EXAM 6: Digestive

Question 1

Differentiate between ingestion, mechanical digestion, chemical digestion, and absorption.

Answer 1

Ingestion: The process of taking in food and liquids through the mouth.
Mechanical Digestion: The physical breakdown of food (e.g., chewing, churning in the stomach).
Chemical Digestion: The enzymatic breakdown of food into smaller molecules (e.g., enzymes in saliva, stomach acids).
Absorption: The process by which nutrients pass through the digestive tract lining into the bloodstream or lymphatic system.

Question 2

Which structures of the GI tract contribute to mechanical digestion or chemical digestion?

Answer 2

Mechanical Digestion: Teeth, tongue, stomach (churning), small intestine (mixing).
Chemical Digestion: Salivary glands (saliva), stomach (gastric juices), pancreas (digestive enzymes), liver (bile), small intestine (enzymes from pancreas and brush border enzymes).

Question 3

What is the gross anatomy, cellular make-up, special adaptations, and function of the following organs: mouth, salivary glands, pharynx, esophagus?

Answer 3

Mouth: Oral cavity, lined by mucous membrane; function: ingestion, mechanical digestion (chewing), chemical digestion (saliva enzymes).
Salivary Glands: Produce saliva containing enzymes for starch digestion (amylase).
Pharynx: Passageway for food, connects mouth to esophagus.
Esophagus: Muscular tube for moving food to the stomach via peristalsis.

Question 4

What is the gross anatomy, cellular make-up, special adaptations, and function of the following organs: stomach, small intestine, large intestine, sigmoid colon, rectum, anus

Answer 4

Stomach: Muscular organ for churning food and chemical digestion (gastric juices, pepsin).
Small Intestine: Primary site for nutrient absorption, with villi for surface area.
Large Intestine: Absorbs water and electrolytes, forms feces.
Sigmoid Colon: Part of the large intestine, stores fecal material before elimination.
Rectum: Stores feces until excretion.
Anus: Controls elimination of feces.

Question 5

What is the gross anatomy, cellular make-up, special adaptations, and function of the following organs: liver, pancreas, and gallbladder

Answer 5

Liver: Produces bile for fat digestion.
Pancreas: Produces digestive enzymes and bicarbonate.
Gallbladder: Stores bile and releases it into the small intestine.

Question 6

What are the visceral and parietal peritoneum, the structure of mesenteries, and the cavity surrounding it?

Answer 6

Visceral Peritoneum: The membrane covering the organs in the abdominal cavity.
Parietal Peritoneum: The membrane lining the abdominal wall.
Mesenteries: Double layers of peritoneum that support organs, contain blood vessels, nerves, and lymphatics.
Cavity: The peritoneal cavity, a space between the visceral and parietal peritoneum filled with serous fluid.

Question 7

What are the general tissue layers (histology) of the whole GI tract, their organization (mucosa, submucosa, muscularis externa, serosa/adventitia), and their functions?

Answer 7

Mucosa: The innermost layer, made of epithelial cells, responsible for secretion and absorption.
Submucosa: Connective tissue containing blood vessels and nerves, providing structural support.
Muscularis Externa: Layers of smooth muscle responsible for peristalsis (movement of food).
Serosa/Adventitia: Outer layer; serosa is a smooth membrane (in the abdominal cavity), adventitia is a connective tissue layer (in areas not covered by serosa).
Histological Changes: The mucosa and muscular layers differ in thickness and structure across the tract, reflecting their functional requirements (e.g., thicker muscularis in the stomach for churning, more villi in the small intestine for absorption).

Question 8

What is the difference between an endocrine vs. exocrine gland?

Answer 8

Endocrine Glands: Secrete hormones directly into the bloodstream or lymph (e.g., pituitary, thyroid).
Exocrine Glands: Secrete substances through ducts to an external or internal body surface (e.g., sweat glands, salivary glands).

Question 9

What is the general composition of saliva, the names of the salivary glands, and their location?

