1. BAHIR DAR UNIVERSITY COLLEDGE OF MEDICINE AND HEALTH SCIENCE
DEPARTMENT OF ACCPM ,2021.
RENAL ANATOMY AND PHYSIOLOGY
YONAS TADESSE(MD)

2. OUTLINES
• Introduction
• Gross anatomy of the kidneys
• Functional anatomy and physiology of renal corpuscle
• Tubular functions
• Renal auto regulation
• Effect of anesthesia , surgery & MV on renal function
• Summary

3. Objectives
• At the end of this seminar presentation, we are expected to
Know Basic applied structural and functional anatomy of the renal system
 Be familiar with common functions of the renal system
Describe Glomerular filtration and its determinants
Have knowledge of Tubular function
Understand renal blood flow and its auto regulation
Describe the effect of Anesthesia , surgery & MV on renal function
Briefing over effect of renal function on anesthetic agents

4. INTRODUCTION
• The kidney exemplifies an exquisite structure-function relationship to regulate intravascular
volume, osmolality, acid base and electrolyte balance, hormonal and to excrete end products of
metabolism and drug
• Change in Renal function , affects many organ , conversely different organ impairment could affect
renal function presents as a challenge for the anesthesiologists.
• Identifying patients with renal dysfunction before surgery is crucial so that their Preoperative
optimization , intra operative safe anesthesia delivery and postoperative management can be
planned effectively.
• In surgical patients without renal disease, all general anaesthetic agents temporarily depress
renal function with urine flow, GFR, RBF, and electrolyte excretion being reduced.

5. Urinary system

6. GROSS ANATOMY OF THE KIDNEY

7. Renal blood supply

8. INNERVATION OF THE RENAL VESSEL
• The renal nerves travel along the renal blood vessels as they enter the kidney.
• They contain many postganglionic sympathetic efferent fibers and a few afferent fibers.
• There alsoappears to be a cholinergic innervation via the vagus nerve

9. Microscopic / functional Anatomy
•

10. What is really the function of renal system?
The main functions of the kidney are to regulate:
• Extracellular fluid volume
• Extracellular fluid electrolyte composition
• Total body water volume
• The body’s acid-base balance
• Arterial blood pressure

11. THE NEPHRON
• The Structural & fundamental unit of the kidney.
• Within each kidney, there are about one-million nephrons.
• It is made up of a single layer of epithelial cells.
• Each measuring about 45-65mm.
• Two types :
i. Cortical nephron
ii. Juxtamedullary nephron

12. COMPONENTS OF THE NEPHRON
• Each nephron is composed of renal corpuscle (filtration) & a renal tubules (reabsorption &
secretion)
• Renal corpuscle /compose of glomerulus & Bowman's capsule/
Glomerulus “”
 about 200 micro m in diameter
tuft of fenestrated capillaries
It receive their blood supply from the afferent arteriole and drain into efferent arteriole
filters a protein-free plasma into the tubular component

13. cont
 Bowman's capsule;
 It has two layers:
Parietal layer “simple squmous epith”
Visceral layer consists of modified simple squamous epithelial cells called
podocytes
Urinary space between these layers

14. What are podocytes ?
• Foot like projections of these cells (pedicels) wrap round the
single layer of endothelial cells of the glomerular capillaries and
form the inner wall of the capsule.
It has two processes:
1. Primary
2. secondary

17. Glomerular filtration
• Definition: is the transfer of fluid and solutes from the glomerular capillaries along a
pressure gradient into Bowman's capsule.
• Filtrate is the fluid within the Bowman’s capsule ,
• It contains electrolytes, glucose and amino acids , same concentrations as in the plasma.
• It is free from:
1. Blood cells
2. Protein
3. Protein-bound molecules (calcium, fatty aids, amino acids)

18. Glomerular Capillary Filtration Barrier
• Each layer in the filtration membrane has a special characteristic:
1. The endothelial cells of glomerular capillaries are fenestrated ( 70-90 nm in diameter)
2. The basement membrane is negatively charged ( presence of sialoproteins)
3. The epithelial cells of Bowman's capsule have foot processes called podocytes ( to
form filtration slits a long the capillary wall)

19. .

