111111111111111111111111Urinary System.pdf

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1. Urinary System
•Maintenance of water, electrolyte and
acid-base homeostasis.
•Excretion of many toxic metabolic waste
products.
•Maintenance of normal blood pressure.
•Ureters, bladder and urethra form the
storage and outlow tract.

2. Kidney
Functions:
•Regulation-maintain an appropriate fluid volume and
concentrations of various electrolytes in the body
fluids, maintain normal blood pressure, and maintain
the pH of blood
•Excretion-elimination of water-soluble metabolic
wastes and foreign substances as urine
•Endocrine-secretion of hormones
–Renin -regulation of blood pressure
–Erythropoietin -stimulates production of red blood cells
–Vitamin D -regulation of calcium levels

3. Nephron
•2 main types of nephrons:
–Cortical nephrons (85% of the total nephron count): renal
corpuscles located in the outer part of the cortex. Short
loops of Henle, extending only into the outer medulla.
–Juxtamedullary nephrons (15%): renal corpuscles in
proximity to the base of a medullary pyramid. Long loops
of Henle.
renal corpuscle renal tubule
•Bowman’s capsule
•Glomerulus
•Proximal convoluted tubule
•Loop of Henle
•Distal convoluted tubule

5. Renal Corpuscle
•The renal corpuscle is spherical and has an
average diameter of 200 μm.
•Bowman’s capsule consists of a single layer of
flattened cells resting on a basement
membrane; it is derived from the distended
blind end of the renal tubule.
•The glomerulus is a globular network of
anastomosing capillaries which invaginates
Bowman’s capsule.
•The layer of invaginated epithelium
flattens and differentiates into
podocytes that become closely
applied to the outer surfaces of
glomerular capillaries.

6. •The efferent vessel has the structure of an
arteriole and is thus called the efferent
arteriole (not venule).
•Arterial portal system of a kidney
•The efferent arteriole is of smaller
diameter than the afferent arteriole,
and a pressure gradient is thus
maintained that drives the filtration
of plasma into Bowman’s space.

7. Glomerulus
•The glomerulus is the conspicuous "little
knot" which occupies most of the
corpuscle.
•Mesangial cells are concentrated between
capillaries at the vascular pole of the
corpuscle.
Renal corpuscle, stained by toluidine blue
•Secrete a matrix of basement membrane-like
material to support the structure of the
glomerulus.

8. •Functions of the
mesangial cells:
–Structural support
–Phagocytosis and
endocytosis
–Modulation of
glomerular
distension
Glomerulus(a)Thinepoxyresinsection,toluidineblue (HP)
(b)Schematicdiagram
Mesangium

9. •Renal corpuscle is the site of
filtration from the glomerular
capillaries into Bowman’s
space to form the glomerular
ultrafiltrate.
•The glomerular filtration
barrier (GFB)
–capillary endothelium
–common basement membrane
–podocyte layer

10. GFB: Capillary
Endothelium
•Capillaries (green) with large round fenestrations (60-
100 nm in diameter) which occupy 20% to 50% of the
endothelial surface area.
•Diaphragm that spans the fenestrations in other
capillaries is absent here.

11. GFB: Basement Membrane
•~350 nm in adults
•Produced by both capillary
endothelial cells and
podocytes
•Feltwork of
–type IV collagen
–structural glycoproteins
(fibronectin and laminin)
–proteoglycans
•3layers:
–lamina rara interna
–lamina densa
–lamina rara externa
•Both laminae rarae are
negatively charged

12. GFB: Podocytes
•1°processes
•short 2°foot processes
(pedicels)
•filtration slits(40 nm)

13. •Slit diaphragm: a single layer of the
transmembrane protein nephrin
•Acts as a size-selective filter
•Negatively charged glycocalyx layer

14. •The subpodocyte space (SPS, between the podocyte foot processes and the podocyte cell
bodies) has been recently shown to be a fourth component of the GFB. The SPS has higher
hydrostatic pressure than Bowman’s space, and it is thought that the podocytes, by altering
the size of the SPS and the exit pore, are able to regulate filtration through the GBM.

15. Filterability of various
molecules
•The factors that influence permselectivity
are the negative charge of the basement
membrane and the podocytic epithelium,
as well as the effective pore size of the
glomerular wall (8nm).
•For macromolecules, 3factors determine
permeability:
1.Charge
2.Size
3.Configuration

16. GFB: Permeability-selectivity
Endothelial Cell
Foot Process
Basement
Membrane
Slit: 2-8 nm
Slit
Diaphragm
Filtration slit
4-11 nm
Blood
Bowman’s Space
70-90 nm
40 nm
Glycocalyx
-
-
- -
-
-
-
- -
-
-
Large and/or
negatively charged
molecules will pass
through far less
frequently than small
and/or positively
charged ones.
-
-
-
-

17. Renal tubule
•~55 mm long
•Lined by a single layer of
epithelial cells
•Selective reabsorption (99% of
water, inorganic ions and other
molecules) from the
glomerular filtrate
•Secretion of some inorganic
ions directly from blood into
the lumen of the tubule

18. Proximal Convoluted Tubule
•~14 mm in length
•Approximately 65% of the glomerular filtrate is reabsorbed from the PCT, a function reflected in
the structure of the epithelial lining
•Large cuboidal cells with a prominent brush border (microvilli)
•Surrounded by a rich network of peritubular capillaries

19. •Surface specializations associated with cells
engaged in absorption
and fluid transport:
–abrush border
–multiple lateral processes
–extensive interdigitation of basal processes
–basal striations, consisting of elongate
mitochondria
concentrated in the basal processes
Schematic drawing of proximal convoluted tubule cells.

