C8 FORMATION OF URINE BY THE KIDNEY

Today I am going to introduce:

1.the microstructure of the Kidney2. glomerular filtration

our goals are

⑴ understand microstructure of the kidney ⑵ understand the characteristic of blood circu

lation in the kidney ⑶ describe glomerular filtration

Functions of The kidney: ⑴ regulate water and inorganic ion equilibrium .maintain constant of internal environmentregulate the osmotic pressure of body fluids;

the osmotic pressure is formed by electrolyte, kidney regulate value of electrolyte , acid and base excretion, and then regulate the osmotic pressure , the electrolyte equilibrium and adjust the balance of acid and base in body fluids.

⑵ excrete metabolic waste end-products into the urine ;

NH3 some poisons

⑶ excrete foreign chemicals drugs metabolites

⑷gluconeogenesis synthesize glucose from amino acids. ⑸endocrine function secrete erythropoietin, renin,

Which is main function of the kidney? excrete urine

produce urine

Store urine

Transport urine

Which is main function of the ureter ? excrete urine

produce urine

Store urine

Transport urine

Mechanisms of urine formation :

(1) Filtration(2) Secretion(3) Reabsorption

Structure of the kidneys and urinary system

cortex

medulla

The Nephron and collecting Duct

2,000,000 nephrons

Functional unit of kidney

① composition of nephron

loop of Henle;

nephron

renal corpuscle

glomerulus

Bowman’s capsule

renal tubule

proximal convoluted

tubule

distal convoluted tubule

The collecting duct

What is functional unit of the kidney? nephron

glomerulus

renal tubule

collecting duct

② types of nephron

(1)cortical nephrons: (85% ) In the outer and middle portion

of the renal cortex (shorter loops)

cortical nephronsjuxtamedullary nephrons

loop of Henle

Collecting duct

② types of nephron(2) juxtamedullary nephrons : (15% ) In the inner cortex (longer loops)

cortical nephronsjuxtamedullary nephrons

loop of Henle

Collecting duct

Juxtaglomerular Apparatus (1)the juxtaglomerular cells: they are specialized myoepithelial cells in afferent arteriole

release renin

(2)the macula densa :

monitor the concentration of NaCl in the tubular fluid and transferthe information to juxtaglomerular cells

What is cell of release renin?

juxtaglomerular cells

extraglomerular mesangial cell

macula densa

What is cell of monitor the concentration of NaCl in the tubular fluid?

juxtaglomerular cells

extraglomerular mesangial cell

macula densa

1.The endothelial layer of the capillary2.The basement membrane 3.The epithelial cell layer of Bowman’s capsule

Glomerular Membrane

physical barrier

special structure

Fenestra: prevent the filtration of all particles with an average size greater than 16 millimicron. Red cell

Meshwork (basement membrane of the capillary)

proteoglycan

prevents the filtration of all particles with diameter greater than 11 millimicron

Slit-pores

Slit-pores

prevent the filtration of all particles with diameter greater than 7 millimicron.(diameter of plasma proteins ﹥7 millimicron)plasma proteins

Electrical barrier

Glycoprotein (negatvely charge)

prevent filtration of negatively charged plasma proteins

﹤2 nm(millimicron) –can be filtered easily﹥4.2 nm--can not be filtered between---can be filtered proportionately

Anionic substances: difficult to be filtered (albumin)

Neutral substances:

The glomerular membrane is almost completely impermeable to all cells and plasma proteins but is highly permeable to all dissolved substances(such as electrolyte, glucose )

In following substance , What substance is not filter through the glomerular membrane.

plasma protein

water

ions

electrolyte

glucose

Innervation of the renal vessels

Sympathetic fiber Sympathetic nerve cause constrict

ion of renal blood vessels, which greatly decreases blood flow to the kidney.

renal artery → afferent arteriole→ glomerular capillaries→efferent arteriole→peritubular capillaries → renal vein

Renal Blood Flow and Regulation

(1)glomerular capillary bed : high pressure →filtering continually out of the glomerulus into Bowman’s capsule

Two capillary beds

(2)peritubular capillary bed :

low pressure → fluid being reabsorbed continually into the capillaries

What is characteristic of the glomerular capillary bed?

low pressure

high pressure

What is characteristic of the

peritubular capillary bed? low pressure

high pressure

① renal blood flow is about 1200ml/minute ② The renal fraction is about 21 per cent

(1)Renal Blood Flow

③ About 94 per cent of renal blood flow goes to the renal cortex.

