Membranes

^ Definition. A layer of epithelium and its underlying connective tissue that covers a surface of the body. A membrane lines almost all surfaces of the body. ^ Types of membranes

• Cutaneous membrane or skin

♦ Covers the exterior surface of the body.

♦ Composition

■ Stratified squamous keratinized epithelium called epidermis

■ Two layers of connective tissue, loose connective tissue and dense irregular connective tissue, called the dermis

♦ May possess hair follicles, sweat glands, and sebaceous glands

• Mucous membrane or mucosa

♦ Lines all interior lumens of organs that open to the exterior, such as stomach, uterus, and trachea.

Cutaneous membrane

Mucous membrane

Serous membrane Visceral layer Parietal layer

Body wall.

figure 9.1. Cross-section through the abdomen, illustrating epithelial membranes.

♦ Composition

■ Epithelium varies depending on the location.

■ The lamina propria, composed of loose connective tissue, lies beneath the epithelium.

■ Muscularis mucosae, a layer of smooth muscle, is frequently, but not always, present in a mucous membrane.

♦ Many mucous membranes are associated with mucus-secreting cells or glands that lubricate the surface of the membrane.

• Serous membrane or serosa

■ Lines the perimeter of all internal body cavities that do not open to the exterior, such as peritoneal cavity (called peritoneum), pleural cavity (called pleura), and pericardial cavity (called pericardium). This lining constitutes the parietal layer of these cavities.

■ Covers and forms the outer layer of any organs that protrude into those body cavities, such as stomach and jejunum (peritoneum), lungs (pleura), and heart (pericardium). This covering constitutes the visceral layer of these cavities.

♦ Composition

■ Simple squamous epithelium called mesothelium

■ Loose connective tissue

Cutaneous membrane

Mucous membrane

Serous membrane Visceral layer Parietal layer

Body wall.

Serous Membrane Body Plan

figure 9.1. Cross-section through the abdomen, illustrating epithelial membranes.

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