How can squamous epithelia both facilitate diffusion and prevent damage from abrasion?
Squamous epithelia can be either simple or stratified. As a single layer of cells, it presents a very thin epithelia that minimally inhibits diffusion. As a stratified epithelia, the surface cells can be sloughed off and the cells in deeper layers protect the underlying tissues from damage.
What are the similarities between cartilage and bone?
Both contain cells other than the traditional fibroblast. Both have cells that lodge in spaces within the tissue called lacunae. Both collagen and elastic fibers are found in bone and cartilage. Both tissues participate in vertebrate skeletal development and formation.
Multiple sclerosis is a debilitating autoimmune disease that results in the loss of the insulation around neuron axons. What cell type is the immune system attacking, and how does this disrupt the transfer of messages by the nervous system?
In multiple sclerosis, the immune system attacks the oligodendrocytes. The death of oligodendrocytes results in the loss of the insulating sheath around the axon of the neurons. When the sheath is gone, the electrical impulses travel much more slowly down the length of the axon.
When a person leads a sedentary life his skeletal muscles atrophy, but his smooth muscles do not. Why?
Skeletal muscles are involved in voluntary motion, so the person has to make the choice to work those muscles through exercise or movement. Smooth muscles are involved in involuntary activities of the body (ex. blood vessel expansion and contraction, intestinal peristalsis) so they are active even when a person is sedentary.