Urinary System Flashcards
What does the urinary system consist of? (4)
Major organs etc
- 2 Kidneys: urine formation
- 2 Ureters: conduit to bladder
- Bladder: for storage of urine
- Urethra: elimination of urine from the body
What are the 5 major functions of the kidney?
- Excretion of metabolic wastes(urea, creatine, bilirubin, drugs, etc)
- Regulation of water, BV, electrolyte balance
- BP regulation: renin-angiotensin-aldosterone system
- Regulation of acid-base balance
- Production of hormones:Erthyropoietin/Vit D (Ca2+ absorption in small intestine
Where are the kidneys located? Shape?
- Paired bean shaped organs located-retro-peritoneally on the posterior abdominal wall
- Paravertebral gutters-either side of the aorta and inferior vena cava
- Left kidney T12-L3
- Right kidney lower d/t liver being large
What is the relations of the R Kidney?
Superiorly, Anteriorly, Posteriorly
- *Superior: *suprarenal glands
- Anteriorly: Liver, duodenum, ascending colon, hepatic flexure, jejunum
- Posteriorly: 12th rib, diaphragm, psoas major, quadratus lumborum, transversus abdominus muscle, iliohypogastric and ilioinguinal nerves
L also is located near rib 11
What are the relations to the L Kidney anteriorly?
Superior/Posterior same for both kidneys
- Spleen
- Splenic flexure
- Stomach
- Pancreas
- Descending colon
- Jejunum
What are the 3 layers and functions of the coverings of the kidneys?
-
Renal Capsule
* Directly covers the renal cortex
* Protects kidney from trauma and damage-penetrates kidney parenchyma to form trabeculae that lobulate the kidney - Perirenal fat
-
Renal fascia (Gerota’s fascia)
* Encapsulates kidneys/suprarenal glands
* Anchors kidney into surrounding structures
* Divides the fat around kidney into perirenal fat/pararenal fat
Acts like a ligament
Parenchyma of the Kidney: 2 layers-distinct features
-
Renal Cortex
* Lies immediately beneath renal capsule
* Extends inwards as the renal column between renal pyramids of the medulla and contains nephrons -
Renal Medulla
* Darker in colour with a striated appearance
* Composed of 8-15 renal pyramids
* Apex of pyramids directed into the sinus of the renal papilla
* Structure of the papilla is perfored by the ducts of Bellini
What is the nephron?
Functional unit of the kidney
What are the two main structures in the nephron?
What are their subdivisions
-
Renal Corpuscle: filters blood
* Glomerulus: capillary network
* Glomerular capsule-double-walled cup surrounded glomerulus -
Renal Tubule: filtered fluid passes into
* Proximal convoluted tubule
* Loop of Henle:divided into thin/thick for ascending/descending
* Distal convoluted tubule
What are the 3 basic functions of the nephron?
- Glomerular Filtration: water and solutes in are filtered and moved into the glomerular capsule
- Tubular Reapsorption:filtered fluid then moves through renal tubules and reabsorbed (99%)
- Tubular Secretion: secretion of other materials such as wastes, drugs, and excess
What are the two layers of the glomerular capsule and what are the cells associated with them?
- Visceral layer:modified simple squamous epithelial cells (podocytes “toe like projections”)-forms the inner wall of the capsule
- Parietal layer: simple squamous epithelium-forms the outer wall of the capsule
Glomerular Filtration: 3 barriers to cross
- Glomerular endothelial cells: fenestrations
- Basal lamina: between endothelium and podocytes (fused together)
-
Pedicels of podocytes create filtration slits
* Permits filtration of water/small solutes
* Prevents filtration of most plasma proteins/blood cells/platelets
How is the volume of fluid filtered so large? (3)
- Large surface area
- Thin and porous membrane
- High glomerular capillary BP
What are the 2 types of nephrons?
