Lesson 2 Processes of Mechanical & Chemical Digestion Bio30SB11-2-02 Describe the processes of mechanical digestion that take place at various sites along the

alimentary canal.

B11-2-03 Identify functions of secretions along the digestive tract.

B11-2-04 Identify sites of chemical digestion along the alimentary canal, as well as the type of nutrient being digested.

What is the alimentary canal?

The whole passage along which food passes through the body from mouth to anus. It includes the esophagus, stomach, and intestines.

4 Main Processes are involved with Digestion:

1) Ingestion – the process of taking in food.

2) Digestion – the process of breaking down food. There are two types:

a) Mechanical Digestion – the process of physically breaking the food into smaller pieces so that

the surface area is increased. This process is aided by various

structures and secretions.

b) Chemical Digestion – the process which involves chemical reactions that break large

molecules into smaller ones. This process is aided by enzymes.

3) Absorption – the process of passing nutrient molecules from the intestine into the blood stream,

and from the blood stream into cells. This occurs by diffusion.

4) Egestion – the process of eliminating undigested and unabsorbed food

Function of the digestive system:

(a) To reduce foods {ie. biomolecules - carbohydrates, proteins, fats (and nucleic acids)} to

molecules which are small enough to pass through the pores of cell membranes.

These molecules are the basic units of the 3 main food groups: monosaccharides, amino acids,

and fatty acids/glycerol, (and nucleotides).

(b) To transfer all nutrients from the digestive system to the blood stream so that the blood

stream can carry the nutrients to all of the cells of the body.

Nutrients which the digestive system passes into the blood stream include:

Monosaccharides

amino acids

fatty acids

glycerol

nucleotides

vitamins

minerals

water

Mouth The mouth is the first structure of the alimentary canal and connects to the oral pharynx. It contains

multiple structures that begin digestion, structures such as: teeth, tongue, salivary glands. The mouth

is involved in both chemical and physical digestion.

Mechanical Digestion in the mouth - food is broken up into smaller bits by your teeth and tongue to

increase the surface area that chemical digestion will act upon.

Saliva

2 Types of Saliva:

1. Thin, watery secretion that wets the food.

2. A thicker, mucous secretion that acts as a lubricant and causes the food to stick together to

form a food mass called a bolus.

Saliva contains a digestive enzyme called salivary amylase which breaks down starch (a

polysaccharide) into maltose (a disaccharide).

Tongue

Pushes the food to the back of the throat (pharynx), which starts the automatic swallowing reflex,

which forces food into the esophagus.

Epiglottis

Prevents food from entering the trachea (airway) during swallowing.

Esophagus

A tube through which food passes from the pharynx to the stomach.

Movement of food is aided by alternate waves of relaxation and contraction in the muscular

walls of the alimentary canal – called peristalsis.

Cardiac sphincter is a ring of muscle that acts as a valve and controls passage of food from the

esophagus to the stomach

Discuss what must be happening to the cardiac sphincter during the following 2 situations:

1. Vomitting: A wave of peristalsis passes upward (revers peristalsis), causing the sphincter to open and the contents of the stomach to be “thrown up”

2. Acid reflux (heartburn): When the cardiac sphincter relaxes, and hydrochloric acid (HCl) from the stomach backs up into the esophagus.

Stomach

A thick walled, muscular sac that can expand to hold more than two liters of food or liquid. Stores food temporarily. Mechanical breakdown of food happens by contractions of the stomach walls. Partial digestion of proteins occur here. Food mixes with acidic gastric juice that is secreted by glands in the stomach walls. 2 Types of Glands:

o Pyloric Glands – secretes mucus that protects the lining from being digestedo Gastric Glands

secretes gastric juice, that has a pH of 1.5 to 2.5 Gastric juice also contains HCl and the digestive enzyme pepsin

Note: Pepsin is secreted in an inactive form called pepsinogen, which is activate after it is mixed with the hydrochloric acid. Pepsin breaks down large protein molecules into shorter chains of amino acids called polypeptides.

