A RENAL ppt.pptx

Kidney Function
Regulation of water and inorganic ions
Excretion of metabolic waste products
Removing of foreign chemicals
• producing ﹠excreting urine
• so that maintain the internal
homeostasis of the body
1.
2.
3.

Kidney Function
4. Secretion of hormones
a. Erythropoietin (EPO --- is produced by
interstitial cells in peritubular capillary.),
which controls erythrocyte production
b. Renin, ( is produced by juxtaglomerular cell)
which controls formation of
1,25-dihydroxyvitamin D3 ,
Angiotensin II
c.
which influences calcium balance

Functional Anatomy of Kidneys and
Renal Circulation
Urinary system :
 paired kidneys
 paired ureters
 a bladder
 a urethra

Anatomical Characteristics of the Kidney
The kidney: renal
renal
renal
cortex
medulla
pelvis

1. Nephrons: functional unit of kidneys
• Nephron is the basic smallest functional unit
of kidney.
• Nephron consists of renal corpuscle and renal
tubule.
Each kidney is composed of about 1 million
microscopic functional unit.
•

Nephron consists of..
glomerulus
renal corpuscle
Bowman’s capsule
Nephron proximal convoluted tubule
proximal tubule
thick descending limb
thin descending limb
thin ascending limb
renal tubule thin segment loop of Henley
thick ascending limb
distal tubule
distal convoluted tubule

Functional unit -nephron:
Corpuscle:
Bowman’s capsule
Glomerulus capillaries
Tubule:
PCT
Loop of Henley
DCT
Collecting duct

Two Types of Nephron
• Cortical nephrons
•
•
>85% of all nephrons
Located in the cortex
• Juxtamedullary
nephrons
• Closer to renal
medulla
Loops of Henle
deep into renal
pyramids
• extend

Differences between a cortical and a Juxtamedullary nephron
Cortical nephron Juxtamedullary nephron
Location Outer part of the cortex Inner part of the cortex
next to the medulla
Big
Glomerulus Small
Loop of Henle Short, next to outer cortex Longer, into inner part of
cortex
AA= EA
T
o form Vasa recta
Diameter of AA* AA> EA
T
o form Peritubular capillary
EA
Sympathetic
nerve innervation
Concentration of renin
Rich Poor
High Almost no
Ratio
Function
90%
Reabsorption and secretion
10%
Concentrate and dilute
urine
* AA = afferent glomerular arteriole
** EA = efferent glomerular arteriole

Cortical and Juxtamedullary Nephrons

Juxtaglomerular apparatus consists
(JGA)
 macula densa --- in initial portion of DCT
Function : sense change of volume and NaCl
concentration of tubular fluid , and transfer
information to JGC through paracrine
fashion
 juxtaglomerular cell (JGC) --- in walls of the
arterioles)
Function: secrete renin
 mesangial cell…it functions as immunity
and GFR regulation
afferent

Juxaglomerular apparatus
JA locate in cortical nephron, consist of juxtaglomerular
cell、 mesangial cell and macula densa.

Tubulo-glomerular Feedback
Macula densa can detects Na+, K+ Cl-
• and
of tubular fluid, and then sent some
information to glomerules, regulation
releasing of renin and glomerular filtration
rate. This process is called Tubulo-
glomerullar feedback.

Renal circulation
1.Characteristics of renal blood circulation
Huge volumes blood：
1200ml/min，1/5 – 1/4
Distribution：
•
of the cardiac output.
•
Cortex 94%, outer medulla 5 - 6%, inner medulla
Two capillary beds:
<1%.
•
Renal artery→interlobar arteries →arcuate arteries
→afferent arterioles →glomerular capillaries →efferent
arteriole →peritubular capillaries →arcuate vein
→interlobar vein →renal vein.

