Download Digestion - WordPress.com

Digestion (Ch.11)
All organisms require energy to run cell processes and maintain
life. The energy needed is in the form of glucose or ATP. The
substances needed to provide energy and materials needed for
metabolism are called nutrients (H20, fats, carbohydrates, proteins,
vitamins and minerals).
Nutrition- process whereby organisms get food and break it down so it
can be used for metabolic activities.
There are 2 patterns of nutrition that we’ve studied before:
Autotrophs- make their own food; materials are absorbed from
environment through the cells and sunlight energy converts these
into energy and cell molecules (i.e. glucose).
Heterotrophs- get their food by digesting other heterotrophs or
autotrophs
In order to understand chemical digestion - we need to do some
organic chemistry.
Organic Chemistry
Organic compounds are compounds that contain the element
carbon and they always bond covalently or by sharing electrons. (Most
compounds also contain Hydrogen and may contain either Oxygen or
Nitrogen or both.
Organic compounds are often larger and complex. This is due to:
- the carbon atom can form 4 covalent bonds
- carbon can bond with other carbon atoms forming long chains and/or
rings
- carbon can form single, double, and/or triple bonds.
Most organic compounds occur naturally in living organisms or in
their products; although many of them can be chemically produced in
laboratories. Organic compounds are classified as one of four types:
- carbohydrates
- nucleic acids (building blocks for DNA, not used for digestion)
- lipids
- proteins
These types of organic compounds are also the basic food nutrient
groups that our food is broken down into during the digestive process.
Carbohydrates
- compounds composed of carbon, hydrogen, and oxygen. As such,
they are known as CHO compounds.
These substances are fairly easily broken down into simple sugars
and provide most of the body's energy for cellular respiration carbohydrates are an energy source.
The simplest carbohydrates are the simple sugars or monosaccharides.
Disaccharides (double sugars) and polysaccharides (many sugars) can be
broken up into monosaccharides.
Monosaccharides
Disaccharides
Polysaccharides
a) Glucose
a) Maltose
a) starch (straight)
b) Fructose
b) Sucrose
b) cellulose (branched)
c) Galactose
c) Lactose
Monosaccharides - Simplest of the Carbohydrates
- all have the C6H12O6 formula chemical formula - they just have
different structural formulas.
*Glucose
Fructose
Galactose
Monosaccharides such as glucose can be absorbed directly into the
bloodstream.
Disaccharides - compounds formed when two monosaccharides
combine.
Ex.
Glucose + Glucose = Maltose
Glucose + Galactose = Lactose
Glucose + Fructose = Sucrose
Sugar molecules can be bonded together chemically through
dehydration synthesis.
Synthesis means ‘putting together’ and
dehydration means ‘removing water’, therefore, Dehydration Synthesis
means putting 2 simple sugars together by removing water. In living
organisms, dehydration synthesis is brought about by the action of
enzymes.
Polysaccharides - compounds formed when 3 or more monosaccharides
are put together.
Ex. Glucose + Glucose + Glucose
Recall that the only organ in our body which uses glucose directly as an
energy source is the brain. All other organs and cells use ATP
(adenosine triphosphate) which is an energy-rich compound stored in
cells.
Glycogen- animal starch
Hydrolysis
- the opposite process of dehydration synthesis.
- disacharides and polysaccharides can be broken apart with the
addition of the parts of a water molecule (H+ and OH-).
Just as a maltose molecule is formed by the addition of two glucose
molecules, maltose can be broken down into two glucose molecules.
Starch is converted into sugar and vice versa in animals; in humans, this
occurs in the liver.
Two hormones produced by the pancreas control blood sugar levels;
they are insulin and glucagon.
Dehydration synthesis takes place when your blood sugar levels
are too high. Insulin tells the liver to convert sugar into starch.
Otherwise, coma could result.
When you have low blood sugar, glucagon tells the liver and
muscles to convert the polysaccharide glycogen (often called ‘animal
starch’) into sugar. This is called hydrolysis - which is also digestion.
