B2.3 - Cell Specialization

• Multicellular organisms begin as a single cell called a zygote, which grows and divides, at first producing unspecialized cells and then forms into many specialized cells
• Specialized cells eventually form the adult adult organism - cells arise by division of existing cells. The time between one cell division and then the next is known as the cell cycle.
• Early stage embryo development: The complex methods of gene expression determine the ways cells differentiate and take on specific roles
• Small number of genes determine body patterns during the embryos development
• Morphogens: Specific signaling molecules that are involved in gene expression
• Morphogens are extracellular (exist outside cells tissue) and occur across a gradient of concentrations. The gradient drives the process of differentiation of unspecialized stem cells into different cell types.
• High concentration of morphogens --> cells will change differently than low concentration
• Initiation/inhibition of gene expression is a result of morphogen concentration which control the way cells differentiate and develop into specific tissues.
• The concentration of morphogens also determines a series of subsequent signals. Responses to these signals determine the direction and extent of cell growth and development.
• Blastocyst: Embryo as fluid filled ball of cells, at the stage of implantation
• Embryonic stem cells: Undifferentiated cell in early stage embryo, capable of continual cell division and of developing into all the cell types of an adult organism
• Adult stem cells: occurring in the growing and adult body, within most organs and they replace dead or damaged cells
• Stem cell niche: Specific microenvironments in the body that either maintain the stem cells or promote their growth and differentiation.
• Bone marrow, hair follicles, and skin are all examples of stem cell niches.
• Certain stem cells act as pigment producing cells, so when hair regenerates, some of the stem cells convert into pigment producing cells that color the hair. With age, fewer of these cells are active and the hair loses its ability to produce melanin.
• The first formed stem cells of a zygote are totipotent and are the most versatile typer of stem cell. They can become any type of body cell, including making more totipotent stem cells and the cells that become the placenta.
• The cells within the first couple of cell divisions after fertilization are the only cells that are totipotent.
• Pluripotent cells are able to develop into many different types of cells or tissues in the body, except for becoming placental cells or totipotent stem cells.
• Pluripotent stem cells are more limited in potential, they can give rise to all of the cell types that make up the body.
• Multipotent stem cells can create, maintain, and repair the cells of one particular organ or tissue. However, they have a limited capacity for self renewal.
• Stem cells in adult tissue, such as bone marrow, are multipotent.
• The egg cell is larger than the sperm. The larger cell body of the egg allows it to store nutrients for the early development of the fertilized egg.
• Red blood cells need to be small so they can fit through the small lumen of capillaries.
• Red blood cells also have a large surface area by being small.
• White blood cells attack when bacterium, viruses, or other bad organisms enter the body.
• Neurons transmit electrochemical impulses through the body allowing coordination and response to stimuli to occur.
• Striated muscle fibers are multi-nucleated cells that attach to muscles to allow movement.
• Invaginations - invaginations of their own cell membrane to increase their surface area
• A-type intercalated cells are specialized for secreting hydrogen ions (acid secretion) and reabsorbing bicarbonate, helping to regulate blood pH. Microvilli are present.
• B-type intercalated cells work oppositely to A-type; they secrete bicarbonate and reabsorb hydrogen ions, playing a role in the body's acid-base balance. They have microvilli/
• Type 1 Pneumocytes: Extremely thin and reduced the distance for gas exchange which helps with rapid diffusion of O2 and CO2. This is crucial for the primary function of lungs.
• Type 2 Pneumocytes: Although fewer in number, they maintain health and functionality of the alveoli. Vesicles discharge a substance called surfactant which reduces surface tension, preventing them from collapsing during exhalation and ensuring they remain open for the next inhalation.
• Cardiac muscles cells are branched and allow for faster signal and contraction and enable cardiac muscles to contract quickly and repeatedly.