Digestive System Flashcards
What are the four stages of the digestive system?
- Ingestion
- Digestion
- Absorption
- Egestion
How long is the digestive tract of adults?
6-9m
What is the digestive system responsible for?
Taking in, storing, breaking down, and absorbing food as well as removing waste materials
How does food move through the digestive system?
Peristalsis; a contractile motion
In order; how does food travel through the digestive system?
- Mouth
- Esophagus
- Stomach
- Small intestine
- Large intestine
- Rectum
- Anus
What happens in the mouth?
The start of sugar/carb breakdown
What is the esophagus?
A connector
What does the liver do?
Makes bile
What does the gallbladder do?
Stores the bile
What does the stomach do?
Starts protein breakdown (HCl)
What is the pancreas?
An enzyme factory
What does the small intestine do?
90% of absorption and digestion
What does the large intestine do?
Site of water absorption
What is ingestion?
The taking in of nutrients by the mouth
What occurs in the mouth?
The early stages of chemical and mechanical digestion
What is food that is taken in called?
Bolus
What is saliva?
A watery, slippery fluid produced by the salivary glands, dissolves food particles and lubricates the food bolus; responsible for chemical digestion
What enzyme does saliva contain?
Amylase
What does amylase do?
Breaks down complex carbohydrates into simpler sugars
What are teeth needed for?
Mechanical breakdown
What is the esophagus?
A long muscular tube that contracts in a rhythmic motion called peristalsis. These contractions push the food bolus towards the stomach and the remainder of the gi tract
What is the epiglottis?
A tissue flap that shuts the trachea when eating so food does not go down that tube causing you to choke
What is the stomach?
A J-shaped sac that is the site of food storage and digestion
What is the stomachs capacity?
1.5L
What part of the stomach contracts and closes preventing the the stomach contents from moving back into the esophagus?
The cardiac sphincter
What is at the bottom of the stomach and regulates the exit of digested food in the into the small intestine?
The pyloric sphincter
What does the stomach secrete?
A number of digestive enzymes and gastric juices that help in the digestion of food particles
In what order, are items released into the stomach?
- Mucus
- Hydrochloric acid (HCl)
- Pepsin
What does mucus do?
Coats the inner lining of the stomach, protecting it from its own digestive juices; comes from mucous cells
What does hydrochloric acid do?
Kills harmful bacteria in the stomach. HCl is also important in activating the protein digesting enzyme pepsinogen to become pepsin, as a result the pH of the stomach is about 1-2. Comes from parietal cells
What does pepsin do?
The enzyme responsible for the digestion if proteins. Pepsin, secreted as pepsinogen, is activated by the presence of HCl. In the active form, pepsin breaks down long chain amino acids into shorter chain polypeptides. Comes from chief cells
What does rennin do?
An enzyme that causes milk to curdle which allows its nutrients to be properly absorbed
What else is absorbed in the stomach?
Alcohol, some drugs and vitamin B
What is food known as when it exits the stomach and enters the small intestine?
Chyme
What is acid reflux?
“heartburn”; caused by the movement of gastric juices (acidic) back into the esophagus, usually caused by failure of the cardiac sphincter to close
What are peptic ulcers?
Lesions or sores on the stomach lining that are irritated by the acidic secretions in the stomach. Caused by the breakdown of the protective mucus lining in the stomach. Induced by stress, diet and the bacteria Heliobacter pylori
What would happen if the stomach is removed?
No real harm would occur
What is digestion?
The further breakdown of macromolecules into smaller components
Where does the most digestion take place?
The duodenum; the first 25-30cm of the small intestine
What is the primary process of digestion?
Chemical process
What helps chemical digestion?
A number of enzymes secreted by the pancreas, liver, and gallbladder
What happens in the pancreas?
When acids enter the small intestine a hormone called secretin is released from the duodenum. This hormones stimulates the pancreas to secrete enzymes that break down the three major components of food
What breaks down long chain polypeptides into shorter chain peptides called peptones?
Trypsin; the inactive enzyme trypsinogen is converted to trypsin by the enzyme enterokinase
What second enzyme is released from the pancreas to complete the digestion of proteins into amino acids?
Erepsin (peptidase) : )
What enzyme does the pancreas release to continue the digestion of carbohydrates in the small intestine?
Amylase
What order does the digestion of carbohydrates go through?
- Amylose
- Maltose/sucrose/lactose
- Monosaccharides : )
What enzymes does the pancreas secrete to digest fats?
