Sciences of Anatomy and Physiology Practice Flashcards
Foundations of Anatomy and Physiology
Anatomy and physiology represent the two core pillars of medical science. Anatomy is defined as the scientific study of the biological structures of an organism and their physical relationships to one another, while physiology focuses on the study of the integrated functions of these body parts and how they work together to support life. Within anatomy, subdivisions include gross anatomy, such as regional, systemic, and surface anatomy, which focuses on structures visible to the naked eye, and microscopic anatomy, such as cytology which is the study of cells and histology which is the study of tissues. Physiology is often subdivided based on the organ systems involved, such as renal physiology, neurophysiology, or cardiovascular physiology.
The human body follows a nested, hierarchical level of organization that can be viewed in ascending or descending order. At the most fundamental level is the chemical level, where atoms combine to form molecules. These molecules then organize into the cellular level, which is the basic functional unit of life. Groups of similar cells with a common function form the tissue level. Different tissue types combine to create an organ at the organ level, which performs a specific complex function. Multiple organs work together in an organ system, and finally, all organ systems work in unison to form the organismal level, the highest level of organization representing the living human being.
Body orientation is standardized through regional terms and specific anatomical planes. The transverse plane, or horizontal plane, divides the body into superior (upper) and inferior (lower) portions. The sagittal plane divides the body into left and right sides, with the mid-sagittal plane specifically cutting through the midline. The frontal or coronal plane divides the body into anterior (front) and posterior (back) sections. Key directional pairs used to locate structures include anterior vs. posterior (front vs. back), ventral vs. dorsal (underside vs. backside), inferior vs. superior (below vs. above), deep vs. superficial (internal vs. external), lateral vs. medial (away from vs. toward the midline), distal vs. proximal (farther from vs. closer to the point of attachment), and caudal vs. cranial or cephalic (toward the tail vs. toward the head).
The human body contains five primary cavities categorized into dorsal and ventral groupings. The dorsal cavity includes the cranial cavity, which houses the brain within the skull, and the vertebral or spinal cavity, which contains the spinal cord protected by the vertebrae. The ventral cavity is much larger and includes the thoracic cavity, containing organs like the heart and lungs, and the abdominopelvic cavity, which houses the stomach, intestines, liver, and reproductive organs. These cavities are separated by the diaphragm. Within these main spaces are specialized serous membranes: the pleural cavity surrounds the lungs, the pericardial cavity encloses the heart, and the peritoneal cavity lines the abdominal organs. These differ from the main cavities by being narrow, fluid-filled spaces between thin membranes that reduce friction during organ movement.
Homeostasis and Control Mechanisms
Homeostasis is the fundamental concept of maintaining a stable, relatively constant internal environment despite changes in the external world. It ensures that variables like body temperature, blood sugar, and $pH$ stay within a narrow physiological range. A homeostatic control mechanism consists of three general components: a receptor that monitors the environment and detects changes (stimuli), a control center that processes the information and determines the appropriate response, and an effector that carries out the response to restore balance.
Control mechanisms are categorized as either negative or positive feedback loops. A negative feedback loop is the primary mechanism for homeostasis, where the output of the system shuts off or reduces the intensity of the original stimulus to return the body to its set point. An example is thermoregulation: if body temperature rises, the control center in the brain triggers sweat glands (effectors) to cool the body down, and as the temperature drops, the stimulus is removed. In contrast, a positive feedback loop enhances the original stimulus so that the response is accelerated and the variable is pushed further from its original value. This is seen in processes like blood clotting or childbirth (oxytocin release), where the cycle continues until a specific goal or event is completed.
Chemical Foundations, Energy, and Metabolism
Metabolism encompasses the sum of all chemical reactions occurring within the body. It is divided into anabolism, the synthetic process where smaller molecules are built into larger ones requiring energy, and catabolism, the degradative process where larger molecules are broken down into smaller ones releasing energy. These processes often involve dehydration synthesis, where a water molecule is removed to bond two molecules together, and hydrolysis, where a water molecule is added to break a chemical bond. Reactions that release energy are termed exergonic, whereas those that require an input of energy are endergonic.
Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, primarily serving as the body’s main energy source. They are synthesized through dehydration synthesis and decomposed via hydrolysis. Based on size, they are classified as monosaccharides (simple sugars like glucose), disaccharides (two sugars like sucrose), and polysaccharides (complex chains like glycogen and starch). Lipids are hydrophobic organic molecules, including neutral fats like triglycerides, which are composed of one glycerol molecule and three fatty acids. Lipids serve functions in long-term energy storage, insulation, and membrane structure. This category includes saturated fats (no double bonds between carbons) and unsaturated fats (containing double bonds), as well as phospholipids, cholesterol, and steroids.
Proteins are complex macromolecules constructed from building blocks called amino acids linked by peptide bonds (C-N linkages). A chain of amino acids is a polypeptide, which must fold into specific primary, secondary, and tertiary structures to become a functional protein. Some even possess a quaternary structure. Proteins are essential for structural support, transport, and as biological catalysts called enzymes. Enzymes are highly specific due to their structure, typically named with the suffix "-ase" (e.g., lactase), and they lower activation energy to speed up metabolic reactions. Their specificity is both structural (lock and key) and functional, ensuring they only react with specific substrates to maintain homeostasis.
Nucleic acids, including DNA and RNA, are formed from nucleotides, each consisting of a sugar, a phosphate group, and a nitrogenous base. DNA serves as the genetic blueprint with a double-helix structure, while RNA is typically single-stranded and involved in translating that blueprint into proteins. ATP (adenosine triphosphate) is the high-energy molecule of the cell, containing three phosphate groups with high-energy bonds. When the terminal phosphate bond is broken, significant energy is released to power cellular work, making it the universal energy currency.
Cellular Biology and Bioenergetics
The cell membrane is a fluid mosaic of phospholipids, proteins, and cholesterol that regulates movement in and out of the cell. Cells are connected by specialized junctions: tight junctions prevent leakage between cells, desmosomes act as anchors to withstand mechanical stress, and gap junctions allow for direct communication via chemical or electrical signals. Major organelles include the nucleus (genetic control), mitochondria (energy production), ribosomes (protein synthesis), endoplasmic reticulum (transport/synthesis), and Golgi apparatus (packaging). Mechanisms of transport through the membrane include passive processes like diffusion and osmosis, which follow a concentration gradient, and active processes like active transport, endocytosis, and exocytosis, which require ATP to move substances against a gradient. The tonicity of surrounding solutions is crucial: an isotonic solution has no effect on cell volume, a hypertonic solution causes cell shrinkage, and a hypotonic solution causes cell swelling or lysis.
The cell cycle includes interphase and the mitotic phase. Mitosis is the process of nuclear division, consisting of prophase, metaphase, anaphase, and telophase, followed by cytokinesis. This process is significant for growth, tissue repair, and asexual reproduction. Protein synthesis follows the Central Dogma: DNA is transcribed into mRNA, which is then translated at the ribosome where tRNA brings specific amino acids to form a polypeptide chain. This chain is then folded in the ER and Golgi to form a functional protein. Complementary base pairing is vital during these stages to ensure the genetic code is accurately translated.
Cellular respiration is the process of generating ATP through three stages: glycolysis (in the cytosol), the Krebs cycle (in the mitochondrial matrix), and the Electron Transport Chain (on the inner mitochondrial membrane). ATP is produced via substrate-level phosphorylation (in glycolysis and Krebs) and oxidative-level phosphorylation (in the ETC). A single glucose molecule yielded approximately ATP. NAD+ and FAD act as electron carriers (hydrogen acceptors) that move high-energy electrons to the ETC. Oxygen serves as the final hydrogen acceptor at the end of the ETC, forming water. If oxygen is absent, the cell undergoes anaerobic respiration (fermentation), which produces significantly less ATP than aerobic respiration.
Tissue Level of Organization
Epithelial tissue is characterized by high cellularity, polarity, and an ability to regenerate, functioning primarily in protection, absorption, and secretion. Subtypes include simple squamous (diffusion in lungs), simple cuboidal (secretion in glands), simple columnar (absorption in gut), pseudostratified columnar (movement in respiratory tract), stratified squamous (protection in skin), and transitional (stretch in bladder). Glands are classified as exocrine, which use ducts to secrete onto surfaces, or endocrine, which secrete hormones directly into the bloodstream. Muscle tissue is divided into skeletal (striated, voluntary), cardiac (striated, involuntary, intercalated discs), and smooth (non-striated, involuntary). Nervous tissue contains neurons for signaling and neuroglia for support.
