What two processes are involved in digestion?
- Breaking down food, followed by absorption and elimination
Name four materials that our bodies are able to absorb.
Sugar, Amino Acids, Glycerol, and Fatty Acids
What process are the teeth responsible for?
Mechanical Digestion (breaking down using physical force)
What two things does the saliva do to your food?
1) liquifies food
2) Lubricates and softens the BOLUS of food.
How does your tongue participate in the digestion?
- protects us against poisons
- Moves food around
- Helps swallow food
Prior to swallowing, the food is pushed to this part of the throat called the ?
swallow reflex center
What is the function of the cardiac sphincter at the end of the esophagus?
ensures that no food re-enters the esophagus
Explain how the stomach is involved in chemical digestion?
-Columnar epithelium produces an inactive enzyme called PEPSINOGEN.
-These cells contain many mitochondria for active transport.
- Chief Cells produce 3M Hydrochloric Acid (HCl).
- HCL is a strong acid and therefore very effective at breaking down materials
How does the pyloric sphincter regulate the activities of digestion?
Move the chyme (an acidic liquid) into the duodenum at a slow, controlled rate.
What happens to bile after it is produced by the liver?
1) The bilirubin is exported in bile to the gall bladder
2) It is also put into the blood stream where it is removed by the kidneys
What is the main function of the small intestine?
To complete digestion and begin absorption of nutrients.
What is the function of the ileum?
to absorb all of the nutrients into the circulatory and lymphatic systems.
What is the function of the rectum?
Compress waste materials into a solid form before being eliminated
What is the function of Hydrochloric acid in the stomach?
Digest proteins into peptides and polypeptides
What are peptidases?
intestinal enzyme that completes digestion of partially digested proteins to amino acids
Before lipase can begin work, what must happen?
Fats must be broken down into smaller pieces using bile produced by blood in the liver.
Swallowing is a reflex action. What does this mean?
Involuntary due to a give stimulus (food entering the back of the mouth)
What directs food into the esophagus?
The pharynx closes off the nose and trachea, and guides food with the help of the tongue
Once in the esophagus, how is food moved towards the stomach?
Involuntary constriction and relaxation of the muscles. (peristalsis of the esophagus)
Why is it important for the stomach contents to be acidic?
Breaks down molecules (acids are very corrosive)
What happens if the pancreatic juice contains an insufficient amount of sodium
acidic chyme will not be neutralized
What happens to gastrin after it has been produced?
Gastric juice is released, killing bacteria and digesting protein
What effect does it have on the stomach?
The stomach becomes more acidic, and also gains the ability to Pepsinogen to Pepsin, and Pepsin to Peptides + Polypeptides
Explain how the production of gastrin is an example of negative feedback.
If HCl formed from Gastrin enters the duodenum, NaHCO3 from the pancreatic juices (high pH) lowers the acidity of the solution.
Explain how insulin controls the blood sugar level in a negative feed back cycle?
If there is excess blood glucose in the liver, insulin converts it to glycogen
Why does insulin promote protein and fat synthesis?
1. Inhibition of glycogen synthesis (liver glycogen 5-6%)
2. Activation of acetyl-CoA carboxylase, leading to an excess of citrate & isocitrate ions and conversion of acetyl-CoA to Malonyl-CoA
3. Activation of lipoprotein lipase which splits triglycerides into fatty acids, which are transported into adipose cells and stored.
The liver produces what from the breakdown of amino acids?
converted into glucose to maintain glucose concentration of plasma (this is called gluconeogenesis).
The liver metabolizes poisonous substance. What does this mean?
The liver detoxifies any poisons or harmful substances that were absorbed by the digestive tract
(ie: alcohol is metabolised into fatty acids).
The liver breaks down old red blood cells and recycles hemoglobin by turning it into what?
bilirubin and biliverdin (the components of bile)
The small intestine has at least three features that increase the surface area. What are those features?
convoluted (folded) walls, VILLI (folds in mucose layer), and MICROVILLI (smaller folds)
Why is increased surface area vital for absorption?
Increases amount of food absorbed (more time to go through the organ)
Within each villus are blood vessels and an extension of the lymphatic system
called a what?
What are the two functions of the blood vessels?
- Carry blood (containing oxygen and nutrients) through the body.
- Carry hormones, and enzymes to stimulate specific functions of organs
What process is used to transport materials from the gut into the blood stream?
The hepatic portal vein (drains blood from the gastrointestinal tract and spleen to capillary beds in the liver)
Where do the products of fat digestion go after they are absorbed into the lacteal?
It travels through the lymphatic system until it is dumped into the circulatory system.
Where do the sugars go after they are absorbed into the bloodstream?
They are carried to all of the body's tissues and are used to supply energy