Biology Chapter on Human Digestion

Types of Organisms Based on Nutrition

• Autotrophs (Self-Feeders): Obtain energy from sunlight and chemicals to produce their own food. Examples include plants and chemosynthetic bacteria.
• Heterotrophs: Cannot make their own food. Obtain energy from other organisms. Examples include animals and fungi.

Plant Nutrition

• Plants need water, carbon dioxide, and sunlight to make carbohydrates (glucose) through photosynthesis.
• Oxygen is also produced during photosynthesis and used by plants for cellular respiration.
• Nutrient absorption occurs through specialized proteins in the plasma membrane of root cells.
• Compacted or waterlogged soil can prevent plants from getting necessary oxygen.

Essential Nutrients

• Macronutrients (0.5% of dry weight): Carbon, Oxygen, Hydrogen, Nitrogen, Potassium, Calcium, Magnesium, and Phosphorus.
• Micronutrients (Trace amounts): Chlorine, Iron, Manganese, Zinc, Boron, Copper, and Molybdenum.

Nutritional Adaptations

• Plants and soil microbes can form symbiotic relationships (e.g., nitrogen-fixing bacteria).
• Symbiosis of plants and fungi can enhance phosphorus transfer.
• Parasitism includes parasitic plants that depend on hosts for survival.
• Predation involves insectivorous plants that attract and digest insects.

Animal Nutrition Feeding Mechanisms

• Substrate feeders live on or in their food source (e.g., earthworms, caterpillars).
• Filter feeders in aquatic environments feed on food particles or small organisms (e.g., whales, coelenterates).
• Fluid feeders acquire nutrients from living hosts (e.g., mosquitoes, leeches, aphids).
• Bulk feeders eat relatively large chunks of food, requiring adaptations like jaws, teeth, or tentacles (e.g., snakes, cats, humans).

Stages of Food Processing

• Mechanical processing/ingestion
• Secretion of digestive enzymes and other digestive aids
• Enzymatic hydrolysis
• Absorption
• Elimination

The Human Digestive System

• Food is broken down and absorbed in the mouth, esophagus, stomach, small intestine, and large intestine.
• Accessory organs (e.g., liver, pancreas) aid in digestion.
• The large intestine absorbs water and mineral salts from undigested food.
• Remaining waste is expelled as feces.

Human Digestive System: Specific Processes

• Mouth: Digestion begins where saliva containing amylase, softens food and breaks it down. The tongue forms the bolus, which is swallowed into the esophagus.
• Esophagus: Peristaltic movement moves food to the stomach (5-10 seconds).
• Stomach: Food stays 2-6 hours. Gastric juices continue digestion.
• Small Intestine: Food moves through the pyloric sphincter to the duodenum, jejunum, and ileum. Bile from the liver and enzymes from the pancreas complete digestion. Nutrients are absorbed through villi into the bloodstream.
• Accessory Organs: The liver produces bile to aid fat digestion. The pancreas produces hormones like insulin to regulate blood sugar. The gallbladder stores and releases bile.
• Large Intestine: Absorbs water and mineral salts; remaining material forms feces which are expelled via the rectum and anus (defecation).

Nutritional Requirements for Animals

• Water: Aids digestion, regulates body temperature, maintains pH, keeps tissues moist.
• Carbohydrates: Major energy source (4 calories/gram).
• Proteins: Building blocks for cells, muscles, and bones (4 calories/gram).
• Fats: Build cell membranes, insulate tissues, and are an energy source (9 calories/gram).
• Minerals: Maintain homeostasis (e.g., calcium for bones/teeth, trace minerals).
• Vitamins: Organic molecules required for normal metabolism (fat-soluble A, D, E, K and water-soluble B, C).

Plant and Animal Nutrition Comparison

• Feeding Mechanism: Plants are autotrophic (self-feeding), animals are heterotrophic (consume other organisms).
• Nutrient Absorption: Plants absorb nutrients through roots and leaves; animals absorb through a digestive system.
• Nutrient Requirements: Plants need macronutrients and micronutrients; animals need water, carbohydrates, proteins, fats, minerals, and vitamins.
• Digestive Process: Plants use photosynthesis to produce glucose; animals use mechanical and enzymatic breakdown of food.

Gas Exchange in Plants

• Plants do not "breathe" like animals but undergo gas exchange through stomata in leaves, lenticels in stems, root hairs, and pneumatophores in aerial roots.
• Carbon dioxide produced during plant respiration may be used in photosynthesis.

Gas Exchange in Animals

• Animals have specialized respiratory organs.
• Invertebrates include integumentary exchange (e.g., flatworms, earthworms), external gills (e.g., aquatic insects, mollusks, crustaceans), and tracheal systems (e.g., insects, spiders).
• Vertebrates include external gills (e.g., larval amphibians), internal gills (e.g., fish), and lungs (e.g., reptiles, birds, mammals).

Factors Affecting Animal Gas Exchange

• Respiratory surface area and permeability
• Partial pressure gradients
• Surface-to-volume ratio
• Ventilation mechanisms
• Respiratory pigments

Breathing Mechanisms in Vertebrates

• Amphibians use positive pressure breathing.
• Birds use unidirectional airflow systems with air sacs.
• Mammals use negative pressure breathing.

Coordination of Gas Exchange and Circulation

• Oxygen diffuses from alveoli into blood, binding to hemoglobin.
• Carbon dioxide diffuses from blood into alveoli to be exhaled.
• The nervous system regulates breathing rate and depth.

Respiratory Adaptations

• High altitude: larger hearts/lungs, hemoglobin with high O2 affinity
• Diving: slower heartbeat, reduced circulation (except brain)
• Humans at high altitude: more alveoli with capillaries in the lungs
• Asthma: bronchiole muscles contract, increasing airflow resistance.
• Emphysema: damaged alveoli, reduced respiratory function.
• Pneumonia: lung inflammation and fluid buildup.

Common Health Conditions in the Philippines

• Malnutrition: Inadequate intake of essential nutrients, leading to stunted growth, underweight, or deficiencies (e.g., anemia).
• Diabetes: Linked to poor dietary habits, affecting the body's ability to regulate blood sugar. Complications include heart disease and nerve damage.
• Hypertension: Linked to poor nutrition (high salt/fat intake), leading to cardiovascular diseases.
• Chronic Obstructive Pulmonary Disease (COPD): Often caused by long-term exposure to pollutants (e.g., smoke or dust), affecting gas exchange in the lungs.
• Pneumonia: An infection of the lungs that affects breathing, common in populations with poor immunity or malnutrition.

Top 3 Morbidity and Mortality in the Philippines

• Pneumonia is a leading cause of illness and death, particularly among children and the elderly.
• Hypertension-related illnesses (heart disease, stroke) are also significant.
• Chronic lower respiratory diseases are a burden due to prolonged illness and disability.