7. Human nutrition

Human nutrition

• Humans require various nutrients to survive, necessitating a balanced diet that includes all food groups in appropriate proportions.

• Carbohydrates are crucial for providing energy during respiration, with rice, pasta, and potatoes serving as prime examples.

• Fats and oils function as long-term energy storage and provide insulation; examples include cheese, fatty meats, and butter.

• Proteins are essential for growth and tissue repair, typically found in fish, meat, and eggs.

• Vitamin C is vital for healthy skin and gums, with its deficiency leading to scurvy; sources include citrus fruits like oranges and lemons.

• Vitamin D aids calcium absorption necessary for strong bones; deficiencies can result in rickets; found in dairy products, fish oil, and eggs.

• Calcium is essential for bone health and blood clotting, present in milk, cheese, and eggs.

• Iron is required for hemoglobin formation in red blood cells to transport oxygen, found in red meat and green vegetables, such as spinach.

• Fiber, or roughage, facilitates food movement through the digestive system, sourced from vegetables, fruits, and whole grains.

• Water is necessary for chemical reactions, obtainable through beverages and food.

Digestive System

• The digestive system's primary function is to break down large insoluble molecules into smaller soluble ones, nourishing the body.

• Key parts of the digestive system include the mouth, esophagus, stomach, small intestine (duodenum and ileum), large intestine (colon), rectum, and anus, collectively forming the alimentary canal.

• Associated organs include salivary glands, pancreas, liver, and gall bladder, each playing a distinct role in digestion.

• The process of digestion includes ingestion (taking in food and drink), digestion (breaking down food), absorption (nutrients into blood), assimilation (nutrient use by cells), and ejection (removal of undigested food).

• Digestion can be physical (mechanical breakdown of food into smaller pieces) or chemical (breaking down food molecules with enzymes). Physical digestion increases surface area for enzymatic action.

Teeth and Digestion

• Humans have different types of teeth-incisors, canines, premolars, and molars-each serving specific functions: incisors for cutting, canines for tearing, and molars for grinding.

• The structure of a tooth includes enamel, dentine, pulp cavity, nerves, blood vessels, and cement. Teeth are embedded in bone and gums.

• Physical digestion also occurs in the stomach, where muscular contractions liquefy food and mix it with digestive juices.

• The liver produces bile, stored in the gall bladder, and released into the duodenum; bile is alkaline, neutralizing stomach acid and emulsifying fats for improved digestion by increasing the surface area for enzymes.

Chemical Digestion

• Chemical digestion is the process that breaks down large insoluble molecules into small soluble molecules that can be absorbed by the body.

• Enzymes play a crucial role in chemical digestion, with each enzyme targeting specific types of molecules.

Role of Enzymes in Digestion

• Amylase breaks down starch into simple sugars; it converts starch to maltose in the mouth and then to glucose in the small intestine.

• Protease is responsible for breaking down proteins into amino acids; pepsin works in the stomach, while trypsin functions in the alkaline environment of the duodenum.

• Lipase digests fats and oils, converting them into fatty acids and glycerol within the duodenum.

Functions of Hydrochloric Acid

• Hydrochloric acid is a component of gastric juice produced in the stomach.

• It serves multiple functions: killing harmful microorganisms in food and creating an acidic pH, which is ideal for enzymes like pepsin to function efficiently.

Role of Bile in Digestion

• Bile, involved in both physical and chemical digestion, emulsifies fats and neutralizes acidic mixtures from the stomach when they enter the duodenum.

• It alters the pH of food to provide an optimal environment for the enzymes in the small intestine, which require a higher alkaline pH for effective activity.

Absorption of Nutrients

• Absorption is the process through which digested food molecules move from the digestive system into the bloodstream, primarily occurring in the small intestine.

• The ileum, part of the small intestine, is adapted for efficient absorption due to its highly folded surface, featuring millions of villi and microvilli that increase the surface area.

• Villi contain capillaries that absorb glucose and amino acids, while lacteals transport fatty acids and glycerol into the lymphatic system.

Structure of Villi

• Villi are finger-like projections in the ileum that enhance nutrient absorption.

• Each villus contains capillaries and a thin surface layer, topped with microvilli, further optimizing absorption.

• Capillaries in the villi absorb glucose and amino acids, and lacteals assist in the transport of fatty substances.