Digestion and Absorption (Part 1)

A vocabulary flashcard defining the fundamental process of digestion based on the lecture notes.

Digestion

The breaking food into components small enough to be absorbed by the body. occurs before entry of nutrients into circulation.

Absorption

The movement of nutrients, including water and electrolytes across the intestinal wall and into blood or lymph

What are the main parts of the digestive system?

The main parts of the digestive system include the mouth, esophagus, stomach, small intestines, large intestines, and anus.

What is the role of the digestive system?

The digestive system's role is to break down food into smaller components, absorb nutrients, and eliminate waste from the body.

Digestive system does not act alone, it needs:

→The Endocrine system: secretion of hormones

➢ The Nervous system: sending signals that control passage of food, hunger, satisfaction, etc.

➢ The Cardiovascular system: transporting nutrients to cells

➢ The Urinary system and Integumentary system: to eliminate waste

Gastrointestinal (GI) tract

Long hollow tube about 30 feet in length which runs from the mouth to the anus

Transit time is between 24 and 72 hours.

➢Transit time is affected by the composition of the diet, physical activity, emotions, medications, and illnesses.

What is segmentation in the GI tract?

Segmentation is a form of intestinal motility that mixes food with digestive juices and enhances nutrient absorption by creating rhythmic contractions.

Secretions (Mucus)

moistens, lubricates, protects

Secretions (Enzymes)

protein molecules secreted by the pancreas that aid in digestion

Secretion (Hormones)

chemical messengers that are secreted into the blood to regulate body function

Immune system

→About 70% of the immune system is located in or around the digestive tract

➢ Underneath the mucosal lining of the stomach is lymphatic tissue

➢ Constantly assessing good versus bad

➢ Secretory IgA antibodies are present in gut mucosa

Gastrointestinal motility

two types of movement (PERISTALSIS and SEGMENTATION)

Peristalsis

is a series of wave-like muscle contractions that move food through the gastrointestinal tract,

essential for the progression of bolus from the esophagus to the stomach and beyond

Glands

groups of cells that secrete materials such as saliva, enzymes, gastric juice, mucus

Digestion (Mouth)

Just the sight or smell of food starts the digestion process by saliva flowing.

✓ Food > local nerve signals > secretion of ghrelin a hormone that tells the brain (hypothalamus) to send a signal of hunger.

✓ Chewing crushes and softens the food, increases the surface area of food and allows for the mixing of saliva.

✓ Saliva helps dissolve the food so that it can be tasted (only particles in solution can react with taste buds). Tong allows to taste food and move food around the mouth, facilitating chewing and swallowing.

✓ Saliva is 99.5% water and amylase (enzyme that breaks starches into sugars)

✓ Once chewed and swallowed is a BOLUS.

Bolus → Epiglottis → Esophagus

Bolus slides across the epiglottis, bypassing the entrance to the lungs. During swallowing the epiglottis closes off the trachea (air passageway to the lungs) to prevent choking.

▪ Pharynx is shared by the digestive tract and the respiratory tract. Is a funnel shaped opening that connects the nasal passages and mouth to respiratory passages and esophagus. Is a common passageway for food and air and is responsible for swallowing.

▪ Esophagus has a sphincter muscle at each end. During swallowing upper sphincter opens, the bolus slides down, the lower sphincter closes behind the bolus so it cannot slip back

Esophagus

It is a tube extending from mouth to stomach

Esophageal sphincter protects food once in the stomach from moving back to the esophagus.

➢ Reflux is caused by weakening of the sphincter.

Stomach

It is a temporary storage place

➢ Food mixes with gastric juices and Hydrochloric acid and transforms the bolus into a semi-liquid mass called chyme.

➢ Some water and alcohol digested.

➢ Size of fist but can expand up to 20 times its size after a large meal.

➢ Comfortably holds about 1 liter of food

➢ Food exits through pyloric sphincter into the small intestine

Gastric Juices

The stomach contains gastric glands that excrete gastric juice (water, enzymes and hydrochloric acid (HCl)

➢Kills most bacteria

➢Stops action of salivary amylase

➢Starts the digestion of protein by activation of the enzyme pepsin

➢Drops the pH of the stomach from 3.5-4.0 to 1.0-2.00 (is the only acidic environment in the body)

➢The stomach releases the chyme through the pyloric sphincter, which opens into the small intestine and closes afterwards

Emptying stomach

empties in about 2 to 6 hours

• A large meal slows emptying

• Solid meal moves slower than a liquid one

• Higher fat slows movement

• Protein alone moves faster than fat

• Carbohydrates move the quickest

• Sadness/fear slow movement

• Aggression/anger speed movement

Small intestines

Is line a narrow tube about 20 ft long: Duodenum: 12 inches Jejunum: 8 feet Ileum: 11 feet

➢The small intestine is the main site for digestion and absorption of water, vitamins, minerals, carbohydrates, fat, and protein

➢Accessory organs (pancreas/gallbladder) aid in digestion