Urinary System Flashcards
What is the functional and structural unit of the kidney?
Nephron
What components does the nephron include?
Renal corpuscle, convoluted tubules, straight tubules, connecting tubules
What does the medullary ray consist of?
Straight tubules, cortical collecting duct
What does the cortical labyrinth consist of?
Convoluted tubules, renal corpuscles, connecting tubules, interlobular arteries and veins, peritubular capillary network
What does renal column anchor cortex to?
Medulla
What does renal column contain?
Interlobular vessels, lymphatics, supportive CT
Renal pyramids are separated by what?
Renal columns/Columns of Bertin
Renal pyramids contain?
Straight tubules, medullary collecting ducts, blood vessels vasa recta
What are the three structures that form the Countercurrent Multiplier System?
Loop of Henle, Vasa Recta, Medullary collecting duct
What is function of Countercurrent Multiplier System?
Creates hyperosmotic urine
What is role of Loop of Henle in Countercurrent Multiplier System?
Acts as countercurrent multiplier, creates and maintains gradient of ion concentration in medulla
What is role of vasa recta in Countercurrent Multiplier System?
Acts as countercurrent exchangers of water and solutes, helps maintains osmotic gradient
What is role of medullary collecting duct in Countercurrent Multiplier System?
Acts as an osmotic equilibrating device
What does a renal LOBE consist of?
One renal pyramid, and associated cortical tissue at base and sides
What does a renal LOBULE consist of?
A medullary ray, surrounding cortical labyrinth on either side
Explain sequence of branching renal arteries
Renal arteries-interlobar arteries-arcuate arteries- interlobular arteries- Afferent arterioles- Glomerular capillary network- Peritubular cortical capillaries- Efferent arteriole- Vasa Recta
What are two parts of vasa recta?
Descending arteriolae ractae
Ascending venulae rectae
What does renal corpuscle consist of?
Glomerulus and bowmans capsule
Where does glomerulus arise from and drain to?
Arise from afferent arterioles, drains by efferent arterioles
What are two layers of bowmans capsule?
Visceral layer, parietal layer
What is parietal layer of bowmans capsule lined with?
Simple squamous epithelium
What is visceral layer of bowmans capsule lined with?
Epithelial cells called Podocytes
Where are Podocytes found?
Covering the glomerulus
Where is Bowmans space/urinary space found?
Between bowmans parietal and visceral layer
What does urinary space receive?
Ultrafiltrate urine
What are renal corpuscles two poles?
Urinary pole, vascular pole
What happens at vascular pole?
Afferent and efferent arterioles penetrate and exit capsule
What happens at urinary pole?
Beginning of proximal convoluted tubule
What is another name for proximal straight tubule?
Thick descending limb
What is another name for distal straight tubule?
Thick ascending limb
What forms the Macula Densa?
Distal straight tubule/thick ascending limb
What composes Loop of Henle?
Proximal straight tubule
Thin descending limb
Thin ascending limb
Distal straight tubule
What are the 3 types of nephrons?
Cortical or Subscapular, Juxtamedullary, Intermediate
What are 3 structures that make up filtration apparatus?
Endothelial glomerular capillaries, GBM, visceral layer of bowmans capsule
Describe structure of endothelial glomerular capillaries
Large fenestrations, no diaphragm, restricts movement of blood cells and formed elements
What channels does the endothelial glomerular capillaries have?
Aquaporin-1 water channels, allows fast movement of water through epithelium
What is glomerular basement membrane made of?
Fused basement membrane of endothelial cell and basement membrane of podocyte
Describe GBM structure
Thick, type 4 collagen that creates extensive network of lamina densa, Type 17 collagen, lamin, nidogen, entactin, proteoglycans, glycosaminoglycans like Heparan Sulfate*
What does the structure of GBM provide for the cell?
Negatively charged basement membrane that repels negatively charged ions trying to pass through
Describe structure of visceral layer of bowmans capsule?
Contains podocytes
What happens with GBM in diabetes?
Thickens, loose effective filtration barrier, Heparan sulfate reduces and allows larger negatively charged ions to pass through, like albumin in urine
This can eventually lead to diabetic nephropathy
What is Alport Syndrome?
Occurs due to type 4 collagen gene mutation, results in thickening of GBM and fails to serve as effective filtration barrier
What are some symptoms of Alport Syndrome?
Hematuria, Protein in urine, progressive renal failure
What is autoimmune glomerulonephritis?
Example can be Good pasture syndrome
Autoantibody cells attack the GBM, becomes ineffective filtration barrier
What do endothelial cells have that help prevent cells in blood from passing through?
Glycocalyx coat
What are podocytes?
Epithelial cells, polarized and rest on basal lamina, similar to smooth muscle, contain actin filaments in cytoplasm
What is important filament in podocytes?
Actin filaments
What processes do podocytes extend around glomerular capillaries?
