Gastrointestinal

These are questions generated based off of the learning objectives.

What is the primary purpose of the oral cavity in digestion?

It is not meant for absorption; its primary role is protection and mechanical digestion through mastication.

What is mastication (cephalic phase) and its importance?

Mastication physically breaks food into smaller pieces to increase surface area; it is functionally the same as chewing and is essential before any chemical digestion is effective.

Which muscles are most important for mastication?

• Masseter - provides force

• Medial and Lateral Pterygoids - assist in grinding and side-to-side motion

• Tongue muscles - position food

What types of digestion occur in the mouth?

Mechanical and chemical

What are the key components of saliva?

• 95.5% water

• 4.5% ions

  • salivary amylase

  • bicarbonate and phosphate ions (keeps pH 6.35-6.85)

  • salivary mucus

  • immunoglobulin A

  • epidermal growth factor

What is the role of salivary amylase?

Begins starch/carbohydrate breakdown and pauses in the stomach

What is the role of lingual lipase?

 Triacylglycerol lipases initiates lipid digestion and remains active in the stomach; optimum pH of 4.5 -5.4

How is salivation regulated?

Controlled by parasympathetic stimulation of the Autonomic nervous system. Sleep, fatigue, and fear inhibit its secretion.

What role do teeth play in the cephalic phase?

Masticate food; exposes more surface area for action of digestive enzymes speeding chemical digestion

What is the trigeminal nerve (V)?

The largest cranial nerve that innervates the muscles of mastication and forks into 3 divisions,

• Ophthalmic division (V₁) - sensory

• Maxillary division (V₂) - sensory

• Mandibular division (V₃) - mixed

What are the intrinsic salivary glands?

• Lingual glands (tongue)

• Labial glands (lips)

• Buccal glands (cheeks)

What are the extrinsic salivary glands?

• Parotid (beneath skin anterior to earlobe)

• Submandibular (halfway along mandible)

• Sublingual (floor of mouth)

Salivary gland structure

Branched ducts ending in acini,

• mucous acini secrete mucus

• serous acini secrete fluid rich in amylase and electrolytes

• mixed acinus has both mucous and serous cells

How much saliva is secreted by extrinsic salivary glands?

1 to 1.5 L per day

Why can mumps symptoms be severe when swallowing acidic substances?

The infection tends to spread to the parotid glands and causes you to lose mucosal and salivary secretions.

What role does the tongue play in mastication?

To manipulate food between teeth, while avoiding being bitten.

What are the extrensic tongue musculature?

• Genioglossus -depresses tongue and moves anteriorly

• Styloglossus - lifts the tongue and retracts it

• Palatoglossus - elevates the back of the tongue

• Hyoglossus - depresses and flattens it

What is gustation?

The ability to detect many flavors due to the presence of taste buds

Which cranial nerves are involved in oral digestion and why?

• CN V controls chewing

• CN VII and IX stimulate salivary secretion

• CN XII controls tongue movement for bolus formation

What are the three phases of deglutition?

1. Voluntary

2. Involuntary I

3. Involuntary II

What happens during the voluntary phase?

Chewing is complete and the process of swallowing begins.

• Bolus of food squeezed to the back of the mouth by pushing tongue against palate

• Nasopharynx sealed off and larynx elevated, enlarging pharynx to receive food

What happens during the involuntary I phase?

Pharyngeal-esophageal phase part 1

• The superior, medial, and inferior pharyngeal constrictor muscles move the bolus through the oropharynx and laryngopharynx.

• The upper esophageal sphincter relaxes and food enters the esophagus

What happens during the involuntary II phase?

Pharyngeal-esophageal phase part 2

• Initiation of peristalsis by muscularis

• The circular muscle layer contracts, pinching the esophageal wall and forcing the bolus forward

• At the same time, the longitudinal muscle layer also contracts shortening this area and pushing out its wall to receive the bolus

What controls deglutition?

The medulla oblongata

What is the primary goal of deglutition?

Protect the airway; the swallowing reflex ensures food enters the esophagus, not the trachea

What role does peristalsis play in swallowing?

A propulsive movement, not absorptive, pushing the bolus toward the stomach.

What are the four layers of the alimentary canal?

1. Mucosa

2. Submucosa

3. Muscularis

4. Serosa

What is the importance of MALT (Peyer’s patches)?

Immune protection; provides immune surveillance in the gut

What is the primary role of the mucosa?

To protect underlying tissue while serving as the main site of secretion and absorption

What does the submucosal plexus control?

Secretion and blood flow; the Meissner plexus regulates glandular secretion and local circulation/blood flow

What does the myenteric plexus control?

Motility; the Auerbach plexus controls smooth muscle contraction and GI movement

What is the role of the serosa/peritoneum?

This layer anchors organs and reduces friction within the abdominal cavity

What is the function of the esophagogastric junction?

The lower esophageal sphincter and diaphragm prevent acidic stomach contents from refluxing into the esophagus

What is the overall purpose of the stomach?

To protect itself from acid while initiating protein digestion and regulating delivery to the intestine

What are gastric pits?

Openings that lead to gastric glands that secrete acid, enzymes, and protective mucus

What are the 5 gastric gland cell types and their secretions?

1. Surface Mucous Cells

   • mucus, trefoil peptide, bicarbonate secretion

2. Mucous Neck Cells

   • alkaline mucus similar to the surface mucus

3. Parietal Cells

   • absorbs protons; excretes HCl and intrinsic factor

4. Enterochromaffin-like (ECL) Cells

   • histamine, after gastrin stimulation

5. Chief Cells

   • pepsinogen, the inactive form of pepsin

How is pepsin regulated?

• Gastrin-releasing peptide (GRP) stimulates gastrin

• Gastrin stimulates ECL and Parietal cells

• ECL cells release histamine stimulating pepsinogen release from Chief cells and HCl from Parietal cells

• Pepsin is now active

Why is intrinsic factor important?

It is required for vitamin B12 absorption later in the ileum and thus RBC production

What happens during the cephalic phase?

Neural stimulation; sight, smell, and thought of food stimulate gastric secretion before food enters the stomach

What happens during the gastric phase?

Positive feedback; food in the stomach increases acid and enzyme secretion via gastrin and stretch receptors

What is chyme?

Semi-liquid food; the mixture of food and gastric secretions produced in the stomach

Which foods empty from the stomach fastest?

Liquids and carbs empty fastest; fats empty slowest

When is there negative feedback?

When pH drops too low, stomach cells suspend HCl secretion and increase mucus secretions

What is the purpose of the mucosal barrier?

A thick coating of bicarbonate-rich mucus that forms a physical barrier that neutralizes acid and stem cells in the gastric pits that replace surface epithelium of the stomach every 3-6 days.

What are the 2 causes of peptic ulcer disease?

• H. pylori bacteria

• NSAID medications

Why is the pancreas called both a digestive and endocrine organ?

The pancreas secretes digestive enzymes, bicarbonate, and hormones.

What are the 3 protein digesting enzymes of the pancreas?

• Trypsinogen

• Procarboxypeptidase

• Chymotrypsinogen

(inactive forms)

What is the composition of pancreatic juice?

Mostly water with some salts, sodium, bicarbonate, and digestive enzymes; pH 7.1-8.2

What is bile and why is it essential?

Fat emulsification; emulsifies fats to allow enzyme access. Without it, fat absorption fails.

What is gastric motility?

A gentle ripple of peristaltic contractions every 20 seconds that becomes stronger at the pyloric region. This is controlled by the pacemaker cells in the longitudinal layer of the muscularis externa.

What is gastric emptying?

Contents of the stomach are completely emptied into the duodenum within 2-4 hrs, fatty foods take 6 hours.

