External and internal Environment

Milieu Interior - internal environment cells are completely closed off from the external environment, and the external environment doesn't change our internal environment. This concept emphasizes the importance of maintaining a consistent internal state in organisms, which is crucial for survival.

Homeostasis - Organisms maintain a stable internal environment despite changes in their external environment. Homeostasis ensures that physiological parameters remain within a narrow range that supports normal function.

• Negative feedback - This is the most common mechanism for maintaining homeostasis. It involves feedback loops that detect deviations from a set point and trigger responses that counteract the deviation, thereby returning the system to equilibrium. For example, For example, when hot the body will start sweating to cool down

• Positive feedback - While less common in maintaining stable internal conditions, positive feedback loops amplify a change, moving the system further away from its set point. These are often involved in processes that need to be completed quickly, such as blood clotting or childbirth. They do not contribute to long-term stability. For example, during childbirth, the initial stimulus of labor is amplified, ultimately leading to a significant change (the birth).

How We Regulate Homeostasis: Glucose levels increase after eating and then return to their set point via homeostasis, which is an example of dynamic constancy. Levels change over a short period, and our energy pathways are highly regulated in this manner.

Key Terms:

• Regulated variable - What is being controlled (e.g., pH, glucose, temperature).

• Set Point - The normal or ideal value (e.g., blood pH of 7.4).

• Sensory Input - Mechanisms that sense the actual value of the regulated variable (e.g., temperature is detected by nerves in the skin and hypothalamus).

• Integrative Center - The location where the actual value and the set point are compared. If a difference is detected, effector systems are activated that change the regulated variable back toward the set point (e.g., brain, chemoreceptors, glucokinase).

• Effector - Mechanisms that return the regulated variable toward the set point (e.g., vasodilation).

• pH - Power of hydrogen.

Vocab:

• HCO3 = Bicarbonate Ion.

• H+ = Hydrogen Ion.

• CO2 = Carbon Dioxide.

• HPO4 = Hydrogen Phosphates.

• ATP = Adenosine Triphosphate.

• ADP = Adenosine Diphosphate.

• H2CO3 = Carbonic Acid.

Acid-Base Buffering in the Human Body:

• Buffer - Substances that resist change and lessen the impact of fluctuations in pH. They are essential for maintaining the pH of blood.

• Chemical Buffer - A chemical buffer in blood that resists change in pH, thereby helping to stabilize the internal environment.

• A buffer is a weak acid or base that can accept or donate hydrogen ions to maintain equilibrium.

Acid: - Molecules that liberate hydrogen ions.

• Acids increase the H+ concentration in a solution. For example, lactic acid is a weak acid while hydrochloric acid is a strong acid.

Base: - Molecules capable of combining with H+.

• Bases decrease H+ concentration in a solution (increasing pH). Bicarbonate (HCO3-) is a weak base, while sodium hydroxide is a strong base.

pH Scale: - The concentration of H+ in a solution is expressed on a pH scale ranging from 0 to 14. A pH of solutions below 7 indicates acidity, whereas those above 7 indicate basicity. The pH of blood is between 7.35 and 7.8, with an average of 7.4.

So, a solution with a pH of 6 has how many more hydrogen ions than a solution with a pH of 7? 10 times more.

Now, a solution with a pH of 3 compared to a solution of pH 6 has how many more? 10 × 10 × 10 = 1,000.

Causes of Acidosis and Alkalosis:

• Acidosis is caused by the loss of bases and the accumulation of acids.

• Alkalosis is caused by the accumulation of bases and the loss of acids.

Conditions and Diseases that Promote Metabolic Acidosis or Alkalosis:
Metabolic Acidosis:

• Gain in the amount of acid in the body (e.g., high-intensity exercise lasting more than 30 seconds).

• Long-term starvation

• Results in increased fat metabolism and elevated production of keto-acids.

• Uncontrolled diabetes, which results in high rates of fat metabolism and diabetic ketoacidosis.

Metabolic Alkalosis:

• Loss of acids from the body (e.g., severe vomiting).

• Kidney disease.

