Excretory system

1. • Formation of urine:
It is the primary function of kidneys and helps in
homeostasis.
• Excretion of Metabolic Wastes:
• Nitrogenous waste products such as urea,
Creatinine,Uric acid, Bilirubin
• Harmful foreign chemical substances like toxins,
drugs, heavy metals, pesticides etc.
• Products of metabolism of other substances
• Regulation of water balance:
Kidneys maintain water balance in the body by
conserving water when it is decreased and excreting
water when it is in excess in the body
• Formation of urine:
It is the primary function of kidneys and helps in
homeostasis.
• Excretion of Metabolic Wastes:
• Nitrogenous waste products such as urea,
Creatinine,Uric acid, Bilirubin
• Harmful foreign chemical substances like toxins,
drugs, heavy metals, pesticides etc.
• Products of metabolism of other substances
• Regulation of water balance:
Kidneys maintain water balance in the body by
conserving water when it is decreased and excreting
water when it is in excess in the body
FUNCTIONS OF KIDNEYS

2. • Regulation of electrolyte balance:
Kidneys retain sodium if the osmolarity of body water
decreases and eliminate sodium when osmolarity increases.
• Regulation of arterial blood pressure
Kidneys play an important role in long term regulation of
arterial blood pressure by two ways; by regulating ECF volume
and through renin angiotensin system
• Regulation of acid base balance:
Maintenance of pH of blood and body fluids within normal
limits is the function of kidneys.
• Regulation of blood calcium level
• Regulation of calcium level by activation of vitamin D,
which is necessary for intestinal absorption of calcium
• Regulation of electrolyte balance:
Kidneys retain sodium if the osmolarity of body water
decreases and eliminate sodium when osmolarity increases.
• Regulation of arterial blood pressure
Kidneys play an important role in long term regulation of
arterial blood pressure by two ways; by regulating ECF volume
and through renin angiotensin system
• Regulation of acid base balance:
Maintenance of pH of blood and body fluids within normal
limits is the function of kidneys.
• Regulation of blood calcium level
• Regulation of calcium level by activation of vitamin D,
which is necessary for intestinal absorption of calcium

3. • Endocrine function i.e. secretion of hormones:
I. Release of renin
II. Release of prostaglandins
III. Release of erythropoietin (stimulates RBC
production)
IV. Activation of vitamin D produced by the skin
• Endocrine function i.e. secretion of hormones:
I. Release of renin
II. Release of prostaglandins
III. Release of erythropoietin (stimulates RBC
production)
IV. Activation of vitamin D produced by the skin
• Hemopoietic function:
I. Kidneys stimulate the production of erythrocytes or
erythropoiesis by secreting erythropoietin.
II. Kidneys also secrete another hormone
thrombopoietin, which stimulates Thrombopoiesis.
• Hemopoietic function:
I. Kidneys stimulate the production of erythrocytes or
erythropoiesis by secreting erythropoietin.
II. Kidneys also secrete another hormone
thrombopoietin, which stimulates Thrombopoiesis.

7. • Each kidney contains
approximately 1 million
nephrons.
• Each nephron begins with a
spherical filtering
component, called the renal
corpuscle, followed by a long
tubule leading out of it that
continues until it merges
with the tubules of other
nephrons to form collecting
ducts, which are themselves
long tubes.
• Collecting ducts eventually
merge with others in the
renal papilla to form a ureter
that conveys urine to the
bladder.

8. Cortical and Juxtamedullary Nephrons

9. CORTICAL NEPHRONS JUXTAMEDULLARY NEPHRONS
85 %
Small sized glomeruli located in
the renal cortex
Short loops of Henle
The descending loop of Henle
contain a thin segment where as
ascending limb contains a thick
segment
Blood supply to tubules are by
peritubular capillaries
Filtration rate slow
Excretion of waste or formation
of urine
• 15 %
• Large glomeruli located at the
junction of the cortex and the
medulla
• Long loops of Henle
• Both the descending and
ascending limbs of loop of
Henle contain thin segments
• Blood supply through vasa
recta
• High
• Counter current mechanism
for the concentration of urine.
Also urine formation

10. RENAL CORPUSCLE
• The renal corpuscle is a hollow sphere (Bowman’s capsule) filled
with a compact tuft of interconnected capillary loops, the
glomerulus
• The function of renal corpuscle is filtration of blood which forms
first phase of urine formation
• Is formed of two parts;
1. Glomerulus
2. Bowman‘s capsule
RENAL CORPUSCLE
• The renal corpuscle is a hollow sphere (Bowman’s capsule) filled
with a compact tuft of interconnected capillary loops, the
glomerulus
• The function of renal corpuscle is filtration of blood which forms
first phase of urine formation
• Is formed of two parts;
1. Glomerulus
2. Bowman‘s capsule

11. GLOMERULUS
• Is a rounded tuft of capillaries enclosed by bowman’s capsule
• Blood enters the capillaries inside Bowman’s capsule through an
afferent arteriole that penetrates the surface of the capsule at
one side, called the vascular pole.
• Blood then leaves the capillaries through a nearby efferent
arteriole on the same side.
• The diameter of efferent arteriole is less than that of afferent
arteriole
• The capillaries are made up of single layer of endothelial cells
• Another cell type—the mesangial cell—is found in close
association with the capillary loops of the glomerulus.
Glomerular mesangial cells act as phagocytes.
• They also contain large numbers of myofilaments and can
contract in response to a variety of stimuli
GLOMERULUS
• Is a rounded tuft of capillaries enclosed by bowman’s capsule
• Blood enters the capillaries inside Bowman’s capsule through an
afferent arteriole that penetrates the surface of the capsule at
one side, called the vascular pole.
• Blood then leaves the capillaries through a nearby efferent
arteriole on the same side.
• The diameter of efferent arteriole is less than that of afferent
arteriole
• The capillaries are made up of single layer of endothelial cells
• Another cell type—the mesangial cell—is found in close
association with the capillary loops of the glomerulus.
Glomerular mesangial cells act as phagocytes.
• They also contain large numbers of myofilaments and can
contract in response to a variety of stimuli

