ch.22 learning outcomes

Which other systems work the digestive system to support the cells and tissues of the human body?

The:

Circulatory System- provides access to the other systems.

Respiratory System- works with the cardiovascular system to supply oxygen to cells and remove carbon dioxide

Urinary System-removes the organic wastes generated by cell activities

Starting at the mouth, identify the major organs of the digestive tract.

• Mouth (Oral Cavity)

• Pharynx

• Esophagus

• Stomach

• Small Intestine

• Large Intestine

List the accessory organs of the digestive tract.

• Teeth

• Tongue

• Salivary glands

• Liver

• Gallbladder

• Pancreas

What is the importance of mesenteries?

They stabilize the positions of the attached organs, thus preventing the intestines from becoming entangled during digestive movements or sudden changes in body position.

Name the four layers of the digestive tract beginning from the lumen of the digestive tract.

• Mucosa

• Submucosa

• Muscular Layer

• Serosa

Compare the submucosal neural plexus with the myenteric plexus.

• Submucosal Neural Plexus:

  • Located in the submucosa layer of the digestive tract..

• Myenteric Plexus:

  • Found between the longitudinal and circular muscle layers.

Describe the orientation of smooth muscle fibers in the muscular layer of the digestive tract.

Inner Circular Layer

• look like little round balls

Longitudinal Layer

• look like little long spindles

Identify the structural characteristics of smooth muscle fibers.

• Smooth muscle fibers lack striations

  • No myofibrils and sarcomeres

  • No T-tubules

  • Sarcoplasmic reticulum forms a loose network through sarcoplasm

• Spindle-shaped cells

• Single nucleus

• Involuntary control

• Corkscrew when it contracts

Why can smooth muscle contract over a wider range of resting lengths than skeletal muscle?

Because it lacks the striations and sarcomeres found in skeletal muscle, allowing for more flexibility in contraction and adaptation to various lengths and shapes in organs like the stomach and blood vessels.

Which is more efficient in propelling intestinal contents along the digestive tract: peristalsis or segmentation. Why?

Peristalsis, this is because peristalsis involves wave-like muscle contractions that move the contents in one direction, while segmentation involves mixing and churning without significant forward movement.

Cite the major mechanisms that regulate and control digestive activities.

1. Local factors: pH, stretch, and presence of nutrients in the digestive tract influence digestion.

2. Neural control: Involves the enteric nervous system and autonomic nervous system. (Myenteric Reflexes)

3. Hormonal control: Hormones like gastrin, secretin, and cholecystokinin regulate digestive activities. (Enteroendocrine Cells)

Describe enteroendocrine cells.

They are specialized cells found in the digestive tract that produce peptide hormones regulating various digestive functions and signaling hunger, satiety, and other physiological processes.

Define ingestion.

Food and liquids enter the digestive tract through the mouth.

Distinguish between chemical digestion and absorption.

• Chemical Digestion: The chemical and enzymatic breakdown of food into substances that can be absorbed by the digestive epithelium.

• Absorption: The movement of nutrients across the digestive epithelium and into the bloodstream.

Describe the function of the large intestine.

Dehydration and compaction of indigestible materials in preparation for elimination.

The oral cavity is lined by which type of epithelium?

Stratified squamous epithelium.

Name the structures that forms the roof of the mouth.

Hard palate: formed by the palatine processes of the maxillary bones and the horizontal plates of the palatine bones

and

Soft palate: muscular and lies posterior to the hard palate

Describe the location of the fauces.

At the opening of the oral cavity, between the oral cavity and the oropharynx. They are formed by the soft palate, the uvula, the palatine arches, and the tonsils.

What effects might a shortened frenulum of the tongue cause?

Ankyloglossia (tongue-tie):

Can lead to speech difficulties, eating challenges, and restricted tongue movement affecting oral hygiene and dental health. Newborns with this condition have difficulty sticking out their tongue, so it interferes with breastfeeding, and learning to speak in toddlers.

Name the three main parts of a typical tooth.

• Crown: The visible part of the tooth above the gum line.

• Neck: The junction between the crown and the root of the tooth.

• Root: The part of the tooth embedded in the jawbone.

What is the name sometimes given to the third set of molars?

“Wisdom teeth"

Name the regions and functions of the pharynx.

• Regions: Nasopharynx, Oropharynx, Laryngopharynx

• Functions: Is an anatomical space and a common passageway for food, liquids, and air

Describe the muscular layer of the esophagus.

