusion and osmosis in Saladin Chapter 3)

19. Two types of “pressure” are involved in these processes of filtration, reabsorption, and secretion.
1) Hydrostatic pressure = weight of water or blood pressure
2) Osmotic pressure caused by different concentrations of solutes on different sides of a membrane. This can cause movement of both solutes and water
A. Solutes diffuse from where
they are in higher concentration
to where they are in lower
concentration

20. Two types of “pressure” are involved in these processes of filtration, reabsorption, and secretion.
1) Hydrostatic pressure = blood pressure
2) Osmotic pressure caused by different concentrations of solutes on different sides of a membrane. This can cause movement of both solutes and water
B. Water moves from
where solutes are in
lower concentration
to where they are in
higher concentration
until hydrostatic
pressure = osmotic
pressure

21. Filtration

22. Structure of Glomerulus

23. Structure of Glomerulus
Capillary wall (simple squamous epithelium, fenestrated)
plus podocytes
plus basement membrane between them
form the filtration membrane across which liquid is filtered from the blood to the glomerular capsule.

24. Filtration:
a) Holes (“fenestra”) of capillary epithelium ~ 75 nm; stop anything larger than that but let smaller molecules pass through

25. Filtration:
a) Holes (“fenestra”) of capillary epithelium ~ 75 nm; stop anything larger than that but let smaller molecules pass through
b) Holes in basement membrane ~ 7 nm; stop anything larger than that

26. Filtration:
a) Holes (“fenestra”) of capillary epithelium ~ 75 nm; stop anything larger than that but let smaller molecules pass through
b) Holes in basement membrane ~ 7 nm; stop anything larger than that
c) Spaces between podocytes (“filtration slits”) ~30 nm;
Thus: only things smaller than ~ 7 nm can be filtered from blood into urine

27. Filtration:
(Only things smaller than ~ 7 nm can be filtered from blood into urine)
Not quite that simple, since electrical charge also affects what can pass through the filtration membrane.

28. All cells & molecules > 7 nm stay in blood
Filtration:
(Only things smaller than ~ 7 nm can be filtered from blood into urine)
Not quite that simple, since electrical charge also affects what can pass through the filtration membrane.
In general:
All cells & molecules > 7 nm stay in blood
Neutral molecules nm pass through, but charged
molecules (ions) this size can not
All molecules & ions < 3 nm pass through
Thus: Water Glucose Electrolytes
Amino acids Fatty acids Vitamins
Most metabolic wastes etc.
are all filtered out of the blood

29. This fluid filtered out of the blood flows into the proximal convoluted tubule, through other parts of nephron, into collecting duct.

30. This fluid filtered out of the blood flows into the proximal convoluted tubule, through other parts of nephron, into collecting duct.
Recall that nephron is surrounded by peritubular capillaries

31. As this filtrate passes through the nephron:
a) Most solutes needed by
body & most of the water
are reabsorbed back into
the blood in peritubular
capillaries
b) Excess solutes & excess
water stay in urine
c) Additional unwanted ions
and molecules secreted
into urine

32. Reabsorption from Nephron:
Substance: Amount Amount Reabsorption
filtered excreted ( % )
per day per day
Water ( L )
Sodium ( g )
Glucose ( g )
Urea ( g )
(From Mader, Human Biology, 1995)

33. Key Feature of Kidney:
Nephrons can concentrate urine by reabsorbing most of the water filtered out of the glomerulus
Substance: Amount Amount Reabsorption
filtered excreted ( % )
per day per day
Water ( L )
Sodium ( g )
Glucose ( g )
Urea ( g )

34. Key Feature of Kidney:
Nephrons can concentrate urine by reabsorbing most of the water filtered out of the glomerulus
Substance: Amount Amount Reabsorption
filtered excreted ( % )
per day per day
Water ( L )
Sodium ( g )
Glucose ( g )
Urea ( g )
This requires kidney to create a large concentration gradient in extracellular fluid of medulla (surrounding loops of Henle)

35. Low osmolarity (concentration of solutes) closer to cortex
Key Feature of Kidney:
(Nephrons concentrate urine by reabsorbing most of the water filtered out of glomerulus. This requires kidney to create a large concentration gradient in extracellular fluid of medulla, surrounding loops of Henle)
Low osmolarity (concentration of solutes) closer to cortex
High osmolarity (concentration of solutes) deeper in medulla