Answer 9

Saliva Composition: Primarily water, electrolytes, mucus, enzymes (e.g., amylase, lipase), and antimicrobial compounds.
Salivary Glands:
Parotid Glands: Located near the ears.
Submandibular Glands: Located beneath the jaw.
Sublingual Glands: Located under the tongue

Question 10

What is the action of salivary amylase?

Answer 10

Salivary Amylase: An enzyme in saliva that begins the breakdown of starch into smaller sugar molecules (maltose) in the mouth.

Question 11

Describe the histology of the esophageal mucosa and Muscularis externa. How does the musculature change along its length?

Answer 11

Esophageal Mucosa: Made up of stratified squamous epithelium to protect against abrasion from food.
Muscularis Externa: Composed of two layers of muscle—skeletal muscle in the upper part (for voluntary control), transitioning to smooth muscle in the lower part (for involuntary control).
Musculature Change: The upper third is skeletal muscle, the middle third is a mix of skeletal and smooth muscle, and the lower third is smooth muscle only.

Question 12

Question: What is peristalsis, what is its function, and how is it coordinated along the esophagus?

Answer 12

Peristalsis: The rhythmic contraction and relaxation of smooth muscles that moves food through the digestive tract.
Function: It helps propel food from the mouth to the stomach.
Coordination in the Esophagus: The smooth muscles contract in a wave-like fashion, with a sequence of contraction and relaxation that pushes food downward. This is controlled by the enteric nervous system and modulated by signals from the brain.

Question 13

What organs are part of the alimentary canal vs. accessory digestive organs?

Answer 13

Alimentary Canal: The continuous tube that runs from the mouth to the anus, responsible for digestion and absorption. It includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.
Accessory Digestive Organs: Organs that assist in digestion but are not part of the continuous alimentary canal. These include the salivary glands, liver, gallbladder, and pancreas.

Question 14

What does retroperitoneal mean? What organs have we studied that are retroperitoneal?

Answer 14

Retroperitoneal: Refers to organs that are located behind the peritoneum, the membrane that lines the abdominal cavity. These organs are not suspended by mesenteries.
Retroperitoneal Organs Studied: The kidneys, pancreas, duodenum, ascending colon, and descending colon are examples of retroperitoneal organs.

Question 15

What are zymogens?

Answer 15

Zymogens: Inactive enzyme precursors that are activated by specific biochemical reactions. They prevent the premature activation of digestive enzymes that could damage tissues. Examples include pepsinogen (inactive form of pepsin) and trypsinogen (inactive form of trypsin).

Question 16

Know your ducts - pancreatic, bile, common hepatic, right and left hepatic, cystic, hepatopancreatic ampulla, and major duodenal papilla.

Answer 16

Pancreatic Duct: Carries pancreatic enzymes and bicarbonate from the pancreas to the duodenum.
Bile Duct: Transports bile from the liver and gallbladder to the duodenum.
Common Hepatic Duct: Carries bile from the liver.
Right and Left Hepatic Ducts: Carry bile from the right and left lobes of the liver, respectively.
Cystic Duct: Carries bile to and from the gallbladder.
Hepatopancreatic Ampulla: Junction where the pancreatic duct and bile duct meet before entering the duodenum.
Major Duodenal Papilla: The opening in the duodenum where bile and pancreatic enzymes enter for digestion.

Question 17

Know the anatomy of the tooth.

Answer 17

Crown: The visible part of the tooth, covered by enamel, the hardest substance in the body.
Dentin: The hard tissue beneath the enamel, forming the bulk of the tooth.
Pulp: The central part of the tooth, containing blood vessels and nerves.
Root: The part of the tooth that anchors it to the jawbone, covered by cementum.
Periodontal Ligament: Connects the tooth root to the surrounding alveolar bone.
Gums (Gingiva): The soft tissue that surrounds the base of the tooth.

