Lecture 10 Flashcards
(13 cards)
What are the functions of your gastrointestinal tract?
Your GI tract is responsible for digesting and absorbing your food, and then secreting the waste. Motility of your waste through your colon also serves a role in immune system surveillance.
- your gut plays a huge role in immunity. If you eat something, your body will see what is happening with the food. Stomach acid will destroy pathogens in dietary intake.
Where does digestion start? Explain the pathway for digestion (from eating to secretion of waste)
1) Mechanical motion of your chewing will make a bolus which will go down your stomach through the esophagus.
2) In the stomach, acids will begin to break down proteins (denaturation to prime the proteins for cleavage)
3) The stuff will head into the duodenum (first part of the small intestine) and will be joined by enzymes and things secreted by the pancreas.
4) It will go through the small intestines (duodenum to jejunum to ileum) and get further broken down and absorbed.
5) Once it reaches the end of the ileum, it will reach a junction between the two intestines. The digested material will go through the large intestine.
6) The colon absorbs water and ions and will concentrate in the rectum to be pooped out.
What is the purpose of the appendix? Are we able to live without it?
It helps store bacteria and the intestines replenish the microbiome so we can digest properly. We can live without it.
Where are most of the hormones which regulate digestive functions secreted? Where do these hormones typically act on and why?
Most hormones are secreted by the digestive system itself. Although it’s carried throughout the blood, only the digestive system reacts to these hormones. The reason the receptors are in the brain is because of negative feedback. Your brain needs to know if you are hungry/full with your food.
What are the roles of digestive hormones in the brain, and what occurs as a result of the interaction between digestive hormones and the brain?
In the brain, these hormones will bind to receptors such that they are able to control hunger, satiety, energy expenditure, and dietary balance. As a result, the brain will regulate the periodicity and levels of secretion of GI hormones.
Explain the roles of gastrin, and the effects of gastrin secretion.
Gastrin is responsible for stimulating gastric acid secretion and pepsin. Stomach acid can help destroy pathogens in dietary intake. Gastrin secretion can also stimulate the secretion of histamine as well as secretion of intrinsic factor.
When is gastrin secreted and where is it produced?
Gastrin is secreted in response to ingesting a meal. The reason that gastrin is secreted is because the gastrin stimulates the secretion of stomach acid and pepsin into the stomach. Neural stimuli can also stimulate secretion of gastrin. Several amino acids and increased CA++ in the serum can stimulate gastrin secretion. Gastin is produced by G cells in the lining of the stomach and upper small intestines.
How is the secretion of gastrin regulated?
There are conscious centers and neural reflexes which both stimulate gastrin secretion. The desire for food, circadian periodicity, the smell of a meal, and seeing food will all play a role in the secretion of gastrin. When food arrives in the stomach pH will increase, the presence of food will continue to stimulate the secretion of gastrin. When the contents of the stomach are digested and sent into the small intestine, the secretion of gastrin is turned off.
Explain the role of secretin and the effects of secretin secretion.
It stimulates the pancreas to secrete water and bicarbonate into the duodenum. The pancreas will secrete water and bicarbonate because they are responsible for increasing pH of stomach contents such that the intestines are not burned by the acidity, and so contents from the stomach can be properly absorbed in the small intestines. The secretion of bicarbonate and water by the pancreas into the small intestine allows pancreatic enzymes to be active. The release of secretin also inhibits gastrin secretion. If we have food in our intestines, we need to have some feedback that the food we ate is being digested and we no longer need to produce stuff to break down food.
Where is secretin produced/secreted, and how is the secretion of secretin regulated?
It’s released by S cells in the duodenum and upper jejunum in order to neutralize the stomach contents. The only known stimulus for secretion of secretin is an increase in acidity in the duodenum. Secretion of secretin is inhibited as the pH of the duodenum increases (less acidity)
Explain the roles of cholecystokinin (CCK)
It stimulates contraction of the gallbladder. The gallbladder stores bile (made in the liver) so stimulation of contraction of the gallbladder will allow for the secretion of these bile salts/acids into the duodenum to emulsify fats.
CCK also stimulates pancreatic enzyme secretion into the small intestine.
Secretion of CCK assists in the digestion of fats and proteins. Cholecystokinin is also produced by neurons in the brain, so it can act as a neurohormone in the CNS. Here, CCK is involved in regulation of appetite and satiety.
Where is cholecystokinin produced/secreted from and why?
CCK is produced from “I” cells in the duodenum and jejunum in response to acidity as well as gastrin. Presence of gastrin tells the intestines that cholecystokinin is needed to help with the secretion from the pancreas in order to facilitate digestion of proteins and fats.
What is the role of AMPK? What triggers AMPK activation, and what is the result of AMPK activation?
AMP Kinase binds AMP, allowing it to become activated that is able to phosphorylate other proteins to activate/inhibit them.
High levels of AMP indicate low energy levels. The activation of AMPK will usually trigger during starvation, fasting, uncontrolled diabetes, or when you are low in energy. Things that also trigger the activation of AMPK are exercise, release of leptin, and food intake.
Activation of AMPK occurs in the event in which you need energy:
- insulin secretion inhibited: Since you are going to have low blood sugar when you’re low on energy, secretion of insulin will be pointless
- fatty acid and cholesterol synthesis in the liver will be inhibited: this is an energy intensive storing process
- fatty acid synthesis and lipolysis: don’t want to store energy when we need it
- Fatty acid oxidation, glucose update, glycolysis in the heart will increase in the muscles
- feeding behavior will increase as a result (AMPK stimulates your brain to tell you that you are hungry)