12. BOWMAN’S CAPSULE
• It encloses the glomerulus
• It is formed of two layers; inner visceral layer and outer
parietal layer
• Visceral layer covers the glomerular capillaries and is
continued as the parietal layer at the visceral pole.
• Parietal layer is continued with the wall of tubular portion
of nephron.
• The space within Bowman’s capsule not occupied by the
glomerulus is called the urinary space or Bowman’s space,
and it is into this space that fluid filters from the
glomerular capillaries. It is continued as the lumen of the
tubular portion.
• Both the layers of bowman's capsule are composed of a single
layer of epithelial cells resting on a basement membrane
BOWMAN’S CAPSULE
• It encloses the glomerulus
• It is formed of two layers; inner visceral layer and outer
parietal layer
• Visceral layer covers the glomerular capillaries and is
continued as the parietal layer at the visceral pole.
• Parietal layer is continued with the wall of tubular portion
of nephron.
• The space within Bowman’s capsule not occupied by the
glomerulus is called the urinary space or Bowman’s space,
and it is into this space that fluid filters from the
glomerular capillaries. It is continued as the lumen of the
tubular portion.
• Both the layers of bowman's capsule are composed of a single
layer of epithelial cells resting on a basement membrane

13. • The proximal tubule, which drains Bowman’s capsule, consists of a
coiled segment, the proximal convoluted tubule (pars convoluta)
followed by a straight segment, the proximal straight tubule (pars
recta) which descends toward the medulla, perpendicular to the
cortical surface of the kidney.
• Made up of single layer of cuboidal epithelial cells
• Apical membrane contain microvilli or hair like projections
directed towards the lumen of the tubule, hence called brush
bordered epithelium
• About 75% of sodium is removed from fluid here (by active
transport, chloride follows passively.
• The proximal tubule, which drains Bowman’s capsule, consists of a
coiled segment, the proximal convoluted tubule (pars convoluta)
followed by a straight segment, the proximal straight tubule (pars
recta) which descends toward the medulla, perpendicular to the
cortical surface of the kidney.
• Made up of single layer of cuboidal epithelial cells
• Apical membrane contain microvilli or hair like projections
directed towards the lumen of the tubule, hence called brush
bordered epithelium
• About 75% of sodium is removed from fluid here (by active
transport, chloride follows passively.
PROXIMAL CONVOLUTED TUBULE

14. • The next segment is the descending thin limb of the loop of
Henle (or simply the descending thin limb).
• The descending thin limbs of different nephrons penetrate into
the medulla to varying depths, and then abruptly reverse at a
hairpin turn and begin an ascending portion of the loop of
Henle parallel to the descending portion.
• In long loops, the epithelium of the first portion of the
ascending limb remains thin. This segment is called the
ascending thin limb. Further up the ascending portion the
epithelium thickens, and this next segment is called the
thick ascending limb.
• In short loops, there is no ascending thin portion, and the
thick ascending portion begins right at the hairpin loop.
LOOP OF HENLE

15. • The thick ascending limb rises back into the cortex to the very
same Bowman’s capsule from which the tubule originated.
Here it passes directly between the afferent and efferent
arterioles at the point where they enter and exit the renal
corpuscle.
• The cells in the thick ascending limb closest to Bowman’s
capsule (between the afferent and efferent arterioles) are a
group of specialized cells known as the macula densa .
• LOOP OF HENLE: act as The counter current multiplier:
– Descending Loop Of Henle: Permeable to water and
other solute
– Ascending Loop Of Henle: Chloride ions--active
transport out. Sodium follows. Water does NOT.

16. • The macula densa marks the end of the thick ascending limb
and the beginning of the distal convoluted tubule.
• Made up of cuboidal epithelial cells which are larger(I cells) in
size and have extensive infoldings of basolateral membrane
without brush border.
• Responds to Aldosterone and ADH
• Distal convoluted tubule: NaCl, Potassium, ammonia,
carbonate removed here.
• The macula densa marks the end of the thick ascending limb
and the beginning of the distal convoluted tubule.
• Made up of cuboidal epithelial cells which are larger(I cells) in
size and have extensive infoldings of basolateral membrane
without brush border.
• Responds to Aldosterone and ADH
• Distal convoluted tubule: NaCl, Potassium, ammonia,
carbonate removed here.
DISTAL CONVOLUTED TUBULE

