Histologic Tissue Type	Description	Implications to Surgical Team
EPITHELIAL TISSUE
A Types
1. Simple	Single layer of cells (endothelium) that lines the blood vessels, heart, and lymphatics	Delicate tissue that is easily damaged by rough handling
2. Stratified	Several layers of cells that form the skin, gastrointestinal tract, genitourinary (GU) tract, reproductive tract, and oropharynx; lines area that serves as a passage; reduces friction with mucus; can convert into keratin	Superficial layer of body cover; surface modifications are performed here; forms hair and nails
3. Transitional	Combination of simple and stratified layers found in ureters and bladder	Encountered during GU reconstruction and neoconstruction
B Cellular surface structure
1. Squamous	Flat
2. Columnar	Tall, cylindric
3. Cuboidal	Square
CONNECTIVE TISSUE
A Fluid	Blood, lymph, chyle, cerebrospinal fluid, synovium vitreous and aqueous, and mucinous material	Care with body substance isolation and provision of hemostasis
B Fibrous
1. Areolar	Loose network forming the frame for subcuticular tissue	Reorganized during liposuction and fat transplantation procedures
2. Adipose	Fat that fills the loose network; visible in fetus at 14 weeks’ gestation; not found in eyelid, penis, scrotum, labia minorum, cranium, and lung tissue
3. Reticular	Forms firmer framework for organs and vessels
C Supportive
1. Cartilage	Avascular, no lymphatics or nerves	Structural integrity is altered during rhinoplasty and otoplasty; cartilage may be used as graft material; radical neck reconstruction may involve tracheal rings or laryngectomy for multidisciplinary treatment
a. Hyaline	Translucent, articular, and rubs against other articular surface; forms the epiphyseal line in long bone, portions of the nose, and trachaeal rings
b. Costal elastic	Becomes fibrous with age; found in ribs, nose, trachea, and larynx
c. White fibrocartilage	Forms circular menisci in joints and between vertebrae
d. Yellow elastic	Found in auricle of ear, eustachian tubes, and epiglottis
2. Erectile	Found in corpus cavernosa, clitoris, and nose
D Hard	Bony surfaces covered with periosteum except at articulations and cartilaginous areas of circulating nurse insertion points	Reconstruction requires framework of underlying bone or graft material; autologous bone may be harvested from graft site for neoconstruction; donor bone may be used as transplant material
1. Cancellous bone	Spaces are filled with red marrow; erythroblasts and smaller vessels
2. Compact bone	Hollow center filled with yellow marrow (higher fat content) and larger vessels
MUSCLE TISSUE
A Visceral	Smooth, involuntary muscle; hollow organs, vessels, glands, areola, scrotum, iris of eye	Skeletal muscle may be used to replace bulk lost to debridement; vascularized flaps replace radical tissue excisions
B Skeletal	Cylindric, striated, voluntary cells
C Cardiac	Branching cells, nonnucleated, less fibrous connective tissue
NERVE TISSUE
A Types
1. Neuron	Cells generate and conduct nerve impulses; has multiple cytoplasmic fibers on one side (dendrites) and a single myelinated extension from the other side (axon)	Nerves may be injured during any procedure
2. Neuroglia	Insulate and support neurons in central nervous system
B Classification by activity type
1. Afferent	Sensory
2. Efferent	Motor

From Fortunato NM, McCullough SM: Plastic and reconstructive surgery, St Louis, 1998, Mosby.

The skin contributes to the health and well-being of the patient. Intact skin is an effective barrier to most harmful elements. Wounded, nonintact skin is an open avenue for microbial entry. Wounds occur intentionally or unintentionally. Most wounds, when treated properly, heal without incident. Unfavorable outcomes occur when wound healing is disrupted by poor circulation, infection, or immune dysfunction.⁷^,⁹

Skin is a multifunction body cover, and skin assessment is an important measurement of generalized wellness. Skin color, texture, and condition can be the best predictors of how well a surgical site will heal. The most intricate procedure can be done in deep tissue layers, but the superficial layers are what the patient sees and measures the outcome against. Durability and viability of the skin of the perioperative patient are influenced by many factors. Within reasonable limits, in the absence of hemorrhage and sepsis, wound healing is predictable.¹⁰ Disregard for the principles of tissue handling and wound management can lead to complications. The intent of this chapter is to provide an overview of body tissues, surgical incisions, and surgical site closure.

