An Overview of Anatomy and Physiology and the Language of Anatomy and the Language of Anatomy
Definitions and Relationships of Anatomy and Physiology
Anatomy (ah-nat’o-me): The study of the structure and shape of the body and its parts, as well as their relationships to one another.
The term is derived from the Greek words ana (apart) and tomy (to cut).
Gross Anatomy: The study of large, easily observable structures such as the heart or bones, often involving the dissection of preserved animals or organs.
Microscopic Anatomy: The study of body structures that are too small to be seen with the naked eye, such as cells and tissues, which require a microscope for observation.
Physiology (fiz‒e-ol’o-je): The study of how the body and its parts work or function.
The term is derived from physio (nature) and ology (the study of).
Subdivisions:
Neurophysiology: Explains the workings of the nervous system.
Cardiac Physiology: Studies the function of the heart.
Relationship between Anatomy and Physiology:
Anatomy and physiology are inseparable because structure determines what functions can take place.
The body is a well-organized unit where each part has a specific job to ensure the body operates as a whole.
Example: The lungs are not muscular like the heart and cannot pump blood, but their very thin-walled air sacs allow for the exchange of gases and the provision of oxygen.
Levels of Structural Organization
The human body exhibits six levels of structural complexity, ranging from the simplest chemicals to the whole organism:
Chemical Level: The simplest level where atoms (tiny building blocks of matter) combine to form molecules such as water, sugar, and proteins (e.g., muscle-building proteins).
Cellular Level: Molecules associate in specific ways to form cells, the smallest units of all living things. Cells vary in size, shape, and role, but share common structures.
Tissue Level: Consists of groups of similar cells that have a common function. There are four basic tissue types.
Organ Level: A structure composed of two or more tissue types that performs a specific function. Extremely complex functions become possible at this level (e.g., the small intestine digests and absorbs food using all four tissue types).
Organ System Level: A group of organs that work together to accomplish a common purpose (e.g., the heart and blood vessels of the cardiovascular system circulate blood to carry nutrients and oxygen).
Organismal Level: The highest level of structural organization, representing the sum total of all structural levels working together to maintain life.
Overview of the Organ Systems
Integumentary System:
Includes the skin, hair, and fingernails.
Functions: Forms the external body covering; waterproofs the body; cushions and protects deeper tissues; produces Vitamin D with sunlight; excretes salts in perspiration; regulates body temperature; contains sensory receptors.
Skeletal System:
Consists of bones, cartilages, and joints.
Functions: Supports the body; provides a framework for movement; protects organs (e.g., the skull protects the brain); acts as the site for blood cell formation (hematopoiesis); stores minerals in the hard bone substance.
Muscular System:
Consists specifically of skeletal muscles (large, fleshy muscles attached to bones).
Function: To contract or shorten, enabling movement (walking, jumping, smiling, etc.) and maintaining posture.
Note: Skeletal muscles are distinct from the muscles of the heart and other hollow organs.
Nervous System:
The body's fast-acting control system.
Structures: Brain, spinal cord, nerves, and sensory receptors.
Function: Detects internal and external stimuli (changes in light, sound, temperature, or oxygen levels); sends electrical signals (nerve impulses) to the central nervous system (CNS); the CNS assesses information and activates effectors (muscles or glands).
Endocrine System:
Slower-acting control system for body activities.
Structures: Pituitary, thyroid, parathyroids, adrenals, thymus, pancreas, pineal, ovaries (female), and testes (male).
Function: Glands secrete hormones (chemical molecules) into the blood to travel to distant target organs to regulate growth, reproduction, and nutrient use by cells.
Cardiovascular System:
Primary Organs: Heart and blood vessels.
Function: Transport of oxygen, nutrients, hormones, and waste (carbon dioxide); heart acts as a pump; white blood cells and chemicals protect the body from invaders.
Lymphatic System:
Complements the cardiovascular system.
Structures: Lymphatic vessels, lymph nodes, spleen, and tonsils.
Function: Returns fluid leaked from blood back to the bloodstream; lymph nodes cleanse the blood and house white blood cells for immunity.
