Anatomy & Physiology Exam Review: Tissues, Cell Structure, and Integumentary System

Tissues of the Human Body

Main Types of Tissue

The human body is composed of four primary tissue types, each with distinct structures and functions essential for maintaining homeostasis and supporting life.

• Epithelial Tissue: Covers body surfaces, lines cavities, and forms glands. Functions include protection, absorption, filtration, excretion, secretion, and sensory reception.

• Connective Tissue: Supports, binds, and protects organs. Functions include structural support, storage of energy (as fat), and immune responses.

• Muscle Tissue: Responsible for movement. Types include skeletal (voluntary movement), cardiac (heart contraction), and smooth (walls of hollow organs).

• Nervous Tissue: Initiates and transmits electrical impulses, allowing communication between body parts. Composed of neurons and supporting glial cells.

Example: The skin contains all four tissue types: epithelial (epidermis), connective (dermis), muscle (arrector pili), and nervous (sensory receptors).

Types of Epithelial Glandular Secretions

Epithelial tissue forms glands that secrete substances necessary for bodily functions. There are two main types of glandular secretions:

• Exocrine Secretions: Released onto body surfaces or into body cavities via ducts (e.g., sweat, saliva).

• Endocrine Secretions: Released directly into the bloodstream (e.g., hormones from the thyroid gland).

Example: Sweat glands are exocrine, while the pancreas has both exocrine (digestive enzymes) and endocrine (insulin) functions.

Types of Connective Tissue

Connective tissue is classified based on its structure and function. The four main types are:

• Connective Tissue Proper: Includes loose (areolar, adipose, reticular) and dense (regular, irregular, elastic) connective tissues. Functions in binding, support, and storage.

• Cartilage: Provides flexible support and cushioning (e.g., hyaline, elastic, fibrocartilage).

• Bone: Rigid support, protection, and mineral storage.

• Blood: Transports nutrients, gases, wastes, and immune cells.

Example: Adipose tissue (a loose connective tissue) stores fat, while bone tissue provides structural support.

Loose vs. Dense Connective Tissue

Connective tissue proper is further divided into loose and dense types, each with unique characteristics:

• Loose Connective Tissue: Fewer fibers, more ground substance. Types include areolar (packing material), adipose (fat storage), and reticular (support for lymphoid organs).

• Dense Connective Tissue: More fibers, less ground substance. Types include dense regular (tendons, ligaments), dense irregular (dermis), and elastic (walls of large arteries).

Example: Tendons are composed of dense regular connective tissue, providing strong attachment between muscle and bone.

Cell Structure and Function

Major Cell Components and Their Functions

Cells contain specialized organelles that perform essential functions for survival and homeostasis.

• Endoplasmic Reticulum (ER): Network of membranes for protein and lipid synthesis and transport. Rough ER has ribosomes for protein synthesis; smooth ER synthesizes lipids.

• Ribosome: Site of protein synthesis; assembles amino acids into polypeptide chains.

• Golgi Apparatus: Modifies, sorts, and ships proteins and lipids for secretion or use within the cell.

• Mitochondrion: Produces ATP through cellular respiration, providing energy for cellular activities.

• Cytoskeleton: Network of filaments (microfilaments, intermediate filaments, microtubules) that maintain cell shape, enable movement, and organize cell contents.

• Nucleus: Contains DNA; controls cell activities and genetic information.

Example: Muscle cells have abundant mitochondria to meet high energy demands.

Biochemistry: Triglycerides Structure

Triglycerides

Triglycerides are a type of lipid important for energy storage. They consist of a glycerol backbone and three fatty acid chains.

• Glycerol: The "head" of the molecule; a three-carbon alcohol.

• Fatty Acids: The "tails"; long hydrocarbon chains attached to glycerol.

Formula:

$\text{Triglyceride} = \text{Glycerol} + 3 \times \text{Fatty Acid}$

Example: Triglycerides are stored in adipose tissue and used for energy during fasting.

Integumentary System: Skin Structure and Function

Layers of the Skin

The skin is composed of multiple layers, each with specialized cells and functions. The main layers are:

• Epidermis: Outermost layer; provides protection and contains several sublayers:

  • Stratum corneum: Dead, keratinized cells; barrier function.

  • Stratum granulosum: Cells with granules; involved in keratin formation.

  • Stratum spinosum: Provides strength and flexibility; contains desmosomes.

  • Stratum basale: Deepest layer; contains stem cells for regeneration.

  • Stratum lucidum: Present only in thick skin (palms, soles).

• Dermis: Beneath the epidermis; contains connective tissue, blood vessels, nerves, and accessory structures.

Example: The stratum basale is responsible for producing new skin cells.

Cell Types in the Epidermis

• Keratinocytes: Produce keratin, a protective protein.

• Melanocytes: Produce melanin, which gives skin its color and protects against UV radiation.

• Langerhans' Cells: Immune cells that help protect against pathogens.

• Merkel Cells: Sensory receptors for touch.

Example: Melanocytes are found in the stratum basale and contribute to skin pigmentation.

Functions of the Integumentary System

• Protection: Against mechanical injury, pathogens, and dehydration.

• Temperature Regulation: Through sweating and blood vessel dilation/constriction.

• Sensation: Sensory receptors detect touch, pain, and temperature.

• Excretion: Removal of waste products via sweat.

• Vitamin D Synthesis: Initiated by exposure to sunlight.

Example: Sweat glands help cool the body through evaporative cooling.

Table: Layers and Cell Types of the Epidermis

Layer	Main Cell Types	Key Features
Stratum corneum	Keratinocytes (dead)	Barrier, protection
Stratum granulosum	Keratinocytes	Keratin formation, granules
Stratum spinosum	Keratinocytes, Langerhans' cells	Strength, immune defense
Stratum basale	Stem cells, melanocytes, Merkel cells	Cell division, pigmentation, sensation

Additional info:

• Desmosomes are specialized junctions in the stratum spinosum that provide mechanical strength and prevent cell separation.

• Loose connective tissue (e.g., areolar) is found beneath epithelial layers and supports organs.

• Dense connective tissue (e.g., tendons) provides strong attachments and resistance to tension.