Animal Classification, Structure, and Function Unit

Unit #2 - Biology

What is Digestion?

The process of breaking down food to provide nutrients and energy for growth, repair, and reproduction

What is Ingestion?

The process of taking food, drink, or another substance into the body by swallowing or absorbing it

What is Absorption?

The transfer of digested nutrients from the digestive system to the bloodstream

What is Egestion?

The removal of waste food materials from the body

What is the Pathway for food? (In order)

1. Mouth

2. Esophagus 

3. Stomach

4. Small Intestine 

5. Large Intestine

6. Rectum

7. Anus

What are enzymes?

A substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process.

What are enzymes role in the body?

Enzymes are biological catalysts that accelerate chemical reactions in the body, enabling essential processes like digestion, metabolism, DNA replication, and detoxification.

What are the two digestion types?

Mechanical Digestion & Chemical Digestion

What is a mechanical digestion?

The act of physically breaking up food into smaller pieces

Goal: To create as much surface area as possible so that digestive enzymes can interact with more of it at once -> gets broken down faster

Ex: Chewing, crushing, squishing, squeezing, smashing, liquifying

What is a chemical digestion?

The act of breaking down food at the molecular level (breaking the chemical bonds)

Goal: Release the energy stored in these bonds to use in the body

Ex: Using enzymes to catalyze (speed the reaction rate), catabolize, cleave (break) bonds, transfer energy)

Where does Ingestion occur?

The mouth

- Ingestion (as food enters the mouth)

- Digestion also begins in the mouth via

breakdown of food molecules by your teeth (Mechanical)

breakdown of food molecules by your saliva (Chemical)

- Absorption

Some small substances (ex. medication, vitamins) can enter the bloodstream through sublingual capillaries (blood vessels under the tongue)

The Mouth - Saliva, Teeth & Tongue

Saliva

- Dissolve food particles to. taste food

- Contain mucus (lubricate), water (soften food), amylase (breaks amylose)

Front teeth

• Incisors & Canines → Grab and cut food

Back teeth

• Premolars & Molars → Broad flattened teeth for grinding and crushing food

Tongue

• Rolls food into “bolus" and contain taste buds

(Bolus - mixture of saliva and food)

★ Ingestion

★ Digestion

The Esophagus, Pharynx & Trachea

Esophagus

• Long tube lined with epithelial tissue, surrounded by smooth muscle tissue

• Bolus stretches the walls of the esophagus

• Undergo contractions called peristalsis (Helps the bolus move down esophagus to the stomach)

Epiglottis

• A lid/flap that covers the trachea during swallowing

• Ensures food goes through the esophagus instead of the lungs (Trachea, air pipe)

Pharynx

• Two way structure, allows air to travel to the lungs and food to travel down the esophagus

★ No Digestion

The Esophagus - Sphincters

Sphincters

• Circular muscles that contract to close an opening in the body

Gastro Esophageal

• Located between esophagus & stomach

• Keeps the food & acid from moving up the esophagus

Pyloric Sphincter

The Stomach

Stomach

• Muscular, J shaped, Sac-like organ, food is temporarily stored

• Stomach walls churn and squeeze mixture

★ Mechanical Digestion

Stomach Acid (Approximately 2L released/day)

• Gastric juice (Made of hydrochloric acid (HCl), digestive enzymes, acid and mucus)

• Break up proteins from the food (Break the peptide bonds in protein)

• Mucus protects stomach lining from acid damage

• Acid (pH 2-3) kills most bacteria / microorganisms

★ Chemical Digestion

The Stomach - Enzymes

Stomach Enzymes

• Convert inactive enzyme (pepsinogen) to active form (pepsin)

• Pepsin enzyme (a protein) require a highly acidic environment (low pH)

• Breaks down other proteins into amino acids

★ Chemical Digestion

The Stomach - 4 Layers

Mucosa

• The innermost layer is an extensively folded layer.

• Secrets the gastric juice, epithelial cells divide rapidly to replace & heal damaged stomach lining

• Entire stomach lining is replaced every three days

Submucosa

• A layer of connective tissue that contains a networks of nerves and blood vessels. 

Muscularis (3 muscle layer)

• Consists of smooth muscles, contracts frequently

• Mixes food w/ gastric juice to produce “Chyme”

★ Chyme - Pulpy acidic fluid mixed w/ gastric juice & food materials

Serosa

• The smooth outermost layer of the stomach

• Holds the stomach in place

• Secretes lubricating fluid, eliminates friction between organs