The skin is the largest and heaviest organ of the body. The two main layers that compose the integument are the epidermis and the dermis. The thickness of the skin and its layers is determined by its location. The combined thickness of the epidermis and dermis ranges from 4 mm on the back to 1.5 mm of scalp. Figure 28-1 shows a cross-section of the integument (skin) and its layers. Areas involving bone will incorporate vascularized periosteum over the bone.

The two basic types of skin are glabrous skin and hairy skin. Glabrous, smooth skin is very thick and is found on the palms and soles. The surface is marked by ridges and sulci arranged in unique configurations referred to as dermatographics, or fingerprints. These ridges first appear in the fingertips during the thirteenth week of fetal life. A marked absence of hair follicles and oil glands is characteristic of this tissue. Hairy, thin skin has hair follicles, sweat glands, and oil glands.

Natural lines of tension are formed by the relationship of the skin to the underlying musculature (Fig. 28-2). Austrian anatomist, Karl Langer (1819-1887) described how incisions could be more cosmetic if natural cleavage lines were followed when planning the surgical incision. The collagen fibers in the epidermis and dermis form an elliptical shape when the skin is incised in fusiform fashion along the natural lines. The angle of the incision should be no more than 30 degrees at each margin. The surgeon may undermine the tissue to minimize the distance between the skin edges. Closure is better when the edges meet during approximation. As the incision heals, tension of the skin is relaxed, causing minimal pulling and widening of the bridge of scar tissue.

FIG. 28-2 Langer’s lines. A, Anterior view. B, Posterior view. C, Forearm. D, Relaxed skin tension lines of face. *(From Fortunato NM, McCullough SM:* Plastic and reconstructive surgery, *St Louis, 1998, Mosby.)*

Epidermis

The epidermis is the outermost layer. It is organized into five levels of stratified squamous epithelium and contains no organs, glands, nerve endings, or blood vessels. It renews itself every 15 to 30 days, depending on the body surface area, the age of the individual, and the individual’s generalized condition. The basic anatomy and physiology of epidermal layers are as follows:

• Stratum corneum: Keratinized cells make up 75% of the epidermal thickness. Cells are shed from this level, which is referred to as the horny layer. It is thinner in hairy, thin-skinned areas.

• Stratum lucidum: Cells are flattened. Organelles and nuclei are absent.

• Stratum granulosum: This level is arranged in three to five layers. Mitotic activity creates cells for renewal of epidermal layers.

• Stratum spinosum: This layer creates cells for renewal of epidermal layers.

• Stratum basale: A single cell layer that lies between the junction of the epidermis and the dermis. Intense mitosis in this layer in combination with the basal layer and the spinosum causes epidermal regeneration. As cells are generated, they migrate upward, toward the surface. Melanocytes, located between basal cells and in hair follicles, create melanin, which causes skin pigmentation. Melanin enters and accumulates in keratocytes, causing superficial skin tone and providing ultraviolet protection. Exposure to sunlight causes darkening of existing melanin and accelerated generation of new melanin.

Each epithelial layer consists of keratin-producing cells (keratinocytes). Keratin is modified into functional components such as hair and fingernails on select body surfaces. Overactivity of the spinosum and basal levels can increase epidermal thickness in normally thin areas, causing psoriasis.

Dermis

The dermis is composed of papillary and reticular layers of flexible connective tissue. Superficially, the dermis has an irregular surface of papilla-like fingers that project into the strata basale of the epidermal layers. The dermis, regardless of location, is a loose areolar connective tissue that contains pain and touch receptors, glands, blood vessels, and lymphatics. It is the key layer in wound repair and tissue healing.

Glandular structures and ducts in the integument

Tissue layers under the integument

Subcutaneous adipose layer.

Below the dermis is a loose, fatty layer that is referred to as the subcutaneous layer. Beneath the subcutaneous tissue is a layer of striated muscle. The looseness of this structure allows for movement of the skin over supporting musculature. In males the distribution is through the nape of the neck, deltoids, triceps, abdomen, lumbosacral region, and buttocks. In females the fatty layer extends through the breasts, abdomen, buttocks, epitrochanteric area, and anterior thighs.

Fascia.

The fascia is a fibrous areolar tissue that supports the superficial skin layers and encases the muscle. Fascia throughout the body covers the muscles anteriorly and posteriorly. The superficial fascia is directly below the integument and is the point to which injection of a local anesthetic agent should extend for the best effect. Sensory nerve fibers run through this area, and an anesthetic agent is easily absorbed. Adipose cells occupy areolar spaces, rendering the fascia soft and pliable and permitting vessels, nerves, and lymphatics to pass through the layers.