- Cortical
-
Juxtamedullary
* flow of fluid is the same except juxtamedullary has thin/thick ascending limb of the loop of henle
Minor Calyx features (5)
- Associated with a single renal pyramid
- Cup-shaped and surrounds a renal papilla
- Receives from renal papilla for passage into ureter
- Delivers urine to the major calyx
- Each kidney has 8-18 of them
Renal Pelvis features (3)
- Expanded upper end of ureters
- Lies within the renal sinus
- Connects 3-4 major calyces together to the ureter
Circulation of blood in the Kidney
- Abdominal Aorta
- Segmental arteries
- Interlobar arteries
- Arcuate arteries
- Cortical radiate arteries (interlobular)
- Afferent arterioles
- Glomerular capillaries
- Efferent arterioles
- Peritubular capillaries “vasa recta”
- Cortical radiate veins
- Arcuate veins
- Interlobar veins
- Renal veins
- Inferior Vena Cava
Bolded is where exchange happens
What renal vein is longer? Why?
Left-IVC is on the right side of the body-has to cross anteriorly to the abdominal aorta
* receives the left suprarenal vein and left gonadal veins
What is the difference between Renal Hilum and Renal Sinus?
Renal Hilum: concavity located on medial border-where structures enter and leave. Contains renal vein, artery and pelvis of the ureter
Renal Sinus: cavity within kidney occupied by renal pelvis, calyces, blood vessels and fat
Polycycstic Kidney Disease features and 2 types
- Inherited kidney disorder
- Tubules have >100 cysts which results in failure
1. Autosomal dominant: renal failure late in life
2. Autosomall recessive: renal failure in early life
TX: kidney transplant
Renal Transplant things to know (2)
- Placed in the pelvis of the recipient-renal artery and vein are attached to a nearby artery and vein
- Transplant ureter attached to the bladder
- Diseased kidneys are left in place
Ureter features
- Musucular tube from renal pelvis to posterior surface of bladder
- Approx 10 inches long
- Retroperitoneal descends on the anterior surface of the psoas major muscle
- Passes anterior to the bifurcation of the common iliac artery before descending into pelvis
What are the 3 constriction points of the ureters?
- Ureteropelvic Junction
- Where is crosses the pelvic brim
- Pierces bladder wall
Histology of the Ureter
3 layers
- Mucuosa: transitional epithelium-stratified epithelium which can stretch, lamina propria
- Muscularis 3 layers: Inner longitudinal, middle circular, outer longitudinal
- Adventitia
First 2/3 of muscularis is: Inner longitudinal, outer circular
What ligament attaches to the bladder?
Median Umbilical ligament (Urachus)
Histology of the bladder
3 layers
-
Mucuosa: transitional epithelium-stratified epithelium which can stretch
* dense lamina propria - Muscularis 3 layers: Inner longitudinal, middle circular, outer longitudinal
- Adventitia: adipose tissue
Bladder Cancer things to know (4)
- More prevalent in males
- Hematuria
- Cytoscopy used to examine structures-take biopsy
- Favourable prognosis if identified early
External/Internal Urethral Sphincters
1. Internal
Smooth muscle
Parasympathetic/Symphatethic
2. External
Skeletal muscle
Somatic (pedundal)
Membranous urethra
Histology of the Urethra
-
Mucosa
Transitional (early)
Stratified columnar (middle)
Stratified squamous (end) - Muscularis: thin layer of circular smooth muscle
- Thin layer of connective tissue
Urinary Incontinence definition and 4 types
-
Stress incontinence
Weakness of deep muscles in pelvic floor-occurs when abdo pressure increases -
Urge incontinence
Abrupt and intense urge to urinate-involuntary loss of urine -
Overflow incontinence
Bladder becomes overfilled-dribbles out -
Functional incontinence
Person is aware they need to void-cant reach a toilet in time (stroke, ALZH)
Definition: lack of voluntary control of micturition
ALZH-alzheimers
Micturition Reflex
“How do we pee”
- Combination of voluntary/involuntary muscle contractions
- Stretch receptors in the wall transmit nerve impulses when bladder exceeds 200-400 mL
- Impulses then propagate to the micturition center in the sacral spinal cord S2-S3 and trigger micturition reflex
- Nerve impulses cause contraction of detrusor muscle and relaxation of internal urethral sphincter
- Contraction of urinary bladder wall-relaxation of spincters-urination
Micturition center inhibits skeletal muscle in the external sphincter
Glomerular Filtrate Definition
Amount per day
Volume of fluid that enters the Bowman’s capsule from the glomerular capillaries
- *Daily volume is 150-180L
Filtration Fraction definition
Fraction of blood plasma in the afferent arterioles of the kidneys that becomes glomerular filtrate
How much plasma that flows through the kidneys actually flow through the nephrons?
