6.1 Cells, Tissues, and Metabolism

Cells, tissues, and metabolism sit in two places at once on the Illinois esthetician path. NIC Scientific Concepts I.D tests the national science. 68 Ill. Adm. Code 1175.835 puts cells, metabolism, and body systems plus human anatomy inside the 150-hour Scientific Concepts block of the 750-hour program. 1175.710 then says the licensing examination covers knowledge of the anatomy of the skin as it relates to applicable services under the Act. That last phrase is the filter: you are not sitting a medical-school paper. You are learning enough structure to choose a peel, a massage stroke, a machine, or a product without injuring the client or stepping into medicine.

The cell is the smallest living unit. Skin is a community of cells organized into tissues, then organs, then systems. When a product, steam towel, or massage stroke reaches the face, it is interacting with those cells and with the barrier they build.

Cell Structure You Must Name

Esthetics items still expect the classic organelles. Learn the name, the job, and the treatment-room hook.

The cell membrane is the first structure to tie to product absorption. It is selectively permeable. Small, lipid-soluble ingredients move more readily than large, water-heavy molecules. That is why an oil-soluble antioxidant behaves differently from a thick occlusive that sits on the surface and slows transepidermal water loss. Illinois chemical scope still stops at the stratum corneum (225 ILCS 410/3A-1). Superficial peels and cosmetic products are meant to act on dead surface cells, not to drive drugs through living membranes in the dermis. Knowing the membrane exists lets you explain absorption without pretending you are delivering a systemic medication.

The nucleus is the control center. Ultraviolet radiation is the classic esthetics example of nuclear stress: melanocytes respond by making more melanin, and poorly repaired DNA in keratinocytes is a reason you finish with sun protection and refer suspicious lesions. You will study cancers in a later chapter. Here, remember that the nucleus is why UV is not just a tan.

Cytoplasm is the working fluid. Mitochondria convert nutrients into ATP so the cell can divide, make protein, and repair. Lysosomes break down debris. Ribosomes, free in the cytoplasm or on rough endoplasmic reticulum, build protein. If a stem asks which organelle produces energy, the answer is mitochondria. If it asks which organelle synthesizes protein, the answer is ribosomes. Do not swap those jobs.

Mitosis Versus Metabolism

Candidates mix these words because both happen inside cells. They are not the same process.

Mitosis is cell division: one parent cell becomes two identical daughter cells. In the epidermis, basal keratinocytes in the stratum germinativum (stratum basale) undergo mitosis to replace cells that desquamate at the surface. A healthy turnover cycle is why the face sheds and why a controlled superficial peel can even the look of the stratum corneum. Mitosis is replacement and repair. It is not burning fat, and it is not metabolism.

Metabolism is the sum of chemical reactions that keep the cell alive. Two directions matter on the exam:

• Anabolism builds larger molecules from smaller ones. Collagen assembly from amino acids is anabolic. So is the manufacture of barrier lipids.
• Catabolism breaks larger molecules into smaller ones and releases energy. Digestive enzyme activity that loosens the protein connections between corneocytes during a superficial enzyme peel is a catabolic-style breakdown at the surface. It is not the same as a lysosome working inside a living cell, but the build-versus-break vocabulary is what NIC is testing.

A client who says they have a slow metabolism is using a lay phrase about body weight. On the exam, metabolism is cellular chemistry. If a question asks how new epidermal cells are produced, the process is mitosis. If it asks how nutrients become energy or how tissue is built and broken down, the process is metabolism.

Four Tissue Types

Cells of the same kind form tissue. NIC expects four types. Every facial service lands on at least one of them.

1. Epithelial tissue covers and lines. The epidermis is stratified squamous epithelium. It is the absorption barrier and the tissue you cleanse, steam, exfoliate, and protect. Stacked corneocytes and lipids are why not every cream soaks in.
2. Connective tissue supports. The dermis is dense connective tissue rich in collagen and elastin, plus ground substance. Adipose in the hypodermis is connective tissue too. This is the layer that gives plumpness and recoil under massage.
3. Nerve tissue carries electrical signals. Sensory receptors in the skin report pressure, temperature, and pain. That is why you stop a peel, wax, or machine the moment the client reports burning — not after you finish a timed recipe.
4. Muscular tissue contracts. Facial muscles move the skin for expression and sit under your massage strokes. Illinois facial massage is non-therapeutic and excludes the scalp (1175.835 Practices). 225 ILCS 410/3A-1 says esthetics is not treatment of a muscular or nervous disorder.

Why epithelial tissue decides peels and product penetration

Epithelial tissue on the face is a stack. The visible surface is dead, keratinized cells — the stratum corneum. Living keratinocytes sit below. A superficial peel, the only chemical-peel depth Illinois allows as esthetics, targets that dead epithelial surface. It loosens corneocytes so they shed more evenly and so the next product sits on a cleaner barrier. It is not permission to reach living dermis. Medium and deep peels intended to affect living layers are the practice of medicine under IDFPR's prohibited-practices line.

Product penetration follows the same epithelial logic:

• Water-based gels hydrate the surface and may sit in the stratum corneum.
• Occlusives reduce transepidermal water loss.
• Smaller, lipophilic actives have a better chance of moving between corneocytes.
• Inflammation, over-exfoliation, or a cracked barrier increases penetration in a way you do not want: living tissue stings, and the client is more likely to pigment or infect.

Epithelial tissue is why you patch-test, why you do not stack five acids on sensitized skin, and why 1175.710 ties anatomy to applicable services under the Act.

Named Cells You Will See on the Exam

Three names repeat. Memorize the cell, the tissue it lives in, and the service connection.

Keratinocytes are the workhorses of the epidermis — the vast majority of cells in a skin cross-section. They produce keratin, flatten as they rise, and become the stratum corneum. Every cleanse, enzyme, alpha hydroxy acid, and dermaplaning pass interacts with keratinocytes or their dead remnants. Healthy keratinocyte turnover is mitosis plus anabolism; the visible flake is the end of that line.

Melanocytes sit in the basal layer and produce melanin. They transfer pigment to nearby keratinocytes. That is the biology behind even tone, post-inflammatory hyperpigmentation, and why heat, picking, and unprotected UV after a peel are contraindications on reactive or deeper-pigmented skin. You do not erase melanocytes with a facial. You manage the surface and you refer pigment that looks like disease.

Fibroblasts live in the dermis (connective tissue). They synthesize collagen and elastin. Massage, controlled warmth, and topical vitamin C conversations all point back to fibroblasts. Illinois licensees do not inject collagen, do not use radio frequency as esthetics, and do not diagnose collagen disease. You protect fibroblasts from UV and smoking in home-care talk. You do not claim a body wrap rebuilds the dermis.

Put the three together and you have the exam map: keratinocytes equal epidermal surface and peels; melanocytes equal pigment and UV; fibroblasts equal dermal firmness. Tissues wrap those cells — epithelial, connective, nerve, muscle. Metabolism keeps them fed. Mitosis replaces them. That is the anatomy Illinois wants applied when you pick a service.