structure and function of kidney and renal circulation

1. Structure and function
of kidney &
Renal circulation
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
R.D. Gardi Medical College, Ujjain, Madhya Pradesh.
Email: dr.goothy@gmail.com

2. The student should be able to
Describe the structure and function of the kidney
Describe the structure and function of the Juxta Glomerular apparatus
Explain the physiological and clinical significance of the renin-angiotensin
system
Explain special features of renal circulation

3. Introduction
Metabolic waste products are generated continuously in the body.
They have to be excreted out to prevent their accumulation.
Urinary system is responsible for
1. Formation
2. Storage
3. Expulsion of urine through which water-soluble wastes are excreted.

4. Urinary system
The urinary system consists of
1. Kidney
2. Ureters
3. Urinary bladder
4. Urethra
Kidney is the primary excretory organ

6. Functions of kidney
Excretory functions
1. Excretes waste water-soluble metabolic products like urea, uric acid,
creatinine, ammonium chloride, urobilinogen, etc.
2. Some drugs and environmental toxins consumed are also excreted into the
urine
3. In Diabetes mellitus, glucose is excreted in the urine

7. Functions of kidney
Non-excretory functions
1. Regulation of blood electrolytes
2. Regulates levels of several electrolytes and ions like sodium, potassium,
calcium, chloride and phosphates.

8. Functions of kidney
Non-excretory functions
1. Regulation of blood pH
2. Acid-base balance
3. Excretes variable amount of hydrogen into the urine
4. Conserves bicarbonate ions

9. Functions of kidney
Non-excretory functions
1. Regulation of blood volume
2. By conserving or eliminating water in the urine.
3. Changes in blood volume affects blood pressure.

10. Functions of kidney
Non-excretory functions
1. Regulation of blood pressure
2. Adjust the level of blood volume which in turn influences B.P.
3. Secretes renin
4. Renin activates renin-angiotensin-aldosterone system
5. This system increases blood pressure

11. Functions of kidney
Non-excretory functions
1. Maintain blood osmolality
2. Regulates levels of solutes in the blood
3. Regulates the water content of the blood
4. Kidney maintains blood osmolality of around 290 milliosmoles

12. Functions of kidney
Non-excretory functions
1. Kidney produces hormones
2. 1,25(OH) cholecalciferol (calcitriol) – regulates the blood calcium level
3. Erythropoietin- regulates the production of RBC
4. Renin- activates renin-angiotensin-aldosterone system
5. Bradykinin and prostaglandins- regulate B.P
6. Thrombopoietin- regulates platelets production

13. Functions of kidney
Non-excretory functions
1. Detoxification
2. Detoxifies toxic substances
3. Excretes them in urine

14. If 75% of renal tissue removed??
After the loss of one kidney, the left-out kidney produces a renal growth
factor which increases the size of glomeruli and length of the nephron
causing the increase in the size of the kidney.

15. Structure of kidney
Two kidneys are situated in the abdominal cavity.
Each kidney weighs about 150 grams.
Bean shaped
Left kidney is placed slightly higher level than the right kidney
Longitudinal slit in the middle third of medial border- hilum/hilus
Renal artery and nerves enter, renal vein, lymphatics and ureter leave the kidney
through the hilum.
Hilum leads to a wide space called the renal pelvis.
Pelvis continues as ureter.

17. Structure of kidney
Pelvis divides into the calyceal system
Each kidney contains 8-10 calyces
The space between two calyces is called a pyramid
Pyramid contains numerous pores- papillae
Ducts of Bellini drain the urine through these pores into the calyx and then
into the pelvis
The ducts of Bellini are formed by collecting ducts
In the LS section, the kidney shows an outer cortex and inner medulla

18. Nephron
Functional and anatomical unit of the kidney
Each kidney has 1-1.5 million nephrons
The length of the nephron varies from 45-65mm
Parts of the nephron
1. Renal of malphigian corpuscles
2. Proximal convoluted tubule (PCT)
3. Loop of Henle (LH)
4. Distal convoluted tubule (DCT)
5. Collecting duct (CD)

20. Renal or malphigian corpuscle
Consist of Bowman’s capsule, Glomerulus
Present in the cortex
Blind cup like the beginning of the nephron is called Bowman’s capsule
It consists of squamous epithelial cells
The parietal layer of BC is continuous with PCT
The visceral layer epithelium is in close contact with the glomerulus
The whole membrane consists of capillary endothelial layer, basal lamina, an
epithelial cell layer

21. Renal or malphigian corpuscle
There are pores in between endothelial cells (70-90 nm)
The epithelial cell layer has pores (25 nm)
The basal lamina prevents filtration of proteins

22. Renal or malphigian corpuscle
Glomerulus
Afferent arteriole divides and forms a tuft of capillaries called the glomerulus
These occupy the space of Bowman’s capsule
The capillaries join and form the efferent arterioles
Glomerular capillaries are 50 times more permeable than capillaries in the
skeletal muscle

