1. Department of Histology and Embryology
15th The Urinary System
Department of Histology and Embryology

2. : components and functions 2. Kidney
1. Introduction
: components and functions
2. Kidney
2.1 General organization
※ 2.2 Nephron
※ 2.3 Filtration apparatus of the kidney
※ 2.4 Juxtaglomerular apparatus
2.5 Kidney tubule function
※ Proximal convoluted tubules
※ The loop of Henle
Distal convoluted tubules
Collecting tubules and collecting ducts
2.6 Blood supply
3.Excretory passages

3. Introduction Components Functions
1. The kidneys conserve body fluid and
electrolytes and remove metablic wastes
Production of the urine
2.Synthesis and secretion the renin and erythropoietin
3.Hydroxylation of 25-OH vitaminD3 to hormonally active 1,25(OH)2vitamin D3
to regulate the calcium balance.

4. Kidney Renal cortex Renal medulla Renal (medullary) pyramids
Medullary rays
Renal cortex
Cortex labyrinth
Renal medulla
Renal column
Renal (medullary) pyramids
Renal papilla
minor calyces
pelvis
major calyces
ureter
Capsule
parenchyma

5. Lobe: one renal pyramid and the cortical tissue at its base and sides
Lobule : a single medullary ray and the cortal tissue surrounding it
Uriniferous tubule:it consists of nephron and it collecting tubule
Uriniferous tubule
lobule
lobe

6. 1. Fuctions The 1st key point -Nephron
1) Filtration of most small molecules from blood plasma to form
an ultrafiltrate of plasma.
2) Selective reabsorption of most of the water and some other molecules
from the ultrafiltrate,leaving behind excess and waste materials to be
excreted
3) Secretion of some excretory products directly from blood into the urine.
4) Maintenance of the acid-base balance by selective secretion of H+ ions
into the urine.

7. 2. Structure 2.1 Renal corpuscle 2.2 Renal tubules
Convoluted
Proximal thick segment
Straight
Thin segment
The tubules of the loop of the
Henle acompanied by a capillary
network.these vessels represent
the vascular part of the
countercurrent exchange system
that regulates the concentration
of the urine.
Convoluted
Distal thick segment
Straight
Loop of Henle
It forms the entire U-shaped
portion of nephron.

8. 1.1 Renal corpuscle
Bowman’s capsule
Glomerulus

9. (1) Glomerulus
Capillaries tuft
intraglomerular mesangium

10. (2) Bowman’s capsule Glomerulus Urinary pole Parietal layer
Afferent arteriole
Efferent arteriole
Urinary pole
Vascular
pole
Parietal layer
Visceral layer
The basment memberane of the tubules and that of bowman’s capsule stains blue in Azan staining method

11. The 2nd key point - Filtration apparatus
(Function of the nephron)
Visceral layer of Bowmans’s capsule--
Podocyte
Glomerular basement membrane,GBM
Endothelium of the glomerular capillaries

12. Diagram of podocyte Secondary process GBM Primary process
Fenestrated endothliun
GBM
Filtration slit membrane

13. Scanning electron micrograph of Podocyte
Cell body
Primary process
Secondary process

14. Endothelium of the glomerular capillaries
1.It possesses numerous fenestrations.
1)These fenestrations are larger,more numerous,and more irregular
in outline than fenestrations in other capillaries.
2)The diaphragm aren’t spaned the fenestrations in capillaries.
2.Endothelial cells possess a large number of water channels
that allow the fast movment of water through the epithelium.

15. Renal filtration barrier
The fenestrated endothelium of the glomerular capillaries
The basal lamina
The filtration slits
It permits passage of water, ions, and small molecules from the blood stream into the capsular space but prevents passage of large and/or most negatively charged proteins, thus forming an ultrafiltrate of blood plasma in Bowman’s space.

