Organisational Hierarchy

No. Cells in body (total)

3.7-4.0x10^13

No. Cells in body (Nucleated)

1.2x10^13

gastrulation

blastla differentiates into different layers (ectoderm, mesoderm, endoderm)

blood and immune Cells per tissue

28-29 trillion (RBC=25T,platelets=1.5T,Leukocytes=1.5-2T)

muscle Cells per tissue

10-12 Trillion

epithelial Cells per tissue

6 trillion (hepatocytes=240B, endolthelium 600B??)

connective tissue Cells per tissue

2 trillion (fibroblasts=2T, adipocytes=30B, excluding endothelial and immune cells)

nervous system Cells per tissue

1.7T (neurons=170B, glia=1.5T)

bone and cartilage Cells per tissue

27-52 billion (osteocytes=42B, chondrocytes=1-2B)

chondrocytes

cartilage cells

gut epithelium tissue turnover rate

2-5 days

neutrophil tissue turnover rate

1-5 days

RBC tissue turnover rate

120 days

Skin epidermal tissue turnover rate

2-4 weeks

Adipocytic tissue turnover rate

8-10 years

bone tissue turnover rate

25 years

chondrocytic tissue turnover rate

decades - llifetime

cardiac muscle tissue turnover rate

1%/year, most are post-mitotic

cortical neurons

neurons in the cerebral cortex

cortical neuron tissue turnover rate

not replaced, post-mitotic

olfactory neuron tissue turnover rate

30-60 days

erythrocyte replacement rate

2.4million/sec

gut epithelial cells replacement rate

1-2 million/sec

keratinocyte replacement rate

0.1 million/sec