Download General Outcome D1: Students will explain how the human

General Outcome D1: Students will explain how the human digestive and respiratory
systems exchange energy and matter with the environment.
A. Organs and Organ Systems
Our cells are specialized to perform certain functions. Our specialized cells include:
muscle cells (contraction), fat cells (stores high energy molecules), nerve cells (transmits
and receives impulses).
Tissues are groups of similarly shaped cells that work together to carry out a similar
function. There are four kinds of tissue:
1. Epithelial – a covering tissue that protects organs, lines body cavities and covers
the surface of the body.
Example: ___________________________________________________
2. Connective – provides support and holds various parts of the body together.
Example: ___________________________________________________
3. Muscle – composed of cells containing special contractile proteins.
Example: ___________________________________________________
4. Nerve – composed of specialized cells (neurons) which have the ability to
transmit an electrochemical impulse.
Example: ___________________________________________________
Organs are structures composed of different tissue specialized to carry out a specific
function. Organ systems are groups of organs that have related functions. All the
systems found in the body are:
1. Integumentary System
2. Muscular System
3. Skeletal System
4. Nervous System
5. Endocrine System
6. Circulatory System
7. Lymphatic System
8. Respiratory System
9. Urinary System
10. Digestive System
11. Reproductive System
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B. The Basics of the Digestive System
Heterotrophs must consume organic compounds (nutrients) to survive. The digestive
tract/gastrointestinal tract/ alimentary canal is an open ended muscular tube that is 6.5-9m
long in adults.
The gastrointestinal tract is for:
1. ingestion – taking in food
2. digestion – breaking down food
3. absorption – absorbs nutrients into the bloodstream via its large surface area
4. egestion – elimination of wastes from the body
Definition – the process by which food substance are changed into forms that can be
absorbed through the cell membranes.
C. Structures of the Digestive System
Organs:
Mouth
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Liver
Gallbladder
Pancreas
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1. Mouth
The process of digestion begins in the mouth. The mouth has the ability to mechanically
reduce the size of the food that is placed in it.
Several structures are located within the mouth including: palate, teeth, gums, lips, and
tongue. All play a vital role in the experience of digesting food.
a) Teeth
 32 teeth are used in the break down of food.
 incisors – bite off large pieces of food.
 cuspid – grasping and/or tearing.
 molar – grinding of food.

Increases the surface area of the food particles, creating a more effective
food particle/digestive enzyme interaction.
b) Taste Buds
 Located along the tongue.
 Involved in a chemical reaction which detects flavors.
 Sweet, salty, bitter and sour are the main flavors detected.
Sense-Sational Facts
 We have almost 10,000 taste buds inside our mouths; even on the roofs of our
mouths.
 Insects have the most highly developed sense of taste. They have taste organs on
their feet, antennae, and mouthparts.
 Fish can taste with their fins and tail as well as their mouth.
 In general, girls have more tastebuds than boys.
 Taste is the weakest of the five senses.
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c) Salivary Glands
 While the dimensions of the food are
being reduced in the mouth, salivary
glands secrete saliva.
 The saliva secreted by these glands is
mixed with the food, causing the food
particles to bind together, forming a bolus.
 Amylase enzymes contained in the saliva
break down starches to smaller chain
carbohydrates called dextrins.
d) Pharynx
 Cavity that leads to the stomach.
 The cavity combines with the
esophagus to create a passage that
food takes to get to the stomach.
 The pharynx has no active role in
digestion, but its muscular walls
attribute to the swallowing of food.
e) Esophagus
 The major passageway from the oral cavity to the stomach.
 Straight collapsible tube ~ 25 cm long
 Peristalsis – rhythmic, wavelike contractions of smooth muscle that moves food
along the gastrointestinal tract.
 http://www.lionden.com/peristalsis.htm
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f) Stomach
 Highly elastic, muscular, J-shaped sack.
 Can store about 1.5L of food.
 Very acidic environment ~ 2-3
 Continues physical digestion by mixing
stomach contents with gastric juices and churning it into smaller pieces.
Functions:
 Receives food from the esophagus.
 Stores food.
 Mixes food with gastric juices.
 Initiates the digestion of proteins.
 Carries on a limited amount of absorption.
 Moves food into the small intestine.
Muscles known as sphincters regulate the movement of food to and from the stomach.
There are 2 sphincters:
1. Cardiac Sphincter/Lower Esophageal Sphincter (LES)
 contraction of this muscle closes the opening to the stomach.
 relaxation of this muscle allows food to enter the stomach.
2. Pyloric Sphincter
 regulates the movement of foods and stomach acids to the small intestine.
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The stomach is lined with secretory cells. The inner lining of the stomach is a thick
mucus membrane that has many small openings. These small openings are called gastric
pits. The gastric pits are located at the end of the gastric glands.
Gastric Glands
Within these gastric glands lies multiple secretory cells.
1. Parietal cells
 Secretes hydrochloric acid
 Located in the deeper parts of the
gastric glands.
2. Peptic cells/Chief cells
 Secretes a protein digestive enzyme
called pepsinogen.
 When pepsinogen interacts with the
HCL produced by the parietal cells, it
changes into pepsin.
 Pepsin is the active form of the
enzyme pepsinogen.
 Pepsin breaks down proteins into
peptones, shorter chains of amino
acids.
Activation Summary:
 HCL forms in the lumen or gut cavity.
 The mucous lining prevents the HCL from dissolving cells, however the HCL is
able to destroy any intruding microbes.
 When pepsinogen enters the lumen, the HCL activates the enzyme, by altering the
form of pepsinogen to pepsin.
 Pepsin is then able to break down proteins, but cannot dissolve the cell, since it is
unable to penetrate the mucous lining.
3. Mucous Cells
 Secrete large amounts of mucous which acts as a protective coating against
pepsin.
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Conclusion:
 When the secretions from all three cells are put together they are called the
“gastric juices”.
 Gastric secretions play a major role in the digestion of food, but it is not the only
tool that the body has that play a part in the digestion of food.
 Muscles of the stomach give the stomach the ability to mix food and gastric
juices.
 The semi-fluid paste, which is a combination of the gastric juices and food
particles is called chyme.
 The chyme is moved towards the pyloric region of the stomach by way of
peristaltic waves.
 The chyme then moves into the small intestine.
Ulcers – When the protective mucous lining of the stomach breaks down, the cell
membrane is exposed to the corrosive acid and protein-digesting enzymes. When the
cells are destroyed an ulcer is formed.
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g) Small Intestine



