IB Biology Chapter 6.1 Digestive System

• 1- Ingestion
• 2- Digestion (a series of biochemical processes that convert large ingested molecules into small soluble molecules through hydrolysis)
• 3-Absorption (from digestive system to blood and lymphatic system)
• 4-Transport (circulatory system delivers nutrients to body parts)

• Specific to substrates
• Have optimum pH
• Speed up biochemical processes

• Breaks down carbohydrates
• Substrate: starch
• Source: mouth
• Product: maltose
• Optimum pH: 7-7.8

• Breaks down polypeptides
• Example: pepsin
• Product: amino acids
• Source: stomach
• pH: 2

• Example: pancreatic lipase
• Substrate: triglycerides
• Product: fatty acids and glycerol
• Source: pancreas, delivered into small intestine

• Chewing (mechanical ingestion)
• Salivary amylase
• Chemical digestion of starch

A wave of muscle contractions (peristalsis) pushes the bolus into the stomach

• Muscular contractions continue digestions.
• Acid kills bacteria
• Pepsin secreted by gastric glands begins digestion of proteins
• Goblet cells: lining that secretes mucus and protects the stomach
• HCl: activates pepsin, kills bacteria

• Involuntary muscular action controlled by autonomous nervous system mixes food with digestive secretions (churning)
• Two layers of smooth muscles:
• Circular (inner)
• Longitudinal (outer)

Feces containing undigested food, dead cells and other waste is forced out of the anus

• 1- Duodenum
• Bile from the liver and gall bladder neutralises acid and emulsifies fats
• Pancreatic juice containing lipase, amylase, maltase, protease, trypsin (protein) is released into the duodenum through the pancreatic duct
• 2- Ileum
• Lower half of the intestine where absorption through the villi occurs

Inner lining, includes villi

Connective tissue between mucosa and muscle

Circular and longitudinal smooth muscles perform peristalsis

Protective outer layer

Single outer layer of each villus (short path for diffusion)

• Epithelial cells: single layer for shorter diffusion pathway
• Microvilli: to increase surface area

Inner vessel, absorption and transport of lipids (glycerol and fatty acids) in the lymphatic system

Transport and absorption of glucose and amino acids (glucose absorbed by liver, amino acids stored)

• 1- Initiated by salivary amylase in the mouth
• 2- Continued by pancreatic amylase in the small intestine
• amylase digests amylose into maltose and amylopectin into dextrins
• Maltose and dextrin are digested by maltase into glucose

• Glucose is cotransported with sodium ions into the epithelial cells of the villus
• Glucose monomers enter the lumen of the villus through facilitated diffusion
• Glucose diffuses into the adjacent capillaries and dissolves into blood plasma
• Hepatic portal vein transfers glucose into the liver
• Liver absorbs excess glucose which it converts into glycogen for storage

• Contains mucus- dead cells and large number of naturally occuring mutualistic bacteria that provide vitamin K
• Reabsorption of water and mineral ions
• The rest is feces, egested via the anus

• Simple diffusion
• Hydrophobic molecules enter cell membrane passively

• Facilitated diffusion
• water-soluble (hydrophilic molecules) enter the epithelial cells through channel proteins

• Active Transport
• Protein pumps use ATP to move amino acids into the epithelial cells

• Endocytosis
• Large molecules too large for diffusion are taken into the lumen using vesicles formed from the cell membrane