Respiratory System:
Structures: Nasal passages, pharynx, larynx, trachea, bronchi, and lungs.
Function: Supplies the body with oxygen and removes carbon dioxide; gas exchange occurs through the thin walls of the alveoli (tiny air sacs in the lungs).
Digestive System:
A tube running from the mouth to the anus.
Structures: Oral cavity, esophagus, stomach, small and large intestines, rectum.
Accessory Organs: Liver (produces bile to break down fats), salivary glands, pancreas (delivers digestive enzymes).
Function: Breaks down food; delivers nutrients to the blood; reabsorbs water; eliminates undigested residue as feces.
Urinary (Excretory) System:
Structures: Kidneys, ureters, bladder, and urethra.
Function: Removes nitrogen-containing wastes (e.g., urea, uric acid) from blood; maintains water and electrolyte (salt) balance; regulates acid-base balance of blood and blood pressure.
Reproductive System:
Function: Production of offspring.
Male: Testes (produce sperm), scrotum, penis, accessory glands, and duct system.
Female: Ovaries (produce eggs/ova), uterine tubes, uterus (site for fetus development), and vagina.
Necessary Life Functions
Maintaining Boundaries: Every organism must keep its ’inside’ distinct from its ’outside’. Cells use membranes; the body uses the integumentary system to prevent desiccation and entry of pathogens.
Movement: Promoted by the muscular and skeletal systems; involves propelling the body or moving substances (blood, food, urine) through internal organs.
Responsiveness (Irritability): The ability to sense and react to stimuli. Nerve cells have high irritability; the nervous system is primarily responsible.
Digestion: The breakdown of food into simple molecules for absorption into the blood.
Metabolism: All chemical reactions in the body. Includes breaking down complex substances, building larger structures ( production), and is regulated by hormones.
Excretion: The removal of waste (). Involves the digestive (feces), urinary (urine), and integumentary (sweat) systems.
Reproduction: Occurs at the cellular level (cell division for growth/repair) and organismal level (sperm and egg union to produce a baby).
Growth: An increase in cell size or number. Requires cell-constructing activities to exceed cell-destroying ones; primarily directed by hormones.
Survival Needs
Nutrients: Provide chemicals for energy and cell building.
Carbohydrates: Major energy fuel.
Proteins/Fats: Essential for structures; fats provide reserve fuel and cushioning.
Vitamins/Minerals: Required for chemical reactions and oxygen transport.
Oxygen: Human cells only survive for a few minutes without it; required for the chemical reactions that release energy from food.
Water: Accounts for to percent of body weight; the single most abundant chemical substance in the body.
Normal Body Temperature: Must be maintained near (). Below this, metabolism slows/stops; above this, proteins break down.
Atmospheric Pressure: The force exerted by air. Essential for gas exchange in the lungs. At high altitudes, low pressure may make gas exchange too slow to support metabolism.
The Language of Anatomy
Anatomical Position: A standard reference point. The body is erect, feet are parallel, arms hang at the sides, and palms are facing forward (thumbs pointing away from the body).
Directional Terms:
Superior (Cranial/Cephalic): Toward the head; above.
Inferior (Caudal): Away from the head; below.
Anterior (Ventral): Toward the front of the body.
Posterior (Dorsal): Toward the back of the body.
Medial: Toward the midline of the body.
Lateral: Away from the midline of the body.
Intermediate: Between a more medial and more lateral structure.
Proximal: Closer to the origin of the body part or point of attachment (used for limbs).
Distal: Farther from the origin of the body part or attachment point (used for limbs).
Superficial (External): Toward or at the body surface.
Deep (Internal): Away from the body surface.
Regional Terms (Surface Landmarks)
Anterior Landmarks:
Abdominal: Anterior trunk inferior to ribs.
Acromial: Point of shoulder.
Antebrachial: Forearm.
Antecubital: Anterior surface of elbow.
Axillary: Armpit.
Brachial: Arm.
Buccal: Cheek area.
Carpal: Wrist.
Cervical: Neck region.
Coxal: Hip.
Crural: Anterior leg (shin).
Deltoid: Curve of shoulder.
Digital: Fingers, toes.
Femoral: Thigh.
