Gastro

Question 1

4 layers of the GIT?

Answer 1

• mucosa
• submucosa
• muscularis externa
• serosa

Question 2

Describe structure of musculris externa

Answer 2

Two layers of smooth muscle separates by a nerve complex. Inner layer = circular, outer = longitudinal

Question 3

What is the difference between the mucosa and subMucosa layers?

Answer 3

Mucosa = innermost layer. Has many ridges in structure (like a wave) that increases surface area for absorption. Also protects from contents of food and secretes compounds for chemical digestion

Submucosa = connective tissue with nerve plexus

Question 4

Describe peristalsis motility

Answer 4

Involves the alternating contractions of the circular and longitudinal muscles of the muscularis externa layer to propel food forward.
Mediated by=
Glossopharyngeal and vagus nerves

Question 5

Describe segmentation motility

Answer 5

Mixing of food and digestive juices. Food is sectioned off in little sections that are closed off by circular muscles. The food moved back and forth within this section, mixing with the juices. The circular muscle then relaxes a little, allowing food to move into adjacent sections. The muscle then closes again, repeating the process. Occurs in small intestine predominantly

Question 6

Glossopharyngeal nerve?

Answer 6

Mediates peristaltic contractions of the esophagus

Question 7

Functions of oral cavity? (4)

Answer 7

Ingestion, mastication, lubrication, digestion

Question 8

Describe digestion in the oral cavity

Answer 8

Very beginnings of digestion.
Salivary amylase breaks down carbohydrates
Lingual lipase breaks down lipids
(Both enzymes are found in the saliva)

Question 9

Describe mastication.

Answer 9

Involves the teeth and tongue. The manual manipulation of food - chewing

Question 10

Where is the parotid gland located and what does it secrete?

Answer 10

Located near the ear. Secretes salivary amylase (carb breakdown enzyme)

Question 11

What does the submandibular gland secrete?

Answer 11

Glyoproteins, pH buffers, salivary amylase

Question 12

What does the sublingual gland secrete?

Answer 12

Mucus - buffering and lubrication

Question 13

What are the first 2 phases of the swallowing reflex?

Answer 13

1. Ingestion

2. Buccal

Question 14

What are the 3rd and 4th phases of swallowing reflex?

Answer 14

3. Pharyngeal

4. Esophageal

Question 15

Describe ingestion phase of swallowing reflex

Answer 15

Moving food to back of mouth voluntarily

Question 16

Describe buccal phase of swallowing reflex (3 elements)

Answer 16

Baroreceptors recognise presence of bolus at the back of the mouth and send APs to medulla via trigeminal and glossopharyngeal nerves.
Food is pushed further into pharynx and the uvula closes

Question 17

Describe pharyngeal phase of swallowing reflex

Answer 17

Glottis closes, preventing food moving into trachea and forcing it into esophagus

Question 18

Describe esophageal phase of swallowing reflex

Answer 18

Food moves down esophagus towards stomach via peristaltic contractions
- vagus and glossopharyngeal nerves mediate these contractions

Question 19

Purpose of mucous in the stomach?

Answer 19

Protection from acidic environment. Prevents HCl from moving into the cells

Question 20

Describe gastric emptying

Answer 20

Sweeping peristaltic contractions. Small portion of chyme is seperate from rest of stomach, which is open to duodenum

Question 21

Gastric mixing?

Answer 21

Pyloric and gastroesophagael sphincter are closed and the chyme bounces off the closed ends, mixing the contents up

Question 22

Describe the function of the parietal cells in the stomach

Answer 22

Excrete HCl for chemical digestion. It is released as H+ and Cl- ions and then comes together in the lumen so the epithelial isn’t damaged

Question 23

Explain the role of HCl in the stomach

Answer 23

HCl is responsible for turning the inactive pepsinogen into pepsin, the enzyme for breaking down proteins

Question 24

Describe the chief cell and what does it excrete

Answer 24

Chief cells are in the stomach lining, and excrete pepsinogen and gastric lipase (lipid digestent)

Question 25

What stimulates the chief and parietal cells to excrete their contents?

Answer 25

- vagus nerve PSNS stimulation - pH change - distension (stretch of stomach due to presence of chyme)

Question 26

What is the role of the G cell in the stomach. What factors stimulate these cells?

Answer 26

Releases Gastrin into the blood stream. This increases the activity of the parietal and chief cells Stimulated by vagus nerve and presence of proteins

Question 27

What do the ECL cells do?

Answer 27

Secrete histamine. Histamine also stimulates chief and parietal cells. Histamine acts locally whereas gastrin acts systemically through the blood stream

Question 28

What do D cells do? What stimulates their activity?

Answer 28

Stimulated by the acid accumulation in the duodenum. Releases somatostatin This decreases the activity of chief and parietal cells

Question 29

What are the 3 phases of gastric secretions? Provide a brief description of each

Answer 29

1. Cephalic Stomach is preparing for food. Very short (mins). Stimulated by sight, smell, taste or thought of food (CNS) Starts producing gastric juices and increases G cell activity 2. Gastric Stomach acts on food both mechanically (peristaltic contractions) and chemically (juices) 3. Intestinal Maximum absorption occurs here. Controlled by enterogastric reflex. Decreases activity of gastric contractions and secretions while activating accessory organs

Question 30

Describe the enterogastric reflex. What is its purpose?

Answer 30

Stretch of the duodenum wall sends messages to spinal cord, sending back APs along efferent neuron which inhibits gastric motility and reduces the rate of gastric emptying. This controls the rate at which food leaves stomach and enters small intestine in order to maximise absorption (purpose).

Question 31

What role do CCK and secretin have?

Answer 31

Activation of accessory organs

Question 32

Which accessory organs does secretin act on?

Answer 32

Liver

Question 33

Which accessory organ does CCK act on?

Answer 33

Gall bladder - relates to how bile is released into the duodenum

Question 34

What triggers the release of CCK and secretin?

Answer 34

CCK = contents (fats, proteins, carbs) of chyme Secretin = acid They get released into the blood stream

Question 35

Describe the acid regulation via secretin

Answer 35

Secretin is released when acid is high. This travels through the blood to pancreatic duct cells which secrete NaHCO3 into the duodenum lumen. This neutralises the acid, therefore reducing secretin production

Question 36

Describe the digestion of carbs, fats and proteins through CCK

Answer 36

CCK is released when C, F and P enter duodenum. CCK travels through bloodstream to pancreatic cells which digestive enzymes

Question 37

Proteolytic enzymes break down what?

Answer 37

Proteins

Question 38

Pancreatic amylase breaks down...

Answer 38

Carbohydrates

Question 39

Pancreatic lipase breaks down ...

Answer 39

Lipids

Question 40

What is bile made of?

Answer 40

Water, ions, etc, bile salts

Question 41

What do bile salts do?

Answer 41

Emulsification - digestion of lipids

Question 42

How is the release of bile from the gallbladder monitored?

Answer 42

Bile is produced in the liver. When it is not needed in the SI, it is stored in the gallbladder. Hormonal and neural stimulation activates the release of bile fro, gallbladder when needed

Question 43

How is CCK related to bile release?

Answer 43

CCK is released when chyme enters the duodenum. It then acts on the gallbladder, causing it to contract and release bile into duodenum

Question 44

Where does most digestion and nutrient absorption occur?

Answer 44

Small intestine

Question 45

Where are the pyloric and ileocecal sphincters found?

Answer 45

``` Pyloric = junction between stomach and SI iliocecal = junction between LI and SI ```

Question 46

Describe the unique features of the SI epithelial

Answer 46

Contains villi and microvilli which increase the surface area available for absorption