Digestive System Summer School

Question 1

Digestive System

Answer 1

We eat food to obtain the energy we need to stay alive and get the building blocks for all tissues

The systems and organs in the body that help with…
→ taking in and breaking down food into smaller pieces
→ Absorption of Nutrients
→ Excretion of Waste

Basically wants to reduce all different kinds of molecules in the food to their most basic forms.
→ Lipids, Carbohydrates, Nucleic acids and proteins
get converted into
→ Fatty acids, Amino acids, sugars and nucleotides

Question 2

Four Stages of Digestion

Answer 2

Ingestion – take food (nutrients) in
Digestion – breakdown of food into smaller molecules
Absorption – taking digested molecules into cells of digestive tract and transferring them to the blood
Egestion – removal of waste from the body

Question 3

Mechanical Digestion

Answer 3

→ This involves the physical breakdown of food particles into smaller pieces using the teeth, tongue and stomach
→ Mechanical digestion is a physical change

Question 4

Chemical Digestion

Answer 4

→ Involves enzymes (biological catalysts)
↪ An enzyme is a molecule that helps chemically breakdown molecules in our bodies by speeding up chemical reactions
→ This is a chemical change 🡪 the resulting molecules are not the same as the reactant molecule(s).
↪ E.g. 🡪 starch is broken down into glucose molecules using the enzyme amylase.
↪ Enzymes can be from saliva, stomach, pancreas & intestines

Question 5

Enzymes

Answer 5

Proteins that living things use as catalysts to speed up chemical processes. In the digestive system this helps break down food into lipids, carbohydrates, proteins and nucleic acids.

Question 6

Mouth (Ingestion) [Oral Cavity] [Buccal Cavity]

Answer 6

→ Stratified Squamous Epithelial tissue (can withstand a lot of friction )
→ Roof is formed by anterior hard palate, flexible posterior soft palate (this anchored to the tongue and throat forming the boundary between mouth and throat) and Uvula (The part at the very back)
↪ This closes the nasopharynx which stops food going into your nasal cavity

Teeth start to break down the food physically by chewing (with teeth and tongue) and chemically with our salivary glands producing saliva
→ Saliva also kills harmful bacteria and keeps the mouth somewhat clean.

Question 7

Types of Teeth

Answer 7

→ Incisors are specialized for cutting. They are chisel-shaped. (Usually the teeth at the front)
→ Canine are specialized for tearing. These are dagger-shaped and sharp. (They are pointy)
→ Premolars are specialized for grinding. These are flattened.
→ Molars are specialized for crushing. These tend to be broader than premolars and have cusps that are more flattened. (Last 3 Teeth at the back)

Question 8

Tongue

Answer 8

→ A large muscle that mixes food with saliva to form a bolus (A small rounded mass of substance, especially of chewed food at the moment of swallowing).

→ The tongue pushes the bolus back to the top of the throat.

Question 9

Salivary Glands

Answer 9

→ There are three salivary glands located in the mouth: Parotid (Mostly serous), Sublingual (Mostly mucus) and Submandibular (Mostly serous)
→ There main function is to produce saliva
→ Saliva helps with…
↪ Lubrication
↪ Helping with swallowing
↪ Protects teeth against bacteria
↪ Aids in the chemical breakdown of food

Mucous cells produce mucus (protective substance) while serous cells produce watery secretion that is full of enzymes.

Question 10

Pharynx

Answer 10

→ Shared area with respiratory system
→ Located at the back of the throat
→ Guides the food from the oral cavity into the esophagus (food tube)

Question 11

Esophagus

Answer 11

→ It carries the bolus to stomach.
→ It uses peristalsis -  muscular contractions that work like a rhythmic wave to carry food down.
→ Works even if you are upside-down.
→ Stratified Squamous Epithelial tissue
→ Connects mouth to the stomach

The esophagus propels (thus “propulsion”) the food to the stomach using times contraction in a movement called “Peristalsis”

Question 12

The Process of Swallowing

Answer 12

1) The tongue rolls up the food into a bolus
2) Pushes the bolus towards the back of the throat
3) The soft palate/uvula combination closes over the nasal cavity
4) The epiglottis closes down upon the trachea preventing food from entering the air pipe and choking
5) A reflex is initiated causing peristalsis in the esophagus to begin

Question 13

Cardiac Sphincter

Answer 13

→ Located between esophagus and stomach
↪ Circular muscle layer
↪ Contracts and relaxes to allow food into stomach, but keeping it from going back to the esophagus

Question 14

The stomach functions

Answer 14

Functions include
→ Short-term storage reservoir (adult capacity - 1500mL)
→ Protein breakdown
→ Liquification of food –> chyme
→ Slowly released into the small intestine-

