9/4/24 - Digestion and Metabolism (Reading 1) Lecture Questions

What is the order of the digestive system organs?

1. Mouth (Oral Cavity)

2. Pharynx

3. Esophagus

4. Stomach

5. Small Intestine

6. Large Intestine

What is the Alimentary Canal?

Tube in the digestive system where food / chyme passes through (also called the Gastrointestinal Tract)

What are the accessory structures of the digestive system?

What is the purpose of these accessory structures?

Salivary Glands, Pancreas, Liver, Gallbladder

Aid in the breakdown of food

How many layers make up the Alimentary Canal?

What are the layers called, on order from inside to outside?

Four layers

1. Mucosa

2. Submucosa

3. Muscularis

4. Serosa

What is the function of the Mucosa Layer of the Alimentary Canal?

What three layers make up the Mucosa?

Mucosa — provides a barrier against foreign particles, captures them in its sticky mucus and clears them out

1. Epithelium

2. Lamina Propria

3. Muscularis Mucosae

What do each of the three layers of the Mucosa do?

1. Epithelium — direct contact with the Lumen

2. Lamina Propria — composed of blood vessels and lymphatic vessels; mucosa-associated lymphatic tissue (MALT), which are used in immune response

3. Muscularis Mucosae — thin layer of smooth muscle that causes folding in the Alimentary Canal to increase surface area for absorption

What is the Lumen?

Interspace of the Alimentary Canal tube where food / chyme passes through

What is the function of the Submucosa Layer of the Alimentary Canal?

Submucosa — contains blood vessel and lymphatic tissues composed of submucosal glands that release digestive fluids

What is the function of the Muscularis Layer of the Alimentary Canal?

What are the two types of muscle in this layer?

Muscularis — necessary for movement and mechanical digestion of food / chyme

1. Circular Muscle

2. Longitudinal Muscle

What is the function of the Serosa Layer of the Alimentary Canal?

What two things composed the Serosa?

Serosa — hold all organs in place

1. Areolar Connective Tissue (ACT)

2. Epithelium

What are the six digestive processes?

1. Ingestion

2. Propulsion

3. Mechanical Digestion

4. Chemical Digestion

5. Absorption

6. Defecation

What is Ingestion?

Entry of food into the Alimentary Canal after going through the mouth

What is Propulsion?

What are the three components of Propulsion?

Propulsion — movement of food / chyme

1. Peristalsis

2. Gastric Emptying

3. Mass Movement

What is Peristalsis?

How does it work?

Peristalsis — big propulsion system that moves through most of the Alimentary Canal

Goes ONE way, using alternating waves of contraction and relaxation of the muscle / muscularis layer of the Alimentary Canal

What is Mechanical Digestion?

What are the three components of Mechanical Digestion?

Mechanical Digestion — physically breaking down food substances into smaller particles

1. Mastication (fancy word for chewing)

2. Gastric Mixing

3. Segmentation

What is Segmentation?

How does it work?

Segmentation — contraction and relaxation of the muscularis muscles to move food / chyme

Goes BACK and FORTH through alternate contraction and relaxation

What is Chemical Digestion?

Breaking down food / chyme with enzymes into smaller and smaller molecules

What is Absorption?

Where does it primarily occur?

Why is it important?

Movement of nutrients from the Alimentary Canal into the blood, which it uses to travel where it is needed

Primarily is done in the Small Intestine

Allows us to absorb nutrients across the Epithelial layer

What is Defecation?

Elimination of undigested materials from the body as feces

Where does the digestive process start?

Which digestive processes occur here?

Starts in the mouth

Chemical and Mechanical Digestion occur here

What are some other accessory organs in the mouth of the digestive system / Alimentary Canal?

What is the primary function of these accessories?

Salivary Glands — synthesize and secrete Saliva

Teeth — used for chewing / mastication

Tongue — synthesize and secrete enzymes; positions chewed up food into Bolus (small round mass)

What is the function of the Saliva?

