Epithelial Tissue

Proteins

• fold up into specific shapes according to the sequence of amino acids in the polymer 

  • the protein function is directly related to the resulting 3D structure

Random mutation

•  can change function of proteins

  • ex: sickle cell → changes function

Chromosome

Threadlike structure of nucleic acids and protein found in the nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes

• Each gene occupies a unique locus (location) on a particular chromosome

Parental Copies of Genes

• Each parent contributes half: DUring reproduction, the mother’s egg cell and the father’s sperm cell each contain 23 chromosomes. 

• Fertilization restores the full set: When sperm and egg join, the resulting zygote has 46 chromosomes-23 from each parent 

• Homologous pairs are formed: The child’s chromosomes are organised into 23 pairs, where one chromosome in each pair comes from the mother and the other from the father.

• Genes come in pairs (alleles): each parent’s version of a gene (allele) combines to determine the child’s traits 

Mitosis

produces two genetically identical “daughter” cells from a single “parent” cell, whereas meiosis produces cells that are genetically unique from the parent with half as much DNA

• 2 daughter cells → each enter their own interphase and begin a new round of the cell cycle

• Mitosis is 10% of average cells lifetime

Somatic cells

• all the cells in the body that are not reproductive cells 

  • Diploid (2 copies) → 46 chromosomes in human

  • Mitosis

Gametic cells (reproductive cells)

• sex cells that fuse together during fertilization to create a new organism

  • Haploid (1 copy of each chromosome) → 23 chromosomes in human

  • Meiosis

Interphase

grows, replicates its chromosomes, and prepares for cell division

• Cells are in Interphase usually. Interphase is 90% of the average cell's lifetime. 

Cytokinesis

• Division of cytoplasm, producing two daughter cells. Each daughter cell can start a new cell cycle

• How daughter cells are separated 

• Creates identical cells in mitosis

G1 checkpioint

•  A cell has to receive a go-ahead signal at the G1 checkpoint. If it does not receive a go-ahead signal at that point, it may exit the cycle, switching into a nondividing state called the G0 phase 

Connective tissue

• supports and connects the body’s organs and tissues

  • Ex: bones, fat, ligaments

Muscle tissue

• allows the body to move

  • skeletal muscle, smooth muscle

nervous tissue

• carries messages throughout the body

  • neurons

Protection

• Epithelial tissue protects the body from the outside environment 

  • The protection can be physical like skin or chemical like stomach lining

Absorption

Epithelial tissue absorbs nutrients from the digestive tract and other body cavities 

Secretion

• Epithelial tissue secretes various substances, such as mucus, hormones, and enzymes 

Sensation

• Epithelial tissue contains sensory receptors that allow us to sense the outside environment

  • These receptors can detect touch, temperature, pain, and other stimuli

ECM

• network of fibrous substances that surround/support cells in tissue 

  • Varies greatly depending on tissue 

  • ECM is made by the cells within the tissue; therefore, it is both unique to each tissue and plastic, depending on the activity of the cells 

  • Example: the ECM of bone tissue is solid while the ECM of the blood is liquid 

  • In the ECM, cells are held in place, guided in their movement (for cells that move), and supported

Collagen fiber

• main component of ECM

• strong protein strands

Proteoglycans

• are protein that are chemically modified with sugar molecules 

• main component of ECM

Tight junctions

• fuses the membranes of two neighboring cells together tightly so that there is no extracellular space between them. 

  • Blocks the movement of substances through the extracellular space between cells. 

  • Important feature of the intestine

Gap junctions

clusters of channels that allow diffusion of ions and small molecules between adjacent cells

Epithelial Tissue

• large sheets of cells covering all the surfaces of the body. 

  • Main function is protection, found in locations that are exposed to the “outside” world, i.e skin and lining of mouth 

    • Lines hollow organs and body cavities 

Inside vs outside spaces

• “Inside” spaces are sterile and no bacteria should be found within them. Blood vessels 

  • Endothelium lines “inside structures”

• “Outside” spaces are nonsterile: the airways, the digestive tract, and the urinary and reproductive systems 

  • Epithellium lines “outside structures” 

 apical side

“Top surface” of the epithelia

• Epithelial cells often have either cillia (A) or microvilli (B) on their apical surface 

Basal side

“bottom surface”

Polar (for ET)

• cells have distinct sides that are structurally and functionally different from each other

Cillia

• Sweep materials off the apical surface 

Microbilli

TO expand the surface area of the cell

Simple ET

• is for tissue with a single layer of cells

Stratified ET

is for tissue consisting of several layers

Simple Epithelium

•  every cell rests on the basal lamina 

Stratified epithelium

•  only the basal layer of the cell rests on the basal lamina

• These epithelia are found in places where the apical surface is subject to more friction and the multiple cell layers protect the underlying tissue from wear and tear

• To maintain the number of layers in the tissue, the cells at the basal layer are constantly undergoing mitosis to generate new layers

Stratified squamous epithelium

• the most common type of stratified epithelium in the human body

• Found in moist places of the body, such as lining the inside of your cheeks. Cells shed frequently.

• When stratified squamous epithelia are found in places of the body that are dry, such as the surface of your skin, the epithelium is modified to help retain moisture. 

  • The apical layer of living cells is topped by additional layers of dead cells that are filled with protein keratin

Epithelial tissue

•  are sheets of cells that cover exterior surfaces of the body, line internal cavities and passageways, and form certain glands 

  • Consist of: 

    • Primary epithelium, covering of surfaces 

    • Glandular epithelium, forms glands

Endocrine gland

• if it secretes within the body and bloodstream 

• Both exocrine and endocrine gland formed by glandular epithelium 

  • Endocrine glands are always ductless and release their secretions directly into surrounding tissues and the bloodstream 

  • Secretions (hormones) are released into the interstitial fluid, diffused into the bloodstream, and delivered to cellular receptors 

    • The endocrine system is part of a major regulatory system coordinating the regulation and integration of body

Exocrine gland

•  if it secretes onto an epithelium to the outside of the body 

• Both exocrine and endocrine gland formed by glandular epithelium 

  • Sweat glands and the glands of the digestive system are two examples of exocrine glands 

  • Exocrine glands often have a duct through which the gland’s secretions leave to reach the epithelium 

  • Exocrine glands release their contents through a duct that leads to the epithelial surface 

    • Mucus, sweat, etc, are examples of secretion from exocrine glands

    • Most exocrine secretions are released through tubular ducts

Goblet cells

• Mucus-secreting cells that are technically unicellular exocrine glands

  • Also thought to be involved  with immunoregulation 

  • Mucus forms a protective gel-like layer over the surface epithelium and protects against bacterial invasion 

  • GOBLET CELLS DO NOT HAVE DUCTS. RELEASE THEIR SECRETION ON THEIR ATYPICAL SURFACE