LEVELS OF BODY STRUCTURAL ORGANISATION AND THE ELEVEN BODY SYSTEM

From the smallest to the largest, six levels of organization will helps us to understand anatomy and physiology: the chemical, cellular, tissue, organ, system, and organismal levels of organization.

 1)     Chemical level: This very basic level and includes atoms, the smallest units of matter that participate in chemical reactions, and molecules, two or more atoms joined together. Certain atoms, such as carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), calcium (Ca), and sulfur (S), are essential for maintaining life. Two familiar molecules found in the body are deoxyribonucleic acid (DNA), the genetic material passed from one generation to the next, and glucose, commonly known as blood sugar.

2)     Cellular level: Molecules combine to form cells, the basic structural and functional units of an organism that are composed of chemicals. Cells are the smallest living units in the human body. Among the many kinds of cells in your body are muscle cells, nerve cells, and epithelial cells.

3)     Tissue level: Tissues are groups of cells and the materials surrounding them that work together to perform a particular function. There are just four basic types of tissues in your body: epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Epithelial tissue covers body surfaces, lines hollow organs and cavities, and forms glands. Connective tissue connects, supports and protects body organs while distributing blood vessels to other tissues. Muscular tissue contracts to make body parts move and generates heat. Nervous tissue carries information from one part of the body to another through nerve impulses.

4)     Organ level: At the organ level different types of tissues are joined together. Organs are structures that are composed of two or more different types of tissues; they have specific functions and usually have recognizable shapes. Examples of organs are the stomach, skin, bones, heart, liver, lungs, and brain. For example, several tissues make up the stomach. The stomach’s outer covering is a layer of epithelial tissue and connective tissue that reduces friction when the stomach moves and rubs against other organs. Underneath are three layers of a type of muscular tissue called smooth muscle tissue, which contracts to churn and mix food and then push it into the next digestive organ, the small intestine. The innermost lining is an epithelial tissue layer that produces fluid and chemicals responsible for digestion in the stomach.

5)     System level: A system consists of related organs with a common function. An example of the system level, also called the organsystem level, is the digestive system, which breaks down and absorbs food. Its organs include the mouth, salivary glands, pharynx (throat), esophagus (food tube), stomach, small intestine, large intestine, liver, gallbladder, and pancreas. Sometimes an organ is part of more than one system. The pancreas, for example, is part of both the digestive system and the hormone-producing endocrine system.

6)     Organismal level: All the parts of the human body functioning together constitute the total organism.

The Eleven Systems of the Human Body

1)     INTEGUMENTARY SYSTEM

·       Components: Skin and associated structures, such as hair, fingernails and toenails, sweat glands, and oil glands.

·       Functions: Protects body; helps regulate body temperature; eliminates some wastes; helps

make vitamin D; detects sensations such as touch, pain, warmth, and cold.

2)     SKELETAL SYSTEM

·       Components: Bones and joints of the body and their associated cartilages.

·       Functions: Supports and protects body; provides surface area for muscle attachments; aids body movements; houses cells that produce blood cells; stores minerals and lipids (fats).

3)     MUSCULAR SYSTEM

·       Components: Specifically, skeletal muscle tissue—muscle usually attached to bones (other muscle tissues include smooth and cardiac).

·       Functions: Participates in body movements, such as walking; maintains posture; produces heat.

4)     NERVOUS SYSTEM

·       Components: Brain, spinal cord, nerves, and special sense organs, such as eyes and ears.

·       Functions: Generates action potentials (nerve impulses) to regulate body activities; detects changes in body’s internal and external environments, interprets changes, and responds by causing muscular contractions or glandular secretions.

5)     ENDOCRINE SYSTEM

·       Components: Hormone-producing glands (pineal gland, hypothalamus, pituitary gland, thymus, thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries, and testes) and hormone-producing cells in several other organs.

·       Functions: Regulates body activities by releasing hormones (chemical messengers transported in blood from endocrine gland or tissue to target organ).

6)     CARDIOVASCULAR SYSTEM

·       Components: Blood, heart, and blood vessels.

·       Functions: Heart pumps blood through blood vessels; blood carries oxygen and nutrients to cells and carbon dioxide and wastes away from cells and helps regulate acid–base balance, temperature, and water content of body fluids; blood components help defend against disease and repair damaged blood vessels.

7)     LYMPHATIC SYSTEM AND IMMUNITY

·       Components: Lymphatic fluid and vessels; spleen, thymus, lymph nodes, and tonsils; cells that carry out immune responses (B cells, T cells, and others).

·       Functions: Returns proteins and fluid to blood; carries lipids from gastrointestinal tract to blood; contains sites of maturation and proliferation of B cells and T cells that protect against disease-causing microbes.

8)     RESPIRATORY SYSTEM

·       Components: Lungs and air passageways such as the pharynx (throat), larynx (voice box), trachea (windpipe), and bronchial tubes leading into and out of lungs.

·       Functions: Transfers oxygen from inhaled air to blood and carbon dioxide from blood to exhaled air; helps regulate acid–base balance of body fluids; air flowing out of lungs through vocal cords produces sounds.

9)     DIGESTIVE SYSTEM

·       Components: Organs of gastrointestinal tract, a long tube that includes the mouth, pharynx (throat), esophagus (food tube), stomach, small and large intestines, and anus; also includes accessory organs that assist in digestive processes, such as salivary glands, liver, gallbladder, and pancreas.

·       Functions: Achieves physical and chemical breakdown of food; absorbs nutrients; eliminates solid wastes.

10) URINARY SYSTEM

·       Components: Kidneys, ureters, urinary bladder, and urethra.

o   Functions: Produces, stores, and eliminates urine; eliminates wastes and regulates volume and chemical composition of blood; helps maintain the acid–base balance of body fluids; maintains body’s mineral balance; helps regulate production of red blood cells.

11) REPRODUCTIVE SYSTEMS

·       Components: Gonads (testes in males and ovaries in females) and associated organs (uterine tubes, uterus, vagina, and mammary glands in females and epididymides, ductus deferens, seminal vesicles, prostate, and penis in males).

o   Functions: Gonads produce gametes (sperm or oocytes) that unite to form a new organism; gonads also release hormones that regulate reproduction and other body processes; associated organs transport and store gametes; mammary glands produce milk.