W2L2 Flashcards
Germ layers and what they differentiate into
Ectoderm
- nervous system
- epidermis
- organ system: nervous
Mesoderm
- skeleton
- muscle
- gonads
- circulatory and lymphatic systems
- organ systems: CV, muscular, skeletal, immune, lymphatic, urinary, reproductive
Endoderm
- digestive tract
- liver, pancreas
- respiratory system
- bladder
- organ systems: digestive, endocrine, respiratory
Sometimes 2 germ layers come together to make up these organ systems; they interact with one another
Tissue types
- Nervous tissue
- mental activity, sensory input and integration, regulates muscles and glands, homeostasis - Muscular tissue (skeletal, cardiac, smooth)
- contraction; movement and support - Connective tissue
- Adipose-based and collage-based (teeth, bones, cartilage, tendons) connective tissue
- supportive role in tissues and organs: energy storage (e.g., nutritional support for epithelium), protection of organs, tissue repair, structure
- Blood (Some people think blood is a separate tissue category btw)
– regulates nutrient and oxygen transport, metabolic waste, immune system - Epithelial tissue
- lines surfaces and cavities; secretion, absorption, protection, etc.
Cell Differentiation
- All cells have the same genome - select different genes to express
- Cells have memory - record of ancestral origin
- if cell is injured, it can go back to its original differentiation. i.e. a damaged epithelial cell will repair itself to become an epithelial cell again. This is process of healing
- Some say that cancer cells have no memory bc they keep proliferating without differentiating - Cell decisions - proliferate or differentiate
- cells can proliferate to heal something (for example), and then re-differentiate afterwards
Tissues and their Extracellular Matrix (ECM)
Holds cells and tissues together
Organized environment for cells to move & interact
Bidirectional transfer of information
- regulates proliferative capacity, differentiation and survival
- Bidirectional: info goes to nucleus, nucleus sends stuff out
What is the ECM?
Meshwork of proteins and polysaccharides secreted by cells into the spaces that surround them
Many functions:
- Structural (bone and teeth)
- Tensile strength (tendons)
- Transparent matrix for sight (cornea)
- Control cell behavior (basal lamina is at the interface between epithelium and connective tissue)
Matrix producing cells in skin
Epithelial and fibroblasts
Matrix producing cells in skin: Epithelial cells
Minor role in making ECM
Located in the epidermis
It is polarized:
- Simple epithelium: apical surface of ep cell faces lumen of a tube or external environment
- Stratified epithelium: spindle orientation (knows which way is ”up”) and cell fate determination (differentiation)
- Basal surface of ep cell rests on (and associates with) the basal lamina - extracellular matrix that supports cells
Connected with adjacent cells by specialized attachments including tight junctions, desmosomes and gap junctions
Bottom cells are more stem-like, they keep proliferating. As you go to the top, some die, some crosslink to make water barrier; this is because they differentiate
Basal lamina = basement membrane in this course
Skin layers
Epidermis, then dermis, then hypodermis
Matrix producing cells in skin - fibroblast
Major role in ECM production
In the dermis
Not attached to adjacent cells, very motile
Do not have apical-basolateral polarity (do not know what is out of the body or inside of the body)
Have leading edge and lagging (or trailing) end polarity (migration)
- migration is on leading edge
Are in contact with extracellular matrix (via focal adhesions)
- Focal adhesion is for traction so it can move
Epithelial tissue vs connective tissue
Epithelial tissue represents epidermis
- ECM is rare
- Existing matrix is called the basal lamina
- Cells tightly bound into sheets called epithelia
- Cells attached to each other by cell-cell adhesions
- Cell-cell adhesions bear most of the mechanical stress
Connective tissue represents dermis
- ECM is abundant
- Matrix is rich in collagen and proteoglycans
- Cells sparsely distributed in the matrix
- Direct attachment between cells is rare
- Matrix bears most of the mechanical stress, not the cells
Cell-Matrix Interactions
Cells adhere to their extracellular matrix with adhesion molecules
These junction types are classified based on the connection to internal cytoskeleton
Integrins are transmembrane proteins. Integrins will bind to diff types of cytoskeleton.
Focal adhesions = integrin binding to actin cytoskeleton
- Are transient, allow for treadmilling/migratory affect
- Found in most cells. But cells with focal adhesions tend to migrate more, such as fibroblasts
Hemidesmosomes = integrin binding to intermediate filaments
- More stable; Don’t move as much, such as epithelial cells
- Plectin is a protein that binds
to intermediate filaments
Resolution power of Immunofluorescence microscopy
Approximately ½ the wavelength of light
For e.g., assuming visible light is 400-600 nm, resolution is 200-300 nm
Therefore, two objects closer than 200-300 nm will superimpose (i.e., they will look like one object)
