Digestive System Functions Quiz

Digestion, Absorption, and Transportation

• Digestion, absorption, and transportation are crucial processes for the body to utilize nutrients from food.
• Nutrients, water, and solids require a passageway to move from the mouth, past the diaphragm, into the stomach.
• Contents in the digestive tract must move at a specific pace, and liquid content needs to be carefully maintained to avoid being too watery or thick.
• Digested nutrients are then absorbed, and waste products are expelled to maintain the correct amount for body functions.
• Foods are not continuously excreted, but rather at intervals varying from person to person.

The Anatomy of the Digestive Tract

• The gastrointestinal (GI) tract is a single flexible tube stretching from mouth to anus.
• The lumen of the GI tract is the inner space inside, where nutrients need access to cross the GI tract wall.
• Food and substances typically are undigested until leaving the GI tract
• Digestion begins in the mouth where mechanical and chemical processes commence.
• Food is chewed/masticated, mixed into a bolus, and swallowed.
• Taste buds respond to various flavors.
• Swallowed food travels through the pharynx (throat) and into the esophagus.

Esophagus

• The esophagus moves the food from the mouth to the stomach.
• Esophageal sphincters regulate movement of contents between the esophagus and the stomach, as well as from the stomach to the small intestine

Stomach

• The stomach mixes food with gastric juices, producing chyme.
• The stomach's strong muscles churn and mix food.

Small Intestine

• Digesting and absorbing nutrients occur throughout the various segments of the small intestine (duodenum, jejunum, and ileum).
• The small intestine is roughly 3 meters long, with a large surface area.
• Villi and microvilli increase surface area for absorption,
• Intestinal glands along the lining secrete enzymes essential for digestion.
• The lining cells secrete mucus protecting cells from acidic chyme.
• The Ileoceal sphincter allows passage into the large intestine.

Large Intestine

• The large intestine absorbs water and electrolytes.
• Large intestine cells absorb any remaining nutrients, such as water and nutrients, from the remaining chyme (semi-digested food).
• Rectum and anus release any remaining waste products.

Muscular Action of Digestion

• Chewing and swallowing break down large food pieces into smaller pieces; saliva moistens food.
• Peristalsis propels food through the GI tract via rhythmic muscle contractions of both circular and longitudinal muscles.
• Stomach and small intestine have different contraction rates.
• Segmentation mixes food with digestive juices, keeping it in contact with nutrients to aid in absorption.

Stomach Action

• Stomach walls have three layers of strong muscles and thickest walls in the GI tract.
• Gastric juices are released into the stomach to aid in digestion.

Sphincter Contractions

• Sphincters are ring-like muscles.
• Sphincters control the movement of materials through the digestive system.
• Examples include the esophageal sphincters (upper and lower) , pyloric sphincter, and ileocecal sphincter.

Chemical Action of Digestion

• Enzymes are proteins that speed up chemical reactions without being changed themselves.
• Digestion utilizes many different enzymes based on the food, breaking down nutrients effectively.
• Different organs in the digestive system secrete digestive enzymes in various locations
• Examples: amylase (carbohydrates), lipase (fats), and protease (proteins).
• These enzymes are produced at different points along the GI tract.

Saliva

• Saliva comes from salivary glands, aiding digestion.
• Saliva contains water, salts, mucus, and enzymes.
• Saliva is crucial to initial carbohydrate digestion, moisturizing food, and protecting the mouth, esophagus, and stomach.

Gastric Juice

• Gastric juices are a mixture of water, enzymes, and hydrochloric acid.
• Hydrochloric acid has an important role in initial protein digestion.
• Mucus protects stomach cells from the acidity of hydrochloric acid.

Pancreatic Juice and Intestinal Enzymes

• Pancreatic juices aid in the digestion of all macronutrients (carbohydrates, proteins, and fats).
• Intestinal enzymes line the surface of small intestine cells.
• Sodium bicarbonate neutralizes acidic chyme entering the small intestine from the stomach.

Bile

• Bile is made in the liver.
• Bile is stored in the gallbladder.
• Bile aids fat digestion but is not an enzyme.

The Final Stage of Digestion

• Carbohydrates, fats, and proteins are absorbed.
• Some fiber is not absorbed and is excreted (removed from body).
• Water, any remaining minerals, and electrolytes are absorbed.
• Remaining materials create stool.
• Bacteria in the colon ferment fiber, releasing energy for colon cells.