Connective tissue (CT) is the most abundant tissue type, consisting of cells and an extracellular matrix (fibers and ground substance). Classification is based on the density and arrangement of these components. Subtypes include dense regular (tendons), dense irregular (dermis), loose areolar (basement membranes), adipose (fat storage), and three types of cartilage: hyaline (joint surfaces), fibrocartilage (intervertebral discs), and elastic (ear). Cancer is the uncontrolled growth of cells, often caused by genetic mutations or environmental factors, and is classified by the tissue of origin (e.g., carcinoma for epithelium, sarcoma for connective tissue).
The Integumentary System
The skin consists of three main layers: the epidermis, the dermis, and the hypodermis. The epidermis is composed of stratified squamous epithelium divided into strata (basale, spinosum, granulosum, lucidum, and corneum). The dermis has a superficial papillary layer and a deep reticular layer, containing dense irregular connective tissue. The hypodermis is primarily adipose tissue that anchors the skin. Skin color is controlled by melanin, carotene, and hemoglobin, and changes in color can indicate clinical conditions like jaundice or cyanosis. Accessory structures include hair follicles and glands. Sudoriferous (sweat) glands include eccrine (thermoregulation) and apocrine (stress/puberty) types, while sebaceous (oil) glands lubricate the skin and hair. Skin cancer types, such as basal cell carcinoma, squamous cell carcinoma, and melanoma, are linked to epidermal damage. Burns are classified by depth: first-degree (epidermis), second-degree (epidermis and upper dermis), and third-degree (full-thickness).
Skeletal System: Structure, Function, and Growth
The skeletal system provides support, protection, movement, mineral storage (calcium), and blood cell formation (hematopoiesis). Bones are classified by shape (long, short, flat, irregular) or location (axial vs. appendicular). A typical long bone features a diaphysis (shaft) and epiphyses (ends), covered by periosteum and containing a medullary cavity with yellow or red marrow. Bone cells include osteoblasts (bone builders), osteocytes (mature cells), and osteoclasts (bone breakers). Bone tissue exists as compact (organized into osteons) or spongy (characterized by trabeculae). Bone develops through endochondral ossification (from cartilage) or intramembranous ossification (from membranes).
Bone growth occurs lengthwise at the epiphyseal plate until adulthood and diametrically (appositional growth) to increase thickness. Bone remodeling is a continuous process of deposition and resorption driven by hormonal signals. Calcitonin stimulates bone deposition by osteoblasts to lower blood calcium, while parathyroid hormone (PTH) stimulates osteoclasts to increase blood calcium via a negative feedback loop. Fractures are healed through a multi-stage process involving hematoma formation, callus formation, and remodeling. Osteoporosis is a condition characterized by high bone porosity and loss of mass, often prevented by diet and weight-bearing exercise.
Articulations and Joint Mechanics
Joints are classified functionally as synarthrotic (immovable), amphiarthrotic (slightly movable), and diarthrotic (freely movable). Structurally, they are fibrous (sutures), cartilaginous (symphyses), or synovial. A synovial joint contains a joint cavity, synovial fluid for lubrication, articular cartilage, and a joint capsule. These joints allow for a wide range of motion and shock absorption. Accessory structures like ligaments (bone to bone), tendons (muscle to bone), menisci (cartilage pads), and bursae (fluid sacs) provide stability and reduce friction. Disorders of the joints include sprains (torn ligaments), dislocations (displacement of bones), and arthritis. The three types of arthritis are osteoarthritis (wear and tear), rheumatoid arthritis (autoimmune), and gouty arthritis (uric acid crystals).
Muscle Tissue and Physiology of Contraction
Skeletal muscles are wrapped in connective tissue: epimysium covers the whole muscle, perimysium wraps bundles called fascicles, and endomysium surrounds individual fibers. A muscle cell, or myofiber, contains myofibrils made of myofilaments: thick (myosin) and thin (actin). The functional unit is the sarcomere, delimited by Z-lines. Muscle contraction is explained by the Sliding Filament Theory: Ca++ is released from the sarcoplasmic reticulum, binds to troponin, and moves tropomyosin to expose binding sites on actin. Myosin heads then form cross-bridges with actin, pulling them inward using ATP. Relaxation occurs when stimulus stops and Ca++ is pumped back into the sarcoplasmic reticulum. Muscle force is determined by motor unit recruitment and the frequency of stimulation. Fiber types range from slow-twitch (red, aerobic) to fast-twitch (white, anaerobic). Muscle metabolism utilizes ATP, creatine phosphate, and glycogen. Training can lead to hypertrophy (increased size) while disuse leads to atrophy.
