Key Takeaways
- Metabolism includes all chemical reactions in the body: anabolism (building up) and catabolism (breaking down)
- Cellular respiration (C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP) produces 36-38 ATP per glucose molecule
- Photosynthesis (6CO2 + 6H2O + light → C6H12O6 + 6O2) is the reverse of cellular respiration
- Enzymes are biological catalysts that speed up reactions without being consumed; they are specific to their substrate (lock-and-key model)
- The hierarchy of organization: atom → molecule → organelle → cell → tissue → organ → organ system → organism
- Four primary tissue types: epithelial (covering), connective (support), muscle (movement), nervous (signaling)
- Homeostasis is the body's ability to maintain a stable internal environment through negative feedback loops
- The pH scale ranges from 0 (acidic) to 14 (basic); blood pH is normally 7.35-7.45 (slightly alkaline)
Metabolism & Body Systems Overview
Understanding how the body produces and uses energy, how it is organized, and how it maintains balance is fundamental to nursing science.
Metabolism
Metabolism is the sum of all chemical reactions that occur in an organism. It has two components:
| Component | Description | Example |
|---|---|---|
| Anabolism | Building complex molecules from simple ones (requires energy) | Building proteins from amino acids, building glycogen from glucose |
| Catabolism | Breaking complex molecules into simpler ones (releases energy) | Breaking glucose into CO2 and H2O (cellular respiration) |
Cellular Respiration
Cellular respiration is the process by which cells break down glucose to produce ATP:
C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP (36-38 molecules)
The three stages of cellular respiration:
| Stage | Location | ATP Produced |
|---|---|---|
| Glycolysis | Cytoplasm | 2 ATP (net) |
| Krebs Cycle | Mitochondrial matrix | 2 ATP |
| Electron Transport Chain | Inner mitochondrial membrane | 32-34 ATP |
- Glycolysis does not require oxygen (anaerobic)
- The Krebs Cycle and ETC require oxygen (aerobic)
- Without oxygen, cells use fermentation (anaerobic respiration), producing only 2 ATP and lactic acid
Photosynthesis
Photosynthesis occurs in chloroplasts of plant cells and is essentially the reverse of cellular respiration:
6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2
- Occurs in two stages: light-dependent reactions (thylakoid) and the Calvin Cycle (stroma)
- Produces glucose and oxygen from carbon dioxide and water
- Chlorophyll absorbs light energy (primarily red and blue wavelengths, reflecting green)
Enzymes
Enzymes are biological catalysts — proteins that speed up chemical reactions without being consumed:
- Each enzyme is specific to its substrate (the molecule it acts on)
- The lock-and-key model describes how the enzyme's active site fits a specific substrate
- The induced-fit model (more accurate) says the enzyme slightly changes shape to fit the substrate
Factors that affect enzyme activity:
- Temperature: Optimal at body temperature (~37°C); denatured at high temperatures
- pH: Each enzyme has an optimal pH range
- Substrate concentration: Increases rate until all active sites are occupied (saturation)
- Inhibitors: Competitive (blocks active site) or non-competitive (changes enzyme shape)
Levels of Body Organization
| Level | Description | Example |
|---|---|---|
| Atom | Smallest unit of an element | Carbon, oxygen, hydrogen |
| Molecule | Two or more atoms bonded together | Water (H2O), glucose (C6H12O6) |
| Organelle | Specialized structure within a cell | Mitochondria, nucleus |
| Cell | Basic unit of life | Red blood cell, neuron |
| Tissue | Group of similar cells | Muscle tissue, nervous tissue |
| Organ | Two or more tissue types working together | Heart, lungs, liver |
| Organ System | Group of organs working together | Cardiovascular, respiratory |
| Organism | A complete living being | Human |
Four Primary Tissue Types
| Tissue Type | Function | Examples |
|---|---|---|
| Epithelial | Covers surfaces, lines cavities, forms glands | Skin, lining of GI tract, glands |
| Connective | Supports, connects, and protects | Bone, blood, cartilage, fat, tendons |
| Muscle | Produces movement | Skeletal, cardiac, smooth muscle |
| Nervous | Transmits electrical signals | Neurons, glial cells |
Homeostasis
Homeostasis is the body's ability to maintain a stable internal environment despite external changes.
Most homeostatic mechanisms use negative feedback loops:
- A receptor detects a change (stimulus)
- A control center (usually the brain) processes the information
- An effector produces a response that reverses the change
Example — Body Temperature:
- If body temperature rises → hypothalamus detects the change → signals sweat glands to produce sweat → evaporation cools the body → temperature returns to normal
Positive feedback amplifies the change (rare): Examples include blood clotting, labor contractions, and lactation.
pH Scale
| pH | Description | Examples |
|---|---|---|
| 0-6 | Acidic | Stomach acid (1-2), lemon juice (2), coffee (5) |
| 7 | Neutral | Pure water |
| 8-14 | Basic (Alkaline) | Blood (7.35-7.45), bleach (13) |
Blood pH must stay between 7.35 and 7.45. Values outside this range can be life-threatening.