Renal circulation
• Glomerular capillaries:
Higher pressure, benefit for filtration
• Peritubular capillaries:
Lower pressure, benefit for reabsorption
Vasa recta
Concentrate and dilute urine
•

Renal circulation
Glomerular
capillary
Peritubular
capillary
cortex
medulla
vasa recta

Regulation of renal blood flow
(Autoregulation, neural, hormonal)
Autoregulation
When arterial pressure is in range of 80 to 180 mmHg, renal
blood flow (RBF) is relatively constant in denervated, isolated
or intact kidney.
Flow autoregulation is a major factor that controls RBF
Mechanism of autoregulation: myogenic theory of
autoregulation

Autoregulation of renal blood flow

Neural regulation
Renal sympathetic nerve
Activity of sympathetic nerve is low, but can increase
during hemorrhage, and stress.

Hormonal
Vasoconstriction
regulation
RBF
•
•
•
Angiotensin II
Epinephrine
Norepinephrine
Vasodilation RBF
•
•
•
Prostaglandin
nitrous oxide
Bradykinin

Basic processes for urine
Glomerular filtration:
Most substances in blood, except for protein
freely filtrated into Bowman's space.
Reabsorption:
formation
and cells, are
Water and specific solutes are reabsorbed
back into blood (peritubular capillaries).
Secretion:
from tubular fluid
Some substances (waste products, etc.) are secreted from
peritubular capillaries or tubular cell interior into tubules.
Amount Excreted = Amount filtered – Amount reabsorbed +
Amount secreted

Three basic processes of the formation of urine.

Basic processes for urine formation
Glomerular filtration, reabsorption,
secretion

Glomerular Filtration
Only water and small solutes can be filtrated----selective.

Composition of the glomerular filtrates
Except for proteins, the composition of glomerular filtrates
same as that of plasma.
is

Figure 26.10a, b
Glomerular filtration membrane
The barrier between the
capillary blood and the
fluid in the Bowman’s
space.
Composition: three layers
Capillary endothelium ---
fenestrations(70-90nm)
Basement membrane ---
meshwork
Epithelial cells (podocyte)
--slit pores
•
•
• -

Showing the filtration membran. To be filtered, a substance must pass
through 1. the pores between the endothelial cells of the glomerullar capillary,
2. cellular basement membrane, and 3. the filtration slits between the foot
processes of the podocytes of the inner layer of Bowman’s capsule.

Selective permeability
membrane
of filtration
Structure Characteristics:
There are many micropores in each layer
Each layer contains negatively charged glycoproteins

Selective permeability
membrane
of filtration
Size selection :
impermeable to substances
with high molecular weight
Charge selection :
Repel negative charged substances

Filtrate Composition
Glomerular filtration barrier restricts the filtration of
molecules on the basis of size and electrical charge
Neutral solutes:
•
•
• Solutes
filtered
Solutes
smaller than 180 nanometers in radius are freely
•
•
greater than 360 nanometers do not
Solutes between 180 and 360 nm are filtered to various
degrees
• Serum albumin is anionic and has a 355 nm radius,
only ~7 g is filtered per day (out of ~70 g/day passing
through glomeruli)
In a number of glomerular diseases, the negative
charge on various barriers for filtration is lost due to
immunologic damage and inflammation, resulting in
proteinuria (i.e. increased filtration of serum proteins
that are mostly negatively charged).
•

Filtration Coefficient ( Kf )
• Filtration coefficient is a minute volume of
plasma filtered through the filtration
membrane by unit effective filtration pressure
drive. Kf =K×S
GFR is dependent on the filtration coefficient
as well as on the net filtration pressure.
GFR=P× Kf
The surface area and the permeability of the
•
•
glomerular membrane can affect Kf.

