Unit 7 - Urinary System Flashcards
functions of kidneys
- clear blood of metabolic waste products
- regulate fluid and electrolyte balance
- produce renal erythropoietic factor and renin
- hydroxylate vit D to active calcitriol
kidney location
retroperitoneally on posterior wall of abdominal cavity on either side of vertebral column
kidney hilus
concave medial border w/ ureter, nerves, blood, and lymphatic vessels
renal sinus
large cavity surrounded by kidney parenchyma
-contains renal pelvis, loose CT, adipose, blood vessels, and nerves
renal pelvis
expansion of upper end of ureter that subdivides into minor and major calyces
kidney capsule
consists of dense irregular cT
renal cortex
darker, granular tissue
- broad outer zone
- inward extensions (renal columns of Bertin)
minor VS major calyces
major: arise from renal pelvis
minor: arise from major
renal medulla
lighter, striated tissue
-made of renal pyramids and medullary rays
renal pyramids
in medulla
- apices (renal papillae) project into minor calyces
- tip is perforated by openings of collecting ducts (area cribosa)
- each pyramid together with its surrounding cortical tissue constitutes a renal lobe
renal lobe
renal pyramid + cortical tissue overlying its base and covering its sides
-each kidney contains 6 to 18 lobes
medullary rays
medullary tissue that projects up into cortex, consisting of collecting tubules and their accompanying proximal and distal tubules
-do NOT include renal corpuscles
renal lobule
medullary ray + surrounding cortical tissue
nephrons
functional unit of kidney
- first part (Bowman’s capsule to distal tubule) forms urine
- second part (collecting system) carries out final concentration of urinary solutes
components of nephron
- Bowman’s capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting tubules
- Collecting ducts
Bowman’s capsule components
thin-walled expansion at proximal end of nephron
- deeply indented by glomerulus
- visceral layer = podocytes and covers glomerular capillaries
- parietal layer = simple squamous epithelium
- urinary (capsular) space between both layers gets glomerular filtrate
- glomerular filtration barrier
- vascular pole = afferent arteriole enters, efferent arteriole leaves
- urinary pole = proximal tubule begins
components of glomerular filtration barrier
in Bowman’s capsule
- capillary endothelium (fenestrated, w/o diaphragms)
- shared basement membrane (endothelium + podocytes)
- filtration slits between secondary processes of podoccytes
- produces glomerular filtrate (similar to blood, except little protein)
what is proteinuria caused by?
release of protein into urine due to defect in glomerular filtration barrier (usually doesn’t let PRO in)
where is urinary space continuous with proximal tubule lumen?
at urinary pole of Bowman’s capsule
proximal tubule composition
convoluted (close to renal corpuscle of origin) and straight part (enters medullary ray)
- lined by simple cuboidal epithelium with brush border
- eosinophilic cytoplasm
- extensive lateral extensions (cell boundaries indistinct b/c large cells)
- lumen has fine precipitated material
how many segments can the proximal tubule be subdivided into by electron microscopy?
can be subdivided into 3 segments by electron microscopy
loop of Henle composition
descending straight proximal (simple cuboidal epithelium with brush border, like convoluted), thin segment (simple squamous, like capillary w/o blood), and ascending straight distal
-located in medulla
distal tubule composition
ascending straight portion (last part of LoH), portion adjacent to renal corpuscle of origin, and convoluted part
- mainly in cortex
- simple cuboidal epithelium that lacks brush border
- cells smaller than proximal tubule, with apical nuclei
- less eosinophilic than proximal tubule
- no precipitate in lumen
- same extensive lateral extensions (indistinct boundaries) like in proximal
collecting tubules and ducts composition
tubules in cortex, and ducts in medulla
- cuboidal epithelium in tubules, columnar in ducts
- cells have clear, pale-staining cytoplasm
- intercellular boundaries are clearly visible
- largest ducts (papillary ducts) communicate with minor calyx at area cribosa)
3 types of nephrons
classified according to position of renal corpuscles in cortex
- superficial (cortical) nephrons - short LoH that extend short distance into medulla
- juxtamedullary nephrons - long LoH penetrate deep in medulla (most important for hypertonic urine)
- intermediate (midcortical) nephrons have intermediate characteristics
what does the juxtaglomerular apparatus do? its components?
responsible for renin production
- located where distal tubule returns to its renal corpuscle of origin
- components:
- -macula densa in wall of distal tubule
- -juxtaglomerular cells: modified smooth muscle cells in tunica media of afferent arteriole
- -extraglomerular mesangial cells (lacis cells): pale staining cells in angle between afferent and efferent arterioles
explain the renin-angiotensin system
regulates fluid and electrolyte balance and blood pressure
- when BP falls, juxtaglomerular cells release renin, that converts angiotensinogen (from liver) to AI to AII (by ACE in capillary endothelial cells of lungs)
- AII stimulates zona glomerulosa of adrenal cortex to make aldosterone to stimulate distal tubule to reabsorb Na and H2O
- -reabsorption increases intravascular fluid volume, which raises blood pressure
- -AII is also a vasoconstrictor
- renin also has localized effect on afferent arterioles (provides for single nephron GFR control)
what does the macula densa do?
senses changes in NaCl concentration in distal tubule
- high [NaCl] inhibits renin secretion
- low [NaCl] stimulates renin secretion
what are extraglomerular mesangial cells?
play a supportive role in the renin-angiotensin system
-may provide signal integrating system
how much of total cardiac output goes to kidneys?
