Histology of the Urinary System-Csoka Flashcards
1
Q
What is the primary function of the urinary system?
A
Urinary system is concerned with filtration of blood because the circulatory system/CNS needs to be cleaned and waste products excreted.
2
Q
What organs are consisted in the urinary system?
A
- 2 kidneys
- ureter
- bladder
- urethra
3
Q
What is the function of the bladder?
A
is the temporary reservoir for the urine
4
Q
What is the difference between the ureter and urethra?
A
- ureter carries filtered blood from kidney to bladder
- urine is sent out of body through urethra
5
Q
What is the main blood supply of the kidneys?
A
renal artery
6
Q
What is the functional unit of the kidney?
A
nephron
7
Q
Uniquely in the kidney, the renal artery doesn’t shuttle off and become a venule but connects to a structure called?
A
glomerulus
8
Q
Macroscopically the structure of the kidney is organized into what 3 large structures?
A
- cortex
- medulla
- renal pelvis
9
Q
What are the functions of the kidney?
A
- acts as a blood filter
- maintains electrolyte, acid-base, and fluid balance of blood
- removes nitrogenous wastes
- homeostatic organ
- releases hormones: calcitriol (vitamin D) and erythropoietin
10
Q
What stimulates the production of erythropoietin and what is its function?
A
- produced by peritubular fibroblasts
- induced by hypoxia
- stimulates bone marrow to produce RBCs
-can be given to dialysis patients to improve RBC counts
11
Q
What macroscopic structure of the kidney branches off into the ureter?
A
renal pelvis
12
Q
Where do the renal columns go to?
A
medulla
13
Q
Where is the renal cortex located?
A
out region of the kidney
14
Q
Where is the renal medulla located?
A
inside the cortex
15
Q
Where is the renal pelvis located?
A
inner collecting tube
16
Q
What are the calyces and what is their function?
A
- calyces (major and minor calyx) are the constituents of the renal pelvis
- funnels urine towards the renal pelvis
17
Q
What are the renal columns?
A
extensions of the cortex-like material inward
18
Q
What are the medullary pyramids?
A
triangular regions of tissue in the medulla (called “lobes” if include cortex)
19
Q
Which structures will you see in the renal cortex? What will you not see?
A
glomerulus, proximal, and distal convoluted tubule
will NOT see: loop of Henle or collecting ducts
20
Q
Which structures will you see in the renal medulla? What will you not see?
A
loop of Henle or collecting ducts
will NOT see: glomeruli
21
Q
Which structures will you see in the renal pelvis?
A
-see mostly collecting ducts and some transitional epithelium as well as adipose
22
Q
How does the essential tissue composition of kidney resemble that of a gland?
A
it has highly modified secretory units (renal corpuscles) and highly specialized ducts (tubules)
each renal corpuscle secretes a filtrate of blood plasma which drains into a renal tubule
renal tubules modify the filtrate by reabsorbing everything that is not waste
23
Q
What is the most abundant tissue of the renal parenchyma?
A
nephrons
24
Q
What are the five parts of a nephron?
A
- renal corpuscle
- proximal convoluted tubule
- loop of Henle (medullary loop)
- distal convoluted tubule
- collecting duct
25
What brings the blood into the nephron? Where does the filter blood collect before it goes off to the proximal tubule?
- afferent arteriole brings blood to the nephron
| - the filtered blood collects in the Bowman's space
26
When the filtrate goes down the loop of Henle and back up to the distal convoluted tubule, which glomeruli does the filtrate return to before going into the collecting duct?
the original glomerulus
27
Where does the process of urine formation begin?
renal corpuscles
28
Each renal corpuscle consists of an epithelial cup called ___________ enclosing a knot of capillaries and other elements called the __________.
Bowman's capsule
glomerulus
29
What is the difference between the proximal and distal convoluted tubule?
PCT:
- has brush borders
- stains more intensely eosinophilic
- simple cuboidal epithelium
- has numerous basal infoldings
- many mitochondria
DCT:
-more open and clear lumen
30
What are the functions of podocytes and mesangial cells?
- Podocytes have legs or feet (pedicels) holding the capillaries in place and stabilizing them; also contribute the formation of the filtration membrane
- Mesangial cells also stabilize the capillaries and secrete hormones and different types of matrix.
31
What type of capillaries are the glomeruli capillaries?
Glomerular capillaries have an endothelium that is fenestrated; fenestrations allow filtration to occur (windows in the capillaries allowing the filtrate to go through the walls of the capillary)
32
What is the filtration membrane?
