Renal Function And Development

Question 1

Accessory renal arteries

Answer 1

Usually arise from the aorta and can superior or inferior to the main renal artery

sometimes crosses anterior to a ureter and obstructs it causing hydronephrosis (distention of the pelvis and chalices with urine)

**if an accessory artery is present and gets injuried = ischemia in the region supplied by the accessory artery

Question 2

Unilateral renal agenesis

only has 1 kidney

Answer 2

1:1000 occurrence rates with 2x more likely in males

Usually occurs with the left kidney and causes the other kidney to undergo spontaneous hypertrophy in order to compensate.
- can still live just fine, however future kidney damage is now more severe

Caused by a failure of the ureteric bud to develop at all. Never penetrates the mesonephric mesenchyme = Nothing there

Question 3

Bilateral renal agenesis

both kidneys are missing

Answer 3

Always associated with oligohydroamnios, twisted skin and facial, renal failure in utero and pulmonary hypoplasia (Potter sequence)

1:3000 occurrence rates, 3x more likely in males and is incompatible with life

can also lead to multi cystic dysplastic kidneys (without penetration form ureteric buds the metanephrogenic blastoma sometimes doesnt degenerate and intends forms cysts). This is usually unilateral though, but if bilateral also leads to potter sequence

is caused by failure of both ureteric buds to form at all

Question 4

Cystic kidney disease

Answer 4

Most common type is autosomal dominant polycystic kidney disease (ADPKD)
- 1: 500 occurrence rates

Causes mutations in the PKD-1/2 genes respectively
- function is to sit receptors on the primary cilia of the kidney and detect urine flow through the tubules

**results in numerous cysts that reduce normal kidney function

Question 5

Malrotation of kidneys

Answer 5

Results in any of the following positions fo the kidneys (all of which reduce kidney function)
- hilum faces anteriorly = no rotation

• hilum faces posteriorly = too much rotation
• hilum faces laterally = medial rotation has occurred

** all of which have incidence rates in ectopic kidneys

Question 6

Ectopic kidneys

Answer 6

One or both of the kidneys are located in abnormal compartments

**most common is in the pelvis of the kidney

Question 7

Crossed fused ectopia

Answer 7

One kidney will cross over to the other side kidney and possibly cause fusion into 1 large kidney (called unilateral fused kidneys)

Question 8

Horseshoe kidney

Answer 8

Most common renal fusion defect
(seen in 0.2% of population)
- Poles of the kidneys are fused together, usually at the inferior poles

Often found in the pelvis just below the inferior mesenteric artery

Does NOT affect function and each has its own ureter and blood supply

Often asymptomatic but increases risk of renal stones, cancer and infections

15% of people with Turner syndrome have this

Question 9

Ectopic ureter

Answer 9

The ureter of one kidney does not enter the urinary bladder and instead enters another part of the pelvis

Caused by the ureter being carried caudally with the mesonephric duct during fetal development

• results in incontinence of leakage of urine unconsciously from urethra or vagina*

Question 10

Urachal cysts/sinus and fistula

Answer 10

All are resulting from a remnant of the urachal lumen remaining present (typically inferior)

Cysts = remnants of the epithelial lining of the urachus condenses and forms cysts (benign)

Sinus = patent inferior end of the urachus dilates to form a urachal sinus (causes pus leakage from the umbilicus

Fistula = entire urachus remains and forms a fistula and allows urine to escape from the umbilical orifice (causes urine leakage from the umbilicus)

Question 11

Exstrophy of the bladder

Answer 11

Severe and rare defect 1:30,000. Predominantly seen in females

Causes exposure and protrusion of the mucosal surface of the posterior wall of the bladder, trigone of the bladder and ureteric orifices

• will look like an exerted buldging mass just inferior to the umbilicus
• causes spontaneous urine leakage

believed to be caused by failure of the mesenchymal cells to migrate between ectoderm and endoderm of the abdominal wall during the 4th week

• almost always sees epispadias and seperation of the pubic bones as well

Question 12

Epispadias

Answer 12

A birth defect in which the urethra opens on the dorsum of the penis

Question 13

Glomerulonephritis

Answer 13

Inflammation of the glomeruli usually steaming from a humoral immune reaction
- con include deposition of antibody-antigen complexes within glomeruli or circulating antibodies binding to either glomerular antigens or extraneous antigens.

