Digestive System

Question 1

Name and describe the four layers of the wall of the GI tract.

Answer 1

• Mucosa - type varies depending on GI location (tough and stratified or delicate and simple epithelium); mucus production
• Submucosa - connective tissue layer
• Muscularis - circular, longitudinal and oblique (in stomach) layers of muscle important in GI motility - peristalsis and segmentation
• Serosa -serous membrane that covers the outside of abdominal organs; it attaches the digestive tract to the wall of the abdominopelvic cavity by forming folds called mesenteries.

Question 2

Name and describe the seven primary mechanisms of the digestive system.

Answer 2

• Ingestion - complex foods taken into GI tract
• Digestion - group of processes that break complex nutrients into simpler ones (mechanical and chemical)
• Motility - a number of GI movements resulting from muscular contraction
• Secretion - release of digestive juices and hormones that facilitate digestion
• Absorption - movement of digested nutrients into the internal environment of the body
• Elimination - movement of resides of digestions out of the alimentary canal
• Regulation - neural, hormonal, and other mechanisms that regulate digestive activity

Question 3

Name the function of the uvula and soft palate.

Answer 3

Uvula and soft plate prevent food and liquid from entering the nasal cavities, and also assist in speech and swallowing (deglutition).

Question 4

Describe the three main parts of a tooth.

Answer 4

• Crown, neck, and root.
• The crown is the part of the tooth that you can see above the gums. The top layer of the crown is enamel.
• The root is the part of the tooth that is below the gums that is covered by cementum.
• The neck or cervical margin is where the crown and root meet.
• Below the enamel is dentin, which surrounds the pulp. Inside the pulp are the blood vessels and nerves of the tooth.

Question 5

Name the three pairs of salivary glands and describe where the duct for each enters the mouth.

Answer 5

• Parotid glands - largest salivary glands open near upper molars
• Submandibular glands - ducts open on either side of lingual frenulum
• Sublingual glands - multiple ducts open into the floor of the mouth

Question 6

Describe the structure of the pharynx.

Answer 6

• Three divisions: nasopharynx, oropharynx, laryngopharynx
• tonsils form a lymphoid ring that prevents digestive tract infection

Question 7

Describe the function of the pharynx.

Answer 7

• Oropharynx is most involved pharyngeal segment in deglutition (swallowing)
• Regulation of deglutition movements via motor cortex of cerebrum (voluntary) and “deglutition center” of brainstem (involuntary)

Question 8

Describe the structure of the esophagus.

Answer 8

• 25 cm long muscular tube that connects the pharynx to the stomach
• muscles in the esophagus propel food into the stomach
• two sphincters (upper esophageal sphincter) and (lower esophageal sphincter - also called cardiac sphincter)

Question 9

Name the functions of the lower esophageal, or cardiac sphincter and the pyloric sphincter.

Answer 9

The lower esophageal sphincter at the top of the stomach regulates food passing from the esophagus into the stomach, and prevents the contents of the stomach from reentering the esophagus. The pyloric sphincter at the bottom of the stomach governs the passage of food out of the stomach into the small intestine.

Question 10

Define peristalsis.

Answer 10

Peristalsis is the automatic wave-like movement of the muscles that line your gastrointestinal tract. Peristalsis moves food through your digestive system, beginning in your throat when you swallow and continuing through your esophagus, stomach and intestines while you digest.

Question 11

What are the three divisions of the stomach?

Answer 11

• Fundus (out-pouched base)
• Body (main part)
• Pylorus (apex)

Question 12

Where does the digestion of carbohydrates begin, and with which enzyme(s)?

Answer 12

• In the mouth, with salivary amylase.

Question 13

What is a hiatal hernia?

Answer 13

• Occurs when the stomach pushes through an opening in the diaphragm, which may cause GERD (gastroesophageal reflex disease)

Question 14

Where does the digestion of proteins begin, and with which enzyme(s)?

Answer 14

• Digestion begins in the stomach
• Enzyme pepsin initiates the digestion of proteins in the stomach. The pro-enzyme proactive form called pepsinogen gets converted to pepsin in the presence of HCl.

Question 15

What are the divisions of the small intestine in sequence?

Answer 15

• Duodenum
• Jejunum
• Ileum

Question 16

What are the main functions of the small intestine?

Answer 16

• Digestion - most digestion takes place in the small intestine with microscopic glands secreting intestinal juice (water, enzymes, ions), and pancreatic and liver secretions
• Absorption - huge absorptive surface area with circular folds (plicae), intestinal villi and microvilli, blood capillaries absorbing sugars and amino acids, and lacteals (lymph capillaries) absorbing liquids
• Motility - smooth muscle fibers contract to produce movements (peristalsis and segmentation)

Question 17

Define segmentation.

