Orris

Write a note. All. Nefron. Eee? Enumerate. It's... Function.

Reading File
Finding Sources
Finding Sources
Searching Images

nephron anatomy diagram parts

Anatomical diagram featuring high-resolution 3D renderings of a single mouse nephron, highlighting renal microstructure and spatial arrangement. Panel (a) provides detailed views of the renal corpuscle (RC), demonstrating the spherical Bowman's capsule (BC) and internal glomerulus (GM). It clearly illustrates the vascular pole with the afferent arteriole (AA), efferent arteriole (EA), and the macula densa (MD) of the distal tubule (DT) forming a v-shaped contact point. The tubular pole shows the exit of the highly convoluted proximal tubule (PT). Panel (b) illustrates the longitudinal progression from the renal corpuscle through the PT and DT to the collecting duct (CD). The rendering distinguishes between the intensely convoluted segments near the corpuscle and the straighter distal segments of the tubules. Key educational concepts include the juxtaglomerular apparatus anatomy, the morphology of glomerular filtration components, and the physical relationship between various segments of the nephron and their associated vasculature, essential for understanding renal physiology and pathology.

Anatomical diagram featuring high-resolution 3D renderings of a single mouse nephron, highlighting renal microstructure and spatial arrangement. Panel (a) provides detailed views of the renal corpuscle (RC), demonstrating the spherical Bowman's capsule (BC) and internal glomerulus (GM). It clearly illustrates the vascular pole with the afferent arteriole (AA), efferent arteriole (EA), and the macula densa (MD) of the distal tubule (DT) forming a v-shaped contact point. The tubular pole shows the exit of the highly convoluted proximal tubule (PT). Panel (b) illustrates the longitudinal progression from the renal corpuscle through the PT and DT to the collecting duct (CD). The rendering distinguishes between the intensely convoluted segments near the corpuscle and the straighter distal segments of the tubules. Key educational concepts include the juxtaglomerular apparatus anatomy, the morphology of glomerular filtration components, and the physical relationship between various segments of the nephron and their associated vasculature, essential for understanding renal physiology and pathology.

Educational panel illustrating the surgical anatomy and complications of an ileal conduit urinary diversion. Part A is an anatomical diagram showing a cross-section of the abdomen with a focal stoma. Key structures labeled include the ileal conduit (1), its associated mesentery containing vascular supply (2), and the right (3) and left (4) ureters. Asterisks mark the uretero-ileal anastomoses. The posterior abdominal wall is noted as deperitonealized (5) following radical cystectomy. Parts B and C are clinical laparoscopic photographs showing intraoperative views of the same anatomy. Photograph B demonstrates complex fibrous adhesions involving the ileal conduit, a common challenge in parastomal hernia repair. Photograph C shows the pinkish, smooth surface of the deperitonealized posterior abdominal wall (5) adjacent to the textured, tubular ileal conduit (1). Small orientation icons indicate the stoma position on the lower abdominal wall. This content is designed to teach the anatomical changes following cystectomy and the specific challenges of treating parastomal hernias in patients with urinary diversions.

Educational panel illustrating the surgical anatomy and complications of an ileal conduit urinary diversion. Part A is an anatomical diagram showing a cross-section of the abdomen with a focal stoma. Key structures labeled include the ileal conduit (1), its associated mesentery containing vascular supply (2), and the right (3) and left (4) ureters. Asterisks mark the uretero-ileal anastomoses. The posterior abdominal wall is noted as deperitonealized (5) following radical cystectomy. Parts B and C are clinical laparoscopic photographs showing intraoperative views of the same anatomy. Photograph B demonstrates complex fibrous adhesions involving the ileal conduit, a common challenge in parastomal hernia repair. Photograph C shows the pinkish, smooth surface of the deperitonealized posterior abdominal wall (5) adjacent to the textured, tubular ileal conduit (1). Small orientation icons indicate the stoma position on the lower abdominal wall. This content is designed to teach the anatomical changes following cystectomy and the specific challenges of treating parastomal hernias in patients with urinary diversions.