Regulation of Glomerular Filtration
If the GFR is too high, needed substances cannot
be reabsorbed quickly enough and are lost in the
urine
If the GFR is too low - everything is reabsorbed,
including wastes that are normally disposed of
Control of GFR normally result from adjusting
glomerular capillary blood pressure
Three mechanisms control the GFR
•
•
•
•
•
•
•
Renal autoregulation (intrinsic system)
Neural controls
Hormonal mechanism (the renin-angiotensin system)

Autoregulation of GFR
• Under normal conditions (MAP =80-180mmHg) renal
maintains a nearly constant glomerular filtration rate
Two mechanisms are in operation for autoregulation:
autoregulation
•
•
•
Myogenic mechanism
Tubuloglomerular feedback
• Myogenic mechanism:
•
•
•
Arterial pressure rises, afferent arteriole stretches
Vascular smooth muscles contract
Arteriole resistance offsets pressure increase; RBF (& hence
remain constant.
GFR)
• Tubuloglomerular feed back mechanism for autoregulation:
• Feedback loop consists of a flow rate (increased NaCl) sensing
mechanism in macula densa of juxtaglomerular apparatus (JGA)
Increased GFR (& RBF) triggers release of vasoactive signals
Constricts afferent arteriole leading to a decreased GFR (& RBF)
•
•

Extrinsic Controls
When the sympathetic nervous system is at
• rest:
•
•
Renal blood vessels are maximally dilated
Autoregulation mechanisms prevail
• Under stress:
•
•
•
Norepinephrine is released by the sympathetic nervous
Epinephrine is released by the adrenal medulla
Afferent arterioles constrict and filtration is inhibited
system
• The sympathetic nervous system also stimulates
renin-angiotensin mechanism
the
• A drop in filtration pressure stimulates the
Juxtaglomerular apparatus (JGA) to release renin

Response to a Reduction in the GFR

Renin-Angiotensin Mechanism
Renin release is triggered by:
•
•
•
•
Reduced stretch of the granular JG cells
Stimulation of the JG cells by activated macula densa cells
Direct stimulation of the JG cells via 1-adrenergic receptors
renal nerves
by
• Renin acts on angiotensinogen to release angiotensin
which is converted to angiotensin II
Angiotensin II:
I
•
•
•
Causes mean arterial pressure to rise
Stimulates the adrenal cortex to release aldosterone
• As a result, both systemic and glomerular hydrostatic
pressure rise

Other Factors Affecting Glomerular Filtration
• Prostaglandins (PGE2 and PGI2)
• Vasodilators produced in response to sympathetic
stimulation and angiotensin II
Are thought to prevent renal damage when peripheral
resistance is increased
•
• Nitric oxide – vasodilator produced by the
vascular endothelium
Adenosine – vasodilator of renal vasculature
Endothelin – a powerful vasoconstrictor secreted
by tubule cells
•
•

Control of Kf
Mesangial cells have contractile properties, influence
capillary filtration by closing some of the capillaries –
effects surface area
Podocytes change size of filtration slits
•
•

Process of Urine Formation
•
•
Glomerular filtration
Tubular reabsorption of
the substance from the
tubular fluid into blood
Tubular secretion of the
substance from the blood
into the tubular fluid
Mass Balance
•
•
• Amount Excreted in Urine =
Amount Filtered through
glomeruli into renal proximal
tubule MINUS amount
reabsorbed into capillaries
PLUS amount secreted into
the tubules

Tubular Secretion
• substances move from peritubular capillaries
tubule cells into filtrate
Tubular secretion is important for:
or
•
•
Disposing of substances not already in the filtrate
Eliminating undesirable substances such as urea
uric acid
Ridding the body of excess potassium ions
Controlling blood pH
and
•
•

Tubular reabsorption and secretion

Tubular processing of urine formation
Characteristics and mechanism of reabsorption and
secretion
Characteristics of reabsorption:
quantitatively large
More than 99% volume of filtered fluid are reabsorbed
(> 178L).
selective
100% glucose, 99% sodium and chloride, 85%
bicarbonate are reabsorbed
Urea and creatinine are partly reabsorbed.

