Canine Splanchnology and Anatomy Flashcards

Introduction to Splanchnology and Body Viscera

• Definitions and Etymology:

  • Splanchnology: The branch of anatomy dealing with the study of the viscera belonging to the digestive, respiratory, and urogenital systems.

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  • Etymology: Derived from the Greek word Splanchnon, meaning "internal organ" or "entrails."

  • Viscera: Plural form (viscus is singular), rooted in Latin meaning "an internal organ, entrails." Describes organs contained within body cavities.

• General Characteristics of Viscera:

  • Each splanchnic system consists of a tube or tract lined with mucous membrane that communicates with the exterior at one or both ends.

  • Viscera are prominent within body cavities and are surrounded by, and (if hollow) lined by, specialized tissue layers.

• Classification of Viscera:

  • Hollow Viscera: Organs containing cavities (e.g., stomach, intestines, urinary bladder).

  • Solid Viscera: Organs lacking cavities (e.g., liver, pancreas, kidneys).

• Anatomical Systems Summary:

  • Skeletal system: Study is Osteology; chief structures are Bones.

  • Articular system: Study is Arthrology; chief structures are Joints.

  • Muscular system: Study is Myology; chief structures are Muscles.

  • Digestive system: Study is Splanchnology; chief structures are Stomach and intestines.

  • Respiratory system: Study is Splanchnology; chief structures are Lungs and airways.

  • Urinary system: Study is Splanchnology; chief structures are Kidneys and urinary bladder.

  • Reproductive system: Study is Splanchnology; chief structures are Ovaries and testes.

  • Endocrine system: Study is Endocrinology; chief structures are Ductless glands.

  • Nervous system: Study is Neurology; chief structures are Brain, spinal cord, and nerves.

  • Circulatory system: Study is Cardiology; chief structures are Heart and vessels.

  • Sensory system: Study is Esthesiology; chief structures are Eye and ear.

Body Cavities and Boundaries

• Body Trunk Zones by Size:

  1. Abdominal Cavity / Abdomen: The largest body cavity.

  2. Thoracic Cavity / Thorax: The second largest body cavity.

  3. Pelvic Cavity / Pelvis: The smallest body cavity.

Thoracic Cavity Anatomy

• Definition & Contents:

  • Space located inside the chest, bounded by structural boundaries and housing the lungs, heart, pleura (lung membranes), pleural cavities, pericardium (heart sac), and pericardial cavity.

• Thoracic Cavity Boundaries:

  • Cranial: Thoracic inlet (cranial thoracic opening).

  • Dorsal: Thoracic vertebral bodies.

  • Ventral: Sternum.

  • Caudal: Diaphragm.

• Thoracic Inlet (Cranial Thoracic Opening):

  • Opening at the front of the thoracic cavity.

  • Formed by: First pair of ribs, first thoracic vertebra ($T1$), and the manubrium (first part of the sternum).

• Diaphragm:

  • Dome-shaped muscle at the caudal end of the thoracic cavity separating it from the abdominal cavity.

  • Serves as the main muscle used for respiration.

  • Innervated by the phrenic nerve.

  • Diaphragmatic Openings (3 Major Hiatuses):

    1. Aortic Hiatus: The most dorsal opening; contains the aorta, azygous vein, and thoracic duct.

    2. Oesophageal Hiatus: Contains the esophagus, as well as the dorsal and ventral vagal trunks.

    3. Caval Foramen: Located within the central tendinous region; contains the caudal vena cava. Fused directly to the vessel wall, preventing movement of the vessel during diaphragmatic contraction.

Pelvic Cavity, Diameters, and Fetal Presentation

• Pelvic Cavity Boundaries:

  • Space bounded dorsally by the sacrum and the first two caudal vertebrae, and laterally/ventrally by the two hip bones (ossa coxarum).

  • Contains the rectum, anal canal, and the pelvic parts of the reproductive and urinary viscera.

• Pelvic Inlet (Cranial Pelvic Aperture):

  • Dorsal border: Sacral promontory.

  • Lateral border: Arcuate line.

  • Ventral border: Pecten of pubis.

• Pelvic Outlet (Caudal Pelvic Aperture):

  • Dorsal border: 3rd–4th caudal vertebrae.

  • Lateral border: Sacrotuberous ligament and associated muscles.

  • Ventral border: Ischiatic arch.

• Pelvic Diameters:

  • Conjugate diameter: Measured from sacrum to pubis.

  • Transverse diameter: Measured across the widest width of the pelvic cavity.

• Fetal Presentations in Dogs (Obstetrics):

  • Anterior Presentation: Head first with head and forepaws extended; ideal for natural birth (normal in the bitch).

  • Posterior Presentation: Tail and hind legs emerging first; also considered normal in the bitch.

  • Breech Presentation: Hips/rump presented first with hind legs folded forward (not stretched out); abnormal. Complications are minimal if expelled rapidly, but continuous straining without progress requires immediate veterinary intervention.

  • Two Front Legs Presentation: Complex presentation requiring veterinary assistance.

Overview of the Digestive System

• Functional Definition:

  • Responsible for breaking down food into smaller chemical components for energy, growth, and cellular renewal via mechanical (churning) and chemical (gastric acid $HCl$ and pepsin) processes.

• Dietary Classifications:

  • Herbivores: Consume only plant material.

  • Omnivores: Consume both plant material and animal tissues.

  • Carnivores: Consume exclusively animal tissue.

• Alimentary Segments & Subdivisions:

  • Digestive Tube: Mouth $\rightarrow$ Oropharynx $\rightarrow$ Esophagus $\rightarrow$ Stomach $\rightarrow$ Small Intestine $\rightarrow$ Large Intestine $\rightarrow$ Anus.

