Please enable JavaScript.

Coggle requires JavaScript to display documents.

The Renal System. 12 (Anatomy (Cardiovascularity (slides 8&9) (Nephron…

- - - - Glomerulus or the baseball:
        ♢ Cluster of capillaries made of fenestrated (porous or leaky) endothelium (single squamous)
        ♢Allows for efficient filtrate formation
      - Glomerular capsule or Bowman's capsule or the pitcher's glove
        
        Parietal Layer: Simple squamous layer in contact with the outside
        
        Visceral Layer: In contact with basement membrane through epithelial podocytes (foot processes), which form filtration slits
    - - Proximal Convoluted Tubule: ♢Simple Cuboidal Epithelia with dense microvilli to increase surface area for re-absorption and secretion
        ♢Have large mitochondria because of role in active transport. Since main function is re-absorption of water (by pumping and changing ion concentrations) (water follows osmotic gradient)
      - Nephron Loop or Loop of Henle: U-shaped structure.
        
        Descending Limb
        
        Ascending Limb
      - Distal Convoluted Tubule:
        ♢Simple cuboidal with few microvilli
        ♢Secretion mainly to maintain gradient
        
        Special Cells: (slide 23)
        ♢Granular Cells-baroreceptors (pressure)
        ♢Macula Densa Cells - chemoreceptors (Ion concentrations)
        ♢Extraglomerular Mesangial Cells-Engulfs proteins
    - - Cortical Nephrons:
        ♢85%
        ♢Found in cortex of kidney
      - Juxtamedullary nephrons: ♢Longer loops of Henle for greater re absorption rates
        ♢More organized capillaries (vasa recta)
  - - - Type A
      - Type B
- - - - Passive process. No metabolic energy required, only osmotic and hydro-static pressure forces are required to push through membrane
        
        Pressures that Affect Filtration
        
        Inward Pressures: Forces inhibiting filtrate formation.
        
        Hydrostatic pressure in capsular space (HPcs): 15 mm Hg
        
        Colloid osmotic pressure in capillaries (OPgc): "pull" of proteins in blood; 30 mm Hg
        
        Net Filtration Pressures (NFP): Sum of forces.
        ♢55-15-30= 10 mm Hg net outward force
        ♢Pressure responsible for filtrate formation.
        ♢Main controllable factor determining GFR
        
        Outward Pressures: Forces that promote filtrate formation
        
        Hydrostatic Pressure in glomerular capillaries (HPgc).
        ♢Chief force: 55 mmHg compared to ~26 mm Hg in average capillaries
        ♢Caused by high resistance (small diameter) in efferent arteriole causing pressure build up.
    - - Basement Membrane: Made of negatively charged glycoproteins. Size and charge exclusion.
      - Foot processes of podocytes: Left with water and small solutes (<7nm, in some books <3nm)
      - Fenestrated endothelium of glomerular capillaries: Size exclusion
      - Macromolecules "stuck" in filtration membrane are engulfed by glomerular mesangial cells
    - - Volume of filtrate formed per minute by both kidneys (normal= 120-125 ml/min)
        
        Directly proportional to:
        ♢Net filtration pressure
        ♢Total surface area available for filtration
        ♢Filtration membrane permeability
        
        Regulation and Controls (Summary slide 44)
        
        Increased GFR causes increased urine output, which lowers blood pressure, and vice versa. Goal of extrinsic controls is to maintain systemic blood pressure. When MAP is out of range, extrinsic controls take over.
        
        Renin-angiotensin-aldosterone Mechanism:
        Main mechanism for increased blood pressure. Three pathways to renin release by granular cells:
        
        Direct stimulation of granular cells by sympathetic nervous system
        
        Stimulation by activated macula densa cells when filtrate NaCl concentration is low
        
        Reduced stretch of granular cells
        
        Sympathetic Nervous System: Under abnormal conditions, such as extremely low blood pressure.
        Norepinephrine is released by sympathetic nervous system and epinephrine is released by adrenal medulla, causing:
        ♢Systemic vasoconstriction, which increases blood pressure
        ♢Constriction of afferent arterioles, which decreases GFR
        ♢Blood volume and pressure increases
        
        Goal of intrinsic controls is to maintain nearly constant GFR in kidney when Mean Arterial Pressure is in range (80-180 mm Hg)
        
        Myogenic mechanism Local smooth muscle contracts when stretched.
        Increased BP causes muscle to stretch, leading to constriction of afferent arterioles.
        ♢Restricts blood flow into glomerulus
        ♢Protects glomerui from damaging high BP
        Decreased BP causes dilation of afferent aterioles
        
        Tubuloglomerular Feedback Mechanism:
        ♢Directed by Macula Densa Cells which monitors filtrate's NaCl concentration and responds by constricting or dilating afferent arteriole
        ♢If GFR increases --> Filtrate flow rate increases --> Decreasing reabsorption time --> Causing high NaCl levels in filtrate --> Constriction of Afferent arteriole --> Lowers NFP and GFR --> More time for NaCl reabsorption
        ♢If GFR decreases opposite mechanism happens