Test 1 (Renal Histology, Dr. Cole) Flashcards
Functions of the Urinary System
1) Elimination:
- Urine and toxic metabolites from the blood
2) Conservation:
- Salts, Glucose, Proteins, and H2O
3) Regulation:
- Blood Pressure, Hemodynamics, and Acid-base Balance
4) Endocrine:
- Produces Vitamin D, Renin, Erythropoietin, and Prostaglandins (Hormonal Control of other tissues/ Organs)
Kidney: Blood Supply
- As a blood filtering organ, the kidney’s Blood Supply is critical to its function
- Supplied by RENAL ARTERIES, branch directly from the AORTA
Blood Supply of the Kidney
1) Segmental (LOBAR) Artery —->
2) INTERLOBAR Artery —->
3) ARCUATE Artery —–>
4) INTERLOBULAR Artery
Map of Blood Supply
1) Renal Artery
2) Segmental Artery
3) Interlobar Artery
4) Arcuate Artery
5) Interlobular Artery
6) Afferent Arteriole
7) Glomerulus
8) Efferent Arteriole
9) Peritubular Capillaries
10) Vasa Recta
11) Interlobular Vein
12) Arcuate Vein
13) Interlobar Vein
14) Renal Vein
Kidney Blood Supply Cont.
- Efferent arterioles drain the Glomeruli and form capillary networks
- Drain cortical Nephrons and form PERITUBULAR CAPILLARY ENTWEK (take up substances resorbed by Tubular Epithelium)
The Nephron: Functional Unit of the Kidney
Parts are modified for specific physiological functions
- RENAL CORPUSCLE filter fluid from Blood
- TUBULAR Portions modifies filtrate into Urine
Nephron
- Two (Three) types depending on location of their Henle Loop
1) CORTICAL (short):
- Can be superficial or Midcortical
2) JUXTAMEDULLARY (long)
Renal Corpuscle
1) Tuft of fenestrated Capillaries- The GLOMERULUS
2) Surrounded by URINARY (Bowman’s) Capsule
- Capillaries INVAGINATE into Bowman’s Capsule**
- Capillaries are in contact with the Visceral Layer (Podocytes)
- Parietal Layer is SIMPLE SQUAMOUS EPITHELIUM
- Separated by Urinary Space
Mesangial Cells
- Supporting Cells
- Modified SMOOTH MUSCLE
- Extraglomerular (Vascular Pole)
- Intraglomelular
Functions of Mesengial Cells
1) Contractile:
- Reduce/ Increase blood flow through capillaries
2) Supportive:
- In area where the Visceral layer of the Renal Corpuscle is absent
3) Phagocytic:
- Resorption and maintenance of the Basal Lamina
4) Secretory:
- Secrete Prostaglandins and Endothelia’s (Induce Constriction of Afferent/ Efferent arterioles)
Glomerular Filtration Barrier
- Fluid from capillaries leaks into the Urinary space through a complex filtration barrier
- FENESTRATED CAPILLARY Endothelium
- BASAL LAMINA (Basement Membrane)
- Podocytes of the Visceral Layers of Bowman’s Capsule
- High POLYANIONIC Charge on some components of both Basal Lamina and surface of Podocyte processes
Glomerular Capillaries
- Fenestrated
- Large pores not covered by a Diaphragm
- Permeable to Water, Urea, Glucose, and Small Proteins
- Barrier only to FORMED ELEMENTS in Blood and Large Macromolecules
Basal Lamina
Lamina Rarae Contains:
1) Type IV Collagen
2) Laminin
3) Fibronectin
4) Negatively-charged Proteoglycans
- Lamina Densa (IV)
- Lamina Rarae
Podocytes
- Have P1 (Big) and P2 (Small) processes
Pedicels and Filtration Slits
- Each pedicel has a GLYCOCALYX of Negatively-charged PODOCALYXIN
- Separated by Clefts- FILTRATION SLITS
- Covered by a porous SLIT DIAPHRAGM
Filtration of Slit Diaphragm
- Diaphragm contain the protein NEPHRIN!!!!!!
- Nephrin seems to RETARD passage of molecules through the Fenestrations and Basal Lamina
- Mutations in gene for Nephirn are associated with CONGENITAL NEPHROTIC SYNDROME
Filtration Process
- Blood enters Glomerulus via Afferent Arteriole
- Arteriole Pressure FORCES FLUID through Fenestrae of Capillary Endothelium
- Large Molecules are trapped by the BASAL LAMINA
- Negatively charged molecules are stopped by the Basal Lamina and Podocytes
- Fluid passes through pores in SLIT DIAPHRAGM to enter the Urinary Space
**GLOMERULAR FILTRATE leaves Urinary space and enters tubule which modifies its Composition!!!!
Proximal Convoluted Tubule
- Site of “BULK OPERATIONS”, it begins at Urinary Pole
- Lined by CUBOIDAL/ LOW COLUMNAR EPITHELIUM
- Microvilli and well-defined BRUSH BORDER
Proximal Convoluted Tubular Cont.
- EXTENSIVE REABSORPTION of Glomerular Filtrate (Microvilli)
1) Na+ (Active Transport)
2) Cl- (Passive Diffusion)
3) H2O (AQP-1, Aquaporin-1) Small transmembrane Channel - Reduction in Fluid Volume
- Proteins and Small Peptides are Endocytosed in PERITUBULAR CAPILLARIES!!!!