17. • DCT is followed by the connecting tubule, which leads to the
cortical collecting tubule.
• Connecting tubules from several nephrons merge to form
cortical collecting tubules, and a number of initial collecting
ducts.
• Seven to ten initial collecting ducts unite to form the straight
collecting duct.
• At the inner zone of medulla, the straight collecting duct from
each medullary pyramid unite to form papillary ducts or ducts
of Bellini, which opens in to papilla.
• Papilla collects urine from each medullary pyramid and drains
in to a minor calyx
• Three or four minor calyces unite to form major calyx
• Each kidney has about 8 minor calyces and 2 or 3 major calyces
• The major calyces open in to renal pelvis which is the expended
portion of ureter
• DCT is followed by the connecting tubule, which leads to the
cortical collecting tubule.
• Connecting tubules from several nephrons merge to form
cortical collecting tubules, and a number of initial collecting
ducts.
• Seven to ten initial collecting ducts unite to form the straight
collecting duct.
• At the inner zone of medulla, the straight collecting duct from
each medullary pyramid unite to form papillary ducts or ducts
of Bellini, which opens in to papilla.
• Papilla collects urine from each medullary pyramid and drains
in to a minor calyx
• Three or four minor calyces unite to form major calyx
• Each kidney has about 8 minor calyces and 2 or 3 major calyces
• The major calyces open in to renal pelvis which is the expended
portion of ureter
COLLECTING DUCT

18. It is made up of three types of cells
(1) Juxtaglomerular cells (granular cells),which are specialized
smooth muscle cells surrounding the afferent arteriole.
• The granular cells are named because they contain
secretory vesicles that appear granular. These granules
contain the hormone renin.
(2) Mesangial cells are of two types;
I. Extraglomerular mesangial cells are also called lacis cells
or agranular cells. These are situated in the triangular
region bound by afferent arteriole, efferent arteriole and
macula densa. Act as relay centre.
II. Intraglomerular mesangial cells or glomerular mesangial
cells are situated between the glomerular capillaries and
form a cellular network which supports capillary loops.
These cells are contractile in nature.
It is made up of three types of cells
(1) Juxtaglomerular cells (granular cells),which are specialized
smooth muscle cells surrounding the afferent arteriole.
• The granular cells are named because they contain
secretory vesicles that appear granular. These granules
contain the hormone renin.
(2) Mesangial cells are of two types;
I. Extraglomerular mesangial cells are also called lacis cells
or agranular cells. These are situated in the triangular
region bound by afferent arteriole, efferent arteriole and
macula densa. Act as relay centre.
II. Intraglomerular mesangial cells or glomerular mesangial
cells are situated between the glomerular capillaries and
form a cellular network which supports capillary loops.
These cells are contractile in nature.
JUXTAGLOMERULAR (JG) APPARATUS

19. (3) The macula densa is the terminal portion of thick
ascending segment of henle’s loop that runs in
between afferent and efferent arteriole.
• The macula densa cells are detectors of the
composition of the fluid within the nephron at the
very end of the thick ascending limb and contribute
to the control of glomerular filtration rate.

20. FUNCTIONS OF JGA
• JG cells act as baroreceptors and responds to changes in
transmural pressure gradient. JG cells also act as vascular volume
receptors and monitor renal perfusion pressure.
• Macula densa act as chemoreceptors and are stimulated by
decreased sodium chloride concentration.
• Mesangial or lacis cells are in contact with both macula densa and
JG cells and relay signals from macula densa to the JG cells.
• Secretion of renin by juxtaglomerular cells and helps in regulation
of BP and in turn RBF and GFR.
• Secretion of other substances i.e.
• Prostaglandins by extraglomerular mesangial cells
• In vitro secretion of cytokines like IL-2 and TNF by mesangial
cells
• Thromboxane A 2 by macula densa
FUNCTIONS OF JGA
• JG cells act as baroreceptors and responds to changes in
transmural pressure gradient. JG cells also act as vascular volume
receptors and monitor renal perfusion pressure.
• Macula densa act as chemoreceptors and are stimulated by
decreased sodium chloride concentration.
• Mesangial or lacis cells are in contact with both macula densa and
JG cells and relay signals from macula densa to the JG cells.
• Secretion of renin by juxtaglomerular cells and helps in regulation
of BP and in turn RBF and GFR.
• Secretion of other substances i.e.
• Prostaglandins by extraglomerular mesangial cells
• In vitro secretion of cytokines like IL-2 and TNF by mesangial
cells
• Thromboxane A 2 by macula densa

23. The juxtaglomerular cells secrete renin. When renin is
released in to the blood, it acts on angiotensinogen and
converts it in to angiotensin I and then in to angiotensin II.
Angiotensin II is short-lived and degrade in to angiotensin III
and then in to angiotensin IV.
Angiotensin II is the most active form. Its actions are;
1. Increases arterial blood pressure by causing
vasoconstriction
2. It stimulates secretion of aldosterone
3. Regulates glomerular filtration
4. Increases sodium reabsorption
5. Increases water intake by stimulating thirst centre
6. Increases secretion of ADH

24. RBF- REGULATION
• 1.2 – 1.3 Liters / min - 21% of CO
• AUTOREGULATION of RBF
– Intrinsic ability of renal blood flow to regulate its own
blood flow is called autoregulation.
– Autoregulation is also seen in other vital organs like
brain and heart. It is highly significant and effective in
kidneys only.
– It is important to maintain the GFR. Blood flow to
kidneys remains normal even when the mean arterial
pressure vary widely between 60 and 180 mm Hg.
RBF- REGULATION
• 1.2 – 1.3 Liters / min - 21% of CO
• AUTOREGULATION of RBF
– Intrinsic ability of renal blood flow to regulate its own
blood flow is called autoregulation.
– Autoregulation is also seen in other vital organs like
brain and heart. It is highly significant and effective in
kidneys only.
– It is important to maintain the GFR. Blood flow to
kidneys remains normal even when the mean arterial
pressure vary widely between 60 and 180 mm Hg.

