Histology of the Renal System Flashcards
1
Q
How do the kidneys act as endocrine organs?
A
- secretion of erythropoietin
- secretion of renin
- hydroxylation of 25-OH vitamin D3
2
Q
What structures does the hilum contain?
A
- renal pelvis
- renal vessels
- renal nerves
- occupy the renal sinus
3
Q
Name the regions of the kidney?
A
- the capsule
- cortex
- medulla
- renal pelvis
4
Q
Describe the cortex?
A
- most superficial region
- light in colour
- granular appearance
5
Q
Describe the medulla?
A
- deep to the cortex
- darker tissue
- cone shaped tissue masses : medullary/renal pyramids
6
Q
Describe the structure of renal pyramids?
A
has a base which is convex, and a apex which tapers toward its apex or papilla
- each medullary pyramid is surrounded by a capsule of cortical tissue to form a lobe
7
Q
Describe renal columns?
A
Inward extensions of cortical tissue that separate the pyramids
8
Q
Describe the microscopic structure of the capsule?
A
- outer fibrous layer - collagen
2. inner cellular layer - myofibroblasts
9
Q
What does the capsule cover at the hilum?
A
- sinus
- walls of renal calyces
- renal pelvis
10
Q
What does the colour of the cortex and medulla reflect?
A
distribution of blood
- cortex : 90-95%
- medulla : 5-10%
11
Q
The cortex contains which structures microscopically?
A
- renal copuscles
- associated tubules
- extensive vascular supply
- medullary rays - eminate from medulla
12
Q
Name the associated tubules found in the cortex?
A
- convoluted and straight tubules of the nephron
- collecting tubules
- collecting ducts
13
Q
Describe the renal corpuscles?
A
- spherical structures composed of glomerulus: capillary network
- proximal segment of the nephron
14
Q
Describe the medullary rays?
A
straight segments of the loop of Henle and collecting ducts
15
Q
What are cortical labyrinths?
A
regions between medullary rays
16
Q
What is found in cortical labyrinths?
A
uriniferous tubule (kidney tubule)
- renal corpuscles
- convoluted tubules of nephrons (proximal +distal)
- collecting tubules
17
Q
The medulla is characterised by which structures microscopically?
A
- straight tubules
- collecting ducts
- vasa recta
- renal columns (of Bertin)
18
Q
The tubules in the medulla form?
A
renal pyramids
- apex (papilla) projects into minor calyx
- tip of papilla (area of cribrosa) is perforated by openings of collecting ducts
19
Q
Medulla is divided into?
A
outer + inner medulla
20
Q
The outer medulla is divided into?
A
- outer stripe
2. inner stripe
21
Q
What are kidney lobes?
A
Formed by each pyramid and its associated cortical tissue at its base and sides (1/2 of renal column)
- Number of lobes = number of medullary pyramids
22
Q
How many lobes are in a human kidney?
A
8 - 18 lobes
23
Q
What is a kidney lobule?
A
Consists of central medullary ray and surrounding cortical tissue
: collecting duct + all nephrons that it drains
- constitute a renal secretory unit
24
Q
What is the uriniferous tubule?
A
main structural and functional unit of the kidneys
- nephron
- its collecting duct or tubule
25
What is a nephron?
structural + functional unit of the kidney
26
The nephron consists of?
1. renal corpuscle
| 2. tubule system
27
How are the types of nephrons determined?
based on location of their renal corpuscles in the cortex
28
Describe subscapular/cortical nephron?
- renal corpuscles located in the outer part of cortex
- have short loops of henle
- hairpin turn occurs in outer medulla
29
Describe juxtamedullary nephrons?
- renal corpuscles located at the base of the medullary pyramid
- have long loops of henle
- long ascending thin segments
30
Describe intermediate/midcortical nephrons?
- Renal corpuscles located in the midregion of the cortex
| - Have intermediate length loop of henle
31
What is the structure of the nephron?
1. renal corpsucle
2. proximal convoluted tubule
3. loop of henle
4. distal convoluted tubule
5. collecting duct - concentrating urine
32
What is the renal/Malpighian corpuscle?
first part of the nephron, where the filtration occur
33
The renal corpuscle consists of?
1. Glomerulus – tuft of capillaries (10-20 capillary loops)
| 2. Bowman’s capsule – double-layered epithelial cup that surrounds the glomerulus
34
Function of Bowmans capsule?
filters blood to produce glomerular filtrate
35
What are the layers of Bowmans capsule?
1. parietal layer
2. visceral layer
3. space between layers - urinary space
36
Describe the external parietal layer?
- simple squamous epithelium associated with connective tissue stroma
- Continuous with simple cuboidal epithelium of the proximal convoluted tubule
- plays no part in the formation of filtrate : contributes to structure
37
Describe the visceral layer?