Salivary amylase (from the saliva) continues to break down starch in the stomach until the low pH of the stomach acid inactivates this enzyme, and starch breakdown stops

Empty stomach has only a small amount of gastric juice Flow of gastric juice increases:

1. Thought, sight, or smell of food2. Food touches stomach lining and stimulates the secretion of some gastric juice3. Food enters the stomach and stretches the stomach wall which stimulates the

lining to secrete the hormone gastrin into the blood. This further stimulates the gastric glands in the stomach to secrete large amounts of gastric juice.

Liquids pass through the stomach in 20 minutes or less. Solids must be turned into a thin, soupy liquid called chyme Stomach empties solids from 2 to 6 hours after a meal Hunger is felt when an empty stomach is churning

Discussion: What is an ulcer? How is it caused? How is it treated?

When the thick mucous layer that protects the stomach wall breaks down, a part of the stomach wall may be digested.

When this happens, a painful ulcer develops because the HCl comes into contact with the exposed stomach wall.

Some ulcers are caused by the oversecretion of gastric juice brought on by stress or nervousness

Treated by diet, medications, or surgery (severe cases only)

The Small Intestine A coiled tube about 6.5 m long and 2.5 cm in diameter Where most chemical digestion takes place After digestion, the intestinal wall absorbs such things as:

o Simple sugars o Amino acids o Vitamins & minerals

Sends absorbed nutrients into the blood vessels of the circulatory system Fatty acids and glycerol are also absorbed into tiny vessels of the lymphatic system called

lacteals.

3 Parts:o Duodenum – shortest section (25 cm long)o Jejunum – middle sectiono Ileum – last section

To aid in absorption it increases it surface area 4 ways:o Very longo Lining has many foldso Lining is covered with millions of finger-

like projections called villio The villi are covered in tiny projections

called microvilli

Mechanical Digestion by peristaltic movements has 4 effects:

1. Squeezes chyme through the intestine2. Mixes the chyme with the digestive enzymes present in the small intestine3. Breaks down food particles mechanically4. Speeds up absorption by bringing the intestinal contents into contact with the intestinal

wall.

Chemical Digestion:Chyme mixes with pancreatic juice (from pancreas), bile (from the liver), and intestinal juice (from glands in intestinal walls)

Pancreatic Juice

When acid chyme from the stomach enters the small intestine, it stimulates cells in the intestinal lining to secrete 2 hormones into the blood:

1. Secretin 2. Cholecystokinin

These hormones then stimulate the pancreas to secrete pancreatic juice and pancreatic enzymes, which pass through the pancreatic duct into the upper part of the small intestine.

Pancreatic juice contains sodium bicarbonate, which neutralizes the acid in the chyme and makes the pH of the contents of the small intestine slightly alkaline (pH 8).

The enzymes secreted by the pancreas act on:

Proteins Carbohydrates Fats Nucleic acids

Pancreatic Enzymes:

Amylase – hydrolizes any remaining starch to maltose Proteases – protein splitting enzymes that continue the breakdown of large protein

molecules:o Trypsin o Chymostrypsin

Lipase – breaks down fats

Bile

Produced by the liver Passes through the bile ducts into the gallbladder, where it is stored Release of bile from the gallbladder is stimulated by the hormone cholecystokinin

(which also acts on the pancreas) Contains no enzymes but breaks fats and oils into tiny droplets through the process of

emulsification Is alkaline so it aids in neutralizing the acid chyme from the stomach

Intestinal Juice

Secreted by millions of intestinal glands in the wall of the small intestine Contains 2 enzymes that complete the digestion of carbohydrates, fats and proteins:

1. Peptidase 2. Maltase

Endproducts

Proteins Amino Acids

Carbohydrates Simple Sugars

Fats Fatty Acids and Glycerol

The Large Intestine 1.5 m long and 6 cm in diameter No digestion occurs here Undigested and unabsorbed materials pass from the small intestine, through a

sphincter, to the large intestine The appendix is located where the small intestine joins the large intestine

Student Practice:

1. Do Activity 5-3 Handout: Human Digestive System2. Do Digestion Practice Worksheet.

Lesson 2 Processes of Mechanical & Chemical Digestion Bio30SB11-2-02 Describe the processes of mechanical digestion that take place at various sites along the

alimentary canal.

B11-2-03 Identify functions of secretions along the digestive tract.

B11-2-04 Identify sites of chemical digestion along the alimentary canal, as well as the type of nutrient being digested.

What is the alimentary canal?

