TBL20 - Kidneys and Ureters

Question 1

What layer of mesoderm arises between paraxial and lateral plate mesoderm?

Answer 1

The three bilateral columns of mesoderm, which differentiate during gastrulation, include the intermediate mesoderm

Question 2

What does the intermediate mesoderm form in the cervical region that disappears?

Answer 2

1) In the cervical region, the intermediate mesoderm forms the rudimentary pronephros, a nonfunctional excretory system that disappears
2) During regression of the pronephros, intermediate mesoderm in the thoracic and lumbar regions forms the mesonephros and mesonephric (aka wolffian) duct

Question 3

What does segmentation of the mesonephros create and where do they open into? What does lengthening of these structures form?

Answer 3

1) Segmentation of the mesonephros creates epithelium-lined excretory tubules that open into the epithelium-lined mesonephric duct, which terminates in the cloaca
2) Lengthening of the excretory tubules forms S-shaped loops that acquire a glomerulus (loop of capillaries) at their medial ends

Question 4

What do angiogenic outgrowths from the dorsal aortae form and where do these structures differentiate? What constitute the renal corpuscles?

Answer 4

1) Angiogenic outgrowths from the dorsal aortae form the glomeruli that become associated with Bowman’s capsules (not labeled), which differentiate at the medial ends of the excretory tubules
2) Glomeruli and Bowman’s capsules constitute renal corpuscles

Question 5

In females, what is the fate of the mesonephric excretory tubules and all but the distal end of the mesonephric duct? In males, what is the fate of caudal excretory tubules and the mesonephric duct?

Answer 5

1) In females, the mesonephric excretory tubules and all but the distal end of the mesonephric duct degenerate and disappear
2) In males, caudal excretory tubules and the mesonephric duct persist to participate in formation of the genital system (to be studied later)

Question 6

How is the ureteric bud formed?

Answer 6

An epithelial outgrowth from the distal mesonephric duct near its entrance into the cloaca forms the ureteric bud

Question 7

Where does the ureteric bud grow into and where is this structure derived from?

Answer 7

The bud grows into the metanephros (ignore term metanephric blastema), which is derived from the intermediate mesoderm in the sacral region

Question 8

How does the renal pelvis form and what does it split into? What do epithelial outgrowths from the calyces create? Where do branches of the tubules travel?

Answer 8

1) Within the metanephros, dilation of the ureteric bud forms the renal pelvis that splits into multiple calyces (ignore major and minor)
2) Epithelial outgrowths from the calyces create collecting tubules
3) Branches of the tubules penetrate deeper into the metanephros

Question 9

As the excretory tubule lengthens, what does it differentiate into? What does this differentiated structure unite with?

Answer 9

1) As the excretory tubule lengthens, it differentiates into a distal convoluted tubule
2) The distal convoluted tubule unites with the collecting tubule, a U-shaped loop of Henle, and a proximal convoluted tubule that unites with Bowman’s capsule

Question 10

When does nephron formation continue until and how many nephrons reside in each kidney at this point?

Answer 10

Nephron formation continues until birth when approximately one million nephrons reside in each kidney

Question 11

Where do the ureteric bud and metanephros originate? What causes the kidneys to ascend into the lumbar region? Where do renal vessels originate from and where are they degenerated?

Answer 11

1) The ureteric bud and metanephros originate in the sacral region
2) Diminution of body curvature and lengthening of the lumbar and sacral regions cause the kidneys to ascend into the lumbar region
3) Renal vessels originate from the aorta and IVC at continuously higher levels and lower level vessels degenerate

Question 12

Why do anuria, oligohydramnios and hypoplastic lungs characterize relatively uncommon bilateral renal agenesis? Why is unilateral agenesis compatible with life?

Answer 12

1) Bilateral renal agenesis, which occurs in 1/10,000 births, results in renal failure
2) The baby presents with Potter sequence, characterized by anuria, oligohydramnios (decreased volume of amniotic fluid), and hypoplastic lungs secondary to the oligohydramnios
3) A lack of kidneys results in a lack of urine production, decreased volume of amniotic fluid, which normally consists partially of urine, and hypoplastic lungs due to a lack of amniotic fluid filling the lungs
4) Unilateral agenesis is compatible with life due to the ability of a single kidney to filtrate blood into urine properly

Question 13

When does a horseshoe kidney occur and is it fatal?

Answer 13

1) During their ascent, the kidneys pass through the arterial fork formed by the umbilical arteries
2) Sometimes, the kidneys are pushed so close together during their passage through the arterial fork, that the lower poles fuse, forming a horseshoe kidney (get stuck under the IMA)
3) No, it is not fatal

Question 14

What constitutes the renal medulla? What forms large collecting ducts in the medulla? What do the collecting ducts empty into and where?

