Patient Anatomy, Physiology, and Pathophysiology for Nursing Care

Effective veterinary nursing starts with a working knowledge of anatomy, physiology, and pathophysiology. You do not need to recite every muscle origin and insertion, but you must know the systems that change nursing decisions: how perfusion is maintained, how oxygenation happens, how the kidney balances water and electrolytes, how the liver clears drugs, and how the nervous system produces mentation. This section reviews those systems with an emphasis on species differences and the pathophysiologic states you will manage in hospitalized patients.

Cardiovascular System and Perfusion

The cardiovascular system delivers oxygen and nutrients to tissues and removes waste. Cardiac output (CO) equals stroke volume (SV) times heart rate (HR): CO = SV x HR. Stroke volume depends on preload (venous return), afterload (systemic vascular resistance), and contractility. Any condition that reduces preload (hypovolemia, dehydration, vasodilation), increases afterload (vasoconstriction), or impairs contractility (heart failure, myocardial depression) lowers cardiac output and threatens perfusion.

Compensatory mechanisms for reduced perfusion include splenic contraction (releases stored red blood cells), tachycardia (maintains CO when SV falls), vasoconstriction (shunts blood to brain and heart), and increased respiratory rate (compensates for metabolic acidosis). Dogs have a large, easily contractible spleen that stores roughly 10 to 20 percent of their blood volume, providing a meaningful PCV buffer during hemorrhage. Cats lack this splenic reserve, which is one reason feline blood loss decompensates more quickly and is harder to detect early — a clinically important species difference for triage and nursing care.

Shock is the pathophysiologic state of inadequate cellular perfusion. Compensated shock preserves blood pressure through tachycardia and vasoconstriction but at the cost of poor tissue oxygen delivery; decompensated shock progresses to hypotension, organ dysfunction, and death. Nursing recognition of compensated shock (tachycardia, increased CRT, pale or tacky mucous membranes, reduced pulse quality, cool extremities) is a core VTNE skill. Clinical signs of poor perfusion include:

• Capillary refill time greater than 2 seconds
• Pale, cyanotic, or injected mucous membranes
• Weak, thready, or bounding pulses
• Tachycardia (dog over 140, cat over 220)
• Cool extremities and rectal temperature below 99 F
• Prolonged mental dullness or obtundation

Respiratory System and Oxygenation

Gas exchange occurs at the alveolar-capillary membrane. Ventilation (air movement) and perfusion (blood flow) must be matched (V/Q matching) for efficient oxygenation. Conditions that impair matching include pneumonia (perfused but not ventilated alveoli = shunt), pulmonary embolism (ventilated but not perfused alveoli = dead space), and atelectasis (collapsed alveoli). Respiratory rate, effort, and pattern are sensitive indicators of respiratory compromise; tachypnea with increased effort precedes cyanosis, and a patient that is breathing slowly and shallowly may be fatiguing and close to respiratory arrest.

Cats with pleural effusion, pneumothorax, or asthma often present with open-mouth breathing and increased abdominal effort. Dogs with laryngeal paralysis or tracheal collapse produce characteristic stridor or honking. Position matters: recumbency worsens V/Q matching in the down lung, so dyspneic patients should be allowed to sit sternal (or stand) rather than be forced laterally for procedures.

Renal, Hepatic, and Gastrointestinal Systems

The kidney regulates water, electrolytes, and acid-base balance through glomerular filtration, tubular secretion, and reabsorption. Renal disease reduces concentrating ability (isosthenuria, urine specific gravity 1.008 to 1.012), causes polyuria and polydipsia, and impairs electrolyte handling (hyperphosphatemia, hypokalemia or hyperkalemia, metabolic acidosis). Nursing implications: monitor urine output (normal 1 to 2 mL/kg/hr), ensure fresh water is always available, and track body weight daily to catch fluid shifts early.

The liver metabolizes most drugs and synthesizes albumin, clotting factors, and bile. Cats have minimal hepatic glucuronidation (UGT1A6 and UGT2B7 activity is very low), which is why acetaminophen is lethal to them and why certain benzodiazepines and NSAIDs are cleared slower in cats than in dogs. Hepatic disease reduces drug clearance, lowers albumin (raising free drug fractions), and impairs clotting (coagulopathy from reduced factor synthesis). Nursing implications: monitor for bleeding tendencies, reduce doses of hepatically cleared drugs, and watch for hepatic encephalopathy signs (head pressing, circling, seizures) in patients with portosystemic shunts or cirrhosis.

Gastrointestinal Transit and Nutritional Nursing

The GI tract moves ingesta from mouth to anus through peristalsis and segmental contractions. Transit time differs by species and diet: dogs typically 6 to 8 hours for liquids and 12 to 24 hours for solids; cats roughly 12 to 24 hours for solids. These times affect medication timing (enteric-coated drugs, drugs absorbed in specific GI regions), feeding schedules for hospitalized patients, and recognition of ileus (absence of gut sounds on auscultation, abdominal distension, vomiting).

Auscultate the abdomen for bowel sounds (borborygmi) every 4 to 6 hours in critical patients. Hyperactive sounds suggest early obstruction or gastroenteritis; absent sounds suggest ileus, peritonitis, or post-anesthetic gut slowdown. Nutritional nursing decisions are guided by resting energy requirement (RER = 70 x body weight in kg to the 0.75 power) and the recognition that cats, especially obese cats undergoing fasting, are prone to hepatic lipidosis within 2 to 3 days of anorexia — a reason to intervene with appetite stimulants or feeding tubes early in feline patients.

Neurologic System and Mentation

The central nervous system (brain and spinal cord) controls mentation, posture, and reflexes. Mentation assessment is covered in section 9.2, but the anatomic basis matters: the cerebral cortex controls consciousness; the brainstem controls vital reflexes (respiration, cardiovascular centers, pupillary light reflex); the spinal cord carries motor and sensory pathways. Lesions above the forebrain produce altered consciousness; brainstem lesions affect cranial nerves and vital functions; spinal cord lesions produce paresis or paralysis caudal to the lesion.

Pathophysiologic states the technician must recognize include:

• Seizures — abnormal cortical electrical discharges; may be generalized (tonic-clonic) or focal. Nursing care: protect from injury, do not restrain forcefully, time the seizure, record progression, administer diazepam or midazolam if the seizure lasts over 2 to 3 minutes (status epilepticus).
• Vestibular signs — head tilt, circling, nystagmus, ataxia; may be central (brainstem) or peripheral (inner ear). Differentiate by presence of cranial nerve deficits or postural reaction deficits (central) versus normal mentation and Horner syndrome (peripheral).
• Spinal cord compression — paresis or paralysis, loss of deep pain (worst prognosis), absent patellar reflexes depending on lesion location.

Species-Specific Considerations for Nursing

Dogs and cats differ in ways that change nursing care:

Knowing these differences is not trivia — they explain why a dog tolerates a 12-hour fast while a cat may develop hepatic lipidosis, why a dog on opioids may pant while a cat may hide and become anorexic, and why cats mask illness until compensation fails. The technician who internalizes these species differences will recognize decompensation earlier and adjust nursing care accordingly, which is the core of Animal Care and Nursing (Domain 5, 20 percent of VTNE items).