Introduction to Veterinary Anatomy and Physiology

Glossary of Anatomic Terms

Palmar (pahl-m\m{e}r)
Parietal layer (pah-r\bar{i}-eh-tahl\ l\bar{a}-\m{e}r)
Pastern (pahs-t\m{e}rn)
Physiology ( $fihz-\bar{e}-ohl-uh-j\bar{e}$ )
Plane of reference (pl\bar{a}n\ of\ rehf-\m{e}r-uhnz)
Plantar ( $plahn-tahr$ )
Pleura ( $ploor-ah$ )
Poll ( $p\bar{o}l$ )
Posterior (p\bar{o}-steer-\bar{e}-\m{e}r)
Proximal ( $prohck-sih-mahl$ )
Regional anatomy ( $r\bar{e}-juhn-ahl\ ah-naht-ah-m\bar{e}$ )
Rostral ( $rohs-trahl$ )
Sagittal plane ( $sahj-ih-tahl\ pl\bar{a}n$ )
Skeletal muscle ( $skehl-ih-tahl\ muhs-u</li></ul><h3 id="1b2392ba-7592-4393-a75e-bfe2ea5195d8" data-toc-id="1b2392ba-7592-4393-a75e-bfe2ea5195d8" collapsed="false" seolevelmigrated="true">Introduction to Anatomy and Physiology</h3><ul><li>Complexity and Fragility of Life<ul><li>Life is difficult, messy, fragile, and requires constant work.</li><li>Living animal bodies demand precise organization and maintenance within narrow limits to sustain life's processes.</li></ul></li><li>The Animal Body as a "Living Machine"<ul><li>Anatomy and physiology are essentially the study of the "animal machine," its components (cells, tissues, organs, systems), and how they function.</li><li>These living parts are intricate, with delicately interrelated functions.</li><li>Veterinary healthcare professionals must understand animal structure and function.</li><li>Normal anatomy and physiology are vital to animal health; deviations often lead to disease or death.</li><li>Health is not automatic but extraordinarily complicated, resulting from many factors working correctly.</li></ul></li></ul><h3 id="0f9375f0-a8c4-48e6-a204-80b34f33ce22" data-toc-id="0f9375f0-a8c4-48e6-a204-80b34f33ce22" collapsed="false" seolevelmigrated="true">Anatomy and Physiology: Complementary Studies</h3><ul><li>Definitions and Scope<ul><li>Anatomy: Deals with the form and structure of the body and its parts (what things look like and where they are located).</li><li>Physiology: Deals with the functions of the body and its parts (how things work and what they do).</li><li>While distinct, these subjects are best studied together for a complete understanding of the animal body.</li></ul></li><li>Approaches to Studying Anatomy<ul><li>Microscopic Anatomy: Focuses on structures so small that a microscope is needed, such as cells and tissues.</li><li>Macroscopic Anatomy (Gross Anatomy): Deals with body parts large enough to be seen with the unaided eye, including organs, muscles, and bones.</li><li>Submicroscopic Level: Occasionally explored to explain microscopic and macroscopic phenomena, including cell components, chemical molecules, and ions.</li><li>Regional Anatomy: Examines all components (cells, tissues, blood vessels, nerves, muscles, organs, bones) within a specific body region (e.g., the neck).<ul><li>Challenge: The body isn't always easily subdivided, leading to overlap between adjacent regions.</li></ul></li><li>Systematic Anatomy: Studies individual body systems (e.g., nervous system, skeletal system) as separate topics.<ul><li>Benefit: Allows clear, logical breakdown of the body and facilitates the description of interrelationships between systems.</li><li>This book adopts a systematic approach, including discussions on cells, epithelial and connective tissues, blood, lymph, and immunity.</li></ul></li></ul></li><li>Main Body Systems<ul><li>Skeletal: Bones and joints</li><li>Integumentary: Skin, hair, nails, and hooves</li><li>Nervous: Central nervous system and peripheral nerves</li><li>Cardiovascular: Heart and blood vessels</li><li>Respiratory: Lungs and air passageways</li><li>Digestive: Gastrointestinal tube and accessory digestive organs</li><li>Muscular: Skeletal, cardiac, and smooth muscle</li><li>Sensory: Organs of general and special sense</li><li>Endocrine: Endocrine glands and hormones</li><li>Urinary: Kidneys, ureters, urinary bladder, and urethra</li><li>Reproductive: Male and female reproductive structures</li></ul></li></ul><h3 id="b3b0cdfd-139f-465c-9817-e883efa241e3" data-toc-id="b3b0cdfd-139f-465c-9817-e883efa241e3" collapsed="false" seolevelmigrated="true">Anatomic Terminology</h3><ul><li>Need for Precision: Clear and accurate descriptions require terms that leave no ambiguity.</li><li>Limitations of Relative Terms: Words like "up," "down," "above," "below," and "beside" are unreliable because they depend on the animal's orientation or the observer's position.</li><li>Standardization: Anatomic terms must have consistent meaning irrespective of the animal's orientation or observer's position.</li><li>Basis of Terminology: Relies on imaginary slices through the body called planes and sets of directional terms with opposite meanings.</li></ul><h3 id="7ce98e72-26fb-4293-b948-3835b74d2ecf" data-toc-id="7ce98e72-26fb-4293-b948-3835b74d2ecf" collapsed="false" seolevelmigrated="true">Anatomic Planes of Reference</h3><ul><li>Four imaginary slices through the body, oriented at right angles to each other.</li><li>Sagittal Plane: Runs the length of the body, dividing it into left and right parts that are not necessarily equal halves.</li><li>Median Plane: A special sagittal plane that runs precisely down the center of the body lengthwise, dividing it into equal left and right halves (also called mid-sagittal plane).</li><li>Transverse Plane: A plane that cuts across the body, dividing it into cranial (head-end) and caudal (tail-end) parts that are not necessarily equal.</li><li>Dorsal Plane: A plane at right angles to both sagittal and transverse planes. It divides the body into dorsal (towards the animal's back) and ventral (towards the belly) parts that are not necessarily equal.<ul><li>Example: If an animal stands partially submerged in water, the water's surface describes a dorsal plane.</li><li>In humans, this plane is referred to as the frontal plane.</li></ul></li></ul><h3 id="3ae0ac6c-b957-42f7-a7df-8910000d53e0" data-toc-id="3ae0ac6c-b957-42f7-a7df-8910000d53e0" collapsed="false" seolevelmigrated="true">Radiography Positioning Terminology (Clinical Application)</h3><ul><li>Radiographs (x-rays): Two-dimensional images of internal body structures.</li><li>Description Method: Named according to the path the x-ray beam takes through the body, using anatomic directional terms.</li><li>Ventro-dorsal (VD) View: X-rays enter the ventral surface and exit the dorsal surface (e.g., animal lying on its back).</li><li>Dorso-palmar (DP) View: X-rays enter the dorsal surface and exit the palmar surface (e.g., a horse's front fetlock joint).</li><li>Lateral Radiographic Views: X-ray beam passes through the area of study from side to side.<ul><li>Named based on which side of the animal is closest to the film (e.g., a "right lateral view" means the animal's right side is closest to the film).</li></ul></li></ul><h3 id="9f0540cd-c2a7-4b3d-9bc5-faf9aef33312" data-toc-id="9f0540cd-c2a7-4b3d-9bc5-faf9aef33312" collapsed="false" seolevelmigrated="true">Directional Terms</h3><ul><li>Provide a standard language for describing body structures accurately, independent of the animal's position.</li><li>Generally occur in pairs with opposite meanings.</li><li>Left and Right: Always refer to the animal's own left and right sides.</li><li>Cranial: Towards the head (cranium).<ul><li>Human equivalent: Superior.</li><li>Example: A horse's shoulder is cranial to its hip.</li></ul></li><li>Caudal: Towards the tail (cauda).<ul><li>Human equivalent: Inferior.</li><li>Example: The xiphoid process is the caudal end of the sternum.</li></ul></li><li>Rostral: A specific term for positions/directions on the head only.<ul><li>Means towards the tip of the nose (rostrum).</li><li>Used because "cranial" loses meaning on the head itself.</li><li>"Caudal" still applies on the head, meaning towards the tail end of the animal.</li><li>Human equivalent: Nasal.</li><li>Example: An animal's eyes are rostral to its ears.</li></ul></li><li>Dorsal: Towards the back or top surface of a standing animal.<ul><li>Human equivalent: Posterior.</li><li>Retains meaning regardless of animal's position.</li><li>Example: A saddle is placed on the dorsal surface of a horse.</li></ul></li><li>Ventral: Towards the belly or bottom surface of a standing animal.<ul><li>Human equivalent: Anterior.</li><li>Retains meaning regardless of animal's position.</li><li>Example: The cinch of a saddle goes around the horse's ventral surface.</li></ul></li><li>Medial: Towards the median plane (towards the center line of the body).</li><li>Lateral: Away from the median plane.<ul><li>Example: The medial surface of a leg is closer to the body; the lateral surface is the outer surface.</li></ul></li><li>Deep (Internal): Towards the center of the body or a body part.</li><li>Superficial (External): Towards the surface of the body or a body part.<ul><li>Example: The deep digital flexor muscle is closer to the center of the leg than the superficial digital flexor muscle.</li></ul></li><li>Proximal: Towards the body, used only for extremities (legs, ears, tail).<ul><li>Example: The proximal end of the tail attaches to the body.</li></ul></li><li>Distal: Away from the body, used only for extremities.<ul><li>Example: The toes are on the distal end of the leg.</li></ul></li><li>Special Terms for Leg Surfaces (Distal Parts)<ul><li>Front Leg:<ul><li>Palmar surface: The back surface of the front leg from the carpus (wrist) distally.</li><li>Proximal to the carpus, this surface is referred to as caudal.</li><li>The front surface of the front leg is dorsal from the carpus distally and cranial proximal to the carpus.</li></ul></li><li>Hind Leg:<ul><li>Plantar surface: The back surface of the hind leg from the tarsus (ankle) distally.</li><li>Proximal to the tarsus, this surface is referred to as caudal.</li><li>The front surface of the hind leg is dorsal from the tarsus distally and cranial proximal to the tarsus.</li></ul></li></ul></li></ul><h3 id="bf064345-ffd7-4135-905b-ef1c98f0d847" data-toc-id="bf064345-ffd7-4135-905b-ef1c98f0d847" collapsed="false" seolevelmigrated="true">Common Regional Terms</h3><ul><li>Barrel: The trunk of the body, comprising the rib cage and the abdomen.</li><li>Brisket: The area at the base of the neck between the front legs, covering the cranial end of the sternum.</li><li>Cannon: The large metacarpal or metatarsal bone found in hoofed animals.</li><li>Fetlock: The joint in hoofed animals between the cannon bone (large metacarpal/metatarsal) and the proximal phalanx.</li><li>Flank: The lateral surface of the abdomen located between the last rib and the hind legs.</li><li>Hock: The tarsus.</li><li>Knee: The carpus of hoofed animals.</li><li>Muzzle: The rostral part of the face, primarily formed by the maxillary and nasal bones.</li><li>Pastern: The area of the proximal phalanx in hoofed animals.</li><li>Poll: The top of the head situated between the bases of the ears.</li><li>Stifle: The femorotibial/femoropatellar joint, equivalent to the human knee.</li><li>Tailhead: The dorsal part of the base of the tail.</li><li>Withers: The area located dorsally to the scapulas.</li></ul><h3 id="471de361-14d7-4f67-b942-7bd527ba0849" data-toc-id="471de361-14d7-4f67-b942-7bd527ba0849" collapsed="false" seolevelmigrated="true">General Plan of the Animal Body</h3><ul><li>Bilateral Symmetry<ul><li>The left and right halves of an animal's body are essentially mirror images of each other.</li><li>This principle reflects the basic inner and outer structure, although it is not absolute.</li><li>Paired structures (e.g., kidneys, lungs, legs) are approximate mirror images.</li><li>Single structures (e.g., brain, heart, gastrointestinal (GI) tract) are generally located near the center of the body, close to the median plane.<ul><li>The GI tract, despite being extensively folded, remains close to the median plane.</li></ul></li></ul></li><li>Body Cavities<ul><li>The animal body has two main cavities:<ul><li>Dorsal Body Cavity: Contains the central nervous system (brain and spinal cord).<ul><li>Cranial Cavity (Cranium): Spherical, located in the skull, houses and protects the brain.</li><li>Spinal Cavity (Spinal Canal): Long and narrow, formed by the vertebrae, houses and protects the spinal cord.</li></ul></li><li>Ventral Body Cavity: Much larger, contains most of the soft organs (viscera).<ul><li>Divided by the thin diaphragm muscle into:<ul><li>Cranial Thoracic Cavity (Thorax or Chest): Contains the heart, lungs, esophagus, and major blood vessels.<ul><li>Organs and cavity lined by the pleura.<ul><li>Visceral layer of pleura: Covers the thoracic organs.</li><li>Parietal layer of pleura: Lines the thoracic cavity.</li><li>A small amount of lubricating pleural fluid fills the potential space between these layers, allowing smooth movement during breathing.</li><li>Pleuritis (pleurisy): Inflammation of the pleural surfaces, causing painful scraping with each breath.</li></ul></li></ul></li><li>Caudal Abdominal Cavity (Abdomen): Contains digestive, urinary, and reproductive organs.<ul><li>Organs and cavity lined by the peritoneum.<ul><li>Visceral layer of peritoneum: Covers the abdominal organs.</li><li>Parietal layer of peritoneum: Lines the abdominal cavity.</li><li>A potential space with peritoneal fluid separates the layers.</li><li>Peritonitis: Painful inflammation of the peritoneum, often caused by a penetrating wound or a rupture/perforation of the GI tract; surgical care is critical to prevent leakage.</li></ul></li></ul></li></ul></li></ul></li></ul></li></ul></li></ul><h3 id="dc5e1e34-9095-4509-a67a-9209ba4cd99b" data-toc-id="dc5e1e34-9095-4509-a67a-9209ba4cd99b" collapsed="false" seolevelmigrated="true">Levels of Organization</h3><ul><li>Cells:<ul><li>The basic functional units of animal life and the smallest subdivisions capable of life.</li><li>In simple, single-celled organisms like an ameba, one cell performs all life functions.</li><li>In complex animals, cells specialize (e.g., intestinal lining for absorption, red blood cells for oxygen, nerve cells for control).</li><li>All cells are interdependent; the survival of one depends on all others, and vice versa.</li></ul></li><li>Tissues:<ul><li>Groups of specialized cells that work together.</li><li>The animal body is composed of four basic tissues:<ul><li>Epithelial Tissue:<ul><li>Characteristics: Composed entirely of cells.</li><li>Functions: Covers body surfaces (skin, linings of internal organs), secretes materials (forms glands like sweat, salivary, mammary glands), and absorbs materials (e.g., in the GI tract).</li></ul></li><li>Connective Tissue:<ul><li>Characteristics: Composed of living cells and nonliving intercellular substances (e.g., fibers).</li><li>Ranges from very soft (adipose tissue/fat) to very firm (cartilage, bone).</li><li>Functions: Holds the body together (connects cells) and provides structural support.</li></ul></li><li>Muscle Tissue:<ul><li>Functions: Responsible for moving the body, both internally and externally.</li><li>Types:<ul><li>Skeletal muscle: Moves the bones of the skeleton; under conscious (voluntary) nervous system control.</li><li>Cardiac muscle: Forms the heart; works automatically (involuntary).</li><li>Smooth muscle: Found in internal organs (e.g., digestive tract, urinary bladder); works automatically (involuntary).</li></ul></li></ul></li><li>Nervous Tissue:<ul><li>Characteristics: Composed of nerve cells (neurons) and supporting cells.</li><li>Functions: Transmits information throughout the body, controls body functions, processes sensory information, and sends instructions for reactions to changing conditions.</li></ul></li></ul></li></ul></li><li>Organs:<ul><li>Groups of different tissues that work together for common purposes (e.g., the kidney, which eliminates waste).</li><li>Can be paired (e.g., eyes, lungs, kidneys) or single structures (e.g., brain, heart, uterus).</li></ul></li><li>Systems:<ul><li>The most complex level of body organization.</li><li>Groups of organs involved in a common set of activities (e.g., the digestive system for nutrient acquisition, digestion, and absorption).</li></ul></li></ul><h3 id="1caad6c7-0277-4c37-8594-d1c3989bf896" data-toc-id="1caad6c7-0277-4c37-8594-d1c3989bf896" collapsed="false" seolevelmigrated="true">Health</h3><ul><li>Definition: Simply, health is a state of normal anatomy and physiology.</li><li>Disease: Results when the body's structures or functions become abnormal.</li><li>Interdependence: Maintaining health is a complex process where the health of the body as a whole depends on the proper functioning of each of its systems, organs, tissues, and cells, and vice versa. There is no isolation in bodily functions.</li><li>Diagram of Interrelationships: Body health$ \leftarrow $System health$ \leftarrow $Organ health$ \leftarrow $Tissue health$ \leftarrow$$ Cell health

Homeostasis

Analogy: Similar to driving a car, requiring active, continuous adjustments to stay on course.
Definition: The active maintenance of a dynamic equilibrium in the body.
- Dynamic: Implies activity, energy, and work.
- Equilibrium: Refers to balance.
Physiological Processes: All physiological processes collectively maintain balance in the body's structures, functions, and properties.
Examples of Regulation: Body temperature, acid-base balance, fluid balance, hormone levels, nutrient levels, and oxygen levels must be kept within fairly narrow operational ranges for normal body function.
Responsibility: Homeostasis is not controlled by one specific part but by the entire body; all body systems are involved.
Energy Requirement: Homeostatic mechanisms require significant energy and work.
Goal: To maintain a fairly constant internal environment in the body despite changing internal and external conditions.
Along with the normal functioning of cells, tissues, organs, and systems, homeostatic processes make life possible.

Homeostasis and Congestive Heart Failure (Clinical Application)

Congestive Heart Failure: A clinical condition where the heart is not pumping adequate amounts of blood, leading to congestion (abnormal fluid accumulation) upstream from the failing heart.
Homeostatic Response: The body's processes attempt to maintain normal blood circulation:
1. Initial Cascade: A drop in cardiac output (blood pumped per minute) leads to decreased blood flow and pressure.
2. Detection: Receptors in the vascular system detect this drop and relay information to the central nervous system (CNS).
3. Sympathetic Activation: The CNS sends signals to activate the sympathetic nervous system (the "fight-or-flight" system).
4. Compensatory Mechanisms (Short-term): The sympathetic system increases blood flow and pressure by stimulating the heart to beat harder and faster and by constricting blood vessels.
  - This temporarily brings blood flow and pressure back towards normal levels.
5. Detrimental Long-term Effects: These compensatory mechanisms force the already weak heart to work harder, further weakening it and causing more significant decreases in cardiac output.
6. Vicious Cycle: This leads to more sympathetic nervous system stimulation, perpetuating the cycle until the heart completely fails or medical intervention occurs.
Role of Homeostasis: While homeostatic mechanisms cannot correct the underlying heart defect, they do help maintain vital blood flow to the rest of the body for as long as possible.
Therapeutic Impact: Medical therapy, combined with the body's natural homeostatic mechanisms, can often extend and improve the quality of an animal's life with congestive heart failure.