Question 18

Be able to list where the enteroendocrine cells along the GI tract are located, their hormones released, and the effector cells and the effects.

Answer 18

G Cells (in the antrum of the stomach): Release gastrin, which stimulates parietal cells to secrete HCl and stimulates motility.
D Cells (in the antrum and body): Release somatostatin, which inhibits the release of gastrin and HCl secretion, as well as inhibiting gastric motility.
Enterochromaffin-like Cells (ECL Cells): Release histamine, which stimulates parietal cells to secrete HCl.
G-Cells (found in pyloric region): Release Gastrin and Ghrelin, stimulating hunger and gastric motility.

Question 19

How does the mucosal lining change in the stomach

Answer 19

• The mucosal lining of the stomach contains gastric pits and gastric glands. The lining changes from simple columnar epithelium in the upper parts to specialized cells such as parietal cells, chief cells, and G cells.
• The mucosa is also lined by a thick mucus layer that protects the stomach from the acidic environment. The mucus layer is produced by mucous neck cells and is continuously renewed.

Question 20

What is the role of HCl and intrinsic factor; which cell makes them, and what is the effect of each secretion?

Answer 20

HCl (Hydrochloric Acid):
- Secreted by parietal cells in the stomach.
- Role: Lowers the pH of the stomach to activate pepsinogen to pepsin, aids in the breakdown of proteins, and provides an acidic environment for enzymatic digestion.

Intrinsic Factor:
- Also secreted by parietal cells.
- Role: Necessary for the absorption of vitamin B12 in the small intestine.

Question 21

What is the role of pepsinogen; how is it activated; what cell makes it?

Answer 21

• Secreted by chief cells in the stomach.
• Role: Inactive precursor to pepsin, an enzyme that begins the breakdown of proteins.
• Activation: Pepsinogen is activated to pepsin when exposed to the acidic environment of the stomach (via HCl from parietal cells).

Question 22

Which cells or glands of the stomach make mucous?

Answer 22

Mucous Neck Cells (found in the neck of the gastric pits): Secrete a thick mucus that protects the stomach lining from the acidic environment.
Surface Mucous Cells: Produce a more viscous mucus that lines the surface of the stomach and protects against mechanical damage and acid.

Question 23

Name an endocrine (enteroendocrine) cell of the stomach and its product.

Answer 23

G Cell: Secretes gastrin, which stimulates parietal cells to secrete HCl and increases gastric motility.

Question 24

Know the 4 regions of the stomach; what is the role of the pyloric sphincter? What are rugae? What’s different about the muscularis?

Answer 24

1. Cardia: Area where food enters from the esophagus.
2. Fundus: The upper portion that stores food and gases.
3. Body (Corpus): The main central part involved in digestion.
4. Pylorus: The lower part that leads to the duodenum

Pyloric Sphincter: Controls the passage of partially digested food (chyme) from the stomach to the small intestine.
Rugae: Folds in the stomach lining that allow for expansion when the stomach is filled with food.
Muscularis: The stomach has a unique three-layered muscularis (longitudinal, circular, and oblique muscle layers) that allows for more efficient churning and mixing of food.

Question 25

What is normal stomach pH?

Answer 25

The normal stomach pH ranges from 1.5 to 3.5, which is highly acidic and necessary for the activation of enzymes like pepsin and for the digestion of proteins.

Question 26

What materials can be absorbed across the stomach wall?

Answer 26

- Alcohol and some lipid-soluble substances (like certain medications) can be absorbed directly across the stomach wall. - However, most digestion and absorption occur in the small intestine, not the stomach.

Question 27

Identify 3 adaptations for increased surface area in the small intestine. What is the major role of the small intestine?

Answer 27

**Circular Folds**: Large folds in the mucosa and submucosa that increase surface area for absorption. **Villi**: Finger-like projections of the mucosa that contain blood vessels and lymphatics for nutrient absorption. **Microvilli**: Tiny projections on the epithelial cells (forming the brush border) that further increase surface area. The small intestine is primarily responsible for the digestion and absorption of nutrients. Most enzymatic digestion occurs here, and absorbed nutrients enter the bloodstream or lymphatic system.