20. Glomerular Filtration Rate
• Definition- The volume of plasma filtered from both kidneys per minute.
• It is the measurement of the kidneys ability to filter plasma.
• 125ml/min ( 7.5L/h or 180L/d) in average male, less by about 10% in females
• 99% or more of the filtered is normally reabsorbed
• The best known formula used is the Cockcroftand Gault formula:

21. Renal Tubular system physiology
• The terminology of the renal tubular system is based on morphology as seen with light microscopy,
• The renal tubular system compensates for the large glomerular filtration by resorption.
• Conserve and regulate molecules within appropriate physiologic ranges.
• The kidneys excrete more than 95% of the ingested Na+ at rates that match dietary Na+ intake.
• A high density of mitochondria and extensive surface area indicate high-energy requirements.
• In normal kidneys, 80% of the energy is required for Na+/K+-ATPase.
• In spite of this high energy demand, the tubular system is supplied by only 10% to 15% of the RBF and is a key etiology for
acute tubular necrosis after hypotension .

22. TUBULAR FUNCTIONS
Generally, the renal tubules perform the following two functions:
1, Reabsorption: Transport of a substance from the tubular lumen to the blood,
2, Secretion: Transport of a substance in opposite direction
Transport of solutes and water is either “paracellular or transcellular
transport”
The mechanisms of transport may be active or passive. They include—
1,Simple diffusion
2, Facilitated diffusion
-

23. PROXIMAL CONVULATED TUBLES
• About 15 mm long and 5 micro m in diameter.
• Simple cuboidal epithelial cells with prominent brush borders of microvilli & canaliculi
• Thigh junction at the apical side between the cells
• Numerous of mitochondria to provide energy for active transport.
• Approximately 65% of filtered sodium, chloride, and water is reabsorbed by the PCTs
• Organic acids and bases are cleared by the PCT.

24. LOOP OF HENELE
• comprised of a thin descending limb, thin ascending limb, a medullary thick ascending limb
• maintenance of an osmotic gradient in the interstitium by a countercurrent system
• In mTAL A Na+/K+/2Cl− cotransporter absorbs Na+, Cl−, and K+ from the tubular lumen
• Na+/K+ pumps reabsorb 25% of the filtered sodium and potassium
• Inhibition of A Na+/K+/2Cl− cotransporter is the mechanism of cationic (positively charged) loop
diuretics such as furosemide

25. Distal convoluted tubles
• About 5 mm in long lined by simple cuboidal epith.Cells with Larger lumen
• Less or lack brush boarders, mitochondria, absencent canaliculi
• The first part of the distal tubule forms the macula densa
• 5% of sodium is reabsorbed /sodium chloride cotransporter & Na+/K+ ATPase
• Thiazide diuretics inhibit this cotransporter
• Water reabsorbation is regulated by AVP

26. COLLECTING TUBULES
• Each collecting duct serves about 4000 nephrons
• Consisting of two principal cells
• Principal cells- use Na+/K+ ATPase to resorb Na+ and K
 sites of action for the potassium-sparing diuretics & amiolaride via Na channel blockage
• intercalated cells
 Type A-use H+-ATPase and H+/K+- ATPase transporters to secrete hydrogen ions &
absorbs bicarbonate ions
 Type B transport hydrogen out of the cell while bicarbonate is excreted into the tubular
lumen while bicarbonate is excreted into the tubular lumen.

27. COLLECTING DUCTS
• About 20 mm in length, simple cuboidal epith,normally impermeable to the water
• Formed as anastomoses of collecting tubules & determine the final composition of
urine.
• The principal cell of the collecting duct is a highly regulated epithelial cell.
• AVP controls water resorption.
• Urea is reabsorbed via transporters to assist in the concentration of urine.
• Hydrogen can also be secreted to regulate acidosis

28. RENAL AUTOREGULATION
• The formation of urine is tightly controlled by complex autoregulation
• It maintains consistency of the RBF, GFR, and the resorption rate in tubules.
• This autoregulation protects the kidney from injury secondary to elevated BP
• Generally, renal autoregulation is by two mechanisms;
autoregulation of RBF
 tubuloglomerular feedback

