Nephron, GFR, countercurrent mechanism, RAAS, acid-base, digestion, gut microbiome.
Renal And Gi Physiology
Nephron
Functional unit of the kidney (~10⁶ per human kidney). Glomerulus filters plasma; tubule (proximal, loop of Henle, distal, collecting duct)…
Glomerular filtration (GFR)
Plasma-ultrafiltration by glomerular capillaries + slit diaphragm. GFR ~125 mL/min in healthy adults; net filtration pressure = P_GC −…
Countercurrent multiplier
Loop of Henle generates corticomedullary osmotic gradient (300→1200 mOsm) by active NaCl reabsorption from ascending limb + passive water…
Renin-angiotensin-aldosterone system (RAAS)
Blood-pressure + volume regulator. Low pressure → juxtaglomerular cells secrete renin → angiotensinogen → Ang I → (ACE) Ang II →…
Digestion
Mechanical + enzymatic breakdown of food into absorbable monomers. Stomach (HCl, pepsin), small intestine (pancreatic…
Gut microbiome
~10¹³-10¹⁴ bacteria + archaea + fungi + viruses colonising mammalian GI tract. Contributes ~150× host gene count; synthesises vitamins B/K,…
Tubular reabsorption
Na⁺-coupled cotransport of glucose/amino acids in proximal tubule; ~99% of filtrate reabsorbed. Aquaporin-2 (collecting duct) under ADH…
Acid-base balance
Henderson-Hasselbalch pH = 6.1 + log([HCO3⁻]/0.03 PaCO2). Lung regulates CO2 (fast); kidney regulates HCO3⁻ (slow). Anion gap classifies…
Liver function
Metabolic hub: gluconeogenesis, urea cycle, bile synthesis, drug metabolism (CYP450), albumin + clotting-factor synthesis. Portal…
Pancreatic function
Exocrine: zymogen granules (trypsinogen, lipase, amylase) secreted via CCK stimulation. Endocrine islets: α-cell glucagon, β-cell insulin,…
Countercurrent multiplier (Kuhn-Stephenson)
Kuhn 1942 / Stephenson 1972: loop-of-Henle multiplies single-step transverse osmotic gradient into axial cortico-medullary gradient ~1200…
Henderson-Hasselbalch buffer titration
pH = pKa + log10([A-]/[HA]) connects buffer composition to pH; bicarbonate/phosphate/protein buffer systems jointly maintain plasma pH…
Nephron function (Pitts 1968)
R Pitts 1968 'Physiology of the Kidney'; modern eGFR + nephron-loss + AKI-CKD continuum.
Counter-current (Kuhn 1942)
W Kuhn-A Ramel 1942 counter-current-multiplier; modern Loop of Henle urine-concentration; ADH-aquaporin V2-receptor.
Gut-microbiome (Sender 2016)
Sender-Fuchs-Milo 2016 1:1 bacteria:human-cells revision; modern Earth-Microbiome-Project + IBD/CRC mapping.
ENS (Furness 1987)
J Furness 1987 + Gershon 1998 'Second Brain'; modern enteroendocrine + vagal-afferent gut-brain axis.
TGF (Vander 1965)
A Vander 1965 + Schnermann 1968 tubuloglomerular-feedback; modern macula-densa NaCl sensing + adenosine signaling.
Two-membrane model (Ussing 1958)
H Ussing 1958 two-membrane epithelial transport; modern Na/K-ATPase + ENaC channels distal-nephron + airway.
Starling forces (1896)
E Starling 1896 oncotic-vs-hydrostatic ΔP-ΔΠ; modern modern foundational text + glomerular-filtration + 2024 SGLT2 inhibitor empagliflozin…
Smith clearance (Homer Smith 1937)
H Smith 1937 inulin-clearance GFR; modern modern foundational text + creatinine + cystatin-C + 2024 deep-learning eGFR personalized.
Countercurrent (Kuhn 1942)
W Kuhn 1942 + Wirz-Hargitay 1951 countercurrent-multiplier; modern modern foundational + nephron-loop urea + 2024 vasopressin-V2 SIADH.
Aquaporin (Agre 1992)
P Agre 1992 (Nobel 2003) AQP1; modern modern foundational text + 13 aquaporin-isoforms + 2024 cryo-EM aquaporin-channel water-selectivity.
Gut microbiome (Savage 1977)
D Savage 1977 + Hugenholtz 2002 + Eckburg 2005 16S; modern modern foundational + HMP 2012 + 2024 strain-level 100k species shotgun.
SGLT2 (Boehringer 2014)
Boehringer Ingelheim 2014 empagliflozin EMPA-REG; modern modern foundational text + cardio-renal-protection + 2024 broader heart-failure…