Primary Sources of H+ in Contracting Skeletal Muscles:
Aerobic Metabolism of Glucose:

• Produces carbonic acid, which drops pH and releases hydrogen ions through the breakdown of glucose.
  Anaerobic Metabolism of Glucose:

• Produces lactate, which also drops pH and releases hydrogen ions.

Sport and Exercise-Induced Disturbances in Acid-Base Balance:
High-intensity exercise lasting more than 30 seconds produces large amounts of H+.

• The risk of acid-base disturbances is directly linked to the athlete's effort.

• Competing at 100% effort increases the risk of acidosis, such as sprinting to finish in a distance event. Acidosis can impair exercise performance, contributing to muscle fatigue.

• Increasing the blood buffering capacity may improve performance in certain events.

Importance of Acid-Base Balance During Exercise:
High-intensity exercise can lead to the production of lactic acid and increased H+ concentration in muscle fibers and blood.

• An increase in H+ can impair performance by inhibiting glycolytic and tricarboxylic acid (TCA) enzyme activity (that is, ATP production).

• H+ can impair muscle contraction by altering the affinity of troponin for calcium ions (Ca+2).

• A reduction in affinity results in fewer interactions between myosin and actin, thereby decreasing muscle fiber function.

3 Main things that contribute to low pH when we exercise intensely:

• Hydrolyze an ATP molecule

• Lactic Acid - anaerobic metabolism

• Carbonic Acid - aerobic metabolism

Why does it matter if pH drops:

• reduces performance

• Muscle contraction - inhibits binding of calcium to troponin

What is a buffer?

• If you add an acid to pure water, the acid increases the hydrogen ions Anaerobic metabolism concentration immediately and significantly

Acid-Base Buffer System: Details

How these molecules keep the pH in blood from dropping

• Bicarbonate - converts strong acid into weak acid - we find bicarbonate in baking soda

• Phosphates - converts strong acid into weak acid

• Proteins - accepts hydrogen

• Histidine-dipepetides - accepts hydrogen

Regulation of Acid-Base Balance during exercise:

Buffering of H+ in the muscle

• 60% by intercellular proteins

• 20-30% by muscle bicarbonate

• 10-20% by intercellular phosphate groups

Buffering of lactic acid in the blood

• Bicarbonate is major buffer

  • Increases in lactic acid accompanied by decrease in bicarbonate and blood pH

Nutritional supplements to Buffer exercise-induced acid-base disturbances and improve exercise performance:

Diets low in acids can increase plasma pH but do not improve performance during very heavy or severe exercise

Some sports regulatory agencies have banned use of sodium buffers during competition

• Supplementation with sodium bicarbonate - baking soda

  • Important extracellular buffer

  • Can increase time to exhaustion during high-intensity exercise (80-120 VO2 Max)

  • Associated with nausea and vomiting

  • Large doses can promote alkalosis

First Line of defense from pH getting low from intense exercise:

• first in muscles cell

  • Biggest buffer is muscles protein #1

  • Muscle bicarbonate #4

  • Phosphates #2

  • Histidine-dipeptides #3

Second line of defense from pH getting low :

• second line is the blood

  • Bicarbonate #1 - absorbs hydrogen ions and become carbonic acid

  • Red blood cells #2 - absorbs carbon dioxide that joins with water then it becomes bicarbonic acid then into bicarbonate

  • Hemoglobin #3 - carries CO2 and binds to hydrogen ions then gets buffered

Highest concentration of CO2 is muscles that aren’t working

Highest concentration of O2 is muscles that are working hard

Also Seconds line of defense from pH getting low :

• Another second line is in the lungs

  • adjusting carbon dioxide levels through breathing

  • Carbon dioxide is a waste product of metabolism, and when it dissolves in water, it forms carbonic acid, which lowers blood pH (making it more acidic)

Last Line of defense from pH getting low:

• Last is the Kidneys

  • ability to regulate the excretion of acids and bases

  • reabsorbing bicarbonate (HCO3-) from the urine, which helps neutralize acids in the blood, and by excreting hydrogen ions (H+) into the urine, further reducing acidity

How we can test the pH of blood without actually testing the pH of blood:

• testing the blood lactate

  • They both change at the same rate and the same time

  • When intense exercise and lactate both go up what also goes up?

    • Heart rate and breathing