Body Systems

Anatomy & Physiology: Introduction

Directional Terminology


Torso - trunk of the body

Midline - imaginary line running vertically from the nose through the umbilicus (belly button)

Medial - toward the midline

Lateral - away from the midline

Proximal - closer to the trunk

Distal - away from the trunk

Superior - above

Inferior - below

Mid-axillary line - imaginary line running vertically from the middle of the armpit to the ankle.

Anterior - toward the front

Posterior - toward the rear

Mid-clavicular line - imaginary line drawn vertically from the middle of the clavicle to the pelvis

Bilateral - pertaining to both sides

Dorsal - toward the back

Ventral - toward the front

Palmar - relating to the palm

Plantar - relating to the sole of the foot

Prone - lying face down

Supine - lying face up

Fowler position - sitting up

Trendelenburg position - feet up, head down position

Musculoskeletal System

The framework for the body, the musculoskeletal system protects vital internal organs and provides for body movement.

The skeletal system is composed of 206 bones. It is divided up into eight components:

1. joints

2. skull

3. facial bones

4. spinal column

5. thorax

6. pelvis

7. upper extremities

8. lower extremities


Joints are the points at which bones connect. Cartilage is located between the bones where they come together to lubricate and cushion the joints. Ligaments hold the bones together. The two types of joints are the ball and socket joints, which move freely in all directions (e.g., hip and shoulder), and the hinged joints (e.g., elbow and knee).

The skull houses and protects the brain. It is divided into four major areas:

1. frontal - anterior

2. occipital - posterior

3. temporal - sides

4. parietal - top

The face is made up of five major bones. The nasal bone forms the nose. Two maxilla form the upper jay. Two zygomatic bones make up the cheek. The mandible (lower jaw) is the only movable facial bone. The orbit (eye socket) is mad up of the edges of the frontal, nasal, zygomatic, and maxilla bones.

The spinal column is composed of 33 individual bones called vertebrae. The first seven vertebrae from the head are called the cervical vertebrae. The next 12 are called thoracic vertebrae. This is followed by five lumbar vertebrae. The end of the spinal column is comprised of five fused sacral and four fused coccyx vertebrae. The spinal column is flexible and holds up the torso and the head. The vertebrae are separated by cartilage discs that cushion the vertebrae and allow the vertebrae to move freely.

The thorax consists of the ribs, sternum, and 12 thoracic vertebrae. The ribs are attached posteriorly to the thoracic vertebrae. Of the 12 pairs of ribs, only 10 pair attach anteriorly to the sternum. The sternum (breastbone) is divided into three sections: the manubrium (superior portion); body (middle portion); and xiphoid process (inferior portion).

The scapula (shoulder blade) lies on either side of the superior back. The acromion can be felt at the lateral edge of the shoulder. The clavicle(collar bone) runs from the superior sternum to the acromion and attaches the upper extremity to the torso. The upper arm bone is called the humerus and the bones of the forearm are called the radius and ulna. The radius is the lateral bone and the ulna is the medial bone in the forearm. The joint where the arm and forearm meet is called the olecranon (elbow). Carpals are the wrist bones. Metacarpals are the hand bones, and phalanges are the finger bones.

The pelvis rests at the inferior section of the torso. The iliac crest makes up the wings of the pelvis. The ischium is the lower, posterior portion and the pubis is the lower, anterior bone that attaches in front of the pubic symphysis.

The lower extremity is composed of the hip, femur, patella, tibia, fibula, ankle, and foot. The hip joint is composed of the head of the femur (ball) and the acetabulum (socket). The thigh bone is called the femur. Bones of the lower leg are called the tibia (shin bone) and the fibula (lateral, smaller bone). The knee joint is shielded by the patella (kneecap) and is where the femur and the tibia come together. The tarsals and metatarsals are the bones of the foot and phalanges are the bones of the toes.

Muscular System

The muscular system works with the skeletal system to protect the body, give it structure, and provide for movement. Muscles are divided into three types: voluntary, involuntary, and cardiac.

   Voluntary (skeletal) muscles are attached to the bones and form the major muscle mass of the body.  They also make up the tongue, eyes, soft palate, pharynx, esophagus, and scalp. They are called voluntary because they are contracted and relaxed at will. Skeletal muscles are attached to bones by tendons which stretch across joints, creating a pull between the two bones when the muscle contracts.

Involuntary (smooth) muscles make up the structure of organs. They control the flow through these organs and carry out the automatic muscular functions of the body. They are not under voluntary control and respond to nerve impulses from the nervous system instead.

