E3: Urinary Flashcards
What are the components of the Urinary system?
2 kidneys
2 ureters
Bladder
Urethra
What are the functions of the urinary system?
Functions:
- Blood filtration: Removal of toxic waste
- Protein metabolism (urea), some drugs
- Water-electrolyte balance: Na+, K+, Ca2+
- Acid-base balance (pH): H+ and HC03-
- BP control: Renin-angiotensin system
- RBC production during hypoxia
- Vitamin D synthesis
Describe the basic anatomy of the Kidney
Renal Anatomy & Function:
Cortex: Initial Filtration
Medulla: Modification of Filtrate
Renal pelvis/Ureter: Drainage of Urine
What is the pathway of Urine flow?
What about blood flow?
Urine flow:
Cortex > Medulla > Papilla > Calyces > Pelvis > Ureter
Blood flow:
Renal artery > Cortex > Medulla > Renal vein
ID the tissue in the image.
What does it primarily consist of?
Renal Cortex
Primarily consists of PCT’s & DCT’s
What is the functional unit of the Kidney?
What is the composition?
Functional Unit: The Nephron
Components:
1. Renal corpuscle (filter)
- Glomerulus + capsule
2. The renal tubules:
- Tubules specialized for absorption/secretion
- PCT, loop of Henle, DCT
3. Collecting ducts
The Renal Corpuscle is composed of what?
Describe it’s formation
Renal Corpuscle = Glomerulus & Capsule
Glomerulus Formation:
- Renal artery splits into numerous arterioles
- Each afferent arteriole splits into fenestrated capillaries, which form a knot (the glomerulus)
* Blood leaves via the efferent arteriole
Capsule Formation:
- Developing renal tubule wraps around the glomerulus, forming Bowman’s capsule
- Visceral layer: Lines glomerular capillaries
- Podocyte Layer
- Parietal layer: Lines the capsule wall
- Visceral layer: Lines glomerular capillaries
What are the (3) layers of filtration?
(3) Layers of Filtration:
- Capillary Epithelium (fenestrated)
- Glomerular BM
- Podocyte Foot processes (epithelial cells of the capsule)
Describe what ultrafiltration is
What molecules can pass through?
Which can’t?
What factors influence permeability?
Ultrafiltration:
Glomerulus: a molecular sieve
- Small molecules can pass
- Glucose, Na+, K+, H+, Cl-, HC03-
- Large molecules stay in plasma
- RBCs, large proteins
Factors that influence permeability:
- Hydrostatic pressure of blood
- Opposed by osmotic pressure of albumin and other plasma proteins
- Size: very little protein can cross
- Charge: (BM is negative)
What are podocytes?
What role do they play in Ultrafiltration?
Podocytes
- Pedicels (Foot processes) wrap around Endothelial cells
- Filtration slits
- Gap bridged by a slit-diaphragm
ID the tissue in this image
Renal Cortex
What are Mesangial cells?
What are their function?
Glomerular mesangial cells
- Located between the capillaries
- Analogous to Pericytes within vasculature
Function:
- Support
- Contractile
- Similar to pericytes in vessels
- Regulate glomerular flow
Where does the majority of reabsorption occur?
What are the methods of reabsorption?
Proximal Convoluted Tubules (PCT):
- Cuboidal epithelium with brush border (microvilli)
- Reabsorbs 80% of filtrate to tissue fluid
- Diffuses into surrounding capillaries
Methods of reabsorption:
- Active transport:
- Glucose
- Amino acids
- Vitamins
- Electrolytes
- Osmosis: water
Some Urea is reabsorbed into the blood stream via diffusion @ PCT
Where does Vitamin D metabolism & conversion occur?
What is the signal pathway associated with it and what is the net effect?
Proximal Convoluted Tubule:
- Brush border contains vitD receptors
- Activation triggers hydroxylase synthesis
- Converts dietary/dermal vit D to active form
VitD functions to Increase Ca2+ absorption from gut
How does the kidney regulate blood oxygen content?
