Anatomy & Physiology
Anatomy and physiology are foundational to understanding medical emergencies and patient care, as they provide essential knowledge about the structure and function of the human body.
Connections exist between anatomy and physiology and various medical topics, including medical terminology, pathophysiology, airway and respiratory management, cardiac and diabetic emergencies, trauma (soft-tissue, musculoskeletal, chest, abdominal, head, neck, and spine), bleeding and shock, and obstetric/gynecologic emergencies.
Reference materials such as medical terms and anatomical illustrations support comprehension of these concepts and facilitate learning across related medical and emergency care subjects.
Standard
Understanding of human anatomy and physiology is essential for EMS practice, as it provides the foundational knowledge needed to assess and manage patient conditions.
Knowledge of the structure (anatomy) and function (physiology) of all human body systems enables you to recognize normal versus abnormal findings during patient assessment.
Application of this knowledge allows for effective decision-making in emergency situations, ensuring appropriate interventions and care for patients.
Core Concept
Major body systems are located in specific regions of the body, and their positions can be identified using topographic landmarks, which help relate external features to underlying internal structures.
Diagrams of organs are used to identify the structures and spatial relationships of body systems, aiding in understanding how injuries to certain areas may affect specific internal organs.
Each organ system has a distinct role in maintaining normal body functions, and the contribution of each system is essential for overall health and homeostasis.
Observable signs and symptoms can indicate dysfunctions in internal organs, allowing you to relate clinical presentations to potential underlying issues within specific organ systems.
Key Terms
Anatomy is the study of body structure, helping you locate organs and organ systems and understand how external injuries may affect internal systems.
Physiology is the study of body function, providing a baseline for how the body should work normally and enabling you to recognize abnormal function and predict the effects of injuries or illnesses.
Knowledge of anatomy and physiology is essential for assessment and treatment, as it allows you to determine which organs and systems may be affected in a patient and how these impacts alter normal body function.
Understanding these sciences guides decision-making in emergency medical situations, helping you assess and manage ill or injured patients effectively.
Locating Body Organs and Structures
Visualizing internal organs involves picturing where organs and structures are located inside the body based on the external appearance.
Topography refers to using external landmarks—such as notches, joints, and bony bumps—to help identify the positions of internal organs and structures.
Some external landmarks are easily recognized (like the navel and nipples), while others have both common and medical names (e.g., "Adam’s apple" is the thyroid cartilage), and some may be unfamiliar (e.g., the xiphoid process at the lower end of the sternum).
Understanding the relationship between internal organs and external landmarks is essential for accurately locating and identifying body structures.
Body Systems
Musculoskeletal system: Composed of bones, joints, and muscles; the skeleton supports and protects the body, forms blood cells, stores minerals, and muscles enable movement.
Respiratory system: Includes the nasal cavity, pharynx, larynx, trachea, bronchial tubes, and lungs; responsible for obtaining oxygen and removing carbon dioxide from the body.
Cardiovascular system: Consists of the heart, arteries, and veins; pumps blood throughout the body to transport nutrients, oxygen, and wastes.
Blood: Made up of plasma, red blood cells, white blood cells, and platelets; transports oxygen, protects against pathogens, and promotes clotting to control bleeding.
Lymphatic system: Contains tonsils, thymus gland, spleen, lymph nodes, and lymphatic vessels; maintains fluid balance and contributes to immune defense.
Nervous system: Composed of the brain, spinal cord, and nerves; receives sensory information and coordinates the body’s responses.
Digestive system: Includes the oral cavity, pharynx, esophagus, stomach, small and large intestines, liver, gallbladder, and pancreas; ingests, digests, and absorbs nutrients.
Integumentary system: Consists of skin, hair, nails, and sweat glands; forms a protective barrier and helps regulate body temperature.
Endocrine system: Made up of glands such as the pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, testes, and ovaries; regulates metabolic and hormonal activities.
Renal (urinary) system: Includes kidneys, ureters, urinary bladder, and urethra; filters waste from the blood and removes it from the body.
