Introduction to Anatomy & Physiology: Structural Organization and the Cell

Introduction to Anatomy and Physiology

Overview

Anatomy and physiology are foundational sciences in understanding the structure and function of the human body. Anatomy focuses on the structure of body parts and their relationships, while physiology studies how these parts work to carry out life-sustaining activities.

• Anatomist: Studies the shape, size, and position of body structures.

• Physiologist: Investigates the function of body parts, such as the role of the liver in nutrition and regulation.

Subdivisions of Anatomy

• Gross (Macroscopic) Anatomy: Study of visible structures.

  • Regional Anatomy: All structures in a particular area (e.g., arm).

  • Systemic Anatomy: Study by organ systems (e.g., cardiovascular, nervous).

  • Surface Anatomy: Study of internal structures as they relate to the overlying skin.

• Microscopic Anatomy: Structures too small to see with the naked eye.

  • Cytology: Study of cells.

  • Histology: Study of tissues.

• Developmental Anatomy: Study of structural changes throughout life (e.g., embryology).

Subdivisions of Physiology

• Based on organ systems (e.g., cardiovascular physiology).

• Focuses on cellular and molecular levels.

Principle of Complementarity of Structure and Function

• Anatomy and physiology are inseparable: Function always reflects structure.

• Example: Bones support organs because they contain hard mineral deposits; heart valves prevent backflow of blood.

Structural Organization of the Human Body

Levels of Organization

1. Chemical Level: Atoms, molecules, and organelles.

2. Cellular Level: Single cell.

3. Tissue Level: Groups of similar cells.

4. Organ Level: Contains two or more types of tissues.

5. Organ System Level: Organs that work closely together.

6. Organismal Level: All organ systems combined to make the whole organism.

Tissue Level

• Tissues: Groups of similar cells working together for a specific function.

• Types of tissues:

  • Epithelial tissue: Covers surfaces (e.g., skin).

  • Muscle tissue: Enables movement (e.g., skeletal muscle).

  • Connective tissue: Supports organs (e.g., bone, blood).

  • Nervous tissue: Transmits electrical signals (e.g., neurons).

Organ Level

• Organ: Made up of at least two tissue types, usually four, working together for a specific function.

• Example: Stomach (contains all four tissue types).

Organ System Level

• Organ systems: Groups of organs working together for a common function.

• Example: Cardiovascular system (heart and blood vessels).

• Other systems: Integumentary, skeletal, muscular, nervous, endocrine, lymphatic, respiratory, digestive, urinary, reproductive.

• Immune system is often associated with the lymphatic system.

Organismal Level

• The sum of all organ systems working together to maintain life; a living human being.

Cells: The Living Units

Cell Diversity

• Over 250 different types of human cells.

• Differences in size, shape, subcellular components, and functions.

Basic Parts of a Human Cell

1. Plasma membrane: Outer boundary.

2. Cytoplasm: Intracellular fluid containing organelles.

3. Nucleus: DNA-containing control center.

Structure of a Generalized Cell

Cytoplasm

• Everything inside the cell but outside the nucleus.

• Composed of:

  • Cytosol: Fluid portion (rich in enzymes, nutrients, ions).

  • Inclusions: Temporary structures (e.g., glycogen granules, lipid droplets).

  • Organelles: "Mini-organs" performing specific functions.

Membranes

• Microenvironments for specialized reactions (e.g., lysosomes need acidic pH).

• Surrounded by a lipid bilayer.

• Includes mitochondria, ER, Golgi apparatus, lysosomes, peroxisomes.

Non-membranous Organelles

• Structural frameworks (e.g., cytoskeleton, centrioles).

• Ribosomes, cytoskeleton, centrioles.

Mitochondria

• "Powerhouse" of the cell: generates most ATP via cellular respiration.

• Unique: Can replicate themselves, contain their own circular DNA (maternal inheritance).

Endoplasmic Reticulum (ER)

• Network of flattened sacs, tubules, and vesicles connected together.

• Continuous with the nuclear envelope.

• Functions as a factory: makes proteins, lipids, and processes molecules.

• Two main types: Rough ER (RER) and Smooth ER (SER).

Rough ER (RER)

• Structure: Ribosomes attached to surface ("rough" look).

• Functions:

  • Protein synthesis for secretion, membranes, or organelles.

  • Protein folding and modification (e.g., adding sugar chains).

  • Sends proteins to Golgi apparatus for further processing.

  • Quality control for proteins (misfolded proteins handled here).

Smooth ER (SER)

• Structure: No ribosomes; smooth, tubular appearance.

