Post on 30-Dec-2015
新疆医科大学生理学教研室
Ch 9 : Urinary physiology
Wei yuanyuan
Urinary physiology
Urinary system homeostasis
Regulate the volume ,electrolytes composition,pH of internal enviroment
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: 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 cortexRenal medulla
Renal pyramid
Renal pelvis
Ureter Renal pyramid
nephron
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
Fig 9-
Renal pelvis
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
Basic three procedures Glomerular filtration Tubular reabsorption Tubular secretion
Urine formation
Urine formationAfferent artery Efferent artery
Peritubular capillary
To venous system
Urine excretion
Kidney tubule
glomerular
Bowman’s capsule
20% of the plasma that enters the glomerulus is filtered.
80% of the plasma that enters the glomerulus is not filtered and leaves through the efferent arteriole
180L/d
Total plasma is 2.75L
2.75L
Glomerular filtration
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 bo
dy 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
Glomerular membrane Filtration
fluid=proteins-free blood plasma into Bowman’s capsule
Permeability is 100 times more than capillary elsewhere
Filtration occurs through entire length of capillary
Afferent arteriole Efferent arteriole
glomerulus
Bowman’s capsule
Proximal tubule
Lumen of glomerular capillary
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
Capillary pore
(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
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
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 Glomerular filtrate produced by both kidneys per unit
time 125ml/min(180L/day) Advantages of high GFR
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 filtration4.Renal blood plasma flow
blood plasma flow↑→ GFR↑ blood plasma flow↓ ↓→ Kf ↓→
GFR ↓
Glomerular filtration 5 Kf↓→ GFR↓
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 Myogenic mechanism Tubulo-glomerular feedback
nervous control Sympathetic nerve system Baroreceptor reflex
Humoral control NE, E, Angiotensine Ⅱ, endothelin, bradykinin
Regulation of renal blood flow Auto-regulation of renal circulation
BPA: 80-180 mm Hg
Mechanism Myogenic mechanism Tubulo-glomerular feedback
Significance Preventing extreme changes in renal excretion
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↑→vasoconstriction
Bp ↓ →vasodilation
Regulation of renal blood flow
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 Constriction of renal blood vessel (esp. afferent artery)
and GFR↓ Angiotensin Ⅱ
Constriction of efferent arterioles Nitric Oxide
Renal blood vessels resistance ↓ Prostaglandins and bradykinin
GFR↑