  • Digestive Glands: Salivary glands, liver, gallbladder, pancreas.

  • Accessory Digestive Organs: Lips, tongue, cheeks, palate.

Anatomy of the Oral Cavity, Lips, and Cheeks

• Oral Cavity (Cavum Oris) Boundaries:

  • Divided into the oral vestibule and oral cavity proper. Represents the first segment of the alimentary canal.

  • Dorsal: Hard and soft palates.

  • Lateral: Cheeks and dental arches.

  • Ventral: Body of the mandible and hyoid muscles.

• Skeletal Contributions:

  • Upper jaw formed by incisive bone and maxilla.

  • Roof formed by palatine bone (hard palate).

  • Lower jaw formed by paired mandibles joined at the mandibular symphysis; articulates with temporal bones at the temporomandibular joint (TMJ).

• Diastema:

  • Toothless gap between canine teeth and cheek teeth; narrow in dogs compared to herbivores (cattle, horses).

• Functions of the Oral Cavity:

  1. Prehension: Grasping food using lips and tongue.

  2. Mastication: Chewing/breaking food into boluses using teeth, tongue, and cheeks.

  3. Lubrication: Secretion of mucus and saliva.

  4. Digestion: Carbohydrate digestion via salivary amylase in omnivores/herbivores (absent in carnivores like dogs/cats due to brief oral retention time).

• Lips (Labia Oris) & Cheeks (Buccae):

  • Lips bound the oral fissure (labium superius and labium inferius meet at angulus oris). Upper lips in dogs are pendulous and termed flews (especially long in hounds, bulldogs, bloodhounds).

  • Philtrum: Central groove on the hairless area of the upper lip/muzzle.

  • Cheeks form caudal lateral walls of the vestibule; small in dogs due to wide mouth opening. Extends medial to masseter muscles to buccinator muscle attachments.

Gingiva (Gums) Structure and Clinical Indicators

• Anatomy & Functions:

  • Firm, pink mucous membrane covering alveolar bone of maxilla and mandible, supporting and sealing teeth against bacterial invasion.

  • Parts: Free (Marginal) Gingiva (forms gingival sulcus), Attached Gingiva (immobile layer resisting chewing forces), Interdental Gingiva / Papilla (fills space between adjacent teeth).

• Gum Color Diagnostic Guide:

  • Bubblegum Pink: Normal, healthy state.

  • Bright Red: Indicates infection or active oral inflammation.

  • Cherry Red: Indicates toxin exposure, heatstroke, or severe high blood pressure.

  • Yellow / White (Pale): Signals anemia, red blood cell destruction, clotting disorders, liver, or heart disease.

  • Purple / Grey / Blue: Indicates cyanosis/low oxygen levels, severe hypothermia, or heart failure.

  • Brown / Black Spots: Normal pigmentation in specific breeds; new dark spots may indicate oral neoplasia/cancer or viral lesions.

• Clinical Pathology:

  • Gingivitis: Plaque-induced mucosal inflammation.

  • Periodontitis: Advanced inflammation destroying supporting bone and periodontal ligaments. Most common oral disease in adult dogs.

Hard and Soft Palate Anatomy

• Hard Palate (Palatum Durum):

  • Forms bony rostral partition between oral and nasal cavities.

  • Bony base formed by: Horizontal plate of palatine bone, palatine process of maxilla, and palatine process of incisive bone.

  • Features 6 to 10 transverse palatine rugae (mucosal ridges) divided symmetrically by a median palatine raphe (forms a crest in dogs, a groove in horses/ruminants). Widest at the 4th upper cheek tooth (carnassial).

  • Incisive Papilla: Small median swelling caudal to central incisors; features openings for incisive ducts communicating with the vomeronasal organ (Jacobson's organ) for sexual olfactory perception.

• Soft Palate (Palatum Molle / Velum Palatinum):

  • Muscular, flexible caudal continuation of the palate that closes off the nasopharynx during swallowing.

• Clinical Import - Elongated Soft Palate:

  • Common component of Brachycephalic Airway Syndrome in short-nosed breeds (English Bulldog, Pug, Pekingese, Shar Pei).

  • Tissue extends over the epiglottis into the laryngeal opening, obstructing airflow, producing snorting/snoring, and severely limiting panting ability (high risk for heat stroke). Treated via surgical excision/laser resection.

Tongue Anatomy, Papillae, and Musculature

• General Anatomy & Regions:

  • Muscular organ composed of intrinsic and extrinsic striated muscle bundles attached to hyoid bone and mandibles.

  • Divided into: Root (caudal third), Body (slender middle portion), and Apex (free spatula-shaped rostral tip).

  • Lingual Frenulum: Ventral median mucosal fold anchoring tongue to oral floor.

  • Lyssa: Specific rod-shaped fusiform spicule of fibrous tissue, adipose tissue, striated muscle, and cartilage running ventrally in the apex of carnivore tongues. Innervated by hypoglossal nerve (CN XII).

• Functional Lingual Papillae:

  • Mechanical Papillae (No Taste Buds):

    • Filiform: Smallest, most numerous; covers rostral $2/3$ of dorsal surface. Functions in prehension and grooming. (In cats: hyper-keratinized, backward-pointing spines acting as hooks to scrape meat and groom).

    • Conical: Larger, less frequent; located at caudal $1/3$ (root). Directs food toward pharynx.

    • Marginal: Present along rostral margins in newborn puppies to facilitate suckling; regresses upon conversion to solid food.

  • Gustatory Papillae (Contain Taste Buds):

    • Fungiform: Mushroom-shaped structures scattered among filiform papillae on apex and body.

