3. Functions of kidney
Urine formation and excretion of waste products
Regulation of ECF volume
Regulation of blood pressure (BP)
Regulation of electrolyte composition of body fluids
Acid-base balance
Regulation of plasma osmolality
Regulation of erythropoiesis
Endocrine functions
Gluconeogenesis
4. Functional Anatomy
1. Gross anatomy
External features
Gross internal structure
2. Microscopic structure of kidney
Structure of nephron
Types on nephron
7. Microscopic structure of kidney
Microscopically, the cortex and medulla of the kidney are composed of nephrons,
blood vessels, lymphatics and nerves
Structure of nephron
Types of nephrons
JGA
10. Proximal tubule
Has 2 parts
Microvilli on apical
surface
Infoldings on basolateral
membrane
Lateral surface have
tight interdigitations
Many mitochondria and
Golgi complex.
The villi and
interdigitations go on
decreasing as they go
down from pars
convolute to pars recta.
11. Loop of Henle
3 parts in JMN
2 parts in cortical nephrons
Thin limb and thick limb
In JMN, thin limb has descending and
ascending parts.
The epithelial cells are flat with relatively
smooth apical and basolateral membranes in
thin limb
In thick limb epithelial cells are small and
cuboidal.
The basolateral membrane of cells has extensive
infoldings.
The luminal surface of cells has less infoldings.
Cells contain numerous mitochondria that are
mainly located toward basal part
Macula densa
12. Distal convoluted tubule
The distal convoluted tubule
(DCT) begins immediately after
the macula densa
Some what larger cells when
compared to thick ascending
limb.
Though, DCT is relatively
impermeable to water,
hormones like aldosterone and
ADH facilitate its absorption in
this segment
13. Connecting segment
The DCT empties into collecting duct through the
connecting segment or tubule.
This is a small and relatively straight tubule with
morphological and transport characteristics similar
to that of collecting duct
14. Collecting duct
It passes through the cortex and medulla
2 parts
Again Medullary collecting duct is divided
into outer and inner.
The epithelial cells of collecting duct are
modified to participate in transport of ions
and water.
The water permeability is controlled mainly
by ADH whereas Na+ transport is controlled
by aldosterone
Epithelial cells are cuboidal with minimal
infoldings of basolateral and apical
membrane
Contains P cells and I cells
Further down no of P and I cells decrease
and near papilla, they coalesce and become
taller cells.
16. Secretory cells of kidney
The secretory or endocrine cells in kidney are mainly two types:
1. Juxtaglomerular (JG cells) cells: JG cells secrete renin that activates renin-angiotensin
system.
2. Interstitial cells (IS cells): Three are two types of interstitial cells: cortical and
medullary.
i. Cortical interstitial cells are of two types: Phagocytic and fibroblast-like cells.
Fibroblast-like cells (peritubular interstitial cells) secrete erythropoietin.
ii. Medullary interstitial cells are of two types: type-I and type-II. Type-I medullary
interstitial cells secrete prostaglandins, especially PGE2.
20. Functions
Regulation of renal blood flow and filtration rate
(Tuberoglomerular feedback mechanism)
Maintenance of Na+ balance & ECV (RAS(Renin angiotensin
system))
Secretion of Erythropoietin
21. Maintenance of Na+ balance & ECV RAS(Renin
angiotensin system)
↓ Systemic blood
pressure (sympathetic
effect on JGA)
↓ Renal perfusion
pressure (renal
baroreceptor)
↓ NaCl concentration at
macula densa (NaCl
sensor)
Renin release from
granular cells
Angiotensinogen→ANG I→ANG
II
Hypothalamus→thirst
and AVP
Adrenal
gland→aldosterone
↓Na+ & water excretion
from kidneys
↓ECV
22. Secretion of Erythropoietin
Renal tissue hypoxia
Release of HIF-I
Binding to HRE element
of erythropoietin gene
↑Synthesis of
erythropoietin
↑Erythropoiesis
23. Innervation of kidney
Parasympathetic innervation is by Vagus nerve, but its function is uncertain
Sympathetic innervation. Pre-ganglionic sympathetic fibers arise from the
neurons of lower thoracic and upper lumbar (T10–L2) intermediolateral segments
of spinal cord.
The cell bodies of the post-ganglionic neurons are located in the ganglia of
sympathetic chain and superior mesenteric ganglion.
The fibers from these neurons are carried by the renal nerves, which travel along
the renal blood vessels as they enter the kidney.