- 1/5-99% of that is returned to blood plasma via tubular reabsorption
Glomerular filtration 3 pressures
- Glomerular blood hydrostatic pressure (GBHP): blood pressure in glomerular capillaries
- Capsular hydrostatic pressure pressure exerted against the filtration membrane by fluid already in the capsular space and renal tubule
- Blood colloid osmotic pressure (BCOP) osmotic pressure due to proteins in the blood plasma
Net Filtration equation
NFP=GBHP-CHP-BCOP
55mmHg-30mmHg-15mmHg=10mmHg NET
Pressure is the total pressure that promotes filtration
What is the average GFR in males/females
- MALES: 125mL/min
- FEMALES: 105mL/min
Any net change in net filtration pressure will affect GFR
What are the 3 Mechanisms Regulating GFR
Not indepth
- Renal Autoregulation: very important for kidneys to do this on their own
- Neural regulation
- Hormonal regulation
Renal Autoregulation 2 main types
- Myogenic Mechanism: occurs when stretching triggers contraction of smooth muscle cells in afferent arterioles-reduces GFR. Normalizes GFR in seconds
- Tubulo-glomerular mechanism: Acts more slowly. Uses JGA apparatus
Juxtaglomerular Apparatus (JGA)
3 types of cells w/ functions
-
Macula densa (osmoreceptors): * Found by the vascular poles (afferent/efferent arterioles).
* Sense changes in Na+ concentration within lumen of distal tubule and send signals to the JG cells.
* Modified cells of the DCT (narrower and taller) -
JG cells:
* Modified smooth muscle fibers found in walls of afferent/efferent arterioles
* Produces renin-cleaves angiotensinogen to angiotensin 1 -
Extraglomerular mesangial cells:
* ?contract to open afferent/efferent arterioles
Tubuloglomerular Feedback Loop
When GFR is elevated d/t systemic blood pressure
- Filtered fluid flows more rapidly along the renal tubules
- Results in less time to reabsorb Na+, Cl-, H20
- Macula densa cells detect the electroyle levels
- Inhibit release of NO from JGA
- Afferent arterioles constrict d/t low levels of NO
- Results in less blood flow into glomerular capillaries and GFR decreases
Neural Regulation of Kidney
(3)
- Kidney blood vessels supplied by sympathetic autonomic nervous system fibers that release norepinephrine causing vasoconstriction
- Moderate stimulation: both afferent/efferent arterioles constrict equally=minimal decrease in GFR
- Greater stimulation: constriction of afferent arteriole is dominate=decrease blood flow into capillaries–>significant GFR decrease
Hormonal Regulation (2)
- Angiotensin II reduces GFR: potent vasoconstrictor of both afferent/efferent
- ANP increases GFR: stretching of atria d/t increased BV causes release of this hormone. ANP relaxes intraglomerular mesangial cells-increases capillary surface area for filtration
Reabsorption Routes (2)
- Paracellular Reabsorptions: fluid can leak between the cells in a passive process in the PCT
- Transcellular Reabsorption: substances pass from the tubular lumen through the apical membrane of a tubule across the cytosol and into the interstitial fluid through basolateral membrane
Transport Mechanisms (2)
- Primary Active Transport: energy is derived from hydrolysis of ATP and used to pump substances across the membrane (NA+K+ATPase)
-
Secondary Active Transport: energy is stored in the electrochemical gradient
* Symporters: same direction movement
* Antiporters: opposite direction across the membrane
Water Reabsoprtion 2 types
- Obligatory Water Reabsorption: water follows solutes and is “obliged” to follow solutes when they are reabsorbed-occurs in PCT and descending limb of the nephron loop
- Facultative Water Reabsorption: Reabsorption of the final 10% of the water-regulated by ADH occurs in the collecting ducts
Proximal Convoluted Tubule Reabsorption
Simple Cuboidal w/ extensive microvilli
-
Largest amount of solute and water reabsorption from filtered fluid occurs here
* 65% of filtered water, sodium, potassium
* 100% of organic solutes (glucose and amino acids)
* 80-90% of the filtered bicarbonate (important buffer)
* 50% of filtered urea
* Variable amount of filtered Ca2+, Mg2+, phosphate
* Secrete variable amount of H+, ammonium ions, and urea - Most solute reabsorption involves Na+ (symporters/antiporters)
At the end of the PCT, tubular fluid is isosmotic-300mOsm/liter
How many Sodium molecules are attached to glucose in the PCT symporter process?