• always presents with proteinuria due to inflammation causing increased permeability of the glomerulus to proteins

Question 14

Diabetic glomerulosclerosis

Answer 14

Thickening and loss of function in the GBM produced as part of the systemic microvascular sclorosis caused by diabetes mellitus

is the leading cause of irreversible end-stage kidney disease in the United States

Treatment requires kidney transplants or artificial hemodialysis

Question 15

Sickle cell nephropathy

Answer 15

A common problem related to sickle cells disease in which affected erythrocytes “sickle” (get stuck) in the vasa recta of the kidney.
- this is due to the low oxygen tension in here

Results from renal infarcts in the renal papillae/pyramids

Question 16

Renal calculi (renallithiasis/ kidney stones)

Answer 16

Are stones that are formed in the renal pelvis usually made up of excess calcium salts and uric acid

• calcium salt stones = large and jagged
• uric acid stones = small and smooth

Can be asymptomatic or cause extreme pain will urinating on the affected side

Treatment = surgical removal or lithotripsy

Question 17

Kidney gross anatomy

Answer 17

Bilateral pair of retroperitoneal organs that are located in the abdominal cavity

Contain:
- capsule = fibrous protective outer layer of the kidney.

• hilum = kidney site of the renal neuro vasculature and outflow of urine into the ureter
• cortex = Light colored cortical tissue that contains the vascular supply of the kidney. Site of glomerular filtration and where modification of tubular fluid occurs (reabsorption of proteins, macronutrients, electrolytes, metabolites)
• medulla = dark-colored medullary tissue that is primarily involved with concentrating the tubular fluid and contains the medullary portion of the collecting ducts which transports the final urine to the minor calyces

Question 18

Broad functions of the kidneys

Answer 18

1) osmoregulation between water/electrolytes/acids-base balances

2) excretion of production of urine by kidneys which passes through the ureters for temporary storage in the bladder before its releases to the exterior by urethra
- metabolic wastes and bioactive substances

3) endocrine functions
- renin = protease used to cleave angiotensin -> angiotensin 1
- erythropoietin = glycoprotein that stimulates erythrocyte production in red bone marrow when O2 is low

Conversion of vitamin D to active form (1,25 dihydroxyvitamin D3/ calcitrol)

Gluconeogenesis

Question 19

Functional divisions of the kidney

Answer 19

Renal lobe: consists of a single renal pyramid and the associated minor calyx and the adjacent renal Columns
- is the functional unit of the kidney (8-15 renal lobes per kidney)

Renal lobules: consists of a medullary ray (collecting duct) and the surrounding cortical tissues (vascular supply and nephrons)

Question 20

What is the functional excretory unit of the kidney?

Answer 20

A nephron

• are classified based on the location of the renal corpuscles and the depth of the nephron loop

Question 21

Types of nephrons

Answer 21

1) Juxtamedulary nephrons (8-10% of total nephrons)
- renal corpuscles located deep in the cortex near the corticomedullary junction
- nephron loops extend only deep into the medullary tissue
- produce the MOST concentrated (hypertonic) tubular fluid

2) midcortical nephrons
- renal corpuscules and nephrons both extend in between the subscapularis and juxtamedullary nephrons
- variable tubular fluid concentrations

3) subcapsular nephrons
- corpuscles are located most superficially
- nephron loops extend only a short distance into medullary tissues
- produce the LEAST concentrated (almost completely isotonic) tubular fluid

Question 22

Parts of a renal corpuscle

Answer 22

1) glomerulus - a tuft of arteriole vasculature

2) bowmans capsule = surrounds the glomerulus with a inner visceral and outer parietal layer of epithelium
- continuous with the lumen of the renal tubule

Question 23

What is a uriniferous tubule?

