Lecture 3 Digestive System Flashcards
(27 cards)
What is the primary function of the digestive system?
The primary function of the digestive system is to break food into smaller components through a process called Digestion.
What happens once the food is “absorbed”?
When these components are being “absorbed”, they are taken into the bloodstream or lymph from the GI tract into the body.
What happens to substances that cannot be absorbed?
They are excreted.
Which part of the digestive system is a continuous tube running from the mouth to the anus?
The GI tract.
Which organs consist of the GI tract?
Organs of the GI tract include: the mouth, most of the pharynx, the esophagus, stomach, small intestine, large intestine and rectum.
How long is the GI Tract?
It is about 5-7 metres long
Which organs are the “accessory” digestive organs? Aka have functions to assist in digestion.
The accessory digestive organs include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
What are the 6 functions of the GI tract? (My Sister Digs And Eats Noodles)
Functions of the GI tract include: Motility, Secretion, Digestion, Absorption, Elimination and nutrient production
What are the 4 main layers of the Digestive Tract Wall?
1) Mucosa (absorption occurs)
2) Sub-mucosa (absorption occurs)
3) Muscle
• Circular muscle
• Longitudinal muscle
4) Serosa
What are the two patterns of motility in the GI tract?
Peristalsis:
Progressive waves of muscle contraction and relaxation that move from one section of intestinal tract to another to propel food forward.
Segmentation:
Mixing contractions that knead material back and forth (breaking it up) without propelling food forward.
What are the two types of digestion processes?
1) Mechanical Digestion:
- Chewing
- Mixing and grinding motions of the stomach and intestines
2) Chemical Digestion:
- Hydrochloric acid in the stomach denatures protein
- Enzymes breakdown food
What do enzymes do for our bodies and digestion?
Enzymes are essentially proteins that act as catalysts to facilitate chemical reactions.
What digests proteins?
- Hydrolysis reactions, lactase, and maltase digest carbohydrates.
- Pepsin, trypsin and peptidase digest proteins.
- Lipase digests lipids.
- “ase” means enzymes and “lip” means “lipids”, for example. Or “lac” breaks down lactose, “ase” means enzyme. Pepsin and Trypsin are exceptions.
What is the 1st step in the flow of food through the GI tract?
1) The Mouth:
- Chewing
- Saliva consists of:
Enzymes help break down simple sugars (salivary amylase) and fat (lingual lipase)
- Mucus to lubricate the food for easier swallowing
- Lysozyme to kill bacteria
What is the 2nd step in the flow of food through the GI tract?
2) The Tongue
- Maneuvers food for chewing and swallowing (now called a bolus)
- Contains 5 different taste receptors (salty, sour, sweet, bitter, umami – like a meaty taste)
- Flavour is enhanced with the olfactory cells
- Swallowing moves food into the esophagus
- The epiglottis closes over the larynx to keep food out of the lungs
What is the 3rd step in the flow of food through the GI tract?
3) Esophagus:
- Connects the mouth to the stomach
What is the 4th step in the flow of food through the GI tract?
4) Sphincters: Circular rings of muscle that control the flow of food stuffs in the GI tract
- Upper esophageal sphincter: controls flow of food into esophagus
- Lower esophageal sphincter: prevents reflux of stomach contents into esophagus
- Pyloric sphincter: separates the from the small intestine.
- Ileocecal valve: prevents large intestine contents (bacteria & fecel matter) from back-flowing into the small intestine
- Anal Sphincter: prevents defecation until person desires to do so
- Heartburn is the pain from highly acidic stomach contents that have back-flowed through the Lower Esophageal Sphincter into the esophagus.
- An ulcer is an area where tissue has been destroyed by gastric juices and stomach acid
- Most common are duodenal ulcers (happens here first- beginning on esophagus)
What is the 5th step in the flow of food through the GI tract?
What are some of the stomach secretions?
