Digestive System

7.12B identify the main functions of each system7.6B distinguish between physical and chemical changes

7.6C recognize how large molecules are broken down into smaller molecules such as carbohydrates are broken down into sugars

You are What You Eat!

Digestive System

• Your cells need a lot of energy for their daily activities

• Cells use nutrients obtained from food, for energy, growth and repair

• The digestive system breaks down the nutrients in food into smaller molecules that can be used for energy and as building materials for these cells.

Key vocab words!

• Carbohydrates – large molecules made of carbon, hydrogen and oxygen.

• Enzymes – a protein made in a cell that is a catalyst (speeds it up) in various biological functions.

• Proteins – Compound made of amino acids.

• Fats – A soft compound stored in the body for energy. Made of lipids.

Key vocab words!

• Bile – A substance produced by the liver that breaks up fat particles.

• Metabolism – All of the chemical reactions that occur within an organism

• Peristalsis – pronounced: per-uh-stawl-sis

involuntary waves of muscle contraction that keep food moving along in one direction through the digestive system.

Food into your body:

1. Proteins (meats), Carbohydrates (sugars = energy), Fats (Lipids), Vitamins, Minerals, and Water

2. Maintain homeostasis

3. No food has every nutrient, so eat a varietyof foods

THE DIGESTIVE SYSTEM’S FUNCTION: breaks food down into

small molecules that are absorbed into bloodstream

1. Mechanical digestion: PHYSICAL process: food is chewed, mixed and churned

2. Chemical digestion: CHEMICAL process: food is turned into a mushy substance using stomach acid, bile, saliva, & other enzymes (proteins that speed up chemical reactions)

Food’s journey Through the Digestive System

Step 1: The Mouth

• The mouth is the beginning of the digestive system , and, in fact, digestion starts here before you even take the first bite of a meal.

• The smell of food triggers the salivary glands in your mouth to secrete saliva, causing your mouth to water. When you actually taste the food, saliva increases.

Food’s journey Through the Digestive System

Step 2: The Pharynx and Esophagus

• Also called the throat, the pharynx is the portion of the digestive tract that receives the food from your mouth.

• Branching off the pharynx is the esophagus, which carries food to the stomach, and the trachea or windpipe, which carries air to the lungs.

Food’s journey Through the Digestive System

Step 3: The Stomach and Small Intestine

• The stomach is a sac-like organ with strong muscular walls. Muscle contractions in the stomach churn and mix food.

• The stomach secretes acid and powerful enzymes that continue the process of breaking the food down and changing it to a consistency of liquid or paste.

• Bile breaks fats into tiny drops

Food’s journey Through the Digestive System

Step 4: Small intestine to the end

• From the stomach, food moves to the small intestine.

• In the small intestine, nutrients are absorbed through the walls and into the bloodstream. What's leftover (the waste) moves into the large intestine

• From the large intestine, waste goes to the colon, rectum, and anus

Chemical Digestion

• Digesting food – pancreatic juices break down carbohydrates, fats and proteins into simpler substances so that enzymes can chemically react with them to break down further

• pH changes in the stomach

• Video: How does digestion work?

Organs of the digestive system

1. Accessory organs: food DOES NOT pass through. Includes tongue, teeth, salivary glands, liver, gallbladder, & pancreas

Organs of the digestive system

2. Digestive tract: food DOES pass through.

Includes mouth, esophagus, stomach, small & large intestine, rectum & anus

Digestion Begins:

1. Mouth: tongue, teeth, & saliva change food into soft mass (called bolus)

2. Esophagus: muscular tube moves food to stomach using peristalsis which are muscle contractions Inside the esophagus!

3. Stomach: muscular sac that turns food into a thin, watery liquid called chyme

a. Mechanical digestion by peristalsis b. Chemical digestion by digestive juices/enzymes

4. Small Intestine: long tube (small diameter) that functions in chemical digestion and nutrient absorption (most digestion occurs here)

Inside the tube (intestine), the surface area for absorption is increased.

How does the surface area

increase? The inside of the “tube” isn’t flat,

it is full of ridges!These ridges are called villi, which

are finger-like projections. And there are smaller ones insides of

these!!

Capillary bed Microvilli

Each villus (single for villi) is composed of cells that have microvilli. Cells transport nutrients from these villi to the bloodstream through

capillary beds to be distributed to the body cells

Explained in a different way:

• If the small intestine were a simple smooth tube without folds and villi, the surface area would be the inside of the tube as seen below.

• The gathering of the intestinal wall into folds lined with villi increases the surface area tremendously – imagine that the folds are a string and you are pulling on the end. It would unravel to a length much greater than that of the smooth tube. In fact, it’s surface area is comparable to a tennis court!

• Let’s do a demo!

Accessory Organs of Small Intestine:

a. Liver: large red-brown organ that makes bile

b. Gallbladder: stores bilewhich is released into the S.I. and helps break down fat

c. Pancreas: makes digestive enzymes & insulin which regulates blood sugar

5. Large intestine: absorbs water from undigested chyme

a. Chyme can be in L.I. as long as three days

b. Appendix: a sac attached to the L.I. that provides immune support in the body

6. Rectum & anus: control release of solid waste(feces) from body

How nutrients are absorbed:

• Enzymes break down foods into smaller particles so that the body can then absorb nutrients!

Enzymes:

• Lactase – breaks down milk sugar

• Sucrase – breaks down table sugar

• Lipase –breaks down fat

• Pepsin – breaks down protein

Our Energy Source• Video: Biological Molecules

• (14min)

Diagram

• You will label the diagram and write down information based on the notes you have just taken.

Digestion Gizmo Lab: