Urinary System Flashcards
1
Q
Kidney
Functions
A
- Water and electrolyte balance
- absorption of H2O and Na+
- Excretion
- urea
- uric acid
- creatinine
- Hormone production
- EPO
- renin
- prostaglandins
- Hydroxylation of Vit D
2
Q
Kidney
Gross Structure
A
Capsule
- outer layer of fibroblasts and collagen fibers
- inner layer of myofibroblasts
Cortex
-
Renal corpuscles
- formed by the glomeruli and Bowman’s capsule
-
Cortical labyrinths
- region that surrounds the renal corpuscles
- formed by the convoluted tubules
- Renal corpuscles
Proximal convoluted tubules
Distal convoluted tubules
Arched collecting tubules - Looks the same regardless of the plane of section
- Renal corpuscles
-
Medullary rays
- longitudinal striations that emanate from the medulla
- formed by the straight portions of uriniferous tubules
- collecting ducts
- straight proximal tubule
- straight distal tubule
Medulla
- Often divided into an inner and outer zone
- Tubules of cortical (superficial) nephrons extend into the outer zone
- Tubules of juxtamedullary nephrons extend into the inner zone
-
Medullary pyramids
- Separated by medullary extensions of the cortex ⇒ cortical columns
- Straight portions of the uriniferous tubules
- Collecting ducts
- Vasa Recta
Renal sinus:
Fat-filled cavity near hilum
Contains minor and major calyces, most of renal pelvis, branches of renal vessels.
3
Q
Medullary Pyramids
A
- Characterized by numerous straight tubules, collecting ducts, and vasa recta converging towards the tip.
- Each pyramid divided into an outer medulla and inner medulla
- Outer medulla subdivided into outer stripe and inner stripe
- Base of the pyramid is surrounded by cortical tissue ⇒ cortical arch
- Apex of the pyramid points towards the hilum
- Called the renal papilla
- Collecting ducts terminate here
-
Area cribrosa ⇒ perforated tip of the renal papilla
- formed by the openings of the collecting (ducts of Bellini)
- Drains into a minor calyx ⇒ major calyx ⇒ renal pelvis
-
Cortical columns flank each side of the pyramid
- Are not considered part of the medulla
4
Q
Kidney
Lobe
A
Defined as all the tissue whose nephrons drain into the same minor calyx.
Includes both cortex & medulla:
1 medullary pyramid
Associated cortical arch
Half of each cortical column that surrounds it
Interlobar arteries and veins located in renal columns at the boundaries between lobes.
5
Q
Kidney Lobule
A
Defined as all the tissue whose nephrons drain into the same medullary ray.
Includes cortex but no medulla:
Medullary ray
Half of each cortical labyrinth on each side
Interlobular arteries and veins located at the boundaries between lobules.
6
Q
Uriniferous Tubule
A
Functional unit of the kidney.
Includes a nephron plus it’s associated collecting duct.
Seperate embryological origin.
7
Q
Nephron
A
~ 1.3 million / kidney
Consists of:
-
Renal corpuscle
- Glomerulus
- Bowman’s capsule
-
Proximal tubule
- Proximal convoluted tubule
- Proximal straight tubule (thick descending limb of loop of Henle)
- Thin limbs of Loop of Henle
-
Distal tubule
- Distal straight tubule (thick ascending limb of loop of Henle)
- Distal convoluted tubule
8
Q
Cortical vs Juxtamedullary Nephrons
A
Cortical Nephrons
- ~ 85% of nephrons
- short LoH or absent
- contributes to medullary rays
- may extend into outer layer of medulla
Juxtamedullary Nephrons
- ~ 15% of nephrons
- long LoH extending deep into medulla
9
Q
Renal Corpuscle
A
Includes glomerulus and Bowman’s capsule
-
Glomerulus
- 10-20 fenestrated capillary loops
- no diaphragms
- afferent & efferent arterioles carry blood
- located at the vascular pole of the renal corpuscle
- 10-20 fenestrated capillary loops
- Bowman’s Capsule
- visceral and parietal layers
- urinary space in between
- two poles
- vascular pole
- where efferent and afferent arterioles located
- where visceral and parietal layers continuous
- macula densa found here
- urinary pole
- where parietal layer is continuous with PCT
- lumen of PCT continuous with urinary space
- epithelium abruptly changes from simple squamous to simple cuboidal
- vascular pole
- visceral and parietal layers
10
Q
Visceral Layer
Bowman’s Capsule
A
- Invaginates and covers outer surface of glomerular capillaries
- Composed of specialized epithelial cells called podocytes
