Anatomy and Physiology Board Notes

Foundations of Anatomy and Physiology

Anatomy: The scientific study of the structures of the human body ("looks of something"). It examines individual body parts across all levels of structural organization.
Physiology: The scientific study of the functions of the human body (the "job/role of a structure that plays in the body"). It covers how body parts work across all levels of structural organization.
Principle of Complementarity: Structure dictates function ( $\text{Structure} = \text{Function}$ ). The specific shape, composition, and structure of a biological feature directly determine and limit the functional roles it can perform.
Cell Differentiation: The developmental process by which unspecialized stem cells become specialized cells with distinct physical structures and specialized physiological roles.
- Unspecialized stem cells possess no unique structural or functional features beyond basic cellular machinery.
- All cells, from the smallest to the largest, share a basic fundamental structure.
Levels of Structural Organization (from smallest/chemical level to largest/organismal level):
1. Atoms (Chemical Level): Individual chemical elements. Examples include iron ( $\text{Fe}$ ) and diatomic oxygen ( $\text{O}_2$ ).
2. Molecules: Chemical structures composed of two or more atoms bonded together. Categorized into:
  - Inorganic Molecules: Chemical compounds that do not contain carbon ( $\text{C}$ ).
  - Organic Molecules / Macromolecules: Carbon-containing molecules, including lipids, proteins, nucleic acids, and carbohydrates.
3. Cells: The fundamental and smallest functional units of life. The study of cells is called cytology. Example: skeletal muscle cell.
4. Tissues: A group of one specific type of cell working together to perform a shared function. The four major tissue types are:
  - Epithelial tissue
  - Muscle tissue (e.g., skeletal muscle tissue)
  - Nervous tissue
  - Connective tissue
5. Organs: A anatomical structure composed of a group of tissues. Organs usually contain more than one tissue type (and generally incorporate all four major tissue types). Example: deltoid muscle.
6. Organ Systems: Groups of more than one related organ that work in tandem to execute a major common body function. Example: skeletal muscle system, which functions in conscious movement.
7. Organism: A single, complete living entity. Example: a human.

Homeostasis and Feedback Mechanisms

Homeostasis: The ability of the body to maintain relatively stable, constant internal conditions ("where we are happiest to stay"), despite external changes occurring outside of the body.
Dynamic Equilibrium: Homeostasis is not static; it is a state of dynamic equilibrium where internal parameters are constantly moving and fluctuating within a narrow, safe range.
Efficiency Concepts:
- Structural Efficiency: Optimized spatial and structural layout requiring minimal energy and physical material.
- Functional Efficiency: Performing biological processes with reduced energy input ( $\text{less energy needed}$ ) while minimizing metabolic waste ( $\text{less waste}$ ).
The Five Components of Homeostasis and Feedback Loops:
1. Stimulus (plural: Stimuli): A specific change occurring in the external environment or within the internal levels of organization of the body.
2. Receptor(s): Specialized body parts or sensory cells that detect and sense the stimulus.
3. Control Center: The organ or structure (typically within the nervous system, such as the brain, or an endocrine gland) that evaluates the incoming sensory data and determines the appropriate response.
4. Effector(s): Body structures (such as muscle tissue or glands) that physically carry out the response dictated by the control center.
5. Response: The physical actions or physiological adjustments executed by effectors needed to return the body to homeostasis.
The Big Three Homeostatic Regulations:
- Thermoregulation: Maintenance of constant body temperature.
- Osmoregulation: Maintenance of precise internal water levels.
- Glucoregulation: Maintenance of proper blood sugar (glucose) concentration.
Thermoregulation Physiological Pathways:
- Response to Increased Ambient Temperature:
  - Stimulus: Increase in ambient temperature.
  - Receptor: Thermoreceptor cells located in the skin.
  - Control Center: Hypothalamus (part of the Central Nervous System).
  - Effector: Sweat glands.
  - Response / Action: Sweat glands produce sweat (water) that leaves the body, removing thermal energy via evaporative cooling.
- Response to Decreased Ambient Temperature:
  - Stimulus: Decrease in ambient temperature.
  - Receptor: Thermoreceptor cells located in the skin.
  - Control Center: Hypothalamus.
  - Effector: Muscle tissue (skeletal muscle).
  - Response / Action: Skeletal muscles contract rapidly (shivering), generating heat via contact exothermic reactions.
Mechanisms of Homeostatic Feedback Loops:
- Negative Feedback Loops:
  - Definition: Physiological pathways where the response lessens or decreases the strength of the original stimulus, bringing conditions back toward a set point.
  - Prevalence: The most common type of homeostatic loop in the body.
  - Dynamic Range: Fluctuates tightly around a set point (e.g., normal body temperature around $98.6^\text{o}\text{F}$ , operating within physiological bounds from $95^\text{o}\text{F}$ to $103^\text{o}\text{F}$ ).
- Positive Feedback Loops:
  - Definition: Physiological pathways where the process amplifies, accelerates, or increases the original stimulus ("more leads to more function").
  - Function: Allows processes to decisively start or stop rather than maintaining a steady state.
  - Examples:
    - Blood Clotting: Platelet aggregation triggers chemical cascades that attract progressively more platelets to seal a vessel break.
    - Childbirth / Labor: Uterine contractions stimulate oxytocin release, which causes progressively stronger and more frequent contractions until delivery is complete.
Homeostatic Imbalance, Illness, and Aging:
- Homeostatic Imbalance: A failure of internal homeostatic control systems to maintain stability, creating the potential for acute or chronic illness.
- Acute Illness: Short-term homeostatic disruption.
  - Example: Common cold (upper respiratory infection).
  - Pathological Pathway: Presence of a virus triggers the immune system to increase its response $\rightarrow$ causes inflammation in the nasal epithelium $\rightarrow$ results in pain, congestion, and increased mucus production $\rightarrow$ causes decreased respiratory capacity.
- Chronic Illness: Long-term, persistent homeostatic failure.
  - Example: Cancer, defined by uncontrolled cellular growth and division.
- Natural Aging: As the human organism ages, the natural ability to maintain homeostasis becomes progressively less efficient. Physiological changes include:
  - Reduced efficiency in thermoregulation.
  - Loss / reduction of subcutaneous fat.
  - Thinning of the epidermis.
  - Decrease in active muscle tissue (less active muscle mass).

Anatomical Terminology and Body Geometry

Standard Anatomical Position: The standardized, universal baseline reference position used when describing human body locations and structures:
- Body is standing erect ("erect").
- Face facing forward.
- Upper limbs at the sides with palms turned forward.
Body Postures in Recumbency:
- Supine: Laying down flat on the back, facing upward.
- Prone: Laying down flat on the belly, facing downward.
Directional Terms: Specialized terms used to describe the relative location of body parts with reference to other known anatomical structures. Presented in opposing pairs.
Midline: An imaginary vertical line extending down the center of the body, dividing it into approximately equal left ( $\text{L}$ ) and right ( $\text{R}$ ) halves.
Proximal and Distal: Directional terms used exclusively within the appendicular region (limbs) to indicate closeness or distance relative to the point of origin/attachment on the trunk.
Regional Terms: Specific terms that identify distinct anatomical regions of the body, typically named after a major internal or external structure present in that area.
Major Regions of the Body:
1. Axial Region: Central core of the body, consisting of the head, neck, and trunk.
2. Appendicular Region: The attached appendages, divided into upper extremities (arms) and lower extremities (legs).
- Boundary Landmarks: The axillary (armpit) and inguinal (groin) regions represent the points where the axial region ends and the appendicular appendages attach.
Body Planes: Imaginary two-dimensional cuts or flat surfaces used to divide the body into three-dimensional sections:
- Sagittal Plane: Vertical plane dividing the body into left ( $\text{L}$ ) and right ( $\text{R}$ ) portions.
  - Midsagittal Plane: Division occurring precisely along the midline, creating equal left and right halves.
  - Parasagittal Plane: Division occurring parallel to the midline or at an angle, creating unequal left and right portions.
- Coronal (Frontal) Plane: Vertical plane dividing the body into anterior (front) and posterior (back) sections.
- Transverse Plane: Horizontal plane dividing the body into superior (upper) and inferior (lower) sections.

Macromolecules and Biochemistry

Macromolecules: Large, complex organic molecules constructed from repeating subunit molecules called monomers.
Biological Interaction with Water ( $\text{H}_2\text{O}$ ):
- Polar / Hydrophilic: Chemical property meaning "loves $\text{H}_2\text{O}$ ". Polar molecules dissolve easily in water and move easily throughout aqueous fluid environments.
- Non-polar / Hydrophobic: Chemical property meaning "hates $\text{H}_2\text{O}$ ". Non-polar molecules do not dissolve in water and struggle to move through aqueous environments.
Carbohydrates (Polysaccharides):
- Monomer: Saccharide / Monosaccharide.
- Chemical Structure: Polar / Hydrophilic.
- Primary Function: Provides quick, immediate cellular energy.
- Storage: Stored for short time periods (measured in hours). In human tissues, carbohydrates are stored as glycogen within liver cells and skeletal muscle cells.
Lipids (Fats, Oils, and Waxes):
- Monomers: Fatty acids and glycerol.
- Chemical Structure: Non-polar / Hydrophobic.
- Primary Functions: Long-term energy storage, thermal insulation, and mechanical cushioning around internal body organs.
- Adipose Tissue Types:
  - Subcutaneous Fat: Fat layer located directly beneath the skin; functions in thermal insulation and energy storage.
  - Visceral Fat: Fat tissue surrounding internal organs; functions primarily in structural protection and cushioning.
- Specialized Lipid Subclasses:
  - Phospholipids: Structural components that construct cell membranes. Built with a polar, hydrophilic phosphate "head" and non-polar, hydrophobic fatty acid "tails".
  - Steroids: Non-polar, hydrophobic lipid structures usually synthesized from cholesterol. Function as hormones (signaling molecules that carry physiological messages through the body; e.g., testosterone).
Proteins (Polypeptides):
- Monomer: Amino acids.
- Chemical Structure: Variable structure that depends directly on the unique variable R-group (side chain) attached to each amino acid.
- Primary Functions: Highly versatile functions determined entirely by the unique R-group composition, including functioning as enzymes, structural framework, and transport/message molecules.
- Biological Significance: Most functional processes in the human body are controlled directly by proteins. They act as biological catalysts, accelerating biochemical reactions.