MCAT Digestive Sys.

Question 1

Intracellular digestion v. Extracellular digestion

Answer 1

Intracellular digestion is metabolism inside the cell and extracellular digestion is nutrients being absorbed from food.

Question 2

Alimentary canal

Answer 2

structure that runs from the mouth to anus and contains lumen which absorbs nutrients from food.

Question 3

Digestion
- Mechanical digestion
- Chemical digestion

Answer 3

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.

Question 4

Absorption

Answer 4

The movement of nutrients throughout body via the bloodstream.

Question 5

Describe the organization of the digestive tract.

Answer 5

oral cavity –) pharynx –) esophagus –) stomach –) small intestine –) large intestine.

Question 6

Role of the enteric nervous system

Answer 6

Controls peristalsis ( rhythmic contraction of the gut). Peristalsis is controlled by the parasympathetic NS while sympathetic NS slows this process down.

Question 7

What effects does these hormones have on feeding behaviors?
- ADH/ Vasopressin
- glucagon
-ghrelin
- leptin
- cholecystokinin

Answer 7

-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.

Question 8

Where does digestion being and end?

Answer 8

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).

Question 9

Pharynx v. Larynx

Answer 9

Pharynx allows air and food while larynx allows just air. Seperated by a flap called the epiglottis.

Question 10

Which part of the NS controls the esophagus?

Answer 10

The top is controlled by skeletal muscle ( Sympathetic NS) while the bottom is controlled by smooth muscle ( Parasympathetic NS).

Question 11

Food contents are emptied into the stomach from the esophagus via what?

Answer 11

The lower esophageal sphincter

Question 12

What are the 3 main sources of energy our body use?

Answer 12

• Proteins
• Fats
• Amino acids

Question 13

What are the 4 anatomical divisions of the stomach?

Answer 13

• 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

Question 14

Gastric glands responds to what part of the NS?

Answer 14

The parasympathetic NS via the vagus nerve.

Question 15

Describe each of the cells of the gastric glands

Answer 15

• 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.

Question 16

Describe the cells of the pyloric glands.

Answer 16

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.

Question 17

What are the parts of the small intestine?

Answer 17

1. Duodenum - responsible for digestion.
   
   • Chyme leaves stomach via pyloric sphincter. Met with brush- border enzymes released by duodenum.
2. Jejunum - responsible for absorption
3. Illeum- responsible for absorption

Question 18

What happens when a person is lactose intolerant?

Answer 18

They don’t have the enzymes to digest a particular carbohydrate. This causes bacteria to metabolize it instead and product methane gas.

Question 19

Peptidase, Lipases, Amylases

Answer 19

• Peptidases- breaks down proteins
• Lipases- breaks down fats
• Amylases- breaks down carbohydrates

Question 20

Role of the following small intestine ( duodenum) enzymes:
- Secretin
- Entereopeptidase
- CCK

Answer 20

• 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).

Question 21

Bile

Answer 21

Created by the liver. Serves to put fats into miscelles so they can be hydrolyzed by lipases.

Question 22

What are the accessory organs of the digestion system? What is the role of the pancreas?

Answer 22

• 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.

Question 23

What is the role of the liver?

Answer 23

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.

Question 24

Gallbladder

Answer 24

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.

Question 25

Describe the function and structure of jejunum and illeum?

Answer 25

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**

Question 26

What are the 2 classes vitamins?

Answer 26

• 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.

Question 27

Describe the function of the large intestines

Answer 27

Primarily absorbs water

1. Cecum- accepts contents from the small intestine via ileocecal valve. Also serves as the attachment to the appendix.
2. Colon - Uses water and salt to form feces.
3. Rectum - holds feces until it’s released through anus, has 2 sphincters.
   *Internal sphincter- involuntary actions ( autonomic NS)
   • External sphincter - voluntary actions ( somatic NS)