• Functions:

  • Lipid synthesis (phospholipids, steroids).

  • Detoxification (liver cells).

  • Calcium storage (muscle cells).

  • Carbohydrate metabolism (liver cells).

Golgi Apparatus

• Structure: Stacks of flattened membrane sacs (cisternae).

• Main role: Modifies, sorts, and packages proteins and lipids from the Rough ER.

• Three faces:

  1. Cis face (receiving): Receives vesicles from ER.

  2. Modification inside: Proteins/lipids are processed (e.g., sugars added/removed, phosphate groups added, folded).

  3. Trans face (shipping): Finished products sorted and packaged into vesicles.

Pathways for Vesicles

• Pathway A – Secretory vesicles: Vesicles fuse with plasma membrane and release contents (exocytosis). Example: Pancreatic cells releasing insulin.

• Pathway B – Membrane vesicles: Vesicles fuse with plasma membrane or other organelles to insert proteins/lipids.

• Pathway C – Lysosomes: Vesicles remain inside as lysosomes, holding digestive enzymes.

Peroxisomes (Detox Centers)

• Structure: Small membrane-bound sacs filled with enzymes.

• Main role: Neutralize toxins and break down fatty acids.

• Functions:

  • Detoxification: Break down reactive oxygen species (ROS), contain oxidases and catalase.

  • Fatty acid metabolism: Break down long-chain fatty acids for energy.

Lysosomes (Cell's Recycling & Digestion System)

• Structure: Spherical sacs with acidic interior, full of hydrolytic enzymes.

• Functions:

  • Digest large molecules (proteins, lipids, carbs, nucleic acids).

  • Destroy bacteria, viruses, and worn-out organelles (autophagy).

  • Release calcium from bone and other breakdown products back to the cytoplasm.

  • Can cause autolysis: cell self-digestion (important in tissue remodeling, but dangerous if uncontrolled).

Cytoskeleton

• Definition: An elaborate network of protein rods and filaments that extends throughout the cytosol.

• Functions:

  • Provides structure (like bones/ligaments/muscles of the cell).

  • Maintains cell shape.

  • Anchors organelles in place.

  • Serves as tracks for movement of organelles, vesicles, and molecules.

  • Plays a role in cell division and cell motility (movement).

Three Main Types of Cytoskeletal Elements

1. Microfilaments (Actin filaments): Thinnest (~7 nm), made of actin protein. Functions: resist tension, help with cell shape changes, increase surface area for absorption (intestinal cells).

2. Intermediate Filaments: Diameter ~10 nm, rope-like, made of keratin-like proteins. Functions: provide mechanical strength, anchor organelles.

3. Microtubules: Largest (~25 nm), hollow tubes made of tubulin proteins, radiate from the centrosome. Functions: form highways for movement of vesicles/organelles, organize cell division, form cilia and flagella.

Centrosome & Centrioles (Microtubule Organizers)

• Centrosome: The "cell center" located near the nucleus, contains a granular matrix and a pair of centrioles (short microtubule cylinders at right angles).

• Functions: Microtubule organizing center (MTOC), helps organize the mitotic spindle during cell division, forms the base for cilia and flagella.

Cellular Extensions

• Certain cells have specialized structures that extend from the cell surface.

• Cilia: Hairlike, motile projections (9+2 pattern of microtubules), coordinated beating moves substances across cell surfaces.

• Flagella: Similar to cilia but longer; only human cell with a flagellum is sperm (propels the cell).

• Basal Body: Modified centriole at the base of cilia/flagella, anchors and organizes microtubules.

• Microvilli: Fingerlike projections (not motile), increase surface area for absorption (e.g., small intestine), supported by actin filaments.

Extracellular Materials

• Substances found outside cells that support, protect, and connect cells.

1. Extracellular Fluids (Body Fluids)

• Interstitial fluid: Bathes cells in tissues.

• Blood plasma: Fluid of blood.

• Cerebrospinal fluid (CSF): Cushions brain/spinal cord.

• These fluids allow transport of nutrients, gases, and waste between cells and environment.

2. Cellular Secretions

• Substances made by cells and released into extracellular space (e.g., saliva, mucus, digestive juices).

• Functions: lubrication, protection, digestion, signaling.

3. Extracellular Matrix

• Definition: Network of proteins and polysaccharides outside cells that acts like "glue."

• Main components:

  • Collagen fibers: Strength.

  • Elastic fibers: Stretch.

  • Proteoglycans & glycoproteins: Hydration, cell signaling.

• Functions: Holds cells together, provides scaffolding for tissue architecture, influences cell behavior (growth, migration, survival).