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↑