Histology of the Kidney and Urinary System Flashcards
Name the 4 components of the urinary system
kidneys, ureters, urinary bladder and urethra
The urinary system functions (4)
- the excretion of waste products of metabolism
- water regulation
- electrolyte balance regulation
- secretion or renin and erythropoietin
Kidney shape
Bean-shaped with concave border (hilum)
What is the outer layer of the kidney
Capsule
What is the layer of the kidney directly below the capsule?
Cortex (grainy)
What is the layer of the kidney directly below the cortex?
Medulla (striated)
What separates the cortex and medulla
Cortico-medullary junction
Medullary pyramids contain… (2)
loops of Henle and collecting ducts
What is found in between medullary pyramids (in the medulla)
columns of Bertin (interlobar cortical tissue and collecting tubules)
The human kidney is divided in … and …
lobes and lobules
What is the area cribrosa?
~25 orifices at the apex of medullary pyramids (renal papilla)
What is the name for the apex of the medullary pyramids?
renal papilla
What are medullary rays?
Collections of tubules extending from the renal medulla to the cortex.
Each renal papilla opens into a…
minor calyx
Two to three adjacent minor calyces fuse to form…
major calyces
Major calyces open into…
the renal pelvis
Each kidney is composed of … nephrons.
1-4 million nephrons
What is another name for glomerular capillaries?
Glomerular tuft
Another name for glomerulus?
renal corpuscle
The PCT is highly
a) acidophilic
b) basophilic
a) acidophilic
What are the 3 portions of the loop of Henle?
Thick straight descending limb
Thin limb
Thick straight ascending limb
Unlike the proximal and distal tubules, the loop of Henle is NOT a convoluted nor a cortical structure.
Describe the 2 parts of the renal tubule.
A) Nephron:
* glomerulus
* proximal convoluted tubule
* loop of Henle
* distal convoluted tubule
B) Collecting tubules/duct
Once the collecting tubules pierce the cortico-medullary junction, they are called…
collecting duct
The collecting duct opens into…
the area cribrosa
Nephrons originate from….
metanephric blastema (metanephric mesenchyme)
The collecting tubules and collecting duct originate from…
ureteric bud
The renal corpuscle (glomerulus) is surrounded by…
the Bowman’s capsule
The parietal layer of the Bowman’s capsule is formed by…
squamous cells, BM and reticular fibres
The visceral layer of the Bowman’s capsule is formed by…
podocytes (specialized epithelial cells)
The visceral and parietal layers of the Bowman’s capsule are continuous at…
the vascular pole
Characteristic feature of podocytes
foot processes
Capsular space is enclosed by…
the visceral and parietal layer of the Bowman’s capsule
Vascular pole vs urinary pole
Two distinct regions of the glomerulus.
Vascular: This is the point where the afferent arteriole enters the glomerulus and the efferent arteriole exits.
Urinary: This is the opposite end of the glomerulus where the Bowman’s capsule transitions into the proximal convoluted tubule.
What marks the beginnning of the proximal convoluted tubule?
urinary pole
Function of juxtaglomerular cells
renin secretion
Location of juxtaglomerular cells
afferent arteriole
Function of macula densa cells
Specialized cells in the DCT.
Detect NaCl levels and signal to the afferent arteriole to either increase or decrease the GFR.
Location of macula densa cells
distal convoluted tubule
What is the name of secondary processes of podocytes
pedicels (branch off the primary process)
The endothelium in the kidney is…
fenestrated
Mesangial cell
Specialized cells in the glomerulus. Maintain structure and function of glomerulus.
What are the 2 types of mesangial cells?
What are their distinct roles
intra-glomerular: support structure of glomerulus
extra-glomerular: at the vascular pole, mediate signal transmission between macula densa cells and juxtaglomerular cells
2 functions of mesangial cells (as seen in lecture)
- Phagocytosis of particles, germs, BM & structural support of capillaries
- Production of cytokines (Interleukin 6)
Pedicels form… around glomerular capillaries
Filtration slits (25nm).
Note the presence of diaphragms
What cannot pass across the filtration slits formed by pedicels?
negatively charged proteins
proteins greater than albumin
Location of medullary rays
Cortex
Proximal tubules have … cells
a) cuboidal
b) columnar
c) squamous
b) columnar
cuboidal to columnar epthelium
Characteristic feature of proximal tubule cells
Brush border (microvilli)
What is found in the infoldings of the cells in the proximal tubule?
Mitochondria
The cells of the thin limb of the loop of Henle are…
a) cuboidal
b) columnar
c) squamous
c) squamous
Which portion of the loop of Henle is permeable to water (free diffusion of water)? Which is not permeable to water?
Descending limb: permeable to water
Ascending limb: impermeable to water
Which cells are more acidophilic (proximal or distal)? How does this translate under the microscope?
Proximal tubule cells are more acidophilic, so they appear more eosinophilic (pink)
What is the difference between the nuclei in proximal and distal tubular cells?
Proximal: in the middle of the cell
Distal: “kissing” the lumen of the tubule
Aldosterone is secreted by…
adrenal glands
What is the site of action of aldosterone? What are its effects?
Acts on the DCT and stimulates the reabsorption of NaCl.
