Domain 2.2Anatomy and Physiology

Cellular Biology And Genetics

Last updated June 16, 2026

Overview

Welcome to your study guide for Cellular Biology and Genetics. While this may sound like a topic for a scientist in a lab, it is the foundation of everything you will encounter as a Medical Assistant. Every disease, every medication, and every diagnostic test interacts with the body at the cellular level.

Why This Matters for MAs:

  • Laboratory Testing: Understanding blood cells (RBCs, WBCs) is essential for hematology and phlebotomy.
  • Patient Education: You may need to help explain genetic conditions (like Down syndrome or Hemophilia) or structural issues (like Hernias) to patients in simple terms.
  • Sample Handling: Knowing that cells are fragile helps you understand why specimens must be handled gently to prevent hemolysis (breaking of blood cells).
  • Homeostasis: Understanding how the body maintains balance helps you recognize when a patient is in a critical state (e.g., dehydration).

1. The Human Cell: Structure and Function

The cell is the basic functional unit of the body. All tissues and organs are made of cells. While cells vary in shape and function (e.g., a nerve cell looks very different from a skin cell), they share common structures called organelles.

Key Organelles

Think of organelles as the "little organs" inside a cell that keep it alive.

Organelle Function Memory Aid / Clinical Note
Cell Membrane The outer boundary; controls what enters and leaves the cell. The "Gatekeeper."
Cytoplasm The jelly-like substance holding the organelles. The "packing peanuts" of the cell.
Nucleus The control center containing DNA (genetic material). Clinical Note: White blood cells have a nucleus. Mature Red Blood Cells (RBCs) do not, meaning they cannot divide and contain no DNA for genetic testing.
Mitochondria Produces energy (ATP) through cellular respiration. The "Powerhouse" of the cell.
Ribosomes Synthesize (make) proteins. Ribs = Meat = Protein.
Endoplasmic Reticulum (ER) Transport system within the cell. Rough ER has ribosomes; Smooth ER does not. The "highway" of the cell.
Lysosomes Contain enzymes to digest waste and foreign bacteria. The "garbage disposal" or "Lysol" cleaner.
Centrioles Tube-like structures that help with cell division. Active only when the cell is dividing.
Cilia Short, hair-like projections on the surface. Clinical Note: In the lungs, cilia "sweep" mucus and trapped dust out of the airways. Smoking damages cilia.
Flagella Long, tail-like projection used for movement. Sperm is the only human cell with a flagellum.

Exam Tip: If a question asks where the cell gets its energy or ATP, the answer is always Mitochondria.

Cellular Processes and Homeostasis

All physiological functions begin at the cellular level.

  • Homeostasis: The body's ability to maintain a stable internal environment (e.g., temperature of 98.6°F, stable blood sugar). The Nervous and Endocrine systems are the main regulators of homeostasis.
  • Water Balance: Water is approximately 50-70% of body weight. A loss of just 10% of total body water is a medical emergency.

Cellular Transport

Cells need to move substances (oxygen, water, nutrients) in and out to survive.

  1. Passive Transport (No Energy Required):
    • Diffusion: Movement of substance from High concentration → Low concentration.
      • Example: Oxygen in the lungs moves from the air (high) into the blood (low).
    • Osmosis: The diffusion of water across a membrane.
    • Filtration: Movement driven by pressure (e.g., blood pressure pushing fluids out of capillaries in the kidneys).
  2. Active Transport (Energy/ATP Required):
    • Movement from Low → High concentration (uphill battle).
    • Example: The Sodium-Potassium pump in nerve cells.
    • Phagocytosis: "Cell eating." White blood cells (specifically Monocytes/Macrophages) engulf and destroy bacteria.

2. Cell Division and Genetics

How do we grow, and how do we pass traits to our children?

Cell Division types

  • Mitosis: Process where one cell divides into two identical daughter cells. Used for growth and repair of body tissues (skin, bone, blood).
  • Meiosis: Process used only by reproductive cells (gametes). Results in cells with half the number of chromosomes (23 instead of 46).
    • Sperm (23) + Egg (23) = Zygote (46).

Genetics Basics

  • DNA (Deoxyribonucleic Acid): The molecule that carries genetic instructions. Found in the Nucleus.
  • Gene: A segment of DNA that codes for a specific trait (e.g., eye color).
  • Chromosome: A thread-like structure of coiled DNA. Humans have 23 pairs (46 total).
    • XX: Female
    • XY: Male (The father determines the sex of the baby).