Type of transportation in renal tubule and
colllecting duct
•
•
Transportation mechanisms For Reabsorption
and secretion
Passive reabsorption (with out energy)
Diffusion, osmosis, facilitated diffusion
Active reabsorption (need energy)
Sodium pump (Na+-K+ ATPase), proton pump (H+-
ATPase), calcium pump (Ca2+-ATPase).
Cotransport (coupled transport):
•
•
•
One transportor can transport two or more substances.
• Symport transport:
Antiport transport:
like Na+ and glucose, Na+ and amino acids
like Na+-H+ and Na+-K+
• Secondary active transport : like H+ secretion

Na+ active transport in PT epithelium

• Passway of transport
Apical membrane, tight
basolateral membrane
Transcellular pathway
juction, brush border,
•
Na+ epithelium
apical membrane Na+ pump peritubular
capillary
Paracellular transport
•
Water, Cl- and Na+ tight juction peritubular capillary
K+ Ca2+
and are reabsorpted with water by solvent drag

Reabsorption of transcellular and paracellular pathway

Location of reabsorption
(Every parts of Nephron)
 Proximal tubule
Brush border can
reabsorption
 Henle's loop
 Distal tubule
 Collecting duct
increase the area of

Reabsorption and secretion in different part
renal tubule
of
• Proximal tubule (PT)
67% Na+, Cl-, K+ and water; 85% HCO3
- and 100%
glucose and amino acids are reabsorbed
H+
secretion
2/3 Transcellular pathway
1/3 Paracellular transport
The key of reabsorption is Na+ reabsorption ( the
action of Na+ pump in the membrane of proximal
tubule).

Na+ transcellular transportation in early part of PT epithelium

Cl- passive reabsorption in later part of PT epithelium

K+ reabsorption
 Most of in PT (70%)，20%
 Active reabsorption
in loop of Henle
Ca2+ reabsorption
 70% in PT
, 20% in loop of Henle, 9% in DCT

Glucose and amino acid reabsorption
Glucose reabsorption:
99% glucose are reabsorbed, no glucose in urine
• Location:
early part of PT
Type of reabsorption:
secondary active transport
Renal glucose threshold
When the plasma glucose concentration
•
•
increases up to a
value about 160 to 180 mg per deciliter, glucose can first
be detected in the urine, this value is called the renal
glucose threshold.

Glucose secondary active transport in early part of PT

Transport maximum (Tm)
Transport maximum is the maximum rate at which
the kidney active
particular
transport
solute
mechanisms can
the
transfer
tubules.
a into or out of
Amino acid reabsorption:
Location and type of reabsorption as same
glucose
as

Co-transport of amino acids via Na+ symport mechanism.

Loop of Henle:
Ascending thick limb of loop of Henle
Na+, Cl- and K+ cotransport
Transportation rate: Na+ : 2Cl- : K+
Distal tubule and collecting duct:
Principal cell: Reabsorption Na+ water and
K+
secretion
Intercalated cell: Secretion H+

Secretion at the DCT
•
•
DCT performs final adjustment of urine
Active secretion or absorption
Absorption of Na+ and Cl-
Secretion of K+ and H+ based on blood pH
•
•
•
•
Water is regulated by ADH (vasopressin)
Na+, K+ regulated by aldosterone

K+ H+
and secretion in distal tubule and collecting duct

Summary of transport across PT
, DT and collecting duct
Proximal tubule
Reabsorption Secretion
filtered Na+ actively reabsorbed; Cl-
follows passively.
All filtered glucose and amino acids
reabsorbed by secondary active
transport,
Filtered H2Oosmoticallyreabsorbed,
Almost all filtered K+ reabsorbed,
H+
Variable secretion,
depending on acid-base
status of body.
Distal tubule and collecting duct
Reabsorption Secretion
Variable Na+ reabsorbed
Aldosterone;
Cl- follows passively. Variable
H2O reabsorption, controlled by
vasopressin (ADH)
Variable H+ secretion,
depending on acid-base
status of body.
by
K+
Variable secretion,
controlled by aldosterone.

Urinary Concentration and Dilution
Hypertonic urine:
Lack of water in body can forms concentrated urine
(1200 mOsm/L).
Hypotonic urine:
More water in body can forms dilute urine (50 mOsm/L).
Isotonic urine：Injury of renal function
Urinary dilution:
The mechanism for forming a dilute urine is continuously reabsorbing
reabsorb water.
Urinary concentration:
The basic requirements for forming a concentrated urine are a high
fluid.
•
•
•
•
solutes from the distal segments of the tubular system while failing to
•
level of ADH and a high osmolarity of the renal medullary interstitial

formation of dilute and concentrated urine.