The deep fascia is tough and less pliable. It runs the length of the muscle bundle and terminates in fibrous tendons that attach to bones beneath the periosteum. The anterior fascia of the abdomen is arranged in three layers that merge around the rectus abdominis muscles. The internal and external oblique muscles cover and surround the rectus muscles to the level of the linea circularis, or the landmark known as the arcuate line sometimes called the semicircular line of Douglas (Fig. 28-3). The arcuate line is formed by three fascial merges one third the distance between the umbilicus and the pubis. Below the level of the arcuate line the fascial layers are fully anterior with no posterior fascial component. The rectus abdominis is behind the layered fascia.

FIG. 28-3 Abdominal tissue layer at the arcuate line. A, Above the arcuate line. B, Below the arcuate line.

Peritoneum.

Lying beneath the posterior fascia of the abdomen is the peritoneum—the thin, two-layer serous membrane that lines the interior of the abdominal cavity (parietal peritoneum) and surrounds the organs (visceral peritoneum). The inferior aspect of the peritoneum overlies or is superior to the dome of the urinary bladder. In other words, the bladder is infraperitoneal, or below the peritoneal cavity. The stomach is superior to the peritoneal sac with the fundus situated supraperitoneally. The kidneys and the aorta are behind the peritoneum (retroperitoneal).

Accessory appendages to the integument

Modifications in the epidermal layer cause varied degrees of keratin deposition. Thickness and durability are functionally related to the location of keratinization. Hair and fingernails are modified keratin.

Other skin appendages include glands, blood vessels, and sensory organs. Glands arise in the dermis, and some exit the body through ducts that penetrate the epidermis. Other glands empty into the superior segment of hair follicles.

Hair follicles.

Hair follicles are keratinized epidermal epithelium that terminates in the dermal layers. The follicle is nourished by a capillary bed. Loss of this blood supply results in death of the follicle. Small bundles of smooth muscle cells, referred to as arrector pili, form attachments to the surrounding connective tissue in a diagonal fashion. As arrector pili contract, the shaft of the hair is straightened to an upright position. This contraction causes the superficial skin to dimple and pucker, creating “goose bumps.”

Nails (ungues).

The dorsal tip of each phalanx is tipped with a plate of specialized keratinized cells. Proximally, the nail root is covered by stratum corneum, which is referred to as the eponychium, or cuticle. The nail plate rests on a bed of epidermis (nailbed). Nails are chemically similar to the surface epidermis. Peripheral blood supply may be assessed through the translucent nail plate but should not be the sole determinant of oxygenation and well-being of the patient.

Surgical landmarks

The primary reference point for abdominal incisions is the umbilicus. Secondary surface landmarks include the xiphoid, the pubis, and the iliac crests. Incisions may be vertical, horizontal, or oblique and may occur in various areas of the torso (Fig. 28-4). Specialty incisions, such as those involving the head, limbs, breast, reconstructive procedures, and other organ systems are described in their respective chapters.

The direction of the incisional line is determined by the anatomic plane in the body (Fig. 28-5). Some specialty instruments are constructed to dissect, debulk, or separate layers in a specific pattern according to the angle of the natural tissue arrangement. One example is a sagittal saw that is designed to cut bone along the sagittal plane.

Placement of the surgical incision

Before the procedure begins, the surgeon chooses the most suitable incision for the procedure being performed. All incisions incorporate, with varying degrees of success, certain characteristics that include the following:

• Condition of the patient

• Knowledge of previous surgery in the same region and the presence of adhesions

• Ease and speed of entry into tissues

• Size of the body habitus and the natural lines of tissue tension (Langer’s lines)

• Maximum exposure of intended surgical site and adjacent structures (i.e, muscles, nerves, vessels, lymphatics)

• Ability to extend the incision if necessary

• Minimum trauma and scar formation

• Least postoperative discomfort

• Maximum postoperative wound strength

Abdominal surgery

A laparotomy involves surgically opening the abdominal wall and entering the peritoneal cavity (Fig. 28-6). The skin and subcutaneous tissue are incised and the blood vessels are ligated or electrocoagulated. Both the posterior fascia and the peritoneum may be cut at the same time, thus exposing the contents of the abdominal cavity. Various types of incisions are used in a laparotomy, but each follows essentially the same technique.