Answer 14

1) The renal cortex covers the cone-shaped pyramids, which collectively constitute the renal medulla
2) Coalescence of collecting tubules in the medulla forms large collecting ducts
3) In the apices of the medullary pyramids, the collecting ducts empty into the funnel-shaped calyces

Question 15

What happens to the renal artery after entering the hilum? What does the parenchymal branch course along and generate? What do cortical branches generate and where do these structure terminate?

Answer 15

1) After entering the hilum, the renal artery immediately splits into multiple parenchymal branches (ignore their names)
2) The parenchymal branch coursing along the corticomedullary junction generates terminal branches at right-angles that penetrate into the cortex
3) The cortical branches generate afferent arterioles, which terminate in the glomeruli of the renal corpuscles

Question 16

Where do glomerular capillaries drain into? What surrounds the proximal and distal convoluted tubules?

Answer 16

1) Glomerular capillaries drain into efferent arterioles that empty into peritubular capillaries
2) Clusters of RBCs (not labeled) in peritubular capillaries surround the proximal and distal convoluted tubules

Question 17

Where do efferent arterioles that drain glomeruli adjacent to the corticomedullary junction empty into?

Answer 17

Efferent arterioles that drain glomeruli adjacent to the corticomedullary junction (aka juxtamedullary glomeruli) empty into the vasa recta i.e., recurrent capillary loops that run in parallel into the medullary pyramids

Question 18

What is found in the medullary stroma? What do both the medullary vasa recta and cortical peritubular capillaries drain into and where do they course?

Answer 18

1) Parallel segments of the vasa recta, collecting ducts, and loops of Henle are found in the medullary stroma
2) Both the medullary vasa recta and cortical peritubular capillaries drain into tributaries of the renal vein that course adjacent to the parenchymal arteries back to the hilum

Question 19

Identify the afferent arteriole, glomerular capillaries, efferent arteriole, and parietal and visceral layers of Bowman’s capsule. What does looping of the capillaries into glomeruli create?

Answer 19

1) Look at picture

2) Looping of the capillaries into glomeruli creates an extensive endothelial surface area for blood filtration

Question 20

What do podocytes form and what do they have? What do these structures terminate as and where?

Answer 20

1) Podocytes, which form the visceral layer of Bowman’s capsule, have multiple processes
2) These processes terminate as pedicels to embrace the basement membrane associated with the glomerular capillary endothelium

Question 21

How do pedicels envelop the basement membrane? What is found between the pedicles and what are they bridged by? What constitutes the glomerular filtration barrier?

Answer 21

1) Pedicels interdigitate to envelop the basement membrane
2) Filtration slits between the pedicles are bridged by slit membranes
3) The filtration slits, slit membranes, and the basement membrane constitute the glomerular filtration barrier

Question 22

What are the capillary endothelium perforated by? What does this allow for?

Answer 22

1) The capillary endothelium is perforated by transcellular openings (fenestrae) without bridging membranes
2) Thus, the fenestrae permit unrestricted passage of plasma proteins and fluid across the endothelium into the basement membrane

Question 23

What do anionic sites in the basement membrane do? What does glomerular filtrate normally include?

Answer 23

1) Anionic sites in the basement membrane repel the plasma proteins and the slit membranes prevent passage of smaller molecules
2) Thus, glomerular filtrate normally includes water, glucose, and amino acids

Question 24

Why are hematuria and proteinuria symptomatic of Alport syndrome?

Answer 24

1) Alport syndrome, or hereditary nephritis, is an inherited progressive nephropathy
2) A genetic mutation results in abnormal type IV collagen in the glomerular basement membrane and leads to renal failure
3) Patients have blood (hematuria) and protein in urine, which is due to leakage of erythrocytes and plasma proteins across the defective membrane

Question 25

What is interspersed between the glomerular capillary loops and what does this contribute to?

Answer 25

Phagocytic activity of mesangial cells interspersed between the glomerular capillary loops contributes to the filtration barrier

Question 26

How many liters of glomerular filtrate cross the filtration barrier daily? What does the filtrate enter and what is this structure enclosed by?

Answer 26

1) About 180 liters of glomerular filtrate cross the filtration barrier daily
2) The filtrate enters Bowman’s space, which is enclosed by the simple squamous epithelium that forms the parietal layer of Bowman’s capsule

Question 27

What is Bowman’s space continuous with? Where is the filtrate reabsorbed into and how much of it is reabsorbed?

Answer 27

1) Bowman’s space is continuous with the lumen of the proximal convoluted tubule
2) 99% of the filtrate is reabsorbed into the peritubular capillaries and vasa recta as the filtrate moves along the nephrons, collecting tubules, and collecting ducts

Question 28

Of the proximal and distal convoluted tubules, which are longer?

