INTRO | Anatomy & Physiology
Definitions: Anatomy vs Physiology
Anatomy: the study of body structures and their relationships to one another.
Physiology: the study of the function of the structures; how the body works.
A grand theme: structure determines function.
Subdivisions of Anatomy
Gross (macroscopic) anatomy: study of large structures visible to the naked eye.
Surface anatomy: study of structures visible without cutting, by surface landmarks.
Systemic anatomy: study of structures that work together to perform a common function (e.g., cardiovascular system).
Cardiovascular system components: heart + blood vessels; functions include delivering nutrients and removing wastes.
Nervous system (nervous tissue): gross anatomy includes brain lobes; microscopic anatomy includes neurons and glial cells.
Major concepts in nervous system anatomy
Brain lobes (gross): temporal, frontal, parietal, occipital.
Microscopic nervous system: neurons and organelles; cytology (cell structure).
Tissues: nervous tissue includes neurons and glial cells (astrocytes, microglial cells, oligodendrocytes).
Histology: study of tissue structure; includes neural tissue.
Cytology: study of cell structure; organelles inside cells (e.g., mitochondria).
Organelles: mitochondria highlighted; inner/outer membranes form the mitochondrion; membrane structure described as a phospholipid bilayer.
Electron microscope: magnification example:
ext{Mitochondria magnified } 236{,}000\times
Light microscopes typically up to about 10^3\times magnification; cannot reveal mitochondrial details.
Practical lab note: basic cytology and histology are often studied with light microscopes; electron microscopy used for ultrastructure.
From cells to tissues to organs
Cells: basic living units; contain proteins, nucleic acids (DNA/RNA), lipids, etc.
Cytology vs histology distinction:
Cytology: study of cell structure.
Histology: study of tissue structure made up of cells.
Tissues: groups of similar cells performing related functions; nervous tissue is an example with neurons and glial cells.
Organs: structures composed of multiple tissue types.
Organ systems: multiple organs working together (e.g., urinary system, cardiovascular system).
Example: urinary bladder contains smooth muscle (detrusor muscle) plus mucosal lining (epithelial tissue) and connective tissue.
Levels of structural organization (6 levels)
Chemical level: atoms and molecules; example: water molecule ext{H}_2 ext{O} formed by chemical bonds.
Cellular level: cells, the smallest living units; contain organelles and biomolecules.
Tissue level: groups of similar cells performing a function (e.g., smooth muscle tissue).
Organ level: two or more tissue types forming a recognizable structure (e.g., bladder with detrusor muscle and mucosa).
Organ system level: multiple organs working together (e.g., urinary system: kidneys, ureters, bladder, urethra).
Organism level: the entire human being.
The video emphasizes: 11 organ systems cooperate to form the human organism.
Major organ systems and their functions
Integumentary system: skin, hair, nails, sensory receptors; functions include protection and detection of touch; contains sweat glands and sebaceous glands.
Skeletal system: bones, cartilage, ligaments; functions include support and movement.
Muscular system: muscles and tendons; function is to contract and produce motion; heat generation through metabolism.
Nervous system: brain, spinal cord, nerves; functions include sensing, processing information, and regulating muscles and glands.
Endocrine system: glands (pituitary, thyroid, pancreas, adrenal, gonads); functions through hormones to regulate other organs.
Cardiovascular system: heart and blood vessels; functions to circulate blood delivering nutrients and removing wastes.
Lymphatic & immune system: lymphatic vessels, lymph nodes, spleen, thymus; functions to drain fluid from tissues and defend against pathogens.
Respiratory system: lungs, bronchi, trachea, larynx, pharynx, nasal cavities, sinuses; functions to bring in air and enable external respiration (Oâ‚‚ in, COâ‚‚ out).
Digestive system: oral cavity, salivary glands, pharynx, esophagus, stomach, small intestine, liver, gallbladder, pancreas, large intestine; functions to ingest, break down, absorb nutrients, and eliminate waste.
Urinary system: kidneys, ureters, urinary bladder, urethra; functions to filter blood, regulate composition, and eliminate waste in urine.
Reproductive system: male (testes, epididymis, ductus deferens, seminal glands, prostate, penis); female (ovaries, uterus, vagina, vulva, mammary glands); functions to produce offspring; sperm and ova fertilize to form a zygote; embryo → fetus.
Anatomical terminology: directional terms, landmarks, and planes
Directional coordinate system in the anatomical position is relative; structure positions are described with respect to immortalized axes.
Key directional terms (relative, not absolute):
Superior (cranial) vs Inferior (caudal)
Anterior (ventral) vs Posterior (dorsal)
Medial vs Lateral
Proximal vs Distal
Ipsilateral vs Contralateral (not explicitly stated in transcript but commonly used)
Cranial vs Caudal equivalents: cranial ~ superior; caudal ~ inferior.
