DAT: Integumentary System

most superficial tissue layer of an animal’s body and the largest organ system; includes the skin, glands, hair, and nails.

Integumentary System

largest organ of the body

Skin

• Control of body temp through sweating and evaporative cooling; sweat absorbs body heat and evaporates to lower temperature.

• piloerection reflex

Thermoregulation

Detection of physical stimuli by cutaneous receptors for touch, temperature, and pain.

Sensory Input

UV light converts precursors in the skin into vitamin D, essential for calcium absorption.

Vitamin D Synthesis

Removal of water, salts, and small amounts of waste through sweat.

Excretion

• outermost skin layer

  • Avascular → gets nutrients by diffusion from dermis

  • Attached to dermis by basement membrane (highly vascular underneath)

Epidermis

• middle layer of skin

  • Made of dense connective tissue

  • Rich in collagen + elastic fibers

  • oxygen & nutrients

  • Vascularized

  • Contains:

    • Hair follicles

    • Glands

    • Nerve endings

    • Blood vessels

    • Nerves

  • houses the lamellar corpuscles

Dermis

Composition

• Loose connective tissue

• Lots of adipose (fat)

Functions

• Shock absorber

• Insulation

• Energy storage

• Anchors skin to muscle

Hypodermis

• Dead, keratin-filled cells

• Hydrophobic barrier

• Prevents tearing + water loss

• Constant shedding

Stratum Corneum

• ONLY palms & soles

• Extra thickness

Stratum Lucidum

• Cells dying + flattening

• Lots of keratin formation

Stratum Granulosum

• Living keratinocytes

• Strength & flexibility

• Cells held by desmosomes

Stratum Spinosum

• Deepest layer – MITOSIS happens here

• aka stratum germinativum

• recently generated epidermal cells are in here

• Contains:

  • Basal stem cells → make new keratinocytes

  • Melanocytes

  • Merkel cells

Stratum Basale

• Produce keratin → waterproof + mechanical protection

• As they move upward:

  • Fill with keratin

  • Flatten → lose organelles → die

• Most abundant cell + protein in epidermis

Keratinocytes

Produce melanin → skin color + UV protection

Melanocytes

• Touch receptors (mechanoreceptors)

• Linked to sensory neurons

Merkel Cells

Fully keratinized dead cells that make up the stratum corneum.

Corneocytes

Give skin elasticity and allow stretch and recoil.

Elastin Fibers

Structures in the dermis from which hair grows; associated with sebaceous (oil) glands.

Hair Follicles

• Secrete sebum (oil)

• Moisturizes + antimicrobial

• Everywhere EXCEPT:
  ❌ palms & soles

Sebaceous Glands

Produce sweat for cooling and excretion; include eccrine and apocrine types.

Sweat Glands

Located in the basale layer; responsible for continuous regeneration of the epidermis.

Epidermal Stem Cells

• Immune cells

• Detect pathogens → present antigens to helper T cells

Langerhans Cells

• Detect light touch

• Located upper dermis

Meissner (Tactile) Corpuscles

• Detect vibration & deep pressure

• Located deep dermis

Pacinian (Lamellar) Corpuscles

• In ear canal

• Make ear wax

• Traps dust & pathogens

Ceruminous Glands

• Produce milk

• Mainly active in females after birth

Mammary Glands

• Everywhere

• Watery sweat

• Main job = cool body (thermoregulation)

• regulating body temperature via perspiration

Eccrine

• Armpits + pubic area

• Thick secretion into hair follicles

• Related to pheromones & odor

Apocrine

To provide the skin extra flexibility and cushioning

Ground substance

active process that relies on evaporative cooling and uses ATP

Sweating

Loses heat in hot temperatures to cool the body

blood vessels dilating

Retains heat in cold temperatures to heat the body

blood vessels constricting

• glycine occurs in every third position of its repeating sequence

• triple helix

• most abundent protein in dermis

Collagen