ANIMAL ENERGY REQUIREMENTS -- MODULE 144
I.
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BIOENERGETICS
Every living organism requires a constant source of energy to carry out normal life processes and
to reproduce.
 The study of energy changes that occur in living organisms is called bioenergetics.
 Energy processes in all animals basically require the same steps.
o Ingestion of organic molecules, such as carbohydrates, lipids, proteins and vitamins.
o Digestion breaks down these molecules to its monomers.
o Many animals absorb the digested monomers into their blood stream and carry them to
cells. In the individual cells, these monomers can be broken down (catabolism) to use
their chemical energy but they can also be used as building blocks of the
macromolecules of the organism (anabolism).
o Waste materials are eliminated from the organism, but energy is also gradually lost as
heat during the various life processes (Second law of thermodynamics)
II.
HOW CAN WE QUANTIFY THE ENERGY USAGE OF AN ORGANISM?
 Metabolic rate – is the rate at which anabolic and catabolic processes occur in joules or
kilojoules per unit of time (usually day). A more commonly used unit for energy measurements
is the kilocalorie or Calorie.
 The metabolic rate of an organism varies greatly depending on various factors:
o With more activity, the metabolic rate also increases
o Cold outside temperature increases the metabolic rate of endothermic organisms, while
warm temperatures decrease it. In ectotherms, however, the warmer outside
temperature increases the body temperature and increases the metabolic rate.
o Cold temperatures can also stimulate torpor (deep sleep) or hibernation in organisms.
These processes drastically slow down the metabolic rate. In some cases hibernation
can be stimulated by light not temperature. Estivation occurs in response to increased
temperatures and dry conditions, but in these cases the metabolic rate also decreases.
o Stress can also increase the metabolic rate for a short period of time.
o The size of the organism also influences its metabolic rate. Smaller organisms usually
have a higher metabolic rate because of their larger SA to V ratio that releases more
heat. There is a lot more to this question that is still being researched. The increased
metabolic rate seems to also correspond with shorter life expectancy and aging.
o Age can also influence the metabolic rate. Older animals (and humans) usually have a
lower metabolic rate than younger ones. Partially this is due to decreased muscle mass.
 The main source of energy for cells is glucose, which is broken down during cellular respiration
to generate ATP for cellular work.
I.
ANIMAL NUTRITION AND DIET -- MODULE 145 (BRIEF)
Essential Nutrients
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Food is not just a source of energy but animals also use it to build important substances that are
necessary for cells to function properly.
Diets, the type of food that animals eat vary. According to their diet and to their teeth structure
they can be in one of the following categories. However, the lines between these types are
more blurred:
o Herbivores
o Carnivores
o Omnivores
Essential nutrients are compounds that organisms need to ingest to be able to form their own
organic compounds. The four types of essential nutrients are:
o Essential amino acids – amino acids that the body cannot build on its own. Without
these amino acids, the animal will not be able to build some important proteins. Amino
acid deficiency can be an issue for vegans.
o Essential fatty acids – fatty acids that have to be ingested because they are not made by
the body.
o Vitamins – small organic molecules that are required in small amounts to form
coenzymes or other molecular components. They are divided into two categories:
Water soluble vitamins, that include C and B vitamins; fat soluble vitamins include A, D,
E, and K vitamins. Taking excess of fat soluble vitamins can have harmful effects on the
body.
o Minerals – inorganic molecules or ions that are needed in trace amounts to form various
molecules or to help to set normal osmotic concentration in the body. For example,
iodine is necessary to build the hormones of the thyroid gland, Ca2+ is required to form
bones, teeth and it is important for normal nerve and muscle function and cell signaling.
Iron is important in forming hemoglobin.
II.
Diet Deficiencies
 Mineral and vitamin deficiencies during pregnancy can result in malformed fetuses, in others it
can result in reduced growth and suppressed immune system or at times in deficiency diseases.
 Enriched foods, such as iodized salt, Ca – fortified juice, Fe fortified cereals help to avoid
deficiency disorders.
I.
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THE PROCESS OF DIGESTION -- MODULE 147
An Overview of the Mammalian Digestive System
Simple animals such as cnidarians and flatworms have an incomplete digestive system with only
one opening. This one opening is used to take in food and expel waste.