Answer 28

The proximal convoluted tubules are longer than the distal convoluted tubules

Question 29

What do greater numbers of mitochondria and surface microvilli enable in the proximal convoluted tubular epithelium? What does the resorbed filtrate re-enter and via what?

Answer 29

1) In the proximal convoluted tubular epithelium, greater numbers of mitochondria and surface microvilli enable the tubules to actively resorb 70% of the glomerular filtrate
2) The resorbed filtrate re-enters the bloodstream via the peritubular capillaries

Question 30

Why do darker stained proximal convoluted tubules constitute more of the cortical parenchyma than the lighter stained distal convoluted tubules?

Answer 30

The darker stained proximal convoluted tubules are about 6x the length of the lighter stained distal convoluted tubules and therefore constitute more of the cortical parenchyma

Question 31

Why is acute necrosis of the tubular epithelium the most common cause of acute renal failure?

Answer 31

1) Acute tubular necrosis is a serious disorder with the histologic feature of destruction of epithelial cells of proximal and distal tubules, which leads to impaired renal function
2) Tubular cells are especially vulnerable to ischemia and toxins in that they have a high rate of energy consumption and can absorb and concentrate toxins
3) They are thus susceptible to interference with oxidative and other metabolic pathways
4) Sloughing and necrosis of epithelial cells, plus a denuded brush border, lead to tubular obstruction and increased intraluminal pressure
5) This disorder is the most common cause of acute renal failure

Question 32

Where do 90% of malignant kidney tumors originate and why is renal cell carcinoma fatal?

Answer 32

1) Renal cell carcinoma, usually arising from proximal tubule epithelium, accounts for more than 90% of malignant kidney tumors
2) It is fatal due to a lack of early warning signs, diverse clinical signs, resistance to treatment by radiation or chemotherapy once metastasis has occurred

Question 33

What does each distal convoluted tubule make contact with? What are macula densa? What forms juxtaglomerular (JG) cells?

Answer 33

1) Each distal convoluted tubule contacts the afferent arteriole of its parent renal corpuscle
2) The tubular epithelial cells contacting the arteriole contain closely packed nuclei; thus, the cells are designated the macula densa
3) Modified smooth muscle cells of the afferent arteriole form juxtaglomerular (JG) cells

Question 34

What does the macula densa monitor? What do JG cells do once Na+ concentrations decrease?

Answer 34

1) The macula densa monitors Na+ concentrations of the glomerular filtrate
2) When Na+ concentrations decrease, JG cells release renin into the afferent arteriole and the circulating hormone acts, in part, by stimulating the adrenal glands

Question 35

Where do loops of henle course? What lines the loops of Henle, what is it highly permeable to, and what does this contribute to?

Answer 35

1) Loops of Henle of the juxtamedullary nephrons course deeply into the medullary pyramids
2) The simple squamous epithelium lining the loops of Henle is highly permeable to water, and thereby contributes to the regulation of urine tonicity

Question 36

What lines the collecting ducts? What does Antidiuretic hormone (ADH) do?

Answer 36

1) Simple cuboidal epithelium lines the collecting ducts
2) Antidiuretic hormone (ADH), a product of the pituitary gland (to be studied later), increases water resorption across the epithelium for uptake by the vasa recta, and thereby decreases urine volume

Question 37

Why do inhibitors of ADH (e.g., alcohol and caffeine) produce polyuria?

Answer 37

1) Inhibition of ADH prevents an increase of water resorption across the epithelium for uptake into the vasa recta
2) This excess of water is released into the filtrate and urine

Question 38

What is the ureteric muscularis externa organized into? What is their peristaltic contraction in response to and what does it do?

Answer 38

1) The ureteric muscularis externa is loosely organized into longitudinal and circular bundles of smooth muscle
2) Their peristaltic contraction, typically in response to distension, delivers urine to the urinary bladder (to be studied later)

Question 39

What is the urothelium and where is it restricted to? What do epithelial cells near the surface of the urothelium adapt to and how?

Answer 39

1) Urothelium is stratified epithelium restricted to the lower parts of the urinary tract i.e., the renal pelvis, ureters, urinary bladder, and urethra
2) Epithelial cells near the surface of the urothelium adapt to repetitive distension and contraction of the lower parts of the urinary tract by flattening and thickening, respectively

Question 40

How is backflow into the ureters prevented when the bladder is filled?

Answer 40

The ureters pierce the bladder wall obliquely as they enter it, so their walls are pressed together when the bladder fills with urine, which helps prevent backflow

Question 41

What does metanephros produce at the end of each collecting tubule and what does this structure consist of?

Answer 41

At the terminal end of each collecting tubule, the surrounding metanephros forms a nephron, which consists of an excretory tubule and its associated renal corpuscle