29. AUTOREGULATION OF RENAL BLOOD FLOW
• AA from the renal arteries branch extensively to supply the renal and peritubular capillaries
• The kidneys receive about 20% of the CO & are responsible for 7% of total body oxygen
consumption.
• Normally, the RBF is about 1200 ml/ min (300- 400 ml/ 100 gm / min )
• The cortex, receives 85% to 90% of RBF ,while medula recieves 6 %
• RBF remains relatively constant over MAP range of 75–170 mmHg
• Autoregulation of RBF is produced by changes in the contraction of AA smooth
muscle in response to changes in perfusion pressure ( EA not involved)

30. The Myogenic Mechanism of the Renal Blood Flow
Autoregulation
• Afferent arterioles contracts in response to the stretching produced by an increase in transmural
pressure.
• Glomerulotubular balance compensates for increased GFR when blood pressure is elevated / >20
seconds/
• An increase in GFR provides enhanced NaCl delivery to the distal tubules.
• Through complex paracrine signaling, constriction of the afferent arteriole results.

31. TUBULOGLOMERULAR FEEDBACK
• The dynamic range of tubuloglomerular feedback is a NaCl conc.15 and 60 mmol/L with maximal
responses at greater than 60 mmol/L.
• Macula densa releases more adenosine, which constricts the afferent arterioles,
• In the tubules, more than 99% of water and most of the solutes are absorbed.
• The transit of fluids is dependent upon balance of hydrostatic and colloid forces.

32. CONTROLS OF RENAL BLOOD FLOW

33. 2,Pressure diuresis

34. Cont--
4, THE SYMPATHETIC NERVE SUPPLY TO THE KIDNEY
oThe kidneys are supplied by noradrenergic sympathetic nerves,
oInitially constricts both AA & EA –favoring filtration.
oNet direct α effect of sympathetic nerve activity in the kidney is to reduce the
GFR .

35. MAINTENANCE OF PLASMA OSMOLALITY
• Osmolality is a measure of the osmoles (Osm) of solute per kilogram of solvent (Osm/kg)
• osmolarity is defined as the number of osmoles of solute per liter of solution (Osm/L).
• Osmolarity is affected by changes in water content, temperature, and pressure.
• Osmolarity is slightly less than osmolality because the total solvent weight excludes any solutes.
• Clinically, the values for osmolarity and osmolality are very similar, and the terms are usually used
interchangeably.
• The bedside calculation from laboratory data (2[Na+ mmol/L] + 2[K+ mmol/L] + BUN mg/dL/2.8 +
glucose mg/dL/18)

36. Regulation of Osmolality
• Plasma osmolality is closely regulated between 275 and 300 mOsm/L.
• Acute alterations in osmolality, either hypoosmolality or hyperosmolality, can result in serious neurologic
symptoms and death as the result of water movement in the brain.
• Normal patients can dilute and concentrate urine within the range of 40 to 1400 mOsm/L. Maintenance of
plasma osmolality is linked to the regulation of sodium.
• It is dependent on the interaction of at least three processes:
 the generation of a hypertonic medullary interstitium by the countercurrent mechanism and urea
recycling,
 the concentration and then dilution of tubular fluid in the loop of Henle,
 action of AVP to increase water permeability in the last part of the distal tubule and collecting ducts.

37. RENAL CONTROL OF INTRAVASCULAR VOLUME
Hypovolemia
• Patients with hypovolemia,, are commonly encountered in the perioperative period.
• This increases sympathetic outflow, activates the renin-angiotensin-aldosterone response,
& releases AVP.
• Na reabsorption in the PCT increases from 66% to 80% by sympathetic activity and
angiotensin II
• Na delivery to the mTAL, distal tubule, and collecting duct is decreased, but aldosterone
promotes reabsorption of sodium at these sites.
Under the influence of AVP, water is also avidly reabsorbed in the collecting duct so that the urine
becomes highly concentrated (osmolality 600 mOsm/kg) but with virtually no sodium (10 mEq/L).

