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🫀 Science · Human Anatomy and Physiology · Lesson 4 of 12 · 4 min

Integumentary system: skin layers, functions and glands

🧴 Skin is the body's largest organ. It blocks germs, holds in water, makes vitamin D and helps set your temperature, and the TEAS asks which layer does what.

💡 Key idea

Epidermis protects and is avascular, dermis holds the vessels, nerves and glands, and hypodermis stores fat.

🧠 The idea

The integumentary system is the skin, hair, nails and glands. The EPIDERMIS is the outer layer of keratinized stratified squamous epithelium with no blood vessels. New cells form in the deepest layer (stratum basale) and move up to the stratum corneum, where dead keratin-filled cells shed. Melanocytes in the basale make MELANIN, which absorbs UV light. The DERMIS is connective tissue with collagen and elastic fibers, blood vessels, nerve endings, hair follicles and glands. Below it, the HYPODERMIS (subcutaneous layer) is fat and loose connective tissue that insulates and anchors skin; it is not technically part of the skin. Functions: protection, preventing water loss, sensation, vitamin D synthesis with UV light, and thermoregulation (sweating and dilating dermal vessels release heat; constricting them conserves it). Glands: SEBACEOUS glands release oily sebum into hair follicles; eccrine sweat glands cool the body all over; apocrine sweat glands in the armpits and groin become active at puberty.

✏️ Worked example

A runner's body temperature climbs. The hypothalamus signals eccrine glands to secrete sweat, and evaporation removes heat. Dermal blood vessels dilate so warm blood moves near the surface and the skin looks flushed. Now a paper cut that does not bleed: it only reached the epidermis, which has no blood vessels. A deeper cut that bleeds has reached the dermis.

📌 Takeaways

  • Epidermis: avascular, keratin, melanin; new cells start in the stratum basale.
  • Dermis: vessels, nerves, follicles, sweat and sebaceous glands.
  • Skin functions: protection, water barrier, sensation, vitamin D, temperature control.

✅ Check yourself

Question 1 of 3

Which layer of the skin contains no blood vessels?

  1. Hypodermis
  2. Dermis
  3. Papillary layer
  4. Epidermis
Show the answer and rationale

Answer: D

The epidermis is avascular and gets nutrients by diffusion from the dermis. The dermis, including its papillary layer, and the hypodermis are supplied by blood vessels.

Question 2 of 3

Which glands secrete an oily substance into hair follicles?

  1. Apocrine glands
  2. Ceruminous glands
  3. Eccrine glands
  4. Sebaceous glands
Show the answer and rationale

Answer: D

Sebaceous glands secrete sebum, an oil that softens hair and skin. Eccrine and apocrine glands produce sweat, and ceruminous glands make earwax in the ear canal.

Question 3 of 3

On a cold day, how do dermal blood vessels help conserve heat?

  1. They make melanin.
  2. They secrete sweat.
  3. They dilate.
  4. They constrict.
Show the answer and rationale

Answer: D

Vasoconstriction reduces blood flow near the surface, so less heat is lost. Dilation releases heat, sweating cools the body, and melanin is made by melanocytes for UV protection, not by vessels.

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