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Functional anatomy and physiology of kideny
1. Functional anatomy and physiology of
Kidney
Dr. Debashis Priyadarshan Sahoo
PGT, First year
Department of General medicine
NEIGRIHMS
2. Outer Structure:
• Pair of bean shaped organs found in lower back region behind
intestines.
• Major excretory and osmoregulatory organ.
• Size: 7-10cm long.
3. Inner structure:
Cortex Medulla Pelvis
Outer region
Uneven echotexture
Content:
1. Renal capsule
2. Proximal
Convoluted tubule
3. Distal convoluted
tubule
Inner region
Surrounds pelvis
Contents:
1. Loop of Henley
2. Collecting ducts
of nephron
The central cavity.
Urine deposition
Cavity continuous
with ureter
4. • High pressure system.
• Starts from arteriole and ends in
arteriole.
• Physiological filtration unit:
Nephron (2-2.4million nephrons
in both kidneys)
7. • Surrounding the capillary tuft, mesangial cells are present, which produces
connective tissue cells.
• Mesangium: Capillary tuft + Mesangial cells + Connective tissue cells.
• Glomerulus :
1. Group of anastomosing capillaries present in kidney,
2. Invested by double layer of epithelial cells making Bowman’s capsule and
3. The capillaries are invaded within mesangium
4. Functionally the filtration unit of nephron.
8. Mesangial cells:
1. Contractile cells, Receptor for Angiotensin II: Influence filtration
2. Phagocytic cells
3. Proliferative cells: Extra amount of connective tissue production
4. If irritated because of disease process: produces inflammatory
molecules
9. PCT:
• Longest part of nephron, located
in cortex
• 80% of GF is resorbed in PCT
• Cuboidal epithelium with
microvilli.
10. Loop of Henley:
• Hairpin bend structure having
descending and ascending limb in
medulla.
• Descending limb: thin walled,
permeable to water, penetrates to deep
medulla.
• Ascending limb: Thick walled,
impermeable, returns to cortex.
• Vasa recta: Surrounding LOH,
network of capillaries in hairpin
structure.
11. Distal convoluted tubule:
• Walls: Similar to PCT containing cuboidal epithelium with microvilli
with numerous mitochondria, carrying out active transport.
• Absorbs inorganic ions and water.
• Water is permeable only in presence of ADH, otherwise not.
• Maintains pH.
12. Collecting duct:
• DCT ends in collecting duct.
• Several nephrons share one collecting duct
• Final modification of filtration.
• Emptied into pelvis.
• Only permeable to water only in presence of ADH.
15. Basic renal processes:
3 Basic processes:
1.Glomerular filtration (from
glomerular capillary to Bowman’s
space)
2.Tubular resorption (From tubular
tumen to peritubular capillaries)
3.Tubular secretion (From peritubular
capillaries to tubular lumen)
ADH dependent water resorption is
optional.
16. Glomerular filtration:
• From glomerular capillary to Bowman’s capsule.
• Filtrate is termed as Glomerular filtrate (GF) or ultrafiltrate and Collected in
Bowman’s space.
• Filtration by filtration barrier: Size and Charge barrier. (Less molecular size. And
Less electronegative/ more electropositive)
• E.g.: Albumin has less size than the filtration barrier but it is not filtered because
of its negative charge.
Filtered Not filtered
Low molecular weight substances,
including small peptides
Most plasma proteins
(Albumin, Globulin)
Water Plasma calcium and fatty acids
17. Glomerular filtration barrier:
• Capillary endothelium has fenestrations: 70-100nM.
• Glomerular BM: Electronegative.
1. Central dense area called Lamina densa and on both
side the less dense area is Lamina rara.
2. Triple Helix of alpha peptide chain of Collagen Type
IV.
Mutations of collagen type IV:
a. Non collagenous domain: Good pasture
syndrome and
b. Collagenous domain: hereditary nephritis
• Visceral epithelial cells : finger like projections
interdigitate the epithelial cells and with BM called
Podocytes. In between podocytes filtration diaphragm
present, made up of Nephrin proteins.
18. Glomerular filtration rate:
• GFR: amount of fluid filtered by all the nephrons of both the kidneys in one
minute.
• GFR: Net ultrafiltration pressure (NUP) X Ultrafiltration coefficient (Kf)
• Kf: (12.5ml/min/mm Hg) (Depends on capillary permeability and surface area)
• NUP: Net hydrostatic pressure – Net oncotic pressure =
(GCHP – BSHP) – (GCOP – BSOP) = (60-18) – (32-0) = 10 mm Hg
• GFR: 12.5 X 10 =125ml/min
19. Decreased GFR
• Constriction of afferent arteriole
cause decrease in hydrostatic
pressure in glomerular capillaries,
causing decreased GFR.
• Dilation of efferent arteriole results
in reduction in hydrostatic pressure
in glomerular capillaries causing
decreased GFR.
Increased GFR
• Constriction of the efferent arteriole
results in an increase in hydrostatic
pressure in glomerular capillaries,
resulting in increased GFR.
• Dilation of afferent arteriole cause
an increase in hydrostatic pressure
in glomerular capillaries, resulting
in increased GFR.
20. Tubular reabsorption:
• Movement of substances from
tubular lumen to interstitial fluid.
• Either by Diffusion or Mediated
transport.
• Substances are returned back to
capillary blood surrounding
kidney tubules.
• Tubular resorption mainly occur
in PCT and LOH.
21. • Diffusion occurs across tight junctions of epithelial cells.
• Mediated transport requires the participation of transport protein in the
membranes of tubular cells.
Diffusion Mediated transport
Water reabsorption creates concentration
gradient across tubular epithelium.
Reabsorption coupled with the reabsorption
of sodium.
Use of transporters. (Secondary active
transport)
e.g.: Urea, Variety of lipid soluble organic
substances.
e.g.: Glucose and Amino acids
22. Tubular secretion:
• Involves transport of substances from peritubular capillaries into tubular lumen.
• Secretion occurs by Diffusion and transcellular mediated transport.
• Organic anion and cations are transported,
• Hydrogen and potassium are the most important substances secreted in the tubule.
• Others: choline, creatinine, penicillin
• Active transport required for movement of the substances from blood to cell or out
of cell to tubular lumen.
• Usually coupled with sodium reabsorption.
23. Renal clearance:
• Renal clearance of any substance is the volume of plasma from which
that substance is completely cleared per unit time.
• Any substance filtered, but not reabsorbed, secreted or metabolized by
kidney is equal to GFR. However, no such substances meet this
criteria.
• For GFR estimation : creatinine clearance.