Maintains a pH of 7 in the mouth and lubricate the Bolus

What are the two enzymes used for digestion that are produced in the mouth?

1. Salivary Amylase

2. Lingual Lipase

Where is Salivary Amylase synthesized and secreted from?

What does it break down?

Where is it active? Inactive?

Synthesized and secreted from Salivary Glands

Breaks down Starch / Glycogen

Active in the Mouth, Pharynx, and the Esophagus

Inactive in the Stomach

Where is Lingual Lipase synthesized and secreted from?

What does it break down?

Where is it active? Inactive?

Synthesized and secreted by the Tongue

Breaks down Lipids

Active in the Stomach

Inactive in the Mouth

Does the Pharynx contain food, air, or both?

Esophagus?

Pharynx — both air and food

Esophagus — only food

What are the three important anatomical features of the Esophagus?

1. Upper Esophageal Sphincter (UES)

2. Esophagus

3. Lower Esophageal Sphincter

What is the function of the Upper Esophageal Sphincter (UES)?

Controls movement of the bolus into the Esophagus (acts as a ‘gatekeeper’)

What is the composition of the Esophagus?

What are the types of contractions used by smooth and skeletal muscles?

Upper 2/3 — smooth muscle AND skeletal muscle

Lower 1/3 — ONLY smooth muscle

Smooth Muscles — INVOLUNTARY contractions

Skeletal Muscles — VOLUNTARY contractions

What is the function of the Lower Esophageal Sphincter?

Prevents gastric juices from entering the Esophagus

What digestive processes occur in the Stomach?

1. Chemical Digestion (via Enzymes)

2. SOME Mechanical Digestion (via Gastric Mixing)

3. Propulsion (gastric emptying)

NO ABSORPTION!!!

What enzymes are used in the stomach for Chemical Digestion?

Pepsin, Lingual Lipase, and Gastric Lipase

What are the five important parts of the Stomach?

What do they do?

1. Fundus — top part of the stomach

2. Rugae — folds that allow the stomach to stretch

3. Body — make up a majority of the stomach

4. Pylorus — end of the stomach

5. Pyloric Sphincter — controls movement of chyme into the Small Intestine

What are the five main cell types in the Stomach?

What are their functions?

1. Parietal cells — s/s HCl to kill microorganisms; s/s Intrinsic Factor (needed to absorb B12)

2. Surface Mucus Cells — s/s Alkaline Mucus, which protects the stomach lining

3. Mucus Neck Cells — s/s Mucus (unknown function)

4. Chief Cells — s/s Pepsinogen (inactive form of Pepsin), used for Protein Digestion

5. Enteroendocrine Cells — s/s hormones

   • G-Cells —> s/s Gastrin

What are the three main structures of the Small Intestine, in order?

1. Duodenum

2. Jejunum

3. Ileum

What digestive processes occur in the Small Intestines?

1. Propulsion (via Peristalsis)

2. Chemical Digestion (via Enzymes)

3. Mechanical Digestion (via Segmentation)

4. Absorption of Nutrients

FIRST PLACE WHERE ABSORPTION OCCURS

What are five important structures in Small Intestine histology?

What are their functions?

1. Circular Folds — Increase S.A. for absorption

2. Villi — Increase S.A. for absorption

3. Microvilli / Brush Border — Increase S.A. for absorption; s/s Brush Border Enzymes (BBEs)

4. Goblet Cells — s/s Mucus

5. Crypt of Lieberkühn — s/s Intestinal Juices

What is the last part of the Gastrointestinal Tract?

The Large Intestines

What are the main functions of the Large Intestines?

• Finish absorption of the nutrients and water

• Reabsorb water for form Feces

• Eliminate the Feces

• Make certain vitamins

What digestive processes occur within the Large Intestines?

