Human Body Essentials: Tissues, Immunity, Digestion & Nutrition

Body Tissues and Their Specialized Roles

Cells within the human body are specialized to carry out specific processes. In a simplified view, based on their function, we can distinguish the following essential tissues:

• Integumentary Tissue: Covers the outside of the body, providing protection.
• Mucosa: Protects internal cavities, such as those in the digestive and respiratory tracts.
• Adipose (Fat) Tissue: Its cells accumulate fat, serving as a vital food reserve and insulation.

Understanding Nutrition: Fueling the Body

Nutrition encompasses the processes that allow us to use and transform the substances we need to stay alive and maintain bodily functions.

Infectious Disease Transmission: How Pathogens Spread

Infectious diseases are contagious because their causative organisms are transmitted (spread) from an ill person to a healthy person through various means. These modes of transmission include:

• Direct contact (e.g., touching, kissing)
• Indirect contact via inanimate objects (fomites)
• Contaminated water
• Ingestion of food contaminated with pathogenic microorganisms
• Airborne transmission (e.g., droplets, aerosols)
• Animal vectors (e.g., insects, rodents)

The Body's Internal Defenses: Immune System at Work

After crossing passive barriers, microbes invade the body's tissues. To stop their advance and eliminate them, the body possesses very effective internal immune defenses. These defenses are based on the performance of leukocytes (white blood cells), which are found in blood and many tissues and come in several kinds. Internal defenses are of two main types: nonspecific and specific defense mechanisms. Both are interrelated and complement one another to achieve greater efficiency.

Nonspecific Defenses: First Line of Attack

Nonspecific defenses act against any type of microorganism or foreign particle. This action is primarily carried out by phagocytes, a type of leukocyte capable of trapping and eliminating pathogenic microorganisms in a process called phagocytosis.

Specific Defenses: Targeted Immunity

Specific defenses act selectively against particular microorganisms or foreign molecules, distinguishing them from the body's own cells. Certain leukocytes produce proteins called antibodies, which are specific for each type of microorganism, designed to destroy or inactivate invading pathogens.

The Human Digestive System: From Mouth to Anus

The digestive tract is approximately 8 feet long and has a variable shape along its route, widening in some stretches and narrowing in others. It begins in the mouth and ends at the anus, comprising the following main parts:

• Pharynx
• Esophagus
• Small Intestine
• Large Intestine

Accessory Digestive Glands: Aiding Digestion

Accessory glands are organs that discharge their secretions into the digestive tube. These include:

• Salivary glands: Located in the mouth, initiating chemical digestion.
• Gastric glands: Found in the stomach lining.
• Intestinal glands: Located in the intestinal walls.

The liver and pancreas are two larger glands that also secrete vital digestive fluids into the digestive tube.