25. TUBULO-GLOMERULAR FEEDBACK
• Macula densa plays an important role in tubulo-
glomerular feedback for controlling the RBF and GFR
• Macula densa act as a sensor and detects the
concentration of sodium chloride in the tubular fluid and
accordingly alters the glomerular blood flow and GFR.
TUBULO-GLOMERULAR FEEDBACK
• Macula densa plays an important role in tubulo-
glomerular feedback for controlling the RBF and GFR
• Macula densa act as a sensor and detects the
concentration of sodium chloride in the tubular fluid and
accordingly alters the glomerular blood flow and GFR.
– Two mechanisms are involved in renal autoregulation
• MYOGENIC MECHANISM OF AUTOREGULATION
• TUBULO-GLOMERULAR FEED BACK MECHANISM

26. • When sodium chloride concentration increases in the filtrate,
macula densa releases adenosine from ATP. It causes constriction
of afferent arteriole. So the blood flow decreases leading to
decrease in GFR.
• When sodium chloride concentration increases in the filtrate,
macula densa releases adenosine from ATP. It causes constriction
of afferent arteriole. So the blood flow decreases leading to
decrease in GFR.
• When sodium chloride concentration decreases, macula densa
secrete prostaglandin, bradykinin and renin.
• PGE2 and kinins cause dilatation of afferent arteriole.
• Renin causes angiotensin activation which causes constriction
of efferent arteriole.
• Both results in increase in RBF & GFR.
• When sodium chloride concentration decreases, macula densa
secrete prostaglandin, bradykinin and renin.
• PGE2 and kinins cause dilatation of afferent arteriole.
• Renin causes angiotensin activation which causes constriction
of efferent arteriole.
• Both results in increase in RBF & GFR.

27. • Whenever blood flow to kidney increases, it stretches the
elastic wall of the afferent arteriole.
• Stretching of vessel wall increases the flow of calcium ions
from ECF in to the cells
• The influx of calcium ions leads to the contraction of
smooth muscles of afferent arteriole which causes
constriction of afferent arteriole
• So the blood flow is decreased
• Whenever blood flow to kidney increases, it stretches the
elastic wall of the afferent arteriole.
• Stretching of vessel wall increases the flow of calcium ions
from ECF in to the cells
• The influx of calcium ions leads to the contraction of
smooth muscles of afferent arteriole which causes
constriction of afferent arteriole
• So the blood flow is decreased

28. Renal circulation
• Renal arteries arises directly from abdominal aorta and
enters the kidney through the hilus.
• The renal artery divides in to segmental arteries, interlobar
artery, arcuate artery, interlobular artery, afferent
arteriole, glomerular capillaries, efferent arteriole.
• The renal circulation forms a portal system by the presence
of two capillaries; glomerular capillaries and peritubular
capillaries or vasa recta.
• Peritubular capillaries and vasa recta drain in to venous
system. It start as peritubular venules and continues as
interlobular veins, arcuate veins, interlobar veins,
segmental veins and finally the renal vein. The renal vein
leaves the kidney through the hilus and joins inferior
venacava.

29. Special features
1. The renal arteries arise directly from the aorta, so the high
aortic pressure facilitatates high blood flow .
2. Receives 26% of cardiac output about 1300ml/minute
3. When blood passes through glomerular capillaries blood is
completely filtered.
4. High pressure is maintained in glomerular capillaries helps in
filtration. Low pressure in peritubular capillaries helps in
tubular reabsorption.
5. It has a portal system; glomerular capillaries and peritubular
capillaries.
6. Renal autoregulation is well developed.

30. Filtration Membrane

31. FILTRATION MEMBRANE
It is formed by three layers;
 The glomerular capillary membrane is formed by single layer
of endothelial cells which are attached to the basement
membrane. The capillary membrane has many pores called
fenestra or filtration pores. Allows water, small solutes but
proteins are not filtered.
 Basement membrane of glomerular capillaries fuses with the
basement membrane of visceral layer. Act as a barrier for the
protein
 Visceral layer of bowman’s capsule composed of single layer
of flattened epithelial cells resting on a basement membrane.
Each cell is connected with the basement membrane by
cytoplasmic extensions called pedicles or podocytes. The
pedicles are arranged in an interdigitating manner leaving
small cleft like spaces in between called slit pores. Filtration
occurs through these slit pores.
FILTRATION MEMBRANE
It is formed by three layers;
 The glomerular capillary membrane is formed by single layer
of endothelial cells which are attached to the basement
membrane. The capillary membrane has many pores called
fenestra or filtration pores. Allows water, small solutes but
proteins are not filtered.
 Basement membrane of glomerular capillaries fuses with the
basement membrane of visceral layer. Act as a barrier for the
protein
 Visceral layer of bowman’s capsule composed of single layer
of flattened epithelial cells resting on a basement membrane.
Each cell is connected with the basement membrane by
cytoplasmic extensions called pedicles or podocytes. The
pedicles are arranged in an interdigitating manner leaving
small cleft like spaces in between called slit pores. Filtration
occurs through these slit pores.

33. GLOMERULAR FILTRATION
• It is the process by which the blood that passes through
glomerular capillaries is filtered through filtration membrane
in to the bowman’s capsule.
• All the substances are filtered except plasma proteins. It is
because plasma proteins are larger than the slit pores
present in capillary endothelium.
• The filtered fluid is called glomerular filtrate.
• The rate at which glomerular filtration takes place is called
GFR.
• Glomerular filtration rate or GFR is defined as the total
quantity of filtrate formed in all nephrons of both the
kidneys in the given unit of time. The normal GFR is 125
ml/minute.

