HESI A2 · Anatomy and Physiology · 6 min read
The Integumentary System
- Differentiate the structural layers of the skin and hypodermis, identifying their primary tissue types and cellular components.
- Describe the functions of accessory cutaneous structures, including hair, nails, and exocrine glands.
- Explain the mechanisms of cutaneous thermoregulation, sensory reception, and vitamin D synthesis.
Structural Organization of the Integument and Hypodermis
The integumentary system is a vital organ system consisting of the skin, hair, nails, and cutaneous glands. Covering the exterior of the body, the skin holds the distinction of being the largest organ of the human body by surface area and weight. Structurally, the skin is organized into two primary layers: a superficial layer known as the epidermis and a deeper layer termed the dermis.
The superficial epidermis is composed of keratinized stratified squamous epithelium. A key anatomical feature of the epidermis is that it is avascular, meaning it entirely lacks its own blood supply. Because it has no direct blood vessels, the living cells of the epidermis must receive oxygen and essential nutrients by diffusion from the underlying vascular network of the dermis.
Directly deep to the dermis lies the hypodermis, which is also called the subcutaneous layer. Although closely associated with the integument, the hypodermis is not considered part of the skin proper; its primary anatomical role is to attach the skin to underlying tissues. The hypodermis consists predominantly of adipose and loose areolar connective tissue. Through this composition, the hypodermis functions effectively in thermal insulation, energy storage, and shock absorption, much like a padded, insulating lining beneath an outer garment.
Common mistakes
- Classifying the hypodermis (subcutaneous layer) as an epidermal or dermal skin layer, rather than recognizing it as a connective tissue layer deep to the dermis that anchors the skin.
- Confusing the sensory functions of Meissner corpuscles (light touch and low-frequency vibration in the dermal papillae) with Pacinian corpuscles (deep pressure and high-frequency vibration deep in the dermis and hypodermis).
- Believing that apocrine sweat is inherently foul-smelling upon secretion, overlooking the fact that it is completely odorless upon release and only produces body odor after bacterial decomposition.
- Assuming active vitamin D is fully synthesized within the skin alone, forgetting that the skin forms cholecalciferol from 7-dehydrocholesterol and previtamin D3, which must subsequently be converted in the liver and kidneys to its active form.
Key points
- The integumentary system includes the skin, hair, nails, and cutaneous glands, with the skin standing as the body's largest organ by surface area and weight.
- The skin consists of two primary layers: an avascular superficial epidermis made of keratinized stratified squamous epithelium and a deeper vascular dermis composed of connective tissue; the underlying hypodermis provides insulation, energy storage, and shock absorption.
- The five strata of thick skin (deep to superficial) are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum, with the stratum lucidum existing exclusively on the palms and soles.
- Dermal architecture features a superficial papillary layer of loose areolar connective tissue whose dermal papillae create fingerprints, and a deeper reticular layer of dense irregular connective tissue providing tensile strength.
- Cutaneous sensory structures include Meissner corpuscles for light touch and low-frequency vibration, Pacinian corpuscles for deep pressure and high-frequency vibration, and free nerve endings for pain, temperature, and itch.
- Glands of the skin include holocrine sebaceous glands that secrete oily sebum, eccrine sweat glands that discharge cooling watery fluid onto the skin surface, apocrine sweat glands in axillary and anogenital areas, and modified ceruminous glands that contribute to earwax.
- Under hypothalamic control, cutaneous thermoregulation relies on vasodilation and eccrine sweating to release heat, and vasoconstriction to conserve heat, while ultraviolet exposure initiates vitamin D synthesis that concludes in the liver and kidneys to facilitate calcium and phosphate absorption.
Practice this section
Explained HESI Anatomy and Physiology questions, no account needed. HESI Anatomy and Physiology practice test
The full lesson continues with 4 more sections with exam tips, audio in English and Spanish, 5 Check yourself questions and 20 flashcards.
- 1 month
$53.99$26.99 - 3 months
$158.99$79.49 - Lifetime
$323.99$161.99
One payment, no subscription.
See HESI plansAlready a member? Log in
Sample lesson: Body Organization: Planes, Directional Terms and Cavities25 practice questions on this exam
Each HESI practice test has 25 original questions with the answers explained. No account needed.
Open the HESI practice testsOriginal lesson written for HESI A2 practice · updated October 15, 2026. Exam names are trademarks of their owners; tests.global is not affiliated with them.