Introduction to Body Systems

Before you dig too deeply into the specifics of paramedicine, it helps to understand the big picture.  In this case, the big picture is the various organ systems which make up the human organism.  Understanding what each system does and which organs are part of each system will help you later when you try to understand how specific therapies affect the body as a whole.

So, let's begin.

Objectives:

• To list the 11 major systems of the human body.
• To explore the primary functions of each of the systems of the human body.
• To list the primary organs that make up each of the human body systems.
• To understand homeostasis.

Homeostasis

In order to properly understand anatomy and physiology, you have to understand what the purpose of all those organs, tissues, and blood vessels are.  Put simply, the primary purpose of the human body is to maintain homeostasis.  Homeostasis is a word with Greek roots which in its simplest form means "Standing Still."  Medically speaking, homeostasis is the management of variables such as temperature, pH, oxygen levels, and blood flow to maintain a stable internal environment.  

Why is homeostasis so important?  Your body is a factory which chemically combines oxygen and sugar molecules in a process called cellular metabolism to create energy.  The body also uses many other chemical reactions to synthesize other molecules required for energy production and continued life.  If the body's internal environment does not remain constant, these chemical reactions necessary for life cannot occur, and the body starts to shut down. 

The primary purpose of the various body systems is to maintain homeostasis.  We will get into how they do this at a later date.  This is important for you because your primary job, whether you are an EMT or a Paramedic, is to maintain homeostasis.  Even if you've never thought of it before, this is the reason for many of the interventions we perform, be they drugs, fluids, bleeding control, artificial ventilation, etc.

Body Systems

The Sages (those that study these things) generally agree that there are 11 body systems, as long as you group the female and male reproductive systems into one category.  If you want to split hairs and call the male and female reproductive systems independent entities, then there are of course 12.  I will list each, and briefly discuss the primary purpose behind each system and the primary organs.  This is not intended to be a definitive guide, but merely a review.  I will explore each system in detail in future post.

1.  The Integumentary System:

This is an easy one.  The integumentary system is the skin that covers the outer surface of the body, a surface area that ranges between 1.5 and 2 square meters, and accounts for 7-8% of body weight.

The primary organs of the integumentary system are the skin and the various glands and other derivatives that arise from the skin such as the nails, hair, sweat glands, and sebaceous glands.  

Primary functions of the integumentary system include:

• Acting as a physical barrier that protects the body from physical injury, trauma, bumps, and scraps, and provides protection from chemicals, toxins, microbes, and heat/cold.
• Prevents loss of water from inside the body.
• Regulates temperature using an extensive bed of capillaries and blood vessels.
• Produces Vitamin D.
• The integument also assists with immune response by housing epidermal dendritic cells.
• Houses sensory cells which sense touch, heat, cold, and other stimuli.
• Excretion of substances in sweat.

2.  The Skeletal System:

The skeletal system provides support and protection to the body.  It is the framework which allows the body to stand, provides muscle attachment points which allow motion, and is the site of red blood cell production.

Primary organs of the skeletal system include:

• The 206 bones that make up the typical adult human body.
• Cartilage, which operates as a connective tissue.
• Ligaments, which hold bones together.

The primary purposes of the skeletal system are to:

• Support soft tissues.
• Provide a smooth articulation surface in joints.
• To protect sensitive/delicate soft tissues such as the heart, lungs, brain, and spinal cord.
• To provide attachment points for muscles.  This allows purposeful movement.
• Production of red blood cells, a process called hemopoiesis.  Hemopoiesis occurs in the shafts of long bones.
• Storage of essential minerals and energy molecules.

3.  The Muscular System:

The muscular system is composed of over 700 skeletal muscles which allow purposeful movement.  Additional muscles in the body allow for movement of food and waste through the digestive tract, and also pump blood throughout the body (it should be noted, however, that these muscles are typically grouped in under the system they work in).  

Primary organs of the muscular system include:

• Over 700 named skeletal muscles.
• Tendons which connect muscles to bones.

Primary functions of the muscular system include:

• Purposeful body movement.
• Maintenance of body posture by locking bones in position and holding them in that position.
• Regulating body temperature.  Head is produced by muscular movement, and this heat is used to maintain a steady temperature.  When body temperature dips low, muscles shiver which creates additional heat.
• Assisting with storage and movement of nutrients and waste through the digestive tract by operating sphincters.
• Support of cavity walls.

4.  The Nervous System:

The nervous system allows you to sense and respond to your environment.  In addition to the external environment, the nervous system allows information to be relayed to the brain about what is happening within the body in the internal environment, and relays instructions back to the body's tissues from the brain.

Primary organs of the nervous system include:

• The brain.
• The spinal cord.
• The nerves which conduct signals from the spinal cord to the target organs and back.
• Organs of sense (such as the eyes, ears, and other sensory apparatus).

Primary functions of the nervous system include:

• Collecting information about the external or internal environment, and transmitting that information to the brain.
• Processing and evaluating information collected about the external or the internal environments, which is done in the brain.
• Responding to information with appropriate responses, and signaling the tissues responsible to carry out the response.

5.  The Endocrine System:

The various organs and organ systems of the body communicate in various diverse ways.  One of these is through chemical signalers called hormones.  Hormones are produced by the glands and cell clusters which make up the endocrine system.