This pathophysiology flow diagram illustrates the multi-step immune signaling pathway leading to glomerular tissue injury in the nephron. The process is initiated by three primary drivers: genetic factors (heritable), environmental exposures, and epigenetic factors coupled with post-translational modifications. These drivers trigger the 'Innate Immune Response' (Non-antigen specific reactions), characterized by the activation of Pathogen-Associated Molecular Patterns (PAMPs) and Damage-Associated Molecular Patterns (DAMPs). This activates the complement system, Toll-Like Receptors (TLRs), and inflammatory cells (neutrophils, macrophages, basophils, NK cells), leading to the release of cytokines, chemokines, and growth factors. The pathway then transitions to the 'Adaptive Immune Response' (Antigen-specific reactions), where antigen-presenting cells activate CD4+ T cells, B cells, and TREGs. Further differentiation into TH1, TH2, and TH17 cells, along with antigen-antibody complex formation, culminates in glomerular tissue injury. The diagram also identifies key mechanisms of immune dysregulation below the main flow, including TREG depletion, molecular mimicry, epitope spreading, epitope conformation, adjuvant effects, and auto-antigen complementarity.

This pathophysiology flow diagram illustrates the multi-step immune signaling pathway leading to glomerular tissue injury in the nephron. The process is initiated by three primary drivers: genetic factors (heritable), environmental exposures, and epigenetic factors coupled with post-translational modifications. These drivers trigger the 'Innate Immune Response' (Non-antigen specific reactions), characterized by the activation of Pathogen-Associated Molecular Patterns (PAMPs) and Damage-Associated Molecular Patterns (DAMPs). This activates the complement system, Toll-Like Receptors (TLRs), and inflammatory cells (neutrophils, macrophages, basophils, NK cells), leading to the release of cytokines, chemokines, and growth factors. The pathway then transitions to the 'Adaptive Immune Response' (Antigen-specific reactions), where antigen-presenting cells activate CD4+ T cells, B cells, and TREGs. Further differentiation into TH1, TH2, and TH17 cells, along with antigen-antibody complex formation, culminates in glomerular tissue injury. The diagram also identifies key mechanisms of immune dysregulation below the main flow, including TREG depletion, molecular mimicry, epitope spreading, epitope conformation, adjuvant effects, and auto-antigen complementarity.

Reading File
Reading File
Reading File
Reading File
Reading File
Loading Image
Loading Image
Reading File
I now have everything I need. The Harrison's diagram is excellent and the text is very comprehensive. Let me compile the full note on the nephron and its functions.

The Nephron - Structure and Functions

Definition and Overview

The nephron is the functional unit of the kidney. Each human kidney contains approximately 900,000 to 1 million nephrons (range: ~200,000 to >2.5 million per kidney). It is composed of the renal corpuscle (glomerulus + Bowman's capsule) and the renal tubules - from the proximal tubule through to the connecting segment. The collecting duct system, though functionally interrelated, is embryologically distinct (ureteric bud origin) and is not strictly part of the nephron.
  • Brenner and Rector's The Kidney, p. 83
  • NKF Primer on Kidney Diseases, 8e, p. 24

Anatomy: Parts of the Nephron

Nephron anatomy showing all major segments - Harrison's Principles of Internal Medicine
Fig. 320-3A from Harrison's: The nephron segments from renal corpuscle to inner medullary collecting duct, with associated vasculature.
SegmentLocation
Glomerulus + Bowman's capsule (renal corpuscle)Cortex
Proximal convoluted tubule (PCT)Cortex
Proximal straight tubuleCortex/outer medulla
Thin descending limb of HenleMedulla
Thin ascending limb of HenleInner medulla
Thick ascending limb (TAL)Outer medulla/cortex
Macula densaCortex (at DCT-TAL junction)
Distal convoluted tubule (DCT)Cortex
Connecting tubuleCortex
Cortical collecting duct (CCD)Cortex
Outer medullary collecting duct (OMCD)Outer medulla
Inner medullary collecting duct (IMCD)Inner medulla

