CGIER 12 - Alimentary Canal, Ingestion, Oesophagus, Stomach, Ulcers

Question 1

What are the two accessory organs to the digestive system?

Answer 1

Pancreas & Liver

Question 2

What is the primary function of the digestive system?

Answer 2

To provide the body with a continual supply of:

1. water
2. nutrients
3. electrolytes

Question 3

What are the three main processes of the GIT?

Answer 3

The three main processes of the GIT are:

1. Transportation (Ingestion)
2. Physical and Chemical Treatment (Mechanical Processing, Digestion, Secretion)
3. Absorption (followed by excretion)

Question 4

What are the names of the three salivary glands in the mouth?

Answer 4

The three salivary glands in the mouth include:

1. Parotid
2. Submandibular
3. Sublingual

Question 5

What triggers the flow of saliva?

Answer 5

Four factors trigger the flow of saliva:

1. taste
2. smell
3. sight
4. thought

Question 6

How much saliva is secreted per day?

Answer 6

1.2 L/day

Question 7

What does saliva contain?

Answer 7

Saliva contains four things:

1. glycoproteins (mucins that give saliva lubricating action, vital for oral health & hygiene)
2. Electrolytes (Na+, HCO3-, Cl-, K+)
3. Salivary amylase (saliva has a pH 6.0-7.4 which is optimal for salivary amylase function)
4. Antibodies

Question 8

How are secretions by the salivary glands controlled?

Answer 8

The autonomic nervous system controls secretions by the salivary glands via the salivary nuclei in the medulla oblongata through the sympathetic and parasympathetic nervous system.

Question 9

What types of secretions does saliva contain?

Answer 9

Saliva contains two types of secretions:

1. Mucus secretion: lubrication
2. Serous secretion: contains salivary amylase

Question 10

What prevents food from entering the trachea?

Answer 10

During swallowing, a flap of tissue called the epiglottis prevents food from entering the trachea.

Question 11

How is food swallowed through the pharynx?

Answer 11

There are three stages to swallowing:

1. voluntary swallowing process –> tongue action
2. pharyngeal involuntary process –> series of reflex actions
3. oesophageal involuntary process –> peristalsis

Question 12

What is peristalsis?

Answer 12

The contraction of circular muscles above food bolus and the relaxation of muscle below food bolus, to push the bolus forward. Peristalsis occurs in the esophagus, stomach, and small intestine and is controlled by the autonomic nervous system.

Question 13

What is the general structure of the GIT from the inside to the outside?

Answer 13

1. Mucosa: (inner: epithelium / outer: lymph nodes & lamina propria)
2. Muscularis Muscosa: (inner: smooth muscle)
3. Submucosa: (inner: connective tissue)
4. Muscularis Externa (inner: smooth circular / outer: smooth longitudinal)
5. Serosa: (inner: loose connective tissue / outer: mesothelium)

Question 14

What is a hernia?

Answer 14

The abnormal exit of tissue or an organ through the wall of the cavity in which it normally resides.

Question 15

What is a hiatus hernia?

Answer 15

A hiatus hernia occurs when the stomach pushes its way up into the oesophageal opening in the diaphragm.

Question 16

Name and describe the regions the stomach is histologically divided into?

Answer 16

There are three regions the stomach is histologically divided into:

1. cardiac: entry into the short cardiac region of the stomach is by the gastroesophageal sphincter
2. fundus and body: has inner foldings called rugae & have gastric pits that have gastric glands that secrete gastric juices such as enzymes and hydrochloric acid into the stomach
3. pyloric: has deep irregular gastric pits that terminate at the pyloric sphincter & is mostly lined with mucous cells

Question 17

Gastric juice is mainly made up of secretions from what two cells?

Answer 17

1. Parietal cells: secretes HCl & found in fundus

2. Zymogen cells: secretes pepsin & found in fundus (base of gastric gland)

Question 18

What other cells secrete gastric juice?

Answer 18

Three other cells are found in the gastric gland:

1. mucous cells: secretes mucous & found in cardiac, fundus & pyloric (found on the luminal surface and in gastric glands throughout the entire stomach)
2. enteroendocrine cells or G-cells: secretes gastrin & found in pyloric (found in the base of gastric glands)
3. stem cells: differentiate into all cell types & found in the neck of gastric gland

Question 19

What happens to food once it enters the stomach?

Answer 19

1. Food is moved by peristaltic waves at 3waves/min and is turned into chyme.
2. Chyme mixes with gastric juice containing pepsin and gastric lipase.
3. Zymogen cells secrete the inactive precursor of pepsin, pepsinogen.
4. Pepsinogen becomes active due to the acidic conditions and the active pepsin present.
5. Pepsin being an endopeptidase hydrolyzes peptide bonds of aromatic amino acids, while gastric lipase is not a very active enzyme.
6. H+ ions are actively transported to the lumen of the canaliculi of parietal cells.

Question 20

How much gastric juice is secreted per day and at what pH?

Answer 20

2L of gastric juice is secreted per day at a pH of 2-3.

Question 21

The secretion of gastric juices is triggered by what two mechanisms?

Answer 21

1. Neurogenic reaction: the vagus X pathway also associated with saliva secretion also initiates gastric juice secretion. Once food enters the stomach it causes distension which is detected by stretch receptors in the stomach lining. Signals are then sent to the brain which then triggers the release of digestive hormones that will stimulate gastric juice secretion.
2. Hormonal: the enteroendocrine cells located in the pyloric region of the stomach secrete a hormone called gastrin that enters circulation and is carried by the blood to the gastric glands at the fundus and body region of the stomach, which then stimulates the release of gastric juice.

Question 22

How does chyme escape the stomach and move into the small intestine?

Answer 22

Chyme can last in the stomach for up to 4 hours before being pushed into the small intestine millimeters at a time by the relaxation of the pyloric sphincter.

Question 23

Explain how stomach ulcers form.

Answer 23

For years stomach ulcers were believed to form from the hypersecretion of HCL from parietal cells and low secretion of mucus from mucous cells. Now, it is known that a bacteria called Helicobacter Pylori burrows into the gastric epithelium, destroying the mucosal layer, leaving it exposed to the HCL secretions.