Major Organs and Organ Systems

Introduction to Major Organs

Understanding the location and function of major organs is foundational in anatomy and physiology. Each organ belongs to a specific organ system, contributing to the body's overall function and homeostasis.

• Nervous System: Brain

• Cardiovascular System: Heart

• Lymphatic System: Spleen

• Respiratory System: Lungs

• Digestive System: Liver, Gallbladder, Stomach, Pancreas, Small Intestine, Large Intestine

• Urinary System: Kidneys, Urinary Bladder

• Endocrine System: Adrenal Glands, Thyroid Gland

Example: The heart is the central organ of the cardiovascular system, responsible for pumping blood throughout the body.

Histology: The Study of Tissues

Introduction to Histology

Histology is the science of studying the microscopic structure of tissues. All tissues in the human body are classified into four general types: epithelial, muscle, connective, and nervous tissue. This lab focuses on epithelial and muscle tissues.

• Epithelial Tissue: Covers body surfaces and lines cavities.

• Muscle Tissue: Responsible for movement.

Epithelial Tissue

General Characteristics of Epithelial Tissue

Epithelial tissues cover surfaces exposed to the environment and line hollow organs and body cavities. The cells are tightly packed with minimal extracellular space and are anchored to underlying tissues by a basement membrane, which consists of the basal lamina and reticular lamina. The apical surface faces the environment or lumen, while the basal surface attaches to the basement membrane.

• Classification Criteria: Cell shape and number of layers.

• Cell Shapes: Squamous (flat), Cuboidal (cube-shaped), Columnar (tall).

Example: The lining of blood vessels is composed of simple squamous epithelium, allowing efficient diffusion.

Classification by Layers

Epithelial tissues are further classified by the number of cell layers:

• Simple Epithelium: Single layer; all cells touch the basement membrane.

• Stratified Epithelium: Multiple layers; named for the shape of the apical cells.

• Pseudostratified Epithelium: Appears multilayered but all cells contact the basement membrane.

Classification Overview

The following chart summarizes the main classes of epithelial tissue, including those required for Lab 1:

Types of Epithelial Tissue

Simple Squamous Epithelium

Composed of a single layer of thin, flat cells, this tissue allows for rapid diffusion, osmosis, filtration, and secretion. Special names include endothelium (lining heart and blood vessels) and mesothelium (lining body cavities).

• Locations: Alveoli, glomerular capsule, lining of body cavities, heart chambers, blood vessels

Simple Cuboidal Epithelium

Consists of a single layer of cube-shaped cells, often involved in secretion and absorption, with limited protective function.

• Locations: Thyroid gland, lining kidney tubules

Simple Columnar Epithelium

Composed of a single layer of tall, column-like cells. May have cilia (for movement) or microvilli (for increased surface area). Functions in absorption and secretion.

• Locations: Lining of the stomach, gallbladder, small intestine, large intestine

Pseudostratified Columnar Epithelium

Appears stratified due to varying cell heights, but all cells contact the basement membrane. Contains goblet cells (mucus production) and cilia (movement of substances).

• Locations: Lining of the trachea, nasal cavities

Stratified Squamous Epithelium

Multiple layers of cells with squamous cells at the apical surface. Provides protection in areas subject to abrasion and mechanical stress.

• Locations: Epidermis, lining of esophagus, anus, rectum, vagina

Transitional Epithelium

Multiple layers with dome-shaped apical cells. Specialized to stretch and recoil without damage.

• Locations: Lining of ureters, urinary bladder

Muscle Tissue

Overview of Muscle Tissue Types

Muscle tissue is specialized for contraction and movement. There are three types:

• Skeletal Muscle: Voluntary, striated, multinucleate, cylindrical cells. Found in skeletal muscles.

• Cardiac Muscle: Involuntary, striated, single nucleus, branched cells, intercalated discs. Found in the heart.

• Smooth Muscle: Involuntary, non-striated, single nucleus, tapered cells. Found in walls of blood vessels and hollow organs.

Lab 1 Study Checklist

• Define all bold terms from the lab manual.

• Identify the major organs listed.

• Classify each tissue as muscle or epithelium.

• Identify the 3 muscle tissues and 6 epithelial tissues by their complete names.

• Label bolded structures for each tissue.

• Give one detailed body location for each tissue, as listed in the manual.

• Use only lab manual definitions and terms.

Summary Table: Epithelial Tissues for Lab 1