Control of Urine Volume and Concentration
• Urine volume and osmotic concentration are regulated
by controlling water and sodium reabsorption
Precise control allowed via facultative water reabsorption
Osmolality
•
•
•
•
The number of solute particles dissolved in 1L of water
Reflects the solution’s ability to cause osmosis
•
•
Body fluids are measured in milliosmols (mOsm)
The kidneys keep the solute load of body fluids constant
at about 300 mOsm
This is accomplished by the countercurrent mechanism
•

 Formation of concentrated and diluted urine
Drink more water
in DCT and CD
Lack of water
in DCT and CD
ADH
diluted
ADH
water reabsorption
urine.
water reabsorption
concentrated urine.
 Role of the vasa recta for maintaining the
high solute concentration (NaCl and urea)
in the medullary interstitial fluid.
Role of countercurrent exchanger

Urinary concentrating environment.

• Basic structure：
“U”type of loop of Henle
Vasa recta’s cliper type
Collecting duct from cortex to medulla
• Basic function：
Different permeability of solutes and water
DCT, CD and loop of Henle.
in
• Osmotic gradient exit from cortex to medulla.

Permeabilities of different segments of the renal tubule
Segments of
renal tubule
Permeability
water
to Permeability to
Na+
Permeability
urea
to
Thick ascending
limb
Almost not Active transport of
Na+, Secondary
Almost not
Cl-
active Transport of
Thin ascending
limb
Almost not Yes Moderate
Almost not Almost not
Thin descending
limb
Yes
K+
Distal convoluted
tubule
Permeable
Under ADH
action
Secretion of Almost not
K+-Na+ exchange
Collecting
duct
Cortex and outer
Medulla almost not
Inner medulla Yes
Permeable
Under ADH
action
Yes

 Mechanisms for creating osmotic gradient in the
medullary interstitial fluid
 Formation of osmotic gradient is related to
physiological characters of each part of renal tubule.
 Outer medulla：
Water are permeated in descending thin limb, but not NaCl
and urea.
NaCl and urea are
not water.
permeated in ascending thin limb, but
NaCl is active reabsorbed in ascending thick limb, but not
Urea and water.
 Formation of osmotic gradient in outer medulla is
due to NaCl active reabsorption in outer medulla.

Inner medulla：
High concentration urea exit in tubular fluid.
•
•
• Urea is permeated in CD of inner medulla
in cortex and outer medulla
NaCl is not permeated in descending thin
NaCl is permeated in ascending thin limb
Urea recycling：
but not
•
•
•
•
limb
Urea is permeated in ascending thin limb, part of urea into
ascending thin limb from medulla and then diffusion to
interstitial fluid again.
Formation of osmotic gradient in inner medulla is
due to urea recycling and NaCl passive diffusion in inner
medulla.
•

Countercurrent Mechanism
Interaction between the flow of filtrate through the loop of Henle
(countercurrent multiplier) and the flow of blood through the vasa
recta blood vessels (countercurrent exchanger)
The solute concentration in the loop of Henle ranges from 300
mOsm to 1200 mOsm
•
•

 Countercurrent exchange
Countercurrent exchange is a common process in
the vascular system. Blood flows in opposite
directions along juxtaposed decending (arterial) and
ascending (venous) vasa recta, and solutes and water
are Exchanged between these capillary blood vessels.
 Countercurrent multiplication
Countercurrent multiplication is the process where
by a small gradient established at any level of the
loop of Henle is increased (maltiplied) into a much
larger gradient along the axis of the loop.

