Renal Function And Development Flashcards
Accessory renal arteries
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
Unilateral renal agenesis
only has 1 kidney
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
Bilateral renal agenesis
both kidneys are missing
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
Cystic kidney disease
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
Malrotation of kidneys
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
Ectopic kidneys
One or both of the kidneys are located in abnormal compartments
**most common is in the pelvis of the kidney
Crossed fused ectopia
One kidney will cross over to the other side kidney and possibly cause fusion into 1 large kidney (called unilateral fused kidneys)
Horseshoe kidney
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
Ectopic ureter
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*
Urachal cysts/sinus and fistula
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)
Exstrophy of the bladder
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
Epispadias
A birth defect in which the urethra opens on the dorsum of the penis
Glomerulonephritis
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
Diabetic glomerulosclerosis
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
Sickle cell nephropathy
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
Renal calculi (renallithiasis/ kidney stones)
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
Kidney gross anatomy
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
Broad functions of the kidneys
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
Functional divisions of the kidney
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)
What is the functional excretory unit of the kidney?
A nephron
- are classified based on the location of the renal corpuscles and the depth of the nephron loop
Types of nephrons
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
Parts of a renal corpuscle
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
What is a uriniferous tubule?
The nephron plus the associated connecting tubule and collecting duct
it is NOT synonymous with nephron
How is the renal blood circulation broken down
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
Difference between cortical and medullary filtration function
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
What are the 3 factors associated with the glomerular filtration rate (GFR) of kidneys
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
What are the 3 factors to altering hydrostatic pressure gradient?
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
How to differentiate proteinuria causes?
Larger proteins in the urine = Problem with the GBM
Smaller proteins in the urine =
Problem with the PCT
Broad major functions of each section of the kidney
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
Cells of the collecting system of the kidney
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
Countercurrent multiplier system
- 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
Direct effects of the urinary system on the body
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
What are the contents of the outer stripe of the outer medulla?
Collecting ducts and straight tubules
- both PCT and DCT
NO THIN LIMBS
What are the what are the contents of the inner stripe of the outer medulla?
Collecting ducts, descending thin limbs, DCTs and thick ascending limbs
- NO PCTs
What are the contents of the inner medulla
Collecting ducts, descending and ascending thin limbs and the papillary ducts of Bellini
Fucntions of mesangial cells in the kidney
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
Glomerulonephritis broad definition
Inflammation of the glomerulus
How to tell DCTs from PCTs histologically
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
PCT vs DCT functions
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
What is the function of the macula densa cells
Specialized columnar cells that sit between the afferent and efferent blood vessels Regulate blood flow based on Na+ and Cl- levels
What is the order of tubules after the glomerulus and their functions
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
What is the function of juxtaglomerular granular cells
Smooth muscle cells in afferent arterioles that secrete renin when needed to activate RAAS
- responds to a decrease in systemic arteriole pressure
Difference between principal and intercalated cells in the collecting duct
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
Difference between peritubular capillaries and the vasa recta
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)
What kidney is taken in live kidney transplants?
Left kidney
- due to it having a longer renal vein
What part of the kidney receives less blood flow?
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
Posterior urethral values
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
Embryonic organs of the urinate system
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
Ureteric differentiation
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
Nephrogenesis
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