- attaches to glomerulus
| - consists of unusual, branching epithelial cells called podocytes, reinforced by basal lamina
38
Describe the podocytes?
have many branches which end in foot processes or pedicels
39
Describe the pedicels of the podocytes?
they inter digitate with one another as they surround the glomerular capillaries
40
Where does the filtrate pass through in Bowmans capsule?
thin filtration slits made by the pedicels into the capsular space
41
What is the glomerulus?
a tuft of capillaries associated with a renal tubule
42
The glomerulus consists of?
1. Glomerular capillaries
2. Mesagium –formed by mesangial cells
3. Podocytes –visceral layer of bowman’s capsule
43
The glomerulus is supplied by?
afferent arteriole
44
The glomerulus is drained by?
efferent arteriole
45
What are the 2 poles of the glomerulus?
vascular and urinary
46
Describe the vascular pole of the glomerulus?
site where efferent and afferent arterioles enter and exit parietal layer of bowman’s capsule
47
What is the urinary pole of the glomerulus?
site where proximal convoluted tubule begins
48
Describe the composition of the filtrate found in the glomerulus capsule?
solute-rich, virtually protein free fluid
| - is processed by the renal tubules to form urine
49
What is the filtration apparatus of the kidney?
found within the renal corpuscle
| - acts as semi permeable barrier
50
What are the 3 components of the filtration apparatus?
1. endothelium of glomerular capillaries
2. glomerular basement membrane
3. visceral layer of Bowmans capsule
51
Describe the endothelium of glomerular capillaries?
1. Contains numerous fenestrations (70-90 nm)
- Fenestrations have no diaphragm - make capillary porous
2. Contains large number of aquaporin-1 (AQP-1) water channels
52
Describe the glomerular basement membrane?
Thick basement membrane (300-350 nm) that acts as a semi-permeable barrier
53
The basement membrane is secreted by?
1. endothelial cells
| 2. Podocytes
54
What is the molecular composition of the glomerular basement membrane?
1. Type IV collagen
2. Sialoglycoproteins
3. Noncollagenous glycoproteins (e.g. laminin, fibronectin, entactin)
4. Proteoglycans
5. Glycosaminoglycans – heparin sulfate
55
What are the layers of the glomerular basement membrane?
1. lamina rara interna
2. lamina externa
3. lamina densa
56
Describe the lamina rara interna?
- Adj. to capillary endothelium
| - Contain polyanions (heparan sulfate)
57
Describe the lamina externa?
- Adj. to podocyte processes
| - Contains similar molecules as lamina rara interna
58
Describe lamina densa?
- Fused portions of laminae
| - Contains: type IV collagen & sialoglycoproteins
59
What is the urinary space/Bowmans space?
lie between parietal and visceral layers of the Bownman’s capsule.
60
Describe the visceral layer of Bowmans capsule?
Contains podocytes or visceral epithelial cells
| - Podocytes extend processes (pedicels or foot processes) around glomerular capillaries
61
Describe what pedicels form?
Spaces between pedicels form filtration slits with a filtration slit membrabe
62
Pedicels contain?
actin filaments
63
What is the mesangium?
intraglomerular structure
64
The mesangium contains?
1. mesangial cells
| 2. extracellular matrix
65
Where is the mesangium found?
in renal corpuscle and extend to vascular pole
66
When mesangial cells extend to the vascular pole they are known as?
extraglomerular mesangial cells or lacis cells
| - juxtaglomerular apparatus
67
What are the functional characteristics of mesangial cells?
```
Contractile
Phagocytotic
Capable of proliferation
Synthesize both matriX and collagen
Structural support
Synthesize and Secrete prostaglandins and endothelins, ( IL-1, PDGF)
```
68
What is the juxtaglomerular apparatus?
Small endocrine structure that lies adj. to vascular pole of renal corpuscle
69
Juxtaglomerular apparatus consists of?
1. Macula densa – cells of distal straight tubule.
2. Juxtaglomerular cells – renin producing modified smooth muscle cells of afferent arteriole
3. Extraglomerular mesangial cells
70
What are the functions of the juxtaglomerular apparatus?
Regulates Bp by activating the renin-angiotensin – aldosterone system
71
What are interstitial cells?
cells located in the interstitial tissue of the kidney and surrounds nephrons vessels
72
What are the 2 types of interstitial cells in the cortex?
1. Fibroblast-like cells – secret collagen +GAG
| 2. Macrophages
73
What do the interstitial cells of the medulla contain?
contain myofibroblast
74
The tubule system of nephron consists of?
1. proximal thick segment
2. thin ascending limb of loop of henle
3. distal thick segment
75
The proximal thick segment consists of?
1. Proximal convoluted tubule (pars convoluta)
2. Proximal straight tubules (pars recta)
- Thick descending limb of loop of henle
- Thin descending limb of loop of henle
76
The distal thick segment consists of?
