C8 FORMATION OF URINE BY THE KIDNEY
Jan 05, 2016
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