Class 4: BIPN MIDTERM 1

Tissue Types pt. 2: Integumentary System, Epi, dermis, subcutaneous

Integumentary System

• skin, hair, glands on surface

• “integument” = covering

Layers of the Skin

1. Epidermis

2. Dermis

3. Subcutaneous

Epidermis

• epithelial

• avascular

• outermost layer, protection

Dermis

• “bulk'“ of skin, hide

• vascular, innervated

  • blood vessels, nerves, oil and sweat glands

• dense irregular CT

Subcutaneous (Hypodermis)

• technically not part of skin

• adipose and areolar CT

  • shock absorption, insulation, stretch

• anchors skin loosely to muscles

Functions of the Skin

1. VD synthesis

2. protection: toxins, microbes, UV

3. Water loss/gain: sweat

4. Thermoregulation: blood flow, sweat

5. Secretion: oil, sweat

6. Absorption: e.g. Nicotine

7. Defense: immunity

8. sensation: nerves

Cells of Epidermis

• Keratinocyte

  • MOST of epi, make keratin

  • strength and water resistance

• Melanocyte

  • make melanin pigment (skin color)

  • protect keratinocytes from UV

• Dendritic (Langerhans)

  • made in bone marrow

  • immune activation: ingest foreign substances

• Tactile EPC (Merkel)

  • sensory receptor: light touch

  • base of epidermis

  • part of nervous system

Epidermal Strata (layers)

Bottom —> Top (keratinized)
1. Stratum basale

2. Stratum Spinosum

3. Stratum granulosum

4. Stratum corneum

Stratum Basale

• deepest layer of epi

• mitotic stem cells, melanocytes, tactile EPCs

Stratum Spinosum

• second deepest layer

• Keratinocytes:

  • unified by desmosomes

  • keratin bundles

Stratum Granulosum

• 4-6 layers of flat cells, dying organelles

• cytoplasm filled with granules

  • release lipids to ECF (waterproof)

  • cross-liked keratin filaments (strength)

Stratum Corneum

• most superficial layer, furthest from blood supply

• 20-30 layers of DEAD, FLAT cells filled w/ keratin

• glycolipids

*new epidermis every 30days

*millions shedded per day

Dermal Cells

• CTPs

  • fibroblasts

  • macrophages

  • mast cells

  • WBCs

• Semifluid matrix w/ collagen and elastic fibers

Dermal Layers

1. Papillary Dermis (Top)

   1. Loose Areolar CT

2. Reticular Dermis (bottom)

   1. dense irregular CT

Papillary Dermis

• loose interlacing collagen and elastic fibers

• movement of phagocytes, immune cells

• Papillae:

  • project into epidermis

  • contain capillary loops: nutrient supply

Dermal Papillae

• free nerve endings (pain)

• touch receptors (Meissner’s corpuscles)

• paired with epidermal ridges

*fingerprints = ridges + sweat

Reticular Dermis

• 80% dermis thickness

• Dense, irregular CT

• naming comes from: Collagen interlaced into reticulum

*NOT named because of high #reticular fibers

• composed of blood vessles

Skeletal System Function

• support

• protection

• movement

• mineral storage

• blood cell formation

Bone Classification

• Axial

  • skull

  • vertebral column

  • thorax

• Appendicular

  • upper/lower limbs

  • attachment sites to the axial

Bone Shapes Classification

• long bone

  • longer than wide, movement

  • humerus, fingers

• flat bone

  • thin and curved, protection for organs, attachment sites

  • sternum

• Short bone

  • cube-like shape

  • tallus (ankle)

• irregular bone

  • everything else

  • e.g. Spine

Cells of Bone

• Osteogenic: stem cells giving rise to many other cell types

• Osteoblasts: deposit bone matrix

• Osteocytes: maintain bone

• *Osteoclasts: reabsorb/breakdown bone

  • derive from HSCs, NOT osteogenic cells

Spongy Bone

• found in epiphysis

• specialized cells + ECM (bone matrix)

  • osteogenic stem cells

  • osteoblasts

  • osteoclasts

• lined by endosteum membrane

• trabeculae

  • contain red/yellow bone marrow

Bone Matrix

• 1/3 organic

  • collagen and polysaccharides

  • FLEXIBILITY

• 2/3 inorganic

  • hydroxyapatite crystals

  • mineral ions: Ca2+, phosphate

  • RIGIDITY

Demineralized bone

• loss of mineral ions = NO RIGIDITY

• flexible, bendy, lost shape

Denatured/heated bone

• loss of organic components

• NO FLEXIBILITY, brittle, fragile

Bone Cell Lines

Osteogenic SCs —> Osteoblasts —> Osteocytes

HSCs —> Osteoclasts (and others)