The small intestine is about 7m in length and 2.5cm in diameter.
Structurally, the small intestine is a tubular organ.
It consists of a complex system of loops and coils, which fills a great deal of the
abdominal cavity.
Functions:
 Receives secretions from the liver and pancreas.
 Finalizes the digestion of the nutrients in the chyme.
 Absorbs different products of digestion.
 Moves the remaining residues to the large intestine.
The small intestine is made of three pieces:
1. Duodenum – site of most digestion (25-30cm)
2. Ileum (5m)
3. Jejunum (1.5m)
 The ileum and jejunum are used for the
absorption of nutrients into the
bloodstream and
lymphatic system.
 The three segments are differentiated on the
basis of cell shape.
 Villi and microvilli line the small intestine and they function to dramatically
increase the surface area available for the absorption of nutrients.
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Problem:
How are the cells within the small intestine suppose to cope with the chyme entering,
which is soaked in HCL and pepsin?
Solution:
 Once the acid enters the small intestine, a chemical called prosecretin is
converted into secretin.
 Secretin is absorbed by the blood stream and carried to the pancreas.
 Bicarbonate ions are then released from the pancreas.
 Bicarbonate ions are carried by way of the pancreatic duct to the small intestine,
where they buffer the HCL from the stomach.
 This reaction raises the pH from a 2.5 to a 9.0 (slightly basic)
h) Pancreas
 Large elongated gland attached to the
duodenum by the pancreatic duct.
 Secretes digestive enzymes that complete
the chemical digestion of all types of
nutrients.
 Also produces hormones – insulin and
glucagon
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Pancreatic secretions complete (finalize) the breakdown of macromolecules.
 Carbohydrates
 Proteins
 Lipids
Carbohydrate Breakdown:
 The initiation of carbohydrate breakdown begins the mouth with amylase
enzymes (present in the saliva) breaking down long chain carbohydrates into
shorter chain carbohydrates.
 When the shorter chain carbohydrates arrive in the small intestine, more amylase
enzymes are released by the pancreas to complete the breakdown into individual
monosaccharides. Intermediate sized chains are fractured into disaccharide’s and
a series of disaccharide enzymes from the small intestine complete the process of
carbohydrate digestion by breaking the bond between the disaccharides to create
monosaccharides.
 When carbohydrates are broken down into monosaccharides, carbohydrate
digestion is finalized.
 Simple sugars (monosaccharides) are taken to the liver and muscles where they
are stored as glycogen until they are needed for energy. The body will then
convert them into glucose – the usable form of energy by the body.
Protein Breakdown:
 When protein is present in the stomach the peptic cells release pepsinogen which
comes in contact with the HCL released from the parietal cells, which converts
pepsinogen into pepsin – the active form of the enzyme. Pepsin breaks down
long chain proteins into shorter chain proteins.
 These shorter chain proteins continue onto the small intestine. In the small
intestine trypsinogen is converted into trypsin with the aid of an enzyme called
enterokinase. Enterokinase is released by the duodenum. This allows trypsin to
act on the already partially digested proteins, by breaking them into smaller
proteins.
 Erepsins (another enzyme) is released to complete the digestion of proteins.
Erepsins are released by the pancreas and the small intestine, and they are
responsible for breaking the bond between the short chain peptones in order to
release individual amino acids. At this point protein digestion is finalized.
 Finally, the small intestine absorbs the amino acid molecules, allowing them to
pass into the bloodstream. The blood then carries the amino acids to the rest of the
body to rearrange into human proteins and use in building its structure. Each part
of the "machine" of digestion must work properly in order for protein to be
broken down into useful amino acids.
 Proteins are used as a last resort for energy.
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Lipid Breakdown:
 Lipids are emulsified (broken down) by bile – more on bile later!!
 Lipid-digesting enzymes are secreted by the pancreas to act on the emulsified fats.
 Most important and common enzyme is called pancreatic lipase. This breaks
down triglycerides into fatty acid and glycerol. Once the lipid has been reduced
to fatty acids and glycerol, lipid digestion is final.
 The fatty acid and glycerol is absorbed by lacteals (specialized lymph vessels) in
the villi. Fats are source of energy – glycerols are used to make glucose, but are
also used as vitamin carriers and as insulation. Fats contain twice as much energy
per gram than the other nutrients.
Macromolecule Breakdown Flowcharts
Carbohydrate’s
Protein’s
Lipid’s
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i) Liver and Gallbladder
The liver is the largest glandular organ in the body. It contains 4 lobes and is about 1.5
kg. The liver has more functions than any other organ in the body.
Major Functions of the Liver
 Detoxification.
 Conversion of glucose to glycogen.
 Conversion of glycogen to glucose.
 Stores vitamins and minerals.
 Manufactures and secretes bile, which is
then stored in the gallbladder (small sac
attached to the liver) and is secreted into
the duodenum through the bile duct.