Male reproductive system: Composed of testes, epididymis, vas deferens, penis, seminal vesicles, and prostate gland; produces sperm and enables reproduction.
Female reproductive system: Includes ovaries, fallopian tubes, uterus, vagina, vulva, and breasts; produces eggs, supports reproduction, and provides an environment and nutrients for a developing baby.
Musculoskeletal System
The musculoskeletal system includes the skeleton, muscles, ligaments, and tendons, and extends throughout the entire body.
The skeleton is organized into major regions: the skull and spine, ribs and sternum, shoulders and upper extremities, and pelvis and lower extremities.
Ligaments connect bone to bone, while tendons connect muscle to bone, enabling movement and stability.
Key bones and regions include:
Skull (with maxilla and mandible)
Spine (cervical, thoracic, lumbar vertebrae, sacrum, coccyx)
Thoracic cage (ribs and sternum)
Shoulders (clavicles, scapula)
Upper limbs (humerus, ulna, radius, carpals, metacarpals, phalanges)
Pelvis (ilium, pubis, ischium, acetabulum)
Lower limbs (femur, patella, tibia, fibula, tarsals, metatarsals, phalanges)
The musculoskeletal system serves three main functions: giving the body shape, protecting vital organs, and allowing movement.
Bone marrow produces blood cells and stores nutrients, adding to the system’s importance.
The skull protects the brain and is divided into the cranium (top, back, sides) and the face (front).
Major skull bones include: frontal, parietal, occipital, temporal, zygomatic, maxilla, mandible, lacrimal, and nasal bones.
Sutures are fibrous joints where skull bones fuse together.
Point of View: Patient
The anterior cranium connects to facial bones such as the mandible (lower jaw), maxillae (upper jaw), and nasal bones, forming facial structures including the orbits (eye sockets) and zygomatic arches (cheeks).
The spinal column consists of 33 vertebrae stacked to protect the spinal cord, which is essential for movement, sensation, and vital functions. The five divisions are:
Cervical (neck) – 7 vertebrae
Thoracic (thorax, ribs, upper back) – 12 vertebrae
Lumbar (lower back) – 5 vertebrae
Sacral (back wall of pelvis) – 5 fused vertebrae
Coccyx (tailbone) – 4 fused vertebrae
Cervical spine injuries are especially dangerous because they can affect breathing muscles, potentially leading to fatal outcomes. The lumbar region is also prone to injury due to lack of skeletal support, while the thoracic, sacral, and coccyx regions are more protected.
The thorax (chest) protects vital organs (heart, lungs, major blood vessels) with 12 pairs of ribs attached to the thoracic vertebrae. Ten pairs connect to the sternum (breastbone), while two are “floating ribs.” The sternum has three parts: manubrium (top), body (middle), and xiphoid process (bottom).
The pelvis is formed by fused bones: the ilium (superior, with iliac crest), ischium (inferior, posterior), and pubis (anterior). The pelvis connects to the sacral spine and forms the hip joint with the femur at the acetabulum (hip socket).
Lower extremities include:
Femur (thigh bone) – largest long bone, common site of “hip” fractures
Patella (kneecap) – anterior to knee joint
Tibia (medial, larger lower leg bone) and fibula (lateral, smaller)
Ankle (tarsals), foot (metatarsals), heel (calcaneus), and toes (phalanges)
Malleoli are the bony protrusions on each side of the ankle (medial from tibia, lateral from fibula)
Upper extremities include:
Shoulder: clavicle (anterior), scapula (posterior), and proximal humerus
Acromion process (top of scapula) forms the acromioclavicular joint with the clavicle
Humerus (upper arm), radius (lateral forearm, thumb side), and ulna (medial forearm)
Wrist (carpals), hand (metacarpals), and fingers (phalanges)
Anatomical terms such as superior, inferior, medial, lateral, anterior, and posterior are essential for accurately describing locations and injuries.
Joints connect bones and come in types such as ball-and-socket (hip) and hinge (elbow), allowing for different types of movement.