Primary processes
What do primary processes branch into?
Secondary processes called Foot processes
Which podocyte processes is involved in filtration?
Foot processes
What do foot processes create when they interdigitate with other podocyte foot processes?
Filtration slit
What is the podocyte filtration slit lined with?
Filtration slit diaphragm
What is function of filtration slit?
Allows filtrate to enter urinary space, acts as physical barrier to bulk flow and free diffusion
What is key functional and structural component in filtration slit diaphragm?
Nephrin transmembrane protein
What does nephrin form when it interacts with neighboring foot processes nephrin proteins?
Central destiny with pores on both sides
What is filtration slit diaphragm anchored to ?
Actin filaments in foot processes of podocytes
Regulation and maintenance of actin cytoskeleton of podocytes is critical for?
Regulating patency and selectivity of filtration slits
What does GBM act as?
Physical barrier and ion selective filter
What are the 3 components of GBM?
Lamin Rara Externa
Lamina Densa
Lamina Rara Intera
What is lamina rara externa rich in?
Heparan sulfate, impedes passage of negatively charged molecules
What provides attachment of lamina rara externa to podocyte?
Laminin
What is lamina densa?
Fused portion of two basal laminae, contains type 4 collagen network that acts as physical barrier, type 17 collagen, perlecan, these provide anionic charge
What are mesangial cells?
Group of cell sin renal corpuscle, located in vascular stalk of glomerulus, derived from smooth muscle precursors
What do mesangial cells secrete?
Their extracellular matrix
What is a mesangium?
Extracellular matrix and mesangial cells together
What are mesangial cells enclosed by?
Basal lamina of glomerular capillaries
What are the cells located outside of the renal corpuscle along the vascular pole?
Lacis cells, component of juxtamedullary apparatus
What are some functions of mesangial cells?
Phagocytosis of trapped molecules in GBM, endocytose immune complexes deposited
Structural support where GBM is incomplete
Secretion of interleukin-1 and PDGF, respond to glomerular injury
Modulation of glomerular distention
Describe modulation of glomerular distention in mesangial cells?
They regulate distention when blood pressure increases with their contractile abilities
When do mesangial cells proliferate?
In kidney diseases where abnormal amounts of protein are deposited in GBM, ex. diabetic nephropathy, lupus nephritis
What are the components of the JGA?
Macula densa, JG cells, Lacis cells
What point of contact does JGA make?
Between distal tubule and vascular pole of its glomerulus
Where is macula densa located?
Distal straight tubule
What forms the JG cells?
Modified smooth muscle cells of afferent arterioles tunica media
What kind of cell is a JG cell?
Mechanoreceptor
What do JG cells cytoplasmic secretory granules contain?
Protease called Renin
What activates the RAAS system?
JG cells
Can JG cells be found in efferent arterioles?
Occasionally
How is angiotensin I produced?
Renin catalyzes hydrolysis of circulating angiotensinogen in blood
What produces Angiotensin II?
Angiotensin I is converted to angiotensin II in lung capillaries
What is angiotensin II?
A vasoconstrictor
What is function of angiotensin II?
Regulated renal and systemic vascular resistance
What does angiotensin II stimulate?
The adrenal glands to synthesize and release aldosterone
What does aldosterone do?
Increases reabsorption of Na+ from connecting tubules and collecting ducts
What is function of macula densa?
Function as osmoreceptors, monitor Na+ concentration in distal convoluted tubule
Also regulate renin secretions from JG cells
What is another name for Lacis cells?
Extraglomerular mesangial cells
How do Lacis cells communicate with each other and with JG cells?
GAP Junctions
How is blood pressure maintained?
JGA cells and RAAS System
Explain process of blood pressure increase
Low Na+ concentrations in distal convoluted tubules stimulate macula densa cells, macula densa cells then secrete mediators like ATP, NO, prostaglandins, these mediators act in paracrine matter and send signals to Lacis cells, Lacis cells then distribute mediators to JG cells via gap junctions, JG cells secrete renin and RAAS is activated. RAAS activation results in aldosterone secretion from adrenal gland, aldosterone increases Na+ reabsorption from the connecting tubules and collecting ducts, this increases blood serum Na+ concentration which increases blood pressure.
Where is proximal convoluted tubule located?
Cortical labyrinth
What does PCT receive from bowmans capsule?
Ultrafiltrate, most is reabsorbed here
What is PCT lined with?
Simple cuboidal or columnar
Structural features of PCT
Acidophilic cytoplasm from abundant mitochondria, apex has long microvilli that form brush border, zonula occludens and zonula adherens junctional complexes, numerous pits and vesicles at base of microvilli, basal striations and invaginations
What do zonula occludens do for PCT?
Seals off intercellular space from the lumen of tubule
What do zonula adherens do for PCT?