Question 28

Name the 3 regions of the small intestine.

Answer 28

1. Duodenum: The first section, where most chemical digestion occurs and where bile and pancreatic enzymes enter. 2. Jejunum: The middle section, primarily involved in nutrient absorption. 3. Ileum: The last section, involved in the absorption of nutrients and bile salts. It also connects to the large intestine.

Question 29

Where do pancreatic and liver secretions enter the small intestine?

Answer 29

- Both pancreatic and liver secretions enter the small intestine at the duodenum. - The pancreatic duct and common bile duct merge at the hepatopancreatic ampulla (Ampulla of Vater) and empty their contents into the duodenum at the major duodenal papilla.

Question 30

How is stomach acid neutralized? Where does it occur? Why does it occur?

Answer 30

- Bicarbonate (HCO₃⁻) secreted by pancreatic cells neutralizes stomach acid. - This occurs in the duodenum, where pancreatic juice is released, and the bicarbonate raises the pH to protect the intestinal lining and facilitate enzyme activity.

Question 31

Be able to describe the anatomy of a villus. Include blood vessels, lacteal, and microvilli.

Answer 31

**Villus**: Finger-like projection in the mucosa of the small intestine that increases surface area for nutrient absorption. **Microvilli**: Tiny hair-like projections on the surface of epithelial cells, forming the brush border that further increases surface area. **Blood Vessels**: A network of capillaries within the villus that absorb nutrients like amino acids and sugars. **Lacteal**: A lymphatic capillary that absorbs fatty acids and lipids in the form of chylomicrons, which eventually enter the bloodstream via the lymphatic system.

Question 32

What is the product of goblet cells? Where are they found in greatest numbers?

Answer 32

**Goblet Cells**: These cells secrete mucus, which lubricates and protects the intestinal lining. **Location**: Goblet cells are found in greatest numbers in the small intestine (especially in the ileum) and in the large intestine.

Question 33

Describe the location of the pancreas, the types of secretions produced (exocrine and endocrine), the role of the exocrine secretion in the intestine.

Answer 33

**Location of the Pancreas**: The pancreas is located behind the stomach and extends across the posterior abdominal wall. **Exocrine Secretion**: The exocrine pancreas produces digestive enzymes (amylase, lipase, proteases) and bicarbonate. These secretions enter the duodenum via the pancreatic duct and help in the digestion of carbohydrates, fats, and proteins. **Endocrine Secretion**: The endocrine pancreas, found in the islets of Langerhans, secretes hormones like insulin, glucagon, and somatostatin into the bloodstream to regulate blood sugar levels.

Question 34

Describe the general structure of the liver, its unusual blood supply, the role of its secretions in the GI tract, and the path of bile outflow to the gallbladder and intestine. Know the names of all ducts.

Answer 34

**Structure of the Liver**: The liver is divided into two main lobes and is composed of functional units called lobules. **Blood Supply**: The liver has a unique dual blood supply: - The hepatic artery brings oxygenated blood from the heart. - The hepatic portal vein carries nutrient-rich blood from the digestive organs to the liver for processing. **Bile Secretion**: The liver produces bile, which is stored in the gallbladder and released into the duodenum for digestion of fats. **Path of Bile Flow**: 1. Bile is produced in the liver and flows through the hepatic ducts (right and left). 2. It then enters the common hepatic duct and can either be stored in the gallbladder via the cystic duct or flow directly to the duodenum through the common bile duct.

Question 35

Understand the liver lobule and the blood flow in the liver. What does the hepatic portal vein bring? What does the hepatic artery bring? How does blood flow back to the right atrium? What functions does the liver do?