Three types of muscles:
Voluntary (skeletal) muscle: under conscious control, attached to bones, responsible for movement
Involuntary (smooth) muscle: found in organs and vessels, not under conscious control, responds to stimuli like stretch, heat, and cold
Cardiac muscle: found only in the heart, has automaticity (can generate/conduct electrical impulses independently), highly sensitive to oxygen supply, and receives blood from the coronary arteries
Respiratory System
The respiratory system's main functions are ventilation and oxygenation, where oxygen () is brought into the bloodstream during inhalation and carbon dioxide () is removed during exhalation.
Air enters through the mouth and nose, passes through the oropharynx and nasopharynx (collectively the pharynx), then moves to the larynx (voice box), which contains the vocal cords and is protected by the cricoid cartilage.
The epiglottis prevents food and foreign objects from entering the trachea during swallowing by closing over the glottis.
The trachea (windpipe) transports air to the lungs and is supported by 16 C-shaped cartilage rings; it splits into two bronchi, each leading to a lung.
Within the lungs, bronchi branch into smaller bronchioles, ending in alveoli, which are tiny sacs where gas exchange occurs between air and blood.
The diaphragm is the primary muscle for breathing, separating the chest and abdominal cavities and controlled by the phrenic nerve.
Inhalation is an active process: the diaphragm and intercostal muscles contract, expanding the chest cavity and creating negative pressure that draws air into the lungs.
Exhalation is a passive process: the diaphragm and intercostal muscles relax, decreasing chest cavity size and creating positive pressure that pushes air out.
Gas exchange occurs in the alveoli, where oxygen moves from the air into the blood and carbon dioxide moves from the blood into the air, a process called ventilation.
Oxygenated blood travels from the lungs to the heart and then to body tissues, where oxygen is delivered to cells and carbon dioxide is collected as waste.
At the cellular level, gas exchange between blood and cells is called respiration, with oxygen moving into cells and carbon dioxide moving out into the blood, which then returns to the heart and lungs to repeat the cycle.
Pediatric Note
Children’s respiratory anatomy differs significantly from adults: All airway structures are smaller, and the tongue occupies more space in the pharynx, increasing the risk of airway obstruction.
The trachea in children is narrower, softer, and more flexible than in adults, making it more susceptible to blockage from swelling or foreign objects and more vulnerable during procedures involving neck pressure.
Cricoid cartilage in infants and children is less developed and less rigid, contributing to easier airway obstruction.
The rib cage and chest wall in infants and children are less curved and more flexible, making it harder to generate negative pressure for breathing and causing greater reliance on the diaphragm, which can result in a visible “seesaw” breathing pattern.
Gas exchange (oxygen in, carbon dioxide out) is vital for life: Oxygen supports cellular function, while carbon dioxide removal helps regulate body pH through the buffer system.
Breathing is classified as adequate or inadequate: Adequate breathing supports life, while inadequate breathing does not.
Cardiovascular System
The cardiovascular (circulatory) system is composed of the heart, blood, and blood vessels, and is responsible for circulating blood throughout the body.
The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle. The right side handles deoxygenated blood, sending it to the lungs, while the left side receives oxygenated blood from the lungs and pumps it to the body.
Blood flow through the heart follows a specific pathway: deoxygenated blood enters the right atrium via the superior and inferior vena cava, moves to the right ventricle, is pumped to the lungs through the pulmonary arteries, returns oxygenated to the left atrium via pulmonary veins, moves to the left ventricle, and is pumped out to the body through the aorta.
One-way valves (tricuspid, pulmonary, mitral, aortic) between chambers and vessels prevent backflow and ensure unidirectional blood flow.
The heart’s contraction is automatic and regulated by the cardiac conduction system: the sinoatrial (SA) node (pacemaker) initiates the electrical impulse, which travels through the atrioventricular (AV) node, bundle of His, bundle branches, and Purkinje fibers, coordinating the heartbeat.
Arteries carry blood away from the heart; veins return blood to the heart. The pulmonary artery is an exception, carrying deoxygenated blood to the lungs, while the pulmonary vein carries oxygenated blood to the heart.