When the pancreatic cells cannot produce these hormones, a
disease called diabetes occurs.
Chitin, which is found in arthropod exoskeletons and fungal cell
walls, is also a polysaccharide.
Lipids
Lipids are made up of C, H and O. Lipids are formed when
fatty acids combine with an alcohol. They are harder to burn or
breakdown into energy.
A fatty acid consists of a chain of carbon and hydrogen atoms with
a carboxyl group at one end. Broken down into fatty acids & glycerine.
There are three types of lipids: waxes, fats, oils
Synthesis of A Fat Molecule:
Alcohol + 3 Fatty Acids
Your body uses fat for 3 things:
Fat Molecule + 3 Water molecules
A) Energy Reserve
B) Thermal Insulator
C) Shock Absorber
Saturated fats
- solids at room temperature, found primarily in animal products.
- increase the amount of cholesterol in the body
A fat is saturated when all the carbon-carbon bonds in the fatty
acid are single bonds....the molecule is saturated (loaded to capacity)
with hydrogen atoms.
Unsaturated fats
- liquids/oils at room temperature, found primarily in vegetable products.
- decrease blood cholesterol levels
cholesterol- an essential compound found in most animal tissues which
plays an important role in the build-up of deposits that harden and
narrow the arteries. This can lead to heart attacks and strokes. Medical
personnel recommend a reduced intake of saturated fats and an increased
intake of unsaturated fats in our diets.
A fat is unsaturated when the carbon-carbon bonds in the fatty acid
are double or triple bonds... there are less hydrogens in a unsaturated fat.
Hydrogenated Fats
- chemically changing an unsaturated fat into a saturated fat by adding
hydrogen.
- chemically reducing double and triple carbon bonds to single bonds
and adding hydrogen atoms to the molecule.
- it has been implied that these fats lead to heart disease.
Proteins
- compounds that contain nitrogen as well as carbon, hydrogen, and
oxygen. Broken down into amino acids (basic building blocks for
proteins; 20-22 of them).
- the number of possible proteins are virtually unlimited.
They have four functions:
- control your traits
- build muscles
- special proteins called enzymes control all the chemical reactions in
your body.
- poor energy reserve
Amino acids contain - a carboxyl group
OH
|
-C=O
- an amino group
H
|
-N-H
- 1 hydrogen atom
-H
- one of twenty carbon groups or chains
- CH2
- CH2-CH3
- R-
Peptide Bond- a bond between 2 amino acids ( C–N– C or C–N bond
which is a special dehydration synthesis bond)
Dipeptide- 2 amino acids bonded together; smallest possible protein
i.e. Alanine + Glycine  Dipeptide + H20
Substrate- material that an enzyme attaches to in order to break proteins
down
Polypeptide- 3 or more amino acids bonded together
Minerals
- inorganic cmpds (no C); needed in very small amts
- enable some chem. rxns.; help build bones & cartilage
- readily absorbed into bloodstream
-essential components of hemoglobin, hormones, enzymes, vitamins
Vitamins
-needed in very small amts
-serve as co-enzymes which are chemicals needed to make enzymes
work
-involved in tissue development & growth, helping resist & fight disease
-bodies can make vitamins D, K & B; stores only vitamins A & D. See
table 11.1 on p. 358.
Water
-needed for digestion and absorption
-carries nutrients & oxygen to cells
-removes wastes & toxins
Fibre
-not considered one of 6 essential nutrients b/c no nutritional value
-plays impt. role in digestion…without fibre, food we eat wouldn’t have
much bulk which would make it difficult for peristalsis to occur.
Digestion in Heterotrophs
Digestion - the two-part process that changes food into a form that can
be absorbed by and is usable by body cells.
Physical digestion breaks large pieces into smaller ones. Most physical
digestion starts in the mouth and passes through digestive tract.
Chemical digestion breaks complex chemicals into simple ones.
Chemical digestion begins in the mouth and continues in the
stomach.