(2) Autoregulation of Renal Blood Flow

When BP changes from

80 to 180 mmHg, a relatively

constant renalblood flow is

maintained.

mechanism

* When BP descends, afferent arteriole relax and decrease resistance

of afferent arteriole, and then the renal blood flow does not change.

* When BP rises, afferent arteriole contract and increase resistance of

afferent arteriole, and then the renal blood flow does not change, too

(3)Neuro-Humoral Control

Sympathetic nerve: → constriction of renal blood vessels →decreases blood flowVasoconstrictor agents : Angiotensin II epinephrine and norepinephrine Vasodilator agents : bradykinin, NO and some prostaglandins

plasma → Bowman’s capsule→ proximal convoluted tubule → loop of Henle → distal convoluted tubule→ collecting duct → papilla → renal alyces

when blood passes through the glomerulus, plasma component (water, ions, and small molecules filter into Bowman's capsule.

Glomerular Filtration

2-2. Filtration Pressure

① capillary pressure (causes filtration )

② colloid osmotic pressure

in the blood

(oppose filtration)

③ capsular pressure

in Bowman’s capsule (oppose filtration)

afferent arteriole efferent arteriole

The effective filtration pressure(EFP)

③ capsular pressure

② glomerular colloid osmotic pressure

①the glomerular pressure

EFP = ① - (②+ ③ ）

① the glomerular pressure : 45 mmHg. ② colloid osmotic pressure in the blood increase from 25 to 35 mmHg.

③ capsular pressure: 10 mmHg

45mmHg 10mmHg

25-35mmHg

45mmHg 10mmHg

25-35mmHg

(1) afferent side : EFP=45-(25+10)=10mmHg filter (2) efferent side : EFP=45-(35+10)= 0mmHg filter stop

2-3.Glomerular Filtration Rate (GFR)

The quantity of glomerularfiltrate formed each minute in all nephrons of both kidneys. (normal:125 ml/min) 180 L/d 99 % reabsorbed 1 % excreted as urine

filtration fraction The ratio that GFR and renal plasma flow.GFR=125ml/minrenal plasma flow =660ml/min

Filtration fraction

=125/660=19%

filtration coefficient (Kf )

It image the condition of the area and permeability of glomerular membrane. a constant in nomal change in kidney disease

GFR= Filtration pressure • Kf

2-4. determinants of the glomerular fitration rate

GFR= Filtration pressure • Kf

Because of autoregulation, 80 mmHg ~ 180 mmHg. the glomerular filtration rate is constant

(1) Effect of Glomerular Capillary

Pressure

BP ↑(over 180mmHg) → glomerular capillary pressure↑ → effective filtration pressure ↑ → GFR↑

Liver function ↓ or proteinuria→ plasma colloid osmotic pressure↓ → effective filtration pressure ↑→ GFR↑

(2) Effect of the Plasma Colloid Osmotic pressure

ureter occlusion caused by ureteral calculus, cancer etc.→ Capsular Pressure↑ → effective filtration pressure → GFR

(3) Effect of Bowman’s

capsule Pressure

③ capsular pressure

② glomerular colloid osmotic pressure

①the glomerular pressure

EFP = ① - (②+ ③ ）

(4) Effect of Renal Blood Flow renal blood flow↑→plasma colloid osmotic pressure rises

slowly → GFR ↑

renal plasma flow

renal blood flow

plasma colloid osmotic pressure rises fastly

flitrate Concentration of plasma protein%

Concentration of plasma protein in normal

renal blood flow

in normal

the glomerular

pressure

glomerular colloid osmotic pressure

capsular pressure

length

renal blood

flow

the glomerular pressu

re

glomerular colloid osmotic pressure

capsular pressure

length

renal blood

flow

the glomerular pressu

re

Glomerular

colloid osmotic pressure

capsular pressure

length

(1)Kf : the area and permeability of glomerular membrane Permeability↑→ Hematuria, proteinuriathe area →urine in chronic

nephritis

(5)Glomerular capillary filtration coefficient

We have studied:

1. the anatomy construction of the kidney

2. the characteristic of blood circulation in the kidney

3. glomerular filtration

Please answer the questions

1.Explain physiology word: Glomerular Filtration Rate filtration fraction2. What is functional unit of the kidney?3. What is composition of nephron4. What are characteristic of the glomerular capillary bed

and peritubular capillary bed 5. The effective filtration pressure 6.Factors Affecting GFR