Chapter 4

Body Tissues and Membranes

Introduction

• Cells are arranged into tissues that provide specific functions for the body

• Cells of different tissues are structured differently, which leads to differences in their function.

• Structure = Function

4 primary tissue types:

1. Epithelial tissue-

covers surfaces, lines cavities, forms glands.

2. Connective tissue-

supports and protects other tissues.

3. Muscle tissue-

causes movement.

4. Nervous tissue-

receives and generates nerve impulses

Characteristics of Epithelial Tissue

• All over the body, covers surfaces (like organs), lines cavities and surfaces, and forms glands.

• Anchored to a basement membrane

• Made of tightly packed cells

• Lack blood vessels

• Contain little extracellular material (matrix)

– space outside the cells.

• Replaced frequently

More epithelial characteristics:

• function is determined by the cell type and number of cell layers.

• Anchored or supported by underlying connective tissue: – Basement membrane: separates the epithelial and

connective tissues.

Epithelial cell shapes:

• Squamous cells- the thinnest of the 4, have a flattened nucleus

• Cuboidal cells- cube-like with a round nucleus in the center of the cell

• Columnar cells- tall with an oval nucleus close to the base of the cell

• Transitional cells- change shape (cuboidal when tissue is relaxed, squamous when the tissue is expanded)

EPITHELIAL TISSUE TYPES

SIMPLE: ONE cell layer

STRATIFIED: TWO OR MORE Layers

Two types of Pseudostratified epi:

Pseudostratified columnar

Pseudostratified ciliated

Simple Squamous • Identification: Small, flat cells arranged

around large, empty circles (air sacs).

– note the multiple cells and nuclei (arrows).

• Where Located: lung (air sacs or alveoli) and lining blood vessels .

• Function: diffusion (gas exchange).

\

Simple Cuboidal

• Identification: Squarish cells with round nuclei in a single row, usually arranged in a circle (tubule)

• Where Located:

kidney tubules

• Function:

absorption and secretion.

Simple Columnar • Identification: Tall rectangular cells, with single, neat

row of oval nuclei, usually more towards the base

– also goblet cells (secretes mucus) found only here and in Pseudostratified Columnar Epithelium

• Where Located: small intestine.

• Function: absorption and secretion

1. goblet cells

2. nuclei

3. Microvilli

Goblet cell secreting mucus

Stratified Squamous

• Identification: Many layers of small, flattened cells. The only other epithelial tissue with so many layers is transitional

• typically has a more evenly contoured surface

• uppermost layers of cells flattened

• Where Located: surface of skin, lining mouth and esophagus

• Function: protection from abrasion and infection

Stratified Cuboidal

• Identification: cube shaped, usually 2 layers (rare tissue)

• Where Located: glands (sweat, salivary and mammary)

• Function: secretion

Stratified Columnar • Identification: column shaped cells

arranged in multiple layers (rare tissue)

• Where Located: vas deferens, male urethra, and parts of the pharynx

• Function:

secretion and protection

Pseudostratified (Ciliated) Columnar • Identification: Tall rectangular cells, with

multiple irregular rows of nuclei (goblet cells)

• Where Located: trachea

• Function: secretion & movement of mucus

1. cilia

2. goblet cells

3. nuclei

Transitional • Identification: Numerous layers of cells of varying and

often irregular shape

• Where Located: ureters and urinary bladder

• Function: elasticity:

stretch and retract