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MBBS ANATOMY AND PHYSIOLOGY OF THE KIDNEYS.pdf
- 1. FUNCTIONAL ANATOMY AND PHYSIOLOGYOF THE KIDNEYS DR. (MRS.) ONU UGOCHI CHIKA MBBS,FISN,FWACP, ISN-ANIO-CNC Cert.
- 2. OUTLINE • Introduction • GrossAnatomy • Renal vasculature • Lymph drainage • Innervation • Kidney function overview • Nephron • Urine production • Summary
- 3. Introduction • The kidneysare paired bean shaped retroperitoneal organs normally situated on either sides of the vertebral column • Develop from intermediate mesoderm (3rd wk IUL)-pronephros, Mesonephros and meta nephros • 0.5% of total body mass but account for approximately 7% of whole-body oxygen consumption.
- 4. Gross Anatomy cont….. •Lie obliquely between T12 –L3 with the long axis parallel to the lateral boarder of psoas major • RK more caudal (right lobe of the liver) • Size reduces with age • LK/solitary kidneys are longer • Weight 115-155g (F) 125-170g (M) • Length= 10-13cm (MRI mean:10.7-14.3M,9.5-13.9F) • Width=5-7.5cm, Thickness =2.5-4cm • Volume=87-223(F) 132-276 (M)
- 5.
- 6. Gross Anatomy cont…. 2boarders: concave (medial)& convex(lateral) 2 surfaces: Anterior and posterior 2 poles: Superior and inferior • Surrounded by easily removable fibrous capsule • Hilum is the medial entrance into the renal sinus
- 8. Gross Anatomy cont…Relationships Superomedial: suprarenal glands cushioned by perirenal (perinephric) fat derived from the extraperitoneal fat • Renal fascia (Gerota’s fascia) fibrous CT that encapsulates kidney and adrenal glands Posteriorly: diaphragm, quadratus lumborum • Right Anterior :liver (heptorenal recess), duodenum, ascending colon • Left anterior : stomach, spleen, pancreas, jejunum, descending colon • Laterally: transversus abdominus
- 9. Kidney cut surface •2 regions :pale outer(cortex), darker inner(medulla) • Medulla: is divided into inner and outer (outer and inner stripes) • Medulla is divided into 8 to 18 striated conical masses (renal pyramids) • Apex of pyramids form renal papilla • The tip of each papilla has 10 to 25 small openings that represent the distal ends of the collecting ducts (ducts of Bellini).
- 10. Gross Anatomy cont… •A renal pyramid + corresponding cortex = renal lobus/ lobe • Renal column: spaced in between pyramids (extensions of cortex towards the pelvis) • Apex (tips) of renal pyramid end in minor calyx • 2-3 minor calyces= major calyx • 2-3 major calyces(collecting sacs) drain into renal pelvis • Renal pelvis: (usually collapsed) flattened, enlarged, funnel shaped expansion continues inferiorly as at the ureter
- 12. Renal vasculature cont….. •Kidneys receive 20-25% of cardiac output(1- 1.2L/min) mainly via renal arteries • The glomerular filtration rate (GFR) normally is approximately 120 mL/min or 170–180 L/day. • No collaterals between the arterial segments • The kidneys often receive aberrant arteries from the superior mesenteric, suprarenal, testicular, or ovarian arteries • NO ARTERY PENETRATES THE MEDULLA
- 13.
- 14. Aorta Renal artery Segmental artery Interlobarartery Arcuate artery Cortical radiate artery Afferent arteriole Glomerulus (capillaries) Nephron-associated blood vessels Inferior vena cava Renal vein Interlobar vein Arcuate vein Cortical radiate vein Peritubular capillaries and vasa recta Efferent arteriole Path of blood flow through renal blood vessels
- 15. • Lymph drainage:Lymphatics drain to paraaortic nodes at the level of origin of renal artery(L2) • Innervation: Sympathetic preganglionic cells T12-L1 and synapse in the coeliac and renal ganglia afferent fibers accompany sympathetic nerves that subserve pain pass to coeliac plexus and then sympathetic trunk • Some afferent also run with the vagal fibers (nausea, vomiting) • Most of the renal functions are regulated by hormones and not dependent on innervation (renal function after complete nerve transection e.g.renal transplantation)
- 16. Functions of thekidneys Excretion (urine formation)-urea, Creatinine, drugs Control of the internal environment • Salt, water, osmolarity, plasma volume/Bp • Acid-base control; H+, HCO3 – • Other ions; K+, Ca++, phosphate, Mg++ Endocrine • RAAS • 1,25 OH Vit. D3 • Erythropoietin (peritubular interstitial fibroblasts)
- 17. FUNCTIONAL ANATOMY • Functionaland histological unit of the kidney –NEPHRON • 1 million (200,000 - 2.5 million) in each kidney at birth • New nephrons cannot be developed, and a lost nephron cannot be replaced • Consist of glomerulus and complex tubule system draining into the collecting duct • Glomerulus: tuft of capillaries which project into a pouch-like extension of the (Bowman capsule) • Glomerulus + Bowman’s capsule= renal/malpighian corpuscle
- 18. NEPHRON Cont …. •Three types of nephron (location of renal corpuscles within the cortex): superficial, midcortical, and juxtamedullary nephrons. • The tubular part of the nephron consists of: proximal tubule (convoluted, straight/pars recta) distal tubule (convoluted, straight/pars recta) loop of Henle (LH) (Intermediate tubule thin descending limb of Henle loop +thin ascending limb of Henle loop)
- 19. NEPHRON Cont….. • Cortex:renal corpuscles, segments of proximal tubules, distal tubules, collecting ducts • Medulla: terminal segments of the pars recta of the proximal tubule, pars recta of the distal tubule, descending and ascending thin limbs of LH, large collecting ducts
- 22.