When fat is present in the small
intestine, a hormone is released into the
blood and is carried to the gallbladder.
The hormone triggers the release of bile
salts from the gallbladder.

Bile salts act as detergents as
they assist in physical digestion…it
emulsifies large fat globules.
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Problems:
1. Gallstones – production and concentration of bile salts is inaccurate and results in
the production of stones. Fat digestion is impaired and blockage gives rise to
pain.
2. Jaundice – an obstruction of the bile duct or accelerated destruction of red blood
cells.
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3. Cirrhosis – damaged liver cells are replaced with connective tissue and fat, which
are not capable of carrying out the detoxification process.
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j) Large Intestine
 The large intestine is
approximately 1.5m long
and is wider in diameter
than the small intestine.
 The largest part of the large
intestine is the colon,
which consists of three
sections: ascending,
transverse and descending
colon.
 Main function of the large
intestine is reabsorption of
water.
 It contains bacteria which
use waste material to
synthesize vitamins B and K.
 Indigestible wastes (cellulose) and mucous are both found here. As these
wastes build up in the large intestine, receptors located in the wall of the large
intestine provide information to the brain, which in turn prompts a bowel
movement. Bowel movements ensure the removal of toxic wastes from the
body.
 The rectum is about 12cm long and ends at the anus.
 Elimination of wastes is controlled by the anal sphincter.
k) Appendix
The appendix is a small extension of the large intestine with no known digestive
function. Toxins that are deadly to the body are stored here.
 Appendicitis – inflammation of the appendix. If the appendix ruptures all the
deadly toxins are released into the abdominal cavity which will ultimately
result in death if not treated immediately.
Absorption Conclusion:
 The small intestine is responsible for most absorption. Long finger-like tubes
called villi greatly increase the surface area of the small intestine. The outer
cell membrane of the small intestine are folded to also help increase the
surface area. This folded area is referred to as the microvilli. Some nutrients
are absorbed by diffusion into the outer cell areas, but the small intestine
expends energy to actively transport materials from the gut.
 The stomach absorbs some water, specific vitamins, and alcohol.
 Any remaining water and vitamins are absorbed by the large intestine.
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