    • Vallate (Circumvallate): Largest, least numerous (typically 4–6 arranged in a V-shaped row rostral to root); surrounded by a deep circular trench.

    • Foliate: Leaf-shaped ridges situated on lateral caudal margins.

• Tongue Musculature & Innervation:

  • Intrinsic Muscle: Propria linguae (dorsal/ventral longitudinal, transverse, vertical bundles); alters tongue shape and prevents self-biting.

  • Extrinsic Muscles (Paired):

    1. Genioglossus (Medial): Originates from mandibular symphysis; depresses tongue; caudal fibers protract, rostral fibers retract apex.

    2. Hyoglossus (Lateral): Originates from thyrohyoid and basihyoid; retracts and depresses tongue.

    3. Styloglossus (Lateral): Originates from stylohyoid bone via 3 heads (short, rostral, long); retracts and elevates tongue.

  • Innervation: Motor control via Hypoglossal nerve (CN XII). Sensory/taste via CN V (Trigeminal), CN VII (Facial), CN IX (Glossopharyngeal), and CN X (Vagus).

Salivary Glands Classification and Histology

• Major Salivary Glands:

  1. Parotid Gland: Located near ear; duct opens into upper buccal vestibule opposite upper 4th premolar ($P4$).

  2. Zygomatic Gland: Present in carnivores; situated medial to zygomatic arch; duct opens near last upper molar.

  3. Mandibular Gland: Located caudal to lower jaw angle; duct opens at sublingual caruncle.

  4. Sublingual Gland: Situated beneath tongue; divided into Monostomatic (duct opens at sublingual caruncle) and Polystomatic (multiple minor ducts opening directly into oral floor).

• Minor Salivary Glands:

  • Includes Labial, Buccal (prominent in cats caudal to last lower molar), Molar, Lingual, and Palatine glandular tissue.

• Histological Distribution in Tongue:

  • Serous glands (gustatory glands) surround bases of vallate and foliate papillae.

  • Mucoserous glands predominate in caudal third lingual mucosa; Seromucous glands populate lateral submucosa.

Pharynx Subdivisions, Openings, and Musculature

• Pharyngeal Subdivisions:

  1. Nasopharynx: Respiratory channel located dorsal to soft palate, extending from choanae to palatopharyngeal arch.

  2. Oropharynx: Digestive channel located ventral to soft palate, extending from isthmus faucium to epiglottis base.

  3. Laryngopharynx: Shared pathway caudal to soft palate and dorsal to larynx, terminating at pharyngoesophageal limen.

• Five Pharyngeal Openings:

  1. Choanae: Rostrodorsal pair connecting nasopharynx to nasal cavity.

  2. Pharyngeal Openings of Auditory Tubes (Eustachian Tubes): Dorsolateral openings to middle ears.

  3. Isthmus Faucium: Opening between oral cavity proper and oropharynx.

  4. Aditus Laryngis: Entrance into larynx, sealed by epiglottis during deglutition.

  5. Aditus Esophagi: Caudal entrance into esophagus.

• Pharyngeal Musculature Functional Classification:

  • Rostral Constrictors: Pterygopharyngeus (shortens/constricts rostral pharynx) and Palatopharyngeus (draws pharynx forward/upward).

  • Middle Constrictor: Hyopharyngeus (composed of Chondropharyngeus and Ceratopharyngeus; constricts mid-pharynx).

  • Caudal Constrictors: Thyropharyngeus and Cricopharyngeus (constrict caudal pharynx; cricopharyngeus acts as upper esophageal sphincter).

  • Pharyngeal Dilator: Stylopharyngeus (dilates, elevates, and draws pharynx rostrally).

• Deglutition (Swallowing) Stages:

  1. Voluntary Stage: Tongue forces bolus into oropharynx.

  2. Involuntary Reflex Stage: Soft palate elevates to block nasopharynx; larynx moves rostrally; epiglottis covers aditus laryngis; pharyngeal constrictors propel bolus into relaxed esophagus.

Dental Anatomy, Formulae, and Classification

• Structural Composition of Brachydont Teeth:

  • Pulp: Soft vascular/nervous central core occupying pulp chamber and root canal.

  • Dentine (Dentinum): Calcified tissue with vertical mineralized tubules surrounding pulp; capable of limited repair. Thermal/fluid movement conveys pressure sensitivity.

  • Enamel: Ultra-dense outer covering of crown ($96\%$ inorganic hydroxyapatite); hardest substance in body; cannot regenerate.

  • Cementum: Thin layer covering dentine of roots; anchors periodontal ligament fibers.

  • Anatomical Zones: Crown (above gum line), Root (below gum line), Cervix/Neck (cementoenamel junction).

• Dental Surfaces:

  • Vestibular (Labial/Buccal): Facing lips/cheeks.

  • Lingual / Palatal: Facing tongue (lower jaw) or hard palate (upper jaw).

  • Contact (Mesial / Distal): Adjacent tooth surfaces; Mesial (toward midline/rostral), Distal (away from midline/caudal).

  • Occlusal: Masticatory contact surface.

• Specialized Teeth & Features:

  • Diphyodont: Developing two sequential sets of teeth (deciduous vs. permanent).

  • Cingulum: V-shaped ridge on lingual surface of incisors.

  • Carnassial / Sectorial Teeth: Shearing teeth represented by the Upper 4th Premolar ($P4$) and Lower 1st Molar ($M1$).

• Permanent Dental Root Structure (Dog):

  • Maxilla: Incisors ($1$ root), Canine ($1$ long root), $P1$ ($1$ root), $P2$ ($2$ roots), $P3$ ($2$ roots), $P4$ ($3$ roots: 2 buccal, 1 palatal), $M1$ ($3$ roots), $M2$ ($3$ roots).