38. ..
• Hypervolemia
• Expansion of the extracellular volume by hypervolemia is countered by an increase in the GFR and filtered
sodium load due to a combination of reflex decreases in sympathetic and
angiotensin II activity and the release of ANP.
• Together with the increase in peritubular capillary hydrostatic pressure, these responses cause sodium
reabsorption in the proximal tubule to decrease from 67% to 50%.
• The decline in plasma aldosterone decreases sodium absorption from the thick
ascending loop of Henle to the collecting duct.
• The presence of ANP and absence of AVP impairs water absorption at the collecting duct so that a dilute
urine (osmolality 300 mOsm/ kg) with abundant sodium (80 mEq/L) is produced

39. EFFECTS OF MECHANICAL VENTILATION ON
RENAL FUNCTION
• MV and PEEP may cause decreases in RBF, GFR, sodium excretion, and urine flow.
• The increased airway and intrapleural pressures lead to decreased venous return,
cardiac filling pressures, and cardiac output.
• The RAAS undoubtedly augments the renal responses to positive pressure ventilation.
• Permissive hypercapnia as employed during ARDS may promote renal vasoconstriction.

40. Induced Hypotension
• During anesthesia with induced hypotension, substantial reduction of GFR and urine
flow rate is common.
• Earlier studies suggested that hypotensive anesthesia can be well tolerated without
permanent impairment of renal function.
• A more recent retrospective analysis suggests that
 mean arterial pressures less than 60 mmHg for 11 to 20 min or
 Less than 55 mmHg for more than 10 min are associated with acute kidney injury

41. Effects of Anesthesia and surgery on Renal Function
• In surgical patients without renal disease, all GA agents temporarily depress renal
function with urine flow, GFR, RBF, and electrolyte excretion being reduced.
• This consistent and generalised depression has been attributed to many factors including
 the type and duration of surgical procedure,
the physical status of the patient ,(CVS & renal systems)
 pre-operative and intra-operative blood volume,
fluid and electrolyte balance,
the choice of anaesthetic agent and the depth of anaesthesia.

42. These are the conclusions of anesthesia effects on kidney function.
1. Reversible decreases in RBF, GFR, urinary flow, and Na+ excretion occur during
both general and regional anesthesia.
2. Such changes are usually less pronounced under regional anesthesia.
3. Most changes are indirect and are mediated by autonomic and hormonal
responses to surgery and anesthesia.
4. AKI is less likely when patients are normovolemic and normotensive.
5. There is no evidence that vapor anesthetics cause kidney injury.

43. Effects of Anesthesia and Surgery on Renal Function

44. Altered renal function and effects on Anesthesia
• Propofol and etomidate are minimally effected
• Barbiturates: patients show increased sensitivity
• Ketamine: Active metabolites are dependent on renal clearance.
• Benzodiazepines: increased sensitivity in patients with
hypoalbuminemia
• Opioids: Most opioids are cleared by the liver.
Meperidine and Morphine have active metabolites

45. Inhalational Agents
• Volatile: Do not rely on kidney for metabolism
• Nitrous: limit to 50% in severely anemic

46. Muscle Relaxants
• Succinylcholine can be safely given in absence of hyperkalemia.
• Cisatracurium and Atracurium are uneffected
• Vecuronium and Rocuronium: 20% metabolized by renal excretion.
• Pancuronium is 60-90% dependent on renal excretion.
• Curare: 40-60% metabolized and excreted by the kidney.
• Reversal agents: Renal excretion is responsible for elimination for
edrophonium, neostigmine, and pyridostigmine.

47. Preoperative Considerations
• Acute kidney failure cause
• End Stage renal disease causes
• Dialysis status

48. Objectives
• At the end of this seminar presentation, we are expected to
Know Basic applied structural and functional anatomy of the renal system
 Be familiar with common functions of the renal system
Describe Glomerular filtration and its determinants
Have knowledge of Tubular function
Understand renal blood flow and its auto regulation
Describe the effect of Anesthesia , surgery & MV on renal function
Briefing over effect of renal function on anesthetic agents

49. References

50. THANK YOU FOR YOU ATTENTION