Genetic and Congenital Disorders

These conditions are caused by mutations in DNA or chromosomal abnormalities.

Condition Description Key Exam Detail
Cystic Fibrosis Genetic disorder causing thick, sticky mucus in lungs and digestive tract. Affects the respiratory and digestive systems.
Phenylketonuria (PKU) Rare genetic metabolic disorder. The body cannot break down the amino acid phenylalanine. Newborn Screening: All babies in the US are tested via heel stick. Untreated PKU causes brain damage.
Down Syndrome Chromosomal disorder caused by an extra copy of chromosome 21 (Trisomy 21). Identified via Amniocentesis (prenatal) or karyotyping.
Hemophilia Hereditary bleeding disorder where blood fails to clot. Usually affects males; passed down by mothers (X-linked).
Color Blindness Genetic inability to distinguish certain colors (usually red/green). Caused by a defect in the Cones of the retina.
Sickle Cell Anemia Genetic disorder where RBCs are shaped like a crescent (sickle). Causes blockages and pain crises. Most common in African American populations.

Exam Tip: Remember PKU is related to metabolism and diet. Babies with PKU must be put on a special diet immediately to prevent intellectual disability.

3. Tissues: Cells Working Together

Cells group together to form tissues. There are four primary types of tissue in the human body.

Tissue Type Function Examples
Epithelial Covers and Lines. Protection, absorption, secretion. Epidermis (skin), lining of the stomach, lining of the mouth. Glands are made of epithelial tissue.
Connective Supports and Connects. Most abundant tissue type. Bone, Cartilage, Adipose (fat), Blood (yes, blood is liquid connective tissue!).
Muscle Contracts to produce movement. Skeletal (voluntary), Cardiac (heart), Smooth (organs/vessels).
Nervous Communicates. Transmits electrical impulses. Neurons (brain, spinal cord, nerves).

Connective Tissue Structures

Within the musculoskeletal system, specific connective tissues hold the body together:

  • Tendons: Connect Muscle to Bone (Mnemonic: MTB).
  • Ligaments: Connect Bone to Bone.
  • Cartilage: Cushions joints.

4. Structural Pathologies

Understanding the cellular and tissue blueprint helps you identify when the structure is damaged or malformed.

Condition Structural Defect Blueprint Connection
Kyphosis Exaggerated forward rounding of the thoracic spine ("Humpback"). Deformity of the skeletal framework.
Scoliosis Sideways curvature of the spine (S-shape). Lateral deviation from the midline.
Hiatal Hernia Part of the stomach pushes upward through the diaphragm. Failure of the barrier between the Thoracic and Abdominal cavities.
Inguinal Hernia Protrusion of intestine through the abdominal wall in the groin area. Weakness in the muscle wall.
Atrophy Decrease in cell/muscle size due to disuse. "A-" (without) + "trophy" (nourishment/growth).
Hypertrophy Increase in cell/organ size. e.g., Prostatic Hypertrophy (enlarged prostate).
Necrosis Death of tissue cells. Irreversible damage to the cellular blueprint.

5. Final Key Takeaways

  • Organelles: The Nucleus holds DNA. The Mitochondria makes energy (ATP). The Ribosome makes protein.
  • Sample Quality: Mature Red Blood Cells (RBCs) have no nucleus and no DNA. You cannot extract DNA from a standard RBC.
  • Transport: Diffusion moves things from High to Low concentration (like oxygen). Osmosis moves water.
  • Homeostasis: A loss of 10% of body water is a medical emergency. The Nervous and Endocrine systems regulate balance.
  • Tissue Types: Blood and Bone are types of Connective Tissue. Skin is Epithelial Tissue.
  • Structural Connections: Tendons connect Muscle to Bone (MTB). Ligaments connect Bone to Bone.
  • Genetics: PKU is detected by a heel stick on newborns. Hemophilia is a bleeding disorder. Cystic Fibrosis affects lungs/pancreas.
  • Structural Defects: Kyphosis is thoracic curvature (humpback); Scoliosis is lateral curvature (S-shape). Hiatal Hernia involves the diaphragm.
  • Phagocytosis: The process where a cell (like a WBC) engulfs/eats a bacteria.