ANA 211 - Muscles and Skin Anatomy

Department of Anatomy, PUMS Introductory Lecture Series - ANA 211

• Topic: Muscles, Bursae, and Synovial Sheaths
• Lecturer: M. A. Amadi

Goal

• Introduce the basic structure of the skin as an important organ.

Learning Objectives

• Provide a suitable definition for the skin.
• Know the principal components (of the skin).
• Describe the recognized layers of the skin.
• Give a brief account of the microscopic anatomy of the skin.
• Understand the anatomical basis of surgical incisions.

Skin

• Part of the integumentary system of organs.
• Largest organ in the human body, weighing 6-9 kg and measuring about 2 square meters
• Acts as a protective container for organs.
• Forms a barrier between internal organs, vital body fluids and the external environment.
• Can be specialized or modified depending on its location and use (e.g., tongue, vagina).
• Displays clinical evidence of internal disease (e.g., peau de range in breast cancer).

Layers of the Skin

• Epidermis (five layers)
• Dermis (two layers)
• Hypodermis

Epidermis

• Most superficial of the three layers of the skin.
• Thickness varies, but averages 0.6-1 mm.
• Multicellular, with up to 50 rows of epithelial cells.
• Normally avascular.
• Composed primarily of keratinocytes (80%), Merkel cells, Langerhans' cells, and melanocytes.
• Thickest in palms and soles.

Dermis

• Deeper layer beneath the epidermis.
• Thicker than the epidermis.
• Responsible for skin's tensile strength, elasticity, and appearance.
• Contains arteriovenous anastomosis for thermoregulation.
• Divided into two anatomical compartments.
• Composed of connective tissue (collagen, reticulin, and elastic fibers) held together by ground substance (mucopolysaccharide gel).
• Contains specific cell types, including mast cells, fibroblasts, endothelial cells, vascular smooth muscle cells, specialized myoepithelial cells, nerve cells, and hematopoietic cells (macrophages, lymphocytes, and plasma).

Hypodermis (Subcutaneous Layer)

• Flexible bridge of areolar connective tissue connecting skin to underlying bones and muscles.
• Largest volume of fatty tissue in the body.
• Fat cells vary in thickness depending on location and use.
• Divided into lobules by fibrous septae.
• Contains blood vessels, lymphatics, and nerves supplying the dermis.

Appendages

• Nails, hair, and teeth.
• Exocrine glands (e.g., sweat glands, apocrine glands, sebaceous glands) open onto the skin's surface.
• Clinical example: Boil (infected sebaceous gland).

Langer's Lines (Skin Tension Lines)

• Invisible cleavage lines along which surgical cuts or incisions should be made for best healing.
• Aligned with the direction of orientation of underlying collagen fibres.

Fasciae (Superficial/Deep)

• Band of connective tissue (primarily collagen).
• Attaches, stabilizes, encloses, and separates muscles and internal organs.
• Classified by layer (superficial, deep, visceral/parietal), function, and anatomical location.
• Arranged in wavy patterns parallel to the direction of pull (similar to ligaments, aponeuroses, and tendons).

Superficial Fascia

• Lowest layer of skin, blending with the reticular dermis.
• Mixture of loose areolar and adipose connective tissue.
• Determines the shape of the body.
• Surrounds organs, glands, neurovascular bundles, and fills unoccupied spaces.
• Absent of fat in specific locations (e.g., eyelids, ear, scrotum, penis, clitoris).
• Functions: Facilitates skin movement on underlying structures, passage for cutaneous vessels and nerves, and protects against heat loss.
• Dense in some areas (e.g., scalp, palm, sole), thin (e.g., eyelids, auricle, scrotum, penis).

Deep Fascia

• Layer of dense fibrous connective tissue.
• Surrounds individual muscles and divides muscle groups into fascial compartments.
• High density of elastin fibers, leading to extensibility and resilience.
• Examples: fascia lata, fascia cruris, brachial fascia, plantar fascia, thoracolumbar fascia, and Buck's fascia.

Visceral (or Subserous) Fascia

• Suspends organs within their cavities and wraps them in connective tissue membranes.
• Each organ has a double-layered sheet of fascia separated by a thin serous membrane.
• Outermost layer: parietal layer; innermost layer: visceral layer.
• Organs have specialized names for their visceral fascias depending on location (e.g., meninges in the brain, pericardium in the heart, pleura in the lungs, peritoneum in the abdomen).

Visceral Fascia (cont.)

• Less extensible than superficial fascia due to its suspensory role in maintaining organ tone consistently.
• Too lax can result in organ prolapse; too tight restricts proper organ motility.

This quiz will test your understanding of the basic structure and components of the skin, along with related anatomical features. You will explore the layers of the skin, its functions, and its significance within the integumentary system. Prepare to discuss microscopic anatomy and surgical implications related to skin anatomy.