- primary processes extend parallel to long axis of capillary
- secondary processes extend perpendicular from primary processes
-
pedicels (foot processes) extend from secondary processes
- filtration slits formed between interdigitating pedicels of neighboring podocytes
- covered by a slit diaphragm
- podocalyxin - polyanionic sialoprotein which forms the glycocalyx of the podocytes
11
Q
Parietal Layer
Bowman’s Capsule
A
- Formed from simple squamous epithelium
- The urinary space lies between visceral and parietal layers of Bowman’s capsule
- Collects plasma ultrafiltrate from glomerular capillaries
12
Q
Intraglomerular Mesangial cells
A
- Scattered along the endothelial side of glomerular basement membrane
- Located between capillary endothelium and basal lamina
- Functions:
- support for capillaries
- acts like macrophages and cleans basement membrane
- contracts to help regulate blood flow through glomerular capillaries
13
Q
Glomerular
Filtration Barrier
A
3 main components:
-
Fenestrated endothelium of glomerular capillaries
- 70-90 nm fenestrae
- lack diaphragms
- impedes passage of molecules > 70 K daltons
-
Fused basal lamina (glomerular basement membrane)
- very thick
- PAS+
- jointly formed by podocytes and endothelial cells
- consists of two laminae rarae surrounding lamina densa
-
Laminae rarae
- laminin, fibronectin, and heparan sulfate
- light staining
-
Laminae densa
- mostly type IV collagen
- dark staining
-
Laminae rarae
-
Podocytes
-
filtration slit membranes connecting interdigitating pedicles
- made of a protein complex
-
filtration slit membranes connecting interdigitating pedicles
14
Q
Proximal Tubule
Characteristics
A
- Reabsorbs ~ 80% of primary filtrate
- Begins at the urinary pole of renal corpuscle
- Drains Bowman’s space
- Absorbs:
- Na, Cl, H2O
- Amino acids, sugars, and polypeptides
- Secretes certain endogenous and exogenous organic solutes
-
Proximal convoluted tubule (pars convoluta)
- longer than other tubule types in cortical labyrinth
- is the type most commonly seen there in sections
-
Proximal straight tubule (pars recta)
- contributes to medullary rays
- extends into medulla
- becomes continuous with thin limb of LoH
15
Q
Proximal Tubule
Structure
A
- Simple cuboidal epithelium
- Complex lateral membrane folds
- lateral cell borders indistinct by LM
-
Basal striations
- infoldings of basal plasmalemma
- mitochondria fill space between folds
- Aciophilic cytoplasm
- Prominent brush border with PAS+ glycocalyx
- Large cell size with nucleus spread further apart
- May have stellate shape to the lumen
16
Q
Thin Limbs
Loop of Henle
A
-
Descending thin limb
- continuous with pars recta of proximal tubule
-
Ascending thin limb
- continuous with pars recta of distal tubule
- Simple squamous epithelium
- Contributes to contercurrent multiplier system
17
Q
Distal Tubule
Characteristics
A
- Initial part is straight ⇒ pars recta
- continuous with ascending thin limb of LoH
- Becomes convoluted in the cortex ⇒ pars convoluta
- impermeable to water and urea
- Activated by aldosterone to absorb Na+
- Macula densa is part of the distal tubule
- Contributes to juxtaglomerular apparatus
18
Q
Distal Tubule
Structure
A
-
Low cuboidal epithelium
- fewer profiles in section
- less acidopihil
-
no brush border
- sparse microvilli by EM
- more clearly defined lumen than proximal tubules
- Lateral cell borders indistinct
- Cells smaller so more nuclei per cross section
- Nuclei located close to apical membrane
19
Q
Juxtaglomerular Apparatus
A
Includes:
-
Macula Densa
- taller, narrower cells on side of distal straight tubule closest to the vascular pole
- closely packed nuclei stains darker
- basment membrane absent between macula densa and JG cells
- respond to changes in BP, blood flow rate, fluid composition in distal tubule
-
Juxtaglomerular (JG) cells
- modified smooth muscle cells in tunica media of afferent more frequently than efferent arterioles
- cytoplasmic vacuoles containing renin
- part of the RAAS system
-
Extraglomerular mesangial cells
- occupy space between macula densa, afferent arteriole, and efferent arteriole
- continuous with intraglomerular mesangial cells
- likely transmit signals between macula densa and intraglomerular mesangial cells to regulate contractility of the latter