24. PCT
Continues down as LH
Lined by cuboidal epithelium
Luminous surface shows numerous microvilli giving brush border appearance
The microvilli increase the surface area for absorption
On luminal side tight junction
Basolateral space- most of the substances absorbed into this space and then
to the peritubular capillary blood

26. LH
Descending limb – Thick and thin parts
Transverse limb
Ascending limb – Thin and thick parts
Thick descending limb is similar to PCT
Thick ascending limb is similar to DCT
LH is arranged like hairpin
Lined by flattened epithelial cells

27. DCT
Lined by cuboidal epithelial cells
Resembles like cells of PCT
But few microvilli
No brush border
Two parts
1. Early DCT/ diluting segment
2. Late DCT

28. Early DCT
Sodium, chloride absorbed
Water not absorbed
Causes dilution of fluid

29. Early DCT
Sodium, chloride absorbed
Water not absorbed
Causes dilution of fluid

30. Late DCT & Cortical collecting duct
Both have similar functional characteristics
Made up of two types of cells
Principal cells (P cells) – absorption of sodium and water and secretion of
potassium
Intercalated cells (I Cells)- H+ secretion and HCO3- and K+ absorption

32. Juxtaglomerular apparatus
JG Apparatus is present at the point of contact of DCT with afferent and
efferent arteriole of the same NEPHRON
Three types of cells
Juxtaglomerular cells (JG cells)
Macula densa cells (MD)
Mesangial or Lacis cells

33. Juxtaglomerular apparatus

34. Juxtaglomerular cells
Modified smooth muscle cells of afferent arteriole present at its contact with DCT
They synthesize, and store proteolytic enzyme- Renin
Innervated by sympathetic nerves
Acts as baro receptors
Respond to hypovolemia and decrease the renal perfusion pressure
Renin act on angiotensinogen and convert it to angiotensin I
Angiotension I converts to Angiotensin II in the lungs by ACE
Angiotensin II is a powerful vasoconstrictor

35. Functions of Angiotensin II
Powerful vasoconstrictor than nor epinephrine
Stimulates aldosterone secretion
Stimulates ACTH secretion
Increase release of norepinephrine
Increase BP
Increase water intake
Increase ADH secretion
Increase sodium, and chloride absorption

36. Macula Densa cells
Specialized tubular epithelial cells
Located at the beginning of DCT at its contact with mesangial cells
Act as chemoreceptors
Detects change in the concentration of sodium and chloride of the luminal
fluid of the tubule
Influence renin release from JG cells

37. Mesangial cells or Lacis cells
Supporting cells of JGA
Two types
Glomerular mesangial cells – present between the loops of the glomerulus
Extra glomerular mesangial cells – present between the glomerulus and
tubule

38. Applied Physiology
Renin-Angiotensin system is implicated in the genesis of hypertension
Drugs that block the action of RAS are used in the treatment of hypertension
(ACE inhibitors)
Two types of nephrons
1. Cortical nephrons
2. Juxtamedullary nephrons

40. Renal blood flow
Arterial blood supply
Each kidney is supplied by a renal artery
It is a branch of the abdominal aorta
On entering the kidney, it divides into branches and passes between the pyramids –
interlobar arteries
The interlobar arteries finally give rise to the afferent arterioles
Afferent arterioles divide into a tuft of capillaries – glomerulus
These in turn join and form efferent arteriole
EA in cortical nephrons forms- peritubular capillary plexus
EA in juxta medullary nephrons gives vasarecta

41. Renal blood flow
Venous drainage
Stellate veins
Interlobular veins
Arcuate veins
Interlobar vein
Renal vein
Inferior vena cava

42. Special features of renal circulation
Portal Circulation
Vein is interposed between capillaries
Venous portal system
In the kidney it is an arterial portal system
Arteriole is interposed between the capillaries
Glomerulus – EA- Peritubular capillaries/ vasa recta

43. Special features of renal circulation
High pressure in the glomerulus
Renal artery is a direct branch of the abdominal aorta
The pressure in the glomerular capillaries is 45 mmHg
Much higher compared to systemic capillary pressure 30mmHg
This high pressure and high permeability is responsible for the formation of
filtrate

44. Special features of renal circulation
High permeability
Glomerulus is 50 times more permeable than capillaries in skeletal muscle

45. Special features of renal circulation
Three types of capillaries
Glomerulus – Tuft of capillaries present in the Bowman’s capsule.
Peritubular capillary plexus
Vasa recta

46. Special features of renal circulation
Autoregulation
Kidneys regulate their own blood flow
Blood flow is maintained constant between the mean systemic pressure of
80-180 mmHg

47. Special features of renal circulation
High renal blood flow
RBF per minute is 1250 ml
25% of cardiac output
Highest blood flow when compared to other organs (except lungs)

48. Special features of renal circulation
Oxygen consumption
6mL/100g/min
Second to heart (8mL/100g/min)