Answer 17

The contraction of intestinal circular smooth muscles that mixes chyme is called segmentation. The small intestine is the site where segmentation occurs. Segmentation plays a large part in both digestion and nutrient absorption and begins once chyme is dumped into the duodenum.

Question 18

Explain how bile from the liver and gallbladder reaches the small intestine.

Answer 18

The liver cells secrete the bile into small canals (hepatic duct) that lead to the common bile duct. From there, a smaller duct (cystic duct) branches off and leads to the gallbladder. The common bile duct ends at the small intestine. The bile produced by the liver flows directly into the small intestine during a meal.

Question 19

What is the function of cholecystokinin?

Answer 19

When fats and proteins enter your small intestine, cholecystokinin triggers your gallbladder and pancreas to contract. They deliver bile and enzymes to your duodenum to help break down the food for absorption.

Question 20

List what is contained in pancreatic juice.

Answer 20

Pancreatic juice contains enzymes (amylase, trypsin, lipase) important for digestion, sodium bicarbonate and an alkaline substance that neutralizes the hydrochloric acid in the gastric juice that enters the intestines.

Question 21

What is the function of bile?

Answer 21

• Bile contains bile salts that emulsify the lipids in chyme
• Bile contains cholesterol that can be eliminated from the body.

Question 22

Describe the structure of the large intestine.

Answer 22

• Cecum - blind-end pouch at beginning of large intestine; chyme enters cecum through ileocecal valve
• Colon - ascending, transverse, descending, and sigmoid segments
• Rectum - empties feces through anal canal and external opening called anus

Question 23

Describe the function of the large intestine.

Answer 23

• Microbiome (flora) - helps digest nutrients, produce vitamins and support immune protection; produces gas
• Absorption - water, salts, vitamins
• Defecation - elimination of feces; regulated by voluntary and involuntary anal sphincters

Question 24

Describe the mesentery and greater omentum.

Answer 24

The mesentery is a distinct part of the peritoneum that connects to the intestines, providing it with nerve innervation, blood supply, and structural support. The omentum is part of the visceral peritoneum that hangs over the stomach and connects to the transverse colon.

Question 25

Describe and give the function of the appendix.

Answer 25

• Blind, worm-shaped tube off cecum
• Functions as an incubator for bacteria of the intestinal microbiome

Question 26

Describe the peritoneum.

Answer 26

• Continuous serous membrane lining abdominal cavity (parietal layer) and covering abdominal organs (visceral layer)
• Retroperitoneal - describes structures outside the parietal peritoneum, such as kidneys

Question 27

Differentiate between mechanical and chemical digestion.

Answer 27

• Mechanical - chewing (mastication), swallowing (deglutition), and peristalsis break food into tiny particles, mix them well with digestive juices, and move them along the digestive tract
• Chemical - breaks up large nutrient molecules into compounds that have smaller molecules; brought about by digestive enzymes

Question 28

Describe the process of carbohydrate digestion.

Answer 28

• Begins in mouth with salivary amylase
• in small intestine pancreatic amylase breaks polysaccharides down to disaccharides
• Intestinal juice enzymes - maltase changes maltose to glucose, sucrase changes sucrose to glucose, lactase changes lactose to glucose

Question 29

Describe the process of protein digestion.

Answer 29

• Starts in stomach, completed in small intestine
• Hydrochloric acid in gastric juice unfolds large proteins and converts pepsinogen to active pepsin
• Pepsin partially digests proteins
• Pancreatic enzyme, trypsin continues digestion
• intestinal enzymes, peptidases, complete digestion of partially digested proteins and convert them to amino acids

Question 30

Describe the process of lipid digestion.

Answer 30

• Mainly in small intestines
• Bile contains no enzymes, but emulsifies lipids (breaks large lipid droplets into very small lipid droplets)
• Pancreatic lipase changes emulsified lipids to fatty acids and glycerol in small intestine

Question 31

Explain the process of absorption.

Answer 31

• Process by which digested nutrients move from intestine into blood or lymph
• Mechanisms include:
  -Diffusion (the movement of particles from areas of high concentration to areas of low concentration)
  -Osmosis (the movement of water across a semipermeable membrane from an area of high water concentration to an area of lower water concentration)
• Active transport (requires energy to move substances against a concentration gradient)

Question 32

What function do lacteals have in absorption?

Answer 32

Lacteals are the central lymphatic vessels in the villi of the small intestine and perform nutrient absorption, especially dietary lipids, and the transportation of antigen and antigen-presenting cells.