6. Digestive System Flashcards
What are the two groups of the digestive system?
- Gastrointestinal (GI) tract: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus
- Accessory digestive organs: teeth, tongue, salivary glands, liver, gall bladder, pancreas
What are the five processes of digestion?
- Ingestion – Taking food into the mouth.
- Propulsion – Swallowing & peristalsis (moving food through the tract).
- Digestion –
• Mechanical: Physical breakdown (chewing, churning).
• Chemical: Enzyme breakdown (e.g., amylase, pepsin). - Absorption – Nutrient transfer to blood/lymph.
- Defecation – Elimination of waste as feces.
What are the four layers of the GI tract?
• Mucosa (innermost)
• Submucosa
• Muscularis (for movement)
• Serosa (outer layer)
What type of epithelium is found in different parts of the GI tract?
• Mouth, esophagus, anus → Stratified squamous
• Stomach, intestines → Simple columnar
What is the function of saliva?
- Dissolves and lubricates food to form a bolus
- Starts digestion of starch (salivary amylase)
What are the three major salivary glands?
• Parotid (largest, near ear)
• Submandibular (under jaw)
• Sublingual (under tongue)
What are the mechanical and chemical digestive processes in the mouth?
• Mechanical: chewing by teeth
Chemical:
• Salivary amylase: breaks starch into maltose
• Lingual lipase: produced but inactive in mouth
What are the three phases of swallowing?
• Voluntary phase: tongue pushes bolus into pharynx
• Pharyngeal phase: involuntary, soft palate closes nasopharynx, epiglottis closes trachea
• Esophageal phase: peristalsis moves bolus down esophagus
What prevents food from entering the airway during swallowing?
The epiglottis covers the trachea
Breathing will halt
What is the function of the esophagus?
Transports food to the stomach via peristalsis
What is peristalsis?
Alternating contractions of circular and longitudinal muscles to move food through GI tract
What are the two esophageal sphincters?
• Upper esophageal sphincter: regulates entry
• Lower esophageal sphincter (LES): prevents reflux
What are the functions of the stomach?
• Holds food
• Churns food into chyme
• Secretes gastric juice
• Begins protein digestion
What are the components of gastric juice?
• Hydrochloric acid (HCl): activates enzymes, kills microbes
• Pepsinogen (inactive) → Pepsin (active, digests proteins)
• Intrinsic factor: necessary for vitamin B12 absorption
• Mucus: protects stomach lining
What are the specialized stomach cells?
• Parietal cells → HCl, intrinsic factor
• Chief cells → Pepsinogen
• G cells → Gastrin (hormone)
• mucus cells → produces protective mucus
How does the stomach protect itself from digestion?
- Pepsinogen is secreted inactive
- Thick mucous barrier with bicarbonate
What is gastroesophageal reflux disease (GERD)?
When the lower esophageal sphincter (LES) fails to close properly, causing acid reflux
What are the functions of the liver?
• Produces bile
• Regulates blood glucose
• Protein metabolism (deamination, plasma proteins)
• Stores vitamins (A, D, E, K, B12) and minerals (Fe, Cu)
• Detoxifies alcohol and drugs
• breakdown of hemoglobin
What is the function of bile?
Emulsifies fats (breaks down fat globules for digestion)
What is the function of the gall bladder?
Stores and concentrates bile
What is the function of the pancreas?
• Produces pancreatic juice, containing:
Sodium bicarbonate (neutralizes stomach acid)
• Enzymes for digestion:
• Pancreatic amylase (carbs)
• Pancreatic lipase (lipids)
• Proteases (inactive form): trypsinogen, chymotrypsinogen, procarboxypeptidase
How are pancreatic enzymes activated?
• Enterokinase (in the small intestine) activates trypsinogen → trypsin
• Trypsin then activates other enzymes (chymotrypsinogen, procarboxypeptidase, proelatase
What are the functions of the small intestine?
• Completes digestion (via brush border enzymes)
• Absorbs nutrients (90%)
• Releases hormones (secretin, cholecystokinin)
What increases surface area in the small intestine?
Villi and microvilli
What hormones regulate digestion in the small intestine?
• Secretin: stimulates pancreas to release bicarbonate
• Cholecystokinin (CCK): stimulates release of bile and digestive enzymes
How are carbohydrates absorbed?
• Glucose & galactose: active transport
• Fructose: facilitated diffusion
• both leave interstitial cell by facilitated diffusion
• Transported to bloodstream → liver
How are proteins absorbed?
• Amino acids: active transport
• leaves interstitial cell through facilitated diffusion
• Transported to bloodstream → liver
How are lipids absorbed?
• Short-chain fatty acids: simple diffusion → bloodstream
• Long-chain fatty acids: form chylomicrons → lymphatic system → blood
What are the functions of the large intestine?
• Absorbs water, vitamins, minerals
• Forms and stores feces
• Hosts gut bacteria (produce Vitamin K & biotin)
What is the defecation reflex
• Feces stretches rectum → spinal reflex
• Internal anal sphincter (involuntary) relaxes
• External anal sphincter (voluntary) contracts until defecation is appropriate
Why is bile important for lipid digestion
bile emulsifies fats, breaking large fat globules into smaller droplets, increasing the surface area allowing for efficient lipid digestion
Name the brush border enzymes found in the small intestine
- Sucrase- glucose + fructose
- Lactase- glucose + galactose
- Maltase- glucose + glucose
- Aminopeptidase- amino acids
- Dipeptidase- amino acids
