The digestive system is a complex network of organs working together to break down food and absorb nutrients. From the mouth to the anus, each part plays a crucial role in processing what we eat and drink.

Regulation of digestion involves a delicate balance of neural and hormonal controls. The enteric nervous system, often called the "second brain," works with hormones to coordinate digestive processes, ensuring efficient nutrient absorption and waste elimination.

Digestive System Structure and Function

Organs of digestive system

• Mouth
  • Mechanical breakdown of food through chewing pulverizes food into smaller particles
  • Initial chemical digestion of carbohydrates via salivary amylase begins starch breakdown
• Esophagus
  • Muscular tube connecting mouth to stomach transports food bolus
  • Peristalsis moves food to stomach through rhythmic contractions
• Stomach
  • Temporary food storage holds food for 2-4 hours
  • Secretion of gastric juices for protein digestion includes hydrochloric acid and pepsin
  • Churning action for mechanical breakdown mixes food with gastric juices
• Small intestine
  • Duodenum receives digestive secretions from pancreas and liver to neutralize stomach acid
  • Jejunum and ileum main sites of nutrient absorption through specialized structures (villi and microvilli)
• Large intestine
  • Water absorption maintains fluid balance
  • Formation and storage of feces through bacterial fermentation of undigested matter
• Rectum and anus
  • Elimination of waste through coordinated muscle contractions

Functions of gastrointestinal tract

• Mechanical digestion
  • Chewing in the mouth breaks down food into smaller pieces
  • Churning in the stomach mixes food with gastric juices
  • Segmentation and peristalsis in small intestine move and mix chyme
• Chemical digestion
  • Breakdown of macronutrients into smaller molecules through enzymatic action
  • Enzymes secreted along the GI tract target specific nutrients (amylase for carbohydrates, lipase for fats)
• Absorption
  • Nutrients pass through intestinal wall into bloodstream via active and passive transport
  • Occurs primarily in small intestine due to its large surface area
  • Villi and microvilli increase surface area for absorption by up to 600 times
• Secretion
  • Release of digestive enzymes and hormones regulates digestive processes
  • Lubrication of GI tract protects mucosal lining

Role of accessory organs

• Liver
  • Bile production for fat emulsification breaks down large fat globules
  • Detoxification of harmful substances metabolizes drugs and toxins
  • Nutrient processing and storage regulates blood glucose levels
• Gallbladder
  • Storage and concentration of bile increases its potency
  • Release of bile into small intestine during digestion aids fat absorption
• Pancreas
  • Secretion of digestive enzymes breaks down macronutrients
    • Amylase for carbohydrates
    • Lipase for fats
    • Trypsin and chymotrypsin for proteins
  • Production of bicarbonate to neutralize stomach acid protects small intestine

Digestive System Regulation

Control of digestive system

• Neural control
  • Enteric nervous system regulates GI motility and secretion independently
  • Autonomic nervous system influences digestive processes
    • Parasympathetic stimulates digestion through vagus nerve
    • Sympathetic inhibits digestion during stress (fight or flight response)
• Hormonal control
  • Gastrin stimulates gastric acid secretion and is released by stomach in response to food
  • Cholecystokinin promotes pancreatic enzyme secretion and gallbladder contraction
  • Secretin stimulates bicarbonate secretion from pancreas and inhibits gastric acid secretion
  • Ghrelin increases appetite and stimulates gastric motility before meals
• Feedback mechanisms
  • Negative feedback loops regulate digestive processes to maintain homeostasis
  • Hormones and neural signals adjust based on nutrient content and volume of food (satiety signals)