Maintains adhesion between cells
What do pits and vesicles indicate in PCT?
Active endocytosis and pinocytosis, vesicles contain small reabsorbed proteins which will be degraded in lysosomes, amino acids will be released into circulation
How are basal striations formed?
By vertically arranged mitochondira, parallel to basal folds
What does basolateral domain of PCT show?
Basolateral folds show lateral interdigitations/plicae with neighboring cells, basal membrane invaginations forming basal striations
What do the transmembrane proteins located in basolateral folds and brush border do?
Mediate tubular reabsorption and secretion
Functions of the PCT?
Reabsorption of water and electrolytes, reabsorption of organic molecules like glucose and amino acids, endocytosis of proteins and large peptides, secretions of organic cations and anions not filtered in renal corpuscle, *Hydroxylation of Vitamin D
What two transmembrane proteins does PCT use for water and electrolyte reabsorption?
Na+/K+ ATPase pump localized in lateral folds and reabsorb Na+
Aquaporin-1 water channel located in plasma membrane
How does PCT secrete unfiltered ions from renal corpuscle?
Taken up by peritubular capillaries and secreted into filtrate, ex. bile salts, antibiotics
How does PCT hydroxylize Vitamin D?
Inactive Vitamin D is converted to active form called Calcitiol, regulated by PTH
Define tubular reabsorption?
Absorption of selected materials from nephric filtrate into blood of peritubular capillaries
What two actions does tubular reabsorption use?
Diffusion and active transport
Define Tubular secretion?
Removal of selected materials from blood of peritubular capillaries into nephric filtrate
What action does tubular secretion use?
Active transport only
Example of tubular reabsorption?
Glucose, amino acids, water, sodium, potassium
Example of tubular secretion?
Removal of ammonia, urea, uric acid, penicillin, harmful drugs
Proximal straight tubule is also called what?
Thick descending tubule
Where is PST found?
Medullary rays
What is PST lined with?
Simple cuboidal
Structural features of PST?
Few short microvilli, randomly dispersed microvilli, few basolateral folds
Functions of PST?
Reabsorption of remaining glucose
What is descending thin segment lined with?
Simple squamous
Where is descending thin segment located?
Inner medullar and outer medullar in inner stripe
In which nephron are long descending thin segments found?
Juxtamedullary nephrons
In which nephron are short descending thin segments found?
Cortical nephron
Function of descending thin segment?
Highly permeable to water
What are cell types found in descending thin segment?
Cell types I-IV
What are specific functions of the 4 cell types in descending thin segment?
Role in the countercurrent multiplication part of urinary concentration by setting up concentration gradient
What are cell types connected by in descending thin segment?
Tight junctions and desmosomes
Where is type I cell in descending thin segment found?
Descending thin limb of cortical nephron, cortex
Where is type II Cell in descending thin segment found?
Descending thin limb of juxtamedullary nephron, cortex
Where is type III Cell in descending thin segment found?
Descending thin limb of juxtamedullary nephron, medulla
Where is type IV Cell in descending thin segment found?
At bend of Loop of Henle, and thin ascending limb of juxtamedullary nephron, medulla
What is ascending thin limb permeable to?
Na+ and Cl- ions
Is ascending thin limb permeable to water?
Highly IMPERMEABLE to water
What is main function of loop of henle?
Set up concentration gradient in medulla for countercurrent multiplier effect
Where is distal straight tubule located?
In medullary to medullary rays in cortex
What is distal straight tubule lined with?
Large cuboidal cells
What do cells in distal straight tubule produce?
Uromodulin
Function of uromodulin?
Protein that influences NaCl reabsorption, modulates cell adhesion and signal transduction, inhibits accumulation of calcium or oxalate crystals which prevent kidney stones, provides defense against UTIs
Is distal straight tubule permeable to water?
No, impermeable to water
What cells does distal straight tubule form, from cuboidal to columnar?
Macula densa cells
Functions of distal straight tubule?
Reabsorbs Na+ and Cl- and transports to interstitium
Where is distal convoluted tubule located?
Cortical labyrinth, extends to connecting tubule
Is distal convoluted tubule permeable to water?
Relatively impermeable to water
Which tubule has highest Na+/K+ ATPase activity?
Distal convoluted tubule
Functions of distal convoluted tubule?
Reabsorption of Na+ and Cl- and HCO3 ions, Secretion of K+ H+ ammonium penicillin and toxic substances
What is distal convoluted tubule under the influence of?
Vasopressin/ADH secreted by the neurohypophysis, also under influence of ANP/ANF atrial natriuretic factor
What happens when ANP is released during stretching of atrial muscles?
ANP inhibits vasopressin ADH secretion, which inhibits reabsorption of water, and increases urination, ANP inhibits renin secretion and aldosterone secretion
What are connecting tubules lined with?