Answer 23

The nephron plus the associated connecting tubule and collecting duct

it is NOT synonymous with nephron

Question 24

How is the renal blood circulation broken down

Answer 24

Arteriole supply:
Renal artery -> segmental artery -> interlobar artery -> arcuate artery -> interlobular artery -> afferent arteriole -> glomerulus -> efferent arteriole -> vasarecta (covers the loop of henle) and peritubular capillaries (cover PCT/DCT)

Venous supply:
Vasarecta/peritubular capillaries -> interlobular vein -> arcuate vein -> interlobar vein -> renal vein

Question 25

Difference between cortical and medullary filtration function

Answer 25

Cortical = tubular reabsorption is primarily to conserve nutrients/minerals and ions needed by the body and to remove excessive and/or toxic substances

Medullary function = tubular reabsorption and secretion occurs primarily for concentration of urea/osmoregulation and acid-base balance

Question 26

What are the 3 factors associated with the glomerular filtration rate (GFR) of kidneys

Answer 26

1) glomerular surface area
2) permeability of glomerular filtration barrier

3) net filtration pressure
- sum of hydrostatic and osmotic pressure between glomerulus and capsular space

Question 27

What are the 3 factors to altering hydrostatic pressure gradient?

Answer 27

1) alter systemic blood pressure

2) alter glomerular pressure
- how much blood is coming in vs how much blood is going out

3) alter tubule pressure

Question 28

How to differentiate proteinuria causes?

Answer 28

Larger proteins in the urine = Problem with the GBM

Smaller proteins in the urine =
Problem with the PCT

Question 29

Broad major functions of each section of the kidney

Answer 29

1) Proximal convoluted tubule (PCT)
- located in cortex
- reabsorption of all organic nutrients, all proteins and most water and electrolytes
- secretion of organic anions and cations (H+/NH4+)

2) thin limb of Henle
- located in medulla
- passive reabsorption of Na+/Cl-

3) thick ascending limb of Henle
- located in medulla
- active reabsorption of electrolytes

4) Distal convoluted tubule (DCT)
- located in the cortex
- passive reabsorption of electrolytes

Question 30

Cells of the collecting system of the kidney

Answer 30

1) principal cells
- found in medullary rays and medulla
- most abundant cell type**
- is cuboidal/columnar and pale staining
- function = reabsorption of water and electrolytes. Regulates selection of potassium

2) intercalated cells
- found in medullary rays
- are few columnar and stain darker than principal cells
- function = reabsorption of potassium

Question 31

Countercurrent multiplier system

Answer 31

• Is produced via countercurrent flow of vasa recta and limbs of the nephron loop*
• this is the cause of maintenance of increasing salt concentrations within the renal pyramids

Allows for movements of water and solutes into and out of the blood supply and kidney tubules

Question 32

Direct effects of the urinary system on the body

Answer 32

Osmoregulation and acid-base balance

Excretion and temporary storage of urea and toxins in the body

Secretes renin and erythropoietin

Converts vitamin D to active form

Gluconeogenesis

Question 33

What are the contents of the outer stripe of the outer medulla?

Answer 33

Collecting ducts and straight tubules
- both PCT and DCT

NO THIN LIMBS

Question 34

What are the what are the contents of the inner stripe of the outer medulla?

Answer 34

Collecting ducts, descending thin limbs, DCTs and thick ascending limbs
- NO PCTs

Question 35

What are the contents of the inner medulla

Answer 35

Collecting ducts, descending and ascending thin limbs and the papillary ducts of Bellini

Question 36

Fucntions of mesangial cells in the kidney

Answer 36

Surround capillaries and provide physical support for the capillaries

Phagocytosis of protein aggregates that adhere to the filtration barrier
- provide defense against antibody-antigen complexes

Secretion of several factors involved in immune defense and glomerular repair (PGE and cytokines)

Facilitates optimal filtration rate by adjusting vasomotor tone in response to changes in blood pressure

Question 37

Glomerulonephritis broad definition

Answer 37

Inflammation of the glomerulus

Question 38

How to tell DCTs from PCTs histologically

Answer 38

DCTs

• stain more purple (neutrophilic)
• clear lumen
• every cell has a centrally located nucleus

PCTs

• stain more pink (eosinophilic)
• have occluded lumen (due to longer cillia)
• not every cell has a centrally located nucleus

Question 39

PCT vs DCT functions

Answer 39

PCT

• reabsorbed the majority of glucose, electrolytes and majority of the organic nutrients/proteins
• secretes organic anions and cations into the tubular fluid (H+ and NH4+)
• hydroxylates vitamin D
• release of erythropoietin
• reabsorbs 50% of water

