Final answer:
The cell membrane's phospholipid bilayer contains protein channels like ion channels, aquaporins, gated channels, ligand-gated channels, and voltage-gated channels, each with specific functions. All epithelial tissues are avascular, with simple squamous epithelium aiding in diffusion and filtration.
Step-by-step explanation:
The phospholipid bilayer of the cell membrane is embedded with various types of protein channels that each play distinct roles. Some of the different types of channels include:
- Ion channels: Allow the specific passage of ions like Na+, K+, Ca2+, and Cl- across the membrane following their concentration gradients.
- Aquaporins: Specialized for the passage of water molecules.
- Gated channels: Open or close in response to a stimulus, controlling ion flow based on cellular needs.
- Ligand-gated channels: Open in the presence of a specific binding substance, typically a hormone or neurotransmitter.
- Voltage-gated channels: Open and close in response to changes in membrane potential, critical in nerve impulses and muscle contraction.
Epithelial tissues are avascular and rely on diffusion for the uptake of nutrients; simple squamous epithelial cells, the thinnest type, facilitate quick diffusion and filtration.
All epithelial tissues, including simple squamous epithelium, are avascular, meaning they do not contain blood vessels.