Skin Functional Anatomy - BIOL 310

Integumentary System Overview

Learning Objectives

  • At the end of this lesson, you should be able to:

    • Describe the general functions of the skin.

    • Identify:

    • Pigments and other factors that produce skin color.

    • The cells that produce pigments, and their location in the skin layers.

    • Describe:

    • The physiology of tanning and vitamin D bio-activation.

    • How variation in skin color benefits populations at different latitudes.

    • The role of the integumentary system in maintaining homeostasis individually and in conjunction with other body systems.

Functions of the Integumentary System

  • Protection and Sensation: Serves a protective role while facilitating sensation through various receptors.

  • Thermoregulation: Regulates body temperature through various mechanisms.

  • Energy Storage: Stores energy in the form of fat.

  • Water Regulation and Excretion: Manages water balance and removes waste through excretion.

  • Protection from UV Radiation: Shields from solar radiation.

  • Vitamin D Synthesis: Enables the production of vitamin D through skin exposure to sunlight.

Sensation: Sensory Receptors in the Skin

  • Types of Touch Receptors:

    • Free nerve endings: Detect pain and temperature.

    • Tactile discs with Merkel cells: Respond to light touch.

    • Tactile (Meissner) corpuscles: Sensitive to light touch and vibration.

    • Lamellar (Pacinian) corpuscles: Detect pressure and vibration.

    • Bulbous (Ruffini) corpuscles: Respond to skin stretch.

    • Root hair plexus: Senses movement of hair.

Physical Protection: Tissue Response to Injury

Step 1: Injury Occurs

  1. Injury: Initial damage to tissue.

  2. Defense Mechanism Activation:

    • Exposure to pathogens and toxins stimulates mast cell activation.

    • Involves the release of mediators: Histamine, Heparin, and Prostaglandins, causing an inflammatory response.

Step 2: Inflammation Response

  1. Signs of Inflammation: Swelling, redness, warmth, pain, throbbing.

  2. Physiological Changes:

    • Dilation of blood vessels.

    • Increased blood flow causing warmth and redness.

    • Enhanced vessel permeability, promoting nutrient delivery and white blood cell (phagocyte) movement.

  3. Outcome: Increased phagocytosis helps remove toxins and debris, moving towards homeostasis.

Various Tissues w/ Different Abilities to Regenerate

  • Tissues with high regenerative abilities include:

    • Epithelial tissues

    • Connective tissues (except cartilage)

    • Smooth muscle

  • Tissues with poor regeneration capacities include:

    • Cardiac muscle

    • Neural tissue, which may regenerate poorly or not at all.

Restoration to Normal Conditions

  • Following cleanup, normal tissue conditions can be restored, though scar tissue may form.

  • Regeneration: Represents healing processes in response to initial injury, scar tissue forming in areas with poor regenerative capacity.

  • Fibrosis: Involves permanent replacement of normal tissue with scar tissue.

Functions and Mechanisms of Thermoregulation in the Skin

  • Hairs trap warm air.

  • Sweat Glands: Evaporating sweat cools the surface of the skin, found in the dermis, formed from epidermal tissue. (more coily)

  • Arrector Pili Muscles: attach to hair shaft, raises hairs to trap air. (goosebumps, being frightened)

  • Vasodilation and Vasoconstriction: Control heat loss through blood vessel regulation.

  • Fat Storage: Insulation and energy storage are provided by (adipose: fat) in the hypodermis.

  • Sebaceous Glands: These glands create sebum (oil), found in the dermis, formed from epidermal tissue, squeezed into duct by arrector pili muscles, provides a barrier to protect hair & skin against bacterial infections.

Water Regulation & Excretion: Sweat Glands

  • Functions:

    • Thermoregulation: Sweat cools skin upon evaporation.

    • Excretion: Sweat contains water, salt, electrolytes, and waste products.

    • Protection: Cleansing and antibacterial properties provided by sweat.

Melanin and Skin Color

  • Influencing Factors:

    • Melanin = pigmented protein that determines hair color and skin tone

    • Melanocyte: melanin-producing cell (most people have about the same # of them, but variations in pigmentation result from the amount and type of melanin produced by these cells, you can also have more melanocytes in various points in your body , which can lead to localized differences in skin color and patterns (ex. light skin - darker hair, freckles)

    • Carotene: Another pigment (orange: think carrots) that can affect skin color, can also result into red hair and a yellowish tint in skin tone, particularly in areas with higher concentrations, such as the palms of the hands and the soles of the feet.

    • Hair Follicle Shape: determines hair texture.

    • Degree of dermal circulation.

    • Epidermis thickness and keratinization.

    • Genetically programmed response to UV radiation.

    • Pigmentation: Skin color is influenced primarily by melanocytes found in the stratum basale.

    • Albinism: Condition where melanocytes fail to produce melanin, leading to lack of pigmentation.

Skin Color Distribution and UV Radiation

Demographics: Skin color is correlated with the intensity of sunlight (UV radiation) encountered in different geographical areas (Low Latitude: how far you are from the equator) Pale skin allows maximum absorption of UV rays (high latitudes).

  • Health Implications: Adequate folate levels are crucial; excessive UV can lead to depletion of folate, resulting in neural tube defects.

Skin Color and Its Biological Relevance

Importance of Skin Color

  • UV Protection: Melanin prevents UV rays from penetrating the epidermis (deeper skin layers) reducing skin cancer risk.

  • Vitamin D Production: UV radiation is essential for the skin to produce vitamin D3, which is crucial for calcium and phosphorus absorption, supporting bone health.

Vitamin D3 (cholecalciferol) Production

  1. Initial Conversion: Cells in the epidermis convert steroid compounds into cholecalciferol (vitamin D3).

  2. Conversion Process: The liver transforms it into an intermediary product; the kidneys convert this into calcitriol (the hormone).

  3. Function of Calcitriol: It promotes the absorption of calcium and phosphorus in the small intestine.

Rickets: A condition that arises from a deficiency of vitamin D, leading to weakened bones and skeletal deformities due to insufficient calcium absorption.

Health Issues Linked to Skin Color and UV Radiation

  • Consequences of Excessive UV: Potential for folate deficiency leading to neural tube defects and increased skin cancer risk.

  • Consequences of Insufficient UV: Risk of vitamin D3 deficiency leading to rickets and associated bone deformities.

  • Adaptative Traits: Populations in lower latitudes have evolved to produce high levels of melanin to mitigate excess UV radiation, whereas those in high latitudes produce less melanin in response to lower UV levels.


Review of 3 Layers of Skin: Epidermis: doesn’t have its own blood supply ex. paper cut (stratified squamous epithelium tissue) Dermis (papillary: areolar-losse proper connective tissue & reticular: dense irregular connective tissue), Hypodermis (adipose (fat) & areolar)