16. Glomerular basement membrane,GBM
1. It is a thick( nm) basal lamina that is joint product
of the endothelium and the podocyte, PAS(+).
2. It acts as a physical barrier and an ion-selective filter.
Three portions of GBM:
The lamina rara interna
The lamina densa
(electron-dense layer)
The lamina rara externa
(more electron-lucent layer)

17. location Lamina rara externa Lamina rara interna Lamina densa
Adjacent to the podocyte
Adjacent to the capillary endothelium
Sandwiched between the laminea rarae
components
Rich in polyanions
Similar to rara externa
Type IV collagen is organized into a network
function
Impede the passage of negatively charged molecules
It act as a physical filter

18. The glomerular filtrate has chemical composition similar to that of blood plasma but contains almost no protein.
The glomerular basement membrane is a selective macromolecular
filter ,in which the lamina densa act as a pysical filter,whereas the
anionic sites in the laminae rarae act as a charge barrier.
1) Particals greater than 10nm in diameter do not readily cross the
basal lamina.
Neatively charged proteins with a molecular mass greater than
that of albumin(69kDa) pass across only sparingly.

19. 3. Type of nephron 1. Superfacial nephron (cortical nephron)
2. Midcortical nephron
3. Juxtamedullary nephron
Criterion :location of the renal corpuscles in the cortex

20. Clinical Considerations
Diabetes mellitus and Glomerulonephritis
The glomerular filter is damaged and markedly its filtering ability is reduced , it becomes much more permeable to proteins, with the subsquent release of protein into the urine.

21. Mesangium Structure The function of the mesangial cell
mesangial matrix
Structure
The function of the mesangial cell
1 Phaocytosis to clean the GBM
2 Structure support to provide support for the podocytes
in the areas where the epithelial basement
memberane is absent or incomplete.
3 Secretion interleukin-1 and platelet-derived growth factor
(PDGF),which play a central role in response to
to glomerular injury.

22. 2. Components 1. Location: 3. Function:
The 3rd key point -Juxtaglomerular (JG) apparatus
1. Location:
3. Function:
They are senstive to the ionic content and water volum of the
tubular fluid,producing molecular signals that promote the
liberation of the ezyme renin in the circulation .
Lying directly adjacent to the afferent and efferent Arterioles at the vascular pole of the renal corpusle
They have a cytoplasm full of secretory granules. Secretion of JG
Cells played a role in the maintance of blood pressure.
2. Components
Juxtaglomerular (JG) apparatus ：
1、Juxtaglomerular cells
部位：入球微A近血管球处，管壁平滑肌细胞演变成上皮样C
形态结构：粗面内质网、高尔基复合体、分泌颗粒
功能：分泌肾素、红细胞生成素
2、 Macula densa cells
部位：远端小管近血管极侧上皮细胞变高，密集排列而成
形态结构：基底面有指状突起伸向近血管球细胞
功能：离子感受器
3、Extraglomerular mesangial cells （球外系膜细胞）
部位：出、入球微A与致密斑间的三角区
形态结构：短小突起、分泌颗粒
功能：不清
4、极周细胞
部位：肾小囊脏层和壁层上皮移行处，包绕血管极
形态结构：体积大，有分泌颗粒
Extraglomerular mesangial cells
Macula densa cells
Juxtaglomerular cells

23. 2.Structure and Function
Contain secretory
granules of renin
Chemoreceptor
perceiving the
change of Na +
in distal tubule lumen
Renin-angiotension-aldosterone-system

24. Chemical composition difference between primary urine(ultrafiltrate) and final urine
The two kidneys produced 125ml of filtrate per minute,but just only 1ml is released into the ureters as urine.
The glomerular filtrate has
chemical composition
similar to that of blood
plasma but contains almost
no protein.
The final urine contains water, electrolytes as well as waste products, such as urea, uric acid, and creatinine,and breakdown products of various substances.
Where did it go to?
Where are they from?

25. Kidney tubule function

26. Function : It is the initial and major site of reabsorption
The 1st key point-Proximal convoluted tubule
Function : It is the initial and major site of reabsorption
Structure :
The cuboidal cells of it have the elaberate surface specializations
associated with cells Engaged in absorption and fluid transport.
1. A brush border
2. A juctional complex
3. Folds located on the lateral surface of the cells
4. Interdigitation of basal process of adjacent cells
5. Basal striations

27. 1.A brush border The 1st key point-Proximal convoluted tubule
It greatly increases the free cell
surface area, correlating with its
absorptive capacity.
1)At the electron microscopic
level , the microvilli constitute
the brush border apically.
2)The PAS staining method has
been used to demonstrate the
prominent brush border.