Simple cuboidal epithelium with two types of cells
Cuboidal distal convoluted tubule cells
Cortical collecting duct cells
What is connecting tubules under influence of?
Aldosterone
Functions of connecting tubules?
Secretion of K+
What are small cortical collecting ducts lined with?
Simple cuboidal
How are medullary collecting ducts formed?
Merging of small cortical collecting ducts
What is medullary collecting duct lined with?
Simple columnar
What do medullary collecting ducts merge to form?
Papillary ducts or Ducts of Bellini
Where do papillary ducts drain into?
Minor calyces
What two tubules are under the influence of PTH?
Distal convoluted tubule and proximal convoluted tubule
What are two cell types that form collecting duct epithelium?
Light cells/Principal cells and Dark cells/Intercalated cells
What are Principal/Light cells?
Main cells of system, show basal membrane infoldings, posses water channel protein Aquaporin-2, under influence of aldosterone
What are Aquaporin 2 channels regulated by?
ADH
What are Intercalated/Dark cells?
Few in number, have many scattered mitochondria, cytoplasmic folds, function in secreting H+ or HCO3 ions depending on the need to excrete acid or alkali
What is renal interstitial tissue?
Connective tissue component of renal parenchyma, surrounds nephrons, collecting ducts, blood and lymphatic vessels
Do healthy individuals have a lot of renal interstitial tissue?
No, minimal CT
What percentage of rental interstitial tissue is in the cortex?
7%
What percentage of renal interstitial tissue is in the medulla?
20%
In renal interstitial tissue, in the cortex there are two cell types?
Cells resembling fibroblasts, found between basement membrane of tubules and adjacent peritubular capillaries
And occasional macrophages
What are the two cell types of renal interstitial tissue called together?
Interstitial cells
What is function of fibroblast like cells in renal interstitial tissue?
Synthesize and secrete type III collagen and GAGs, and evidence of erythropoietin production
What is EPO primarily produced by?
Pericytes of peritubular capillaries
What do interstitial cells resemble in the medulla?
Myofibroblasts, containing bundles of actin filaments
Origin of fibroblasts in renal interstitium happens through a mechanism called?
Epithelial-mesenchymal transition EMT
What is the epithelial mesenchymal transition?
Tubular epithelial cells transform to mesenchymal tissue, initiated by alteration of balance of local cytokine concentration
Can mesenchymal tissue transform back to epithelial cells in EMT transition?
Yes
What happens during persistent renal injury?
Fibroblasts increase and secrete excessive extracellular matrix, causing renal fibrosis and leads to irreversible damage and renal failure
What is mucosa of urinary passages?
Transitional epithelium and lamina propria
What are two muscularis layers in urinary passgaes?
Inner longitudinal and outer circular
Is adventitia or serosa seen in urinary passages?
NO
What is structure of ureter?
Transitional epithelium, thick muscular wall
What layers are in upper 2/3 of ureter?
Inner longitudinal and outer circular
What layers are in lower 1/3 of ureter?
Inner longitudinal, middle circular, outer longitudinal
What kind of contractions move urine through ureters?
Peristaltic
What does lamina propria in bladder contain?
Higher proportions of collagen and elastic fibers
How many layers does muscularis of bladder have?
Three
What is first layer of transitional epithelium?
Single layer of small basal cells resting on thin basement membrane
What is second layer of transitional epithelium?
Intermediate regions containing one to several layers of cuboidal or low columnar cells
What is third layer of transitional epithelium?
Superficial layer of large umbrella cells, sometimes binucleated
What is function of umbrealla cells?
Protect underlying cells against cytotoxic effects of hypertonic urine
What are structural features of umbrella cells?
Extensive intercellular junctional complexes, most of apical surface consists of asymmetric unit membrane, outer lipid layer is twice as thick as inner leaflet
What are asymmetric regions in transitional epithelium composed with?
Lipid rafts that contain abundant uroplankins
What do membranous plaques and tight junctions serve as in transitional epithelium?
An osmotic barrier, protect cells from urine and prevent dilution of stored urine
What are membranous plaques hinged together by in transitional epithelium?
Narrow regions of typical membrane
What happens when bladder is empty?
Mucosa folds, umbrella cells decrease apical surface area by folding membrane at the hinge regions and internalizing the folded plaques in discoid vesicles
What happens when bladder fills?
Vesicles rejoin the apical membrane, increase surface area, tight junctions are reorganized
What are the three distinct segments of male urethra?
Prostatic urethra, membranous urethra, penile urethra
What is the prostatic urethra lined with?
Transitional epithelium
What is membranous urethra lined with?
Stratified or psuedostratified columnar
What is penile urethra lined with?
Bulbar and spongy urethra lined by psuedostratified columnar, glandular urethra is lined by stratified squamous keratinized
What is female urethra lined with?
Transitional epithelium, and stratified squamous non keratinized before the end
