q4 scie

• Across the whole planet, humans eat on average between one and 2.7 kilograms of food a day
• That's over 365 kilograms a year per person, and more than 28,800 kilograms over the course of a lifetime
• Every last scrap of food makes its way through the digestive system
• Digestive system


  • Comprised of ten organs covering nine meters
  • Contains over 20 specialized cell types
  • One of the most diverse and complicated systems in the human body
• Digestive system


  Continuously works in unison to transform the raw materials of food into the nutrients and energy that keep you alive
• Main components of the digestive system

  • Gastrointestinal tract
  • Pancreas, gallbladder, and liver
  • Body's enzymes, hormones, nerves, and blood
  • Mesentery
• Gastrointestinal tract


  • A twisting channel that transports food
  • Has an internal surface area of between 30 and 40 square meters, enough to cover half a badminton court
• Pancreas, gallbladder, and liver


  • Break down food using an array of special juices
• Body's enzymes, hormones, nerves, and blood


  • Work together to break down food, modulate the digestive process, and deliver its final products
• Mesentery


  • A large stretch of tissue that supports and positions all digestive organs in the abdomen, enabling them to do their jobs
• Digestive process


  1. Anticipation of food triggers saliva production

  2. Chewing and saliva turn food into a moist lump called the bolus

  3. Peristalsis propels the bolus into the stomach

  4. Stomach walls break down the bolus

  5. Hormones trigger release of acids and enzymes to dissolve and break down food

  6. Bile, pancreatic and intestinal juices break down fats, proteins and carbohydrates in the small intestine

  7. Villi in the small intestine absorb molecules into the bloodstream

  8. Leftover fiber, water and dead cells make it to the large intestine where most fluid is drained out

  9. Remaining soft mass is squeezed into the rectum and expelled as stool
• The digestive process typically lasts between 30 and 40 hours
• Ingestion


  The process of taking in food and liquids through the mouth
• Mouth


  • Entry point for food
• Teeth


  • Mechanical breakdown of food through chewing
• Saliva


  • Contains enzymes (amylase) that begin the chemical breakdown of carbohydrates
• Tongue


  • Helps manipulate food and form a bolus for swallowing
• Digestion


  The breakdown of food into smaller, absorbable components through mechanical and chemical processes
• Mechanical Digestion


  Physical breakdown of food (chewing in the mouth, churning in the stomach)
• Chemical Digestion


  Enzymatic breakdown of macromolecules into their monomers
• Stomach


  • Secretes gastric juices, including hydrochloric acid and pepsin, which begin protein digestion
• Small Intestine


  • Primary site for digestion, with enzymes from the pancreas (lipase, amylase, proteases) and bile from the liver aiding in the digestion of fats, carbohydrates, and proteins
• Absorption


  The process by which nutrients from digested food are absorbed into the bloodstream or lymphatic system
• Small Intestine


  • Main site of nutrient absorption, particularly the jejunum and ileum
• Villi and Microvilli


  • Increase surface area for absorption; nutrients pass through epithelial cells into blood capillaries or lacteals (for fats)
• Nutrients Absorbed


  • Monosaccharides (glucose)
  • Amino acids
  • Fatty acids
  • Glycerol
  • Vitamins
  • Minerals
• Assimilation


  The process by which absorbed nutrients are utilized by the body's cells for energy, growth, and repair
• Distribution


  Nutrients are transported via the bloodstream to various tissues and cells
• Cellular Use


  Cells use nutrients for metabolic processes, including ATP production, protein synthesis, and storage of excess nutrients (e.g., glycogen in the liver and muscles)
• Egestion (Elimination)


  The process of expelling undigested and unabsorbed food residues from the body
• Large Intestine (Colon)


  • Absorbs water and electrolytes from remaining indigestible food matter
• Rectum


  • Stores feces until they are expelled
• Anus


  • The final part of the digestive tract where egestion occurs
• Summary

  • Ingestion: Intake of food
  • Digestion: Breakdown of food into absorbable molecules
  • Absorption: Nutrients entering the bloodstream
  • Assimilation: Utilization of nutrients by the body
  • Egestion: Elimination of waste
• Water Reabsorption


  The process by which water is absorbed back into the bloodstream from the digestive tract, particularly in the large intestine (colon)
• Key Reasons for Water Reabsorption

  • Maintenance of Fluid Balance
  • Concentration of Waste
  • Efficient Nutrient Absorption
  • Energy Conservation
  • Protection Against Dehydration
• Maintenance of Fluid Balance

  • Helps maintain the body's fluid balance, ensuring that the body has the right amount of water for physiological functions
  • Reabsorbing water into the bloodstream helps maintain blood volume and pressure, which are crucial for proper cardiovascular function
• Concentration of Waste


  • By reabsorbing water, the large intestine compacts waste into solid feces, making it easier to store and eliminate
  • Effective water reabsorption prevents the loss of too much water in feces, which can lead to dehydration and electrolyte imbalance
• Efficient Nutrient Absorption


  • Adequate water levels in the body ensure that nutrients dissolved in the bloodstream can be transported efficiently to cells and tissues
  • Water reabsorption helps maintain the balance of electrolytes (e.g., sodium, potassium), which are critical for cellular functions, including nerve impulses and muscle contractions
• Energy Conservation


  • The process of reabsorbing water conserves energy as it reduces the need for the body to constantly intake and excrete large volumes of water
  • Concentrating waste allows for more efficient processing and elimination, reducing the energy expenditure required for continuous digestion and excretion