1.4 Requirements for Human Life

Requirements for Human Life

Overview

  • Humans have been adapting to life on Earth for at least 200,000 years.

  • Earth and its atmosphere provide vital components: air, water, food.

  • Survival requires more than these components; it also necessitates specific temperature and pressure ranges.

  • This section explores four essential requirements for human life.

Oxygen

  • Definition: Atmospheric air consists of approximately 20% oxygen, which is crucial for chemical reactions in the body, especially those producing ATP (adenosine triphosphate).

  • Importance:

    • Brain cells are highly sensitive to oxygen deficiency due to their high ATP demands.

    • Lack of oxygen can lead to brain damage in about five minutes and death in approximately ten minutes.

Nutrients

  • Definition: Nutrients are substances in foods and beverages essential for human survival.

  • Types of Nutrients:

    1. Macronutrients: Required in large amounts:

    • Water: Most critical nutrient; survival without it is limited to a few days, depending on environmental and health factors.

      • Functions: Solvent for functional chemicals, medium for chemical reactions, largest component of cells and blood, crucial for temperature regulation, provides cushioning, and lubricates joints.

    • Energy-yielding Nutrients: Primarily carbohydrates and lipids; proteins supply amino acids for body building.

      • Carbohydrates and lipids are metabolized to produce ATP.

      • Survival is possible without these for several weeks, despite the discomfort.

    1. Micronutrients: Required in smaller amounts; includes vitamins and minerals.

    • Participates in essential chemical processes (e.g., nerve impulses).

    • Some can be stored in body tissues, while others (like vitamins C and most B vitamins) are water-soluble and need daily ingestion.

Narrow Range of Temperature

  • Chemical reactions in the body can only occur within a narrow temperature range:

    • Normal body temperature: Slightly below to slightly above 37°C (98.6°F).

    • Consequences of Temperature Extremes:

    • High body temperature can denature proteins (enzymes), hindering metabolic reactions.

    • Short-term responses to heat include sweating:

      • Evaporation of sweat cools the body but requires adequate hydration to maintain the body's fluid balance.

      • Humid conditions can impede sweat evaporation, leading to overheating.

    • Low body temperature can lead to:

      • Shivering (heat generation) and increased energy consumption.

      • If core temperature drops significantly, blood cells may not release oxygen effectively, leading to confusion and potential death.

      • Body minimizes blood flow to extremities to maintain core warmth, risking frostbite and subsequent gangrene.

Controlled Hypothermia

  • Definition: Hypothermia = abnormally low body temperature (hypo- = 'below').

  • Clinical Use: Controlled hypothermia lowers metabolic rates to protect organs during procedures like open-heart surgery.

    • Typical cooling range: Body temperature is reduced to 25–32°C (79–89°F).

    • Heart is cooled to below 15°C (60°F), reducing blood supply needs during surgery to prevent damage.

  • Emergency Medicine: Utilized post-cardiac arrest to lower metabolic rates and reduce workload on the heart.

    • Induced coma with a target body temperature of approximately 91°F maintained for 24 hours.

Narrow Range of Atmospheric Pressure

  • Definition: Atmospheric pressure is the force exerted by air gases, primarily nitrogen and oxygen, on the body.

    • Constant pressure necessary for dissolving gases in body fluids.

  • Altitude Effects:

    • Sudden exposure to low pressure (e.g., from a spaceship) leads to gas expansion in the blood (e.g., nitrogen forming bubbles), causing cell damage and blocking blood vessels.

    • Symptoms of altitude sickness include dizziness, headache, and nausea, linked to reduced gas exchange.

  • Decompression Sickness (DCS):

    • Condition where gases previously dissolved in blood and tissues form bubbles due to a rapid decrease in pressure.

    • Common in divers surfacing quickly and in pilots at high altitudes.

    • Symptoms: Joint pain, headaches, and potentially death if untreated.

  • Immediate Treatment:

    • Administer pure oxygen and transfer to a hyperbaric chamber to gradually restore pressure and dissolve nitrogen safely back into the body fluids.

  • Dynamic Pressure:

    • Importance of maintaining appropriate blood pressure to enable effective circulation to tissues while preventing damage to blood vessels from excess pressure.

Key Figures

  • Figure 1.8: Illustration of human adaptation to extreme heat (credit: McKay Savage/flickr).

  • Figure 1.9: Conditions faced by climbers on Mount Everest: extreme cold, low oxygen, and low atmospheric pressure (credit: Melanie Ko/flickr).