MCAT Digestive Sys. Flashcards
Intracellular digestion v. Extracellular digestion
Intracellular digestion is metabolism inside the cell and extracellular digestion is nutrients being absorbed from food.
Alimentary canal
structure that runs from the mouth to anus and contains lumen which absorbs nutrients from food.
Digestion
- Mechanical digestion
- Chemical digestion
Digestion is the breaking down of macromolecules into it’s constituents.
- Mechanical digestion- chewing, breaking large pieces into large pieces.
- Chemical digestion - breaking apart chemical bonds using enzymes.
Absorption
The movement of nutrients throughout body via the bloodstream.
Describe the organization of the digestive tract.
oral cavity –) pharynx –) esophagus –) stomach –) small intestine –) large intestine.
Role of the enteric nervous system
Controls peristalsis ( rhythmic contraction of the gut). Peristalsis is controlled by the parasympathetic NS while sympathetic NS slows this process down.
What effects does these hormones have on feeding behaviors?
- ADH/ Vasopressin
- glucagon
-ghrelin
- leptin
- cholecystokinin
-ADH/ Vasopressin - causes sensation of thirst causing us to drink.
- glucagon and ghrelin ( secreted by stomach) causes sensation of hunger
- Leptin and cholecystokinin causes feelings of satiety.
Where does digestion being and end?
Begins in the oral cavity and ends in the duodenum of the small intestine.
In the oral cavity there is mechanical digestion ( mastication = chewing, and creates ball of food = bolus). Chemical digestion ( saliva lipase, saliva amylase).
Pharynx v. Larynx
Pharynx allows air and food while larynx allows just air. Seperated by a flap called the epiglottis.
Which part of the NS controls the esophagus?
The top is controlled by skeletal muscle ( Sympathetic NS) while the bottom is controlled by smooth muscle ( Parasympathetic NS).
Food contents are emptied into the stomach from the esophagus via what?
The lower esophageal sphincter
What are the 3 main sources of energy our body use?
- Proteins
- Fats
- Amino acids
What are the 4 anatomical divisions of the stomach?
- Fundus and body- contains the gastric glands ( muscosal cells, parietal cells, and chief cells).
-Antrum and pylorus- contains pyloric glands. Contains G cells that increase HCl secretions and contractions making of chyme
- Less curvature- internal curvature of the stomach
- Greater curvature - exterior curvature of the stomach
- Rugae- lining of the stomach into folds
Gastric glands responds to what part of the NS?
The parasympathetic NS via the vagus nerve.
Describe each of the cells of the gastric glands
- Mucous cells - produce bicarbonate rich mucous that protects stomach lining of stomach.
- Chief cells - secrete pepsinogen which are the zymogen form of pepsin.
- Parietal cells - secretes HCl which cleaves the zymogen form, pepsinogen, into pepsin. Which is a peptidase. They also secrete intrinsic factor which works to absorb vitamin B12.
Describe the cells of the pyloric glands.
Contains G-cells which secrete gastrin. Gastrin activates parietal cells of the gastric glands.
This results in stomach contraction that leads to a semifluid called chyme.
What are the parts of the small intestine?
- Duodenum - responsible for digestion.
- Chyme leaves stomach via pyloric sphincter. Met with brush- border enzymes released by duodenum.
- Jejunum - responsible for absorption
- Illeum- responsible for absorption
What happens when a person is lactose intolerant?
They don’t have the enzymes to digest a particular carbohydrate. This causes bacteria to metabolize it instead and product methane gas.
Peptidase, Lipases, Amylases
- Peptidases- breaks down proteins
- Lipases- breaks down fats
- Amylases- breaks down carbohydrates
Role of the following small intestine ( duodenum) enzymes:
- Secretin
- Entereopeptidase
- CCK
- Entereopeptidase- converts trypsinogen ( zymogen form) to trypsin, which is a peptidase.
- Secretin - secretes pancreatic enzymes into duodenum which decreases HCl release from parietal cells and increase mucosal release ( therefore it’s a rise in the pH).
+ Also an entereogastrone, which serves to decrease motility of digestive tract serving to increase absorption. - CCK- causes release of bile and pancreatic juices( bicarb rich alkaline solution that neutralizes acidity and has enzymes that participate in digestion).
Bile
Created by the liver. Serves to put fats into miscelles so they can be hydrolyzed by lipases.
What are the accessory organs of the digestion system? What is the role of the pancreas?
- Liver, pancreas, gallbladder
** Exocrine structures functions through ducts**
+ Pancreas- carries out endocrine functions ( islets of langerhans) and exocrine functions ( acinar cells) which secrete pancreatic juices that neutralize the pH and has enzymes for digestion.
* Pancreatic amylase - breaks down carbohydrates, trypsinogen/ chymotrypsin. carboxypeptidase A&B are all peptidases that cleave proteins., pancreatic lipase hydrolyses triglycerides into glycerol and free fatty acids.
What is the role of the liver?
Creates bile and serves a role in detoxification.
- Once bile is made it’s either carried to gallbladder for storage or to the duodenum of the small intestine.
- The liver receives blood coming from the hepatic portal system, this serves the detoxification role.
*Liver receives bilirubin ( comes from the breakdown of hemoglobin) and conjugates it with a protein and puts it in bile so it can be secreted. If there is a buildup of bilirubin it can cause jaundice. - Liver also creates albumin which mantains oncotic pressure and is a carrier protein. The liver also creates clotting factors.
Gallbladder
Stores and release bile into duodenum via the biliary tree where it travels into the duodenum via the pancreatic duct.
* Bilirubin and cholesterol can buildup in the duodenum and create stones, causing inflammation.
Describe the function and structure of jejunum and illeum?
Jejunum and illeum play a role in absorption and therefore has villi. Within the villi there is microvilli ( contains capillary bed) which absorbs water- solube molecules and contains lacteals which transports triglycerides into the lymphatic system via the left subclavian vein.
** Triglycerides are packaged into chylomicrons before lacteals deposit them into the lymphatic system**
What are the 2 classes vitamins?
- Fat soluble ( A, E, D, K) vitamins- because their fat soluble they must be packaged into chylomicrons before being put into the lymphatic system by lacteals.
- Water soluble vitamins - absorbed directly into bloodstream via amino acids, carbohydrates, and water.
Describe the function of the large intestines
Primarily absorbs water
- Cecum- accepts contents from the small intestine via ileocecal valve. Also serves as the attachment to the appendix.
- Colon - Uses water and salt to form feces.
- Rectum - holds feces until it’s released through anus, has 2 sphincters.
*Internal sphincter- involuntary actions ( autonomic NS)- External sphincter - voluntary actions ( somatic NS)
Peritoneal cavity
The cavity that surrounds the gastrointestinal tract and prevent leakage of gastric contents.
