A human cell has about 1000–2000 mtDNA molecules

A human egg has about 500,000 mtDNA molecules

A sperm has only about 100 mtDNA molecules

TLS Online TPP Program

#Id: 1221

#Unit 7. System Physiology – Animal

The receptor for PTH is coupled, via a Gs protein, to adenylyl cyclase.

TLS Online TPP Program

#Id: 1222

#Unit 7. System Physiology – Animal

In bone, PTH receptors are located on osteoblasts but not on osteoclasts.

TLS Online TPP Program

#Id: 1223

#Unit 7. System Physiology – Animal

PTH stimulates osteoclast activity and bone resorption by maturation of osteoclast cells.

TLS Online TPP Program

#Id: 1224

#Unit 7. System Physiology – Animal

Two osteoblast proteins responsible for osteoclast maturation: 

1. Receptor activator for nuclear factor κ-B ligand  

2. Macrophage colony-stimulating factor

TLS Online TPP Program

#Id: 1225

#Unit 7. System Physiology – Animal

Osteoblasts also produce osteoprotegerin, a cytokine that inhibits bone resorption. ate osteoclast activity and bone resorption.

TLS Online TPP Program

#Id: 1226

#Unit 7. System Physiology – Animal

Vitamin D and PTH appear to stimulate production of mature osteoclasts through the dual action:

 1. Inhibiting OPG production

2. Stimulating RANKL formation