36. Low osmolarity (concentration of solutes) closer to cortex
Key Feature of Kidney:
(Nephrons concentrate urine by reabsorbing most of the water filtered out of glomerulus. This requires kidney to create a large concentration gradient in extracellular fluid of medulla, surrounding loops of Henle)
Low osmolarity (concentration of solutes) closer to cortex
High osmolarity (concentration of solutes) deeper in medulla
so that
As newly formed urine passes
through collecting, most of the
water will diffuse out of collecting
duct, into the extracellular fluid,
from which it will diffuse back into
blood of the peritubular capillaries,
leaving high concentration of
solutes in urine which reaches pelvis & leaves kidney

37. Your text goes into great detail about how this happens (including these diagrams):
You don’t need to understand details, but you should understand that it allows the final urine to be concentrated by pulling water out of it as it passes through the collecting duct

38. Your text goes into great detail about how this happens (including these diagrams):
You don’t need to understand details, but you should understand that it allows the final urine to be concentrated by pulling water out of it as it passes through the collecting duct.
How much water gets pulled out can increase or decrease if body needs to retain or lose water. This is under control of antidiuretic hormone (ADH) produced by posterior pituitary.

39. Increased reabsorption of water from urine back into blood
(How much water gets pulled out can increase or decrease if body needs to retain or lose water. This is under control of antidiuretic hormone (ADH) produced by posterior pituitary).
Increased reabsorption of water from urine back into blood
Less urine, more concentrated
Increase in ADH
Decreased reabsorption of water from urine back into blood
More urine, less concentrated
Decrease in ADH

40. Kidney also has important function in regulating systemic blood pressure.

41. Kidney also has important function in regulating systemic blood pressure.
Each nephron has a juxtaglomerular apparatus which detects pressure of blood in the afferent arteriole and secretes the hormone renin.
The lower the blood pressure in the afferent arteriole, the more renin the juxtaglomerular apparatus will secrete.

42. (Each nephron has a juxtaglomerular apparatus which detects blood pressure in afferent arteriole and secretes hormone renin. The lower the blood pressure in the afferent arteriole, the more renin the juxtaglomerular apparatus will secrete.)

43. Urine passes from a
collecting duct into a
minor calyx, then a
major calyx, then
the pelvis of the
kidney.

44. Urine leaving the pelvis
enters the ureter, which
carries it to the
urinary bladder.

45. Ureters: Retroperitoneal.
Pass anterior to common iliac arteries & veins.

46. Ureters: Retroperitoneal.
Anterior to common iliac arteries & veins.
Deliver urine to posterolateral parts of urinary bladder.

47. Ureter:
Mucosa: Transitional epithelium
Lamina Propria (loose C.T.)
Muscularis: Thick wall of smooth muscle
Adventitia: Dense irregular C.T.

48. Urinary Bladder:
In pelvis, posterior to pubic bone
Superior surface covered by peritoneum

49. Urinary Bladder:
In pelvis, posterior to pubic bone
Superior surface covered by peritoneum
Female:
Anterior to uterus/vagina

50. Urinary Bladder:
In pelvis, posterior to pubic bone
Superior surface covered by peritoneum
Female:
Anterior to uterus/vagina
Male:
Anterior to rectum
Superior to prostate

51. Urinary Bladder:
Mucosa: Transitional epithelium
Lamina propria
Muscularis: Thick smooth muscle
(“detrusor”)
Adventitia (C.T.) covers
most of bladder
Serosa on its superior
surface

52. Urinary Bladder:

53. Urinary Bladder:

54. Urinary Bladder:
Muscularis (detrusor muscle)
and
Internal Urethral Sphinter both
smooth muscle;
thus involuntary
Urine leaving bladder enters urethra

56. Urethra:
Adventitia: Dense irregular C.T.
Muscularis: Thick wall of smooth muscle
Mucosa: Epithelium varies from transitional near bladder
to stratified squamous at end
Male urethra much longer, has middle region of
stratified columnar. Female urethra does not.
Lamina Propria (loose C.T.)

57. External
Urethral
Sphincter
External
Urethral
Meatus

58. Urine not modified in ureter
bladder
urethra
Thus: Urine leaving body through external urethral meatus
unchanged since it left kidneys

59. Urine not modified in ureter
bladder
urethra
Thus: Urine leaving body through external urethral meatus
unchanged since it left kidneys.
Also: Bacteria & other organisms can travel through urethra
into bladder (“cystisis”); much more common in
shorter urethra of women.
From bladder, organisms can travel through ureters
into kidneys (“pyelonephritis”)

60. Tonight:
On yourself or another person, locate kidneys
ureters
bladder
urethra