34. DETERMINANTS OF GFR
 The rate of filtration in all capillaries, including the
glomeruli, is determined by the hydraulic permeability of
the capillaries, their surface area, and the net filtration
pressure (NFP) acting across them, given as follows:
Rate of filtration = Hydraulic permeability × Surface area ×
NFP
 Because it is difficult to estimate the area of a capillary
bed, a parameter called the filtration coefficient (Kf) is
used to denote the product of the hydraulic permeability
and the area.
 The NFP is the algebraic sum of the hydrostatic pressures
and the osmotic pressures resulting from protein(the
oncotic, or colloid osmotic pressures)on the two sides of
the capillary wall.

35. • There are four pressures to consider: two hydrostatic
pressures and two oncotic pressures. These are the
Starling forces.
NPF = (PGC – PBC) – (πGC – πBC)
where PGC is glomerular capillary hydraulic pressure
(promotes filtration), πBC the oncotic pressure of fluid in
Bowman’s capsule (promotes filtration),, PBC the hydraulic
pressure in Bowman’s capsule (opposes filtration), and πGC
the oncotic pressure in glomerular capillary plasma(opposes
filtration).
• Because there is normally little total protein in Bowman’s
capsule, πBC may be taken as zero and not considered in
our analysis.
• Accordingly, the overall equation for GFR becomes:
GFR = Kf (PGC – PBC – πGC)

36. • The Kf is a measure of the product of the hydraulic conductivity
and surface area of the glomerular capillaries.
• The normal Kf is calculated to be about 12.5 ml/min/mm Hg of
filtration pressure
• The GFR can therefore be expressed as
GFR = Kf x (PGC – PBS – pGC + pBS)
Forces Favouring Filtration (mm Hg)
• Glomerular hydrostatic pressure= 60
• Bowman’s capsule colloid osmotic pressure = 0
Forces Opposing Filtration (mm Hg)
• Bowman’s capsule hydrostatic pressure =18
• Glomerular capillary colloid osmotic pressure= 32
Net filtration pressure = 60 – 18 – 32 = +10 mm Hg

38. FACTORS AFFECTING GFR
1. GFR is directly proportional to renal blood flow, glomerular
capillary pressure, surface area of capillary membrane,
permeability of capillary membrane.
2. GFR is inversely proportional to colloidal osmotic pressure
and hydrostatic pressure in bowman's capsule
3. Constriction of afferent arteriole reduces blood flow and in
turn decreases GFR
4. Constriction of efferent arteriole increases GFR initially due
to stagnation of blood and then declines
5. Tubuloglomerular feedback
6. Sympathetic stimulation causes initial increase and then
decreases.
7. Contraction of glomerular mesangial cells decreases
surface area of capillaries resulting in reduction in GFR
8. Hormonal or other factors: many hormones alter GFR
FACTORS AFFECTING GFR
1. GFR is directly proportional to renal blood flow, glomerular
capillary pressure, surface area of capillary membrane,
permeability of capillary membrane.
2. GFR is inversely proportional to colloidal osmotic pressure
and hydrostatic pressure in bowman's capsule
3. Constriction of afferent arteriole reduces blood flow and in
turn decreases GFR
4. Constriction of efferent arteriole increases GFR initially due
to stagnation of blood and then declines
5. Tubuloglomerular feedback
6. Sympathetic stimulation causes initial increase and then
decreases.
7. Contraction of glomerular mesangial cells decreases
surface area of capillaries resulting in reduction in GFR
8. Hormonal or other factors: many hormones alter GFR

39. FACTORS INCREASING GFR BY VASODILATION are
I. Natriuretic Peptide[ANP & BNP]
II. cAMP
III. Dopamine
IV. Endothelial derived nitric oxide
V. Prostaglandin E2
FACTORS DECREASING GFR BY VASOCONSTRICTION are
VI. Angiotensin II
VII. Endothelins
VIII.Noradrenaline
IX. Platelet activating factor
X. Platelet derived factor
XI. Prostaglandin F2
FACTORS INCREASING GFR BY VASODILATION are
I. Natriuretic Peptide[ANP & BNP]
II. cAMP
III. Dopamine
IV. Endothelial derived nitric oxide
V. Prostaglandin E2
FACTORS DECREASING GFR BY VASOCONSTRICTION are
VI. Angiotensin II
VII. Endothelins
VIII.Noradrenaline
IX. Platelet activating factor
X. Platelet derived factor
XI. Prostaglandin F2

40. TUBULAR REABSORPTION
• It is the process by which water and other substances are
transported from renal tubules back to the blood
• It is selective reabsorption
• Essential substances such as glucose, aminoacids and vitamins
are completely reabsorbed from renal tubule.
SITES OF REABSORPTION
 PCT: (about 88%) mainly glucose, aminoacids, sodium,
potassium, calcium, bicarbonates, chlorides, phosphates , uric
acid and water.
 Loop of Henle: Sodium and chloride
 DCT: Sodium, calcium, bicarbonate, and water
SITES OF REABSORPTION
 PCT: (about 88%) mainly glucose, aminoacids, sodium,
potassium, calcium, bicarbonates, chlorides, phosphates , uric
acid and water.
 Loop of Henle: Sodium and chloride
 DCT: Sodium, calcium, bicarbonate, and water

41. TUBULAR SECRETION
• It is the process by which the substances are transported from
blood in to renal tubules
• Substances secreted are
• Potassium is secreted actively by sodium potassium pump
in proximal and distal convoluted tubules and collecting
ducts
• Ammonia is secreted in the proximal convoluted tubules
• Hydrogen ions are secreted in the proximal and distal
convoluted tubules

