Regulation of Body Temperature and Acid-Base Balance

These flashcards cover key concepts related to the regulation of body temperature and acid-base balance.

Heat balance

The heat production minus the heat loss in the body.

Basal metabolic rate (BMR)

The amount of kilocalories burned per day simply by being alive, without additional activity.

Thyroid hormones

Influence metabolism; high levels increase metabolism and low levels decrease metabolism.

Diet-induced thermogenesis (DIT)

The increase in heat production due to digesting, absorbing, and repackaging macronutrients from food.

Exercise

Increases heat production through muscular activity.

Shivering thermogenesis

Muscle contraction without producing useful work, generating heat in response to cold stress.

Brown adipose tissue (BAT)

A specialized form of adipose tissue with high concentrations of mitochondria and uncoupling proteins, increasing heat production.

Heat loss mechanisms

Four primary mechanisms: radiation, conduction, convection, and evaporation.

Radiation

Heat transfer between two objects based on their temperatures through electromagnetic waves.

Conduction

Heat transfer through direct physical contact between objects of different temperatures.

Convection

Heat loss through a medium such as air or water, where moving fluid carries away heat.

Evaporation

Heat loss through the conversion of sweat into vapor.

Fever

An elevated body temperature that can decrease bacterial growth and increase immune activity.

Antipyretics

Drugs such as aspirin or Tylenol that lower fever without significantly affecting illness outcome.

Endotoxins

Molecules from Gram-negative bacteria that can induce fever.

Endogenous pyrogens

Substances like bile acids or urate crystals that can increase body temperature.

Cytokines

Signaling molecules that contribute to fever, including Interleukin-1 beta, Interleukin-6, Tumor Necrosis Factor alpha, and Interferon alpha.

Prostaglandins

Lipid molecules produced through COX enzymes that mediate fever signals to the brain.

Cyclooxygenase (COX) enzymes

Convert arachidonic acid into prostaglandins such as PGE2.

Prostaglandin E2 (PGE2)

Binds to EP3 receptors on preoptic anterior hypothalamic neurons to induce fever.

EP3 receptors

G-protein coupled receptors expressed in the brain, particularly in the anterior and preoptic areas of the hypothalamus.

Hypothalamus

The brain region where neurons control heat retention and heat dissipation.

Hyperthermia

Elevated body temperature not caused by a change in the set point, such as during heat stroke.

Diurnal/circadian rhythm

The normal daily fluctuation in body temperature.

Cyclic variations

Normal temperature changes across the menstrual cycle.

Axillary temperature

Measured under the armpit; easy but less accurate.

Pulmonary artery temperature

Highly accurate core temperature measurement that requires an indwelling catheter.

Esophageal temperature

Measured via a probe in the esophagus; very accurate if feasible.

Oral temperature

Measured sublingually; accuracy may be affected by ventilation.

Rectal temperature

Measured in the rectum; often used in children.

Tympanic temperature

Measured via infrared on the eardrum; accuracy may be limited.

Normal body temperature range

Between 36.5°C and 37.5°C.

Low-grade fever

Ranges from 37.8°C to 38.3°C.

High fever

Ranges from 39.4°C to 40°C.

Hyperpyrexia

An extremely high body temperature above 41.1°C, which can cause neurological damage.

Acid-base balance

The physiological regulation of hydrogen ion concentration to maintain body fluid pH.

pH scale

A logarithmic scale that reflects hydrogen ion concentration.

Logarithmic relationship

Each pH unit represents a tenfold change in acidity.

Normal arterial blood pH

Approximately 7.4.

Acidity

Refers to the amount of free hydrogen ions in solution.

Physiological pH range

Spans from pH 1 in the stomach to pH 8 in pancreatic secretions.

pH indicator/pH paper

Changes color to indicate pH.

Acidic pH

Associated with red colors and high hydrogen ion concentration.

Basic/Alkaline pH

Associated with blue or purple colors and low hydrogen ion concentration.

Gastric acid

Stomach acid with a pH near 1.

Parietal cells

Actively secrete hydrogen ions into the stomach.

Hydrochloric acid (HCl)

Formed when hydrogen ions combine with chloride.

Lysosomes

Acidic intracellular organelles.

Low internal pH

Maintained by lysosomes.

Intracellular fluid (ICF) pH

Approximately 6.81 at 37°C.

Venous blood pH

Averages about 7.2.

Acidosis

Lowers pH by increasing hydrogen ion production.

Arterial blood pH

Approximately 7.4.

Blood pH range

Maintained between 7.35 and 7.45.

Alkalosis

A blood pH above 7.45.

Pancreatic juice

Has the highest physiological pH.

Bicarbonate buffer system

The primary extracellular buffer.

Bicarbonate (HCO₃⁻)

Neutralizes gastric acid.

Acidosis (blood)

A blood pH below 7.35.

Alkalosis (blood)

A blood pH above 7.45.

Buffer

Binds hydrogen ions to resist pH changes.

Buffer systems

Can reversibly bind hydrogen ions.

Volatile acids

Eliminated through respiration as CO₂.

Carbon dioxide (CO₂)

Acts as an acid through carbonic acid formation.

Carbonic anhydrase

Converts CO₂ and water into carbonic acid.

Non-volatile acids

Must be excreted by the kidneys.

Sulfuric acid (H₂SO₄)

Produced from sulfur-containing amino acids.

Phosphoric acid (H₃PO₄)

Originates from phospholipid metabolism.

Metabolic acids

Produced during metabolism, e.g., lactic acid, ketoacids.

Bases

Reduce hydrogen ion concentration.

Intracellular buffers

Include proteins and phosphates.

Buffer capacity

Approximately 25 mM per pH unit.

Hemoglobin

A major protein buffer in the blood.

Buffer curve/titration curve

Shows buffer response to pH change.

pKa

The pH at which buffer forms are equal.

Henderson-Hasselbalch equation

Calculates blood pH.

PaCO₂

Measures the partial pressure of arterial CO₂.

Cellular metabolism

The main source of acid production.

Stomach acid production

Produces approximately 15,000 mM of acid daily.

Metabolic acid production

Produces approximately 40 mM of acid daily.

Kidneys

Eliminate non-volatile acids.