Major arteries include: aorta (largest artery, supplies the body), coronary arteries (supply the heart muscle), carotid arteries (supply the head), femoral artery (thigh), brachial artery (upper arm), radial artery (forearm), posterior tibial artery (lower leg), and dorsalis pedis artery (foot).
Arteries branch into arterioles, which lead to capillaries. Capillaries are the site of exchange of gases, nutrients, and wastes between blood and body cells.
Blood returns from capillaries via venules (smallest veins), which merge into larger veins, eventually forming the superior and inferior vena cava that return blood to the right atrium.
Blood is composed of plasma (watery fluid carrying cells and dissolved substances), red blood cells (carry oxygen via hemoglobin), white blood cells (defend against infection), and platelets (involved in clotting).
The coronary arteries supply the heart muscle itself; blockage can cause chest pain or heart problems.
The left ventricle is the most muscular chamber, as it must pump blood throughout the entire body.
The cardiac control centers in the brain, along with hormones like epinephrine, regulate heart rate and strength of contraction.
The pulmonary and systemic circuits describe the two main circulatory routes: pulmonary (heart to lungs and back) and systemic (heart to body and back).* Blood serves multiple functions: It transports gases like oxygen and carbon dioxide, acts as a reservoir for dissolved oxygen, fights infection, produces clotting factors, and regulates body pH through buffer chemicals.
Pulse is a pressure wave: Created by the left ventricle contracting and sending blood through arteries; felt by compressing an artery over a bone. Peripheral pulses (radial, brachial, posterior tibial, dorsalis pedis) are felt on the body's outer areas, while central pulses (carotid, femoral) are felt in larger, central arteries and remain detectable even when peripheral pulses are weak.
Blood pressure is the force exerted by blood on vessel walls: Systolic pressure is the force during ventricular contraction, and diastolic pressure is the pressure during ventricular relaxation. Blood pressure is reported as systolic over diastolic, such as .
Perfusion is the adequate supply of oxygen and nutrients to cells: It involves efficient circulation of blood to all body parts, ensuring waste removal. Hypoperfusion (shock) is inadequate perfusion, leading to insufficient oxygen delivery and waste removal, which can be life-threatening.
Major arteries and veins have specific roles: Carotid arteries supply the head and neck; subclavian arteries supply the upper chest and arms; brachial, radial, and ulnar arteries supply the arms and forearms; abdominal aorta branches to supply kidneys, pelvis, and legs; femoral, popliteal, tibial, and peroneal arteries supply the lower extremities.
Lymphatic system components: Tonsils protect against pathogens in the throat, thymus is essential for immune system development, spleen cleanses blood and removes old red blood cells, lymph nodes cleanse lymph fluid, and lymphatic vessels transport lymph fluid.
Cardiopulmonary System
The cardiopulmonary system consists of the respiratory and cardiovascular systems working together to deliver oxygen and glucose to cells, which are essential for energy production.
Aerobic metabolism occurs when oxygen is present, efficiently converting glucose into ATP (energy) and producing minimal waste (carbon dioxide and water).
Anaerobic metabolism happens when oxygen is insufficient, resulting in less energy production and more waste products like lactic acid, which can cause acidosis and harm cells.
Perfusion is the process of moving oxygen from the blood into the cells and removing waste products; it is vital for normal cell function.
Effective perfusion requires:
Oxygen-rich air reaching the alveoli in the lungs.
Adequate blood flow through pulmonary capillaries for gas exchange.
Proper matching of air and blood supply, known as a ventilation/perfusion (V/Q) match.
Effective heart pumping to circulate blood.
Sufficient oxygen in inhaled air.
Blood with enough oxygen-carrying capacity (e.g., not affected by anemia).
Proper mechanics of respiration to move air in and out of the lungs.
Any disruption in the cardiopulmonary system—such as airway obstruction, blood loss, heart failure, anemia, or impaired breathing mechanics—can threaten perfusion and, therefore, cell function.
Lymphatic System
The lymphatic system is a network of organs, tissues, vessels, and fluids distributed throughout the body, with the main function of capturing and returning escaped fluid (lymph) to the bloodstream, maintaining fluid balance.
It plays a crucial role in the immune system by producing lymphocytes and other white blood cells that help fight infection.
