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.