There is no serosa, but an adventitia of connective tissue outside the muscular layer anchors the esophagus to the posterior body wall.

Describe the major event in each of the three phases of swallowing.

• Buccal Phase: Food is chewed and mixed with saliva to form a bolus.

• Pharyngeal Phase: The bolus is propelled to the back of the mouth and into the esophagus.

• Esophageal Phase: The bolus is moved down the esophagus to the stomach through peristalsis.

What is the falciform ligament?

Theremanet of the ventral mesentery between the liver and the anterior wall of the peritoneal cavity.

What is the function of the lesser omentum?

To connect the stomach to the liver and help in the support and stabilization of these organs.

Explain the significance of peritoneal fluid.

It serves as a lubricant and shock absorber for organs in the abdominal cavity.

Name the four major regions of the stomach in order from its junction with the esophagus to the small intestine.

• Cardia

• Fundus

• Body

• Pylorus

What anatomical feature of the stomach allows the organ to form chyme?

The additional layer called the “Oblique Layer”of smooth muscle strengthens the stomach wall and assists in the mixing and churning to form chyme.

Describe the lining of the stomach.

• The stomach is lined with a mucous membrane composed of simple columnar epithelium.

• The membrane secrete gastric juices to further digest food.

Explain the significance of the alkaline mucous layer lining the interior surface of the stomach.

It protect the stomach lining from the acidic environment created by gastric juices, preventing self-digestion and maintaining a suitable pH for enzyme activity.

What is the function of parietal cells?

They secrete intrinsic factor, a glycoprotein that helps absorb vitamin B12 across the intestinal lining. This vitamin is necessary for erythropoiesis. They also secrete hydrochloric acid to keep the stomach contents at a pH of 1.5-2.0.

Describe the alkaline tide.

It refers to the increase in blood pH and bicarbonate levels that occur after a meal, particularly one high in protein. This is due to the release of hydrochloric acid (parietal cells) in the stomach during digestion, leading to the absorption of bicarbonate into the bloodstream, causing a temporary alkaline shift.

Name the layers of the small intestine from superficial to deep

1. Serosa: Outermost layer

2. Muscular Layer: Smooth muscle layer

3. Submucosa: Connective tissue layer

4. Mucosa: Innermost layer containing villi and crypts

Describe the anatomy of the intestinal mucosa

It has circular folds, villi, and intestinal glands.

Explain the function of lacteals.

They transport materials that cannot enter blood capillaries. For example, absorbed fatty acids are assembled into protein–lipid packages that are too large to diffuse into the bloodstream.

Name the three segments of the small intestine from proximal to distal.

• Duodenum

• Jejunum

• Ileum

Identify the segment of the small intestine found within the epigastric region.

The duodenum.

What is the primary function of the duodenum?

It is a "mixing bowl." It receives chyme from the stomach and digestive secretions from the pancreas and liver.

A traumatic injury to the umbilical region could affect which segments of the small intestine?

All three segments of the small intestine would be affected.

Name the major hormones that regulate digestive activities.

• Gastrin: stimulates gastric acid secretion

• Secretin: stimulates pancreas to release bicarbonate

• Gastric Inhibitory Peptide (GIP): secreted when fats and carbohydrates—especially glucose—enter the small intestine.

• Cholecystokinin (CCK): stimulates gallbladder contraction and pancreatic enzyme secretion

• Vasoactive Intestinal Peptide (VIP): stimulates the secretion of intestinal glands, dilates regional capillaries, and inhibits acid production in the stomach

• Enterocrinin: acts on the duodenum and induces the secretion of large quantities of alkaline mucus.

How would the pH of the intestinal contents be affected if the small intestine did not produce secretion?

The pH of the intestinal contents would likely become more acidic due to the lack of neutralizing bicarbonate ions from secretions.

Does a high fat meal raise or lower the level of CCK in the blood?

A high-fat meal raises the level of CCK.

Name and briefly describe an important characteristic of each of the three phases of gastric secretion.

• Cephalic Phase: Triggered by sight, smell, or thought of food, stimulating vagus nerve to increase gastric secretion.

• Gastric Phase: Food in stomach stimulates gastrin release, enhancing acid secretion.

• Intestinal Phase: Food in duodenum triggers release of secretin and CCK to inhibit gastric secretion.

Describe two central reflexes triggered by the stimulation of the stretch receptors in the stomach wall.

• Gastroenteric Reflex: stimulates motility and secretion along the entire small intestine.