Animal Digestion
 One way traffic
Animals from roundworms to mammals have a true digestive
system of one way digestion with a mouth, gut and anus. Food is
broken down in different areas within the digestive tract.
In the mouth, food is moistened while in the gut (stomach,
intestine) food is ground up. In the lower digestive tract, food is further
broken up and absorbed into the circulatory system and wastes are
eliminated through the anal opening.
Earthworm
There are 2 openings. The mouth moistens the food which is
sucked in by the muscular contractions of the pharynx. From the
pharynx, food moves into the esophagus where it continues to be pushed
into the crop which is stretchable and can store food. Next, it passes
into the thick-walled gizzard where it is ground into smaller pieces.
This allows for enzymes to work on more surface area of food.
Chemical digestion begins in the intestine which is the longest
portion of the digestive tract and is folded to give it more surface area so
it can digest and absorb the maximum amount of food. This is where
most of the absorption occurs. Water and minerals are also absorbed at
this time. The nutrients get absorbed by the cells lining the intestine.
From here, the nutrients enter the bloodstream and get transported to all
body parts.
Human Digestion
Recall, digestion is a two-part process…physical & chemical
digestion.
Fats, carbohydrates, and proteins are digested and converted to
fatty acids, glycerine, monosaccharides, and amino acids. The human
cell then rebuilds these into its own complex compounds or burns them
up for energy.
Water, minerals, and vitamins are also required for the digestive
process to take place.
Mouth
Digestion begins when you put food in your mouth. Teeth bite off
and chew/grind food into a soft pulp that is easy to swallow. Enzymes
will mix better with the food when it is ground up. The mouth also
evaluates texture and taste which would allow us to get rid of spoiled
food or foreign particles before it enters further down the digestive tract.
Papillae- tiny structures on tongue containing most of taste buds
Uvula- hangs @ middle of soft palate preventing food from
entering pharynx when swallowing
Salivary Glands
Chewing mixes the food with watery saliva from 3 sets (6) of
salivary glands along the mouth. Taste, thoughts of food, and smell all
stimulate salivary action. The saliva flows through small tubes called
ducts. Saliva contains mucus that moistens the food for
swallowing...this mucus-covered mass of food particles is called bolus.
Saliva also contains an enzyme (protein) called salivary amylase that
begins the break down of starch into disaccharides called maltose units.
Fats and proteins are not digested in the mouth.
Pharynx
When food is chewed sufficiently, the tongue pushes it to the back
of the throat or pharynx which starts the automatic swallowing reflex.
This area contains the opening to the esophagus and the trachea
(windpipe).
Epiglottis
This is a muscular flap of tissue over the trachea which closes it off
during swallowing to prevent food from entering the trachea.
Esophagus
The chewed up, moistened, and partly broken food enters the
esophagus. The esophagus, or gullet, is a muscular tube which has
mucus on its walls to help bolus move along. It takes food from the
throat and pushes it down through the neck, and into the stomach.
Digestive juices are not added in the esophagus , but the food moves by
waves of involuntary muscle contraction called peristalsis. The
relaxation and contraction of muscles of the digestive tract push food
down into the stomach.
Regurgitation- movement of food to mouth from stomach when
sick
Stomach
The stomach has two main parts:
a) the larger muscular part is called the fundus
b) the smaller, more narrow part is called the pyloris
The stomach is a large organ that performs 3 functions:
1) In the fundus, the muscular wall churns food up and breaks down the
food physically. The fundus walls also secrete HCl (a gastric juice) to
break down the food into a white, soupy paste called chyme. A mucus
coating is also secreted to prevent HCl from burning the stomach lining.
2) The stomach secretes a digestive enzyme called pepsin to start the
break down of proteins into smaller polypeptides.
3) The stomach (fundus) acts as a storage area for the slow release of
food into the intestines; this allows time for it to be absorbed by the
small intestine. The proteins are only partly broken down in the
stomach by pepsin (digestive enzyme).