20. Loop of Henle
•4segments:
1.thick descending limb (pars recta of
PCT)
•simple cuboidal epithelium that is
structurally similar to the proximal
convoluted tubule
2.thin descending limb
•simple squamous epithelium
3.thin ascending limb
•simple squamous epithelium
4.thick ascending limb (pars recta of
DCT)
•simplecuboidalepitheliumthatis
structurallysimilartothe distal
convolutedtubule

21. Loop of Henle
Thin descending
and ascending
limbs
The main function of the
loops of Henle is to
generate a high osmotic
pressure in the
extracellular fluid of the
renal medulla (counter-
current multiplier system).

22. Distal Convoluted Tubule
•Within the cortex among the
proximal convoluted tubules
•DCT is much shorter than the
PCT
•Differences from PCT:
–absence of a brush border
–a larger more clearly defined
lumen
–more nuclei per cross-section
–paler cytoplasm
•Responsible for
–reabsorption of sodium ions, an
active process controlled by the
aldosterone
–secretion of hydrogen or
potassium ions into the DCT

23. Juxtaglomerular apparatus (JGA)
Located near the vascular pole
of the glomerulus
Components:
1.macula densa of the DCT
2.renin-secreting
juxtaglomerular cells of
the afferent arteriole
3.extraglomerular
mesangial cells (lacis cells)

24. Macula Densa
•Area of closely packed,
specialized DCT epithelial
cells
•The cells are sensitive to
the ionic content
(chemoreceptors) and
water volume
(baroreceptors) of the
tubular fluid, producing
molecular signals that
promote the liberation of
the enzyme renin in the
circulation.

25. Juxtaglomerular cells
•Modified smooth
muscle cells of the
wall of the afferent
arteriole
•Juxtaglomerular cell
cytoplasm contains
membrane-bound
granules of the
enzyme renin

26. Extraglomerular mesangial cells
•Goormaghtigh cells or lacis
cells
•Flat and elongated, with
extensive fine cytoplasmic
processes extending from
their ends and surrounded by
a network (‘lacis’) of
mesangial material.
•Responsible for transmission
of a signal arising in the
macula densa to the
intraglomerular mesangial
cells, which then contract or
relax to make the capillary
loops narrower or wider.

28. Collecting tubules and collecting ducts
•Collecting tubule is a straight terminal portion of
the nephron
•Several collecting tubules converging to form a
collecting duct
•Collecting ducts descend through the cortex in
parallel bundles (medullary rays)
•Form in the medulla ducts of Bellini, which open
at the tips of the renal papillae
Medullary rays
Ducts of Bellini

29. •Lined by simple cuboidal epithelium.
•The intercellular limits of the collecting tubule and duct cells are clearly
visible in the light microscope.
•Concentrate urine by passive reabsorption of water into the medullary
interstitium and to the general circulation.
•The amount of water reabsorbed is controlled by antidiuretic hormone
(ADH, vasopressin).
The effects of ADH on the collecting ducts

30. Renal vasculature
renal artery interlobar arteries
arcuate arteries
interlobular arteries
afferent arterioles
glomerulusefferent arterioles
peritubular capillaries vasa recta
interlobular veins
arcuate veins interlobar veins renal vein

31. Diagram showing movement of substances
into and out of the nephron and collecting
system.

32. Counter-current multiplier mechanism
•A countercurrent
mechanism system is a
mechanism that expends
energy to create a
concentration gradient.
•Provide the process of urine
concentration-the
production of hyperosmotic
urine.

33. 4. The countercurrent flow within the descending and
ascending limb thus increases, or multipliesthe osmotic
gradient between tubular fluid and interstitial space
1. The descending limb of the loop
of Henle: permeable to water but
impermeable to solutes
hypertonic filtrate
2. The ascending limb:
impermeable to water but
permeable to solutes
hypotonic filtrate
single effectof
the
countercurrent
multiplication
process
3. The interstitium is now hypertonic,
and will attract water
5. Vasa recta removes water so it does
not dilute the medullary gradient

34. Lower urinary tract
•Renal calyces
•Renal pelvis
•Ureters
•Urinary bladder
•Urethra
specialised for the storage and excretion of urine
The same general structures:
•mucosa (lined by transitional epithelium)
•muscularis
•adventitia (serosa)

35. Ureters
•Transitional epithelium
(urothelium)
•Lamina propria
•Muscularis externa
–Inner longitudinal layer
–Outer circular layer
–Outer longitudinal layer
(in the lower third of
the ureter)
•Adventitia

36. Urinary bladder
•Transitional
epithelium
(urothelium)
•Lamina propria
•Muscularis
externa
–Inner
longitudinal
layer
–Outer circular
layer
–Outer
longitudinal
layer
•Adventitia
Detrusor muscle

37. Urethra
•Fibromuscular tube that conveys urine from
the urinary bladder to the exterior.
•In the male (about 20 cm long), 3 distinct
segments
–Prostatic urethra (3-4 cm), transitional
epithelium
–Membranous urethra (1 cm), stratified or
pseudostratified columnar epithelium
–Penile (spongy) urethra (15 cm),
pseudostratified columnar epithelium and
stratified squamous epithelium at distal end
•In the female, the urethra is short, measuring 3 to 5 cm. Transitional epithelium
changes to stratified squamous epithelium before its termination.