• Gastroileal Reflex: triggers the opening of the ileocecal valve, allowing materials to pass from the small intestine into the large intestine.

Why might severing the branches of the vagus nerves that supply the stomach provide relief for a person who is suffering from chronic gastric ulcers?

It can reduce stomach acid secretion, which may help in healing chronic gastric ulcers by decreasing acid-related irritation and promoting ulcer recovery.

Name the major functions of the large intestine.

1. Reabsorbing water and compacting the intestinal contents into feces

2. Absorbing important vitamins generated by bacterial

   action

3. Storing fecal material prior to defecation

Identify the four regions of the colon.

• Ascending colon

• Transverse colon

• Descending colon

• Sigmoid colon

Describe mass movements.

They are powerful peristaltic contraction that occur a few times each day in response to distension of the stomach and duodenum. These contractions begin at the transverse colon and push materials along the distal portion of the large intestine.

How does digestion occur in the large intestine?

Digestion results from enzymes introduced into the small intestine or from bacterial action.

Define hemorrhoids.

Caused by high venous pressures due to straining during defecation or pregnancy, the veins can become distended.

Describe the two positive feedback loops involved in the defecation process.

1. Short intrinsic myenteric defecation: stretch receptors in the rectal walls, which promote a series of peristaltic contractions in the colon and rectum, moving feces toward the anus

2. Long parasympathetic defecation: the sacral parasympathetic system, also activated by the stretch receptors, which stimulates peristalsis via motor commands distributed by the pelvic nerves

What is the function of salivary glands?

It helps in moistening food, initiating digestion of carbohydrates, and protecting the oral cavity from pathogens.

Distinguish between the exocrine and endocrine secretions of the pancreas.

Exocrine cells: secrete buffers and digestive enzymes

Endocrine cells: secrete insulin, glucagon, pancreatic polypeptide (PP), and GH–IH

Which accessory organ of the digestive system is responsible for almost 200 known functions.

The liver.

Name the three pairs of salivary glands.

• Parotid glands

• Submandibular glands

• Sublingual glands

Damage to the parotid glands would affect the digestion of which nutrient?

These glands secrete the carbohydrate-digesting enzyme salivary amylase would interfere with the digestion of complex carbohydrates.

Which pair of salivary glands contributes most to saliva production?

The submandibular glands produce 70% of saliva.

Which pair of salivary glands secretes substances that reduce oral bacteria populations?

The submandibular glands transport antibodies (IgA).

Describe the outer covering of the liver.

The liver is wrapped in a tough fibrous capsule and is covered by a layer of visceral peritoneum.

What structure marks the division between the left lobe and right lobe of the liver?

The falciform ligament.

Name the lobes of the liver.

• Right lobe

• Left lobe

• Caudate lobe

• Quadrate lobe

What is the function of the gallbladder?

It temporarily stores bile produced by the liver.

Define hepatocyte.

They are liver cells that form a series of irregular plates arranged like the spokes of a wheel.

Describe a portal triad.

A portal area that contains three structures:

1. An interlobular vein

2. An interlobular artery

3. An interlobular bile duct.

Branches from the arteries and veins of each portal triad deliver blood to the liver sinusoids, or hepatic sinusoids, of adjacent liver lobule.

Define stellate macrophages and indictate their functions.

They are phagocytic cells, part of the monocyte–macrophage system and they engulf pathogens, cell debris, and damaged blood cells. They are also responsible for storing iron, some lipids, and heavy metals (such as tin or mercury) that are absorbed by the digestive tract.

Define emulsification.

The process of bile salts breakinging the lipid droplets apart in the lumen.

Trace a drop of bile from the hepatic ducts to the duodenal lumen.

Hepatic ducts —> Common hepatic duct —> Common bile duct —> Duodenal ampulla and papilla —> Duodenal lumen

What is the primary digestive function of the pancreas?

It produces pancreatic juice that contains buffers and several digestive enzymes necessary for the breakdown of starches, lipids, nucleic acids, and proteins.

Describe hepatitis.

An inflammation of the liver, can be caused by alcohol abuse, drugs, or infection.

Describe cholecystitis.

The gallstones are so large that they damage the wall of the gallbladder or block the cystic duct or bile duct. In that case, the gallbladder may need to be surgically removed. This removal does not seriously impair digestion, because bile production continues at normal levels.

What bacterium is responsible for most peptic ulcers?

The bacterium Helicobacter pylori is responsible for over 8-% of these ulcers.

Name the major and accessory organs of the digestive system.