42. MODIFICATION OF URINE
• Changes in concentration of urine : Either concentrated [if
water content in the body decreases] or dilute urine [for
excreting excess water]is formed.
• Acidification of urine is done [by excreting excess hydrogen
ions and retaining bicarbonate ions] for maintaining acid-
base balance
MODIFICATION OF URINE
• Changes in concentration of urine : Either concentrated [if
water content in the body decreases] or dilute urine [for
excreting excess water]is formed.
• Acidification of urine is done [by excreting excess hydrogen
ions and retaining bicarbonate ions] for maintaining acid-
base balance

43. Formation of DILUTE Urine
• Formation of dilute urine occurs when the fluid reaches DCT
• It occurs when there is excess of water in the body and
decreased osmolarity, which is achieved by inhibition of ADH
secretion.
• When volume of body fluid increases or osmolarity decreases,
ADH secretion stops. So water reabsorption from renal tubules
does not take place and leads to excretion of large amount of
water in urine making the urine dilute
Formation of DILUTE Urine
• Formation of dilute urine occurs when the fluid reaches DCT
• It occurs when there is excess of water in the body and
decreased osmolarity, which is achieved by inhibition of ADH
secretion.
• When volume of body fluid increases or osmolarity decreases,
ADH secretion stops. So water reabsorption from renal tubules
does not take place and leads to excretion of large amount of
water in urine making the urine dilute

44. Formation of concentrated urine
It involves two important processes ;
1. Medullary gradient
2. Secretion of ADH
Formation of concentrated urine
It involves two important processes ;
1. Medullary gradient
2. Secretion of ADH
• ADH is a hormone secreted by posterior pituitary in
response to either decreased body fluid volume or
increased sodium concentration. ADH increases the
water reabsorption from DCT & collecting duct resulting
in concentration of urine

45. Medullary gradient
• The osmolarity of cortical interstitial fluid is isotonic to
plasma i.e. 300 mOsm/L. The osmolarity of medullary
interstitial fluid near the cortex is 300 mOsm/L.
• It then increases gradually and reaches the maximum of 1200
mOsm/L at the innermost part of medulla near the renal
sinus.
• This type of gradual increase in the osmolarity of medullary
interstitial fluid is called medullary gradient.
• Maintenance of medullary gradient and hyperosmolarity of
interstitial fluid is done by countercurrent system.

46.  In kidneys, counter current system composed of
 Loop of Henle, act as counter current multiplier and is
responsible for production of hyperosmolarity and
medullary gradient
 Vasa recta, act as counter current exchanger ad is
responsible for the maintenance of medullary gradient and
hyperosmolarity.
 In kidneys, counter current system composed of
 Loop of Henle, act as counter current multiplier and is
responsible for production of hyperosmolarity and
medullary gradient
 Vasa recta, act as counter current exchanger ad is
responsible for the maintenance of medullary gradient and
hyperosmolarity.

47. Loop of Henle act as counter current multiplier
 Medullary gradient is developed by active reabsorption of sodium
chloride and other solutes from ascending limb of loop of Henle in
to medullary interstitium. These salts get accumulated in the
medullary interstitium and increase the osmolarity.
 Now due to concentration gradient the sodium and chloride ions
diffuse from medullary interstitium into descending limb of
henle's loop.
 Sodium and chloride ions are repeatedly recirculated between
ascending and descending limb.
 In addition more and more new sodium and chloride ions are
added by constant filtration.
Loop of Henle act as counter current multiplier
 Medullary gradient is developed by active reabsorption of sodium
chloride and other solutes from ascending limb of loop of Henle in
to medullary interstitium. These salts get accumulated in the
medullary interstitium and increase the osmolarity.
 Now due to concentration gradient the sodium and chloride ions
diffuse from medullary interstitium into descending limb of
henle's loop.
 Sodium and chloride ions are repeatedly recirculated between
ascending and descending limb.
 In addition more and more new sodium and chloride ions are
added by constant filtration.

48. Vasa recta act as counter current exchanger
• It runs parallel to loop of Henle.
• Sodium chloride reabsorbed from ascending limb of henle's loop
enters medullary interstitium. From here it enters the
descending limb of vasa recta
• Simultaneously water diffuses from descending limb of vasa
recta.
• The blood flows very slowly through vasa recta. So a large
quantity of sodium chloride accumulates in descending limb of
vasa recta and flows slowly towards ascending limb of vasa recta
• Increase in sodium chloride concentration causes diffusion of
sodium chloride in to medullary interstitium
• Water from medullary interstitium enters ascending limb and
cycle is repeated.
Vasa recta act as counter current exchanger
• It runs parallel to loop of Henle.
• Sodium chloride reabsorbed from ascending limb of henle's loop
enters medullary interstitium. From here it enters the
descending limb of vasa recta
• Simultaneously water diffuses from descending limb of vasa
recta.
• The blood flows very slowly through vasa recta. So a large
quantity of sodium chloride accumulates in descending limb of
vasa recta and flows slowly towards ascending limb of vasa recta
• Increase in sodium chloride concentration causes diffusion of
sodium chloride in to medullary interstitium
• Water from medullary interstitium enters ascending limb and
cycle is repeated.

