B.2.3 cell specialization

Following fertilisation, an unspecialised zygote will divide and develop into a mass of specialised cells (early embryo) via differentiation

gene regulating chemicals (transcription factors) called morphogens

impact of the morphogen will be determined by its relative concentration
Cells closer to the morphogen source receive higher concentrations of morphogen, resulting in the activation of more genes
Cells further away from the morphogen source receive lower concentrations of morphogen, resulting in the expression of fewer genes

morphogen gradients control the differential expression of genes within an early-stage embryo

divde indefinitely to create more stem cell. no limit to number of time stem cells can divide, divide via mitosis and replace damage tissues/cells
differentiate to become a specialized cell type and produce new tissue

present in many tissues including the bone marrow, skin and liver.
the location of the stem cells within tissue
provides a micro-environment with the conditions needed for the stem cells to remain inactive and undifferentiated over a long period of time or to proliferate rapidly and differentiate when required.

Bone marrow( hematopoietic stem cells) - can become different type of blood cells and treat leukaemia
hair follicles(hair follicle stem cells (HFSC) - These can differentiate into keratinocytes and sebocytes to replace hair in the skin.

Totipotent: Form any cells type and develop into entirely new organism, early stages of cells of embryo
pluripotent: a little bit later in embryo development, Can produce most cell types but not whole organisms, Only in embryo, arising from the three germ layers(ectoderm, mesoderm, and endoderm)
multipotent: Late embryo through adulthood, a number of closely related cell types

Totipotent - zygote
Pluripotent -inner cell mass of blastocysts
Multi-potent - bone marrow

Allow them to form any cell of the organism, The cells of the early embryo are the most versatile. As the embryo develops, the cells gradually become more differentiated.

Sperm: very narrow and have one of the smallest volumes of any cell. very streamlined shape so they can swim efficiently to the egg.
Egg: one of the largest volumes of any human cell. This enables them to store a large amount of food reserves in the cytoplasm for the developing embryo.
red blood cell: very small and have a relatively large surface area compared with their volume, due to their biconcave shape. This enables them to travel down very narrow capillaries and the large surface area enables efficient transfer of oxygen.
Motor neurons: Motor neurons have a large cell body. This enables them to make enough proteins to maintain the very long axon.
striated muscle fibers: can be as long as 100mm long. This enables greater force and contraction of the muscle than smaller muscle cells.

at the surface, oxygen and nutrients are absorbed, while waste is excreted. At the cells interior, metabolic reactions happen, which need nutrients and oxygen, and produce waste.

Surface area = 6s^2, volume = s^3, SA:V ratio = 6/s (where s is the side length of the cube).

Benefits: simplicity and ease of calculation
limitations: cells have more complex shapes, affecting actual surface area and volume.

As cell size increases, the SA:V ratio decreases, limiting the efficiency of material exchange and metabolic processes.
volume increases at a far greater rate than their surface area.

cells are limited in size by the SA:V ratio because a lower ratio reduces the efficiency of nutrient uptake, waste removal, and overall cellular function.