AP2 - Day 14 - Ch 20 pt 2_student.pdf

Review Questions

  • Blood Volume and Pressure Responses

    • A decrease in blood volume and blood pressure results in:

      • Release of renin from kidneys.

      • Activation of the angiotensin-aldosterone system.

      • Increased thirst and fluid retention.

  • Urine Color and Vasopressin Levels

    • Pale yellow, large volume urine infers low vasopressin levels.

      • Low levels indicate less water reabsorption in kidneys, diluting urine.

  • Nephron Loop

    • Descending Limb:

      • Water exits the tubule due to high osmolarity in the medulla, concentrating the urine.

    • Ascending Limb:

      • Sodium, potassium, and chloride are reabsorbed, making urine less concentrated.

  • Aldosterone Production and Target

    • Produced in the adrenal cortex.

    • Targets principal cells in the distal nephron for sodium and potassium balance.

Water Balance

  • Water Gain vs. Loss

    • Gain:

      • Food and drink: 2.2 L/day.

      • Metabolism: 0.3 L/day.

    • Loss:

      • Skin: 0.9 L/day.

      • Lungs: 0.3 L/day.

      • Urine: 1.5 L/day.

      • Feces: 0.1 L/day.

    • Total Intake: 2.2 L/day.

    • Total Output: 2.5 L/day (balance = 0).

Potassium Balance

  • Hormone Regulation

    • Aldosterone:

      • Regulates potassium levels, acting on principal cells of the nephron.

      • Involved in both reabsorption and secretion.

  • Action Mechanism of Aldosterone:

    1. Combines with cytoplasmic receptor in the principal cell.

    2. Initiates transcription for new channels and pumps.

    3. Increases sodium reabsorption and potassium secretion in distal nephron.

Importance of Potassium

  • Effects of K+ Concentration on Neurons

    • Decrease in plasma K+:

      • Increases resting membrane potential, leading to reduced excitability.

    • Increase in plasma K+:

      • Decrease in resting membrane potential, leading to greater excitability.

Behavioral Mechanisms

  • Thirst Mechanism

    • Osmoreceptors in hypothalamus signal thirst when osmolarity rises above 280 mOsM, triggering drinking response.

  • Salt Appetite Mechanism

    • Craving for salty foods when Na+ concentrations drop.

    • Centers for appetite linked to aldosterone.

Acid-Base Balance

  • pH and Hydrogen Ion Concentration

    • Normal pH range in the body: 7.38 - 7.42.

  • Effects of pH Changes

    • Acidosis: Neurons less excitable; CNS depression may occur.

    • Alkalosis: Neurons become hyper excitable; symptoms include muscle twitches and paralysis.

Mechanisms of Acid-Base Control

  • Three Mechanisms:

    1. Buffers: HCO3 in extracellular fluid, proteins, and hemoglobin.

    2. Ventilation: Adjusting CO2 levels via breathing.

    3. Renal: Directly excreting H+ or changing HCO3- levels.

Disturbances in Acid-Base Balance

  • Classification: Acidosis or Alkalosis, Metabolic or Respiratory based on hydrogen ions/CO2 levels.

  • Compensation Mechanisms:

    • Renal and respiratory mechanisms can adjust pH but may not correct the underlying problem.

  • Common Disturbances:

    • Respiratory Acidosis (hypoventilation) vs. Respiratory Alkalosis (hyperventilation).

Critical Review

  • Case Study in Acid-Base State:

    • Example: Patient with asthma attack showing:

      • HCO3- = 30 mEq/L, PCO2 = 70 mmHg, pH = 7.24 indicating respiratory acidosis.

Exam Preparation

  • Review Schedule: Regularly review material and complete problem sets before exam dates.