Flashcards in Digestive System 2 Deck (103):
What is the first part of the digestive system?
What are the six main components of the mouth?
What are the three major functions of the mouth?
Sensory analysis of material before swallowing
What part of the mouth is responsible for the sensory analysis of material before swallowing?
What are the three components of the mouth involved in mechanical processing?
What is mechanical processing in the mouth also called?
How is food lubricated in the mouth?
By mixing food with mucus and saliva.
What is the purpose of lubricating food in the mouth?
It helps us to swallow the food.
Where does digestion start?
In the mouth. It is very limited digestion but it is still digestion.
What is digested in the mouth?
Carbohydrates and lipids.
What breaks down starch/large polysaccharides in the mouth?
What breaks down lipids in the mouth?
What component in the mouth produces saliva?
What are the three types of salivary glands?
What percentage of saliva is produced by parotid glands?
What percentage of saliva is produced by submandibular glands?
What percentage of saliva is produced by sublingual glands?
What is produced by the parotid gland?
Lots of salivary amylase
What is produced by the submandibular gland?
What is produced by the sublingual gland?
Buffers, glycoproteins (mucins) and salivary amylase
How much saliva is produced per day?
What percentage of saliva is water?
Other than water, what makes up saliva?
Enzymes (salivary amylase)
Buffers, mucins, electrolytes (Na+, Cl-, HCO3-) and waste products
What is IgA?
Immunoglobulin A: it protects against foreign substances.
What is the role of lysozymes?
To help target and break down bacteria.
What is the role of enzymes in saliva?
To help with digestion.
What are the functions of saliva?
Lubrication of mouth and pharynx (mucins)
Cleanse mouth and teeth
Dissolve food and chemicals (stimulate taste buds)
Describe the structure of the oesophagus.
A hollow muscular tube about 25 cm in length
Where does the oesophagus begin and where does it extend to?
It begins just after the pharynx (at the back of the oral cavity) and extends to the stomach.
What are the roles of the oesophagus?
Convey food to stomach by peristalsis
Pierces diaphragm though oesophageal hiatus (makes the digestive system an organised tube)
What are two vital components of the oesophagus?
What are the roles of the sphincters in the oesophagus?
Prevents air from entering the oesophagus rather than the trachea
Prevents backflow (reflux) of acid from the stomach, which can damage the oesophagus.
What is swallowing also called?
What are the four stages of swallowing?
Bolus enters the stomach
Describe the buccal stage of swallowing.
Bolus is moved to the Oropharynx
Describe the pharyngeal stage of swallowing.
Bolus is moved to the oesophagus
Describe the oesophageal stage of swallowing.
Bolus enters the stomach
What physiological function takes place to ensure food/drink does not enter the nasal cavity or trachea during swallowing?
The larynx elevates and epiglottis folds to stop food/drink from entering the nasal cavity or trachea.
What four sections can the stomach be divided into?
What is the stomach made of?
3 layers of smooth muscle and rugae
In informal terms, what is the stomach?
A storage and mixing chamber.
What four processes occur in the stomach?
Starch digestion continues
Protein and triglyceride digestion begin
What occurs to digestion enzymes from the mouth in the stomach?
from mouth are
acid in the stomach
and replaced by stomach
Describe mechanical digestion in the stomach.
Mixing waves every 15-25 sec
Forms chyme (partially digested semi-fluid material)
Forces chyme into duodenum
What three main chemicals are involved in chemical digestion in the stomach?
What is the role of hydrochloric acid in chemical digestion in the stomach?
To denature proteins.
What is the role of pepsinogen in chemical digestion in the stomach?
It is converted into pepsin and hydrolyses peptide bonds.
What is the role of gastric lipase in chemical digestion in the stomach?
To hydrolyse triglycerides.
Does absorption take place in the stomach?
Why does absorption not occur in the stomach?
There is no absorption due to the very low permeability of water: too much mucous and not the right contents. The stomach prepares for digestion in the small intestine.
How can alcohol damage the stomach?
Also can damage the stomach by breaking down mucous.
What do secretory cells form in gastric pits?
Secretory cells form gastric glands which line gastric pits
What are the four types of secretory cells that form gastric glands which line gastric pits?
What is the role of parietal cells?
It produces hydrogen and chloride ions to form hydrochloric acid
It has an intrinsic factor required for the absorption of vitamin B12, which is used to make red blood cells.
What do chief cells create?
What is the role of G cells?
To secrete gastrin (a hormone)
What is the role of gastrin?
Stimulate parietal and chief cells
Increase secretions and motility.
What does the regulation of gastric activity occur through?
Central Nervous System
Enteric Nervous System
How are the three overlapping phases of gastric activity regulation named?
