Physiology Chapter on Homeostasis Regulation

Carbon Dioxide Concentration Regulation

• The respiratory system regulates carbon dioxide concentration in the extracellular fluid.
• The lungs expel carbon dioxide from the body, decreasing its concentration.
• Increased carbon dioxide concentration triggers an increase in respiration to reduce its level.
• Conversely, decreased carbon dioxide concentration results in decreased respiration to increase its level.

Glucose Concentration Regulation

• The liver and pancreas control glucose concentration in the extracellular fluid.

Electrolyte Concentration Regulation

• The kidneys regulate the concentration of hydrogen, sodium, potassium, phosphate, and other ions in the extracellular fluid.

Arterial Blood Pressure Regulation

• The baroreceptor system is a rapid-acting control mechanism for blood pressure.
• Baroreceptors located in the carotid arteries and aortic arch sense stretch in the arterial walls.
• Increased arterial pressure stretches the baroreceptors, which send signals to the medulla of the brain.
• These signals inhibit the vasomotor center in the medulla, leading to decreased sympathetic nervous system activity.
• Decreased sympathetic activity causes blood vessel dilation and reduced heart pumping, returning arterial pressure toward normal.

Oxygen Concentration Regulation

• Oxygen is crucial for cellular reactions.
• Hemoglobin, a molecule in red blood cells, binds to oxygen in the lungs and transports it throughout the body.

Extracellular Fluid Constituents and Values

• The extracellular fluid contains vital components, including oxygen, carbon dioxide, sodium, potassium, calcium, chloride, bicarbonate, glucose, and other ions.
• These components are meticulously regulated to maintain homeostasis.

Important Constituent Values

• Oxygen (venous) - Normal value: 40 mm Hg, Normal range: 25–40 mm Hg.
• Carbon dioxide (venous) - Normal value: 45 mm Hg, Normal range: 41–51 mm Hg.
• Sodium ion - Normal value: 142 mmol/L, Normal range: 135–145 mmol/L.
• Potassium ion - Normal value: 4.2 mmol/L, Normal range: 3.5–5.3 mmol/L.
• Calcium ion - Normal value: 1.2 mmol/L, Normal range: 1.0–1.4 mmol/L.
• Chloride ion - Normal value: 106 mmol/L, Normal range: 98–108 mmol/L.
• Bicarbonate ion - Normal value: 24 mmol/L, Normal range: 22–29 mmol/L.
• Glucose - Normal value: 90 mg/dl, Normal range: 70–115 mg/dl.
• Body temperature - Normal value: 98.4 °F (37.0°C), Normal range: 98–98.8 °F (37–37.1°C).
• Acid–base (venous) - Normal value: 7.4, Normal range: 7.3–7.5.

Homeostasis and Automaticity of the Body

• Homeostasis is the maintenance of a stable internal environment crucial for cell survival.
• The body functions as a coordinated system of cells and organs working together to maintain homeostasis.
• Each organ contributes to the stability of the extracellular fluid, the internal environment.
• Cells thrive in a stable internal environment and contribute to its maintenance. This reciprocal interplay provides the body's automaticity.
• Dysfunctional systems disrupt homeostasis, leading to sickness or death.

Physiological Variability

• Physiological variables can differ significantly among individuals and even within the same individual over time based on numerous factors, including age, sex, genetics, environment, and diet.
• Although some variables are tightly regulated, others exhibit significant variability.
• The 70-kg young, lean male is often used as a reference for physiological functions, but actual values may vary.
• Body weight has significantly increased worldwide, requiring consideration when interpreting data.
• While male physiology is often used as a reference, there are notable differences in male and female physiology.