A species is resistant to certain diseases to which other species are susceptible.



Species resistance Mechanical barriers Chemical barriers


Inflammation Phagocytosis

A species is resistant to certain diseases to which other species are susceptible.

Unbroken skin and mucous membranes prevent the entrance of some infectious agents.

Enzymes in various body fluids kill pathogens. pH extremes and high salt concentration also harm pathogens. Interferons induce production of other proteins that block reproduction of viruses, stimulate phagocytosis, and enhance the activity of cells such that they resist infection and the growth of tumors. Defensins damage bacterial cell walls and membranes. Collectins grab onto microbes.

Elevated body temperature inhibits microbial growth and increases phagocytic activity.

A tissue response to injury that helps prevent the spread of infectious agents into nearby tissues.

Neutrophils, monocytes, and macrophages engulf and destroy foreign particles and cells.


(2) Some undifferentiated lymphocytes are processed in the thymus gland to become T cells.

(1) Stem cells in red bone marrow give rise to undifferentiated lymphocytes

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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