Mammals have a complete digestive system with two separate opening. One opening, the
mouth takes in food, while the other, the anus expels waste. Between the two openings, the
alimentary canal has several compartments with accessory organs, mostly glands attached.
The digestive system of animals is greatly adapted to their type of nutrition. Plant foods are
generally harder to digest than meat, so the digestive system of herbivores is longer, the
stomach is frequently more complex and have multiple different functions. The tooth structure
also varies depending on the type of food organisms eat. Carnivores usually have larger incisors
to be able to rip flesh. All of these adaptations evolved over a long period of time to make the
most efficient use of the nutrients that are taken in by animals.
II.
The Upper Digestive System (Mouth, Pharynx, Esophagus)
 Mechanical and chemical digestion starts in the mouth. Mechanical digestion means chewing
the food into smaller particles so larger surface area results and enzymes can get to more of the
molecules during chemical digestion.
 Salivary glands secrete saliva which is composed of water, mucus, amylase enzyme (to digest
starch) and lipase enzyme (to digest lipids). Mucus contains materials to form a bolus, a piece of
the food that can easily be swallowed, also mucus has various antimicrobial agents that protects
the digestive system from bacteria and other microbes in our food.
 The food next is pushed into the pharynx (throat). This part is shared between the respiratory
and digestive system. To protect the food from going down into the respiratory system through
the trachea, a structure, called epiglottis closes up the trachea during swallowing.
 The food moves into the esophagus – a long tube of muscle and mucus membrane that
forwards the food into the stomach. The top and bottom part of the esophagus can be closed
down by ring-shaped muscles called sphincter muscles. These ring-shaped muscles are
common structures in the digestive system to separate the various compartments of the
alimentary canal. The esophagus is also the first place that performs peristaltic motion – the
regular waves of involuntary contractions of the wall of the alimentary canal. These waves of
contractions move the bolus forward.
III.
Digestion in the Stomach
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Once food arrives into the stomach, the lower esophageal sphincter muscles prevent the food
from returning back into the esophagus (unless acid reflux occurs). The stomach wall muscles
regularly contract and relax to mix freshly released stomach juices and the bolus.
The stomach juice is composed of an enzyme called pepsin, which is first produced as
pepsinogen in an inactive form. Food arriving into the stomach accelerates the production of
stomach acid and pepsinogen. Pepsinogen turns to pepsin, once it mixes with the stomach acid
and become active. The only type of food digested by pepsin is PROTEINS. The production of
pepsin activates more pepsinogen to be activated – positive feedback mechanism.
The stomach acid is also antimicrobial so it breaks down and destroys various microorganisms.
The stomach is also important for temporary storage of food. The stomach content only
gradually enters the small intestine.
No other digestion is occurring in the stomach.
IV.
Digestion and Absorption In The Small Intestine
 After some time the partially digested stomach content (called chyme) enters the small
intestine.
 The first segment of the small intestine is the duodenum, where several secretions mix with the
chyme. The duodenal secretions are filled with various digestive enzymes that digest all kinds of
polymers on fairly basic conditions.
 The pancreas also releases various enzymes here and bicarbonate ions to neutralize the
stomach acid.
 The liver/gall bladder releases bile. Bile is acts as a solvent for fats. Bile helps to form smaller
fat droplets and create larger surface area for more efficient digestion. Bile also helps to
neutralize stomach acid.
 The small intestine is about 6 m (20 feet) long. The reason for this is that this is the main area
for nutrient absorption. Absorption means the process that moves digested substances from
the intestine into the blood/lymph circulation. The efficient absorption of all nutrients requires
a very large surface area. This surface area is provided by the gradual inner folding of the
epithelial tissue of the small intestine.
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The inner wall of the small intestine is folded. On the folds, there are finger-like projections that
increase the surface area even further. These projections are called villi. Inside each villus,
there is a lacteal – beginning of a lymph vessel and capillaries for rich blood supply.
The villus is made up of cells with a brush-like border for even more surface area – microvilli.
The total surface area of the small intestine is about as large as a tennis court, because of all the
folding, villi and microvilli to enhance the rate of absorption. The rich blood supply inside of the
villus provides the method of transportation for most absorbed monomers, except fatty acids
and monoglycerides that are transported in the lacteals.
The nutrient rich blood is transported to the liver for processing, detoxification and storage.
V.
