Pathophysiology

Pathophysiology Study Guide

Chapter 2: Host Defense/Hematology Objectives: 1. Understand alterations and disorders of the skin. 2. Identify common elements of wound healing major disorders along with their etiology, causes, diseases, treatment and complications. 3. Discuss alterations in the immune system and the role of immunization. 4. Explain alterations in the hematological system comprising the disorders in red blood cells, white blood cells, platelets, plasma, and hemostasis. 2.1 Alterations in Integument Function One of the best ways to prevent infections is to prevent pathogens from entering the body. Skin is the largest organ of the body, which provides a vast surface area for micro-organisms to enter. In fact, a large number of different micro-organisms live on the skin, but do not harm the host unless they enter the skin through an opening. Skin acts as the first defense against infections. This section describes the mechanical barriers and skin disorders that help the pathogens enter and harm the host. Mechanical Barriers The skin is made of two layers: dermis and epidermis. The dermis is the inner layer of skin; it is thick and has many connective tissues. In contrast, the epidermis is the outer visible layer of the skin, which is thin and has many epithelial cells. The epidermis constantly maintains direct contact with the external environment. The top layer of the epidermis is made from dead cells and contains keratin, which is protein that protects the skin. When the upper layer of the skin sheds periodically, it helps in removing the microbes. Therefore, dryness of the skin helps in inhibiting the growth of micro- organisms. Skin infections, like athlete’s foot, are most common among moist skin types. It is not possible for micro-organisms to penetrate through healthy skin layers. Skin also contains endothelial cells, which line the blood and lymph cells and help in the movement of defensive cells between the blood and tissues. However, these cells also become the portal for movement of pathogens. Another part of the skin, known as the mucous membrane, constitutes the connective layer of tissues and is above the layer of epithelial cells. It provides a protective lining surrounding the gastrointestinal, respiratory, and genitourinary tracts. Mucous membranes secrete thick fluid, known as mucus, containing glycoproteins, proteoglycans, and other enzymes that provide protection to the epithelial cells and prevent infection. The epithelial surface secretes antimicrobial peptides, known as defensins, that fight against fungi, bacteria, and inhibit virus growth. If the epithelial surface of the skin breaks, it can lead to the development of sub-cutaneous infection. Staphylococci are the most common bacteria that penetrate the epidermis, hair follicles, and oil glands of the skin. Some causes of infections in skin are burns, cuts, abrasions, stab wounds, and others by which the skin gets broken. When skin is lost, serious infections may develop; for instance, in the case of serious burn injuries. Hence, the skin acts as a major barrier against pathogens.

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