Anatomy and Physiology

Anatomy and Physiology Defined

• Anatomy is the study of structure and form
• Physiology is the study of the function of body parts

Anatomy: Details of form

• Microscopic anatomy requires magnification and includes cytology and histology
• Cytology studies body cells and their internal structures
• Histology studies tissues
• Gross anatomy (macroscopic anatomy) examines visible structures and relationships, like intestines, stomach, brain, heart, and kidneys
  • Systemic anatomy: studies anatomy of each functional body system
  • Regional anatomy: examines structures in a particular region as a complete unit
  • Surface anatomy: focuses on superficial markings and related internal structures
  • Comparative anatomy: examines similarities and differences across species
  • Embryology: studies developmental changes from conception to birth
• Specialized anatomy branches aid in diagnosing conditions and advancing research, including pathologic and radiographic anatomy
• Pathologic anatomy examines anatomic changes resulting from disease
• Radiographic anatomy investigates internal structures via scanning procedures like ultrasound, MRI, or X-ray

Physiology: Details of Function

• Physiologists study organ system functions, often at the molecular or cellular level
• Sub-disciplines of physiology include cardiovascular, neuro-, respiratory, reproductive, and pathophysiology
• Cardiovascular physiology studies the heart, blood vessels, and blood
• Respiratory physiology studies respiratory gas exchange between the lungs and blood vessels

Reproductive and Patho- Physiology

• Reproductive physiology studies how reproductive hormones regulate cycles and influence sex cell production/maturation
• Pathophysiology investigates relationships between organ system function and disease/injury

Integration of Anatomy and Physiology

• Anatomy (form) and physiology (function) are interrelated sciences
• Anatomists require an understanding of structure function
• Physiologists require knowledge of the forms of structures

Characteristics of Living Things

• Shared properties of organisms include organization, metabolism, growth, development, responsiveness, regulation, and reproduction
• Organization refers to the body's complex hierarchical structure
• Metabolism includes all chemical reactions in the body, divided into anabolism and catabolism
• Anabolism builds larger molecules from smaller ones
• Catabolism breaks down large molecules into smaller ones
• Growth refers to the enlargement of an organism's size
• Development (differentiation) occurs as cells become specialized for specific functions like nerve cells
• Responsiveness is the ability to sense/react to stimuli
• Regulation maintains a constant internal environment (homeostasis) despite external changes
• Reproduction creates new cells for growth, maintenance, and repair
  • Sex cells are responsible for developing a new organism

Levels of Organization

• Anatomists and physiologists recognize several levels of increasing complexity
  • Chemical level: atoms and molecules (simplest)
  • Cellular level: cells as basic units of structure and function
    • Biochemical macromolecules like carbohydrates, lipids, proteins, and nucleic acids interface with chemical levels
    • Organelles are formed from cellular substructures
  • Tissue level: groups of similar cells with common functions
  • Organ level: two or more tissue types performing complex functions
  • Organ system level: organs working together for a common function
  • Organism level: all organ systems functioning together (highest level)

Introduction to Organ Systems

• Complex metabolic processes are divided into physiological tasks performed by organ systems
• Each system has a primary task reflected in its name
• Organ systems multi-task, performing vital secondary tasks in addition to their major function
• Tasks like acid/base balance are shared among organ systems such as the respiratory and renal systems, enhancing organization
• Some organs are included in more than one organ system due to their primary and secondary functions

Anatomic Position

• Anatomic position is a standardized reference point for anatomical descriptions
• The position involves standing erect, limbs at sides, palms facing anteriorly, and feet together at a 45-degree angle

Sections and Planes

• A section is an actual cut or slice through a structure
• A plane is an imaginary flat surface through the body
• The coronal (frontal) plane divides the body into anterior and posterior parts
• The transverse (horizontal) plane divides the body into superior and inferior parts
• The sagittal plane divides the body into right and left halves:
  • If halves equal, it is termed a midsagittal plane
  • Unequal halves sectioned is termed just sagittal
• Coronal, transverse, and sagittal planes are at 90-degree angles to each other
  • A plane cut at another angle is termed an oblique plane

Anatomic Directions

• Directional terms become relevant once the body is in the standard anatomic position
• Anterior: Towards the front surface of the body
• Posterior: Towards the back surface of the body
• Dorsal: Situated at the back side of the human body
• Ventral: Situated at the belly side of the human body
• Proximal: Closer to the point of attachment on appendages
• Distal: Farther from the point of attachment on appendages

Regional Anatomy

• The axial region (head, neck, trunk) and appendicular region (limbs attaching to the axial region) create the main partitions of the human body

Body Cavities and Membranes

• Internal organs/systems are housed in cavities named by surrounding bones or contained organs
• The main cavities are the posterior and ventral cavities
• The posterior body cavity is fully encased in bone and distinctly different from the ventral cavity.
• The posterior cavity divides into the endocranium (cranial cavity which is formed by the bones of the cranium) and vertebral (spinal cord) cavities
• The ventral cavity is large and anterior, containing thoracic and abdominopelvic cavities but does not fully encase organs
• Ventral cavities are lined by serous membranes, unlike posterior cavities
• A serous membrane is a continuous layer of cells composed of a parietal and visceral layer
• The parietal layer lines the body wall's internal surface
• The visceral layer covers the organ's external surface within a cavity
• The serous cavity is the potential space between parietal and visceral layers
  • Contains serous, oily lubricant produced by the membranes to reduce friction
• The thoracic cavity, a subdivision of the ventral cavity, contains:
  • mediastinum cavity (heart, thymus, esophagus, trachea, major blood vessels)
  • pericardial cavity (encloses the heart via pericardium)
    • parietal pericardium (outermost layer)
    • visceral pericardium (heart's external surface)
  • pleural cavities (lungs)
    • parietal layer (surrounds the internal surface of the thoracic wall)
    • visceral layer (covers the external surface of the lungs)
• The abdominopelvic cavity is another ventral cavity subdivision, separated from the thoracic cavity by the diaphragm
  • It divides into abdominal (digestive organs, kidneys, ureters) and pelvic (large intestine, ureter, bladder, reproductive organs) cavities
    • The division is at the level of the superior aspects of the hip bones
• The peritoneum, like pericardial and pleural membranes, lines the abdominopelvic cavity
• Parietal peritoneum (outermost layer) lines the cavity walls
• Visceral peritoneum (inner layer) covers abdominopelvic organs
• The peritoneal cavity is the potential space between visceral and parietal peritoneum, containing serous lubricating fluid

Abdominopelvic Regions and Quadrants

• The abdominopelvic cavity can be divided into smaller compartments for accurate location description
• Two methods exist: the nine compartment and the quadrant method
• The nine-compartment method includes umbilical, epigastric, hypogastric, right/left hypochondriac, right/left lumbar, and right/left iliac regions
• The quadrant method divides the abdomen into four quadrants via transverse and midsagittal planes passing through the umbilicus
  • Right/left upper and right/left lower quadrants are formed

Maintaining Homeostasis

• Homeostasis is maintaining a stable internal environment despite changing conditions

Components of Homeostatic Systems

• Homeostatic control systems maintain homeostasis, composed of a receptor, control center, and effector
• The receptor detects changes in a variable
• The stimulus is the variable change
• The control center interprets receptor input and initiates changes via the effector
• The effector alters the stimulus to bring the variable back to its optimal range
• Components form a dynamic control system known as the feedback loop
  • The loop operates by sending a stimulus to the receptor
  • Then receptor info is sent to the control center, which dictates change and sends it to effectors
  • Effectors bring the body back to homeostasis
• Two types of homeostatic control systems exist
  • One type reverses the stimulus
  • One type amplifies the stimulus

Feedback Loops

• Negative feedback opposes or reverses a stimulus to maintain a variable at a set point
• Most body processes are controlled by negative feedback. Temperature regulation is an example
• Temperature receptors in skin/blood send signals to the hypothalamus (control unit)
• The hypothalamus signals thermal effectors (blood vessels, sweat glands, skeletal muscles, hair follicle muscles)
• In cold environments:
  • Surface blood vessels constrict, reducing heat loss
  • Muscles shiver
  • Hair follicle muscles cause goosebumps
• In hot environments:
  • Blood vessels dilate
  • Muscles decrease motion
  • Sweat glands activate

Positive Feedback

• Positive feedback reinforces a stimulus until a climactic event occurs, then the body returns to homeostasis
• Breastfeeding exemplifies positive feedback:
  • The baby's suckling stimulates receptors in the nipple skin
  • Receptors signal the hypothalamus
  • The hypothalamus signals the anterior pituitary gland to release oxytocin (hormone)
  • Oxytocin goes to mammary glands (effectors), stimulating milk secretion
  • The intensity of suckling influences milk secretion
  • Cycle stops when the baby stops suckling

Homeostasis and Health

• Homeostatic imbalance results in disease
• Imbalances may occur due to normal aging
• Normal homeostatic ranges alter with aging
• Diagnosis identifies the cause of homeostatic imbalance
• Some drugs create homeostatic imbalance to treat disease
  • For example, SSRIs increasing serotonin to treat depression
• Some medications have side effects that adversely alter processes/chemical levels

Medical Imaging

• Medical imaging is a relevant clinical view
  • Radiography is used for the primary diagnosis of most body parts
  • Sonography (ultrasound) creates images of the body using sound
  • CT scans use sophisticated X-rays
  • Digital Subtraction Angiography is a 3D X-ray technique to observe blood vessels
  • Dynamic Spatial Reconstruction produces 3D moving images of organs
  • MRI provides non-invasive images of soft tissues using magnetic fields and radio waves
  • PET scans use radioactive tracers to analyze tissue metabolic activity

Anatomy studies body structure, while physiology studies the function of body parts. Microscopic anatomy looks inside cells and tissues needing magnification. Gross anatomy looks at the visible structure of major body parts.