The efferent fibers are mainly distributed to afferent and efferent arterioles, cells of
renal tubule and also to JG cells.
Afferents run along with the efferent fibers and enter in the spinal cord through
the thoracic and upper lumbar dorsal roots.
24. Renal blood flow
Kidneys receive about 23.5% of the cardiac output though they constitute less than
0.5% of the total body weight.
The blood flow to kidneys is about 1260 mL/min or 420 mL/100 g of tissue/min.
Thus, blood flow per unit weight of the kidney tissue is much more in comparison
to other organs.
26. In the medulla of kidney, blood supply is derived from efferent arteriole of
juxtamedullary glomeruli.
These efferent arterioles in juxtaglomerular nephrons, in addition to formation of
peritubular capillaries, form an extra set of capillaries called vasa recta
there are descending and ascending limbs of vasa recta that remain in close contact
with each other.
This arrangement of vasa recta helps it to function as the counter exchanger in urine
concentrating mechanism
Functions of vasarecta
1. It provides oxygen and nutrients to the nephron segments.
2. It delivers substances to the nephron for secretion into the tubular lumen.
3. It serves as a pathway for the return of reabsorbed water and solutes to the
circulatory system.
4. It participates in concentration (as counter current exchange) and dilution of urine
27. Importance of Renal Blood Flow (RBF)
1. Supplies oxygen, nutrients, and hormones that control kidney functions.
2. Delivers metabolites and waste products to the kidney for their excretion in the
urine.
3. Controls concentration and dilution of urine.
4. Influences solute and water reabsorption from kidney.
5. Determines GFR (RBF is the main determinant of GFR)
28. Oxygen Consumption of Kidneys
The oxygen consumption by kidneys per unit tissue (6 mL per 100 g of tissue per min) is more
than other metabolically active organs like
liver (2 mL per 100 g of tissue per min) and brain (3.3 mL per 100 g of tissue per min).
Its is second only to Myocardium(8ml/100mg tissue).
A greater blood flow to kidneys (23.5% of the cardiac output) ensures a higher oxygen supply
to the organs.
The oxygen consumption by kidneys as a whole is much less, which is about 18 mL per min, in
comparison to
52 mL per min for liver,
50 mL per min for skeletal muscles,
45 mL per min for brain and 30 mL per min for heart
In spite of adequate oxygen supply to kidneys, damage to renal tissues occurs in hypoxic
conditions as in shock as most of the blood is shunted from capillaries to venules.
29. Regulation of Renal blood flow
The regulatory mechanisms affect the renal
blood flow (RBF) and glomerular filtration
rate (GFR) by changing the arteriolar
resistance
1. Constriction of afferent arteriole decreases
both RBF and GFR without change in the
filtration fraction (FF).
2. Dilatation of the afferent arteriole increases
both RBF and GFR without change in the
(FF) .
3. Constriction of the efferent arteriole
decreases the RBF and increases GFR and
(FF).
4. Dilatation of the efferent arteriole increases
the RBF and decreases the GFR and (FF).
31. Autoregulation
The RBF and thus the GFR remain constant over a
wide range of renal arterial pressures (80–200 mm
Hg)
2 mechanisms, Myogenic mechanism and
Tubuloglomerular feed back mechanism.
1. Myogenic - When renal arterial pressure is raised,
the afferent arterioles are stretched, which contract
and increase the vascular resistance.
32. Tubuloglomerular feedback mechanism
↑ Renal arterial
pressure
↓ Renal arterial
pressure
↑ GFR ↑ RBF ↓ GFR ↓ RBF
↑ NaCl in
tubular fluid
Sensed by
macula
densa cells
Constriction of afferent
arteriole
↓ NaCl in
tubular fluid
Sensed by
macula
densa cells
Dilation of afferent
arteriole
34. Nervous regulation
Under normal circulatory conditions, sympathetic tone is minimum.
Mild-to-moderate stimulation of sympathetic nerves usually has mild effects on
RBF because of autoregulation mechanism.
Strong acute stimulation of sympathetic nerves may produce marked fall in RBF
(even to 10−30% of normal) temporarily due to constriction of both afferent and
efferent arterioles. This effect is mediated mainly by α1-adrenergic receptors
sympathetic stimulation to kidneys stimulate the production of local
prostaglandins (PG E2 and I2) that produce vasodilation and oppose the
vasoconstriction effects.