25%
what are the 8 components of the arterial supply of the kidneys?
- renal artery
- interlobar arteries
- arcuate arteries
- interlobular arteries
- afferent arterioles
- glomerular capillaries
- efferent arterioles
- vasa recta
renal artery?
enters at hilus and divides into anterior and posterior divisions
interlobar arteries?
arise from anterior and posterior divisions of renal artery
- run peripherally in renal columns
- form arcuate arteries at corticomedullary junction
arcuate arteries?
arise from interlobar arteries
- run parallel to kidney surface
- give rise to interlobular arteries
interlobular arteries
arise from arcuate arteries
- run radially through cortex
- give rise to afferent arterioles
afferent arterioles
arise from interlobular arteries
- enter renal corpuscles at vascular poles
- supply glomerular capillaries
- site of juxtaglomerular cells
glomerular capillaries?
arise from afferent arterioles
-unite to form efferent arterioles
efferent arterioles?
arise from united glomerular capillaries
- leave renal corpuscle at vascular pole
- give rise to peritubular capillary network that nourishes proximal and distal tubules from cortical nephrons
- give rise to vasa recta from juxtamedullary nephrons
vasa recta
arise from efferent arterioles of juxtamedullary neprhons
-make hairpin loops in medulla to form countercurrent system of vessels
what are the 5 components of venous drainage of the kidney?
closely paralleles arterial supply
- stellate veins
- interlobular veins
- arcuate veins
- interlobar veins
- renal vein
stellate veins
drain capillaries in capsule and peritubular capillary network
-form interlobular veins
what does EPO do? how is it used? downsides?
glycoprotein whose major function is to promote RBC formation in bone marrow by stimulating proliferation, differentiation, and precursor survival
- used as anti-anemia drug in chronic and post-operative anemia, and cancer patients
- -neuroprotection, CVD treatment, and induction of bone remodeling by OC activation
- downsides: erythrocytosis and potentially tumor growth
how is EPO made and stimulated by?
made by endothelial cells lining peritubular capillary plexus, and stimulated by hypoxia from:
- hemorrhage
- EPO destruction
- pulmonary function compromise
- CHF
- high altitude
motile VS non-motile cilia?
motile: 9+2 microtubule axoneme pattern that are coordinated in wave-like beats
non-motile: 9+0 microtubule axoneme pattern found singly on most cells
- responsive to mechanical and chemical signals and sense fluid flow in uriniferous tubule
- regulate cell proliferation
what cilia type are defective in polycystic kidney disease?
non-motile
-leads to cellular over-proliferation and cyst formation
what composes the extrarenal collecting system? their structure compared to each other?
minor and major calyces, renal pelvis, ureter, bladder, and urethra
-all but urethra are similar histologic structure
mucosa of calyces, renal pelvis, ureter, and bladder
transitional epithelium with thin lamina propria of connective tissue
- barrier to rapid salt and water diffusion
- gives distensibility to lining layer
- thickness increases from calyces to bladder
- superficial cells are large and rounded (umbrella cells)
- luminal surface has angular appearance (uroplakin particles)
- apical cytoplasm rich in filaments and flattened vesicles
- plasma membrane can stretch and contract triggered by ATP
- 90% of urinary bladder tumors originate in epithelium
muscularis of calyces, renal pelvis, ureter, and bladder
loose anastomosing strands of smooth muscle separated by abundant connective tissue
-thickest in bladder, where 3 layers are present (LCL)
adventitia of calyces, renal pelvis, ureter, and bladder
composed of connective tissue
-upper part of bladder is covered by serosa (peritoneum)
what is the urethra?
fibromuscular tube through which urine passes from the urinary bladder to the exterior
three segments of the male urethra
- prostatic urethra
- membranous urethra
- penile urethra (spongy)
- glands of Littre (throughout)
prostatic urethra?
first part of male urethra
- from neck of bladder through prostate
- lined by transitional epithelium
membranous urethra
second part of male urethra
- extends from lower pole of prostate to bulb of corpus spongiosum of penis
- traverses urogenital and pelvic diaphragms
- lining varies from transitional to pseudostratified columnar epithelium
- surrounded by external sphincter of bladder (skeletal muscle)
penile urethra
third part of male urethra
- passes through corpus spongiosum of penis
- lined by mostly pseudostratified columnar epithelium
- fossa navicularis has lining of stratified squamous epithelium
- contain most glands of Littre
glands of Littre
mucous secreting glands that empty into male urethra
-most abundant in penile urethra
female urethra
relatively short (3-5 cm)
- lined by stratified squamous epithelium, plus some pseudostratified
- staghorn shaped lumen
- thick layer of smooth muscle in wall
- urethra sphincter (skeletal muscle) in middle