Key lymphoid organs include the adenoids, tonsils (protect against pathogens in the pharynx), spleen (cleanses blood and removes old red blood cells), thymus (essential for immune system development), and sometimes the appendix (due to its lymph tissue density).
Lymph nodes, which are soft and round or irregularly shaped, filter lymph fluid, removing bacteria and foreign cells, and produce infection-fighting cells.
Lymphatic vessels transport lymph fluid throughout the body.
Enlarged or tender lymph nodes can indicate infection, which is why healthcare providers often check them during examinations.
After a mastectomy, blood pressure should not be taken on the arm on the same side as the surgery, as removal of lymphatic tissue makes the remaining tissue more vulnerable to damage from compression.
Nervous System
The nervous system is composed of the brain, spinal cord, and nerve tissue, and is responsible for transmitting impulses that control sensation, movement, thought, and both voluntary and involuntary activities.
It is divided into the central nervous system (CNS) and peripheral nervous system (PNS):
The CNS includes the brain (which coordinates body functions and consciousness) and the spinal cord (which transmits messages between the brain and body).
The reticular activating system within the brain is crucial for maintaining wakefulness.
The PNS consists of sensory nerves (which carry information from the body to the CNS) and motor nerves (which carry commands from the CNS to the body).
The autonomic nervous system, a division of the PNS, controls involuntary functions like digestion and heart rate, and is further divided into:
The sympathetic nervous system (fight-or-flight response), which increases heart rate, breathing, and constricts blood vessels during crisis or stress.
The parasympathetic nervous system (feed-or-breed response), which promotes relaxation, increases blood flow to the digestive and reproductive organs, slows the heart, and dilates blood vessels.
Activation of the sympathetic nervous system can be recognized by signs such as increased heart and respiratory rates, pale and sweaty skin, and blood vessel constriction, which are important indicators of the body’s response to injury or illness, even if symptoms are atypical.
Digestive System
The digestive system breaks down food into absorbable forms and moves it through the body, starting at the mouth and ending with waste elimination.
Food is initially broken down in the mouth by chewing and saliva, then passes through the oropharynx and esophagus to the stomach.
The oral cavity and pharynx work together to ingest, chew, and swallow food, moving it to the esophagus.
Salivary glands produce saliva, aiding in the initial breakdown of food.
The esophagus is a muscular canal that transports food from the pharynx to the stomach.
The stomach is a hollow, expandable organ where acidic gastric juices begin the chemical breakdown of food.
The small intestine, divided into the duodenum, jejunum, and ileum, continues digestion and is the primary site for nutrient absorption through its walls.
The large intestine (colon) reabsorbs water from waste and stores feces for elimination.
The liver produces bile to help digest fats, detoxifies substances, stores sugar, and assists in blood product formation.
The gallbladder stores bile produced by the liver and releases it into the small intestine as needed.
The pancreas produces insulin to regulate blood sugar and secretes digestive enzymes that break down proteins, carbohydrates, and fats in the small intestine.
The spleen, though not directly involved in digestion, filters old blood cells and stores blood reserves.
The appendix, located near the junction of the small and large intestines, is made of lymphatic tissue; its function is unclear but it is associated with abdominal pain when inflamed.
Most digestive organs are located in the abdominal cavity, except for the mouth and esophagus.
Organs outside the direct digestive tract (liver, gallbladder, pancreas, spleen, appendix) play supporting roles in digestion, absorption, and overall body function.
Integumentary System
The integumentary system is mainly composed of the skin, which serves multiple essential functions: protection, water balance, temperature regulation, excretion, and shock absorption.
Protection: The skin acts as a barrier against microorganisms, debris, and chemicals, safeguarding underlying tissues and organs and maintaining the chemical balance of body fluids.
Water balance: The skin prevents excessive water loss from the body and blocks external water from entering.
Temperature regulation: Skin blood vessels dilate to release heat and constrict to conserve heat; sweat glands produce perspiration for cooling through evaporation, and the subcutaneous fat layer insulates against temperature changes.
