FNH 250 M.3 - Digestion & Absorption

what is digestion?

chemical and mechanical processes that break down food into absorbable units

what is absorption?

the process of moving digested nutrients from the GI tract into blood or lymph

Q: What is the gastrointestinal (GI) tract?

A: A muscular tube from mouth to anus through which food passes, is digested, absorbed, and excreted.

Q: List the major organs and accessory organs of the digestive system.

• Major organs: Mouth, esophagus, stomach, small & large intestines

• Accessory organs: Salivary glands, liver, pancreas, gallbladder

Q: What is peristalsis?

A: Involuntary wavelike muscle contractions that move food through the GI tract.

Q: What is segmentation?

A: Mixing movement in the small intestine that enhances digestion and absorption.

Q: What are sphincters and their roles in digestion?

A: Ring-like muscles that control food movement and prevent backflow in the GI tract.

Q: What happens in the mouth during digestion?

A: Food is chewed, mixed with saliva (which contains salivary amylase), and formed into a bolus for swallowing.

Q: What is the role of the stomach in digestion?

A: Holds and mixes food, secretes acid and enzymes, begins protein digestion, forms chyme.

Q: What is chyme?

A: A semi-liquid mixture of partially digested food and digestive juices from the stomach.

Q: What happens in the small intestine?

A: Most digestion and absorption occur here. Pancreatic enzymes and bile aid digestion; nutrients are absorbed.

Q: What happens in the large intestine?

A: Absorbs water and some nutrients, forms and excretes feces.

Q: What increases surface area for nutrient absorption in the small intestine?

A: Folds, villi, and microvilli ("brush border").

Q: What transport methods are used to absorb nutrients into cells?

A: Passive diffusion, facilitated diffusion, and active transport.

Q: Which nutrients enter the blood vs. lymph after absorption?

• Blood: Proteins, carbs, water-soluble vitamins, small lipids → liver via portal vein

• Lymph: Fat-soluble vitamins, large lipids → thoracic duct → bloodstream

Q: What is the role of the liver in nutrient transport?

A: First to receive blood-absorbed nutrients, detoxifies harmful substances.

Q: What hormone stimulates HCl release in the stomach?

A: Gastrin – triggered by food in the stomach; turned off when pH is low.

Q: What hormone stimulates pancreatic juice release?

A: Secretin – released in response to chyme in the small intestine; neutralizes acid.

Q: What does cholecystokinin (CCK) do?

A: Released when fat/protein enters small intestine; stimulates bile and pancreatic enzyme release; slows GI motility.

Q: What is the enteric nervous system?

A: A nervous system within the GI tract that regulates motility and secretion independently and in coordination with the brain.

Q: How does the brain influence digestion?

A: The parasympathetic nervous system stimulates digestion; stress inhibits it. The vagus nerve triggers hormone release.

Q: What is the gut microbiota?

A: Trillions of bacteria in the GI tract (mainly large intestine) that support digestion, immunity, and health.

Q: Define probiotics.

A: Live beneficial bacteria found in foods like yogurt, kombucha, sauerkraut.

Q: Define prebiotics.

A: Dietary components (like fiber) that promote the growth of beneficial gut bacteria.

Q: Define synbiotics.

A: Products that contain both probiotics and prebiotics.

what are the functions of the accessory organs?

1. salivary glands:

   secretes saliva (water, mucus, salts, salivary amylase) moisten foods, begins digestion of carbohydrates via salivary amylase

2. liver:

   secretes bile which goes to the gallbladder to be stored for later use or sometimes goes directly to the common bile duct which empties into the duodenum of the small intestine;

   produces bile to aid fat digestion, regulates and stores nutrients, detoxifies harmful substances

3. gallbladder:

   releases bile into the small intestine when stimulated by fat (via CCK);

   stores and concentrates bile from the liver; does not produce bile, but secretes stored bile into the small intestine

4. pancreas:

   secretes pancreatic juice into the small intestine via the pancreatic duct when stimulated by secretin and CCK containing digestive enzymes (amylase, lipase, proteases - secreted as inactive zymogens) and bicarbonate (neutralizes acidic chyme)

   produces enzymes and bicarbonate for digestion, neutralizes stomach acid in chyme

what are the parts of the small intestine and what function do they serve?

1. duodenum

   • primary site for chemical digestion

   • receives chyme from the stomach, bile from the gallbladder/liver (for fat emulsification), and pancreatic juices (enzymes + bicarbonate to neutralize acid)

   • begins digestion of carbohydrates, proteins and fats

2. jejunum

   • major site of nutrient absorption

   • absorbs carbohydrates (as monosaccharides), proteins (as amino acids/peptides), and most vitamins and minerals

   • has many villi and microvilli to maximize surface area

3. ileum

   • continues nutrient absorption (especially vitamin B12, bile salts and any remaining nutrients)

   • transfers remaining undigested material to the large intestine via the ileocecal sphincter

what is the function of the epiglottis?

to move food into the esophagus and prevent food from entering the trachea

what are some things that might occur if your pyloric sphicter was not function properly?

• food may not be able to pass from the stomach to the small intestine

• there may be backflow from the small intestine into the stomach

• stomach contents may be emptied into the small intestine too quickly

fill in the blanks: lipids are absorbed into the ___ system and enter the blood at the ___ vein.

which system are lipids absorbed into? and which vein is used to enter the blood?

lymphatic system

subclavian vein