Regional and surface terms (examples):
Cephalic (head), cranial (skull region)
Oral (mouth), mental (chin)
Frontal (forehead), nasal (nose), ocular (eye), buccal (cheek)
Axillary (armpit), brachial (upper arm), antecubital (anterior elbow), antebrachial (forearm)
Carpal (wrist), palmar (palm), digital/Phalangeal (fingers/toes); pollex (thumb)
Femoral (thigh), patellar (knee), crural (leg), tarsal (ankle), hallux (big toe)
Pedal (foot), plantar (sole), sural (calf)
Olecranal (posterior elbow), acromial (shoulder), axillary (armpit)
Lumbar (lower back and lateral abdomen), gluteal (buttock)
Popliteal (posterior knee), calcaneal (heel)
Regional names sometimes derive from Latin/Greek roots; historical meanings can differ from anatomical usage (anchor with context).
Examples of region relationships: hubliteal region proximal and superior to sural region; acromial region lateral to cervical region and proximal to olecranal region.
Sectioning planes and body cavities
Planes of section:
Sagittal plane: vertical plane dividing body into right and left portions; midsagittal goes through midline producing equal halves; parasagittal is offset from midline.
Frontal (coronal) plane: longitudinal plane dividing body into anterior and posterior portions.
Transverse (horizontal) plane: divides body into superior and inferior portions.
Oblique section: any plane at an angle other than sagittal, frontal, or transverse.
Body cavities (axial body): dorsal and ventral cavities.
Dorsal cavity: cranium (contains brain) and vertebral canal (contains spinal cord).
Ventral cavity: thoracic cavity and abdominal–pelvic cavity.
Thoracic cavity subdivisions: left and right pleural cavities (lungs), pericardial cavity (within mediastinum; contains the heart); superior mediastinum contains trachea and esophagus and major vessels.
Mediastinum: area between the lungs; superior mediastinum includes major structures (e.g., trachea, esophagus, large vessels).
Diaphragm: skeletal muscle forming boundary between thoracic and abdominal–pelvic cavities.
Abdominal cavity contains most digestive organs (stomach, small intestine, liver, pancreas, spleen, kidneys, adrenal glands).
Pelvic cavity contains urinary bladder; in females, uterus; in males, prostate.
Abdominopelvic quadrants: right upper (RUQ), left upper (LUQ), right lower (RLQ), left lower (LLQ).
RUQ: majority of liver and gallbladder.
LUQ: stomach, spleen.
RLQ: portions of intestine including appendix and cecum; ascending colon.
LLQ: portions of intestine including descending colon and sigmoid colon; portions of small intestine, urinary bladder, reproductive organs (depending on gender).
Abdominopelvic regions (nine-region scheme):
Right hypochondriac, Epigastric, Left hypochondriac
Right lumbar, Umbilical, Left lumbar
Right iliac (inguinal), Hypogastric, Left iliac
The appendix commonly located at the border between the right iliac region and hypogastric region.
Right iliac region contains cecum; left iliac region contains sigmoid colon.
Imaging techniques and considerations
X-rays: oldest imaging modality; use high-energy electromagnetic radiation; good for bone/tissue contrast; 2D projection images.
Chest X-ray: evaluates lungs; example shows normal vs tuberculosis.
Mammography: breast cancer screening using X-ray; contraindications and risk awareness.
Fluoroscopy: real-time X-ray with contrast (barium) to visualize GI tract; uses contrast agents to improve visibility.
Angiography: X-ray with injected contrast to visualize blood vessels.
Computed Tomography (CT / CAT scan): cross-sectional imaging by combining numerous X-ray slices into 3D models; provides detailed anatomy.
Positron Emission Tomography (PET): imaging radiopharmaceuticals that emit radiation to show metabolic activity; often combined with CT or MRI (PET/CT or PET/MRI).
PET-CT and PET-MRI: integrated imaging for structure and function.
Radiation exposure and risk:
Ionizing radiation can damage DNA and increase cancer risk.
Reproductive organ exposure may cause developmental effects in offspring.
Typical comparative dose references (illustrative):
Dental/skeletal X-ray: about 0.02\ \text{mSv}.
Mammography: about 0.4\ \text{mSv}.
Chest CT: commonly higher; variable by protocol.
CT or PET scans: about 5\–\,20\ \text{mSv}.
High-altitude exposure (Denver-like): comparable to year-long exposure in high elevation.
ALARA principle: as low as reasonably achievable; balance diagnostic value against risk.
Magnetic Resonance Imaging (MRI): uses strong magnetic field and radiofrequency signals; does not involve ionizing radiation.
Strengths: excellent soft tissue contrast; does not damage DNA.
Limitations/risks: long scan times; claustrophobic and noisy; not suitable with certain metal implants or devices; ferromagnetic risk.
