SA Node<span> which is also known as the sinus node, is the natural pacemaker of
the heart. It controls the heart rate by generating electrical impulses
and then sending electrical signals through the heart muscle, causing
the heart to contract and pump blood throughout the body. </span>
The SA Node is located in the outer layer of the right atrium of the heart, near the superior vena cava. It is made up of a group of cells (myocytes) positioned on the
wall of the right atrium, at the center of the heart and near the
entrance of the superior vena cava. These cells contract at a rate of
about 70-80 times per minute, which make up the natural heart beat.
1. Simple squamous epithelium
The cells are flat and only one layer.
2. Simple cuboidal epithelium
The cells are cuboid and only one layer.
3. Simple columnar epithelium.
The cells are columnar and only one layer.
4. Stratified squamous epithelium
The cells are flat and containing several layers.
5. Stratified cuboidal epithelium
The cells are cuboid and containing several layers.
6. Stratified columnar layer
The cella are columnar and containing several layers.
Well honestly, when someone turns the light in, your bodies automatic response is to close and cover your eyes.
Answer:
Estimates of historical world population
Year 1400 1600
population (in billions) 0.35–0.40 0.50–0.58
growth p.a. >0% 0.15–0.3%
Much more because you have a weather nation over the other.