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RENAL PHYSIOLOGY - Coggle Diagram

- - - - Wall of the capillary consists of 3 layers
        
        Capillary endothelium
        
        single layer of cells with cytoplasmic extensions pierced by fenestrae (provide channel for passage of water and non-cellular components from the blood to basement membrane)
        
        Basement membrane
        
        acellular structure composed of various glycoproteins
        
        Visceral epithelium
        
        a layer of intricate, interlocking cells called podocytes
  - - - The capillaries later coalesce to form efferent arteriole, which conducts the filtered blood away from the glomerulus
  - - - contains both mammalia-type and reptilian-type nephrons
  - - - forces favoring filtration: hydrostatic forces of the blood within capillary and oncotic pressure of the fluid within Bowman's capsule
        
        blood travels through glomerular capillary
        
        a large proportion of the fluid component of the plasma is forced across the capillary wall
        
        the plasma proteins are retained in the capillary lumen
        
        therefore, the plasma oncotic pressure increases significantly along the capillary bed and causes a decrease in hydrostatic pressure of the capillary
        
        opposing forces: plasma oncotic pressure within capillary and hydrostatic pressure in Bowman's space
      - NET FILTRATION PRESSURE (Pf): force driving fluid out of the capillary and into the tissue spaces
      - Glomerular Filtration Rate (GFR): the product of the mean net filtration pressure, the permeability of the barrier and the surface area available for filtration
    - - Size of the components and plasma proteins (radius less than 4nm)
      - Net electrical charge of a molecule
        
        cationic (+) more freely filtered than neutral form and anionic (-) due to charge-selective barrier in the glomerular wall created by negatively-charged residues of glycoproteins in basement membrane.
        
        the negatively-charged wall repel the negatively-charged plasma thus reduce their passage across the filtration barrier
      - Shape and deformability of the molecule
        
        a long, flexible molecules cross barrier more easily than globular protein
    - - SYSTEMIC FACTOR
        
        Mediated primarily through humoral factors, particularly renin-angiotensin-aldosterone system
        
        Renin: stimulated by a decrease in renal perfusion pressure most often caused by systemic hypertension
        
        Renin catalyzes the transformation of angiotensin produced by the liver to angiotensin I.
        
        Angiotensin-converting enzyme (ACE) converts angiotensin I to more active angiotensin II
        
        Angiotensin II (potent vasoconstrictor) increases systemic blood pressure and renal perfusion pressure
        
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      - INTRINSIC FACTOR
        
        The myogenic reflex: a mechanism of autoregulation of renal blood flow and GFR due to glomerular arterioles respond to changes in arteriolar wall tension
        
        Increase in arteriolar wall tension, afferent arteriole constricts
        
        Decrease in arteriolar wall tension, afferent arteriole dilates
        
        may be influenced by chemical mediators such as nitric oxide
        
        The tubuloglomerular feedback
        
        Juxtamedular apparatus consists of macuala densa of distal tubule, juxtamedular cells and extraglomerular mesangial cells
        
        Increase in sodium chloride concentration in the tubule fluid at the macula densa causes a signalling cascade in the macula densa cells
        
        Leads to generation of paracrine factors that suppress renin release from juxtaglomerular cells
        
        Increases resistance in the afferent arteriole and decreases glomerular capillary perfusion pressure
        
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- - - - Na+ is actively transported from the cell into the interstitial fluid
        
        Na+ and other solutes are removed from tubule fluid by secondary active transport or passive diffusion creating a slight gradient favoring the movement of water into cells
        
        The proximal tubule apical brush border and complex basolateral plasma membrane create a large surface area for reabsorption
        
        The small chemical gradient results in rapid movement of water from tubule fluid to the interstitial fluid
        
        The high oncotic pressure in peritubular capillary favor the movement of water and solutes from interstitial fluid to the blood
  - - - excretion of concentrated urine is to conserve water and thus reduces the volume of water must be consumed each day to prevent dehydration
        
        the hypertonicity of the medullary interstitium is produced and maintained by:
        
        the reabsorption of osmotically active substances by tubules in the medulla
        
        the removal of water from the medullary interstitium by the vasa recta
- - - - the structure of the proximal tubule and its proximity to peritubular capillary facilitate the movement of tubule fluid components into two pathways:
        
        The transcellular pathway (mediated transport)
        
        Substances transported through transcellular pathway cross the apical plasma membrane and discharge across the basolateral plasma into interstitial fluid on the blood side of the cell
        
        The paracellular pathway (passive transport)
        
        Substances pass through the paracellular pathway from the tubule fluid across zona occludens at the junction of the apical and basolateral plasma membrane domains
      - Starling's force: drives movement of water and solute from the interstitial fluid into bloodstream aided by proximity of the peritubular capillary
        
        MAMMAL
        
        the peritubular capillary originates at the glomerular efferent arteriole, subdivides and wraps closely around basal aspect of the proximal tubule
        
        the plasma leaving the glomerulus has high oncotic pressure because water and salts are filtered but proteins are retained in the capillary
        
        the peritubular capillary has low resistance and thus the hydrostatic pressure in the capillary is low
        
        high peritubular plasma oncotic pressure and low peritubular capillary hydrostatic pressure
        
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        BIRDS
        
        presence of a renal portal circulation
        
        renal portal veins anastomose with the efferent arteriole and supply peritubular blood to reptilian-type nephrons and proximal and distale tubules of mammalian-types nephrons
        
        the tubules are supplied with a mixture of portal venous and arterial blood
    - - driven by Na+,K+-ATPase pump in the basolateral plasma membrane
    - - Reabsorbs sodium and secrete potassium
        
        SODIUM REABSORPTION AND POTASSIUM SECRETION
        
        Aldosterone release is stimulated by systemic hypotension through the RAS.
        
        Aldosterone act on connceting segment cells and principal cells of collecting duct to enhance Na+ reabsorption
        
        Aldosterone increases permeability of the apical plasma membrane Na+ channels and stimulates Na+,K+-ATPase activity
        
        SODIUM TRANSPORT
        
        enhanced sodium transport by stimulating aldosterone release and angiotensin II
  - - - Ca2+ transport in the thick ascending limb is suppressed when serum Ca2+ elevated through activation of the basolateral calcium-sensing receptor (CaSR)
      - basolateral plasma membrane of distal convoluted tubule and connecting segment cells contain Ca2+-ASE pump
        
        actively extrudes intracellular Ca2+ into interstitial fluid
      - Na+/Ca2+ antiporter
        
        exchange extracellular Na+ for intracellular Ca2+
      - REGULATION BY PARATHYROID HORMONE AND CALCITONIN
        
        CALCITONIN
        
        reduces the serum Ca2+ concentration by stimulating Ca2+ deposition in bone
        
        PARATHYROID HORMONE (PTH)
        
        Hypecalemia (low plasma Ca2+ leve) stimulates parathyroid hormone release
        
        Affects bone, intestines and kidney to raise plasma Ca2+ level
        
        Parathyroid hormone increase apical uptake of Ca2+ in distal convoluted tubule by increasing the activity of the apical Ca2+ channel
        
        PTH also increases Cl-conductance at the basolateral plasma membrane which hyperpolarize the cells
        
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