Also process
2-carries them from tubular fluid into the tubule cell.
* Glucose then exit via facilitated diffusion-diffuse into the peritubular capillaries
* This is a similar process for phosphate, sulphate ions, ALL amino acids and lactic acid
How does the PCT cells produce H+ to keep the antiport system running?
Formula
C02 +H20–carbonic anhydrase–>H2CO3–>H+ + HCO3-
Reabsorption of the solutes in the PCT create what?
An osmotic gradient that *promotes reabsorption of water via osmosis
- With water leaving the concentration of the remaing filtered solutes increase
What happens in the second half of the PCT electrochemical gradients?
Cl-, K+, Ca2+, Mg 2+ and urea passively diffuse into the peritubular capillaries via both paracellular and transcellular routes
Is any water reabsorbed in the ascending loop of henle?
NO-impermeable to H20
This causes the osmolarity to progressively decrease as the fluid moves towards the end of the ascending limb
What is reabsorbed in the Loop of Henle?
*Note: Chemical composition of fluid entering is different from the filtrate but the osmolarity is very close to blood
Reabsorbs: 15% of filtered H20
* 20-30% of filtered Na+/K+
* 35% of Cl-
* 10-20% of HCO3-
What is the major site that the parathyroid hormone works on?
Early Distal Convoluted Tubule
Late distal convoluted tubule & collecting duct
Simple cuboidal epithelium w/ principal cells and intercalated cells
*Amount of water reabsorption/secretion depends on body’s needs
- Principal cells reabsorb Na+ and secrete K+
- Na+ leakage channels in apical membranes of principal cells
- Intercalated cells reabsorb K+ and HCO3 and secrete H+
Hormonal Regulation of Tubules: Angiotensin II
- Increases reabsorption of Na+, Cl- and H20 in the PCT by stimulating Na+/H+ antiporters
- Constricts afferent arterioles, decreases GFR
- Stimulates aldosterone release from adrenal cortex (glomerulosa)
Hormonal Regulation of Tubules: ADH
Increases H20 reabsorption by increasing the water permeability of principal cells allowing water to move more rapidly from tubular fluid in the cells
Aquaporin II
Hormonal Regulation of Tubules: PTH
- Increases Ca+reabsorption in the DCT
- Decreases phosphate reabsorption
Hormonal Regulation of the Tubules: ANP
- Increase in BV causes stretch in atria and release of ANP
- Decreases Na+ and water reabsorption in PCT and collecting duct (increases GFR)
- Suppresses the secrtion of Aldosterone/ADH
RESULTS: Decreases BV and BP
Hormonal Regulation of the Tubules: Aldosterone
- Na+ reabsorption and K+ secretion in late DCT and collecting duct
Evaluation of Kidney Function: Urinalysis
- Total urine volume, water, electrolytes, drugs toxins etc
- If disease alters metabolism or kidney functions, abnormal amounts may appear
Evaluation of Kidney Function: Blood tests
- BUN
- Cr
Evaluation of Kidney Function: Renal plasma clearance
Most useful in diagnosis of kidney problems
A substance that is filtered but neither reabsorbed or secreted has a clearance that equals GFR
Histology of Renal Tubule and Collecting Duct
PCT: Simple cuboidal epithelial cells w/ prominent microvilli
Nephron loop (descending limb and thin ascending: simple squamous epithelial
Nephron loop (thick ascending limb: simple cuboidal to low columnar epithelial cells
DCT Simple cuboidal epithelial cells
DCT last part/collecting duct: simple cuboidal epithelium w/ principal cells and intercalated cells
Renin-Angiotensin-Aldosterone
