Renal physiology 2 dr osama elshahat22

1. Dr. Osama El-Shahat
Consultant Nephrologist
Head of Nephrology Department
New Mansoura General Hospital (international)
ISN Educational Ambassador

2.  A retroperitoneal organ
 T11-L3
 Normal size: 11-15cm in adults.
 located in the upper region of the
abdominal cavity just above the
waistline.
 protected by the ribcage.
 Right kidney usually shorter than
the left (upper limit of variation in
length between right & left 1.5
cm)

5. The Kidney Nephron Diagram

6. The Nephron
Locations for filtration, reabsorption,
secretion & excretion

7.  Once in the tubule the
substance need not be
excreted , it can be
reabsorbed.
 These processes do not
apply to all substances.
E.g.
- Glucose (completely
reabsorbed.)
- Toxins ( Secreted and
not reabsorbed)

8. Nephron structures and functions
Proximal Convoluted Tubule (PCT)
 A thick, constantly active segment of the nephron
 that reabsorbs most of the useful substances of the
filtrate: sodium (65%), water (65%), bicarbonate
(90%), chloride (50%), glucose (nearly 100%)
 The primary site for secretion (elimination) of
drugs, waste and hydrogen ions.

9. Nephron structures and functions
Decending Limb of the Loop of Henle
 A part of the counter current multiplier
 fully permeable to water and completely impermeable to
solutes (salt particles)
 receives filtrate from the PCT, allows water to be
absorbed and passes “salty” filtrate to the next segment.
“Saves water and passes the salt”

10. Nephron structures and functions
Ascending Limb of the loop of Henle
 a part of the counter current multiplier
 impermeable to water and actively transports (reabsorbs)
salt (NaCl) to the interstitial fluid of the pyramids in the
medulla.
“Saves salt and passes the water.”
 the passing filtrate becomes dilute and the interstitium
becomes hyperosmotic

11. Nephron structures and functions
Peritubular
Capillaries
 transport reabsorbed
materials from the PCT
and DCT into kidney
veins and eventually
back into the general
circulation
 help complete the
conservation process
(reabsorption) that takes
place in the kidney

12. The two types of Nephrons
Cortical
• The loop of Henle does
not extend past the
cortex of the kidney.
Juxtamedullary
• Loop of Henle extends
past the cortex and into
the medulla of the
kidney.

13. PHYSIOLOGY

15. Kidney nephron
The nephrons are the functional units of the
kidney and are the site of:
1. Filtration of blood
2. Maintainance of Renal blood pressure
3. Formation of urine
4. Counter current mechanism
5. Acid-base balance
6. Regulation of electrolytes
7. Reabsorption of materials
8. Secretion of materials( production of hormones)
9. Excretion of wastes

16. 1. Filtration of Blood
The glomerulus is the site of filtration of blood

17. The Bowman’s capsule (basement membrane +
podocytes)
 filters blood,
 hold back large molecules such as proteins,
 passes through small molecules such as water,
salts, and sugar
 Aids in the formation of urine

19. Podocytes:
• Also known as visceral epithelial cells
• Cells in the Bowman's capsule in the kidneys that wrap
around the capillaries of the glomerulus leaving slits
between them.
• They are involved in regulation of glomerular filtration
rate (GFR). When podocytes contract, they cause
closure of filtration slits. This decreases the GFR by
reducing the surface area available for filtration.

20. 2. Maintainance of Renal Blood
Pressure
• This process is achieved by the
Juxtaglomerular apparatus.

21. The three cellular components of the
apparatus are the
1. juxtaglomerular cells
2. macula densa,
3. extraglomerular mesangial cells .

22. The Juxtaglomerular Apparatus

23. Function of the JC cells
1. Release of Renin
Stimulus : Low blood pressure
Action : Release of Renin
Angiotensin Angiotensin I Angiotensin II
Angiotensin II
 It acts as a vasoconstrictor to raise blood pressure.
 It stimulates the release of aldosterone hormone from the
adrenal cortex.

24. 2. Release of Aldosterone hormone
 It stimulates the DCT to reabsorb salt.
3. Reabsorption of salt (NaCl)
 Salt reabsorption induces the
movement of water to the blood
by osmosis thereby raising the
blood volume and hence
increasing the blood pressure.

25. Function of the Macula Densa Cells
 It monitors the salt content of the blood.
 If concentration of salt is raised, the macula densa cells
inhibit the release of renin from the JC cells.
 No release of renin No angiotensin II , No
aldosterone . Blood pressure decreases until it is sent
back to normal.

27. Function of the extra glomerular
mesangial cells
 It secretes erythropoietin
 Erythropoietin is a glycoprotein hormone which
controls erythropoiesis or red blood cell
production.