Question 15

More about le stomach

Answer 15

→ Columnar Epithelial tissue
↪ Secretes mucus to line the organ so that it does not get digested by its own enzymes and hydrochloric acid
→ Can hold 2-4 liters of material

→ The stomach uses Hydrochloric acid and enzymes to break down the food to smaller sizes (Chemical Digestion)
↪ The resulting material is called Chyme
→ It contracts and expands to move the food to the intestines (Propulsion)
→ Muscles contract and expand to “churn” the food (Mechanical Breakdown)
→ Kills a lot of harmful viruses and bacteria

→ Rugae are small fold in the stomach that increase the surface area to absorb nutrients and to expand and contract

We are breaking down the food to increase its surface area so that it can encounter more enzymes.

Question 16

Pyloric Sphincter

Answer 16

→ Chyme leaves the stomach via the pyloric sphincter
→ Circular muscle layer at junction of stomach and small intestine
→ Contracts and relaxes to control the flow of food leaving the stomach

Question 17

Small Intestine

Answer 17

→ Overall Function of small intestine is to chemically and mechanically break down food products and absorb the dissolved nutrient into the bloodstream
→ Columnar Epithelial tissue
↪ Secretes mucus to line the organ so that it does not get digested by its own enzymes

→ Smooth muscle segments in the small intestine contract and relax in a process called segmentation (Mechanical Breakdown and Propulsion)
→ Chemically breakdown the food with enzymes from the liver, gallbladder and pancreas (Chemical Digestion)
→ The Small intestines are lined with villi and microvilli which are hair-like projections responsible for collecting nutrients. They have capillaries that absorb the broken down micro molecules. Once absorbed they can get put into the blood stream and go to any cell (Absorption)

→ Divided into three parts:
↪ Duodenum
↪ Jejunum
↪ Ileum

Question 18

Small Intestine: Duodenum

Answer 18

→ First portion of small intestine
→ U-shaped, shortest, widest
→ Pancreatic and bile ducts open into here
→ Circular folds
→ Main function is chemical digestion

Question 19

Small Intestine: Jejunum

Answer 19

→ 2.5m long
→ More folds than duodenum
→ Main function is absorption of nutrients

Question 20

Small Intestine: Ileum

Answer 20

→3m long
→ Functions to absorption of nutrients
→ Functions to push undigested material into the large intestine

Question 21

Large Intestine

Answer 21

→ 4 parts: caecum, colon, rectum, anal canal
→ Appendix hangs off of the caecum
→ 1.5m long, but much wider than small intestine
→ Separated from ileum by a valve (ileocecal)
→ Bacteria break food down further and produce vitamins B-12, K and amino acids
→ Columnar Epithelial tissue
↪ Secretes mucus to line the organ so that it does not get digested by its own enzymes
→ Absorbs the water and turns the food into feces (Defecation)
→ Has good bacteria that digest anything your body could not. (These are responsible for producing gas as well).
→ Breaks down your feces with contractions and expansions (Mechanical breakdown)
→ Peristalsis is used to transport the feces to your anus.

Question 22

Anus

Answer 22

→ Rings of circular muscles – sphincters

→ Control the release of feces

Question 23

Accessory Organs

Answer 23

→ Accessory organs to the digestive system are indirectly involved in the digestion process
→ They include:
↪ Liver
↪ Gallbladder
↪ Pancreas
→ Tongue and salivary glands are also considered accessory organs

Question 24

Accessory Organs - Liver

Answer 24

→ 1.5kg
→ Largest gland in body
→ Located above stomach
→ Stores carbohydrates and vitamins
→ Detoxifies many harmful substances in the blood
→ The main role is to make Bile for the digestive system
↪ This solution stops fat from clumping so that it can be broken down
→ It can regenerate with only 25% of its original tissue

Question 25

Accessory Organs – Gallbladder

Answer 25

→ Sac-like structure located under the lobes of the liver
→ Stores bile and releases it to duodenum to assist in the breakdown of fat molecules
→ Transferred to the duodenum via the cystic and bile ducts

Question 26

Accessory Organs – Pancreas

Answer 26

→ Located slightly below and behind stomach
→ Produces sodium bicarbonate, which raises pH of chyme from 2.5-9.0 in the duodenum (so intestinal wall is not digested by acidity of chyme)
→ Secretes enzymes important for digestion of carbohydrates, fats and proteins
→ Its secretions reach the duodenum via the common bile duct
→ Makes an enzyme cocktail called pancreatic juice which can break down a lot of things