28. The 1st key point-Proximal convoluted tubule
The cytoplasm immediately beneath the
brush border contains many pinocytotic
veicles V and lysoomes L which are
involved in reabosorption and degradation
of small amounts of protein that have
leaked through the glomerular filter.
reaborbed solutes are transported into
surrounding cap with attenuated
endothelium E resting on a very thin
basement memberane.

29. 2. Folds located on the lateral surface of the cells
They creates interdigitating cytoplasmic process of adjoining cells.
no discrete limites can be observed (in the LM) between cells of the proximal tubule .
They increase the lateral surface area of the cell and are particularly
prominent in epithelia that are engaged in fluid and eletrolyte ransport
In active fluid transport ,sodium ions are pumped
out the cytoplasm memberane by Na+/K+ATPase
located in the memberane.

30. Na+-K+-ATPase Location : Function :
It is a kind of transmembrane proteins that are localized
In the lateral folds of the plasma membrane.
Location :
The active transport of Na+ out of the cell is acompanied by facilitated transport into the cells of Cl- , glucose and amino acids by means of transport proteins .almost 100% of filrated glucose and amino acids is reabsorbed by the PCT。
Function :
When the amount of glucose in the filtrate exceeds
the absorbing capacity of the proximal tubule, urine
become more abundant and caintain glucose.
Clinical thinking:

31. 3. Iterdigitation of basal process
Some of the interdigitating process extend
the full height of the cell.the process are
long in the basal region and create an
elaberate extracelluar compartment adjacent
to the basal lamina.
They increase the basal surface area of the cell and are particularly
prominent in epithelia that are engaged in fluid and eletrolyte ransport.

32. 4. Basal striations Mitochondria M are present in the cell
within the interdigitating process P. M are
responsible for the appearance of the basal
Striations in LM.
The cytoplasm of PCT epithelial cells stain intensely due to a high content of organelles, principally mitochondria.

33. 5. A juctional complex
It consists of a narrow ,tight junction that seals off the intercelluar space from the lumen of the tubule and a zoula adherens that maintains the adhension between neighboring cells .
The tight junction at the apical end of the intercelluar space
prevents fluid from moving in the opposite direction.

34. Components: Function : The 2nd key point-Loop of henle
The pars recta of the proximal tubule
The thick ascending limb(the distal
staight tubule)
The thin descending limb
The thin ascending limb
Function :
It is to produce an increasing
osmotic gradient from the cortex
to the lip of renal papilla by the counter-current
multiplier mechanism.

35. Structure : 1. The pars recta of the proximal tubule
The 2nd key point-Loop of henle
Structure :
1. The pars recta of the proximal tubule
The cells of it are not as specialized for absorption as are those of
the proximal convouluted tubule.
1) They are shorter, with a less well developed brush border and with
fewer and less complex lateral and basal-lateral processes.
2) The mitochondria are smaller than those of the cells of the
convoluted segment and are randomly distributed in the cytoplasm.
3) There are fewer apical invaginations and endocytotic vesicles, as
well as fewer lysosomes.

36. 2. The thin limb, T
The thin limbs T are lined by a flattened squamous epithelium Which has no capicity for active transport .
The thin desending limb allows free diffusion of H2O
but impermeable to NaCl .
The thin asending limb has also active function but allows passive diffussion of NaCl into the interstitium, not H2O.
The vasa recta take up water from the medullary interstitium and return it to the general circulation.

37. 2. The thin limb, T
The interstitial fluid in the medulla is hyperosmotic
Water diffuses out of ,salt diffuses into the nephron at this site
Passive momment of water into the connective tissue,and of salt and urea into the thin desending limb.

38. 3.The thick ascending ,A Active transport of NaCl again occurs here
The appearance of the cuboidal epithelium
1) Basolateral process interdigitate with each
other forming an extensive intercellular
space in a similar maner to the PCT.
2) The active transport process is fuelled by
ATP produced by many mitochondria found in these process .
3) It is also impermeable to water which maybe related to its thick glycocalyx composed of the glycoprotein, tamm-horsfall protein.

39. Light microscope: The distal convouluted tubule DCT The 3rd key point-
DCT maybe differentiated from PCT by
1) the absence of brush border (PAS-positive)
2) A larger more clearly defined lumen
3) more Nuclei per cross section (since DCT
cells Are smaller than PCT cells)
4) paler cytoplasm
5) Sections of DCT are much less numerours
than sections of PCT since the DCT is a
much more shorter segment of the renal
tubule than the PCT

40. The main features of Electron micrograph
1. Lateral cell interdigitations and
large numbers of mitochondria.
2.The basal plasma memberane
contains the Na+-K+ATPase.
3.It have only a few irregular
Microvilli at the luminal surface
4.The overlaying cytoplam contains
Large number of tiny vesiles.

