Ingestion, Digestion, Absorption, and Metabolism

Ingestion

The process of consuming food via the mouth and
moving it through the digestive tract

Digestion

The systemic breakdown and absorption of nutrients

Absorption

Nutrients pass through the digestive tract into the
bloodstream and lymphatic system.

Metabolism

is the sum of all chemical processes in the body to
maintain homeostasis

Catabolism

Breakdown of substances to release energy.

Anabolism

Use of energy to build or repair tissues.

Energy nutrients

are metabolized into:
– Carbon dioxide (CO₂)
– Water (H₂O)
– Adenosine triphosphate (ATP)

Excess nutrient storage:

– Glucose → Glycogen (stored in liver and muscles)
– Surplus glucose → Fat
– Glycerol + fatty acids → Triglycerides (stored in adipose tissue)
– Amino acids → Body proteins

The liver removes nitrogen from amino acids;

remaining components are used for glucose or fat production.

Basal Metabolic Rate (BMR) / Basal Energy Expenditure (BEE):

Energy used over 24 hours for involuntary bodily functions (e.g., temperature regulation, heartbeat, respiration).
– Measured at rest after a 12-hour fast

Resting Metabolic Rate (RMR) / Resting Energy Expenditure (REE):

Similar to BMR but does not require a 12-hour fast

used as an indirect measure of BMR.

Thyroid function tests

Factors Affecting Metabolic Rate

• Increase BMR
  • Increase BMR
  • Conditions: Increase Metabolism (Hyperthyroidism)
  vs Decrease Metabolism (Hypothyroidism)

Increase BMR medications:

• Epinephrine
• Levothyroxine
• Ephedrine sulfate

Decrease BMR medications:

• Opioids
• Muscle relaxants
• Barbiturates

Assessment/Data Collection for BMR

• Weight and history of recent weight patterns
• Medical history for diseases that affect metabolism and nitrogen balance
• Extent of traumatic injuries, as appropriate
• Fluid and electrolyte status
• Laboratory values: albumin, transferrin, glucose, creatinine
• Clinical findings of malnutrition: pitting edema, hair loss, wasted
appearance
• Medication adverse effects that can affect nutrition
• Usual 24-hr dietary intake
• Use of nutritional supplements, herbal supplements, vitamins, and
minerals
• Use of alcohol, caffeine, and nicotin

Nursing Interventions for BMR

• Monitor food intake.
• Monitor fluid intake and output.
• Use client-centered approach to address disease-specific
problems with ingestion, digestion, or medication regime.
• Collaborate with dietitian.
• Provide adequate calories and high-quality protein.