Answer 35

**Liver Lobule**: The functional unit of the liver, consisting of hepatocytes arranged around a central vein. **Hepatic Portal Vein**: Brings nutrient-rich blood from the stomach, intestines, and spleen to the liver for detoxification and nutrient processing. **Hepatic Artery**: Brings oxygen-rich blood from the heart to the liver. **Blood Flow Back to the Right Atrium**: After passing through the liver sinusoids, blood drains into the central vein, which then joins the hepatic veins to return blood to the inferior vena cava, and finally to the right atrium of the heart. **Functions of the Liver**: The liver performs critical functions, including detoxification, metabolism, protein synthesis, bile production, storage of glycogen, and cholesterol regulation.

Question 36

What is the role of the gallbladder? Can one live without it?

Answer 36

**Role of the Gallbladder**: The gallbladder stores and concentrates bile produced by the liver. It releases bile into the duodenum when fat is present in the stomach, aiding in the digestion of fats. **Living Without It**: Yes, a person can live without a gallbladder. The liver will still produce bile, but it will flow directly into the small intestine rather than being stored in the gallbladder. This may lead to less efficient digestion of fats.

Question 37

Where is Vitamin B12 absorbed?

Answer 37

- Vitamin B12 is absorbed in the ileum of the small intestine. Specifically, it binds to intrinsic factor produced in the stomach, which facilitates its absorption by specialized receptors in the ileum.

Question 38

What are Peyer’s patches, Brunner’s glands, Intestinal crypts?

Answer 38

**Peyer’s Patches**: Clusters of lymphoid tissue located in the ileum of the small intestine. They monitor and protect against pathogens in the digestive tract by mounting immune responses. **Brunner’s Glands**: Located in the duodenum, these glands secrete an alkaline mucus that helps to neutralize stomach acid as it enters the small intestine. **Intestinal Crypts**: Also known as crypts of Lieberkühn, these are glandular structures found in the mucosa of the small intestine. They secrete intestinal juices and house enterocytes (absorptive cells) and goblet cells (mucus-secreting cells).

Question 39

Name all regions of the colon and flexures

Answer 39

Cecum Ascending Colon Right Colic Flexure Transverse Colon Left Colic Flexure Descending Colon Sigmoid Colon

Question 40

What is the major function of this region of the tract (colon)?

Answer 40

The major function of the colon is the absorption of water and electrolytes, which converts chyme into more solid stool. It also plays a role in fermentation of undigested carbohydrates by gut bacteria and the storage of feces prior to elimination.

Question 41

Identify the ileocecal valve, the appendix. Identify haustra and tenia coli.

Answer 41

**Ileocecal Valve**: The valve located at the junction of the ileum (last part of the small intestine) and the cecum (first part of the large intestine). It regulates the passage of material from the ileum to the cecum and prevents backflow. **Appendix**: A small, finger-like projection of lymphatic tissue attached to the cecum, often considered a vestigial organ but may play a role in immune function. **Haustra**: The pouches or sacs formed by the tenia coli in the colon that help to segment and mix contents. **Tenia Coli**: Three longitudinal bands of smooth muscle running along the length of the colon, which contract to form the haustra and aid in the movement of fecal material.

Question 42

Be familiar with these additional terms or conditions covered in lecture: Ulcers, cirrhosis, hepatitis, gallstones, pancreatitis.

Answer 42

**Ulcers**: Open sores that form on the lining of the stomach, small intestine, or esophagus, often caused by an imbalance between digestive acids and protective mechanisms. **Cirrhosis**: A chronic liver disease characterized by liver scarring and impaired liver function, often caused by alcohol abuse or viral hepatitis. **Hepatitis**: Inflammation of the liver, commonly caused by viral infections (e.g., Hepatitis A, B, C), leading to liver damage. **Gallstones**: Solid particles that form in the gallbladder and can block the normal flow of bile, leading to pain and potential complications. **Pancreatitis**: Inflammation of the pancreas, often caused by gallstones or excessive alcohol consumption, leading to digestive enzyme leakage and potential damage to the pancreas.