Cardiac muscle is specialized muscle found only in the heart. It functions similar to involuntary muscles, however, it can generate its own contractions, a property know as automaticity. Cardiac muscle cannot tolerate an interruption in blood flow for more than a few minutes before death of the muscle occurs. 

Respiratory System

The critical functions of supplying the body with oxygen and getting rid of carbon dioxide, a waste product generated by metabolism, is the role of the respiratory system. The respiratory system is divided into the the upper and lower airways. Air enters the upper airway through the nose and mouth and then passes into the pharynx. The nasopharynx is the airway directly behind the nose and the oropharynx is the airway directly behind the mouth. Air then passes through the larynx (voicebox) and then enters the lower airway through the trachea. The trachea is 4-5 inches long. At the top of the larynx is the epiglottis, a leaf-shaped structure that prevents food and liquids from entering the trachea during swallowing. The vocal cords, which produce sound, are located within the larynx. Because the air passages must be kept open at all times, the trachea and larynx are composed of cartilaginous rings connected by ligaments. 

The trachea divides at the carina into two smaller tubes called the bronchi, with one bronchus going to each lung. Air moving through the bronchi passes through smaller tubes called bronchioles and finally into the alveoli. The alveoli are tiny, sac-like clusters contained within the lungs. They are surrounded by capillaries which bring oxygen-poor blood to the alveoli. Carbon dioxide is removed and the blood is re-saturated with oxygen. The bronchi, bronchioles, and alveoli make up the lungs. The lungs are bounded superiorly by the clavicles and inferiorly by a dome-shaped muscle called the diaphragm. The exterior of the lungs are wrapped in a thin membrane called the visceral pleura which is in contact with the parietal pleura, a membrane lining the inside of the chest wall. Fluid between the pleura prevent friction during breathing.

During inhalation, the intercostal muscles, found between the ribs, contract, pulling the chest upward and outward. The diaphragm also contracts, increasing the chest space. This causes the external air pressure to be greater than that within the chest cavity so, air rushes into the lungs (inhalation). As the muscles relax, this creates a decrease in chest space and the exhalation of air from the lungs. Respiration is controlled by the central nervous system, which monitors the oxygen and carbon dioxide levels in the blood using sensors located in the aorta, carotid arteries, and brain. The sensors use the carbon dioxide levels to determine when to breathe.

Assessment of a patient's breathing requires a determination of respiratory rate, rhythm, quality, and depth (tidal volume). Normal respiratory rates are 12-24 breaths per minute for adults, 15-30 breaths per minute for children, and 25-50 breaths per minute for infants. Respiratory rhythm refers to whether breathing is regular or irregular. Tidal volume is approximately 500-700 ml in the average adult.  Inadequate breathing is suspected when breath sounds are diminished or absent, chest expansion is unequal or inadequate (shallow breathing), or there is increased effort to breathe. In infants and children, the airways are smaller and are therefore easily obstructed. They depend more heavily on the diaphragm for breathing because their chest walls are softer. 

Cardiovascular System

The cardiovascular system transports oxygen and nutrients to the tissues and removes waste products to be excreted from the body. The three major components of this system are the heart, blood, and blood vessels. 

The heart serves as the pump and is made up of three layers: the epicardium (outer layer), myocardium (middle layer), and the endocardium (inner layer). The myocardium is the actual muscle which contracts. The pericardium is a thin sac that surrounds and protects the heart. Coronary arteries supply the heart with oxygenated blood. The heart is divided into four chambers: left and right atria and left and right ventricles. The right atrium receives oxygen-poor blood and pumps it into the right ventricle which pumps it out to the lungs through the pulmonary arteries. Oxygen-rich blood returns from the lungs through pulmonary veins and enters the left atrium.  Blood the then pumped into the left ventricle which pumps it out to the body through the aorta. Valves prevent backflow into the chambers and to keep the blood flowing in the right direction. The heart is composed of specialized muscle tissue that generates its own electrical impulses which causes the muscle fibers to contract. It is the contraction of the heart that pumps blood throughout the body.

Three major types of vessels carry blood: arteries, veins, and capillaries. Arteries always carry blood away from the heart. Except for the pulmonary arteries, arteries always carry oxygen-rich blood. The largest artery is the aorta which descends down from the heart into the abdominal cavity where it divides into the iliac arteries at the level of the navel. The carotid arteries carry blood from the heart to the head. They can be palpated on either side of the trachea. The lower extremities receive blood through the femoral arteries. They can be palpated in the groin at the crease between the abdomen and the thigh. The major artery of the upper arm is the brachial artery. It can be felt on the medial aspect of the arm between the elbow and the shoulder. The brachial artery is the primary site for measuring blood pressure. In the lower arm, the radial artery is the major vessel. It is the most common site to check a patient's pulse. It can be felt on the thumbside of the anterior aspect of the wrist. In the foot, pulse can be palpated at the posterior tibial, located on the posterior surface of the medial malleolus (ankle), or the dorsalis pedis, located at the anterior surface of the foot.