The major function of the endocrine system is to secrete the various hormones needed to regulate the body's internal environment.  The hormones produced are diverse, and are involved in many functions.  A few specific functions the endocrine system is involved in include:

• The movement of glucose from the blood stream into cells, where it is needed for cellular respiration, is mediated by a hormone called insulin, which is secreted by the pancreas.
• Breast feeding stimulates the release of a hormone called oxytocin, which stimulates the release of milk in the mammary glands.
• The hormones epinephrine and norepinephrine, released by the adrenal glands, play significant roles in the sympathetic nervous system and help produce the "fight or flight" reaction.

Major organs of the endocrine system include:

• The hypothalamus.
• The pituitary gland.
• The adrenal glands.
• The kidneys.
• The pineal gland.
• The thyroid and the thymus.
• The pancreas.
• the testes in males and the ovaries in females.
• The heart and the digestive tract, which are typically assigned to other organ systems, also secrete important hormones.

6.  The Cardiovascular System:

This is perhaps the best known body system to to the average individual on the street, and is highly significant to the practice of paramedicine.  The cardiovascular system contributes heavily to the maintenance of homeostasis, and is involved in every other body system in some way, shape, or form.

Major functions of the cardiovascular system include:

• Movement of deoxygenated blood to the lungs for gas exchange (CO2 out, oxygen in).
• Movement of oxygenated blood throughout the body to the tissues and cells which require oxygen for cellular respiration.
• Transport of glucose, immune system materials, and chemical messengers within the body.

Major organs of the cardiovascular system include:

• The heart, which is the pump of the system.
• Blood, which is the fluid compound made up of many smaller cellular components (more on blood later).
• Arteries, which carry oxygenated blood away from the heart.
• Veins, which carry deoxygenated blood back to the heart.

7.  The Lymphatic System:

In contrast to the cardiovascular system, the average individual knows very little about the lymphatic system, beyond some surface information about lymph nodes.  The lymphatic system is a second network which moves fluid throughout the body, and is a very important component of the immune system.

Major functions of the lymphatic system include:

• Movement of interstitial fluid (which is fluid pushed out of the blood vessels by internal blood pressure) back to the heart.
• Transport of large fat molecules.
• Generation of immune response to threats from the external environment.

Major organs of the lymphatic system include:

• Lymph vessels, which transport interstitial fluid (called lymph).
• Lymph nodes, which are found in the neck, armpits, and groin.
• The spleen.
• Mucosa Associated Lymphatic Tissue (MALT), which is found in the small intestine.
• Various ducts, which are large passages lymph vessels drain into.
• The thymus.

8.  The Respiratory System:  

The respiratory system is another system of great importance to the paramedic.  Respiratory emergencies make up a large percentage of EMS calls.  The respiratory system works closely with the cardiovascular system to introduce adequate amounts of oxygen for cellular respiration to proceed, and to remove waste carbon dioxide.

Major functions of the respiratory system include:

• Gas exchange.  Oxygen is introduced to the body through inhalation, carbon dioxide is removed from the body through expiration.
• Production of sounds and (in humans) comprehensible speech.
• Assists with the detection of odors.
• The respiratory system also filters pathogens out of inhaled air, assisting the immune system in keeping the body healthy.

Major organs of the respiratory system include:

• The upper and lower respiratory tracts.
• The lungs.
• The diaphragm.

9.  The Digestive System:

Everyone loves to eat, and the digestive system makes it possible.  The glucose required to maintain homeostasis through cellular respiration enters the body as food, which is taken in through the digestive tract.  Understanding the various afflictions that can affect the digestive tract is very important to the paramedic, especially since they are frequently very painful and can be very serious.

Major functions of the digestive system include:

• Intake and storing of food.
• Breaking the food down into molecules which can be absorbed from the digestive tract into the blood stream.
• Excretion of waste.

Major organs of the digestive system include:

• The oral cavity.
• The esophagus.
• The stomach.
• The liver.
• The large intestine.
• The small intestine.

10.  The Urinary System:

How does your body spell relief?  K-I-D-N-E-Y.  The process of cellular respiration breaks down glucose and uses it to produce energy molecules called ATP.  The synthesis of ATP produces waste, most notably CO2, which is transported to the lungs and removed via exhalation.  ATP synthesis also leaves a lot of waste nitrogen, which cannot be removed by the lungs.  The urinary system removes waste from the blood stream in the kidneys, turns it into urine, and removes it from the body.

Primary functions of the urinary system include:

• Filtration of the blood to remove waste and excess electrolytes.
• Excretion of waste from the body through urination.

Major organs of the urinary system include:

• The kidneys.
• The ureters.
• The bladder.
• The Urethra.

11.  The Reproductive Systems:

If you want to be technical, you can separate the male and female reproductive systems into two systems.  They are similar, in many ways, but have significant differences (duh).  The reproductive system's primary function is reproduction of offspring.  Understanding the reproductive systems is important to the paramedic as their structures can be delicate, they tend to be highly vascular so trauma to the reproductive system can produce significant bleeding and pain, and reproductive system complications, including childbirth and pregnancy issues, can be incredibly serious.

Major functions of the reproductive systems include:

• Production of gametes, or sex cells (sperm in the male reproductive system, ova or eggs in the female reproductive system).
• Providing a perfect environment for fertilization and subsequent implantation.
• Protecting and supporting developing offspring.

Major organs of the male reproductive system include:

• The testis and scrotum.
• The penis.
• The prostate gland
• The seminal vesicles, the epididymis, and the urethra.

Major organs of the female reproductive system include:

• The mammary glands.
• The ovaries.
• The Fallopian tubes.
• The uterus.
• The vagina.

In the coming weeks, we will look at the various body systems and organs in more depth.  If you have questions, feel free to email them to me or leave them in the comments.