新疆医科大学
生理学教研室
Ch 9：Urinary physiology
Wei yuanyuan
Urinary physiology

Urinary system
Regulate the volume ,electrolytes
composition,pH of internal enviroment
homeostasis
Urinary physiology

ECF

Simple marine organ


ECF: sea-maintain constant
Terrestrial animals

ECF: kidney maintain water and electrolyte balance within
very narrow range
Urinary physiology
Major Functions of the Kidneys

Regulation of:



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body fluid osmolarity and volume
electrolyte balance
acid-base balance
blood pressure
Excretion of



metabolic products
foreign substances (pesticides, chemicals etc.)
excess substance (water, etc)
Major Functions of the Kidneys

Secretion of




erythropoietin
1,25-dihydroxy vitamin D3
renin
prostaglandin
Structure of kidney
Gross Anatomy
of the Kidney
Structure of kidney
Functional unit of kidneys ？
Structure of kidney

The nephron is the functional unit of the kidney:



1 million microscopic functional unit
Perform almost all kidney’s functions
Distinction between the cortical and medullary regions
of the kidney
Kidney -- nephron
Renal cortex
Renal
pyramid
nephron
Renal medulla
Renal pelvis
Ureter
Renal pyramid
Structure of nephron

Vascular component





Afferent arteriole:no O2 and
nutrients used
Glomerulus: a tuft capillaries
Efferent arteriole
Peritubular capillaries:supply
blood
Tubular component




Bowman’s capsule: cups around
Proximal tubule:in cortex
Loop of Henle
Distal tubule and collecting duct
Structure of Nephron

Nephron

Renal corpuscle


Glomerulus
Bowman’s capsule

Renal tubular system

Collecting duct
Renal pelvis
Fig 9-
Structure of kidney

Nephron


Renal corpuscle
Renal tubular system




Proximal tubule
Loop of Henle
Distal tubule
Collecting duct


Renal pelvis
Cortical nephron and Juxtamedullary nephron
Regional differences in nephron structure

Cortical nephron (80-90%)




Glomuruli lie in the outer layer of the cortex
Hairpin loop dips only slightly in the medulla
Peritubular capillaries entwine around short loops of
Henle
Juxtamedullary nephron(10-20%)


Glomeruli lie in the inner layer of the cortex
Hairpin loop plunges entire depth of the medulla


For establishment of the medullary vertical osmotic
gradient
Peritubular capillaries form vasa recta and run in
closely with long loops of Henle
The structure of nephron

Cortical nephron or Juxtamedullary nephron ？
Juxtaglomerular apparatus
Juxtaglomerular apparatus
Juxtaglomerular apparatus


Granular cell(specialized vascular cells): secretion
renin
Macula densa(specialized tubular cells):



sensing change in ECF volume↓/[NaCl] ↓/ blood
pressure↓
Control renin release
Mesangial cell


Function as phagocytes
Contraction : close off the filtration capillaris
(sympathetic nerve excitation)
Note:
The distinction between
juxtamedullary nephrons and
juxtaglomerular apparatus
Blood supply to kidney
Blood supply to kidney
Renal artery
Segmental arteries
Interlobar arteries
Arcuate arteries
Interlobular arteries
Afferent arterioles
Venous return of blood is via
similarly named veins.
Blood supply to kidney
Blood supply to kidney

Features of the renal blood
flow:


abundant blood flow
1200ml/min
Two capillary beds


High hydrostatic pressure in
glomerular capillary (about 60
mm Hg)--filtration
low hydrostatic pressure in
peritubular capillaries (about 13
mm Hg)—reabsorption
Vesa recta
The efferent arterioles are the
only arterioles in the body that
drain from capillaries
Urine formation
Urine formation
Basic three procedures



Glomerular filtration
Tubular reabsorption
Tubular secretion
Urine formation
Afferent
artery
Efferent artery
glomerular
Glomerular filtration
20% of the plasma that
enters the glomerulus is
filtered.
2.75L
Bowman’s
capsule
180L/d
Peritubular
capillary
Kidney
tubule
To venous
system
Urine excretion
80% of the plasma that enters the
glomerulus is not filtered and leaves
through the efferent arteriole
Total plasma is 2.75L
Urine formation

Tubular reabsorption:

selective movement of
filtered substances from
the tubular lumen into the
peritubular capillaries


99% H2O and salts
Active and passive
mechanism
Urine formation

Tubular secretion

selective transfer of nonfiltered substances from the
peritubular capillaries into the tubular lumen

Active transport
Urine formation


Urinary excretion
refers to the elimination of substances from the
body in the urine
Urinary excretion rate(1.5L/d)


Filtration rate(180L/d) －Reabsorption rate(178.5L/d)
+ Secretion rate
Note: do not confuse excretion with secretion
 Glomerular
filtration
Urine formation
Glomerular filtration


Structure:glomerular membrane
Force:effective filtration pressure
Glomerular filtration
Afferent arteriole