Enumerated Functions of Each Nephron Segment

1. Glomerulus (Renal Corpuscle)

  • Ultrafiltration of blood plasma across the glomerular filtration barrier (endothelium, glomerular basement membrane, podocytes with slit diaphragms)
  • Produces approximately 180 L/day of ultrafiltrate (GFR ~125 mL/min)
  • Filters water, electrolytes, small solutes; retains large proteins and blood cells
  • The glomerular filtration rate (GFR) is the key measure of renal function

2. Proximal Tubule (PCT + Straight Segment)

The proximal tubule is the "workhorse of the kidney" - it handles the bulk of reabsorption. Key functions:
  1. NaCl and water reabsorption - ~60% of filtered NaCl and water is reabsorbed isosmotically. Primary apical transporter is Na+/H+ exchanger 3 (NHE3). Water follows through aquaporin-1 channels (constitutively active - no hormonal regulation needed).
  2. Glucose reabsorption (~100%) - via SGLT2 (Na+-glucose cotransporter) in early PCT; SGLT1 in late PCT. (SGLT2 inhibitors block this to lower blood glucose in diabetes.)
  3. Amino acid reabsorption (~100%) - Na+-coupled amino acid transporters on apical membrane.
  4. Bicarbonate reclamation (~90%) - filtered HCO3- is titrated by H+ (from NHE3) → H2CO3 → CO2 + H2O (carbonic anhydrase IV on brush border), CO2 diffuses into cell → reconverted to HCO3- (carbonic anhydrase II) → exits basolaterally via NBC1.
  5. Phosphate reabsorption - via Na+-phosphate cotransporters; regulated by PTH (which inhibits reabsorption, causing phosphaturia).
  6. Uric acid, organic acids, and drug secretion - proximal tubule is the main site of organic anion/cation secretion (e.g., penicillin, furosemide, methotrexate, creatinine).
  7. Ammonia generation - from glutamine metabolism; NH4+ is excreted via NHE3 (K+ position); critical for acid-base homeostasis.
  8. Protein catabolism - small filtered proteins are endocytosed and degraded by lysosomes.
The brush border of microvilli greatly amplifies surface area. Paracellular reabsorption (via leaky tight junctions) allows passive movement of Cl-, K+, and water. Bulk fluid reabsorption is driven by high oncotic and low hydrostatic pressure in peritubular capillaries.
  • Harrison's Principles of Internal Medicine 22E, p. 2410
  • NKF Primer on Kidney Diseases, 8e, p. 24

3. Loop of Henle

The loop of Henle is the concentrating segment of the nephron. It establishes the medullary osmotic gradient essential for urine concentration.
Thin Descending Limb:
  1. Permeable to water (but NOT solutes) - water exits into the hypertonic medullary interstitium, concentrating tubular fluid
  2. Fluid becomes progressively hyperosmotic as it descends
Thin Ascending Limb:
  1. Impermeable to water - solutes (NaCl) passively diffuse out into the interstitium
Thick Ascending Limb (TAL):
  1. Active NaCl reabsorption (~25-30% of filtered NaCl) - via apical NKCC2 (Na+/K+/2Cl- cotransporter); inhibited by loop diuretics (furosemide, bumetanide)
  2. Impermeable to water - dilutes tubular fluid ("diluting segment")
  3. K+ recycling - K+ secreted back into lumen via ROMK channel to sustain NKCC2 (luminal K+ is limiting)
  4. Ca2+ and Mg2+ reabsorption - paracellular, driven by lumen-positive voltage generated by K+ recycling; accounts for ~50-60% of Mg2+ reabsorption
  5. NH4+ reabsorption - absorbed via NKCC2 in the K+ position; important for acid-base handling
  6. The net result: medullary interstitium becomes highly hyperosmotic (up to ~1200 mOsm/kg), the only compartment in the body with higher osmolality than serum
  • NKF Primer on Kidney Diseases, 8e, p. 24

4. Macula Densa

Located at the junction of the TAL and DCT:
  1. Tubuloglomerular feedback (TGF) - senses luminal NaCl concentration via NKCC2; if NaCl is high → signals afferent arteriole to constrict → reduces GFR (autoregulation)
  2. Renin secretion control - low luminal NaCl → stimulates juxtaglomerular cells to release renin → activates RAAS