Nervous Tissue and Principles of Neural Communication
The nervous system is organized into the Central Nervous System (CNS - brain and spinal cord) and Peripheral Nervous System (PNS). The PNS includes sensory (afferent) and motor (efferent) divisions, further divided into somatic and autonomic (sympathetic and parasympathetic) systems. Neurons are the signaling cells, supported by neuroglia like astrocytes, Schwann cells, and oligodendrocytes. A neuron at rest maintains a resting potential of approximately . Stimuli cause graded potentials which, if they reach a threshold, trigger an action potential involving depolarization (sodium entry) and repolarization (potassium exit). Saltatory conduction allows impulses to "leap" across myelinated nodes (Nodes of Ranvier), increasing speed. At the synapse, neurotransmitters are released to produce EPSPs (excitatory) or IPSPs (inhibitory) in the postsynaptic neuron. Integration occurs through temporal and spatial summation of these inputs.
The Central Nervous System: Brain and Spinal Cord
The brain is divided into regions including the cerebral cortex (higher thinking), brain stem (vital functions), and cerebellum (coordination). Gray matter contains cell bodies, while white matter contains myelinated tracts. The brain is protected by the meninges (dura, arachnoid, and pia mater), cerebrospinal fluid (CSF), and the blood-brain barrier. CSF flows from the choroid plexus through ventricles and is reabsorbed via arachnoid villi. Major brain systems include the Reticular Activating System (RAS) for alertness and the limbic system for emotion. The spinal cord features a central canal and white columns (funiculi) containing ascending sensory tracts and descending motor tracts. Spinal reflexes provide rapid, involuntary responses to stimuli through a reflex arc consisting of a receptor, sensory neuron, integration center, motor neuron, and effector.
Peripheral Nervous System and Sensory Physiology
The PNS includes pairs of cranial nerves and pairs of spinal nerves. Somatic senses originate from receptors classified by modality (chemoreceptors, mechanoreceptors, etc.) and location (exteroceptors, proprioceptors). Specific receptors include Meissner's corpuscles (touch), Pacinian corpuscles (pressure), and muscle spindles (stretch). Sensory information is sent to the CNS via action potentials where the brain decodes them based on the specific nerve path (projection) and internal mapping. Referred pain is a phenomenon where pain from a visceral organ is felt in a somatic area. Nerve regeneration in the PNS is possible if the cell body remains intact and Schwann cells provide a guide for repair. Spinal nerves are organized into plexuses (cervical, brachial, lumbar, sacral), and skin regions associated with specific spinal nerves are called dermatomes.
The Autonomic Nervous System
The ANS regulates involuntary body functions and consists of the sympathetic and parasympathetic divisions. The sympathetic system (thoracolumbar) is the "fight-or-flight" mechanism, using norepinephrine and adrenergic receptors to prepare the body for stress. The parasympathetic system (craniosacral) is the "rest-and-digest" mechanism, using acetylcholine and cholinergic (nicotinic or muscarinic) receptors for maintenance and energy conservation. Most organs have dual innervation, receiving input from both systems to balance function. The adrenal medulla plays a unique role in the sympathetic response by releasing epinephrine into the blood for a mass body effect. Autonomic disorders include hypertension (high blood pressure) and Raynaud’s disease (exaggerated vasoconstriction). Control of the ANS is primarily governed by the hypothalamus and cerebral cortex.
Sensory Organs: Vision, Audition, and Equilibrium
Vision involves the eye focusing light onto the retina via the lens (accommodation) and pupil. The retina contains photoreceptors: rods for dim light/peripheral vision and cones for color/sharpness concentrated in the fovea centralis. Visual signals travel to the brain via the optic nerve. Olfaction (smell) and gustation (taste) are chemical senses. Receptors in the olfactory epithelium detect odors, while taste buds on papillae detect five basic tastes: sweet, sour, salty, bitter, and umami. The ear is divided into the outer, middle (ossicles), and inner (cochlea and canals). Sound waves vibrate the tympanic membrane and move fluid in the cochlea, stimulating hair cells in the organ of Corti to create auditory signals. Equilibrium is maintained by the vestibular apparatus: the utricle and saccule handle static equilibrium (head position relative to gravity), while the semicircular canals handle dynamic equilibrium (rotational movement) via the crista ampullaris.