Loop of Henle: Countercurrent Multiplication
Vasa Recta prevents loss of medullary osmotic gradient equilibrates with
the interstitial fluid
•
•
•
Maintains the osmotic gradient
Delivers blood to the cells in the area
• The descending loop: relatively impermeable to solutes, highly permeable to
water
The ascending loop: permeable to solutes, impermeable to water
Collecting ducts in the deep medullary regions are permeable to urea
•
•

Countercurrent Multiplier and Exchange
• Medullary
gradient
osmotic
• H2OECFvasa recta
vessels

Formation of Concentrated
ADH (ADH) is the
signal to produce
Urine
•
concentrated urine
inhibits diuresis
This equalizes the
osmolality of the
filtrate and the
interstitial fluid
In the presence of
ADH, 99% of the
water in filtrate is
reabsorbed
it
•
•

Formation of Dilute Urine
• Filtrate is diluted in the ascending
loop of Henle if the antidiuretic
hormone (ADH) or vasopressin is not
secreted
Dilute urine is created by allowing this
filtrate to continue into the renal pelvis
Collecting ducts remain impermeable
to water; no further water
reabsorption occurs
Sodium and selected ions can be
removed by active and passive
mechanisms
Urine osmolality can be as low as 50
mOsm (one-sixth that of plasma)
•
•
•
•

Figure 20-6: The mechanism of action of
Mechanism of ADH (Vasopressin) Action:
Formation of Water Pores
• ADH-dependent water reabsorption is called facultative
water reabsorption
vasopressin

Water Balance Reflex:
Regulators of Vasopressin Release
Figure 20-7: Factors affecting vasopressin release

Regulation of Urine Formation in the Kidney
Way of regulation for urine formation：
Filtration, Reabsorption and Secretion
•
•
•
Autoregulation
Solute concentration of tubular fluid
Osmotic diuresis -- diabatic、mannitol
Glomerulotubular balance
•

 Nervous regulation
 Role of Renal Sympathetic Nerve
 Reflex of renal sympathetic nerve
Reflex of cardiopumonary receptor
renorenal reflex
 Renin-angiotention-aldosterone system

Renin-Angiotension-Aldosterone System

Regulation by ADH
• Released by posterior
pituitary when
osmoreceptors detect
an increase in plasma
osmolality.
Dehydration or excess
salt intake:
•
• Produces sensation
of thirst.
Stimulates H20
reabsorption from
urine.
•

The regulation of ADH secretion
 Source of ADH
Hypothalamus supraoptic and
paraventricular nuclei
The change of crystal
pressure
osmotic
Effective stimuli
The change of effective blood
volume

Effects of ADH on the DCT and Collecting Ducts
Figure 26.15a, b

Regulation of ADH release: over hydration

Regulation of release: hypertonicity

Atrial Natriuretic Peptide Activity
 Increase GFR , reducing water reabsorption
 Decrease the osmotic gradient of renal medulla
and promotes Na+ excretion
 Acting directly on collecting ducts to inhibit Na+
and water reabsorption, promotes Na+ and
water excretion in the urine by the kidney
 Inhibition renin release and decrease
angiotensin II and aldosterone, promotes Na+
excretion

 Endothelin (ET)
Constriction blood vessels, decrease GFR
 Nitic Oxide (NO)
Dilation blood vessels, increase GFR
 Epinephrine (EP), Norepinephrine (NE)
promote Na+ and water reabsorption
 Prostaglandin E2 ,I2
Dilation blood vessels, excretion Na+ and water.

A Summary of Renal Function
Figure 26.16a

Renal clearance
1. Concept:
Renal clearance of any substance is the volume of
plasma that is completely cleaned of the substance
the kidneys per unit time (min)
2. Calculate
concentration of it in urine ×urine volume
by
C =
concentration of it in plasma

Renal Clearance
RC = UV/P
RC = renal clearance rate
U = concentration (mg/ml) of the substance in urine
V = flow rate of urine formation (ml/min)
P = concentration of the same substance
Renal clearance tests are used to:
in plasma
•
• Determine the GFR
•
•
Detect glomerular damage
Follow the progress of diagnosed renal disease

Theoretical significance of clearance
3.1 Measure GFR
• A substance---freely filtered, non reabsorbed,
non secreted--its renal clearance = GFR
Clearance of inulin or creatinine can be used to
estimate GFR
•

3.2 Calculate RPF and RBF
A substance--freely filtered, non reabsorbed, secreted
completely from peritubular cells ---a certain
concentration in renal arteries and 0 in venous.
Clearance of para-aminohippuric acid (PAH) or diodrast
can be used to calculate RPF
.

