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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