  • Mandible: Incisors ($1$ root), Canine ($1$ long root), $P1$ ($1$ root), $P2$ ($2$ roots), $P3$ ($2$ roots), $P4$ ($2$ roots), $M1$ ($2$ roots), $M2$ ($2$ roots), $M3$ ($2$ roots).

• Dental Formulae:

  • Canine Permanent:         $2 \times \left( \text{I} \frac{3}{3}, \text{C} \frac{1}{1}, \text{PM} \frac{4}{4}, \text{M} \frac{2}{3} \right) = 42$ total teeth.

  • Canine Deciduous:         $2 \times \left( \text{I} \frac{3}{3}, \text{C} \frac{1}{1}, \text{PM} \frac{3}{3} \right) = 28$ total teeth. (Lacks premolar 1 and all molars).

• Modified Triadan Numbering System:

  • Quadrants: Right Upper = $100$ ($500$ deciduous), Left Upper = $200$ ($600$ deciduous), Left Lower = $300$ ($700$ deciduous), Right Lower = $400$ ($800$ deciduous).

  • Teeth numbered mesial to distal ($01$ to $11$). E.g., Permanent Left Upper Canine = $204$; Deciduous Left Upper Canine = $604$.

• Eruption Timeline (Dog):

  • Deciduous: Incisors ($3\text{--}4$ weeks), Canines ($3$ weeks), Premolars ($4\text{--}12$ weeks).

  • Permanent: Incisors ($2\text{--}5$ months), Canines ($4\text{--}6$ months), Premolars ($4\text{--}6$ months; $P1$ at $4\text{--}5$ months), Molars ($5\text{--}7$ months).

Esophagus Structure and Histology

• Topography & Course:

  • Muscular tube (~$30\text{ cm}$ long, $2\text{ cm}$ diameter collapsed in medium dogs) connecting laryngopharynx to cardiac sphincter of stomach.

  • Courses dorsal to trachea, shifts to the left side of neck, traverses thoracic cavity, passes through diaphragmatic esophageal hiatus at $T10$ level, terminates at cardia.

• Sphincters & Landmarks:

  • Upper Esophageal Sphincter (UES): Formed by cricopharyngeus muscle.

  • Lower Esophageal Sphincter (LES / Cardiac Sphincter): Controls entry to stomach.

  • Limen pharyngoesophageum: Internal mucosal ridge marking pharyngoesophageal junction.

• Species Muscular Composition:

  • Dog: Muscular coat consists of $100\%$ striated muscle throughout its entire length.

  • Cat: Cranial $2/3$ is striated muscle; caudal $1/3$ converts to smooth muscle.

• Histological Layers (Outside to Inside):

  1. Tunica Adventitia: Dense fibrous connective tissue (cervical/thoracic regions).

  2. Tunica Muscularis: Inner circular and outer longitudinal muscle layers.

  3. Tela Submucosa: Loose CT with blood vessels, nerves, and mucosal glands.

  4. Tunica Mucosa: Folded stratified squamous epithelium.

Stomach Structure, Divisions, and Layers

• Gross Topography & Capacity:

  • Simple, musculoglandular organ located in left cranial abdomen. Capacity ranges from $100\text{ to }250\text{ cc}$ per kg body weight (average empty weight $100\text{ g}$ in a $15\text{-kg}$ dog).

• Anatomical Divisions:

  • Cardia: Smallest region immediately surrounding esophageal orifice.

  • Fundus: Blind outpocketing dorsal and to the left of cardia.

  • Body: Large central mixing chamber.

  • Pyloric Part: Distal third divided into thin-walled Pyloric Antrum, Pyloric Canal, and muscular Pylorus (sphincter). Separated from body by the angular incisure ($50\text{--}70^\text{o}$ notch).

• Curvatures & Omenta:

  • Greater Curvature: Long convex border (~$30\text{ cm}$); gives attachment to greater omentum.

  • Lesser Curvature: Short concave border; gives attachment to lesser omentum.

• Histological Layers of Stomach Wall (Outside to Inside):

  1. Serosa (Tunica Serosa): Visceral peritoneum.

  2. Muscularis (Tunica Muscularis): 3 smooth muscle layers — Outer longitudinal, Middle circular, and Inner oblique (unique churning layer). Forms cardiac and pyloric sphincters.

  3. Submucosa (Tela Submucosa): Vascularized dense connective tissue.

  4. Mucosa (Tunica Mucosa): Simple columnar mucous epithelium featuring internal folds (rugae) and gastric glands secreting $HCl$, pepsinogen, gastrin, and protective mucus.

Small Intestine: Duodenum, Jejunum, and Ileum

• General Features:

  • Longest alimentary segment ($3.5 \times$ body length in live animals). Suspended from dorsal abdominal wall by mesentery.

• Duodenum:

  • Fixed proximal segment (~$25\text{ cm}$ / $10\text{ inches}$ long) attached by mesoduodenum.

  • Divided into 4 parts: Cranial, Descending (right side), Transverse (caudal), and Ascending portions. Features Cranial and Caudal duodenal flexures, ending at the duodenojejunal flexure.

• Jejunum:

  • Longest, highly mobile middle segment forming extensive sagittal/transverse coils in ventrocaudal abdomen. Supported by mesojejunum and supplied by cranial mesenteric artery.

• Ileum:

  • Short terminal segment (~$10\text{ cm}$ long), firmer and more muscular. Courses cranially on right side of mesenteric root to join ascending colon at the ileocolic orifice. Demarcated from jejunum by the ileocecal fold.

Large Intestine: Cecum, Colon, Rectum, and Anus

• General Characteristics:

  • Short, simple tube (~$2\text{ cm}$ diameter, ~$25\text{ cm}$ long in Beagles). Lacks haustra, tenia, or spiral folds. Dehydrates fecal waste.

• Cecum:

  • Comma/S-shaped blind pouch located in right dorsal abdomen. Exists as a diverticulum of ascending colon, communicating via the cecocolic sphincter/orifice.

• Colon:

  • Suspended by mesocolon in a question-mark (?) orientation:

    • Ascending Colon: Short, right-sided.

    • Transverse Colon: Passes right-to-left cranial to root of mesentery.

    • Descending Colon: Longest part, left-sided, extending to pelvic inlet.

  • Flexures: Right colic flexure (between ascending/transverse); Left colic flexure (between transverse/descending).

• Rectum & Anal Canal:

  • Rectum: Straight pelvic segment (~$5\text{ cm}$ long, $3\text{ cm}$ diameter) suspended by mesorectum.

  • Anal Canal: Short terminal segment (~$1\text{ cm}$ long) lined by stratified squamous epithelium.

Defecation Reflex and Anal Sacs

• Anal Sphincters:

  • Internal Anal Sphincter: Involuntary smooth muscle thickening of circular coat; supplied by autonomic nerves.

  • External Anal Sphincter: Voluntary striated muscle surrounding internal sphincter; innervated by pudendal nerve (caudal rectal branch).

• Anal Sacs (Sinus Paranalis):

  • Paired cutaneous invaginations located ventrolateral to anus at 4 o'clock and 8 o'clock positions between internal and external sphincters.

  • Lined with inner sebaceous/sweat glands producing foul-smelling secretion expressed during defecation for territorial marking.

• Defecation Reflex Sequence:

  1. Rectal distension activates stretch receptors.

  2. Afferent impulses travel via sacral nerves ($S1\text{--}S3$).

  3. Parasympathetic pelvic nerves cause rectal contraction and internal sphincter relaxation.

  4. Pudendal nerve mediates voluntary control over external sphincter.

  5. Abdominal muscle contraction increases intra-abdominal pressure, expelling feces.

Liver Anatomy, Lobes, and Peritoneal Attachments

• Physical Characteristics & Location:

  • Largest gland in body; dark red, firm, friable. Positioned immediately caudal to diaphragm in thoracic abdomen (diaphragmatic surface contacts ribs 6–12 on right, rib 10 on left).

• Four Major Lobes & Subdivisions:

  1. Left Hepatic Lobe: Makes up $1/3\text{ to }1/2$ of mass; divided into Left Lateral and Left Medial lobes.

  2. Right Hepatic Lobe: Divided into Right Medial (contains gallbladder fossa) and Right Lateral lobes.

  3. Caudate Lobe: Divided into Papillary Process (tongue-shaped, fits into stomach lesser curvature) and Caudate Process (caps cranial pole of right kidney, forming deep renal impression at rib 12).

  4. Quadrate Lobe: Medial wedge between right medial and left medial lobes, forming left boundary of gallbladder fossa.

• Porta Hepatis: Hilus on visceral surface where portal vein, hepatic artery, and nerves enter.

• Peritoneal Attachments (5):

  1. Coronary Ligament: Reflects around bare area (area nuda) onto diaphragm.

  2. Right Triangular Ligament: Connects right lateral lobe to diaphragm.

  3. Left Triangular Ligament: Connects left lateral lobe to diaphragm; may contain appendix fibrosa hepatis.

  4. Falciform Ligament: Remnant of ventral mesentery between quadrate/left medial lobes and ventral body wall (contains round ligament ligamentum teres).

  5. Hepatorenal Ligament: Connects caudate process to right kidney (inconstant).

Gallbladder and Biliary Duct System

• Anatomy & Function:

  • Sac located in fossa between Quadrate and Right Medial liver lobes; stores and concentrates hepatic bile for lipid emulsification.

• Duct Architecture:

  • Hepatic ducts drain liver lobes $\rightarrow$ Join Cystic duct from gallbladder $\rightarrow$ Form Common Bile Duct ($Ductus\,choledochus$) $\rightarrow$ Opens into descending duodenum on Major Duodenal Papilla alongside pancreatic duct.

Pancreas Structure and Duct Anatomy

• Gross Topography:

  • V-shaped lobulated gland (pink-gray alive, yellow-gray preserved) located caudal to liver.

  • Body: Located caudomedial to pylorus.

  • Right Lobe: Slender; runs in mesoduodenum ventromedial to right kidney.

  • Left Lobe: Thicker; runs in deep leaf of greater omentum.

• Duct Systems in Dogs:

  1. Pancreatic Duct (Ventral Duct): Smaller cranial duct; opens on Major Duodenal Papilla with bile duct (inconstant/may be absent).

  2. Accessory Pancreatic Duct (Dorsal Duct / Duct of Santorini): Larger main duct in dogs; always present; opens into duodenum on Minor Duodenal Papilla.

Clinical Gastroenterology Summary

• Lips & Oral Cavity: Stomatitis, ulcers $\rightarrow$ Drooling, halitosis $\rightarrow$ Antiseptics, antibiotics, analgesics.

• Teeth: Periodontal disease $\rightarrow$ Halitosis, gingivitis, pain $\rightarrow$ Scaling, extractions.

• Tongue: Glossitis, foreign bodies $\rightarrow$ Swelling, drooling $\rightarrow$ Antibiotics, FB removal.

• Salivary Glands: Sialocele, sialadenitis $\rightarrow$ Fluctuant jaw mass, dysphagia $\rightarrow$ Surgical excision, drainage.

