unit 2 - histology (halfway done)

tissue

a group of similar cells & their similar cell products that work together & originate from the same region of embryo

embryonic tissue

undeveloped/unspecialized cellular structures formed during early embryo development that eventually gives rise to all organs/systems/tissues of the body.

totipotent cell

• single fertilized cell that gives rise to the whole organism (zygote)

• ½ genetic info from egg + ½ genetic info from sperm

blastocyst

• hollow cluster of many cells

• contains inner cell mass

• *rings = placenta

pluripotent cells & embryonic stem cells

gives rise to a variety of cells

somatic lineages

differentiation

original tissue layers

• endoderm

• mesoderm

• ectoderm

endoderm

• innermost layer

• forms lungs, stomach, pancreas, liver, intestine

mesoderm

• middle layer

• forms cardiovascular, musculoskeletal, and urinary systems

ectoderm

• outermost layer

• forms nerves and epidermis→waterproof shield on skin against UV radiation, bacteria, & damage)

epithielium

• covers body surface

• lines body cavities/organs

• makes up most glands

• cells are too densely packed for nutrients/waste to pass→depends on adjacent connective tissue/basement membrane for its blood to transport these things.

basement membrane

• layer of collagen and glycoproteins between epithelium/connective tissue

• diffuses nutrients/waste

simple epithelium

• one layer of uniform cells atop the basement membrane

  • all cells have equal access to the basement mem

stratified epithelium

• 2-20 layers of cells, with one layer touching basement mem

  • layers closest to the basement men are larger/healthier due to having first & greater access to its nutrients

pesudostratified columnar epithelium

• one layer of misshapen cells that all touch the basement mem, nuclei do not form a neat row'

  • goblet cells: produces mucus and helps w moving mats thru airways and digestive tract

stratified squamous epithelium

• as new cells form, older ones get pushed upward→eventually dies/flakes off (exfoliating)

  • deeper layers go through constant mitosis to replace these dying surface cells

• 2 types:

  • keratinized→dead cells @ surface (dry & water repellent, ex:skin)

  • nonkeratinized→living cells @ surface (not dry on surface, ex: tongue, mouth, esophagus, vagina)

connective tissue

• most abundant tissue in the body w/ lots of variation

  • often connects organs to each other, ex: tendons connect muscle and bone

• ALL contain: cells, fibers, ground substance

connective tissue functions

1. binding organs together—tendons connect bone→muscle; ligaments connect bone→bone)

2. support: gives structure to body

   • bones, cartilage | tendons & ligaments offer support/structure to joints

3. physical protection—bones, fat cells (adipose (body fat) tissues)

4. immune protection: hacks/destroys invaders

   • microphages, white blood cells

   • plasma cells = make antibodies

5. movement—bones, cartilage, tendons, ligaments

   • forms moveable/stable joints

6. storage—fat (energy), bones (calcium, phosphorus)

7. heat protection

   • brown fat (contains more mitochondria=produces more heat)

     • common in infancy/hibernating mammals

8. transport

   • blood moves gases, nutrients, waste, minerals, hormones, heat, blood cells

ground substance

• gelatinous→protective material for cells and fibers

  • helps absorb compression

• helps regulate water & balance of electrolytes, & holds cells/tissues together

reticular fibers

• thin collagen fibers w/ glycoprotein coat

• sponge-like framework

• present in spleen/lymph nodes

elastic fibers

contains elastin (protein)→stretches/recoils like rubber band

collagen fibers

• 25% of body’s protein

• tough/flexible, but resists stretch

• found in tendons, ligaments, dermis, bones, cartilage

fibroblasts

secrete collagen & help w healing wounds

fibrous connective tissue

2 types:

• loose→lots of ground substance & space between cells/fibers

• dense→more fibers compacted together & less ground substance

more connective tissue examples

• tendons, ligaments, adipose (fat)

• cartilage = chondroblast cells (secrete rubbery matrix→flexibility), collagen/elastic fiber

• bone (osseous tissue)

  • spongy bone & compact (dense) bone both store minerals

• blood

ehlers-danlos syndrome

• group of tissue conditions

• caused by gene mutations impacting proteins for strength/elasticity of connective tissue

• signs: hypermobility, stretchy/fragile skin that bruises easily and heals slowly (stitches can cause more damage)

  • physical therapy can help with building stronger/more stable joints

• **risk of joint dislocation

marfan syndrome

• genetic condition impacting connective tissue, often from a new mutation

• signs: often tall/thin, long arms/fingers/toes, “loose joints” & “bulging eyes”→from damage to the fat/connective tissue holding the eyes in place

• weakened heart/blood vessels→especially arteries b/c they can experience more pressure

  • can lead to widening of vessels, especially in aorta

• **medical intervention can repair aorta before it becomes life threatening

nervous tissue

• neurons→detect and respond to stimuli & send information

  • dendrites: receive stimuli signals)

  • soma: cell body

  • axon: sends outgoing signals

• glial cells→assist/protect neurons

muscular tissue

respond to stimuli by contracting

skeletal tissue

• striated (alternating light/dark bands) due to proteins in cell (areas of overlap are darker)

• voluntary movement

• usually attached to bone

• multiple nuclei

cardiac tissue

• heart

• striated

• monocytes (shorter)→cardiac muscle cells

• only 1 nucleus

• joined end-to-end by intercalated discs

  • electrical junctions→allow cells to be stimulated/contract almost simultaneously

• involuntary movement

  • strong connection keep cells from being pulled apart during muscle contractions

smooth tissue

• no striations

• involuntary movement

• fusiform cells (kinda eye shaped?)

• 1 nucleus

• EX: bladder, stomach, esophagus, uterus, iris, blood vessels

change in (epithelial) tissue type

often a temporary change due to extra stress/pressure to limit damage to underlying connective tissue

tissue growth

• may result from increased number of cells (mitosis)

• may result from hypertrophy (enlargement of existing cells→common in muscle growth)

• **neoplasia→(abnormal) development of a tumor bc of growth of nonfunctional tissue

atrophy

• decrease in tissue size due to loss of cell size or number

• generally due to:

  • aging→cells die faster than they can be replaced

  • disuse (ex: a broken bone being kept in a cast for months may lead overall limb becoming smaller bc of the less demand on it)

necrosis

• premature death of tissue

• due to: trauma, toxins, infection

• **gets worse if left untreated

gangrene

• necrosis due to insufficient blood supply (no O₂ or nutrients)

• causes:

  • pressure/extreme vasoconstriction→ex: bed sores from continuous pressure on same spots, or hypothermia

  • infection damaging blood vessels

infarction

• sudden death of tissue whose blood supply is cut off (typically linked w blood clot cutting off blood flow suddenly)

• ex: stroke & heart attack

apoptosis

• programmed cell death-normal, cell death is bc cells are no longer needed

  • completed their function, so the body wants them out of the way

tissue repair

2 types:

• regeneration: replacement of damaged cells w same cell’s type→restores normal function (ex: liver/skin)

• fibrosis: replacement of damaged cells w scar tissue instead

  • helps to hold an organ together (ex: skin)

  • does not restore normal function (w/ skin, scars don’t sweat or grow hair in follicles)