3.3 Estimate of tubular handling for a substance
If the clearance of substance>125ml/min?
---it must be secreted
If it <125ml/min? --- it must be reabsorbed

Physical Characteristics of Urine
 Color and transparency
•
•
•
Clear, pale to deep yellow (due to urochrome)
Concentrated urine has a deeper yellow color
Drugs, vitamin supplements, and diet can change the color
urine
of
•
pH
•
•
Cloudy urine may indicate infection of the urinary tract

Slightly acidic (pH 6) with a range of 4.5 to 8.0
Diet can alter pH
 Specific gravity
•
•
Ranges from 1.001 to 1.035
Is dependent on solute concentration

Chemical Composition of Urine
•
•
Urine is 95% water and 5% solutes
Nitrogenous wastes include urea, uric acid,
creatinine
Other normal solutes include:
and
•
•
•
Sodium, potassium, phosphate, and sulfate ions
Calcium, magnesium, and bicarbonate ions
• Abnormally high concentrations of any urinary
constituents may indicate pathology

Urine Volume and Micturition
1. Urine volume


Normal volume : 1.0~2.0L/day
Obligatory urine volume ~400ml/day
Minimum needed to excrete metabolic wastes of
waste products in body.


Oliguria--- urine volume < 400ml/day
Anuria---urine volume < 100ml/day
Accumulation of waste products in body. Polyuria---
urine volume > 2500ml/day long time Abnormal urine
volume: Losing water and electrolytes.


Micturition
Functions of ureters and bladder:
Urine flow through ureters to bladder is
propelled by contractions of ureter-wall
smooth muscle.
Urine is stored in bladder and intermittently
ejected during urination, or micturition.

Micturition
• Micturition is process of emptying
urinary bladder
Two steps are involved:
the
•
• (1) bladder is filled progressively
pressure rises
until its
•
•
above a threshold level (400~500ml);
(2) a nervous reflex called micturition
reflex occurs that empties bladder.

Micturition
• Pressure-Volume curve of the bladder has
a characteristic shape.
There is a long flat segment as the initial
increments of urine enter the bladder and
then a sudden sharp rise as the micturition
reflex is triggered.
•

Pressure-volume graph for
bladder
normal human
1.25
1.00
Sense of
0.75
0.50
0.25
100 200 300 400
Volume (ml)
Pressure
(kPa)
Discomfort
1st desire urgency
to empty
bladder

Micturition (Voiding or Urination)
•
•
Bladder can hold 250 - 400ml
Greater volumes stretch bladder walls initiates
micturation reflex:
Spinal reflex
•
• Parasympathetic stimulation
contract
Internal sphincter opens
causes bladder to
•
• External sphincter relaxes due to inhibition

Urination: Micturation reflex
Figure 19-18: The micturition reflex

Figure 25
Micturition (Voiding or Urination)
.20a, b

Review Questions
Explain concepts
1.Glomerular filtration rate
2. Effective filtration pressure
3. Filtration fraction
4.Renal glucose threshold
5.Osmotic diuresis
6.Renal clearance

Review Questions
the functions of the kidneys?
autoregulation of renal plasma
1. What are
2. Describe
flow.
3. What are three basic processes for urine
formation?
4. Describe the forces affecting glomerular
filtration.
5. Describe the factors affecting GFR.
6. What is the mechanism of sodium
reabsorption in the proximal tubules ?

Review Questions
7. What is the mechanism of hydrogen ion
secretion and bicarbonate reabsorption?
What is the mechanism of formation of
concentrated and diluted urine?
After drinking large amount of water, what does
8.
9.
the amount of urine change? Why?
10. Why a patient with diabetes has glucosuria and
polyuria?

A RENAL ppt.pptx

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