• Pharynx: Pharyngitis, foreign bodies $\rightarrow$ Gagging, dysphagia $\rightarrow$ Removal, anti-inflammatories.

• Esophagus: Megaesophagus, esophagitis $\rightarrow$ Regurgitation, aspiration pneumonia $\rightarrow$ Upright feeding, prokinetics.

• Stomach: Gastritis, Ulcers, GDV (Gastric Dilatation-Volvulus) $\rightarrow$ Vomiting, severe distension, shock (GDV) $\rightarrow$ Decompression, emergency surgery (GDV).

• Small Intestine: Enteritis, Intussusception $\rightarrow$ Diarrhea, vomiting, dehydration $\rightarrow$ Dewormers, fluids, surgery.

• Large Intestine: Colitis, Prolapse $\rightarrow$ Tenesmus, mucus/bloody stool $\rightarrow$ High-fiber diet, laxatives.

• Liver: Hepatitis, Cirrhosis, Lipidosis $\rightarrow$ Jaundice, ascites, lethargy $\rightarrow$ Hepatoprotectants, fluids.

• Gallbladder: Cholecystitis, Mucocele $\rightarrow$ Jaundice, abdominal pain $\rightarrow$ Cholecystectomy, antibiotics.

• Pancreas: Pancreatitis, EPI $\rightarrow$ Vomiting, fatty diarrhea, weight loss $\rightarrow$ IV fluids, low-fat diet, pancreatic enzymes (EPI).

• Peritoneum: Peritonitis $\rightarrow$ Fever, rigid abdomen, shock $\rightarrow$ Surgical lavage, broad-spectrum antibiotics.

Respiratory System Overview and Mechanics

• Primary Functions:

  • Gas exchange ($O_2$ intake and $CO_2$ removal).

• Secondary Functions:

  • Acid-base balance ($pH$ regulation), thermoregulation (panting), water elimination, phonation (vocalization).

• Respiration Stages:

  1. External Respiration: Alveolar-capillary gas exchange in lungs.

  2. Internal Respiration: Systemic capillary-tissue cell gas exchange.

• Species Resting Respiratory Rates:

  • Cat: $16\text{--}40\text{ breaths/min}$.

  • Dog: $18\text{--}34\text{ breaths/min}$ (Resting average $24\text{ breaths/min}$; values >40\text{ breaths/min} at rest are abnormal).

  • Horse: $10\text{--}14\text{ breaths/min}$.

  • Dairy Cow: $26\text{--}50\text{ breaths/min}$.

  • Sheep: $16\text{--}34\text{ breaths/min}$.

  • Pig: $32\text{--}58\text{ breaths/min}$.

• Respiratory Tract Divisions:

  • Upper Respiratory Tract (URT): External nose, nasal cavity, pharynx, larynx.

  • Lower Respiratory Tract (LRT): Trachea, bronchi, bronchioles, alveoli.

  • Gaseous Exchange Sites: Respiratory bronchioles, alveolar ducts, alveolar sacs, pulmonary alveoli.

External Nose, Planum Nasale, and Nasal Cavity

• Skeletal Boundaries:

  • Dorsal: Nasal bones; Lateral: Maxillae; Ventral: Palatine processes of incisive/maxillary/palatine bones; Caudal limit: Cribriform plate of ethmoid bone.

• Planum Nasale (Nasal Plane):

  • Hairless, non-glandular apical surface surrounding nostril openings (nares), divided by a central furrow (philtrum).

  • In dogs: Bare, black, comma-shaped nostrils kept moist and cool by secretions of the lateral nasal glands.

Larynx Cartilages and Functions

• Functions:

  • Regulates airflow volume, guards tracheal entrance against foreign material aspiration, acts as organ of voice.

• Nine Laryngeal Cartilages:

  • Unpaired (3):

    1. Epiglottis: Leaf-shaped elastic cartilage that flaps over laryngeal entrance during deglutition.

    2. Thyroid Cartilage: Largest, shield-shaped cartilage.

    3. Cricoid Cartilage: Complete ring-shaped base articulating with trachea.

  • Paired (3 pairs = 6 total):

    1. Arytenoid Cartilages: Pyramid-shaped; control vocal cord tension and glottis opening.

    2. Corniculate Cartilages: Horn-like nodules capping arytenoids.

    3. Cuneiform Cartilages: Rod-like supports embedded in aryepiglottic folds.

Trachea Structure and Comparative Anatomy

• Topography & Composition:

  • Patent fibrocartilaginous tube extending from cricoid cartilage to tracheal bifurcation (bifurcation tracheae) dorsal to heart base.

  • Divides into right and left primary bronchi.

• Species Tracheal Ring Characteristics:

  • Dog: $40\text{--}45$ incomplete C-shaped hyaline cartilage rings (dorsal ends do not touch; completed by membranous wall and trachealis muscle).

  • Pig: $32\text{--}35$ rings.

  • Sheep / Goat / Ox / Horse: $48\text{--}60$ rings.

• Trachealis Muscle Location:

  • Situated internally/retromucosal in carnivores, swine, sheep, and goats; situated externally in cattle and horses.

Lung Anatomy and Fetal Characteristics

• Lobular Architecture:

  • Left Lung (2 Lobes): Cranial Lobe (subdivided into cranial and caudal parts) and Caudal Lobe.

  • Right Lung (4 Lobes): Cranial Lobe, Middle (Cardiac) Lobe, Caudal Lobe, and Accessory (Azygos) Lobe.

• Normal vs. Fetal Lung Differentiation:

  • Normal Postnatal Lung: Soft, spongy, pink, crepitates on palpation, floats in water (contains air/surfactant).

