Histology Study Notes: Tissues in Anatomy & Physiology

Histology of Human Tissues

Nervous Tissue

Nervous tissue is specialized for communication and control within the body. It consists of neurons and supporting glial cells, and is essential for signal transmission and coordination.

• Main Cell Types: Neurons (signal transmission), Neuroglia (supporting cells)

• Identification: Neurons are large cells with axons and dendrites; glial cells are smaller.

• Nuclei: Neurons have one nucleus; glial cell nuclei vary.

• Polarity: Yes, especially in neurons (distinct axon/dendrite regions).

• Vascularity: Highly vascular tissue.

• Location: Brain, spinal cord, peripheral nerves.

• Function: Signal transmission, coordination, sensory input/output.

Muscle Tissues

Muscle tissues are responsible for movement and force generation. They are classified into skeletal, cardiac, and smooth muscle types, each with distinct structure and function.

1. Skeletal Muscle

• Cell Type: Skeletal muscle fibers

• Identification: Long, cylindrical, striated, multinucleated cells

• Nuclei: Many per cell, peripheral location

• Polarity: No

• Vascularity: Highly vascular

• Location: Attached to bones

• Function: Voluntary movement, posture

2. Cardiac Muscle

• Cell Type: Cardiomyocytes

• Identification: Striated, branched, intercalated discs

• Nuclei: Usually one, central

• Polarity: No

• Vascularity: Highly vascular

• Location: Heart walls

• Function: Pumping blood (involuntary)

3. Smooth Muscle

• Cell Type: Smooth muscle cells

• Identification: Spindle-shaped, non-striated

• Nuclei: One, central

• Polarity: No

• Vascularity: Moderately vascular

• Location: Walls of hollow organs (intestines, blood vessels)

• Function: Involuntary movement (peristalsis, vasoconstriction)

Epithelial Tissues

Epithelial tissues cover body surfaces, line cavities, and form glands. They are classified by cell shape and number of layers.

General Features

• Polarity: Yes (apical and basal surfaces)

• Vascularity: Avascular (nutrients via diffusion)

• Nuclei: Varies by type

Types of Epithelial Tissue

1. Simple Squamous

• Identification: Flat, single layer

• Location: Alveoli, blood vessels

• Function: Diffusion, filtration

2. Simple Cuboidal

• Identification: Cube-shaped, single layer

• Location: Kidney tubules, glands

• Function: Secretion, absorption

3. Simple Columnar

• Identification: Tall cells, single layer

• Location: Digestive tract lining

• Function: Absorption, secretion

4. Stratified Squamous

• Identification: Multiple layers, flat surface cells

• Location: Skin, esophagus

• Function: Protection

5. Pseudostratified Columnar

• Identification: Appears layered, but all cells touch basement membrane

• Location: Trachea lining, vas deferens

• Function: Secretion, movement of mucus

6. Transitional

• Identification: Varies with stretch

• Location: Lines ureters, bladder, urethra

• Function: Stretching

Connective Tissues

Connective tissues support, bind, and protect organs. They vary widely in structure and function.

General Features

• Polarity: No

• Vascularity: Varies (cartilage is avascular; bone is highly vascular)

• Nuclei: Varies

Types of Connective Tissue

Loose Connective (Areolar)

• Cells: Fibroblasts, macrophages

• Location: Under epithelium

• Function: Cushioning, immune defense

Summary Table: Major Tissue Types

Tissue Type	Main Cells	Key Features	Location	Function
Nervous	Neurons, Neuroglia	Excitable, highly vascular	Brain, spinal cord, nerves	Signal transmission
Skeletal Muscle	Muscle fibers	Striated, multinucleated	Attached to bones	Voluntary movement
Cardiac Muscle	Cardiomyocytes	Striated, branched, intercalated discs	Heart	Pumping blood
Smooth Muscle	Muscle cells	Spindle-shaped, non-striated	Hollow organs	Involuntary movement
Simple Squamous Epithelium	Squamous cells	Flat, single layer	Alveoli, blood vessels	Diffusion, filtration
Loose Connective (Areolar)	Fibroblasts, macrophages	Loose matrix	Under epithelium	Cushioning, defense

Key Definitions

• Polarity: Structural and functional differences between the apical (top) and basal (bottom) surfaces of a cell.

• Vascularity: Presence of blood vessels within a tissue.

• Striated: Having a striped appearance due to organized contractile proteins (seen in skeletal and cardiac muscle).

• Multinucleated: Cells containing more than one nucleus (e.g., skeletal muscle fibers).

• Intercalated Discs: Specialized connections between cardiac muscle cells for synchronized contraction.

Example: Diffusion in Simple Squamous Epithelium

Simple squamous epithelium in alveoli allows rapid gas exchange by diffusion, essential for respiration.

Example: Peristalsis in Smooth Muscle

Coordinated contraction of smooth muscle in the intestines propels food along the digestive tract.

Additional info:

• Some tissue types (e.g., cartilage, bone, adipose) are not fully covered in these notes but are important in connective tissue classification.

• For histology, identification often relies on cell shape, arrangement, and staining characteristics.