4 Main Processes are involved with Digestion:

1) _____________________ – the process of taking in food.

2) ____________________ – the process of breaking down food. There are two types:

a. ______________________________ – the process of physically breaking the food into smaller

pieces so that the surface area is increased. This process is aided by various

structures and secretions.

b. _______________________________ – the process which involves chemical reactions that

break large molecules into smaller ones. This process is aided by ____________________.

3) _______________________ – the process of passing nutrient molecules from the intestine into

the ________________ _______________, and from the blood stream into ____________. This

occurs by ______________________.

4) ____________________________ – the process of eliminating undigested and unabsorbed food

Function of the digestive system:

(c) To reduce foods {ie. _________________________ - carbohydrates, proteins, fats (and nucleic

acids)} to molecules which are small enough to pass through the pores of cell membranes.

These molecules are the basic units of the 3 main food groups: monosaccharides, amino acids,

and fatty acids/glycerol, (and nucleotides).

(d) To transfer all nutrients from the digestive system to the blood stream so that the blood

stream can carry the nutrients to all of the cells of the body.

Nutrients which the digestive system passes into the blood stream include:

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

Mouth The mouth is the first structure of the alimentary canal and connects to the oral pharynx. It contains

multiple structures that begin digestion, structures such as: _________________________________.

The mouth is involved in both __________________ and _________________ digestion.

Mechanical Digestion in the mouth - food is broken up into smaller bits by your _____________ and

___________________ to ________________ the surface area that chemical digestion will act upon.

Saliva

2 Types of Saliva:

1. Thin, watery secretion that wets the food.

2. A thicker, mucous secretion that acts as a lubricant and causes the food to stick together to

form a food mass called a ______________.

Saliva contains a digestive enzyme called ________________ _______________ which breaks down

_______________ (a polysaccharide) into __________________ (a disaccharide).

Tongue

Pushes the food to the back of the throat (_______________), which starts the automatic swallowing

reflex, which forces food into the ____________________.

Epiglottis

Prevents food from entering the ___________________ (airway) during swallowing.

Esophagus

A tube through which food passes from the pharynx to the _____________________.

Movement of food is aided by alternate waves of relaxation and contraction in the muscular

walls of the alimentary canal – called ____________________.

__________________ ___________________ is a ring of muscle that acts as a valve and

controls passage of food from the esophagus to the stomach

Discuss what must be happening to the cardiac sphincter during the following 2 situations:

1. Vomitting:

2. Acid reflux (heartburn):

Stomach

A thick walled, muscular sac that can expand to hold more than ___ liters of food or liquid. Stores food ______________________. Mechanical breakdown of food happens by contractions of the stomach walls. Partial digestion of proteins occur here. Food mixes with acidic ______________ _____________ that is secreted by glands in the

stomach walls. 2 Types of Glands:

o _________________ Glands – secretes mucus that protects the lining from being digested

o ________________ Glands secretes gastric juice, that has a pH of ____ to _____ Gastric juice also contains ______________ and the digestive enzyme

_____________Note: Pepsin is secreted in an inactive form called pepsinogen, which is activate after it is mixed with the hydrochloric acid. Pepsin breaks down large protein molecules into shorter chains of amino acids called polypeptides.

Salivary amylase (from the saliva) continues to break down starch in the stomach until the low pH of the stomach acid inactivates this enzyme, and starch breakdown stops

Empty stomach has only a small amount of gastric juice Flow of gastric juice increases:

1. Thought, sight, or smell of food2. Food touches stomach lining and stimulates the secretion of some gastric juice3. Food enters the stomach and stretches the stomach wall which stimulates the

lining to secrete the hormone gastrin into the blood. This further stimulates the gastric glands in the stomach to secrete large amounts of gastric juice.

Liquids pass through the stomach in _________________ or less. Solids must be turned into a thin, soupy liquid called _________________ Stomach empties solids from ___ to ___ hours after a meal Hunger is felt when an empty stomach is __________________

Discussion: What is an ulcer? How is it caused? How is it treated?