- capillary/podocyte basement membrane
- has capillary fenestrations and podocyte filtration slits
- is a fusion of the endothelial basement membrane with the basement membrane of the podocytes
- Pedicel and Filtration Slit forming an additional filtration besides the fenestrations.
33
Bowman's capsule is the outer epithelium which encloses the Bowman's space. What type of epithelium is the Bowman's capsule?
This epithelium is simple squamous, becoming cuboidal at the proximal tubule.
34
The Bowman's space is entirely lined by epithelium. What forms the outer parietal epithelium and what forms the inner visceral epithelium?
The outer, "parietal" epithelium of the renal corpuscle is Bowman's capsule.
The inner, "visceral" epithelium is comprised of podocytes.
35
Each renal corpuscle is roughly spherical and which two "poles" at opposite ends? What is the difference between the two poles?
vascular and urinary pole
- vascular pole: receives the afferent (where the blood is coming in) and efferent arterioles
- urinary pole: is the location of the proximal tubule, the outflow for the glomerular filtrate
36
What is the juxtaglomerular complex?
- Is associated with the vascular pole of the renal corpuscle
- has two components: macula densa and juxtaglomerular cells
- macula densa has a specialized function as a sensor for sodium and/or chloride concentration
- Juxtaglomerular cells ("J-G cells") are specialized smooth muscle cells containing secretory granules, the source of the hormone renin
-they are baroreceptors and mechanoreceptors sense changes in BP and stretch thus secreting chemicals like renin to regulate BP
37
What is arguably the most significant component of the nephron? Without this, filtration will not occur?
glomerulus: the source of the initial filtrate of plasma that is eventually processed into urine
38
Where are mesangial cells concentrated?
between the capillaries at the vascular pole of the corpuscle
39
What types of substances can pass through the fenestrations and the filtration membrane?
Plasma passes through the capillary fenestrations, water, ions, and small molecules pass through the filtration membrane into Bowman's space, while serum proteins are retained in the capillaries
fenestrations are too small to allow blood cells through, but plasma can pass freely out of the holes and into the filtration membrane
filtration membrane holds back cells and large plasma proteins, but the remaining fluid (water, mineral ions, and small molecules) passes
40
Within the podocytes are specialized protein such as actin and crosslinking that connect adjacent pedicels called?
nephrin
41
What is the function of the proximal convoluted tubule components?
- microvilli absorb water, sodium, glucose, amino acids
- tubulovesicles capture peptides for degradation in lysosomes (peptides are bound to megalin)
- mitochondria provide energy for transport of sodium and other molecules
- reabsorbs water, nutrients, and solids
- reabsorbs most minerals and other nutrients from the tubular fluid and passes them to blood in the peritubular capillaries
42
What is the function of the loop of Henle?
dips into the medulla where it helps establish the hypertonic environment of medullary interstitial fluid
43
What is the function for the distal convoluted tubule?
returns to the juxtaglomerular apparatus of the corpuscle from which the tubule arose
juxtaglomerular apparatus: JG cells and macula densa put together
44
What is the function of the collecting duct?
leads back through the medulla to drain into the pelvis
45
The functional differences of the different tubular segments are associated with variation in what?
the structure of tubular epithelial cells, reflected in the microscopic appearance of the tubules
PCT: simple cuboidal
46
When blood is being filtered into the glomeruli, can RBCs and large proteins go through the capillary fenestrations?
NO
47
Juxtaglomerular cells are activated by macula densa to secrete?
renin
48
What are the two types of mesangial cells and what are their functions?
glomerular mesangial cells
- concentrated toward the vascular pole
- produce the mesangial matrix and may contribute to maintenance of the filtration membrane
extra-glomerular mesangial cells AKA lacis cells
-between the glomerulus and the macula densa of the distal tubule
49
What are the structural components of the proximal tubule cell?
- simple cuboidal epithelium
- long apical microvilli can occlude the lumen
- apical tubulovesicles
- basally located mitochondria
50
Describe the vascular filtration and reabsorption process in the nephron.
- Filtrate goes into Bowman’s space then to PCT
- There is some Reabsorption into the peritubular capillaries.
- So the afferent arteriole does not immediately go back to the main blood supply it continues to be associated with the nephron.
- That comes down and parallel to PCT to reabsorb various substances and go back out through renal structures to the renal vein.