Describe the epithelium of the thick descending limb?
similar to proximal convoluted tubule
Describe the epithelium of the thick ascending limb?
similar to distal convoluted tubule
The thick descending limb of the loop of Henle is located in…
medullary rays (cortex) and upper medulla
The thin limb of the loop of Henle is located in…
medulla
The thick ascending limb of the loop of Henle is located in…
medulla and medullary rays (cortex)
Diameter of collecting tubules
40-50 um
Where can we find collecting tubules?
in cortex and medullary rays
How can we distinguish the collecting tubules from the collecting duct? (3)
Collecting duct is 200nm in diameter (much larger than 40-50um CTs).
Found in medulla
Nuclei are less centered
What is the site of action for ADH? What are its effects?
Collecting duct.
ADH makes the CD permeable to water (promotes water reabsorption).
What is the juxtaglomerular apparatus?
It comprises 3 groups of cells:
* macula densa of the DCT
* juxtaglomerular cells of the afferent arteriole
* extraglomerular mesangial cells
Define juxtaglomerular cells. They are rich in…
Modified smooth muscle cells of afferent arterioles. They are rich in granules containing renin.
What is important about the junction between juxtaglomerular cells and macula densa cells?
The basal lamina (BM) is absent.
When is renin released by juxtaglomerular cells? (3)
- low blood pressure
- low Na in DCT
- sympathetic nervous system activation
What are the effects of renin secretion?
Renin converts angiotensinogen to angiotensin I.
Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme (ACE).
What are the effects of angiotensin II? (3)
- Vasoconstriction to increase BP
- Aldosterone secretion to promote sodium and water reabsorption
- Antiduretic hormone (ADH) secretion to promote water reabsorption
Explain the function of the macula densa.
The macula densa is made of specialized epithelial cells in the DCT that detect the sodium concentration of the filtrate.
If sodium levels are high, the MD signals to reduce the GFR via vasoconstriction of the afferent arteriole.
If sodium levels are low, the MD signals to increase the GFR via vasodilation of the afferent arteriole.
How does the macula densa trigger vasoconstriction and vasodilation?
Vasoconstriction: MD signals to the juxtaglomerular cells to release vasoconstrictors like adenosine
Vasodilation: MD signals to the juxtaglomerular cells to release vasodilators like nitric oxide (NO).
Under the microscope, most of what we see in the medulla are…
collecting ducts
In the medulla, smaller openings in between the collecting ducts are…
thin limb of the loop of Henle
At the level of the medullary pyramids, the renal arteries branch into…
interlobar arteries
The interlobar artery forms an elbow called…
arcuate artery
The arcuate artery is located at the level of the…
cortico-medullary junction
The arcuate artery branches into…
lobular arteries
Lobular arteries are located in…
the cortex
How do the lobular arteries branch?
Lobular arteries travel all the way to the capsule and form a capillary network underneath the capsule.
What gives rise to the afferent arteriole?
Lobular artery
The afferent arteriole branches into a capillary network in the glomerulus before converging into the efferent arteriole.
The efferent arteriole branches into…
peritubular capillaries, which surround the PCT and DCT.
Blood from the peritubular capillaries is collected by…
post-capillary venules, that drain into the lobular vein
Blood from the capillary network beneath the capsule will be collected by…
stellate veins, that drain into the lobular vein
Which capillaries are involved in the secretion of erythropoietin?
Peritubular capillaries
What is erythropoietin?
Glycoprotein that promotes proliferation and differentiation of erythrocyte precursors.
What is the major site of erythropoietin production?
Kidney
(liver is the major extra-renal site of production)
Define juxtamedullary renal corpuscles.
Renal corpuscles located near the junction of the cortex and medulla.
What are the vasa recta?
Capillaries that emerge from efferent arterioles of juxtamedullary renal corpuscles and drain into the arcuate veins.
What is the location of the vasa recta?
Medulla
The vasa recta are a type of…
peritubular capillary
What is the role of the vasa recta?
Return the water reabsorbed in the medulla to the circulation
How are the vasa recta oriented in terms of the loop of Henle?
they are parallel to the loop of Henle
There is a high concentration of…? in the medulla.
Na+ (sodium)
Normally, the collecting ducts are…
a) impermeable to water
b) permeable to water
a) impermeable to water
How does vasopressin (ADH) affect the permeability of the collecting ducts?
it makes the CD permeable to water
Name 2 conditions in which the glomerular filtration is altered?
- diabetes mellitus
- glomerulonephritis
How does diabetes mellitus and glomerulonephritis impact glomerular filtration?
Becomes much more permeable to proteins with subsequent release of protein into the urine (proteinuria)
How can a significant hemorrhage impact kidney function, and how will the kidney respond.
Decreased blood pressure will result in increased renin secretion.
This will cause the production of angiotensin II.
Angiotensin II will increase blood pressure by constricting arterioles and stimulating the secretion of aldosterone.
Aldosterone increases the absorption of Na by the DCT.
What is Addison’s disease (chronic adrenal insufficiency)? What does it result in?
Chronic endocrine disorder.
Adrenal glands do not produce sufficient steroid hormones, including aldosterone.
Results in excess loss of Na in the urine.
What is the consequence of excessive Na loss in the urine?
Very low blood pressure and coma.