Diffusion Tensor Imaging (DTI): MRI technique to map white matter tracts in the CNS.
Functional MRI (fMRI): detects blood flow changes to study brain function.
PET-MRI: combines metabolic and anatomical data.
Ultrasound (sonography): uses high-frequency sound waves; no ionizing radiation; real-time imaging.
Common use: fetal development; assess organs such as heart, kidney, bladder, gallbladder.
Echocardiogram: ultrasound imaging of the heart.
Vascular ultrasound: imaging of blood vessels to diagnose blockages, aneurysms, etc.
Specific anatomical example: elbow joint (structure determines function)
Elbow anatomy: hinge joint formed by humerus and ulna.
Trochlea: distal end of the humerus that articulates with the ulna; the trochlea fits into the semilunar (trochlear) notch of the ulna.
The tight fit between the trochlea and trochlear notch enables elbow flexion and extension in the sagittal plane, while limiting rotation and abduction/adduction.
This example illustrates how joint structure constrains range of motion and determines function.
Neural and hormonal control: negative and positive feedback
Negative feedback (homeostasis maintenance): a sensor/receptor detects a variable outside the set point; input is relayed to a control center (usually CNS); control center issues commands to an effector to counteract the stimulus and restore the set point.
Example: body temperature regulation
Set point: 37^{\circ}\text{C} = 98.6^{\circ}\text{F}
If temperature rises above the set point, thermoreceptors send input to hypothalamus (thermoregulatory center) which initiates sweat production; evaporation reduces body temperature toward the set point.
Another example: pH homeostasis (acid-base balance)
If hydrogen ion concentration is too high (acidosis, low pH), sensors detect this; brain/throax control centers increase respiration to remove COâ‚‚, reducing carbonic acid and raising pH toward ~7.40.
If pH is too high (alkalosis), respiration rate decreases to retain COâ‚‚ and lower pH toward the same set point.
Positive feedback (amplifies the stimulus until a big change occurs): the output reinforces the stimulus until a terminating event occurs.
Childbirth example: cervix stretch activates input to brain; pituitary releases oxytocin; oxytocin stimulates uterine contractions; more stretching leads to more oxytocin release, continuing until birth.
Blood clotting example: activated platelets release clotting factors, recruiting more platelets and factors until the vessel is sealed.
Connections to practical biology and real-world relevance
How structure informs function across scales from molecules to organ systems.
Understanding organ systems helps in clinical diagnosis and treatment planning (e.g., imaging to assess anatomy and function; recognizing when a system is not functioning properly).
Ethical and practical implications of imaging: balancing diagnostic benefits with radiation exposure risks; considering patient safety and necessary precautions.
Key numbers, terms, and formulas (quick reference)
Temperature set point: 37^{\circ}\text{C} = 98.6^{\circ}\text{F}
Normal blood pH: approximately \mathrm{pH} = 7.40
Water molecule formula: \text{H}_2\text{O}
Mitochondrial magnification example: 236{,}000\times (electron microscopy) vs \sim 10^3\times (light microscopy)
X-ray exposure ranges (illustrative):
Dental X-ray: \approx 0.02\ \text{mSv}
Mammography: \approx 0.4\ \text{mSv}
CT / PET: \approx 5\–\,20\ \text{mSv}
Planes and scanning contexts: MRI uses no ionizing radiation but involves strong magnetic fields; PET involves radiopharmaceuticals emitting radiation.
Practical vocabulary recap (selected terms)
Cephalic: head region; cranial: skull region
Facial terms: oral (mouth), mental (chin)
Frontal: forehead; nasal: nose; ocular: eyes; buccal: cheek
Axillary: armpit; brachial: upper arm; antecubital: anterior elbow; antebrachial: forearm
Carpal: wrist; palmar: palm; digital/phalangeal: fingers/toes; pollex: thumb
Lower limb: femoral (thigh); patellar (kneecap); crural (leg); tarsal (ankle); hallux: big toe; pedal: foot; plantar: sole; sural: calf
Other landmarks: olecranal (posterior elbow); acromial (shoulder); lumbar (lower back); gluteal (buttocks); popliteal (back of knee); calcaneal (heel)
Summary: big picture takeaways
Anatomy and physiology are distinct but deeply interconnected disciplines.
The body is organized hierarchically from chemical building blocks to the organism.
Structure constrains and enables function (e.g., joint architecture, organ systems).
The body maintains stability through negative feedback; big changes occur via positive feedback loops and certain physiological processes (e.g., childbirth, clotting).
A wide array of imaging technologies lets us visualize structure and infer function, each with benefits and risks; understanding these tools helps in safe, effective clinical use.
A solid grasp of directional terms, planes, and body cavities/regions is foundational for describing location, pathology, and surgical planning.