MBBS ANATOMY AND PHYSIOLOGY OF THE KIDNEYS.pdf

MBBS ANATOMY AND PHYSIOLOGY OF THE KIDNEYS.pdf

1. FUNCTIONAL ANATOMY AND
PHYSIOLOGY OF THE KIDNEYS
DR. (MRS.) ONU UGOCHI CHIKA
MBBS,FISN,FWACP, ISN-ANIO-CNC Cert.

2. OUTLINE
•Introduction
•Gross Anatomy
•Renal vasculature
•Lymph drainage
•Innervation
•Kidney function overview
•Nephron
•Urine production
•Summary

3. Introduction
•The kidneys are paired bean shaped
retroperitoneal organs normally situated on
either sides of the vertebral column
•Develop from intermediate mesoderm (3
rd 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. GROSS ANATOMY

6. Gross Anatomy cont….
2 boarders: 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. Renal vasculature cont…
Vasa recta

14. Aorta
Renal artery
Segmental artery
Interlobar artery
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 the kidneys
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
•Functional and 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. The renal corpuscle

24. PODOCYTES

•Bowman capsule visceral 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-between the 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 between glomerular 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
•Glomerular capillary 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. The renal corpuscle

32. JGA cont…..
•The macula 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
•Renin is 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
•Relies on: 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
•The renal 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. Renal
interstitium

45. Summary
•Kidney has a 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. THANKS
FOR
LISTENING!!!