50. The excretion of
hydrogen ions is done by
kidneys for preventing
metabolic acidosis.
Three mechanisms are
1. By bicarbonate
mechanism
2. By phosphate
mechanism
3. By ammonia
mechanism

52. PROPERTIES OF URINE
1. VOLUME: Normal urine output per day is 800-2500 ml.
abnormalities are polyuria, oliguria, and anuria
2. COLOUR : Yellow colour is due to presence of urochrome a
compound of urobilin and urobilinogen with peptide. On
standing colour deepens.
I. Brownish yellow indicates jaundice ,
II. Cloudy appearance seen in strongly alkaline urine,
III. Frothy appearance indicates proteinuria,
IV. Red dark brown tinge seen in porphyria
3. OSMOLALITY AND SPECIFIC GRAVITY: Normal urinary
osmolality varies from 50 to 1200 mom/kg and specific gravity
from 1.003 to 1.030.
4. pH: Normally varies from 4.5 to 8

53. ABNORMAL CONSTITUENTS OF URINE
1. PROTEINURIA: Excretion of greater than 150 mg/day of
protein. It occurs in conditions like congestive heart failure,
after prolonged standing, renal diseases and in toxaemia of
pregnancy
2. GLYCOSURIA: Refers to the presence of glucose in the urine. It
may be due to diabetes mellitus, renal disorders, GIT
disorders.
3. KETONURIA: Refers to the presence of ketone bodies in the
urine. It occurs in patients suffering from ketosis due to
severe DM or prolonged starvation
4. BILIRUBINURIA: Refers to the presence of bilirubin in the
urine occurs in jaundice
5. HAEMOGLOBINURIA: Presence of hemoglobin in urine
indicates intravascular haemolysis
6. HEMATURIA: Presence of blood in the urine is seen in acute
glomerulonephritis and renal stone disease

54. URINARY BLADDER

55. NERVE SUPPLY TO URINARY
BLADDER AND SPHINCTERS
• Sympathetic nerve fibres
arise from first two lumbar
segments of spinal cord
through hypogastric nerve
causes of filling of bladder by
relaxation of detrusor muscle
and constriction of internal
sphincter
• Parasympathetic nerve fibres
arises from S2,S3,S4
segments through pelvic
nerve causes emptying of
urinary bladder by
contraction of detrusor
muscle and relaxation of
internal sphincter.
NERVE SUPPLY TO URINARY
BLADDER AND SPHINCTERS
• Sympathetic nerve fibres
arise from first two lumbar
segments of spinal cord
through hypogastric nerve
causes of filling of bladder by
relaxation of detrusor muscle
and constriction of internal
sphincter
• Parasympathetic nerve fibres
arises from S2,S3,S4
segments through pelvic
nerve causes emptying of
urinary bladder by
contraction of detrusor
muscle and relaxation of
internal sphincter.
• Somatic nerve supply arising
from S2,S3,S4 innervates
external sphincter through
pudendal nerve causes its
constriction. Inhibition of
pudendal nerve results in
micturition by relaxation of
external sphincter
• Somatic nerve supply arising
from S2,S3,S4 innervates
external sphincter through
pudendal nerve causes its
constriction. Inhibition of
pudendal nerve results in
micturition by relaxation of
external sphincter

56. MICTURITION CENTRES
• Micturition process is
controlled by
• Spinal centres which are
located in sacral, lower
thoracic and upper
lumbar segments of
spinal cord.
• Higher centres
regulating spinal centres
are of types;
• Inhibitory centres
situated in midbrain
and cerebral cortex
• Facilitatory centres
situated in pons and
cerebral cortex
MICTURITION CENTRES
• Micturition process is
controlled by
• Spinal centres which are
located in sacral, lower
thoracic and upper
lumbar segments of
spinal cord.
• Higher centres
regulating spinal centres
are of types;
• Inhibitory centres
situated in midbrain
and cerebral cortex
• Facilitatory centres
situated in pons and
cerebral cortex

57. Micturition reflex
• It is the reflex by which micturition occurs and is elicited by
stimulation of stretch receptors situated on the wall of urinary
bladder and urethra.
• It is a self generative reflex i.e. the initial contraction of
bladder further activate the receptors to cause still further
increase in sensory reflex contraction of bladder and urethra.
These impulses in turn cause further increase in reflex
contraction of bladder
• During micturition the flow of urine is facilitated by the
increase in the abdominal pressure due to voluntary
contraction of abdominal muscle
Micturition reflex
• It is the reflex by which micturition occurs and is elicited by
stimulation of stretch receptors situated on the wall of urinary
bladder and urethra.
• It is a self generative reflex i.e. the initial contraction of
bladder further activate the receptors to cause still further
increase in sensory reflex contraction of bladder and urethra.
These impulses in turn cause further increase in reflex
contraction of bladder
• During micturition the flow of urine is facilitated by the
increase in the abdominal pressure due to voluntary
contraction of abdominal muscle
• Micturition is the process by which the urinary bladder
empties when it becomes filled.

58. Filling of urinary bladder
Filling of urinary bladder
Stimulation of stretch receptors in the bladder
Stimulation of stretch receptors in the bladder
Afferent impulses via pelvic nerve to sacral segments of spinal
cord
Afferent impulses via pelvic nerve to sacral segments of spinal
cord
Contraction of detrusor muscle and relaxation of internal
sphincter
Contraction of detrusor muscle and relaxation of internal
sphincter
Flow of urine in to urethra from the bladder
Flow of urine in to urethra from the bladder
stretch receptors in the urethra stimulated and impulses send to
spinal cord
stretch receptors in the urethra stimulated and impulses send to
spinal cord
Results in inhibition of pudendal nerve and
relaxation of external sphincter
Results in inhibition of pudendal nerve and
relaxation of external sphincter
Voiding of urine
Voiding of urine
MICTURITION
REFLEX

