2. 2
The Urinary System
Paired kidneys
A ureter for each kidney
Urinary bladder
Urethra
3. 3
Main Functions of Urinary System
Kidneys filter blood to keep it pure
Toxins
Metabolic wastes
Excess water
Excess ions
Dispose of nitrogenous wastes from blood
Urea
Uric acid
Creatinine
Regulate the balance of water and electrolytes,
acids and bases
4. 4
Kidneys are retroperitoneal organs (see next slide)
Superior lumbar region of posterior abdominal wall
Lateral surface is convex
Medial surface is concave
Hilus* is cleft: vessels, ureters and nerves enter and leave
Adrenal glands* lie superior to each kidney
(the yellow blob in pic)
*
*
9. 9
Kidney has two regions
Cortex: outer
Columns of cortex divide medulla into “pyramids”
Medulla: inner
Darker, cone-shaped medullary or renal pyramids
Parallel bundles of urine-collecting tubules
10. 10
The human kidney has lobes
Pyramid and cortical tissue surrounding it
5-11 per kidney
Renal pelvis (=basin)
Expanded, funnel shaped, superior part of ureter
Branches to form two or three major calices (seen best on right pic below)
Each of these divides again, minor calices: collect urine from papillae of
pyramids
11. 11
The Arteries
Aorta gives off right and left renal arteries
Renal arteries divides into 5 segmental arteries as enters hilus
of kidney
Segmentals branch into
lobar arteries
Lobars divide into
interlobars
Interlobars into arcuate in
junction of medulla and
cortex
Arcuates send interlobular
arteries into cortex
Cortical radiate arteries
give rise to glomerular
arterioles
12. 12
Vasculature of the kidney
The glomerular capillary bed is unusual in
having arterioles going both to it and away from
it (afferent and efferent), instead of a vein going
away as most
It is also unusual in having two capillary beds in
series (one following the other)
13. 13
Uriniferous tubule is the main structural and
functional unit
To left is a single, generalized
uriniferous tubule
More than a million of these
tubules act together to form the
urine
Three main mechanisms
a. Glomerular filtration
b. Tubular reabsorption
c. Tubular secretion
Two major parts
1. A urine-forming nephron
2. A collecting duct which
concentrates urine by removing
water from it
14. 14
Outline
Uriniferous tubule (anatomical unit for
forming urine)
Nephron
Renal corpuscle (in cortex)
– Glomerulus (tuft of capillaries)
– Glomerular (Bowman’s) capsule
Tubular section
– Proximal convoluted tubule
– Loop of Henle
– Distal convoluted tubule
Collecting duct
15. 15
Outline
Uriniferous tubule (anatomical unit for
forming urine)
Nephron
Renal corpuscle (in cortex)
– Glomerulus (tuft of capillaries)
– Glomerular (Bowman’s) capsule
Tubular section
– Proximal convoluted tubule
– Loop of Henle
– Distal convoluted tubule
Collecting duct
16. 16
Understand at least this much:
Filtration
a. Fluid is squeezed out of
the glomerular capillary
bed
Resorption
b. Most nutrients, water ad
essential ions are
returned to the blood of
the peritubular
capillaries
Secretion
c. Moves additional
undesirable molecules
into tubule from blood of
peritubular capillaries
17. 17
Nephron
Renal corpuscle
Tubular section
Renal corpuscle: only in
cortex
Tuft of capillaries called
glomerulus
Surrounded by cup-shaped,
hollow glomerular
(Bowman’s) capsule
Uriniferous tubule (anatomical unit for forming urine)
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of
capillaries)
Glomerular (Bowman’s)
capsule
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
18. 18
(refer to this(refer to this
pic as we go)pic as we go)
Visceral layer of
capsule has
podocytes
Unusual branching
epithelial cells
Foot processes with
slit processes
between them
-------------------
19. 19
Scanning EM of podocytes clinging to
capillaries (left) and filtration membrane
diagram (right) The capillary pores (fenestrations)
restrict the passage of the largest
elements such as blood cells
The basement membrane and slit
diaphragm hold back all but the smallest
proteins while letting through small
molecules such as water, ions, glucose,
amino acids, and urea
20. 20
Nephron
Renal corpuscle
Tubular section
(processes the filtrate)
Proximal convoluted
tubule
Loop of Henle
Distal convoluted
tubule
(ends by joining
collecting duct)
Uriniferous tubule (anatomical unit for forming urine)
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries)
Glomerular (Bowman’s) capsule
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
21. 21
Proximal convoluted
tubule
Confined to renal
cortex
Cuboidal
epithelial cells
with long
microvilli (fuzzy
appearance in
pics)
Resorption of
water, ions and
solutes
Uriniferous tubule (anatomical unit for forming urine)
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries)
Glomerular (Bowman’s) capsu
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
*
22. 22
Loop of Henle
Descending limb
Thin segment
Thick ascending
limb
Uriniferous tubule (anatomical unit for forming urine)
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries)
Glomerular (Bowman’s) capsule
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
23. 23
Distal convoluted tubule
Confined to the
renal cortex