Glomerular membrane
 Filtration
fluid=proteins-free glomerulus
blood plasma into
Bowman’s
capsule
Bowman’s capsule
 Permeability is 100
times more than
capillary elsewhere
 Filtration occurs
through entire
length of capillary
Efferent arteriole
Lumen of
glomerular
capillary
Proximal tubule
Glomerular filtration
Layers of glomerular membrane
(1)The wall of the glomerular capillaries (pore: more permeable)
(2)Basement membrane (collagen and glycoproteins)
(3)The inner layer of Bowman’s capsule
Glomerular filtration
(1)The endothelium of the capillaries
pore: more permeable fenestrae 70-70nm
prevent hemocyte from filtration
negative charges： hinder plasma proteins
hemocyte
Glomerular filtration
(2) Basement membrane
 Consists of a meshwork of collagen and glycoproteins
 Effectively prevents filtration of plasma proteins—strong
negative electrical charges associated with the proteoglycans
Capillary pore
Glomerular filtration
(3) The epithelial cells of Bowman’s capsule (podocytes)
The foot processes are separated by gaps called slit pores
(4-11nm)
 Provide additional restriction to filtration of plasma
proteins.—negtive charges
Glomerular filtration

Permeability of
filtration membrane

Molecular size



Large protein
Albumin (albuminuria)
Electrical charges of
the molecule


Negative charges
Albumin (albuminuria)
Glomerular filtration

Effective filtration pressure, EFP (Net filtration
pressure)

Force favoring filtration



Capillary blood pressure (BP:60mmHg)
Bowman’s capsule colloid osmotic pressure (πB:0mmHg)
Force opposing filtration


Bowman’s capsule hydrostatic pressure (CP:18mmHg)
Capillary colloid osmotic pressure (πC, COP: 32mmHg)
Glomerular filtration

Net filtration pressure (EFR)
EFR=(BP+ πB) －(πC +CP)
=BP－(πC +CP)
= 60-(18+32)=10mmHg

How does filtration stop?


Increased glomerular capillary colloid osmotic
pressure decreases GFR
Filtration equilibrium
Glomerular filtration

Glomerular filtration rate (GFR)

Definition



125ml/min(180L/day)
Advantages of high GFR



Glomerular filtrate produced by both kidneys per unit time
Rapidly remove waste products
Precisely and rapidly control of the volume and composition
of the body fluid
The fraction of plasma filtered by the glomerular
capillaries 20%

filtration fraction (FF)= GFR/ renal blood plasma flow
Glomerular filtration

Determinants of GFR:


EFP (net filtration pressure)
Kf : filtration coefficient

the properties of the glomerular membrane



How much glomerular surface area is available
How permeability the glomerular membrane is
GFR = Kf ×EFP
Glomerular filtration

Factors that affect the GFR
Glomerular filtration
1 Favoring force-Capillary blood pressure (60mmHg)


Depend on heart contraction (source of energy)
BP ↓→GFR↓ <80mmHg

Shock, hemorrhage,
Glomerular filtration
2 opposing force-hydrostatic pressure in
Bowman’s capsule:15mmHg↑→GFR↓

Urinary tract obstruction (stone)

Precipitation of calcium or uric acid
Prostatic enlargement

Glomerular filtration
3 opposing force-Capillary colloid osmotic pressure
(COP:30mmHg) ↑→GFR↓

Reduction in plasma protein concentration → COP ↓ →GFR↑
Lose a large quantity of protein-rich
fluid through the exposed burned surface

Glomerular filtration
4.Renal blood plasma flow


blood plasma flow↑→ GFR↑
blood plasma flow↓ ↓→ Kf ↓→
GFR ↓
Glomerular filtration

5 Kf↓→ GFR↓



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How much glomerular surface area is available
How permeable the glomerular membrane is
4.2 ml/min/mm Hg per 100 grams of kidney weight (others
capillary bed was only 0.01 ml/min/mm Hg per 100 grams )
Renal disease , Diabetes , Hypertension
Regulation of renal blood flow
Regulation of renal blood flow

Auto-regulation

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nervous control
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Myogenic mechanism
Tubulo-glomerular feedback
Sympathetic nerve system
Baroreceptor reflex
Humoral control

NE, E, Angiotensine Ⅱ, endothelin, bradykinin
Regulation of renal blood flow

Auto-regulation of renal circulation


Mechanism



BPA: 80-180 mm Hg
Myogenic mechanism
Tubulo-glomerular
feedback
Significance
Preventing extreme changes
in renal excretion

Regulation of renal blood flow

Myogenic mechanism

BPA :80 mmHg--180 mmHg


BPA↑→ constriction of afferent artery → the blood flow
relatively less
Contraction or relaxation in response to the stretch by
blood pressure change
Bp ↓ →vasodilation
Bp↑→vasoconstriction
Regulation of renal blood flow

Tubulo-glomerular feedback
BP ↓ →filtration ↓ →rate of
fluid flow through tubules ↓
→macular densa(+)→Afferent
arteriolar resistance↓
(mechanism remain elusive)


→release AngⅡ ↑ → efferent
arteriolar vasoconstriction
→Glomerular hydrostatic
pressure ↑ → filtration ↑
Regulation of renal blood flow
Regulation of renal blood flow

Neural regulation of renal blood flow


Sympathetic nerve (+) →constriction of renal arteries
(esp. afferent artery) → renal blood flow↓
Cause the mesangial cells to contract,close off a
portion of the filtering capillaries.
the para-sympathetic
nerve does not exert
any influence on
the kidneys

Regulation of renal blood flow

Neural regulation of renal blood flow

BPA↓ (hemorrhage)→ arterial carotid sinus and aortic
arch baroreceptors (+) → BPA↑→renal blood flow
remain constant
Regulation of renal blood flow

Humoral control

Norepinephrine, epinephrine , endothelin


Angiotensin Ⅱ


Constriction of efferent arterioles
Nitric Oxide


Constriction of renal blood vessel (esp. afferent artery) and
GFR↓
Renal blood vessels resistance ↓
Prostaglandins and bradykinin

GFR↑