Lipase
What are fats digested into?
Fatty acids and glycerol
What else does the pancreas release?
Bicarbonate ions which neutralize the stomach acids that flow into the small intestine, so that it does not denature the pancreatic enzymes; protects and creates optimal zones
What does the liver continually produce that helps with fat digestion?
Bile (fluid)
Where is bile stored?
The gallbladder
What do fats in the small intestine stimulate the release of?
The hormone CCK (cholecystokinin)
What does CCK do?
Triggers the gallbladder to release bile salts
What do bile salts do?
Act as an emulsifying agent; causes the fat droplets to be broken apart into smaller particles
What does the increased surface area of the smaller fat droplets do?
Allows the lipase to work more effectively
What type of digestion is this process?
Mechanical digestion
What is mechanical digestion?
The physical breakdown of food into smaller pieces to increase surface area
What is chemical digestion?
The breaking of bonds by enzymes to make something new
Where does mechanical digestion occur?
Mouth and liver + gallbladder
Where does chemical digestion occur?
Mouth and small intestine
What is a catabolic reaction?
Breakdown of large molecules by hydrolysis; energy is released
What is an anabolic reaction?
The making/formation of a large molecule; energy is required
What occurs in the digestive tract in order?
- Polymers
- Monomers
- Absorbed into the blood
- Cells
- Mitochondria
- Energy (ATP)
What are the 2 roles of metabolism?
Catabolic and anabolic reactions
What is the main role of the digestive system?
To metabolize food
Unlike plants, what must heterotrophs do?
Consume large organic molecules and break them down
What else does the liver do?
Breaks down hemoglobin from red blood cells and stores the products in the gallbladder; removes many toxins and harmful substances from the body
What does the resulting bile pigments give fees?
Its characteristic colour
What else does the liver store?
Glycogen and vitamins A, B12, and D
What are the final products of the three main nutrients that is needed for absorption?
Carbohydrates- monosaccharides
Proteins- amino acids
Lipids- glycerol and 3 fatty acids
What does the stomach absorb?
Some water, some vitamins, medications, and alcohol
Where does most absorption occur?
The small intestine
What are the fingerlike projections in the small intestine called?
Villi
What are the villi lined with?
Individual cells arranged in long extensions of the membrane called microvilli
Some of the nutrients are absorbed into the capillary network by what?
Active transport
How are other nutrients absorbed?
Diffusion
What can only be absorbed here?
Amino acids and monosaccharides
What is each villus supplied with?
A capillary network that intertwines with lymph vessels called lacteals; only glycerol and the 3 fatty acids are absorbed here
When is chemical digestion done?
When food reaches the large intestine (colon)
What does the large intestine do?
Re-absorbs water, minerals, and some vitamins
Bacteria in the large intestine uses waste materials to make what?
Vitamins B and K
Where does undigested waste materials accumulate?
The large intestine until a bowel movement is made
What does the movement remove?
Potentially toxic waste from the body
What stimulates bowel movements?
Un-digestible fibrous material in the colon such as plant fibre
What is feces?
Either food that wasn’t digest or couldn’t be digested because no enzyme was present
Where does the breakdown of carbohydrates occur?
Begins in the mouth where salivary amylase breaks down polysaccharides (food) into disaccharides. In the duodenum the pancreas releases pancreatic amylase which also breaks down polysaccharides into disaccharides. Then intestinal enzymes (maltase, lactase, sucrase) break down disaccharides into monosaccharides
Where does the breakdown on proteins occur?
Begins in the stomach where HCl activates pepsinogen (gastrin) into pepsin which breaks down large proteins into smaller proteins. Then in the duodenum the pancreas (secretin) releases trypsinogen which becomes trypsin and breaks down large proteins into smaller proteins. The pancreas then releases erepsin which breaks down small peptide chains into amino acids
Where does the breakdown of lipids occur?
Occurs in the duodenum where the liver (CCK) releases bile which breaks down fats through emulsification into smaller lipids (mechanical). Then the pancreas releases pancreatic lipase which breaks down fat into glycerol and 3 fatty acids
Where does absorption occur?
Across the cell membrane of the villi/microvilli in the small intestine and into the capillaries; occurs by diffusion
Where does excess glucose go?
Goes to the liver where it is converted into glycogen
Where are lipids absorbed?
Across the cell membrane of the microvilli and into the lacteals which are lymph vessels
Where is water and electrolytes absorbed?
In the colon; flows into the colon via osmosis