5. Distal Convoluted Tubule (DCT)

  1. NaCl reabsorption (~5-8%) - via apical NCC (Na+/Cl- cotransporter); inhibited by thiazide diuretics
  2. Ca2+ reabsorption (regulated) - transcellular, stimulated by PTH and 1,25(OH)2 vitamin D; via apical TRPV5 channels and basolateral NCX1
  3. Mg2+ reabsorption - via apical TRPM6 channels; this is the main regulated segment for Mg2+
  4. Fine-tuning of K+ - some K+ reabsorption and secretion

6. Collecting Duct (Cortical + Medullary) - Principal and Intercalated Cells

The collecting duct has two major cell types with distinct functions:
Principal Cells:
  1. Na+ reabsorption - via apical ENaC (epithelial Na+ channel); tightly regulated by aldosterone (which increases ENaC expression and activity) and proteolytic enzymes. Blocked by amiloride/triamterene.
  2. K+ secretion - via apical K+ channels (ROMK); driven by high intracellular K+ (from Na+/K+-ATPase) and lumen electronegativity created by Na+ reabsorption. Promoted by aldosterone and fast flow.
  3. Water reabsorption - via aquaporin-2 (AQP2) on the apical membrane, inserted in response to ADH/vasopressin (V2 receptor → cAMP → AQP2 trafficking). AQP3/AQP4 on basolateral membrane. Absence of ADH → dilute urine; presence of ADH → concentrated urine.
Intercalated Cells (A and B types): 4. Acid secretion (Type A) - apical H+-ATPase (proton pump) secretes H+ into lumen; basolateral Cl-/HCO3- exchanger reclaims HCO3-. Stimulated by aldosterone. Predominates in acidemia. 5. Bicarbonate secretion (Type B) - apical Cl-/HCO3- exchanger secretes HCO3-; basolateral proton pump reabsorbs H+. Predominates in alkalemia. Mediated by the protein hensin.
Inner Medullary Collecting Duct (IMCD): 6. Urea reabsorption - regulated by ADH via UT-A1/UT-A3 urea transporters; urea recycling into the medullary interstitium is key to concentrating urine 7. Final water reabsorption - under ADH control, further concentrates urine

Summary Table: Functions by Segment

Segment% NaCl reabsorbedKey FunctionsKey Transporter/Channel
Glomerulus-FiltrationSlit diaphragm/GBM
Proximal tubule~60%NaCl, H2O, glucose, AA, HCO3-, PO4, organic secretionNHE3, SGLT1/2, AQP1, NBC1
Thin descending limb-H2O reabsorption (passive)AQP1
TAL~25-30%NaCl reabsorption, dilution, Ca2+/Mg2+ reabs.NKCC2, ROMK
DCT~5-8%NaCl, Ca2+, Mg2+ reabsorptionNCC, TRPV5, TRPM6
Collecting duct~2-3%Na+/K+/H2O/acid-base final regulationENaC, AQP2, H+-ATPase

Types of Nephrons

There are two functional types:
  • Cortical nephrons (~80%): short loops of Henle, remain in cortex/outer medulla; primarily involved in reabsorption
  • Juxtamedullary nephrons (~20%): long loops of Henle extending deep into inner medulla; critical for generating the medullary concentration gradient and producing concentrated urine

Overall Renal Functions Performed by the Nephron

  1. Excretion of metabolic waste products (urea, creatinine, uric acid)
  2. Regulation of body fluid volume (Na+ and H2O balance)
  3. Regulation of electrolyte composition (Na+, K+, Ca2+, Mg2+, PO4)
  4. Acid-base homeostasis (H+ secretion, HCO3- reabsorption/generation)
  5. Blood pressure regulation (RAAS activation via renin)
  6. Erythropoiesis (erythropoietin secretion by peritubular fibroblasts)
  7. Vitamin D activation (1-alpha hydroxylase converts 25-OH-D to active 1,25(OH)2-D)
  8. Gluconeogenesis (proximal tubule during fasting)
Sources: Harrison's Principles of Internal Medicine 22E (2025), pp. 2409-2412; NKF Primer on Kidney Diseases, 8e; Brenner and Rector's The Kidney.
This is a shared conversation. Sign in to Orris to start your own chat.