Question 27

What does chemical Digestion produce

Answer 27

Macromolecule → Subunit
Carbohydrates → Simple sugars (like glucose)
Proteins → Amino acids
Lipids → Fatty acids

→ Once broken down, the subunits are absorbed into the bloodstream from the ileum and jejunum

Question 28

Carbohydrate Digestion

Answer 28

→ Salivary Amylase
↪ Produced in Salivary Glands
↪ Located in the Mouth
↪ Has a pH of 7

→ Pancreatic Amylase
↪ Produced in Pancreas
↪ Located in the Small intestine (Duodenum)
↪ Has a pH of 8

→ Lactase
↪ Produced in Small Intestine
↪ Located in the Small Intestine (Duodenum)
↪ Has a pH of 8
↪ Breaks down lactose, a sugar found in milk

→ Enzymes produced in the pancreas travel to the duodenum via the common bile duct

Question 29

Lipid/Fat Digestion

Answer 29

→ Lipase
↪ Produced in Stomach
↪ Located in the Small Intestine (Duodenum)
↪ Has a pH of 8

→ Pancreatic Lipase
↪ Produced in Pancreas
↪ Located in the Small Intestine (Duodenum)
↪ Has a pH of 8

→ Bile
↪ Produced in Liver and stored in Gallbladder
↪ Located in the Small Intestine (Duodenum)
↪ Has a pH of 8

→ Lipase produced in the stomach isn’t very active because it is too acidic. It becomes active in the small intestine
→ Enzymes produced in the pancreas travel to the duodenum via the common bile duct
→ Bile is a complex fluid, containing many different chemicals. Its main role in fat digestion is that it emulsifies the fat molecule, which helps the enzymes break down the fats. Bile is also released into the small intestine using the common bile duct.

Question 30

Protein Digestion

Answer 30

→ Pepsin
↪ Produced in Stomach
↪ Located in the Stomach
↪ Has a pH of 1-2

→ Trypsin
↪ Produced in Pancreas
↪ Located in the Small Intestine (Duodenum)
↪ Has a pH of 8

→ Pepsinogen and Hydrochloric acid are produced by the stomach. Pepsinogen is activated by the HCl, forming pepsin, the enzyme that is used to break down proteins
→ Enzymes produced in the pancreas travel to the duodenum via the common bile duct

Question 31

St. Martin’s Stomach

Answer 31

One day a furtrapper, St Martin got shot. He was expected to die but a doctor named Beaumont kept him alive.

He performed a lot of surgeries and Beaumont decided to keep the stomach hole open. Beaumont performed experiments and found out how the stomach digests and how the brain affects this digestion.

Question 32

Stomach: Chemicals

Answer 32

→ Parietal cells release HCl
→ Chief cells release pepsinogen which combines with HCl to make pepsin
→ Enteroendocrine cells release serotonin and histamine to increase the release of these chemicals and amino acids. Somatostatin inhibit secretions
→ G cells produce Gastrin which stimulates gastric activity (stimulates fluid release and muscular activity)

Question 33

Stomach Controls: Cephalic Phase

Answer 33

This is when the brain sends a signal to the stomach to prepare for digestion. This is triggered when you see, hear, smell or think about food. This is a conditioned reflex, only works if you want to eat the food.

Question 34

Stomach Controls: Gastric Phase

Answer 34

When the food comes to the stomach, hormones and neurons start to tell the stomach to digest.

Question 35

Stomach Controls: Intestinal phase

Answer 35

Speeds or slows the rate at which the stomach empties so that small intestine does not get overloaded.

Question 36

Bile

Answer 36

Produced by the liver and acts as a emulsifier.
Bile is made of Bile salts which have a hydrophobic end (that sticks to the fat) and a hydrophilic end (keeps fat away). By attaching all around fat molecules, it prevents fat from clumping.

Question 37

Celiac Disease

Answer 37

An autoimmune disease: any gluten would trigger the immune system and damage the small intestine
→ Results in improper digestion of food
→ Chronic disease (Has ongoing symptoms for more than one year)
→ Symptoms include: Staggered growth, gastrointestinal problems (diarrhea and vomiting), Anemia can result as person is not absorbing enough nutrients, Irritable bowel disease (Symptoms that affect the gut)
→ Diagnosed with a serology test where the immune antibodies can be detected through the blood.
↪ Take a endoscopy of the lining of the gut and biopsy. Small camera is passed through small intestine via throat.
↪ Genetic tests can also reveal the two genes that are related to the disease. The gene is associated with the HLA protein
→ Can be classified on severity based on IEL (Epithelial lymphocytes), crypts (absorption organ and protective layer) and villi
→ Treatment: They have to remove gluten from diet