According to the location of the food.
What are the three overlapping phases of regulation of gastric activity?
Describe the cephalic phase
The Central Nervous System and brain prepares stomach for arrival of food; when you see, smell, taste or think about food.
Sends impulses to the submucosal plexus (Vagus nerve) to increase gastric secretion and increase secretion from gastric glands and motility.
Describe the gastric phase
The process builds on the cephalic phase, starting when undigested food/materials arrive in the stomach.
Triggers stretch receptors and chemoreceptors (which respond to changes in pH) to enhance the secretion of gastrin, pepsinogen and Hydrochloric Acid; and stimulate gastric motility.
When does the intestinal phase begin?
When chyme arrives in the duodenum.
What is the cephalic phase stimulated from?
Describe the intestinal phase
Increased intestinal secretion of secretin, CCK and GIP
Controls rate of chyme exiting from stomach (gastric emptying)
What is the role of secretin?
To reduce gastric secretion
What does CCK stand for?
What is the role of CCK?
To inhibit gastric emptying.
What does GIP stand for?
Gastric Inhibitory Polypeptide
What is the role of GIP?
Inhibit gastric emptying and secretions
What is vomiting?
The forceful expulsion of gastric contents out through the mouth caused by a major force of expulsion from the diaphragm and abdominal muscles.
Does the stomach participate in vomiting?
The stomach does not actively participate in vomiting.
What are the 6 steps in the vomiting reflex?
1. Deep inspiration and closure of the glottis
2. Contraction of the diaphragm and abdominal muscles, compressing the stomach
3. Gastric contents are forced out through the relaxed gastroesophageal sphincter
4. Distension of the oesophagus induces peristalsis to force contents back to the stomach
5. The cycle repeats (retching)
6. Pressure in oesophagus increases, the jaw thrusts out, the pharyngeal sphincter opens and gastric contents are forced out.
What is vomiting usually preceded by?
Rapid Heart Rate
These sensations are characteristic of rapid discharge by the Autonomic Nervous System
What are the preceding events of vomiting coordinated by?
The vomiting centre in the medulla.
What can excessive vomiting lead to?
Excessive vomiting can lead to large losses of secreted fluids and acids that are normally reabsorbed, leading to decreased plasma volume and metabolic alkalosis.
What is the main role of the small intestine?
Digestion and absorption of nutrients.
Where does 90% of nutrient absorption occur?
In the small intestine.
What is the approximate length of the small intestine?
What is a vital physical characteristic of the small intestine?
If has a large surface area due to:
Circular folds (plicae circulares) – many present, mix chyme
Villi – capillaries and lacteals
Microvilli – brush border
What is the total absorptive capacity of the small intestine?
200 metres squared.
Describe intestinal villi
Small finger-like projections, covered by simple columnar epithelium (microvilli/brush border) that contain lamina propria.
Describe lamina propria.
Contain a network of capillaries to carry absorbed nutrients to the liver and then around the body
Contain lacteals to transport material that cannot enter capillaries such as fatty acids (chylomicrons)
What are the three main sections of the small intestine?
How long is the duodenum?
How long is the jejunum?
How long is the ileum?
What are the roles of the duodenum?
Receives chyme from stomach
Mixes with digestive enzymes from pancreas
Avoid damage to absorptive surfaces
Avoid inactivating digestive enzymes
What are the roles of the jejunum?
Chemical digestion and nutrient absorption
What are the roles of the ileum?
Nutrient absorption (Vitamin B12, bile salts and leftover undigested products)
Controls flow of from ileum to large intestine
What does small intestinal movement involve?
Contraction and relaxation of smooth muscle from duodenum to ileum
Describe Peristalsis and Segmentation.
Weaker peristaltic contractions slowly propels bolus forward along length of digestive tract (moves along Small Intestine in approximately 90-120 minutes)
Contractions are in cycles. This helps to mix with intestinal secretions and make absorption more efficient by allowing contact with villi.
What process coordinates activities in the small intestine?
What are the three regions of the pancreas?
Head, body and tail.
What is the pancreas connected to?
The duodenum via the pancreatic duct.
Describe a specific physical characteristic of the pancreas.
Pancreas has distinct lobules – contain acini and islets.
Does the pancreas have exocrine or endocrine functions?
Describe the exocrine functions of the pancreas.
Acinar glands secrete pancreatic juice
Digestive enzymes and buffers
Describe the endocrine functions of the pancreas.
Pancreatic islet cells
Secrete insulin and glucagon into bloodstream.
Approximately how much fluid is secreted by the pancreas per day?
What is the function of the pancreas controlled by?
What materials are secreted by the pancreas?
Water, Salts, Bicarbonate & Phosphate buffers