The Small Intestine A coiled tube about 6.5 m long and 2.5 cm in diameter Where most chemical digestion takes place After digestion, the intestinal wall absorbs such things as:

o ________________________

o ________________________

o ________________________

Sends absorbed nutrients into the blood vessels of the _______________________ system Fatty acids and glycerol are also absorbed into tiny vessels of the lymphatic system called

____________________.

3 Parts:

o ___________________ – shortest section (25 cm long)

o ___________________ – middle section

o ___________________ – last section

To aid in absorption it increases it surface area 4 ways:o Very long

o Lining has many ________________

o Lining is covered with millions of finger-

like projections called _____________

o The villi are covered in tiny projections

called ____________________

Mechanical Digestion by peristaltic movements has 4 effects:

1. ______________________ chyme through the intestine

2. ______________________ the chyme with the digestive enzymes present in the small

intestine

3. ________________ ______________ food particles mechanically

4. Speeds up ____________________ by bringing the intestinal contents into contact

with the intestinal wall.

Chemical Digestion:Chyme mixes with ____________________ ____________ (from pancreas), ___________ (from the liver), and __________________ _____________ (from glands in intestinal walls)

Pancreatic Juice

When acid ______________ from the stomach enters the small intestine, it stimulates cells in the intestinal lining to secrete 2 hormones into the blood:

1. _________________________

2. _________________________

These hormones then stimulate the pancreas to secrete pancreatic _____________ and pancreatic ___________________, which pass through the pancreatic ______________ into the upper part of the small intestine.

Pancreatic juice contains __________________ _________________, which ____________________ the acid in the chyme and makes the pH of the contents of the small intestine slightly alkaline (pH 8).

The enzymes secreted by the pancreas act on:

_______________________ _______________________ _______________________ _______________________

Pancreatic Enzymes:

________________ – hydrolizes any remaining starch to maltose ________________ – protein splitting enzymes that continue the breakdown of large

protein molecules:o ______________________ o ______________________

___________________ – breaks down fats

Bile

Produced by the ______________________ Passes through the bile ducts into the ___________________, where it is stored Release of bile from the gallbladder is stimulated by the hormone

_____________________ (which also acts on the pancreas) Contains no ____________________ but breaks fats and oils into tiny droplets through

the process of _________________________________ Is alkaline so it aids in ____________________ the acid chyme from the stomach

Intestinal Juice

Secreted by millions of intestinal glands in the wall of the small intestine Contains 2 enzymes that complete the digestion of carbohydrates, fats and proteins:

1. ________________________

2. ________________________

Endproducts

Proteins ___________________ _____________

Carbohydrates ___________________________

Fats ____________________________________

The Large Intestine 1.5 m long and 6 cm in diameter No _______________________ occurs here ________________________ and ________________________ materials pass from

the small intestine, through a sphincter, to the large intestine The appendix is located where the small intestine joins the large intestine

Student Practice:

1. Do Activity 5-3 Handout: Human Digestive System2. Do Digestion Practice Worksheet.

3.

Bio30S Digestion Practice Worksheet Name: KEY

Secretions of the Human Digestive SystemOrigin Digestive Secretions & Enzymes Function

Salivary glands Saliva

Salivary amylase

Wets food. Helps to form food into bolus.

Breaks down starch into maltose.

Stomach Gastric juice: Pepsin

Hydrochloric acid

Breaks down proteins into smaller molecules (peptones and proteoses).

Activates pepsin.

Liver Bile Breaks down fat mechanically into small droplets (emulsification).

Pancreas Pancreatic juice:Amylase

Trypsin

Lipase

Continues the digestion of starch to disaccharides.

Digests peptones and proteoses into peptides

Digests fat droplets into fatty acids and glycerol

Small Intestine (intestinal glands)

Intestinal juice:Peptidase

Maltase

Breaks down peptides into amino acids

Breaks down maltose (a disaccharide) into glucose (a monosaccharide).

Bio30S Digestion Practice Worksheet Name: _______________

Name of Step What it means Where it occursIngestion

Digestion

Absorption

Egestion

Origin Digestive Secretions & Enzymes Function

Salivary glands1. ____________________

2. ____________________

1.

2.

Stomach Gastric juice:1. ________________

2. _________________

1.

2.

Liver 1. _____________________

Pancreas Pancreatic juice:1. ___________________

2. ___________________

3. ___________________

1.

2.

3.

Small Intestine (intestinal glands)

Intestinal juice:1. ___________________

2. ___________________

1.

2.

Secretions of the Human Digestive System