28. 3. Formation of urine
 Takes place in 3 main steps;
1. Ultrafiltration
◦ seeping of fluid from glomerular capillaries to the
Bowman’s capsule along with useful substances (e.g.
glucose, vitamins ,amino acids)
2. Reabsorption along the nephron
◦ PCT; selective reabsorption of useful substances
◦ LOH, DCT and CD Reabsorption of water and salts
3. Secretion from blood to tubule

29. 4.Counter Current Multiplier
 Down the descending limb of the LOH, fluid becomes
more concentrated due to loss of water.
 Na+ and Cl- concentration increase as fluid turns and
heads on towards the ascending limb.
 All the way up osmotic pressure of fluid in LOH is
almost equal to the osmotic pressure in interstitial fluid.
 The fluid again passes through hypertonic interstitial
fluid loosing water again until into the collecting duct.
 The final product in the CD is urine!!!!

30. 4.Counter Current Multiplier
 A system of limbs
running in opposite
directions
 Consists of;
Descending limb and
Ascending limb of the
Loop of Henle.
 Helps in the absorption
of water from fluid
found in the LOH

31. Counter current multiplier
Na+ is actively pumped out
of the ascending limb into the
interstitial fluid.
 Cl- follows Na+ passively
 Increases the Na+ and Cl-
of interstitial fluid by about
4 times.
 Water seeps out of the of
the descending limb into
the interstitial fluid by
osmosis

33. 5. Regulation of electrolyte
Electrolytes are substances that become ions in solution and
acquire the capacity to conduct electricity.
The primary ions of electrolytes are sodium (Na+), potassium(K+),
calcium (Ca2+), magnesium (Mg2+), chloride (Cl−), hydrogen
phosphate (HPO4
2−), and hydrogen carbonate (HCO3
−).
 Maintenance of an electrolyte balance occurs so that the
osmolarity of both the body fluids and the urine is the same.
 Maximum electrolyte balance is maintained by the release of
hormones which are going to trigger the reabsorption of certain
ions thereby preventing electrolyte disbalances.

34. ADH
 Also known as vasopressin
 Released by hypothalamus
Stimulus: Low blood level
 Prevents the production of dilute urine
 Helps in reabsorption of water in kidneys
 Maintains osmolarity of plasma levels
normal

35. 6. Acid-base balance
 Forms part of human homeostasis
 Is important to maintain cellular stability
 Alterations in the acid-base balance are resisted by
extracellular and intracellular chemical buffers and by
respiratory and renal regulation.
In acid-base balance, the kidney is responsible
for 2 major activities:
◦ Reabsorption of filtered bicarbonate: 4,000 to 5,000 mmol/day
◦ Excretion of the fixed acids (acid anion and associated H+): about 1
mmol/kg/day.

36. 7. Reabsorption of materials
Nutrients such as glucose, amino acids
and other metabolites are reabsorbed in
the medulla such that the body does not
lose important nutrients.
Location: proximal convoluted tubule
situated in the cortex of the kidney

37. 8. Secretion of substances
Release of several substances occur in
order to aid in the functions of the kidney:
1. Calcitriol (activated form of vitamin D promotes intestinal
absorption of calcium and the renal reabsorption of phosphate)
2. Renin
3. Erythropoietin
4. ADH
5. Prostaglandins
6. Kinins
7. 1,25-dihydroxyvitamin D3

38. 9. Excretion of wastes
The kidney is also involved in the excretion
of wastes such as:
1. Urea ( from protein metabolism)
2. Uric acid ( from nucleic acid metabolism)
3. Creatinine (from metabolic breakdown of
creatine phosphate)
4. End-products of Hb metabolism
5. Metabolites of hormones
6. Foreign substances: drugs, pesticides,
other chemicals ingested in food

39. Metabolism by Tubules
The cells of the renal tubules synthesize
glucose and add it to the blood.
Cells also catabolize substances such as
peptides which are taken from the tubular
lumen or peritubular capillaries.
Catabolism eliminates these substances
from the body.

40. Finding the amount of a substance
excreted per unit time
Given
 Amount filtered in NaCl g/day
 Amount reabsorbed in NaCl g/day
 Amount excreted in NaCl g/day
Amount excreted =
Amount filtered – Amount reabsorbed

41. Plasma clearance rate
It is defined of the amount of blood cleaned of a
substance per unit time.
Clearance is a function of glomerular filtration,
secretion from the peritubular capillaries to the
nephron, and reabsorption from the nephron back
to the peritubular capillaries.

42. Finding plasma clearance rate
C = V x U/P
C = plasma clearance rate in ml/min
V =urine production rate in ml/min
U= concentration of a substance in urine in mg/ml
P= concentration of a substance in plasma in mg/ml
Units of plasma clearance rate: ml/min

44. Questions?

47. OSMOLARITY:
Osmolarity is the measure of solute concentration, defined
as the number of osmoles (Osm) of solute per liter (L) of
solution(osmol/L or Osm/L).
NOTE: Molarity measures the number of moles solute per
unit volume of solution,

48. Counter current Multiplier
Interstitial fluid should be
hypertonic for water to be
reabsorbed