Digestive system

Question 1

How does the enteric nervous system regulate smooth muscle activity?

Answer 1

excites smooth muscle through nerves secreting acetylcholine or substance P and inhibits smooth muscle with vasoactive intestinal peptide (VIP) or nitric oxide (NO).

Question 2

What role do hormones play in GI regulation?

Answer 2

respond to local chemical factors, nerve signals, or stretch and can act locally or travel via the blood to influence secretory or contractile activity in adjacent organs

Question 3

What is the digestive function of the mouth?

Answer 3

The mouth is the only part of the GI tract for ingestion - - Its digestive functions involve mechanical (chewing) and chemical processes (enzyme secretion from salivary glands)
- also starts the propulsive act of swallowing

Question 3

What are the mechanical and chemical digestive processes in the mouth?

Answer 3

• Mechanical digestion: Chewing (mastication), which is partly voluntary and partly reflexive.
• Chemical digestion: Enzymes from the salivary glands begin the breakdown of food, especially starches.

Question 4

Does the mouth absorb nutrients?

Answer 4

does not absorb nutrients, with some exceptions such as nitroglycerine.

Question 4

What are the functions of saliva?

Answer 4

• Cleanses the mouth.
• Dissolves food chemicals for tasting.
• Moistens and compacts the food bolus.
• Contains salivary amylase, which begins starch digestion.

Question 5

What are the different types of salivary glands and their contributions to saliva?

Answer 5

• Parotid glands: Predominantly serous cells, produce ~25% of saliva.
• Submandibular glands: Serous & mucous cells, produce ~70% of saliva.
• Sublingual glands: Predominantly mucous cells, produce ~5% of saliva.

Question 6

What are intrinsic salivary glands and their secretions?

Answer 6

Intrinsic (buccal) salivary glands secrete lingual lipase

Question 6

What is the composition of saliva?

Answer 6

• 97-99.5% water (hypo-osmotic), pH 6.75-7.
• Contains electrolytes, amylase (for starch digestion), mucin (for lubrication), urea & uric acid (metabolic waste products).

Question 7

What other secretions are found in saliva, and what is their purpose?

Answer 7

contains IgA antibodies, lysozyme, and defensins
- make sure that bad bacteria is denatured

Question 8

What is the average output of saliva per day?

Answer 8

1000-1500 ml/day

Question 9

What is the role of intrinsic salivary glands in salivation?

Answer 9

provide continuous secretion of 0.1 ml/min to keep the mouth moist

Question 10

How do extrinsic salivary glands differ in their secretion?

Answer 10

• activated by food intake or other stimuli
• can produce up to 4 ml/min of saliva.

Question 11

How is salivation regulated?

Answer 11

ANS
- chemoreceptors and mechanoreceptors in the mouth signal the salivatory nuclei in the brainstem
- increased parasympathetic activity promotes serous secretion

Question 12

What stimulates chemoreceptors and mechanoreceptors in the mouth?

Answer 12

• chemoreceptors are activated most strongly by acids
• mechanoreceptors are activated by any mechanical stimulus in the mouth

Question 13

How does sympathetic stimulation affect salivation?

Answer 13

• increases mucous secretion and can constrict blood vessels serving the salivary glands, leading to dry mouth (xerostomia)
• stress

Question 14

What external factors can trigger salivation?

Answer 14

sight, smell, or even the thought of food, and also by irritation in the lower GI tract, such as from bacteria, spicy food, or hyperacidity.

Question 15

What is deglutition (swallowing), and how is it coordinated?

Answer 15

• the process of swallowing, involving over 22 muscle groups in the tongue, soft palate, pharynx, and esophagus
• It occurs in two phases: buccal and pharyngeal-esophageal

Question 16

What happens during the buccal phase of swallowing and what does stimulation of the tactile cells do?

Answer 16

• the tongue forces the food bolus against the hard palate, then contracts to push the bolus into the oropharynx
• tactile receptors in the pharynx stimulate reflex activity.

Question 17

What happens during the pharyngeal-esophageal phase of swallowing?

Answer 17

• is involuntary and controlled by the swallowing center in the medulla and lower pons
• Cranial nerves, including the vagus nerve, coordinate peristalsis to move food into the esophagus.

Question 18

What is heartburn, and what causes it?

Answer 18

burning, radiating pain due to gastric juice regurgitation into the esophagus
- causes: gastric reflux, overeating, obesity, pregnancy, GERD

Question 19

What is the function of the stomach?

Answer 19

serves as a temporary storage tank and begins the chemical breakdown of proteins, converting food into chyme

Question 20

What is the mechanical digestion process in the stomach?

Answer 20

occurs via the churning action of the stomach, which involves the muscular layers of the stomach (specifically the smooth muscle layers) and propulsion of food

Question 21

What is the primary type of enzymatic digestion in the stomach?

Answer 21

pepsin - protein digester

Question 22

What role does rennin play in the stomach, and in which population is it secreted?

Answer 22

Renin - enzyme that helps digest milk - children's primary food source

Question 23

What types of drugs can be absorbed by the stomach?

