Computer Science Basics

The body's organs are composed of four basic tissue types: epithelial, connective, muscular, and nervous.
Substances entering or leaving an organ must pass through epithelial tissue first.
Epithelial tissue forms coverings on all internal and external surfaces, lines cavities and organs, and is the primary tissue in glands. Its functions include protection, secretion, and absorption, varying by location.

Epithelial tissue is made of epithelial cells that come in various shapes and are arranged in single or multiple layers based on their function and location.
Cells make up all living organisms and tissues. Over 30 trillion cells make up the human body.
Epithelial cells form cohesive sheets covering many body surfaces (skin, gut), and form secretory glands (breast, tear ducts, sweat, salivary). Ducts are lined with other epithelial types.
Epithelial cell layers vary from single cells thick to several cells deep, affecting their overall shape (cuboidal, columnar, stratified/flattened).
Specialized epithelial cell surface features called microvilli increase surface absorption (small intestine) and protect from bacteria.
Cilia are tiny hair-like structures that move substances along surfaces (respiratory tract, fallopian tubes). Specialized cilia-like structures called stereocilia are found in structures like the inner ear, helping hearing and balance.

Epithelial cells are classified by shape and arrangement.
Shape-based categories: squamous (flat and sheet-like), cuboidal (cube-like, equal width, height, and depth), columnar (column-like, taller than wide).
Arrangement-based categories: simple (one layer of cells), stratified (multiple layers of cells), pseudostratified (appears layered but is single).

Simple squamous: lines blood vessels, body cavities, allowing substance passage.
Simple cuboidal: found in glandular tissue and kidney tubules.
Simple columnar: specialized for absorption and secretion; lines stomach and intestines. Often has microvilli and/or cilia.
Stratified squamous: protects against microorganisms and water loss; outer skin layer (epidermis).
Stratified cuboidal: less common, found in excretory ducts of salivary/sweat glands.
Stratified columnar: less common, lines mucous membranes (eyelids).
Pseudostratified columnar: lines upper respiratory tract, often ciliated.

Transitional: several layers of cells that become flattened when stretched; lines most of the urinary tract, allowing the bladder to expand.
Glandular: specialized to produce and secrete hormones, proteins, and other substances; found in glands.
Olfactory: located in nasal cavity; has receptor cells with cilia to detect odor molecules, transferring information to the brain for interpretation.

Pathology is laboratory examination of cells to diagnose conditions.
Epithelial cells in urine: Part of urinalysis, checking cell number for conditions.
Pap smear: examination of cervical cells for abnormal or cancerous cells.
Biopsy: Tissue examination, including epithelial samples (e.g., prostate, small intestine, lining of the body cavities).
Cytology: Cell examination; includes samples from various areas like the respiratory tract, thyroid, eye, and reproductive tissues

These are three types of epithelial cell layers lining internal organs and body cavities, and forming the outer layer of skin.
Epithelium generally lines pathways open to the external environment, like the respiratory and digestive systems.
Endothelium lines internal pathways such as blood vessels.
Mesothelium lines major body cavities (peritoneum, pleura, pericardium) and secretes serous fluid.

Body membranes are tissue sheets covering the body, lining cavities, and covering organs.
Epithelial membranes: Consist of epithelial tissue and underlying connective tissue. Mucous and serous membranes are main types.
- Mucous membranes: Line body cavities open to the outside. Found in the digestive, respiratory, excretory, and reproductive tracts.
- Serous membranes: Line closed body cavities; secrete serous fluid to reduce friction. Have two layers: parietal (lining the cavity wall) and visceral (covering the organ).

Connective tissues connect, support, and protect body structures.
They have an abundant extracellular matrix with relatively few cells.
They can reproduce, but not as rapidly as epithelial cells.
Most connective have good blood supply, some do not.
Types of connective tissues include: loose (areolar, adipose, reticular), dense regular (tendons and ligaments), dense irregular, and specialized (elastic, cartilage, bone, blood, and lymph).
Cells in connective tissue can be stationary or migrating.

Connective tissues have three main components: ground substance, fibers, and cells. Extracellular matrix is formed by these.
Ground substance consists of large molecules that absorb water, making it resistant to compressive forces.
Fibers include collagen (most abundant protein), elastic, and reticular.
Cells can be stationary (fibroblasts, chondrocytes) or migrating (macrophages).

Resistance to stretch and tear
Structural support
Insulation
Storage of body fuels
Medium for intercellular exchange
Specialized cells in connective tissue include osteocytes (bone), chondrocytes (cartilage). ECM varies widely per location

Connective tissue disorders can result from abnormalities (mutations/inherited faults, autoimmune response) affecting collagen synthesis, blood vessels. Examples include systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and scleroderma.