L11 - Wound Healing, Regeneration and Aging

What is physiological regeneration?

Natural, ongoing replacement of cells (e.g., hair, intestinal lining)​.

What is reparative regeneration?

Regrowth in response to injury, such as liver regrowth or limb regrowth in certain animals​.

What is the difference between physiological and reparative regeneration?

Physiological is routine and episodic; reparative is injury-induced​.

How many cells does the body replace daily?

About 330 billion cells/day (~4 million/second)​.

Which cells have low or no renewal in adulthood?

Oocytes, lens cells, and neurons​.

How fast do deer antlers grow?

Up to 2.75 cm per day; they are fully regrown each year​.

What model shows liver regeneration?

In mice, 70% hepatectomy results in full liver weight restoration in ~14 days​.

What is unique about zebrafish regeneration?

They regrow fin tissue within ~20 days post-amputation (dpa)​.

How does aging affect wound healing?

Healing deteriorates—slower inflammation, fewer progenitor cells, and less tissue remodeling​.

What structural skin changes occur with age?

• Flattened dermo-epidermal junction

• ↓ collagen, elastin, proteoglycans

• ↑ susceptibility to trauma​.

What is extrinsic aging?

Aging from environmental factors like UV exposure; increases structural decline​.

What is the difference between scar and scar-free healing?

• Scar: dense collagen, poor remodeling

• Scar-free: minimal inflammation, preserved tissue architecture​.

What animal models show scar-free regeneration?

Leopard geckos, axolotls, and dolphins—they restore normal skin with little fibrosis​

What are the three phases of wound healing?

• Inflammation

• Tissue formation (fibroblasts, vessels)

• Tissue remodeling (collagen, structure)​.

How does aging affect these phases?

• ↓ Inflammatory response

• ↓ Fibroblast & vessel formation

• Poor collagen remodeling & tensile strength​.

What happens to axolotls after metamorphosis?

They regenerate more slowly and with skeletal defects—100% show abnormalities compared to 7% in juveniles​.

What is paedomorphism in axolotls?

Retaining juvenile features (and high regeneration) into adulthood​.

Do younger animals regenerate better?

Yes—tadpoles, juvenile mammals, and embryonic stages show better regenerative ability than adults​.

What parts of the mammalian body can regenerate postnatally?

Limited—digit tips, parts of the heart, and fetal skin show some regeneration​.