Cellular Structure, Tissue Types, and Glands: Anatomy & Physiology Study Notes

Cellular Structure and Function

Cell Size and Components

Cells are the fundamental units of life, and their size and structure are determined by their function and environment.

• Smallest Living Unit: Cells are considered the smallest living units in organisms.

• Plasma Membrane: The plasma membrane surrounds the cell, controlling the movement of substances in and out. It is primarily composed of a phospholipid bilayer.

• Main Component of Tissues: Cells are the main component of tissues, each specialized for specific functions.

• DNA: DNA is located in the nucleus and contains genetic information that determines cell function.

• Protein Synthesis: Proteins are synthesized by ribosomes using instructions from DNA.

• Endoplasmic Reticulum and Ribosomes: The endoplasmic reticulum (ER) and ribosomes are involved in protein and lipid synthesis. The rough ER is studded with ribosomes, while the smooth ER is not.

• Microtubules: Microtubules are part of the cytoskeleton, providing structural support and enabling cell movement.

Example: Colchicine is a chemotherapy drug that targets microtubules, inhibiting their dynamic ability and affecting cell division.

Additional info: Tay-Sachs disease affects lysosomes, leading to neuron swelling due to improper breakdown of cellular waste.

RNA vs. DNA

Both RNA and DNA are nucleic acids involved in genetic information storage and transfer.

• DNA: Double-stranded, contains deoxyribose sugar, and stores genetic information.

• RNA: Single-stranded, contains ribose sugar, and is involved in protein synthesis.

• Key Difference: DNA remains in the nucleus, while RNA can travel to the cytoplasm.

Cell Junctions and Tissue Organization

Cell Junctions

Cell junctions connect adjacent cells, allowing communication and maintaining tissue integrity.

• Tight Junctions: Prevent leakage of extracellular fluid between cells.

• Gap Junctions: Allow direct communication between cells through channels.

• Desmosomes: Anchor cells together, providing mechanical strength.

Tissue Types and Functions

Tissues are groups of cells with similar structure and function. The main tissue types include epithelial, connective, muscle, and nervous tissues.

• Epithelial Tissue: Covers body surfaces and lines cavities. Main components include cells and a basement membrane.

• Connective Tissue: Supports, binds, and protects organs. Contains ground substance, fibers, and cells such as fibrocytes.

• Cartilage: A type of connective tissue with irregular tissue structure; chondrocytes are the main cells.

• Air Sacs in Lungs: Lined by simple squamous epithelium, allowing efficient gas exchange.

• Blood: Considered a connective tissue due to its origin and function.

Glands and Ducts

Types of Glands

Glands are specialized epithelial cells that secrete substances. They are classified based on the presence or absence of ducts.

• Exocrine Glands: Have ducts that carry secretions to body surfaces or cavities (e.g., sweat glands, salivary glands).

• Endocrine Glands: Ductless; secrete hormones directly into the bloodstream (e.g., thyroid gland).

Example: Sweat glands are exocrine glands, while the pituitary gland is an endocrine gland.

Sweat Glands

Sweat glands are exocrine glands involved in thermoregulation and waste excretion.

• Types: Eccrine (merocrine) and apocrine sweat glands.

• Eccrine Glands: Found all over the body; secrete watery sweat for cooling.

• Apocrine Glands: Located in specific areas (e.g., armpits); secrete thicker sweat, often associated with body odor.

• Functions: Thermoregulation, excretion of waste products.

Skin Structure and Pigmentation

The skin consists of multiple layers and contains specialized cells responsible for pigmentation.

• Layers of Skin: Epidermis (outer layer), dermis (middle layer), and hypodermis (deepest layer).

• Melanocytes: Cells in the epidermis that produce melanin, the pigment responsible for skin color.

• Number of Melanocytes: All humans have the same number of melanocytes; differences in skin color are due to melanin production and distribution.

• Stratum Corneum and Stratum Basale: The stratum corneum is the outermost layer of the epidermis, while the stratum basale is the deepest layer where cell division occurs.

Table: Comparison of Exocrine and Endocrine Glands

Feature	Exocrine Glands	Endocrine Glands
Presence of Ducts	Present	Absent
Secretion Destination	Body surface or cavity	Bloodstream
Examples	Salivary, sweat, sebaceous glands	Thyroid, pituitary, adrenal glands
Main Function	Local effect	Systemic effect

Key Terms and Definitions

• Fibrocyte: A cell found in connective tissue that maintains the extracellular matrix.

• Chondrocyte: A cell found in cartilage responsible for maintaining cartilage structure.

• Melanocyte: A cell in the skin that produces melanin pigment.

• Stratum Corneum: The outermost layer of the epidermis, composed of dead keratinized cells.

• Stratum Basale: The deepest layer of the epidermis, where new skin cells are generated.

Formulas and Equations

• Protein Synthesis: The process by which cells build proteins using genetic instructions from DNA and RNA. $\text{DNA} \xrightarrow{\text{transcription}} \text{mRNA} \xrightarrow{\text{translation}} \text{Protein}$

• Cell Division: Mitosis is the process by which a cell divides to produce two identical daughter cells. $\text{Parent Cell} \xrightarrow{\text{Mitosis}} 2 \text{Daughter Cells}$

Additional info: Some content was inferred and expanded for academic completeness, such as the functions of cell junctions, types of sweat glands, and the structure of skin layers.