- 24. PODOCYTES • Bowman capsulevisceral epithelial cells • Terminally differentiated cells The podocytes are the largest cells in the glomerulus (others: endothelial, mesangial, parietal epithelial cells) • Podocytes have a voluminous cell body that floats within the urinary space • Being fixed to the GBM only by the regularly interdigitating foot processes • Easily lost as viable cells in the urine. • Apoptosis plays no relevant role in podocyte loss
- 25. podocytes cont…… • In-betweenthe foot processes are slit diaphragms (30-40nm) • Slit diaphragm are covered by a thick surface coat rich in sialoglycoproteins responsible for the high negative surface charge of the podocytes. • Podocytopathies: MCD, FSGS, Diffuse mesangial sclerosis, collapsing glomerulopathy
- 26. Glomerular Basement Membrane(GBM) • The GBM is the skeleton of the glomerular tuft • The outer aspect is covered with podocytes foot processes and the interior by capillary walls and the mesangium. • It measures 373+/-42(males), 326+/-45nm(females) • On EM it is a trilaminar structure: lamina rara interna, lamina densa and lamina rara externa. • GBM is electronegative due to its proteoglycans • The mature GBM consists of mainly of type IV collagen made of α3, α4, α5 chains (instead of α1,α2 chains of most BMs) • Type IV collagen is the antigenic target in Goodpasture disease and Alport syndrome
- 27. Mesangium • Found betweenglomerular capillary loops • Provides support for the capillary loops • Consists of contractile mesangial cells which secrete mesangial matrix • Also have receptors for Ang11, vasopressin, Atrial natriuretic petide, PG • Matrix contains: collagen IV, V, IV, glycoproteins, proteoglycans
- 28. FILTRATION BARRIER • Glomerularcapillary endothelial pores, GBM, Podocyte slit membrane/diaphragm • Provide 3 layers of water permeable but solute limited permeability (size, charge, shape) • Size selectivity is determined mainly by the slit diaphragm, fenestrated glomerular capillary wall. • The charge selectivity results from the dense accumulation of negatively charged molecules (e.g. proteoglycans in the GBM).
- 30. The juxtaglomerular apparatus(JGA) • Comprises the BEAM: Beginning portions of the efferent arteriole, Extraglomerular mesangium, terminal portion of the Afferent arteriole with its renin-producing granular cells (also often termed juxtaglomerular cells), and Macula densa • JGA regulates blood flow and glomerular filtration in each individual nephron via tubular glomerular feedback mechanism and regulation of renin release
- 31.
- 32. JGA cont….. • Themacula densa is a plaque of columnar epithelial specialized cells in the wall of the thick ascending limb of Henle at the site where the limb attaches to the extraglomerular mesangium • Macula densa senses Na conc of tubular fluid: • High flow rate=high Na delivery→ adenosine-mediated afferent arteriole vasoconstriction →↓glomerular filtration (tubular glomerular feedback). • Low flow rate=low Na delivery→ RAAS activation→aldosterone release→Na/water retention
- 35. Renin-Angiotensin-Aldosterone System • Reninis synthesized in and stored in specialized afferent arteriolar cells that form part of the JGA and released into the circulation in response to (1) increased renal sympathetic nervous discharge (2) reduced stretch of the afferent arteriole after a reduction in renal perfusion pressure (3) reduced delivery of NaCl to the macula densa region of the nephron • Renin catalyzes conversion of angiotensinogen (synthesized in the liver) to Angiotensin I→ Angiotensin II by angiotensin-converting enzyme (ACE) produced in the kidneys, lungs,heart • Angiotensin II : arteriolar vasoconstriction (renal efferent>>afferent arterioles)→↑arterial pressure but ↓RBF
- 36. Urine production • Relieson: glomerular filtration, tubular reabsorption, tubular secretion • Glomerular filtration α net filtration pressure • Urine is about 95% water • usually contains urea, uric acid, and creatinine • May contain trace amounts of amino acids and varying amounts of electrolytes • Volume varies with fluid intake and environmental/ hormonal factors force favoring filtration (glomerular capillary hydrostatic pressure) forces opposing filtration(capsular hydrostatic pressure, glomerular capillary osmotic pressure ) Net Filtration Pressure =
- 39. Renal tubules • Therenal tubules are outlined by a single-layer of flat or cuboidal epithelium anchored to a basement membrane. • Route of transport: • Paracellular transport (tight junction) • Transcellular transport (specific channels, carriers, transporters) • Types of transport: A. Passive transport: • Simple diffusion (electrochemical gradient) • Facilitated diffusion (coupled or carrier-mediated diffusion) • B. Active transport: Energy (ATP) dependent channels: (symport/cotransport or antiport/countertransport)
- 42. Na+-H+ exchanger, AQP1 (acetazolamide,osmotic diuretics) Osmotic diuretics Na+-K+-2Cl− cotransporter, AQP1 (loop diuretics) Na+-Cl− cotransporter (Thiazides) AQP2, ADH (vasopressin) (Aldosterone antagonists, osmotic diuretics) ENaC Renal interstitium Special consideration ADH Aldosterone Urea
- 43.
- 45. Summary • Kidney hasa complex structure reflecting is many functions • The most easily recognised function: excretion • Its functions are regulated by external, internal and hormonal factors • The kidneys are essential for life
- 46.