1. Absorption (of final nutrients)

2. Mechanical Digestion

   • Mass Movement (strong contraction that moves chyme)

   • Haustral Contractions (sluggish Segmentation)

   • Propulsion (via Peristalsis)

NO CHEMICAL DIGESTION!!!

What is the order of structures within the Large Intestines for chyme to move through?

1. Ileocecal Valve / Sphincter

2. Cecum (Blind Alley; goes one way)

3. Ascending Colon

4. Transverse Colon

5. Descending Colon

6. Sigmoid Colon

7. Rectum

8. Anal Canal (terminates in Anus)

What are the functions of the Liver?

1. Secretes Bile

2. Removes all RBCs from the blood

3. Processes metabolic nutrients AFTER meals

4. Processes metabolic nutrients BETWEEN meals

5. Synthesizes Hormones

6. Synthesizes Plasma Proteins

7. Elimination of Wastes

8. Stores essential molecules

How does the Liver process metabolic nutrients AFTER meals?

Stores excess Glucose as Glycogen

Turns Amino Acids into Fatty Acids

Synthesizes Triglycerides and Cholesterol

How does the Liver process metabolic nutrients BETWEEN meals?

Turns Glycogen into Glucose

Turns Amino Acids into Glucose

Turns Fatty Acids into Ketones (energy sources)

What is the main function of the Gallbladder?

Stores and concentrates Bile

What are Bile Salts?

What is their main function?

Where are they synthesized from?

Amphipathic molecules used to EMULSIFY fats

Synthesized in the Liver by Cholesterol and secreted within Bile into the Duodenum of the Small Intestine

What does it mean when a fat globule is emulsified?

Big fat droplets are turned into lots of little fat droplets, increasing their SURFACE AREA

Why do fat globules emulsify when exposed to Bile Salts?

1. Nonpolar parts of the Bile Salts interact with the fat

2. Polar parts interact with the water

3. Allows water to surround the little fat droplet

DOES NOT DIGEST / BREAK DOWN THE FATS

ONLY SAY IT BREAKS APART THE FATS!!

What is the main function of the Pancreas?

Synthesize and secretes Pancreatic Juice

What are the main components of Pancreatic Juice?

1. Zymogens

2. Bicarbonate Buffer Juice — buffers Gastric Juice

3. Co-Lipase

4. Enzymes, including Pancreatic Amylase (starch) and Pancreatic Lipase (lipids / fats)

What are Zymogens?

What are the three types of Zymogens we focus on?

Where are they stored?

How are they secreted? Activated?

Inactive, storage form of Proteases produced via Exocrine Acinar cells of the Pancreas

1. Trypsinogen

2. Chymotrypsinogen

3. Procarboxypeptidase

Stored in Zymogen Granules (secretory vesicles)

Secreted via Exocytosis

Activated by Proteolytic Activation in the Small Intestine

Why is it important that Zymogens are INACTIVE?

If they were activated, they would digest the Pancreas

What are the steps of Zymogen Production and transportation to the Small Intestine?

1. Created by Acinar Cells

2. The Acinar Cell secretes Zymogen Granules via Exocytosis into the Pancreatic Duct

3. Zymogen Granules go down to where the Pancreatic Duct meets with the Bile Duct (Ampulla of Vader)

4. Zymogen Granules leave through the open Sphincter of Oddi into the Duodenum of the Small Intestine

Why do Proteases (including Zymogens) have to use Exocytosis?

They are Hydrophilic

Starting at the Pancreatic Acinar Cell, how are Zymogens used?

1. DNA transcription into mRNA in Nucleus

2. mRNA translation to a Peptide in the Rough ER (within Ribosome)

3. Travels to Golgi Apparatus

4. Secretory Vesicles / Zymogen Vesicles

5. Exocytosis of Zymogen Vesicles into Pancreatic Duct

6. Goes through Ampulla of Vader

7. Sphincter of Oddi

8. Duodenum of Small Intestine

9. Activated through Proteolytic Activation

10. Degrades / chemically digests the proteins