Photosynthesis vs. Cellular Respiration — Comparison
| Feature | Photosynthesis | Cellular Respiration |
|---|---|---|
| Equation | 6CO2 + 6H2O + light → C6H12O6 + 6O2 | C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP |
| Energy | Absorbs light energy | Releases chemical energy |
| Organisms | Plants, algae, cyanobacteria | All living organisms |
| Location | Chloroplasts | Mitochondria (and cytoplasm) |
| Reactants | CO2 and H2O | Glucose and O2 |
| Products | Glucose and O2 | CO2, H2O, and ATP |
| Gas exchange | Takes in CO2, releases O2 | Takes in O2, releases CO2 |
| Time | Light required | Occurs continuously |
These two processes are essentially reverse reactions — the products of one are the reactants of the other. Together, they cycle carbon and oxygen through the biosphere.
Water Properties and Their Biological Importance
Water's unique properties are due to its polar nature and hydrogen bonding:
| Property | Description | Biological Importance |
|---|---|---|
| Cohesion | Water molecules stick to each other | Surface tension; water column in plants |
| Adhesion | Water sticks to other surfaces | Capillary action in blood vessels; meniscus |
| High specific heat | Resists temperature changes | Body temperature regulation |
| Universal solvent | Dissolves more substances than any other liquid | Transports nutrients, electrolytes, waste |
| Ice floats | Solid water is less dense than liquid water | Insulates aquatic ecosystems in winter |
| High heat of vaporization | Requires a lot of energy to evaporate | Cooling effect of sweating |
Aerobic vs. Anaerobic Respiration
| Feature | Aerobic | Anaerobic |
|---|---|---|
| Oxygen | Required | Not required |
| ATP yield | 36-38 per glucose | 2 per glucose |
| Stages | Glycolysis + Krebs + ETC | Glycolysis + fermentation |
| End products | CO2 + H2O | Lactic acid (animals) or ethanol + CO2 (yeast) |
| Efficiency | High | Low |
| When used | Normal conditions | During intense exercise (when O2 is insufficient) |
Lactic acid fermentation in muscle cells causes the burning sensation during intense exercise when oxygen demand exceeds supply.
Macronutrients and Micronutrients
Understanding nutrition connects biology to patient care:
Macronutrients (needed in large amounts)
| Nutrient | Calories/gram | Function | Sources |
|---|---|---|---|
| Carbohydrates | 4 kcal/g | Primary energy source | Bread, pasta, fruits, vegetables |
| Proteins | 4 kcal/g | Growth, repair, enzymes, antibodies | Meat, fish, beans, dairy |
| Fats | 9 kcal/g | Energy storage, insulation, cell membranes | Oils, butter, nuts, avocado |
Key Vitamins
| Vitamin | Function | Deficiency |
|---|---|---|
| Vitamin A | Vision, immune function | Night blindness |
| Vitamin C | Collagen synthesis, antioxidant | Scurvy (bleeding gums, poor healing) |
| Vitamin D | Calcium absorption, bone health | Rickets (children), osteomalacia (adults) |
| Vitamin K | Blood clotting | Bleeding disorders |
| B12 | RBC formation, nerve function | Pernicious anemia |
| Folic acid (B9) | DNA synthesis, cell division | Neural tube defects in pregnancy |
Key Minerals
| Mineral | Function | Deficiency |
|---|---|---|
| Iron | Hemoglobin (O2 transport) | Iron-deficiency anemia |
| Calcium | Bones, teeth, muscle contraction | Osteoporosis |
| Potassium | Heart rhythm, muscle function | Cardiac arrhythmias |
| Iodine | Thyroid hormones | Goiter |
| Zinc | Immune function, wound healing | Impaired immunity, slow healing |
| Magnesium | Muscle/nerve function, energy | Muscle cramps, cardiac arrhythmias |
Water-Soluble vs. Fat-Soluble Vitamins
| Category | Vitamins | Storage | Toxicity Risk |
|---|---|---|---|
| Water-soluble | B-complex, C | Not stored; excess excreted in urine | Low (rare toxicity) |
| Fat-soluble | A, D, E, K | Stored in liver and adipose tissue | Higher (can accumulate) |
Memory aid: Fat-soluble vitamins spell ADEK — and they need fat for absorption.
Nursing relevance: Patients with fat malabsorption (celiac disease, cystic fibrosis, liver disease) are at risk for fat-soluble vitamin deficiencies.
ATP: The Energy Currency of the Cell
Adenosine triphosphate (ATP) is the primary energy carrier in all living cells:
- ATP consists of adenine + ribose sugar + 3 phosphate groups
- Energy is released when the terminal phosphate bond is broken: ATP → ADP + Pi + Energy
- ATP is constantly recycled — the body produces and uses approximately its own body weight in ATP every day
- ATP is produced primarily through cellular respiration in the mitochondria
Uses of ATP in the body:
- Muscle contraction (actin-myosin interaction)
- Active transport (sodium-potassium pump)
- Nerve impulse transmission
- Protein synthesis
- Cell division
Which of the following is the correct equation for cellular respiration?
Which stage of cellular respiration produces the most ATP?
Enzymes function by:
Arrange the levels of body organization from simplest to most complex.
Arrange the items in the correct order
The normal pH range for blood is:
Which tissue type forms the outer layer of the skin and lines the digestive tract?
The process by which the body maintains a stable internal environment is called _____.
Type your answer below