Major Organs and Organ Systems

Introduction to Major Organs

The human body is organized into several organ systems, each with specific major organs that perform essential physiological functions. Understanding the location and function of these organs is foundational for the study of anatomy and physiology.

• 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

Overview of Tissue Types

Histology is the science of studying the microscopic structure of tissues. All tissues in the human body are classified into four main 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.

• Connective Tissue: Supports and binds other tissues (covered in Lab 2).

• Nervous Tissue: Conducts electrical impulses (covered in Lab 2).

Example: The epidermis is composed of epithelial tissue that protects underlying structures.

Epithelial Tissue

General Characteristics

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.

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

• Layers: Simple (one layer), Stratified (multiple layers), Pseudostratified (appears multilayered but all cells touch the basement membrane).

Example: Simple squamous epithelium is found in the alveoli of the lungs, facilitating gas exchange.

Classification of Epithelial Tissue

Epithelial tissues are classified based on the combination of cell shape and layering. The main classes are summarized in the following diagram:

Additional info: Ciliated and nonciliated forms exist for some columnar and pseudostratified epithelia, affecting their function in moving substances.

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

Example: The alveoli in the lungs are lined with simple squamous epithelium to facilitate gas exchange.

Simple Cuboidal Epithelium

This tissue consists of a single layer of cube-shaped cells, often involved in secretion and absorption, with limited protection.

• Locations: Thyroid gland, lining kidney tubules

Example: The kidney tubules are lined with simple cuboidal epithelium to allow for selective reabsorption and secretion.

Simple Columnar Epithelium

Composed of a single layer of tall cells, often with cilia or microvilli. This tissue is specialized for absorption and secretion.

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

Example: The lining of the small intestine contains simple columnar epithelium with microvilli to increase surface area for nutrient absorption.

Pseudostratified Columnar Epithelium

This tissue appears to have multiple layers due to varying cell heights, but all cells contact the basement membrane. It often contains goblet cells (mucus production) and cilia (movement of substances).

• Locations: Lining of the trachea, nasal cavities

Example: The trachea is lined with pseudostratified ciliated columnar epithelium to trap and move particles out of the airway.

Stratified Squamous Epithelium

Composed of multiple layers with squamous cells at the apical surface, this tissue provides protection against mechanical stress.

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

Example: The epidermis of the skin is made of stratified squamous epithelium to protect against abrasion and dehydration.

Transitional Epithelium

This tissue consists of multiple layers with dome-shaped cells at the apical surface. It is specialized to stretch and recoil without damage.

• Locations: Lining of the ureters, urinary bladder

Example: The urinary bladder is lined with transitional epithelium, allowing it to expand as it fills with urine.

Muscle Tissue

Types of Muscle Tissue

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

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

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

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

Example: Cardiac muscle tissue is found only in the heart and is responsible for pumping blood throughout the body.

Lab 1 Study Checklist

• Define all bold terms from the lab manual.

• Identify the major organs listed for each organ system.

• Classify each tissue as muscle or epithelium.

• Identify and name the 3 muscle tissues and 6 epithelial tissues covered in this lab.

• Provide the complete tissue name and a detailed body location for each tissue.

• Label bolded structures for each tissue.

• Use only definitions and terms from the lab manual for credit.

Additional info: Accurate spelling and complete answers are required for full credit on quizzes and practicals.