Absorption

• Most absorption happens in the small intestine.
• The small intestine, although smooth, has folds (villi) and tiny projections (microvilli) that greatly increase surface area to aid in efficient nutrient absorption.
• Villi, microvilli, crypt glands, and goblet cells are important structures for absorption.
• Water-soluble nutrients go directly into the bloodstream.
• Fats and fat-soluble vitamins go into lymphatic vessels.

Preparing Nutrients for Transport

• After nutrients cross the intestinal wall (villi and microvilli), water-soluble nutrients enter the bloodstream.
• Fat-soluble nutrients form clusters (chylomicrons) and travel through the lymphatic system.

Transportation

• Nutrients travel through the vascular and lymphatic systems.

Vascular System

• The vascular system (blood circulatory system) is made up of vessels and pumps blood through the body.
• Blood carries absorbed nutrients and oxygen to tissues and removes waste products.

Nutrient Transport

• Nutrients, along with oxygen, are carried in the blood to body tissues.
• Waste products (carbon dioxide) travel from tissues through the blood to be expelled.

Capillaries, Arteries, and Veins

• Capillaries are tiny vessels carrying blood.
• Arteries carry blood away from the heart, and veins carry blood toward the heart.
• These vessels are important for blood flow in both the lymphatic and vascular systems.

The Liver

• The liver is a vital organ first receiving water-soluble nutrients.
• It's highly metabolically active, filtering and preparing blood for the body and removing metabolic waste products.
• The liver samples blood to remove toxins and create or process substances needed by the body.

The Lymphatic System

• The lymphatic system also transports materials, but it does not have a pump.
• It collects fluid from tissues (lymph) and sends it to the heart using lymph vessels, veins, and capillaries—all functioning in conjunction with the vascular system.
• Fat-soluble nutrients and large fat products of digestion are carried through the lymphatic system to the bloodstream, and then to other parts of the body.

Health and Regulation of the GI Tract

• The GI tract has homeostatic mechanisms maintaining a stable environment.
• Hormones and nerves control secretions and movement.
• Feedback mechanisms cause a response to conditions needing adjustment.

GI Hormones and Nerve Pathways

• Hormones and nerves coordinate digestive and absorption processes.
• Hormones and nerves signal when secretions and movements are needed.
• Feedback mechanisms detect or regulate changes.

Maintenance of Stomach pH

• Gastrin is released in the stomach when food is present.
• Gastrin stimulates the stomach to release components preparing it to digest substances.
• Increasing acidity stimulates cells to stop releasing gastrin as needed for digestion.

Secretin

• Secretin is released into the bloodstream in response to acidic chyme in the duodenum.
• Secretion of bicarbonate neutralizes the acidity and relaxes the pyloric sphincter, allowing digestion to continue.

Cholecystokinin (CCK)

• Presence of fat triggers the release of CCK.
• CCK signals the gallbladder to release bile and pancreas to secrete enzymes and bicarbonate.
• Emulsified fat signals CCK to stop.

How Does the Pancreas Know How Much Enzyme Needs to Be Secreted?

• GI hormones signal the pancreas based on macronutrients consumed.
• This signaling allows the body to adjust to changing nutrient requirements.
• Pancreas releases digestive enzymes in an inactive form, to be active and fully digest once they reach the small intestine.

GI Health

• Lifestyle factors (sleep, physical activity, stress) affect GI health.
• Diet quality and quantity influence GI health.
• Probiotics and prebiotics support a healthy microbiome in the gut.

Gut Bacteria

• Bacteria are essential for many functions.
• Maintaining a healthy balance of bacteria is crucial for the digestive system, immunity, and overall body health.
• Beneficial bacteria support immunity, and reduce inflammation.
• Harmful bacteria can cause problems or inhibit helpful bacteria.

Probiotics

• Probiotics are beneficial microorganisms found in food and supplements.
• Specific species are beneficial for the digestive system.
• Certain strains are useful in aiding digestion issues such as diarrhea.

Gastrointestinal Conditions

• Choking, belching, intestinal gas, GERD, ulcers, vomiting, diarrhea, constipation, Irritable bowel syndrome(IBS), Celiac disease, and inflammatory bowel disease (IBD) are common conditions affecting the GI tract.

Cleansing Diets

• Cleansing diets are often touted, but their claims are often unsupported
• Effectiveness and safety are questionable.