Cell Differentiation, Stem Cells, and Morphogen Gradients in Development

Totipotent vs pluripotent cells

Totipotent can form all cell types including extra-embryonic tissues; pluripotent can form all body cells but not extra-embryonic tissues

Differentiation

Process where unspecialized cells become specialized with specific structures and functions

Morphogens effect on gene expression

Gradients activate different genes based on concentration, determining cell fate

Role of morphogen gradients

Ensure neighboring cells develop into different tissues

Genome during differentiation

All genes remain but only some are expressed

Importance of morphogens in medicine

Used to grow specific tissues for repair and transplants

Effect of disrupted morphogens

Cause congenital abnormalities such as limb defects

First stage of specialization

Totipotency in early embryonic cells

Final stage of specialization

Expression of genes for specific cell function

Morphogens in Drosophila

Bicoid and Nanos regulate body segmentation

Cell location in embryo

Determines gene activation and cell fate

Regulatory factors

Proteins that switch genes on or off

Gene expression analogy

Cells use different genes like playlists from the same genome

Outcome of gradients

Prevent developmental chaos and ensure organized tissue formation

Therapeutic uses of stem cells

Tissue repair, blood disorders, neurodegenerative diseases

Self-renewal

Ability of stem cells to divide repeatedly without differentiation

Stem cell potency types

Totipotent, pluripotent, multipotent

Totipotent stem cells

Can form all cell types including extra-embryonic tissues

Pluripotent stem cells

Can form all body cell types but not extra-embryonic tissues

Multipotent stem cells

Can form several related cell types

Importance of stem cell division

Allows formation of tissues during development

Stem cells in adults

Replace damaged or worn-out cells

Example of regeneration

Geckos regrow tails using stem cells

Limitation of stem cells

Some cannot form all cell types

Definition of stem cells

Undifferentiated cells that can self-renew and differentiate

Stem cell niche

Microenvironment supporting stem cells

Chemical signals in niche

Control stem cell behavior

Cell interactions in niche

Maintain stem cell activity

Bone marrow stem cells

Hematopoietic stem cells

Hematopoietic stem cells

Produce all blood cell types

Bone marrow niche functions

Maintain stem cells and promote differentiation

Response to blood loss

Increased red blood cell production

Hair follicle stem cells

Epithelial stem cells for hair and skin repair

Hair follicle niche roles

Control hair cycle and skin repair

Skin injury response

Stem cells migrate to repair tissue

Stem cell niche support

Provided by extracellular matrix and neighboring cells

Niche importance in medicine

Used to grow tissues for transplants

Niche and cancer

Cancers can originate in niches

Bone marrow analogy

Factory producing blood cells as needed

SA:V ratio importance

Determines efficiency of material exchange

Effect of increasing cell size

SA:V ratio decreases

Why large cells need adaptations

Lower SA:V reduces exchange efficiency

RBC size

6-8 micrometers

RBC function and shape

Transport oxygen with biconcave shape for high surface area

Sperm size

5-10 micrometers

Egg size

About 100 micrometers

WBC size

10-20 micrometers

Neuron size

Up to 1 meter long

Muscle fiber size

30-40 micrometers wide and long

Cell size and energy

Larger cells have higher energy demands

Need for material exchange

Obtain nutrients and remove waste

Surface area role

Determines exchange capacity

Volume role

Determines metabolic needs

SA:V ratio trend

Decreases as size increases

SA of cube formula

6 x side length squared

Volume of cube formula

Side length cubed

SA:V formula

6 divided by side length

Jelly cube experiment

Shows effect of SA:V on diffusion

Diffusion in small cubes

Faster due to higher SA:V

Diffusion in large cubes

Slower due to lower SA:V

Limitations of low SA:V

Slow diffusion and high metabolic demand

Adaptations for SA:V

Flattening, microvilli, multicellularity

Microvilli

Projections increasing surface area for absorption

Invagination

Folding of membrane to increase surface area

Root hairs

Increase absorption in plants

Importance of adaptations

Improve exchange and efficiency

Pneumocytes function

Gas exchange in alveoli

Type I pneumocytes

Thin cells for diffusion covering most surface

Type II pneumocytes

Produce surfactant

Surfactant

Reduces surface tension and prevents collapse

Lamellar bodies

Store surfactant

Alveolar thickness

Very thin to allow fast diffusion

Cardiac muscle cells

Branched with one nucleus and involuntary control

Skeletal muscle fibers

Long, multinucleated, voluntary control

Myofibrils

Contain actin and myosin for contraction

Sliding filament theory

Filaments slide to shorten muscle

Intercalated discs

Allow electrical signal transmission

Syncytium

Skeletal muscle formed by fused cells

Gametes

Reproductive cells sperm and egg

Sperm mitochondria

Provide ATP for movement

Sperm tail

Propels sperm

Acrosome

Contains enzymes to penetrate egg

Egg cell size

Large for nutrient storage

Zona pellucida

Protects egg and prevents multiple fertilization

Egg function

Supports early embryo development

Genetic contribution

Sperm and egg each provide half

Sperm specialization

Movement and fertilization

Egg specialization

Nutrient storage and development support