1. Distal straight tubule (pars recta)
- thick ascending limb of loop of henle
: makes contact with vascular pole of renal corpuscle
- Epithelial cells form macula densa
2. Distal convoluted tubule (pars convoluta)
- empties into collecting duct via arched collecting tubule or connecting tubule
77
What are connecting tubules?
- Begins in the cortical labyrinth as connecting tubules or arched collecting tubules
- Join collecting ducts in the medullary rays
78
Describe the 2 types of collecting ducts?
1. Cortical collecting ducts
- located within the cortex
2. Medullary collecting ducts
- travel to the pyramidal apex.
- Merge into larger ducts : papillary ducts (ducts of Bellini)
- open at area cribrosa
79
What are the functions of the proximal convoluted tubule?
1. Initial and major site of re-absorption 150L/day of fluid (80% ultrafiltrate)
2. Re-absorbes amino acids, sugars and polypeptides
3. Endocytoses proteins and large peptides
80
What are the special features of the cuboidal cells in the proximal convolutes tubules?
1. Brush border –long straight microvilli
2. Junctional complex
3. Plicae or folds on lateral surface
4. Inter-digitation of basal processes
5. Basal striations – contained elongate mitochondria
81
What causes the striated look of the cuboidal cells of the proximal convoluted tubule?
numerous basal infoldings & plenty of mitochondria
82
Describe the cells of the proximal straight tubule?
1. Have shorter cells with less well developed brush borders
2. Very few and less complex lateral and basalateral processes
3. Have randomly distributed small mitochondria
83
Describe the epithelium of the thin segment of the loop of henle?
simple squamous epithelium
84
What are the 4 types of epithelial cellls in the thin segment of the loop of henle?
1. type I epithelium
2. type II
3. type III
4. type IV
85
Describe the Type I epithelium of thin segment of the loop of Henle?
- Located in descending and ascending limbs of loop of henle
(short looped nephrons)
- Have no interdigitations with other cells
- Few organelles
86
Describe the Type II epithelium of thin segment of loop of Henle?
- Found in thin descending limb of long looped nephrons in cortical labyrinth
- Tall epithelium
- Have many small brunt microvilli
- Varying interdigitations
87
Describe the Type III epithelium of the thin segment of loop of Henle?
- Found in thin descending limb in inner medulla
- Cells have simpler structure and fewer microvilli
- No lateral interdigitations
88
Describe the Type IV epithelium of thin segment of loop of Henle?
- Found at the bend of long looped nephrons and the entire ascending limb.
- Cells have low flattened epithelium
- No microvilli
89
What is the medullary loop?
Consists of an descending limb, a thin segment and a ascending limb
90
Describe the histology of the medullary loop?
the thin part is lined by simple squamous epithelium resting on a thin BL
- the sq. cells bulge into the lumen of tubule
91
Where is the medullary loop?
Extends from corticomedullary junction to medulla
92
What is the function of the medullary loop?
Functions as a counter-current multiplier system to determines osmolarity of urine
- blood flow in the loop is counter to that in medullary vasa recta
93
Name the 2 types of collecting tubules?
1. collecting tubules
| 2. medullary collecting ducts
94
Describe the histology of collecting tubules?
Have squamous to cuboidal epithelium
95
Describe medullary collecting ducts?
Have simple cuboidal epithelium + tansition to columnal as the duct sizes increase
96
What are the 2 distinct cell types of collecting tubules + ducts?
1. light cells - collecting duct or CD cells
| 2. dark cells - intercalated (IC) cells
97
Describe light cells?
- Principal pale staining cells
- Cells have basal foldings
- Posses a single cilium + short microvilli
98
What are dark cells?
- Have dense cytoplasm and many mitochondria
- Have apical cytoplasmic folds (microplacae)
- Have microvilli
99
The renal artery is a branch of?
abdominal aorta
100
Describe the blood supply within the renal sinus?
interlobar arteries - pass between pyramids
101
Describe the bloody supply at the base of the pyramid?
interlobar arteries > arcuate arteries (interlobular arteries) > afferent arterioles > glomerular capillaries > efferent arterioles > peritubular capillaries
- afferent arterioles are capillaries that form glomerulus
102
Describe the course of efferent arterioles?
From cortical glomeruli > Lead to peri-tubular capillary network
From Juxtaglomeruli > Descends with loop of henle to form vasa recta
103
Describe the venous drainage?
Peritubular cortical capillaries > interlobular veins > arcuate veins > interlobar veins > renal vein
Capsular capillaries > into stellate veins > interlobular veins
104
What are the 2 major lymphatic networks?
1. Outer regions of the cortex - drain into lymphatic vessels in the capsule
2. Deep regions - drain into large lymphatic vessels in renal sinus