The Large Intestine
 The unabsorbed material travels from the small intestine into the large intestine. Here, more
water is being absorbed into the circulatory system but the nutrient absorption is basically
finished in the small intestine.
 The waste material is moved into the rectum and removed from the body.
 The large intestine is also home to trillions of bacteria. These bacteria live in mutualistic
relationship with us. These bacteria provide vitamins for us, immunological protection against
harmful bacteria and secrete enzymes to digest fibers and other undigestable material for us.
Some of these materials can be absorbed back into our blood stream but this process is mostly
significant for herbivores. These bacteria also compose a large percentage of the feces.
Acid reflux: http://www.purplepill.com/acid-reflux-disease/index.aspx
Regulation of stomach secretion: http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter43/animations.html#
Organs of digestion: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html -good summary
Great animations on the entire digestive system:
http://www.argosymedical.com/Digestive/index.html
CIRCULATORY SYSTEMS -- MODULE 151
I.
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Overview
Specialized structures that some animals use for nutrient, gas and waste transport is the
circulatory system.
The simplest organisms generally live in water and are very thin, so nutrients can pass directly
from the surrounding water into the organism and waste to the opposite direction. Diffusion is
the main process to transport nutrients, gases and waste.
All true circulatory systems have the same basic composition.
o Circulatory fluid to move substances in the body – hemolymph or blood
o Vessels to hold the fluid (like arteries – vessels leaving the heart, veins – vessels leading
toward the heart and capillaries – smallest blood vessels that participate in the diffusion
of molecules that need to be exchanged)
o Pump to move the fluid in the vessels (heart)
II.
Major Evolutionary Steps of The Circulatory System
 Open circulation lacks completely closed vessels. They carry hemolymph. This fluid first flows
in vessels, than flows out into the body cavities (interstitial space), than sucked back into vessels
with the help of the heart. The circulation of these animals is less efficient, slower, so they
constantly have to move to help to make the flow of hemolymph more efficient. However, this
system requires less energy to operate so animals can maintain a lower metabolic rate.
 Closed circulatory system – the vessels form a closed circuit and blood always remains in them.
Only gases, waste and nutrients diffuse through the cells of the smallest blood vessels. The
blood flow is more efficient, because of higher blood pressure but requires more energy to
maintain this blood flow.
 Closed circulatory systems can have one or two circuits.
 Single circulation is found in fish, in which blood passes through the heart only once per cycle,
than moves through the gills to refresh with oxygen, than blood flows through the capillaries of
the body and back into the heart.
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Double circulation – in this case blood passes through the heart twice. Blood flows out of the
heart toward the lungs to refresh with oxygen, than it flows back into the heart – pulmonary
circuit. The second circuit starts when blood flows out of the heart and carries oxygen rich
blood toward the body. The CO2 rich blood returns into the heart again at the end of the second
circuit – systemic circuit.
This system provides more efficient transport of blood because the blood flow is faster.
The blood is always refreshed on the respiratory surface of a respiratory organ. This organ can
be the gills in fish, lungs in amphibians, reptiles, birds and mammals. The skin also supports
respiration in amphibians.
Air breathing fish, like mudskippers and lungfish provide an evolutionary intermediate between
organisms with gills and organisms with lungs. These fish have blood flowing from their lungs
into the heart. They can get oxygen from air on dry land and the lungs release oxygen into the
blood, but the oxygen rich blood mixes with CO2 rich blood when the blood in the heart. This
makes the circulation of lungfish more inefficient.
III.
Increased Number of Heart Chambers
 Increased number of heart chambers is also a major evolutionary adaptation.
 The heart is a pump that keeps up the movement of blood in blood vessels. The upper chamber
of the heart –atrium (pl. atria) is responsible for receiving blood, while the lower chambers,
ventricles, are responsible for moving the blood toward the lungs, gills and the body. Fish have
only one atrium and one ventricle, since they have only one circuit of blood stream, this setup is
sufficient. Amphibians have 2 atria but only one ventricle, so the oxygen rich blood from the
lungs and the CO2 rich blood from the body mixes in the ventricle. Some reptiles still retain the
3-chamber system, while others have a partially separated ventricle. Birds and mammals have
completely separated 2 ventricles, so they have four chambers. This provides complete
separation of O2 rich and CO2 rich blood and makes the circulation more efficient. The
appearance of the 4-chambered heart made endothermic temperature regulation possible.
This is the end of Unit 5