5) Stomach:
- Between the lower esophageal sphincter and pyloric sphincter
- Capacity of ~50ml (2 oz.) empty, to 4 liters (128 oz.) when extremely full i
- 2 liters of gastric juice (combination of hydrochloric acid, enzymes and hormones) are released by the stomach every day to aid digestion.
- The following include some of the stomach secretions:
•Hydrochloric acid - which aids protein digestion, and destroys harmful bacteria & viruses
•Gastrin – a hormone which stimulates HCL and pepsinogen release
•Mucous - which protects the stomach wall from being digested by HCL and pepsin
oContraction of the muscular layers of the stomach thoroughly mixes the food with the digestive juices forming chyme. (soupy liquid)
oIt takes about 1-4 hours for meals to leave the stomach (longer if they are large or high in fat)
What is the 6th step in the flow of food through the GI tract?
5) Small intestine:
- Is about 2.5 cm in diameter and 3 meters long.
- It begins at the pyloric sphincter of the stomach and ends at the ileocecal valve.
- 3 Sections of small intestine: Duodenum, jejunum, ileum
- Most digestion and absorption of nutrients occurs here.
- The digestion and absorption of nutrients is aided by the large surface area of the small intestine.
- It has a large surface area due to its:
• Long length
• Circular folds (which also make the chyme spiral to aid mixing and allow absorption)
• Villi (increases surface area)
• Microvilli (enzymes on here help break down food)
• The pancreas releases pancreatic juice into the duodenum.
• Pancreatic juice contains:
• Bicarbonate which neutralizes stomach acid
• Digestive enzymes to break down proteins, fats and carbohydrates
o The liver produces bile which is stored in the gall bladder. It also is released into the duodenum.
o Bile aids:
• Fat digestion (emulsification) and absorption
• Cholesterol excretion (the only way our body can do this!)
o Once foodstuffs are small enough, they can then be absorbed. (~95% of the absorption occurs in the small intestine)
o Absorption is the process of nutrients entering into the small intestine absorptive cells.
What is nutrient transport?
Nutrient transport:
• Once nutrients are absorbed through the intestinal cells, they are transported throughout the body by one of 2 systems:
o Cardiovascular system (water soluble nutrients like amino acids or carbohydrates) OR…
o Cardiovascular system (Fat-soluble nutrients)
What makes up the Cardiovascular System?
Cardiovascular System:
• Heart, blood vessels etc.
• Proteins, carbs, short and medium chained fatty acids, B vitamins etc. are transported this way.
• Travels directly to the liver via the hepatic portal vein.
• The nutrients then enter the general circulation where they can be transported to all body cells.
What makes up the Lymphatic System?
Lymphatic System:
• Contains lymph which flows in lymphatic vessels, circulated by muscular contractions not the heart
• Transports larger molecules that cannot fit into capillaries (most fats, fat soluble vitamins (A,D,E,K) & large proteins.
• Lymphatic vessels transport nutrients to the cardiovascular system via the large left subclavian vein and then to all the body cells.
Where is the large intestine located and what are its 3 functions?
Large Intestine:
o Begins after the ileocecal valve.
o Is 6cm wide and 1.5m long
o By this point 95% of the digestion and absorption has occurred.
o Only water, some minerals and undigested food fibers are left in large intestine
o Performs 3 functions:
1) Houses bacterial flora
• Beneficial bacteria control the growth of pathogenic bacteria
• Beneficial bacteria also synthesize Vitamin K and biotin
2) Absorbs water and electrolytes (Na+ and K+)
3) Forms and expels feces.
• ~75% water and 25% solids (The solids are indigestible plant fibers & connective tissue from animals, and some bacteria.)
What are the two pancreatic secretions?
Pancreatic Secretions:
1) Exocrine (99% of the gland)
• Secreted into the digestive system via a duct.
• Includes enzymes & buffers (HCO3-)
2) Endocrine (1% of the gland)
• Secreted directly into the blood stream
• Includes hormones such as insulin and glucagon