41. Function of DCT The distal convoluted tubule exchanges Na+for K+into
the ultrafiltrate to conserve Na+ under aldosterone regulation.
1. Reabsorption of Na+and secret K+into the the ultrafiltrate
to conserve Na+
2. Reabsorption of bicarbonate ion
3.Conversation of ammonia to ammonium ion.

42. collecting tubule 1. Structure: 2.Function
The simple columnar epithelium consist two types of cells:
1) Light cells are princinple cells of the system.
2) Intercated cell : occur in considerably smaller numbers.
2.Function
1) They concentrate urine by paasive reabsorption of H2O Into the medullary interstium following te osmotic gradient Creeated by the counter-current multiplier system of the Loop of henle.
2) The amount of H2O reabsorbed is controled by antidiuretic hormone(ADH) secreted by the posterior pituitary in response to dehydration.
3) They can secrete H+.
They are readily ditinguished by Virtue of the cell boundaries that can be seen in the LM

43. Medical application Aldosterone deficiency in adrenalelectromized
animalsand in humans with Addison disease
result in an excessive loss of sodium in the urine.

46. 5. Renal blood circulation
Capsule capillary network
Stellate veins
Afferent arterioles
Efferent arterioles
capillary network
Glomerulus
Interlobular arteries
Interlobular veins
Arcuate arteries
Arcuate veins
Interlobar arteries
Interlobar veins
Renal veins
Renal artery

47. 1.An interlobular artery IA can be seen branching to form the afferent
Aterioles AA of a glomerulus G.
2.The efferent aterioles EA leaving
G is of much smaller diameterthan the
AA, to maintain pressure withinG cap
for plasma to be filtered into
Bowman’s space BS. Blood pressure
whithin G is controlled by variation of
the diamter of the AA and EA
3.In the superficial and midcortex as
shown here , EA give rise toa network
of cap which surround the renal tubules
RT.Towards the medula EA give rise to
the vasa recta.moleculesreabsorbed from
G filrtrate returned tothe general
circulation via this cap net which drain
into the renal venous system.
Section from kidney which has been perfused with
a red dye in order to demonstrate the renal blood supply.
Nephrons remain unstained.

48. Bladder and urinary passages
Structure of the wall :
They have same basic histologic
Structure:
Transitional epithelium
1. Mucosa :
Lamina propria of loose –to –dense
connective tissue
2.The muscular layer
3.Adventia

49. Review Test (A) a renal corpuscle (B) a distal convoluted tubule
1. A nephron includes all of the following components EXCEPT
(A) a renal corpuscle
(B) a distal convoluted tubule
(C) a thin limb of the loop of Henle
(D) a collecting tubule
(E) pars recta of the proximal tubule

50. 2. Which cells form the visceral layer of Bowman’s capsule
(A) Medullary interstitial cells
(B) Mesangial cells
(C) Podocytes
(D) Cells lining the proximal convoluted tubule
(E) Juxtaglomerular cells
3. Renal filtration barrier consists of all of the following components EXCEPT
(A) The fenestrated endothelium of the glomerular capillaries
(B) The basal lamina
(C) The filtration slits with diaphragms between pedicels
(D) Medullary rays

51. Summary 1.The components of the urinary system
The paired kidneys and ureters
and the unpaired bladder and
urethra.
the maintenance of water and electrolyte homeostasis, which requires that any input into the system is balanced by an equivalent output.
2. The principal function of the urinary system

52. Renal filtration barrier
It is composed of the fenestrated endothelium of the glomerular capillaries, the basal lamina, and the filtration slits with diaphragms between pedicels.
The structure of the
Renal filtration barrier
It permits passage of water, ions, and
small molecules from the blood stream
into the capsular space but prevents
passage of large and/or most negatively
charged proteins, thus forming an
ultrafiltrate of blood plasma in Bowman’s
space.
The function of the
Renal filtration barrier

53. homework
Give me a summary on what we talked about the structure of the renal tubule associated with its function in the class.

54. Have a good time !