20
Q
Collecting Tubules and Ducts
A
- found in cortex and medulla
- distinguished from proximal and distal tubules due to distinct lateral boundaries
- have two distinct cell types:
- Principal cells
- Intercalated cells
- Alpha and beta types
21
Q
Principal Cells
Collecting Ducts
A
- Light cells
- More common
- Single nonmotile cilia
- senses fluid flow
- defect in cilia causes polycystic kidney disease
- membranes contain aquaporin channels
22
Q
Intercalated Cells
Collecting Ducts
A
- darker staining
- interspersed amount prinicpal cells
- Found in the cortical CD and proximal part of the medullary CD
- Absent near papilla
- Have microplicae on apical plasmalemma
- Two types help regulate acid/base balance:
- 𝛼-intercalated cells actively secrete hydrogen ions
- 𝛽-intercalated cells release bicarbonate via membrane exchanger
26
Q
Renal Blood Supply
A
renal arteries ⇒ anterior and posterior divisions (hilum)
⇒ segmental arteries (in renal sinus)
⇒ interlobar arteries (bisect renal columns, run towards capsule)
⇒ arcuate arteries (runs parallel to corticomedullary boundary near base of pyramids)
⇒ interlobular arteries (bisect cortical labyrinths towards capsule)
⇒ afferent arterioles (arise from interlobular artery, lead to glomeruli)
⇒ glomerular capillaries
⇒ efferent arterioles (one from each glomerulus)
⇒ peritubular capillaries (irregular network anastomosing vessels mainly in cortex, empty into interlobular or arcuate vein)
or
vasa recta (long straight vessels in medulla, arise from efferent arterioles of juxtamedullary nephrons, empty into interlobular or arcuate vein)
Last 3 form an Arterial Portal System.
29
Q
Renal Papillae
A
- Found at the apex of medullary pyramids
- Each fits into a minor calyx
-
Area cribrosa is on the tip of the papilla
- formed by the openings of the collecting ducts of Bellini
- Covered by transitional epithelium
30
Q
Renal Calyces
A
- Each minor calyces receives a renal papilla
- protrudes into lumen of minor calyx
- epithelium covering papilla becomes continuous with epithelium lining calyx
- Unit to form major calycles
- Lined with transitional epithelium
- Wall has smooth muscle deep to lamina propria
- Propels urine to the renal pelvis
31
Q
Renal Pelvis
A
- Formed by the union of all major calyces
- Transitional epithelium
- Thin layer of smooth muscle deep to lamina propria
- Continuous with ureter at hilum
- Adventitia with fat that blends with fat of renal sinus
32
Q
Ureter
A
-
Mucosa
- transitional epithelium
- lamina propria of dense fibroelastic CT
- no muscularis mucosae
-
Muscularis
- layers of smooth muscle produce peristaltic waves
- proximal 2/3 of ureter
- inner spinal layer = longitudinal
- outer layer circular
- distal 1/3 of ureter: addtional outer longitudinal layer
- inner longitudinal
- middle circular
- outer longditudinal
-
Adventitia
- Blends into surrounding CT
33
Q
Urinary Bladder
A
-
Mucosa
-
transitional epithelium
- Thickened plasmalemmal plaques by EM in distended bladder
- Fusiform vesicles in apical cytoplasm by EM in relaxed bladder
-
lamina propria
- dense irregular Ct
- collagen and elastic fibers
- no glands except at urethral orifice
- dense irregular Ct
-
transitional epithelium
-
Muscularis
- three interlaced layers of smooth muscle form a thick muscularis ⇒ detrussor muscle
-
Adventitia or Serosa
- dense irregular CT
- some elastic fibers
- Superior surface has a serosa
- Remainder has an adventitia
34
Q
Female Urethra
A
- mucosa lined by transitional epithelium
- Fibroelastic lamina propria
- small mucous-secreting glands empty into lumen
- coat of erectile tissue
- numerous wide, thin-walled vessels
- where it passes through the urogenital diaphragm it is surrounded by skeletal muscle ⇒ extrenal urethral sphincter
35
Q
Male Urethra
A
-
Prostatic urethra
- lined by transitional epithelium
-
Membranous urethra
- lined by stratified columnar and pseudostratified columnar epithelium
- passes through skeletal muscle of the urogenital diaphragm
-
Penile urethra
- lined by stratified columnar / pseudostratified columnar proximally
- lined by stratified squamous distally
- this portion surrounded by vascular erectile tissue of corpus spongiosum
-
Lamina propria
- fibroelastic CT
- contains mucous producing glands of Littre