DCT

• responds to aldosterone and reabsobs sodium
• responds to parathyroid hormone and reabsobs calcium
• secretes ammonium ions into fluid to create bicarbonate ions which are then secondarily reabsorbed via HC03-/H+ exchanger. This raises the pH of the blood plasma

Question 40

What is the function of the macula densa cells

Answer 40

Specialized columnar cells that sit between the afferent and efferent blood vessels Regulate blood flow based on Na+ and Cl- levels

Question 41

What is the order of tubules after the glomerulus and their functions

Answer 41

PCT

Thick descending limb (proximal straight)

• look histologically similar to PCT but are parallel to the collecting duct
• reabsorb any glucose remaining in the tubular fluid after the PCT (via Na+/glucose cotransporter)

Thin descending limb
- possess high levels of aquaporins and reabsorbed water, increasing the concentration of Na+ and urea

Thin ascending limb

• impermeable to water
• reabsorbed Na/K/Cl-

Thick ascending limb (TAL/distal straight)

• active transport of sodium out of urine
• reabsorption of other ions also via K+/Cl- transporters (mg/ca/etc.)

DCT

Collecting ducts

• reabsorption of urea as needed
• ADH-mediated water channels (aquaporin-2) which are controlled by principle cells
• secretion of H+ and HCO3- by alpha and beta intercalated cells respectively

Question 42

What is the function of juxtaglomerular granular cells

Answer 42

Smooth muscle cells in afferent arterioles that secrete renin when needed to activate RAAS
- responds to a decrease in systemic arteriole pressure

Question 43

Difference between principal and intercalated cells in the collecting duct

Answer 43

indistinguishable on histology

Principal (light) cells = ADH-regulated aquaporin-2 channels
- determines final concentration of urine

Intercalated (dark cells) = secretes H+ (alpha cells) and HCO3- (beta cells)
- determines final pH or urine and contributes to acid-base balance of blood plasma

Question 44

Difference between peritubular capillaries and the vasa recta

Answer 44

Peritubular capillaries:

• found in the cortex of the kidney and surrounds the convoluted tubules
• reabsorbs solutes and materials between the blood and tubular filtrate

Vasa recta:

• found in the medullary pyramid of the kidney and surrounds the collecting ducts and loops of Henle
• maintains the concentration gradient between blood and tubular fluid “counter-current exchange”
• contains descending arterioles (which lose water but gain ions) and the ascending venules (which lose ions but gain water)

Question 45

What kidney is taken in live kidney transplants?

Answer 45

Left kidney

- due to it having a longer renal vein

Question 46

What part of the kidney receives less blood flow?

Answer 46

Medulla receives less blood flow than the cortex
- seems counterintuitive especially because there is high overall renal blood flow

because of this medulla function is impaired first in ischemic events

Question 47

Posterior urethral values

Answer 47

Membrane remnants in the posterior urethra in males remain

• leads to urethra obstruction in neonates
• *most common cause of bladder obstruction in male infants
• may also show oligohydromanios

Diagnosis = bilateral hydronephrosis and dilated bladder on ultrasound of newborn

Question 48

Embryonic organs of the urinate system

Answer 48

1) ureteric buds
- arise from the distal mesonephric duct after it has fused with the urogential sinus
- comprised of intermediate mesoderm

2) metanephrogenic blastema
- derived from intermediate mesoderm also however it is NOT derived from the Nephrogenic cord
- give rise to the kidney after receiving signals from the penetrating ureteric bud

3) urogential sinus
- forms within the distal portion of the intraembryonic portion of the allantoin. Forms the cloaca

Question 49

Ureteric differentiation

Answer 49

Ureteric bud penetrates the blastema and receives signals from the metanephrogenic mesenchyme

• starts bifurcation of the ureteric buds
• renal pelvis = 1st bifurcation
• major calyces = 2-4 bifurcations
• minor calyces 5-9 bifurcations
• collecting ducts = 10-22 bifurcations

Question 50

Nephrogenesis

Answer 50

Induction signals from the tips of the branching ureteric bud which promotes formation of the renal vesicles within the metanephric mesenchyme.

• these vessels undergo further elongation and differentiation into the entire renal tubule
• proximal portion of renal tubule = glomerulus
• middle portion of renal tubule = majority of nephron
• distal portion of renal tubule = becomes the collecting tubule