(3.6) Membranes

Types of membranes

1. Cutaneous 2. Mucous 3. Serous 4. Synovial

Dermis

Consists of dense irregular connective tissue and areolar connective tissue.

Epidermis

Consists of keratinized stratified squamous epithelium, which protects underlying tissues.

Cutaneous membrane

Covers the entire surface of the body and consists of a superficial portion called the epidermis and a deeper portion called the dermis. Dry membrane.

Membranes

Flat sheets of pliable tissue that cover or line a part of the body. Are composed of at least two types of primary tissue and are simple organs.

Synovial membranes

Line freely movable joint cavities. Composed of synoviocytes with a layer of connective tissue (adipose & areolar). Synoviocytes secrete components of the synovial fluid.

Lamina propria

The connective tissue layer of a mucous membrane is areolar connective tissue. It is so named because it belongs to (is owned by) the mucous membrane. The lamina propria supports the epithelium, binds it to the underlying structures, allows some flexibility of the membrane, and affords some protection for underlying structures. It also holds blood vessels in place and is the vascular source for the overlying epithelium. Oxygen and nutrients diffuse from the lamina propria to the covering epithelium; carbon dioxide and wastes diffuse in the opposite direction.

Epithelial membranes

The majority of membranes consist of an epithelial layer and an underlying connective tissue layer.

Serous membrane or serosa(e)

Lines a body cavity that does not open directly to the exterior (thoracic or abdominal cavities), and it covers the organs that are within the cavity. Serous membranes consist of areolar connective tissue covered by mesothelium (simple squamous epithelium) . Serous membranes have two continuous layers: The layer attached to and lining the cavity wall is called the parietal layer; the layer that covers and adheres to the organs within the cavity is the visceral layer. The mesothelium of a serous membrane secretes serous fluid, a watery lubricant that allows organs to glide easily over one another or to slide against the walls of cavities. The serous membrane lining the thoracic cavity and covering the lungs is the pleura. The serous membrane lining the heart cavity and covering the heart is the pericardium. The serous membrane lining the abdominal cavity and covering the abdominal organs is the peritoneum.

Mucous membrane or mucosa(e)

Lines a body cavity that opens directly to the exterior. Line the entire digestive, respiratory, and reproductive tracts, and much of the urinary tract. Moist membranes bathed by secretions (or urine). Epithelial sheet lies over layer of connective tissue called lamina propria. May secrete mucus. The epithelial layer of a mucous membrane is an important feature of the body's defense mechanisms because it is a barrier that microbes and other pathogens have difficulty penetrating. Usually, tight junctions connect the cells, so materials cannot leak in between them. Goblet cells and other cells of the epithelial layer of a mucous membrane secrete mucus, and this slippery fluid prevents the cavities from drying out. It also traps particles in the respiratory passageways and lubricates food as it moves through the gastrointestinal tract. In addition, the epithelial layer secretes some of the enzymes needed for digestion and is the site of food and fluid absorption in the gastrointestinal tract. The epithelia of mucous membranes vary greatly in different parts of the body. For example, the mucous membrane of the small intestine is nonciliated simple columnar epithelium and the large airways to the lungs consist of pseudostratified ciliated columnar epithelium