59. • When about 300 to 400 ml of urine is collected in the bladder,
the pressure inside the bladder increases
• This stretches bladder wall resulting in stimulation of stretch
receptors and generation of sensory impulses
• Sensory impulses reaches the sacral segments of spinal cord via
pelvic nerve
• The motor impulses from the spinal cord travel through motor
fibres of pelvic nerve towards bladder and internal sphincter
• It causes contraction of detrusor muscle and relaxation of
internal sphincter so that urine enters urethra from bladder
• Once urine enters urethra the stretch receptors in the urethra
are stimulated and send impulses to spinal cord via pelvic nerve
• These impulses inhibit pudendal nerve resulting in relaxation of
external sphincter and micturition occurs
• When about 300 to 400 ml of urine is collected in the bladder,
the pressure inside the bladder increases
• This stretches bladder wall resulting in stimulation of stretch
receptors and generation of sensory impulses
• Sensory impulses reaches the sacral segments of spinal cord via
pelvic nerve
• The motor impulses from the spinal cord travel through motor
fibres of pelvic nerve towards bladder and internal sphincter
• It causes contraction of detrusor muscle and relaxation of
internal sphincter so that urine enters urethra from bladder
• Once urine enters urethra the stretch receptors in the urethra
are stimulated and send impulses to spinal cord via pelvic nerve
• These impulses inhibit pudendal nerve resulting in relaxation of
external sphincter and micturition occurs

60. • Renal clearance of a substance is the volume of plasma that is
completely cleared of the substance by the kidneys per unit time
• Renal clearance of a substance is calculated from the urinary
excretion rate (Us V) of that substance divided by its plasma
concentration.
Cs = Us x V
Ps
where Cs is the clearance rate of a substance s, Ps is the plasma
concentration of the substance, Us is the urine concentration of
that substance, and V is the volume of urine excreted.

61. If a substance is freely filtered and is not reabsorbed or secreted
by the renal tubules, then GFR = CS
A substance that fits these criteria is inulin and creatinine.
If a substance is completely filtered and secreted but not
reabsorbed, the clearance rate of that substance is equal to the
total renal plasma flow. The clearance of PAH can be used as an
approximation of renal plasma flow. PAH {PARA-AMINOHIPPURIC
acid}
If renal plasma flow is 650 ml/min and GFR is 125 ml/min, the
filtration fraction (FF) is calculated as
FF = GFR/RPF = 125/650 = 0.19

62. • Urinary incontinence (UI) is loss of bladder control.
• Most bladder control problems happen when muscles are too
weak [stress incontinence] or too active [urge incontinence or
overactive bladder].
 Atonic bladder
• Caused by destruction of sensory nerve fibres
 Automatic bladder
• Caused by spinal cord damage above the sacral region
 Uninhibited neurogenic bladder
• Caused by lack of inhibitory signals from the brain, which
results in frequent and relatively uncontrolled
micturition.

63. Diuretics
• A diuretic (colloquially called a water pill) is any drug that
elevates the rate of bodily urine excretion (diuresis)
• Diuretics also decrease the extracellular fluid (ECF) volume,
and are primarily used to produce a negative extracellular
fluid balance.
• Caffeine, cranberry juice and alcohol are all weak diuretics.
In medicine, diuretics are used to treat heart failure, liver
cirrhosis, hypertension and certain kidney diseases.
Diuretics alleviate the symptoms of these diseases by
causing sodium and water loss through the urine.
• Some diuretics, such as acetazolamide, help to make the
urine more alkaline and are helpful in increasing excretion
of substances such as aspirin in cases of overdose or
poisoning.

64. Diabetes Insipidus
• This is caused by the deficiency of or decrease of ADH.
• The person with (DI) has the inability to concentrate
their urine in water restriction, in turn they will void up
3 to 20 litres/day.
• There are two forms of (DI), neurogenic, and
nephrogenic.
• In nephrogenic (DI) the kidneys do not respond to
ADH. Usually the nephrogenic (DI) is characterized
by the impairment of the urine concentrating
capability of the kidney along with concentration of
water. The cause may be a genetic trait, electrolyte
disorder, or side effect of drugs such as lithium.
• In the neurogenic (DI), it is usually caused by head
injury near the pituitary.

65. Kidney stones, also known as nephrolithiases, urolithiases or
renal calculi
• are solid crystals of dissolved minerals in urine found
inside the kidneys or ureters.
• They vary in size and texture.
• Kidney stones typically leave the body in the urine
stream; if they grow relatively large results in obstruction
of a ureter and distention with urine.
• It may cause severe pain most commonly felt in the flank,
lower abdomen and groin.
• Few symptoms of kidney stones
1. Pain in the abdomen or back
2. Pain spreading to the groin area or testicles
3. Blood in the urine
4. Nausea or vomiting
5. Burning sensation during urination

66. • Glomerulonephritis is usually caused by an abnormal immune
reaction that damages the glomeruli.
• In about 95 per cent of the patients with this disease, damage to
the glomeruli occurs 1 to 3 weeks after an infection elsewhere in
the body, usually caused by certain types of group A beta
streptococci.
• antibodies develop against the streptococcal antigen and
antigen react with each other to form an insoluble immune
complex that becomes entrapped in the glomeruli, especially in
the basement membrane portion of the glomeruli.
• Large numbers of white blood cells become entrapped in the
glomeruli. Many of the glomeruli become blocked by this
inflammatory reaction, and those that are not blocked usually
become excessively permeable,allowing both protein and red
blood cells.

67. (1) acute renal failure, in which the kidneys abruptly stop
working entirely or almost entirely but may eventually recover
nearly normal function, and (2) chronic renal failure, in which
there is progressive loss of function of more and more
nephrons that gradually decreases overall kidney function