Excretion: The skin eliminates salts and excess water through sweat.
Shock absorption: The skin and its underlying fat cushion and protect organs from minor impacts and pressure.
The skin has three main layers:
Epidermis: The outermost layer, consisting of four strata (five on palms and soles), with dead cells on the surface and living, dividing cells deeper; contains pigment granules but no blood vessels or nerves.
Dermis: Located beneath the epidermis, rich in blood vessels, nerves, sweat glands, oil glands, and hair follicles; contains specialized nerve endings for touch, temperature, and pain; injuries here can lead to significant bleeding, pain, and infection risk.
Subcutaneous layer: Composed of fat and soft tissue, providing insulation and shock absorption; injuries can result in contamination, bleeding, and pain.
Endocrine System
The endocrine system produces hormones that regulate many body activities and functions.
The pineal gland regulates circadian rhythm and is located deep in the center of the brain.
The pituitary gland is at the base of the brain and controls many other endocrine glands.
The thyroid gland (front of the neck) regulates metabolic rate, while the parathyroid glands (embedded in the thyroid) regulate blood calcium levels.
The thymus gland (between the lungs, above the heart) aids in the development of the immune system.
The adrenal glands (on top of each kidney) regulate water and electrolyte levels and have two parts: the outer cortex and inner medulla.
The pancreas (upper abdomen) regulates blood sugar levels by secreting insulin, which is essential for glucose use in the body.
The ovaries (in females, beside the uterus) regulate the female reproductive system; the testes (in males, within the scrotum) regulate the male reproductive system.
The adrenal glands secrete epinephrine (adrenaline) and norepinephrine, which act as neurotransmitters and activate the sympathetic nervous system.
During the fight-or-flight response, norepinephrine activates beta 2 receptors in the lungs (causing bronchiole dilation for increased airflow) and beta 1 receptors in the heart (increasing heart rate and contraction force).
Renal System
The renal (urinary) system regulates fluid balance, filters chemicals, and adjusts body pH.
The kidneys are the main organs, filtering blood to remove waste (such as urea), regulating sodium uptake, and controlling urine excretion.
The kidneys help maintain acid-base balance by producing bicarbonate, which is crucial for regulating blood pH.
Urine formation and excretion involve several structures: kidneys produce urine, ureters transport urine to the bladder, the bladder stores urine, and the urethra carries urine out of the body.
In males, the urethra is longer and passes through the penis; in females, the urethra is shorter and exits just above the vaginal opening.
The renal system can adjust urine output to compensate for changes in fluid intake or loss (e.g., bleeding), helping maintain homeostasis.
Reproductive System
The male reproductive system includes the testes, epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral gland, and penis. The testes produce sperm and secrete testosterone, while the epididymis stores sperm. The vas deferens transports sperm to the urethra. The seminal vesicles, prostate gland, and bulbourethral gland all secrete fluids that combine with sperm to form semen. The penis delivers semen during intercourse and is also used for urination.
The female reproductive system consists of the ovaries, fallopian tubes, uterus, vagina, vulva, and breasts. The ovaries produce ova (eggs) and secrete estrogen and progesterone. The fallopian tubes transport the ovum to the uterus and are the site of fertilization. The uterus is where the fetus develops during pregnancy and is highly vascular, making it susceptible to bleeding during pregnancy. The vagina serves as the birth canal and receives semen during intercourse. The vulva protects the vaginal opening and urinary meatus, while the breasts produce milk.
Key relationships include the connection of the testes to the penis via the epididymis and vas deferens in males, and the connection of the ovaries to the uterus via the fallopian tubes in females. In females, the uterus connects to the vagina, which functions both as the birth canal and as the organ for sexual intercourse. The male and female reproductive systems are specialized for their roles in reproduction, with distinct organs and functions.
Think Like an EMT
The bones just above the wrist are called the radius and ulna, which are the two long bones of the forearm.
The solid organ located in the left upper abdominal quadrant is the spleen, which can cause severe internal bleeding if injured.
The large bone in the thigh is the femur, and fractures of the femur are associated with significant blood loss due to the bone's size and blood supply.