  • Fetal Lung: Small, firm, solid (liver-like consistency), pale gray, does not crepitate, sinks in water (indicates stillbirth if untaken breath).

Canine Circulatory System: Heart Structure and Topography

• Topography & Orientation:

  • Located in middle mediastinum between 3rd and 6th intercostal spaces (ICS).

  • Base directed dorsocranially; Apex formed by left ventricle directed caudoventrally and to the left.

• Heart Wall Layers:

  1. Pericardium: Outer fibroserous sac. Anchored by sternopericardiac ligament (to sternum floor) and phrenopericardiac ligament (to diaphragm). Contains pericardial cavity with ~$1\text{ mL}$ lubricating fluid (liquor pericardii).

  2. Epicardium: Visceral layer of serous pericardium.

  3. Myocardium: Thick muscular layer (thickest in left ventricle).

  4. Endocardium: Smooth inner endothelial lining.

Cardiac Valves and Conduction System

• Chambers & Valves:

  • Right Atrium: Receives blood from Cranial/Caudal Vena Cavae and Coronary Sinus.

  • Right Ventricle: Pumps blood to Pulmonary Trunk; guarded by Tricuspid Valve (2 major cusps in dogs: septal & parietal) and Pulmonary Semilunar Valve.

  • Left Atrium: Receives oxygenated blood from Pulmonary Veins.

  • Left Ventricle: Thickest chamber wall; pumps blood to Aorta; guarded by Mitral / Bicuspid Valve and Aortic Semilunar Valve.

  • Chordae Tendineae & Papillary Muscles: Structural cords preventing AV valve eversion into atria during ventricular systole.

• Auscultation Locations (Dog):

  • Mitral Valve (Left): 5th ICS at costochondral junction.

  • Pulmonic Valve (Left): 2nd–4th ICS just above sternum.

  • Aortic Valve (Left): 4th ICS just above costochondral junction.

  • Tricuspid Valve (Right): 3rd–5th ICS near costochondral junction.

• Conduction System Sequence:

  1. SA Node (Sinoatrial Node): Primary pacemaker near cranial vena cava entrance. Intrinsic rate in dogs = $90\text{--}160\text{ beats/min}$.

  2. AV Node (Atrioventricular Node): Located in interatrial septum; delays impulse (~$0.1\text{ sec}$) to permit ventricular filling.

  3. Bundle of His: Crosses cardiac fibrous skeleton.

  4. Purkinje Fibers: Subendocardial conduction network causing apex-to-base ventricular contraction.

Blood Vessels, Systemic Pathways, and Injection Sites

• Vessel Structural Differences:

  • Arteries: Deep, thick muscular tunica media, elastic membranes, no valves (except heart outlets), carry high-pressure oxygenated blood away from heart (except pulmonary artery).

  • Veins: Superficial, thin walls, thin muscle layer, contain internal valves, carry low-pressure deoxygenated blood to heart (except pulmonary veins).

  • Capillaries: Endothelial single-cell thickness, no muscle or valves; site of nutrient/gas exchange.

• Common Canine Clinical Injection & Venipuncture Sites:

  • Intravenous (IV): Cephalic vein, Lateral saphenous vein, Medial saphenous vein, Jugular vein.

  • Intramuscular (IM): Epaxial muscles, Hamstring group (Biceps femoris, Semitendinosus, Semimembranosus), Quadriceps, Triceps brachii.

  • Subcutaneous (SQ) Standard Vaccine Locations:

    • Right Front / Shoulder: DHPP.

    • Right Rear: Rabies.

    • Left Front / Shoulder: Bordetella (injectable) / Influenza.

    • Left Rear: Lyme / Rattlesnake.

Urinary System: Kidneys, Ureters, Bladder, and Urethra

• Kidney Gross Anatomy & Topography:

  • Paired, smooth bean-shaped retroperitoneal organs embedded in fat caudal to diaphragm.

  • Right Kidney: Located below last ribs to $L1\text{--}L3$ (contacts caudate liver lobe).

  • Left Kidney: Located below $L3\text{--}L5$ (more mobile).

  • Dimensions (Dog): $6\text{--}9\text{ cm}$ length, $4\text{--}5\text{ cm}$ width, $3\text{--}4\text{ cm}$ thickness. Weight: $25\text{--}35\text{ g}$.

• Renal Zonation & Microscopic Structure:

  • Capsule: Fibrous outer layer.

  • Cortex: Outer dark red zone containing renal corpuscles (Glomerulus + Bowman's capsule) and convoluted tubules.

  • Medulla: Pale inner zone containing renal pyramids, loops of Henle, and collecting ducts.

  • Renal Pelvis: Whitish fibrous basin collecting urine for entry into ureter.

  • Nephron: Functional unit (~$1,000,000$ per kidney).

• Renal Blood Flow Pathway:

  • Aorta $\rightarrow$ Renal Artery $\rightarrow$ Interlobar Arteries $\rightarrow$ Arcuate Arteries $\rightarrow$ Interlobular Arteries $\rightarrow$ Afferent Arterioles $\rightarrow$ Glomerulus (filtration) $\rightarrow$ Efferent Arterioles $\rightarrow$ Peritubular Capillaries $\rightarrow$ Interlobular Veins $\rightarrow$ Arcuate Veins $\rightarrow$ Interlobar Veins $\rightarrow$ Renal Vein $\rightarrow$ Caudal Vena Cava.

• Ureters & Urinary Bladder:

  • Ureters: Paired transitional epithelium-lined muscular tubes ($12\text{--}16\text{ cm}$ long, $0.6\text{--}0.9\text{ cm}$ diameter) suspended by mesoureter, conveying urine via peristalsis.