Renal Cortex:
Hypoxia (Low O2 levels)
> Triggers peritubular fibroblasts in the cortex to synthesize erythropoietin (Epo)
> Epo acts on the BM to increase RBC production
What type of epithelium does the Distal Conv. Tubule have?
What special functions occur there?
Distal Convoluted Tubule:
- Epithelium: Simple cuboidal (No brush border)
Homeostatic functions: (hormones involved)
- pH balance (H+/HC03-)
- salt balance (Na+, K+)
- Aldosterone regulated; Na+ & water retention
- Ca2+ homeostasis
- PTH regulated; promotes Ca2+ reabsorption
- BP control (JG apparatus)
Some diuretics inhibit Na & Cl reabsorption in DCT
What is the Juxtaglomerular Apparatus?
What is it’s function?
Juxtaglomerular apparatus (JG):
- Specialized structure at vascular pole of glomerulus
- Includes JG cells & Macula Densa
JG cells: modified Smooth m. in the AA
- Synthesizes & releases Renin in response to low NaCl levels in DCT (or baroreceptors in the AA)
Macula Densa (MD): modified epithelial cells in the DCT Function
- Tightly packed cells
How does the JG cells regulate stimulate water retention & thus secondarily regulate BP & NaCl balance?
Renin-angiotensin-aldosterone system (RAAS):
Decreased BP (reduced GFR):
- Low NaCl in DCT > sensed by MD
- MD stimulates JG cells to release Renin into plasma
- Low bp detected by baroreceptors in the AA
- Also stimulate JG cells to release renin
Renin
- Converts plasma angiotensinogen to angiotensin I
- Angiotensin I converted into angiotensin II by ACE
- Angiotensin II raises bp by;
- Directly stimulating vasoconstriction
- Stimulating aldosterone & ADH release
- Aldosterone: Stimulates Na+ absorption & K+ excretion @ DCT, which stimulates water retention
- ADH increases DCT & CD permeability to H2O via aquaporins, stimulating Water retention
What is the arrow pointing to?
Macula Densa
What primarily occurs in the Renal medulla?
What is the primary portion of the tubules in the Medulla?
Describe them
Reabsorption of more salt & water from urine
Henle’s loop:
- Makes interstitial fluid in the medulla hypertonic (‘salt bath’)
Descending limb:
- Impermeable to ions
- Water retention via Osmosis
Ascending limb:
- Pumps Na+ and Cl- ions into surrounding tissue
- Larger diameter due to energy needs for active transport
- Water doesn’t follow because it’s impermeable to water
Describe the Collecting Ducts
Collecting Ducts:
- Epithelium: Simple cuboidal
- Function:
- Further concentrates urine
- Water reabsorbed by aquaporins (ADH-regulated)
With a High salt meal;
- Plasma Na+ increases
- Detected by osmoreceptors in hypothalamus
- Triggers ADH release
- ADH induces;
- Increased water retention by CDs
- Increased plasma volume
- Resulting in Scant urine
Describe the pathway of urine drainage from the renal pelvis
What kind of epithelium is found here?
Trend in Muscularis Propria?
Pathway: Renal pelvis > Ureter > Bladder
Epithelium: Transitional
- St. cuboidal or st.sq (depending on distension)
Muscularis propria:
- Increasing amounts of SM
What is this image of?
Ureter
Describe the Bladder histologically
Where are the sphincters located?
Bladder:
- Transitional epithelium
- Wall: bands of Smooth m.
Sphincters:
Internal urethral sphincter (IUS):
- Provides involuntary control of urination
External urethral sphincter (EUS):
- Provides voluntary control of urination
ID the image
What muscle is present here?
How do mouse & human bowman’s capsule differ?
Mouse: Parietal layer shows sexual dimorphism
- Females: Squamous
- Males: Cuboidal
*Proteinuria is normal in mice
Where is the kidney Cortex?
Top or bottom half?
Bottom half
What’s the most likely problem with this biopsy?
- Psoriasis
- Melanoma
- Ringworm
- Bullous Pemphigoid
Melanoma
What part of the urinary system is this?
- Glomerulus
- Renal Corpuscle
- Ureter
- Collecting Duct
- Loop of Henle
- Minor Calyx
Ureter
