1. YU Yanqin, PhD Zhejiang University, School of Medicine
Kidney Physiology
YU Yanqin, PhD
Zhejiang University, School of Medicine

2. The paired kidneys form a filtrate of the blood that is modified by reabsorption and secretion; urine designated for excretion moves along the ureters to the bladder.

3. Overview – Functions of the Kidney
Regulation of body fluid osmolality (渗透压)
Production of hormones:
Erythropoietin（促红细胞生成素）, Kinins（激肽） and Renin（肾素）, Prostaglandins（前列腺素），1,25-dihydroxycholecalciferol（1,25-羟基维生素D3）
Regulation of electrolyte and water
Excretion of waste products
Regulation of acid and base

4. Structure of the Kidney

5. Nephron（肾单位） Renal corpuscle（肾小体） Renal tubular system（肾小管）
- Glomerulus （肾小球）
- Bowman’s capsule（肾小囊）
Renal tubular system（肾小管）
Proximal convoluted tubule
Loop of Henle（髓袢）
- Descending thick limb
- Descending thin limb
- Ascending thin limb
- Ascending thick limb
Distal convoluted tubule
Collecting duct system

6. Types of the Nephron Cortical nephron（皮质肾单位）
Juxtamedullary nephron （近髓肾单位）

7. Differences between the Nephrons
Size
Number in
percentage
A.A / E.A
in diameter
Renin production
Cortical nephron
small
80 to 90
2:1
yes
Juxtamed nephron
big
10 to 20
1:1 or 1:1+ no

8. Juxtaglomerular Apparatus（球旁复合体）
Juxtaglomerular cells球旁细胞
Renin-producing granular cells
Macula densa致密斑
Extraglomerular mesangial cells球外系膜细胞

9. The intersection of the macula densa in the distal tubule
with the afferent and efferent arterioles forms the
juxtaglomerular apparatus, which secretes the endocrine
signal known as renin into blood in the afferent arteriole.

10. Blood Supply of the Kidney
1200 ml/min, 20 % of the cardiac output
 Cortex: 94 %
Outer medulla: 5-6 %
Inner medulla: < 1 %
 two capillary networks

11. Autoregulation of Renal Blood Flow
Range of regulation
BP: 80 ~ 170 mmHg
Mechanisms
Myogenic mechanism 肌源学说
Flow dependent mechanism
(Tubuloglomerular feedback管球反馈)

12. 1. Myogenic mechanism肌源学说
Arterial blood pressure  → contraction of the vascular smooth muscle
→ constriction of the blood vessel → the blood flow relatively constant

13. 2. Tubuloglomerular feedback管球反馈
Renal blood flow  → glomerular filtration  → Na+ content in the renal filtrate  → detection by the macula densa → a signal sent to the renal arterial system → restoration of the renal blood flow and glomerular filtration rate to normal

14. Neural Regulation of Renal Blood Flow
Activation of the renal sympathetic nerves → constriction of the renal arterioles → renal blood flow and glomerular filtration rate (GFR) 

15. Humoral Regulation of Renal Blood Flow
Norepinephrine去甲肾上腺素, Epinephrine肾上腺素, and Endothelin内皮素
To constrict renal blood vessel and  GFR
Angiotensin II血管紧张素II
To constrict efferent arterioles
Nitric Oxide一氧化氮
 renal vascular resistance and ↑GFR
Prostaglandins 前列腺素and Bradykinin缓激肽
Tend to increase GFR

16. Urine Formation

17. Filtration
Filtrate (glomerular urine原尿 )=blood plasma-proteins 180L/day
Final urine终尿
1.5L/day

18. Composition in the Filtration Fluid

19. Structure of the Filtration Membrane
 Capillary endothelium
 Basement membrane
 Epithelial cells of the visceral layer of the renal capsule

20. Permeability of the Filtration Membrane __Molecular barrier分子屏障
 Capillary endothelium
Fenestrae: 70 ~ 90 nm
 Basement membrane
Meshwork of collagen & proteoglycan fibrillae:
2 ~ 8 nm
 Epithelial cells of the visceral layer of the renal capsule
Slit pore: 6 ~ 11 nm

21. Electrostatic Barrier 电荷屏障 of the Filtration Membrane
Negatively charged glycoproteins in the endothelial cells & basement membrane

22. Effective Filtration Pressure (有效滤过压，EFP)
EFP = Hydrostatic pressure in the glomerulus肾小球毛细血管血压 – (Oncotic pressure of plasma 血浆胶体渗透压+ Hydrostatic pressure of the liquid in the renal capsule肾小囊内压)
The net filtration pressure (NFP)

23. Glomerular Filtration
Glomerular filtration rate (肾小球滤过率，GFR)
The quantity of the glomerular ultrafiltrate formed each minute in all nephrons of both kidneys
GFR = Kf X Net filtration pressure
Normal value: 125 ml / min
Filtration fraction (滤过分数，FF)
FF = GFR / Renal plasma flow
Normal value: 19%

24. Glomerular Capillary Filtration Coefficient (Kf)
 Definition
The product of the hydraulic conductivity and surface area of the glomerular capillaries
= # of pores per unit area x total area of filtration
 Kf = GFR / Net filtration pressure

25. Factors Affecting Filtration
1) Glomerular hydrostatic pressure肾小球毛细血管血压
Late hypertension  diameter of A.   renal blood flow   glomerular hydrostatic pressure   GFR 

26. Factors Affecting Filtration
2) Colloid osmotic pressure of plasma血浆胶体渗透压
Malnutrition  Colloid osmotic pressure of plasma  GFR 
3) Bowman’s capsule pressure肾小囊内压: stone or cancer

27. Factors Affecting Filtration
4) Renal plasma flow
5) Filtration area滤过面积: >1.5m2
Acute glomerulonephritis急性肾小球肾炎
6) Permeability通透性 of the filtration membrane
Albuminuria蛋白尿 or hematuria血尿

28. Summary Terms Glomerular filtration rate Filtration fraction
Net filtration pressure
Filtration coefficient
Tubuloglomerular feedback

29. Summary
List the factors affecting glomerular filtration

30. Intensive Reading Textbook of Medical Physiology (Guyton & Hall)
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