  • Urinary Bladder: Musculomembranous sac holding $100\text{--}120\text{ mL}$ urine in a $25\text{-lb}$ dog. Contains smooth muscle (Detrusor muscle) and a smooth triangular mucosal base (Trigone) bounded by two ureteral openings and the internal urethral orifice.

  • Sphincters: Internal (smooth muscle, involuntary); External (striated muscle, voluntary).

• Urethra Sex Differences:

  • Female: Short tube opening at external urethral orifice on the urethral tubercle in vaginal vestibule.

  • Male: Long tube divided into pelvic and penile portions.

Male Reproductive System Anatomy

• Scrotum & Thermoregulation:

  • Cutaneous pouch divided by a median septum. Layers include Skin, Tunica Dartos (smooth muscle contracting/wrinkling skin to retain heat), Cremaster Muscle (striated muscle raising/lowering testes), Spermatic Fascia, and Vaginal Tunics.

  • Dog vs. Cat: Dog scrotum is inguinal with oblique testes; Cat scrotum is perineal (below anus) with horizontal testes. Cats lack an active cremaster muscle, using a levator scroti muscle instead.

• Testes & Spermatic Cord:

  • Paired oval gonads (~$3\text{ cm}$ long, $2\text{ cm}$ wide, $8\text{ g}$ weight in $25\text{-lb}$ dog) producing sperm and testosterone. Descend through inguinal canal guided by the gubernaculum testis (failure to descend = cryptorchidism).

  • Structure: Tunica albuginea sends septa into parenchyma, dividing it into lobules containing contorted seminiferous tubules $\rightarrow$ straight tubules $\rightarrow$ Rete Testis $\rightarrow$ $8\text{--}12$ Efferent Ducts $\rightarrow$ Epididymis head.

  • Spermatic Cord Contents: Ductus deferens, testicular artery, testicular vein (pampiniform plexus for countercurrent heat exchange), nerves, and vaginal tunic.

• Epididymis & Ductus Deferens:

  • Epididymis: Convoluted maturation/storage tube divided into Head (Caput), Body (Corpus), and Tail (Cauda). Duct length: Dog ($5\text{--}8\text{ m}$), Cat ($4\text{--}6\text{ m}$), Horse ($72\text{--}81\text{ m}$), Bull ($40\text{--}50\text{ m}$), Boar ($17\text{--}18\text{ m}$).

  • Ductus Deferens: Continuation of epididymal duct terminating at the ampulla; opens into pelvic urethra at the colliculus seminalis.

• Accessory Sex Glands Comparative Anatomy:

  • Bull & Stallion: Possess all 4 glands (Ampullary, Vesicular, Prostate, Bulbourethral).

  • Boar: Vesicular, Prostate, Bulbourethral.

  • Cat: Ampullary, Prostate, Bulbourethral.

  • Dog: Possesses ONLY Ampullary and Prostate glands (lacks vesicular and bulbourethral glands). Prostate is large, globular, and completely encircles pelvic urethra.

• Penis Classification & Canine Specializations:

  • Musculocavernous Penis: Found in dogs, cats, stallions (large vascular spaces expanding in length and diameter during erection, vs. fibroelastic penis of ruminants/swine with sigmoid flexure).

  • Canine Structural Modifications:

    1. Os Penis (Penile Bone): Ventrally grooved bone housing urethra; common site for urethral calculus obstruction.

    2. Bulbus Glandis: Expanded proximal portion of glans that swells during copulation to form the "tie" with the female vestibular sphincter.

Female Reproductive System Anatomy

• Gross Structural Plan:

  • Bicornuate (two-horned) multiparous system adapted for litters. Suspended by the Broad Ligament (Mesovarium for ovaries, Mesosalpinx for uterine tubes forming ovarian bursa, Mesometrium for uterus).

  • Surgical Landmark: Suspensory ligament of the ovary anchors ovary to dorsal body wall near kidney and must be broken/ruptured during an ovariohysterectomy (spay).

• Ovaries & Folliculogenesis:

  • Paired abdominal gonads with outer Zona parenchymatosa (follicles/corpora lutea) and inner Zona medullaris (vessels/nerves).

  • Follicle Progression: Primordial $\rightarrow$ Primary $\rightarrow$ Secondary $\rightarrow$ Tertiary $\rightarrow$ Graafian Follicle (ruptures under LH influence at the stigma to release ovum).

  • Post-ovulation ruptured follicle forms corpus hemorrhagicum $\rightarrow$ corpus luteum (produces progesterone) $\rightarrow$ regresses to corpus albicans scar if unfertilized.

  • Ovulation Mode: Dog (spontaneous ovulation); Cat (copulation-induced ovulation).

• Uterine Tubes (Oviducts / Fallopian Tubes):

  • Convoluted tubes ($4\text{--}7\text{ cm}$ long) transporting ova. Features an Infundibulum with finger-like fimbriae catching ova at the abdominal ostium. Site of fertilization.

• Uterus & Cervix:

  • Consists of two long Uterine Horns ($5 \times$ body length), a short Uterine Body, and a muscular Cervix acting as a sphincter.

  • Uterine Wall Layers: Endometrium (glandular inner mucosal lining), Myometrium (smooth muscle coat), Mesometrium (peritoneal attachment).

• Vagina, Vestibule, Vulva, and Mammary Glands:

  • Vagina: Extends from cervix to external urethral orifice; features longitudinal folds.

  • Vestibule: Shared urogenital space from urethral orifice to vulva.

  • Vulva: External lips (labia) enclosing clitoris in clitoral fossa.

  • Mammary Glands:

    • Bitch (Dog): 5 pairs ($10$ glands total).

    • Queen (Cat): 4 pairs ($8$ glands total).