The food leaves a narrow part of the stomach called the pyloris
and empties into the small intestine. A valve called the pyloric
sphincter (ring of sphincter muscle) keeps chyme from going back into
the stomach from the small intestine.
Pancreas…food doesn’t pass through here
The pancreas, like the stomach, makes powerful pancreatic juices
called enzymes which help to digest food further as it enters the small
intestines. First, a chemical called sodium hydrogen carbonate
(NaHCO3) is produced by the pancreas to neutralize the HCl that coats
the chyme when it leaves the stomach and enters the small intestine.
Otherwise, the acid would burn a hole in the small intestine.
Lipase is an enzyme produced by the pancreas that breaks fat up
into glycerol and fatty acids (dehydration synthesis) which can then be
absorbed.
An enzyme, pancreatic amylase, is also produced in the pancreas.
This enzyme (having the same function as salivary amylase) breaks
starch up into maltose units (hydrolysis) in case you swallow your food
too quickly.
Protease is another enzyme produced in the pancreas that breaks
down polypeptides into smaller dipeptides.
Gall Bladder…food doesn’t pass through here
This small bag-like part is tucked under the liver. It stores a fluid
called bile, (and bile salts) which are both made in the liver and stored
here in the gall bladder. As food from a meal arrives in the small
intestine, bile flows from the gall bladder along the bile duct into the
intestine. Bile helps emulsify fat into tiny droplets so enzymes can
break it down.
Small Intestines
Most of the chemical digestion takes place and nutrients are
absorbed in the small intestine. This part of the tract is narrow, but very
long - about 7 meters in adults. The length of the small intestine
ensures that food will stay long enough to be broken down and
absorbed. The small intestine is a twisted (folded) set of tubes which
contain finger-like projections called villi inside its lining to absorb
nutrients into the circulatory and lymphatic system. The amount of
folding, length of intestine and the villi slow down digestion and allow
for maximum absorption. The small intestine is made up of three
regions; the duodenum, the jejunum, and the ilium.
Here in the small intestine, more enzymes continue the chemical
attack on the food to finish digestion. The enzymes maltase, sucrase,
-and lactase are produced in the wall of the small intestine. These
enzymes break up the disaccharide sugars maltose, sucrose, and lactose
into simple sugars (hydrolysis) which are needed for energy.
Earlier in the digestive process, polypeptides were broken down in
to smaller dipeptides by the enzyme protease. Now in the small
intestine, an enzyme called peptidase (which is produced in the wall of
the small intestine) breaks the dipeptides into amino acids.
Finally the nutrients are small enough to pass through the lining
of the small intestine and into the blood. They are carried away to the
liver and other body parts to be processed, stored and distributed.
Anything else that is left over after digestion is finished in the small
intestine is called feces. Feces will then leave the small intestine
(pushed by peristalsis) and enter the large intestine.
Liver…food doesn’t pass through here
Blood from the intestines flows to the liver, carrying nutrients,
vitamins and minerals, and other products from digestion. The liver is
like a food-processing factory with more than 200 different jobs. It
stores some nutrients, changes them from one form to another, and
releases them into the blood according to the activities and needs of the
body.
Large Intestine (Caecum & Colon)
Any useful substances in the leftovers, such as spare water and
body minerals, are absorbed through the walls of the large intestine,
back into the blood. The remaining feces is almost ready to be removed
from the body. No digestion takes place in the colon, however, bacteria
in our colons are able to take material from the feces and make Vitamin
K and B-Complex. Peristalsis pushes the feces along to the end of the
colon called the rectum.
Appendix- organ suspended from caecum; no function for
digestion (maybe for fighting infection)
Rectum and Anus
The end of the large intestine and the next part of the tract, the
rectum, store the feces. The feces then leaves the body through the anal
canal which opens into anus.
Peristalsis- series of wavelike contractions and relaxation of muscles;
involves circular and longitudinal muscles that surround parts of
digestive tract
Rhythmical segmentation- related to peristalsis; used to mix partially
digested food on intestines; food squeezed back & forth