The kidneys are paired organs located retroperitoneally that filter waste from the blood to form urine. Each kidney contains around 1 million functional filtration units called nephrons. The kidneys regulate fluid and electrolyte balance and excrete wastes via the urinary system. They have critical endocrine functions as well through the production of erythropoietin and the active form of vitamin D. The kidneys filter the blood, reabsorb necessary substances back into circulation, and excrete the remaining wastes and water as urine.

1. The Kidney
Dr. Farhana Mahfuz
Resident (MS Phase A)
Department of Gyne & Obs
SSMC Mitford hospital

2. Anatomy
• Kidneys are pair essential excretory organ which is a part of
the urinary system.
• Synonym : also call the Renes, from which have the
derivative renal.
• Situation : Retroperitoneally in the posterior abdominal wall by
the side of the vertebral column along the borders of
psoas muscles. Therefore, they are obliquely placed.
Kidneys occupy the epigastric, hypochondriac, lumbar
and umbilical region.

3. Location
• Vertically they extend from the Upper
border of the T12 To the centre of the
body of L3 vertebra .
• Right kidney is 1-2 cm lower than the
Left (due to position of liver).
• Left kidney is a slight longer and
narrower than right kidney.
• Transpyloric plane passes through upper
part of hilus of right kidney and lower
part of hilus of left kidney.

4. Measurements
• Size : Length : 10-12 cm
Breadth : 5-7.5 cm
Thickness: 2.5- 3 cm
• Weight : 125 to 170 gm (female 10-15 g less )
• Supports : 1. Perineral fat
2. Abdominal muscle tone
3. Renal vascular pedicle
4. General bulk of abdominal viscera
Variation of these factors permit variations in the degree of renal
mobility during different phases of respiration,body positon and
presence of anatomic anomalies.

5. External features
• Kidney has:
• 2 Poles – Upper & Lower
• 2 borders – Medial & lateral
• 2 surfaces – anterior & Posterior
• Hilum of Kidney:
• Following structures are seen in the
hilum from anterior to posterior-
• The renal vein
• The renal artery
• The renal Pelvis
• Posterior segmental artery

6. Supply
• Arterial supply by
Renal artery,
branches of
abdominal aorta
• Vein drain from
kidney through
renal vein to
Inferior vena cava

7. • Lymphatic drain into the lateral aortic node, occasionally retrocrural
nodes.Right renal lymphatic drainage primarily goes to right
interaortocaval and right paracaval lymph nodes,left lymphatic drainage
directly into the thoracic duct above the diaphragm.
• Nerve supply by renal plexus, an offshoot of coeliac plexus. It contains
sympathetic fibre ( T10 – L1). Sympathetic preganglionic nerves with
contributions mainly from coelic plexus and a lesser contributions from
greater splanchnic , intermesenteric and superior hypogastric
plexuses.Postganglionic sympathetic fibres travel to kidney via autonomic
plexus. In addition parasympathetic fibers from vagus nerve travel with
sympathetic fibers to autonomic plexus. Sympathetic causes
vasoconstriction and parasympathetic causes vasodilatation.

8. Covering of kidney
1. The fibrous capsule
2. The perirenal or perinephric fat
3. Renal fascia or fascia of Gerota.
It consists of anterior layer or
fascia of Told and a posterior
layer or fascia of Zuckerkandl
4. Pararenal Fascia

9. Relation
• Anterior relation

10. Posterior relationship

11. Structure of kidney
• (a)Naked eye examination of a coronal section section of the kidney
shows : (1) An outer cortex : Reddish brown in color
(2) An inner medulla: Pale in color
(3) A space : Renal sinus
Renal medulla : About 8-18 conical masses, called renal pyramids. Their
apices form renal papillae which indent the minor calices( 1 to 3 papillae
in each minor calyx).
Renal cortex : It is divided into 2 parts : (a) Cortical arches or lobules ,
(b) Renal columns of Bertin

12. • Renal sinus : It is cavity within
kidney and communicates
outside through the hilum. It
contains:
(i) Renal blood vessels, lymph
vessels and nerves
(ii)Perinehric fat
(iii) Excretory apparatus of
kidney which includes minor
(7-13) and major calyces (2-3)
and pelvis of ureter.

13. Histology
Each kidney is composed of 1 to 3 million uriniferous tubules.
Each tubule consists of 2 parts . These are-
• Secretory part : Called nephron. It is the structural and functional unit
of kidney. Each kidney has 0.4 to 1.2 million nephron.
It comprises: (i) Renal or Malpighian corpuscle (for filtration of
substances from the plasma). It is made up of Glomerulus
and Bowman’s capsule
(ii) Renal tubule(For selective resorption of substances from
glomerular filtrate) : It is made up of PCT, LH , DCT

14. • Collecting tubule(excretory
part): It begins as a junctional
tubule.
Many tubules unite together to
form ducts of Bellini (16 to 20
or more)which open into minor
calices through renal papillae.

15. Lining epithelium
Glomerular capillaries : Simple squamous epithelium
• Bowman’s capsule : Parietal layer: Simple squamous epithelium
Visceral layer: Podocytes
• PCT & DCT : Cuboidal epithelium with a brush border of tall microvilli
• LH : Thin segment: Low cuboidal to squamous epithelium
Thick segment: Cuboidal epithelium
• CD : Simple cuboidal or columnar epithelium

16. Embryology
• The nephric system develops progressively as 3 distinct entities:
(a) Pronephros ]- Temporary kidney (degenerate)
(b)Mesonephros ]- Temporary kidney (degenerates)
(c)Metanephros ]- Permanent kidney.
Pronephros: It is the earliest nephric stage, extends from cranio-caudal
direction and disappears completely by the 4th weeks of embryonic life.
Mesonephros: It is the principal excretory organ during early embryonic life
(4-8 weeks).Then it gradually degenerates and its ductal system becomes
associated with male reproductive organs.

17. • Metanephros: It appears last in lumbo-sacral region. It consists of 2
parts:
(I) Collecting parts : From ureteric bud or diverticulum develops-
(a)Major calyces,
(b)Minor calyces
(c) pelvis of ureter

18. • Secretory part: From metanephric mesoderm or metanephric
blastemal develops-
(a) Renal glomerulus
(b) Bowman’s capsule
(c) PCT
(d) LH
(e) DCT

20. Physiology of kidney
Functions:
• Formation of urine in nephron by – 1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion
• Regulation of water,electrolyte and acid base balance
• Regulation of body fluid osmolarity
• Excretory function: It excretes metabolic waste products (ammonia,urea,
uric acid,creatinine), toxic substances, foreign bodies
(drugs, pigments)

21. • Endocrine function : Formation of 1,25 (OH)2 D3 under the influence
of PTH hormone
• Metabolic function : Transamination and deamination of AAs,
Gluconeogenesis

22. Juxtaglomerular apparatus
• It is a combination of specialized tubular and vascular cells, located at
the vascular pole where the afferent and efferent arteriole enter and
leave the glomerulus.
• Types of cells : Their location
JG cells : Afferent arterole and efferent arteriole
Macula densa : Distal tubule
• Lacis cells/cells of polkinson: Junctions of outer layers of afferent and
efferent arterioles

23. Functions of JGA
• Formation of erythropoietin in response to hypoxia, which stimulates
erythropoiesis
Secretion of renin which converts angiotensinogen to angiotensin –I,
thus regulation of blood pressure
It controls GFR
It controls blood flow to the nephron

24. GFR(Glomerular filtration rate)
• The quantity of glomerular filtrate formed per minute by all the functioning
nephrons of both kidneys is alled glomerular filtration rate.
• Normal value:125ml/min. or 7.5 L/hr or 180L/day (less than 10% in women).
• Due to effective filtration pressure (10 mm Hg) glomerular filtrate is formed through
glomerular membrane.
• Factors affecting GFR:
1.Glomerular hydrostatic pressure: 60 mm Hg
2.Glomerular colloidal osmotic pressure: 32 mm Hg
3. Bowman’s capsule hydrostatic pressure: 18 mm Hg
4. Renal blood flow
5. Arterial pressure and size of capillary bed

25. • Permeability of glomerular capillary
• Glomerular filtration co-efficient(Kf)
• Sympathetic stimulation
• Constriction of afferent and efferent arteriole
• Effects of hormones: Vasoconstrictor hormones: Catecholamines,
Angiotensin-II, Adenosine,
Vasodilator agents: Prostaglandins, Bradykinin

26. Tubular reabsorption:
• In PCT : 60-70% of glomerular filtrate is reabsorbed.
Water ,glucose,AAs,vitamins,electrolytes are reabsorbed
completely.
The fluid remains isotonic to plasma.
25-30% glomerular fitrate remains.
• In DL of LH : Reabsorption of water and Na+ takes place.
Filtrate is hypertonic to plasma.
20% of glomerular filtrate remains.

27. • In AL of LH : Only Na+ reabsorption takes place.
Fluid remains hypotonic to plasma.
In CT : Reabsorption of Na+ due to aldosterone and water due
to ADH.
The filtrate remains hypertonic.
Only 1% filtrate passes as urine.

28. • Tubular secretion:
• In PCT : H+, K+,NH4+ is secreted.
• In DL of LH: Na+ by passive diffusion.
• AL of LH : Urea and H+ by passive diffusion.
• DCT : NH4+ secretion by diffusion. K+ and H+ secretion by
exchange pump.
• In CT : Secretion of K+ and NH3 by exchange pump with the help
of aldosterone.

29. • Urine formation: (a) Kidney forms dilute urine(Volume about 20L/day
or 16 ml/min. and osmolarity about 50 mosm/L) in
the absence of ADH,when body fluid osmolarity is
decreased.
(b) When body fluid volume is decreased, kidney
forms concentrated urine to conserve water and
regulate water, electrolyte balance.

30. Basic requirements for forming concentrated urine:
• (A) A high level of ADH: In DCT,CT and CD
• (B) A high osmolarity of medullary interstitial fluid: It is produced and
maintained by counter current mechanism.
Counter current mechanism is a system in which the inflow runs
parallel to, counter to and close proximity to the outflow for some
distance. It occurs in both the loops of henle(counter current multipler)
and ‘U’ shaped vasa recta in renal medulla(counter current exchanger).