Loop of Henle
Concentration of INTERSTITIAM!!!!***
FUNCTION:
- To assist in forming HYPERTONIC URINE by establishing an OSMOTIC GRADIENT in the Interstitial Fluid of the Medulla
Loop of Henle Structure
- U shaped Epithelial Tube
- Consists of a Thick Proximal Convoluted Tubule and thin descending dumb and a thick and thin Ascending Limb
** Thick Ascending is really found only in the JUXTAMEDULLARY NEPHRONS
- Thick and Thin denote and Epithelial Change (Cuboidal to Squamous) in both the Descending and Ascending limbs
Loop of Henle Descending Portion
- PERMEABLE to BOTH Water and Salt
- As Filtrate (Isotonic) in the lumen passes deeper into the Medulla, it loses Water to the Interstitial
- Filtrate becomes more HYPERTONIC
- Filtrate volume also DECREASES with Loss of Water
Loop of Henle Ascending Portion
- Plays a more active role in setting up the OSMOTIC GRADIENT required to make the INTERSTITIAL HYPERTONIC
- Contains Na+/ K+/ Cl- Pump (Symporter)
- Constantly pumps these ions form the Filtrate into the Interstitium
- IMPERMEABLE to WATER (Water cannot follow Salt into Interstitium)
- Loss of salt, but not Water, causes the filtrate in HENLE’S LOOP to become ISOTONIC or even HYPOTONIC
- Filtrate ascends toward the DCT in the CORTEX
NOT PERMEABLE TO WATER!!!!
Diastal Convoluted Tubule
- Lined by LOW CUBOIDAL EPITHELIUM
- Fewer Microvilli in Comparison to PCT (Lumen looks Larger)
Two Cell Types:
1) PRINCIPAL CELLS:
- RESORB Na+ and Secrete K+
2) INTERCALATED CELLS:
- SECRETE H+ or HCO3-
Macula Densa
- Modified segment at Transition between the THICK ASCENDING LOOP of HENLE and the DCT wall
- Sensitive to Cl- ion or NaCl content of TUBULAR FLUID
- Produces molecular signals promoting constriction of AFFERENT Arteriole
- Regular the RATE of GLOMERULAR FILTRATION (G.F.R)
***Macula Densa Cells are Tall Cells with TIGHLY packed Nuclei
Juxtaglomerular Apparatus
- Involved in maintaining Blood Pressure and volume through production of RENIN
- Juxtaglomerular (JG) cells of AFFERENT ARTERIOLE (Produce RENIN)
- Extraglomerular Mesangial Cells (Lacis, Polkissen)
- Macula Dens of Loop of Henle/ DCT Transition
Juxtaglomerular Apparatus
- MACULA DENSA acts as a SENSOR, regulating JUXTAGLOMERULAR FUNCTION by monitoring Na+ and Cl- levels in the DCT
- Decrease BLOOD VOLUME/ Pressure elicits Secretion of Rening by JG Cells
- ANGIOTENSINOGEN —-> Active Angiotensin
- Angiotensin causes SUPRARENAL Glands to secrete ALDOSTERONE
Angiontensinogen activation
1) Angiotensinogen (Renin acts on it) —>
2) Angiotensin I (Angiotensin Converting Enzyme) —->
3) Angiotensin II —->
4) Aldosterone (Suprarenal Gland) —->
5) Reabsorption of Na and Water by DCT, CT
DCT and Aldosterone
- Crucial to Acid- Abase balance and Urine concentration
- ALDOSTERONE (Adrenal Cortex) cause DCT cells to resorb remaining Na+
- Pump H+ and K+ ions into Lumen
- Control body’s Extracellular K+ level and Urine Acidity
DCT and A.N.F./ Urodilatin
1) ATRIAL NATRIURETIC FACTOR (Auricular, Atriopeptin)
- Secreted by Atrial Myocytes
- INCREASES Na+ (Natriuresis) and WATER (Diuresis) excretion
- Opposes action of Aldosterone, Inhibits the release of ADH
2) URODILATIN is secreted by DCT and CD cells and INHIBITS NaCl and Water Reabsorption by the Medullary part of the Collecting Ducts
Collecting Tubules and Ducts: Function
- COLLECTING TUBULES receive Isotonic urine from DCT
- COLLECTING DUCTS receive Isotonic Urine from Collecting Tubules
- Leave Cortex in Medullary Rays and Enter Medulla
- Collecting cuts open at Papilla into MINOR CALYX
- Play important role in Final Concentration of URINE (Interstitial and Vasa Recta)
Collecting Ducts
- Epithelium responsive to ANTIDIURETIC HORMONE (ADH, Vasopressin) released by the NEUROHYPOPHYSIS
1) ADH: Water is lost from Collecting Ducts —> HYPERTONIC URINE
2) Without ADH: Ducts remain IMPERMEABLE to Water —> Isotonic/ Hypotonic Urine
Disposal of Urine
1) Minor Calyces
2) Major Calyces
3) Renal Pelvis
4) Ureter
Urothelium (In Bladder)
- Stratified
- Surface layer of Umbrella Cells linked by DESMOSOMES and TIGHT JUNCTIONS
- Possibly IMPERMEABLE to Water and Salt
- Forms Osmotic Barrier