Arteries subdivide into arterioles and then into capillaries. Capillaries are small blood vessels where oxygen, nutrients, and waste products are exchanged at the cellular level. Veins always carry blood back to the heart. Except for the pulmonary veins, veins always carry oxygen-poor blood. Veins are under much lower pressure than arteries due to the distance the blood has traveled away from the heart. Valves are found in veins to prevent backflow of blood.  The vena cavae are the major veins of the body which deliver blood back to the right atrium. The superior vena cavareturns blood from the head and upper body and the inferior vena cava returns blood from the lower body. 

Blood is composed of plasma and three types of cells: red blood cells, white blood cells, and platelets. Plasma is the liquid in which the blood cells and nutrients are suspended. Red blood cells carry oxygen and carbon dioxide to and from body tissue. Hemoglobin is a protein found in red blood cells which binds with oxygen and carries it to the tissues. White blood cells exist to fight infection and establish immunity against certain diseases. Platelets are specialized cells to form clots which occurs whenever they come into contact with a surface other than the normal lining of the blood vessels.

Adults contain about 5-6 L of blood and children have approximately 80 ml of blood for each kilogram body weight. Blood pressure has two components: systolic and diastolic. The systolic (upper number) pressure is created when the left ventricle contracts and the diastolic (lower number) pressure is the pressure exerted against the walls when the left ventricle is at rest.

Perfusion is the circulation of blood through an organ or structure. When something occurs that prevents circulation, shock (hypoperfusion) can occur. Shock is a serious complication (see Trauma, Bleeding, and Shock lesson).

Nervous System


The nervous system is the control center of the body. It is divided into two division:

1. Central Nervous System (CNS) - composed of the brain and spinal cord.

2. Peripheral Nervous System (PNS) - comprised of nerves that carry messages to and from the CNS. There are two types of nerves in the PNS:

   a) sensory - carry messages from the body to the CNS.

   b) motor - carry messages from the CNS to the body.

The nervous system carries out voluntary and involuntary functions. Involuntary functions are carried out by the autonomic nervous system (ANS). The ANS is divided into two divisions:

   a) sympathetic - has more of a excitatory effect on the body.

   b) parasympathetic - has more of an inhibitory effect on the body.

Integumentory System

The skin is the largest organ of the body. It helps protect the body from infection, injury, and helps regulate body temperature and prevent water loss. The skin is composed of three layers:

1. Epidermis - outer layer that consists mostly of dead cells that provide a waterproof barrier.

2. Dermis - contains the sweat glands, sebaceous glands, hair follicles, blood vessels, and nerve endings. 

3. Hypodermis - composed mostly of adipose (fat) and connective tissue that connects the skin to the organs and provides protection and cushioning for the organs of the body.

Endocrine System

The endocrine system secretes hormones from the glands directly into the bloodstream which regulate bodily activities and functions. Two major hormones are epinephrine and insulin. Epinephrine enhances the activity of the sympathetic nervous system and is produced in times of stress. Insulin is produced by the pancreas and metabolizes glucose, which is necessary for the production of energy.

Abdominal Cavity

The abdominal cavity lies immediately inferior to the thoracic cavity and contains the major organs of digestion and excretion. It is divided into four quadrants by imaginary lines that intersect at the umbilicus. The left upper quadrant (LUQ) contains the stomach, spleen, and parts of the colon. The right upper quadrant (RUQ) contains the liver, gall bladder, and part of the colon. Both the right (RLQ) and left (LLQ) lower quadrants contain parts of the colon. The RLQ also contains the appendix. The abdominal cavity is lined by a thin membrane called the peritoneum. The kidneys lie behind the abdominal cavity in what is referred to as the retroperitoneal space which is located behind the peritoneum superior to the umbilicus from about the L3 to T11.

Review Questions:

1. Describe where the shoulder is located relative to the elbow.

2. What position is a patient in if found lying face down?

3. What are the bones of the lower arm?

4. What muscles are attached to the skeleton and control movement?

5. What is the major stimulus to breathe in a normal person?

6. Blood is pumped from the right ventricle to where?

7. The nervous system is divided into what divisions?

8. List four places a peripheral pulse may be felt.

9. Describe the physical processes of inhalation and exhalation.

10. Describe the location of the heart relative to the breastbone using correct terminology.