Fibular: Lateral part of leg.
Frontal: Forehead.
Inguinal: Groin.
Mental: Chin.
Nasal: Nose area.
Oral: Mouth.
Orbital: Eye area.
Patellar: Anterior knee.
Pectoral: Chest.
Pelvic: Area overlying the pelvis anteriorly.
Pubic: Genital region.
Sternal: Breastbone area.
Tarsal: Ankle region.
Thoracic: Area between neck and abdomen.
Umbilical: Navel.
Posterior Landmarks:
Calcaneal: Heel of foot.
Cephalic: Head.
Gluteal: Buttock.
Lumbar: Area of back between ribs and hips.
Occipital: Base of skull.
Olecranal: Posterior surface of elbow.
Popliteal: Posterior knee area.
Sacral: Area between hips at base of spine.
Scapular: Shoulder blade region.
Sural: Calf.
Vertebral: Area of spinal column.
Plantar: Sole of foot (inferior surface).
Body Planes and Sections
Sagittal Section: Cut along the lengthwise plane dividing the body into right and left parts.
Median (Midsagittal) Section: Cut down the median plane resulting in equal right and left halves.
Parasagittal Section: All other sagittal cuts that are not on the midline.
Frontal (Coronal) Section: Cut along a lengthwise plane dividing the body into anterior and posterior parts.
Transverse (Cross) Section: Cut along a horizontal plane dividing the body into superior and inferior parts.
Internal Body Cavities
Dorsal Body Cavity:
Cranial Cavity: Houses the brain within the skull.
Spinal Cavity: Houses the spinal cord, protected by vertebrae.
Ventral Body Cavity:
Thoracic Cavity: Superior cavity separated by the diaphragm; contains heart and lungs. The mediastinum is the central region separating the lungs.
Abdominopelvic Cavity: Inferior to diaphragm. Subdivided into the abdominal cavity (stomach, liver, intestines) and the pelvic cavity (reproductive organs, bladder, rectum). Note: There is no physical structure dividing these two.
Abdominopelvic Subdivisions
Quadrants (Medical usage):
Right Upper Quadrant (RUQ)
Right Lower Quadrant (RLQ)
Left Upper Quadrant (LUQ)
Left Lower Quadrant (LLQ)
Nine Regions (Anatomist usage):
Umbilical Region: Centermost, around the navel.
Epigastric Region: Superior to the umbilical region.
Hypogastric (Pubic) Region: Inferior to the umbilical region.
Right/Left Iliac (Inguinal) Regions: Lateral to the hypogastric region.
Right/Left Lumbar Regions: Lateral to the umbilical region.
Right/Left Hypochondriac Regions: Lateral to the epigastric region; contain lower ribs.
Homeostasis
Definition: The body’s ability to maintain relatively stable internal conditions despite continuous external changes; a dynamic state of equilibrium.
Homeostatic Control Systems: Consist of three components:
Receptor: Sensor that monitors the environment and responds to stimuli. Sends input to the control center via the afferent pathway.
Control Center: Determines the set point; analyzes input and determines the response.
Effector: Provides the means for the response. Information flows from the control center to the effector via the efferent pathway.
Feedback Mechanisms:
Negative Feedback: The response shuts off or reduces the intensity of the original stimulus (e.g., body temperature regulation, heart rate, blood pressure, blood glucose levels).
Positive Feedback: Rare; the response increases the original disturbance to push the variable farther from its original value. Typically for infrequent, explosive events (e.g., blood clotting, childbirth).
Homeostatic Imbalance: A disturbance of homeostasis, often associated with disease or aging as body organs become less efficient.
Questions & Discussion
Q: How does anatomy relate to the naming of sections?
A: Sections are cuts made along imaginary lines called planes. A sagittal section divides left from right, a frontal section divides front from back, and a transverse section divides top from bottom. Using these specific terms allows for clear communication regarding the location and view of internal organs, such as those seen in an MRI scan.
Q: Why is the abdominal cavity more vulnerable than the pelvic cavity?
A: The abdominal cavity walls are formed only of trunk muscles and are not reinforced by bone, whereas the pelvic organs receive some protection from the bony pelvis.