Body Systems

Human Body Systems in Brief

The human body has several organ systems.  One thing to understand is that we divide the body into organ systems mostly to make it easier to study.  In reality all of the body’s parts work together.  However, if we tried to study the human body as a whole we would get lost pretty quickly because it is complicated, so we learn piece by piece.  Here is a list of the body’s organ systems including a few organs from each and the major functions of each system:

  • Integumentary system:
    • This is the skin and its associated structures (hair, nails, glands, receptors, etc.)
    • Major jobs include:  control body temperature (by deciding how much heat to let go of), protection from infection (mostly as a barrier defense) and from trauma, also helps produce vitamin D.
  • Skeletal system
    • Consists of bones (clavicle, humerus, femur, etc.), joints, and associated tissues (like ligaments and cartilage)
    • Major jobs include:  protection of vital organs (skull protects brain for example), blood cell production (in red bone marrow), mineral storage (mostly calcium and phosphorus), energy storage (yellow bone marrow is fat tissue), pH homeostasis (phosphate acts as a pH buffer)
  • Muscular system
    • Consists of skeletal muscles (pectoral muscles, biceps brachii, gluteus maximis, etc).  Also consists of three types of muscle tissue (skeletal, smooth, and cardiac muscle).
    • Major jobs include:  All body movements (includes outward movements like walking and dancing and also movements inside of the body such as pumping blood and moving food along the digestive tract), produce body heat, maintain posture (try to sit or stand up straight without contracting muscles….  actually don’t try it— you will fall over).
  • Nervous system
    • Includes structures like the brain, the spinal cord, and nerves.
    • Major jobs include “command and control” or regulation and coordination of the body (helps to keep many functions of the body stable)…  also thinking, memory, emotions, etc.
  • Sensory system
    • Includes special senses like sight, hearing, equilibrium, smell, and taste—  as well as general senses like touch, pressure, stretching, and pain.  Parts include ears, cochlea (hearing), eyes, retina (sight), lamelar corpuscles (pressure), etc.
    • Major job is to give the brain information about what is happening in the outside world as well as what is happening inside the body (Examples:  Your eyes are sending visual information to your brain now, and chemical receptors in your major arteries are detecting levels of oxygen and carbon dioxide to help decide how much you need to breathe).
  • Endocrine system
    • Includes all endocrine glands (glands that make hormones) such as the pituitary, pancreas, thyroid, etc.
    • Like the nervous system this system’s major job is “command and control” or regulation and coordination; the endocrine system  just acts more slowly, it is interested in maintaining equilibrium of such things as blood sugar, blood pressure, water and electrolyte balance, as well as being important for some major functions like growth and development, reproduction, and metabolism (rate of chemical reactions in the body, especially energy usage).
  • Cardiovascular system
    • Includes blood, the heart, and the blood vessels.
    • Major job is transportation.  The blood is pushed by the heart through all of the blood vessels.  In doing this all of the body’s tissues receive important nutrients and signals that are carried in the blood and waste products are transported away from the tissues.
  • Lymphatic system
    • Includes lymphatic vessels and lymphatic trunks as well as lymph nodes, the spleen, thymus, and red bone marrow (shared between lymphatic system and skeletal system).
    • Major jobs include taking away excess tissue fluid, filtering that fluid, and body defense (the lymphatic system houses the majority of the immune system’s cells).
  • Immune system/body defense
    • Includes defenses such as barrier defenses, chemical defenses, and defenses mediated by white blood cells (lymphocytes, macrophages, neutrophils, etc.) that defend the body from infection and rogue cells (cancers).
    • Major job of preventing and eliminating infection with foreign organisms as well as killing cells that are becoming cancer.  This is performed through non-specific and specific defenses.  Non-specific defenses target all or broad categories of potentially infections organisms.  Specific defenses (immunity proper) is mediated by certain white blood cells capable of recognizing organisms very specifically (Example:  Your body has B-lyphocytes that are capable of producing antibodies against not just viruses and not just influenza viruses but specifically against the influenza A virus).
  • Respiratory system
    • Includes organs such as the lungs, bronchi, trachea, larynx, etc.
    • Major job is gas exchange with outside air.  In performing that job the respiratory system also helps to maintain pH balance as well as oxygen and carbon dioxide levels.
  • Digestive system
    • Includes organs like the esophagus, stomach, small intestine, liver, pancreas, large intestine, etc.
    • Major jobs of ingestion, digestion, absorption of nutrients, and elimination of fecal waste (everybody poops).
  • Urinary system
    • Includes organs such as the kidneys, ureters, urinary bladder, urethra, etc.
    • Major jobs include elimination of nitrogenous wastes and many drugs, water and electrolyte balance, blood pressure control, pH balance, stimulate red blood cell production, activate vitamin D.
  • Reproductive system
    • Includes organs such as the vagina, clitoris, uterus, penis, testicles, vas deferens, etc.
    • Major job is to make more humans in order to increase or maintain human populations.  This is also the only body system that we can survive without as individuals (this system is really only required because all humans are mortal— the average human life span is less that 80 years of age).

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