Simple cuboidal
epithelium
Selective
secretion and
resorption of ions
Uriniferous tubule (anatomical unit for forming urine)
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries
Glomerular (Bowman’s) caps
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
24. 24
Classes of
nephrons
Cortical nephrons
85% of all
nephrons
Almost entirely
within cortex
Juxtamedullary
nephrons
Renal corpuscles
near cortex-
medulla junction
25. 25
Collecting Ducts
Each receives
urine from
several
nephrons
Run straight
through cortex
into the deep
medulla
Uriniferous tubule (anatomical unit for forming urine)
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries)
Glomerular (Bowman’s) capsule
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Collecting Duct
26. 26
Collecting Ducts
At papilla of
pyramid* ducts
join to form larger
papillary ducts
Empty into minor
calices
Role: conserve
body fluids
Uriniferous tubules
1. Nephron
2. Collecting ducts
*
27. 27
The collecting ducts
The most important role is to conserve body
fluids
When the body must conserve water, the
posterior pituitary gland secretes ADH
(antidiuretic hormone)
ADH increases the permeability of the collecting
tubules and distal tubules to water so more is
reabsorbed
This decreases the total volume of urine
Alcohol inhibits the release of ADH, so less
water is reabsorbed producing copious amounts
of dilute urine (can cause dehydration)
28. 28
Vessels
Afferent and efferent arterioles associated with glomerular capillaries
Allows high pressure for forcing filtrate out of blood
About 20% of renal plasma flow is filtered each minute (125 ml/min): this is the
glomerular filtration rate (GFR), an important clinical measure of renal function
This is about one liter every 8 minutes (only 1% ends up as urine)
Peritubular capillaries arise from efferent arterioles
Absorb solutes and water from tubule cells
29. 29
The Vasa recta is a
portion of the
peritubular capillary
system which enters the
medulla where the
solute concentration in
the interstitium is high.
It acts with the loop of
Henle to concentrate
the urine by a complex
mechanism of counter
current exchange using
urea. If the vasa recta
did not exist, the high
concentration of solutes
in the medullary
interstitium would be
washed out.
____vasa recta
(vessels, continued)
The Vasa recta
34. 34
For studying
Parts of the kidney:
1. Renal pyramid
2. Efferent vessel
3. Renal artery
4. Renal vein
5. Renal hilum
6. Renal pelvis
7. Ureter
8. Minor calyx
9. Renal capsule
10. Inferior renal capsule
11. Superior renal capsule
12. Afferent vessel
13. Nephron
14. Minor calyx
15. Major calyx
16. Renal papilla
17. Renal column
35. 35
The Ureters
Slender tubes about
25 cm (10 “) long
leaving each renal
pelvis
One for each kidney
carrying urine to the
bladder
Descend
retroperitonealy and
cross pelvic brim
Enter posterolateral
corners of bladder
Run medially within
posterior bladder wall
before opening into
interior
This oblique entry
helps prevent backflow
of urine
36. 36
Ureters play an active
role in transporting urine
(it’s not just by gravity)
Three basic layers
Transitional epithelium
of mucosa stretches
when ureters fill
Muscularis
Inner longitudinal, outer
circular layers
Inferior 3rd
with extra
longitudinal layer)
Stimulated to contract
when urine in ureter:
peristaltic waves to
propel urine to bladder
Adventitia (external)
37. 37
Urinary Bladder Collapsible
muscular sac
Stores and expels
urine
Lies on pelvic floor
posterior to pubic
symphysis
Males: anterior to
rectum
Females: just
anterior to the
vagina and uterus
See also brief atlas
41. 41
If full: bladder is spherical and extends into
abdominal cavity (holds about 500 ml or 1 pt)
If empty: bladder lies entirely within pelvis with
shape like upside-down pyramid
Urine exits via the urethra
Trigone is inside area between ureters and
urethra: prone to infection (see slide 38)
42. 42
Bladder wall has three layers (same as ureters)
Mucosa with distensible transitional epithelium and
lamnia propria (can stretch)
Thick muscularis called the detrusor muscle
3 layers of highly intermingled smooth muscle
Squeezes urine out
Fibrous adventitia
43. 43
The Urethra
Smooth muscle with inner mucosa
Changes from transitional through stages to stratified squamous near end
Drains urine out of the bladder and body
Male: about 20 cm (8”) long
Female: 3-4 cm (1.5”) long
Short length is why females have more urinary tract infections than males -
ascending bacteria from stool contamination
Urethra____
urethra
44. 44
Urethral sphincters
Internal: involuntary sphincter of smooth muscle
External: skeletal muscle inhibits urination voluntarily
until proper time (levator anni muscle also helps
voluntary constriction)
Males: urethra has
three regions (see
right)
1. Prostatic urethra__________
2. Membranous urethra____
3. Spongy or penile urethra_____
_________trigone
female
46. 46
Micturition
AKA:
Voiding
Urinating
Emptying the bladder
(See book for diagram
explanation p 701)
KNOW:
Micturition center of brain:
pons
(but heavily influenced by
higher centers)
Parasympathetic: to void
Sympathetic: inhibits
micturition