10 IB Biology

The Digestive System

Responsible for converting what we eat and drink into substances our bodies need to function

Water, protein, carbohydrates, lipids, amino acids, vitamins and

minerals

Also known as the Alimentary Canal or Gastrointestinal Tract (GI tract)

The gastrointestinal tract is 9m long and made up of 4 functional parts.

Ingestion

The digestive process begins here with food entering the

gastrointestinal tract through the Oral Cavity.

The oral cavity consists of the mouth, tongue, teeth, salivary glands, epiglottis, pharynx and esophagus.

Digestion

Food is passed from the oral cavity to the Stomach and Small Intestine where it is broken down into smaller more basic substances. This is done in 2 forms:

1. Mechanical Digestion - complex substances are broken down into smaller more absorbable pieces without being chemically changed.

2. Chemical Digestion - complex substances are chemically broken down into more absorbable pieces.

Absorption

Material from the "broken down food" that can be used by the body is absorbed by the Small and Large Intestines.

Egestion

Undigestable material and waste must be removed from the body.

These materials are passed to the Rectum and released through the Anus.

Oral Cavity

The process of ingestion takes place in the oral cavity.

The oral cavity consists of the mouth, teeth, pharynx, epiglottis, salivary glands, tongue and esophagus.

The Mouth

The mouth consists of several structures.

(A) Cheek - supports the oral cavity and holds food

(B) Lips - keeps food in the mouth during chewing

(C) Vestibule - the gap between the lips and the gums

(F) Hard Palate - the "roof" of the mouth supported by bone

(G) Soft Palate - the "roof" of the mouth supported by skeletal muscle

The Teeth (D)

The primary agent of mechanical digestion in the mouth.

Humans have two sets of teeth

20 deciduous (milk) teeth which are replaced

by 32 permanent (adult) teeth of which 12 are molars.

Regions of the Tooth

There are 3 general

regions of each tooth:

1. The Crown - the top of the tooth

2. The Neck - the central area of the tooth that contains the gums and nerve endings

3. The Root - area below the gums that contains the blood vessels and supporting structures

Other Features of the Tooth

Enamel - covers the crown of the tooth and is the hardest substance in the body.

Nerves - in the neck of the tooth, they register sensation (hot, cold, pain)

Pulp Cavity - a hollow tube that runs through the middle of the tooth that contains blood vessels and nerve cells

Dentin - hard tissue that

supports the enamel and contains no nerve endings

Periodontium - holds the roots in the jaw

Cementum - bone with a high concentration of connective tissue

Gums (E)

Tissue that surrounds and supports the teeth and associated tissues

Also known as the gingiva

Tonsils (R)

Part of the immune system

Act as a filter for foreign material in the mouth

Pharynx (T)

The muscle group that coordinates swallowing.

Controls the intersection between the digestive and respiratory system

Structures found in this area: (U) Epiglottis - the flap of tissue

that prevents food from entering the trachea

(S) Eustachian Tube - equalizes pressure between the middle ear, throat and nasal cavities

Salivary Glands (Q)

There are 3 sets of salivary glands

(sublingual, submandibular and parotid)

Produce Saliva

Saliva contains the enzyme

Salivary Amylase which chemically breaks down starch into glucose.

Saliva also contains enzymes that clean the surfaces of the mouth

Saliva is used to lubricate food

Toungue (K)

The primary organ of the oral cavity

Made up of two parts:

The Root (O) - contains a series of muscles and nerve endings that link the tongue to the nervous system

The Body (N) - involved in eating and drinking.

Surface covered with Papillae (P) commonly referred to as "taste buds"

The Esophagus

A long tube that connects the oral cavity to the stomach.

Uses waves of muscular contractions called peristalsis to move the food down to the stomach.

Deglutition - Stage 1: Oral Phase

In the oral phase, the food is mechanically digested by the teeth.

The tongue mixes the mechanically digested mass with saliva from the salivary glands to form a bolus.

The tongue creates a downward slope to move the bolus pharynx.

Deglutition - Stage 2: Pharyngeal Phase

The pharynx contains nerves that directly connect to the central nervous system. The presence of the bolus stimulates these nerves.

The vagus nerve is responsible for the three activities in this area.

1. The nasopharynx is blocked by the uvula and the pulling up of the soft palate.

2. The vocal cords are pulled together and the epiglottis falls over the trachea.

3. The larynx is elevated and moved forward, muscles in the back of the throat contract to lead the bolus towards the esophagus. The upper esophageal sphincter relaxes to allow the bolus to enter the esophagus.

Deglutition - Stage 3: Esophageal Phase

The esophagus is a muscular tube that contracts to move the bolus down towards the stomach.

This peristalsis begins in the pharynx and continues in the esophagus.

The lower esophageal sphincter (cardiac sphincter) relaxes to allow the bolus to enter the stomach.

Enzymes

An enzyme is a biological catalyst that speeds up chemical reactions without being consumed or altered.

An enzyme will lower the activation energy (the energy needed for a reaction to occur). This makes it easier for a chemical reaction to take place.

Enzymes are protein molecules

There are thousands of different enzymes in the body

Usually end in the suffix " - ase"

Enzyme Function

The Active Site

The active site is the region of the enzyme where the reactants

(substances that are going to react) bind and where the chemical reaction takes place.

Substrate

A reactant that binds to the active site of an enzyme is called a

substrate.

There may be more than one substrate attached to the active site of an enzyme depending on the type of reaction that will take place.

The binding of the substrate to the active site forms the

Enzyme - Substrate Complex.

When the chemical change is complete, the products are

released from the active site and the enzyme remains

unchanged.

Inhibitor

Enzyme activity must be controlled (homeostasis)

When enzyme activity is not needed an Inhibitor Molecule will bind to the enzyme's active site

This blocks the substrate molecules from being able to bind with the enzyme thus preventing the chemical reaction from occurring.

The Stomach

Once the bolus has been swallowed it moves down the esophagus into the stomach.

The stomach is a J-shaped organ of the abdominal cavity where digestion occurs.

Divided into 3 regions:

The Fundus - closest to the esophagus

The Body - the largest part, responsible for the formation of Chyme

The Pylorus - closest to the duodenum