Explain the intestinal phase

• Low pH chyme in duodenum → releases intestinal gastrin → increases stomach secretory activity → distended duodenum → enterogastric reflex → inhibits secretory activity/closes pyloric sphincter

• Cholecystokinin (CCK) and secretin are released → inhibits stomach prod. of HCl, pepsin, & gastric motility

• Duodenum has time to break down chyme

What is the purpose of the gallbladder?

To store and concentrate bile

What is the primary role of the duodenum?

To mix chyme with bile and pancreatic enzymes

What is the primary role of the jejunum?

To absorb most carbohydrates, proteins, and lipids

What is the primary role of the ileum?

To absorb vitamin B12 and bile salts; contains Peyer’s patches.

Why are villi and microvilli critical?

Increased surface area; dramatically increases absorptive capacity. Loss leads to malnutrition.

What are the 3 major functions of the liver?

1. Bile production

2. Hormone production

3. Remove toxins

What are the 5 stages of digestion?

• Ingestion - food intake

• Digestion - mechanical and chemical breakdown

• Absorption - nutrient uptake

• Compaction - water absorption and consolidation to poop

• Defecation - elimination of poop

Which digestive organs have simple columnar cells?

The stomach and intestines

Which digestive organs have stratified squamous cells?

The mouth, pharynx, esophagus, and anal canal

What 3 stimuli are responsible for the release of pancreatic juice and bile?

• Acetylcholine (ACh)

  • from vagus and enteric nerves

• Cholecystokinin (CCK)

  • secreted by duodenum in response to fats arrival

• Secretin

  • released from duodenum in response to acidic chyme

What molecules complete carbohydrate absorption?

Brush border enzymes

Where are proteins absorbed?

The duodenum and the jejunum

How are lipids absorbed?

Broken down by lipases and enclosed in micelles by bile salts, and diffuse into the columnar cell. In the cell chylomicrons are created, which are absorbed by lacteals and enter into the circulatory system.

How are nucleic acids absorbed?

Transported by carriers across the villus epithelium and enter the bloodstream.

What is theorized to be held by the vermiform appendix?

Bacterial colonies

What are the 3 distinctive features of the colon?

1. Taeniae coli - smooth muscles

2. Epiploic appendages - visceral peritoneum

3. Haustra (sacculations) - pouches formed by taeniae coli

What is the gastroileal reflex?

An increase in the force of ileal segmentation and ileal motility is enhanced by gastrin release in the stomach.

What is a haustral contraction?

Contractions that occur every 30 min in the transverse and descending colons, and involves an expansion and squeezing motion.

What are mass movements?

Strong waves that start midway through the transverse colon and quickly force contents toward the rectum, occurring 1-3 times a day.

How long does it take the large intestine to reduce a meal to poop?

12 to 24 hours

What is saccrharolytic fermentation?

Chemical digestion that occurs in the large intestine, exclusively because of bacteria in the lumen of the colon.

What is the purpose of the rectum?

To separate the excrements from gas via rectal valves, lateral bends.

What is defecation?

Valsalva’s maneuver → rectal wall stretches → sigmoid colon and rectum contracts → signals the brain to open external anal sphincter

What is Valsalva’s maneuver?

An increase in intra-abdominal pressure by contracting the diaphragm and abdominal wall muscles, closing the glottis.

How are minerals absorbed in the small intestine?

• Iron - active transport via iron-ferritin complexes

• Calcium - PTH stimulates uptake by activating vitamin D in the kidney

• Fat-solube Vitamins (A,D,E,K) - simple diffusion with lipids in micelles

• Water-soluble Vitamins (Most B, C) - simple diffusion

• Vitamin B12 - via endocytosis in terminal ileum in a B12-intrinsic factor complex

What is intestinal motility?

Gradual movement of contents toward colon, with migrating motor complex that milks chyme for 2 hours.