Digestive System: Digestion and Absorption

What is digestion?

The process that breaks food into nutrients the body can absorb and use.

• Mechanical aspects: Chewing, peristalsis, segmentation

• Chemical aspects: Digestive juices and enzymes that break down food into absorbable molecules

What is absorption?

The process of taking in end products of digestion into the bloodstream or lymphatic system.

What is circulation in digestion?

The process of transporting absorbed nutrients throughout the body to nourish cells and tissues.

What quote defines life as a chemical process?

“Life is a chemical process”-Antoine Lavoisier, emphasizing that the body constantly renews tissues using nutrients from food.

How quickly are certain body cells replaced?

• Taste cells - every 7 days

• Intestinal lining - every 3 days

• Skin - every month

• Red blood cells - every 120 days

What are the time frames for digestion of food?

• Mouth: <1 minute

• Stomach: ~1-2 hours

• Small intestine: ~7-8 hours

• Large intestine: ~12-14 hours

What is peristalsis?

Wavelike muscular contraction of the GI tract that push its contents along.

What are the mechanical actions of digestion?

• Chewing: Breaks food and mixes with saliva

• Peristalsis: Moves food through GI tract.

• Stomach churning: Mixes food with gastric juices

• Segmentation: Mixes food with digestive juices.

• Sphincter contractions: Prevent reflux

What does gastric juice contain?

• Water

• Enzymes

• Hydrochloric acid (HCI)

  • Mucus protects the stomach lining from acid damage.

What enzymes are produced by the pancreas?

• Pancreatic amylase - breaks down carbohydrates

• Pancreatic lipase - breaks down fats (aided by bile)

• Trypsin - breaks down proteins

  • Also secretes bicarbonate to neutralize stomach acid.

What is the function of bile, and where is it made and stored?

• Produced by: Liver 

• Stored in: Gallbladder 

• Function: Aids in fat digestion and absorption by emulsifying fats.

Where does most nutrient absorption occur?

In the small intestine, which secretes enzymes to break down carbohydrates, proteins and fats.

What happens in the large intestine?

• Absorbs water and minerals

• Houses bacteria that digest undigested carbohydrates and some fibre.

What enhances nutrient absorption in the intestines?

Villi and microvilli, which increase surface area (~675 sq ft). These cells need high nutrient levels to maintain structure.

How are nutrients transported in the body?

• Blood vessels: carry carbohydrates and proteins (via arteries & veins)

• Lymphatic system: carries fat breakdown products to the bloodstream near the heart. 

What happens to dietary fibre during digestion?

• Passes through largely unchanged

• Adds bulk to stool and helps muscle movement.

• Some fibre digested by bacteria in the large intestine.

What percentage of nutrients are absorbed efficiently?

• Carbohydrate: 99%

• Protein: 92%

• Fat: 95%

What are common digestive disorders?

• IBS (Irritable Bowel Syndrome)

• Constipation & Hemorrhoids

• Ulcers & Heartburn

• Diarrhea

• Diverticulosis

• Flatulence

• Lactose Intolerance

What are symptoms and prevention of IBS?

• Gas, bloating, diarrhea, constipation 

• Prevention: low-fat, high-fibre diet, probiotics, medication

What causes constipation and hemorrhoids?

• Diets low in fibre and lack of physical activity

• Prevention: 25-30 g fibre/day + fluids

What foods can trigger ulcers or heartburn?

• Fatty foods, coffee, alcohol, citrus, and soft drinks

• Prevention: High-fibre diet.

What causes diarrhea?

• Bacterial or viral contamination, or nutrient deficiencies (Vitamin A, zinc)

• Danger: can cause dehydration, heart & kidney malfunction, death in severe cases. 

How is diarrhea treated and prevented?

• Prevention: Sanitation, immunization, adequate diet

• Treatment: Rehydration fluids (Pedialyte), followed by nutrient-rich foods (yogurt, milk, rice, potatoes, beans)

• Avoid sugary drinks.

What is diverticulosis?

• Bulging pouches in intestinal walls that trap feces and become infected (diverticulitis)

• Prevention: High-fibre diet to increase fecal mass and strenghten muscles.

What causes flatulence?

1. Swallowed air

2. Bacterial breakdown of undigested carbohydrates

   1. Foods like beans, broccoli, onions, and cauliflower cause more gas.

What causes lactose intolerance?

Low lactase enzyme production, leading to undigested lactose in large intestine.

What are symptoms of lactose intolerance?

Nausea, bloating, diarrhea, gas, abdominal cramping

What foods are easier to tolerate for lactose-intolerant people?

Yogourt, aged cheeses, cultured buttermilk: bacteria help digest lactose.

How can lactose intolerance be managed?

• Fortified plant milks

• Low-lactose milk

• Lactase tablets

• Yogurt or lactose-free dairy

What are key takeaways about digestion and absorption?

• Digestion converts food into absorbable nutrients

• Absorption happens mostly in the small intestine

• Fibre supports movement and health of the GI tract.

• Adequate fibre intake helps prevent many digestive disorders.