-The blood supply goes into the glomerulus and then out through efferent arteriole. The story doesn't end there because it goes down in parallel to the PCT and facilitate reabsorption of AA and other substances back into the peritubular capillaries and back into the blood. So its like an additional filter for things that may have not gotten filtered the first time.
excretion= filtration-(reabsorption plus secretion)
51
What is the function of the loop of Henle?
loop helps to establish a hypertonic saline environment in the medulla which allows recovery of water from collecting ducts and concentration of urine within the collecting ducts)
52
What are the structural components to the loop of Henle?
Thick (cuboidal) descending limb, thin (simple squamous) segment, and thick ascending limb of loop
thin segment has a more open lumen
53
Sodium is actively transported out of the________ loop and establishes a concentration gradient in the interstitium.
ascending
54
What is the vasa recta and what is its function?
they are accessory capillaries that adhere to the loop of Henle removing the water and solute that is continuously added to the medullary interstitium thus maintaining the medullary gradient
55
What is the function of the distal convoluted tubule?
- Reabsorbs most of substances contained in ultrafiltrate especially glucose and amino acids
- reabsorption is regulated by ADH and aldosterone
56
The macula densa are part of what structure in the nephron?
DCT
macula densa are chemoreceptors
57
What is the function of the collecting duct?
Drain urine from nephron to renal pelvis
58
What are the two types of cells in the collecting duct?
-collecting duct (principal) cells: cuboidal in cortical part, columnar in medullary; less abundant in mitochondria; has cilium that enables altered distribution of aquaporins in the collecting
-intercalated /dark cells: resemble those of DCT but
bulge into lumen of the
collecting duct; has lots of mitochondria
Both rest on a thin basement membrane with no basal infoldings. Permeability of collecting duct to water and ions is regulated by ADH.
59
Collecting duct are exposed to what level of sodium concentration for water reabsorption?
high level of sodium in the medullary interstitium
60
What hormone alters the distribution and function of aquaporin-2 in the cells of the collecting ducts?
antidiuretic hormone (ADH)
-ADH causes aquaporin 2 vesicles to fuse with the plasma membrane
61
What is the function of the ureter?
conducts urine from kidney to bladder
62
What are the 3 tissue layers of the ureter?
- mucosa: lined by 5-6 cell layers of transitional epithelium that rests on lamina propria of loose connective tissue having blood vessels, lymphatics and with tubular mucus glands in the equidae
- muscularis: has outer longitudinal and middle layer of smooth muscles
- serosa/ adventitia
63
What are the different types of cells found in the ureter?
- transitional epithelium
- lamina propria (loose connective tissue)
- smooth muscle
- serosa
64
What special characteristic distinguishes transitional epithelium?
- has the property of the expandability and contractility matching the volume of urine
- Located on ureter and bladder
65
How does the urinary epithelium adapt to stretch? What is the mechanism used?
to flatten out, surface cells must acquire more plasma membrane to cover the same amount of cytoplasm with an expanded surface area of membrane
stretching induces migration of vesicles (which are filled with plasma membrane) to the lumen surface allowing for increased surface area.
66
What are the 4 tissue layers of the urinary bladder?
- mucos: lined with up to 14 cell layers of transitional
- submucosa: highly vascularized and rich with elastic fibers
- muscularis: has inner and outer longitudinal and middle layer of smooth muscle cells (dextruser muscles)
- serosa/adventitia: longi muscles form sphincters at ureterovesicular junction to prevent backflow of urine and at neck of bladder to regulate urine emptying
67
What are the 4 tissue layers of the urethra?
- mucosa: transitional BUT changes to stratified squamous at external urethral orifice
- submucosa: has cavenrous tissue spaces that are typical of erectile tissue
- muscularis: just like bladder but towards the external urethral orifice, acquires an external layer of skeletal muscle called urethralis muscle
- serosa/adventitia
68
What is the polycystic kidney disease?
- causes increasing kidney malfunction that becomes prominent by age 40
- characterized by outgrowths from normal tubules that enlarge into huge fluid filled cysts
- kidneys may enlarge to 3-4 times normal weight and volume
- incidence is 1 in 1,000 people
69
What is the causative gene for polycystic kidney disease?
polycystin 1 or 2 which codes for a protein that localizes to single cilia in renal tubule cells
kidney cells with abnormal or missing cilia appear to become dysfunctional and cause the formation of cysts
70
What is the function of aquaporins?
regulates the porosity of the collecting duct and its permeability to water; it is an additional regulator under the control of ADH