Answer 23

alcohol and NSAIDS are easily absorbed through the stomach mucosa - regular absorption can irritate the stomach lining

Question 24

What is the essential function of the stomach for life?

Answer 24

the production of intrinsic factor, which is required for VB12 absorption in the small intestine

Question 25

How does the secretion of hydrochloric acid (HCl) aid in digestion?

Answer 25

- break down food particles into chyme - denature proteins and nucleic acids - activate pepsinogen into pepsin for protein digestion - destroy bacteria to prevent infection

Question 26

What are the 3 phases of gastric secretion that are the same as the head, stomach and small intestine?

Answer 26

Head - cephalic Gastric - stomach Intestinal - intestine

Question 27

What triggers the Cephalic Phase of digestion?

Answer 27

triggered by sensory inputs such as smell, taste, sight, or even the thought of food - activates the vagal nuclei in the brainstem stimulating gastric juice secretion

Question 28

How long does the Cephalic Phase last?

Answer 28

short-lived, lasting only a few minutes before food enters the stomach

Question 29

What is the main stimulus for the Gastric Phase?

Answer 29

- stomach distension, peptides and low acidity - lasts 3-4 hours and contributing to the majority of gastric secretion

Question 30

What happens when the stomach is distended during the Gastric Phase?

Answer 30

- activates mechanoreceptors, leading to vagal reflexes that release Ach, stimulating the secretion of gastric juices

Question 31

What does gastrin do in the Gastric Phase?

Answer 31

- stimulates the release of gastric juices, including HCL from parietal cells - is triggered by peptides and low pH in the stomach

Question 32

How does caffeine affect the gastric phase?

Answer 32

increases gastrin secretion, promoting more gastric juice production

Question 33

What triggers the Intestinal Phase of digestion?

Answer 33

triggered by intestinal gastrin from the duodenum, stimulated by the entry of chyme into the small intestine

Question 34

What is the role of enterogastrones in the Intestinal Phase?

Answer 34

secretin and cholecystokinin slow down gastric secretion and emptying to protect the small intestine for excess acidity and ensure efficient digestion

Question 35

How is HCl secretion regulated in the stomach?

Answer 35

- HCl is pumped into the stomach lumen in response to gastrin, ACh and histamine - H+ derived from carbonic acid, with Cl- following to maintain balance

Question 36

What is the alkaline tide?

Answer 36

the increase in blood pH caused by the release of bicarbonate into the bloodstream (from parietal cells) as Cl is secreted into the stomach where it joins with H+ to form HCl

Question 37

What is the cause of ulcers in the GI tract and where is it most likely to happen?

Answer 37

acid secretion damages the lining of the stomach or duodenum, often due to a lack of protective mucus, - duodenum and esophagus

Question 38

What are the major risk factors for ulcers?

Answer 38

smoking, NSAID, alcohol, chronic disease and infection with helicobacter pylori

Question 39

How does cimetidine (Tagamet) help with ulcers?

Answer 39

inhibits the histamine-H2 receptor interaction, reducing acid production in the stomach and promoting healing of ulcers

Question 40

What is receptive relaxation in the stomach?

Answer 40

the process that allows the stomach to stretch without increasing internal pressure, enabling it to accommodate food - mediated by interstitial cells set by basic electrical rhythm (BER)

Question 41

How does the basic electrical rhythm (BER) function in gastric motility?

Answer 41

generates subthreshold depolarization every 20 seconds in the stomach - contributes to the rhythmic movement of food - regulated by neural and hormonal factors to produce depolarization

Question 42

How long does it typically take for the stomach to empty?

Answer 42

within 4 hours after meal - depends on the meal's volume and contents

Question 43

How do the contents of a meal affect gastric emptying?

Answer 43

Carbs empty quickly, while fatty meals slow down gastric emptying because fats coat the chyme (emptying time up to 6 hours)

Question 44

What regulates the rate of gastric emptying?

Answer 44

feedback from the duodenum through neural and hormonal signals, which adjust the rate based on food contents and digestion needs

Question 45

What triggers vomiting (emesis)?

Answer 45

excessive stretching of stomach or intestines - also irritants: toxins, alcohol, or spicy food - stimulate the emetic center in medulla (abdominal and diaphragm contractions)

Question 46

What are the components of bile?

Answer 46

- bile salts - bile pigment (bilirubin) - cholesterol - neutral fats - phospholipids - electrolytes

Question 47

What is the role of bilirubin in bile?

Answer 47

derived from hemoglobin breakdown - pigment - converted by intestinal bacteria into stercobilin, giving feces their brown color

Question 48

What is the only digestive function of the liver?

Answer 48

produce bile - important for emulsifying fats for digestion and absorption

Question 49

What is the role of the gallbladder in digestion?

Answer 49

stores bile and releases it into the duodenum upon stimulation, aiding in the digestion of fats

Question 50

Why is bile important for digestion?

Answer 50

acts as a fat emulsifier, breaking down large fat molecules into smaller droplets for the digestive enzymes

Question 51

What stimulates bile production and release into the duodenum?

Answer 51

present of fat in the small intestine is the most potent stimulus for bile production and release via the hormone cholecystokinin (CCK)