Animals are heterotrophs, meaning:
they obtain energy and nutrients they need from other organisms rather than making their own food as plants do
any material that contains nutrients
How do animals get the chemical energy and carbon-containing building blocks they need?
from carbohydrates and fats
nutrients that cannot be synthesized and must be obtained in the diet
What do carbohydrates and fats provide?
energy to make ATP and building blocks for organic molecules. Proteins can also provide energy
8 Essential Nutrients
cannot be synthesized by humans and must be obtained from food in proteins
organic compounds that are vital for health but are required only in very small amounts; many function as coenzymes in critical reactions
inorganic ions that influence osmotic balance and are required for normal membrane function
-essential for humans: Na+, K+, Cl-
fulfill a variety of functions not performed by electrolytes. Often they are important components of cofactors or structural materials
-essential for humans: Ca, F, I, Fe, Mg, P, S
Biologists assign animal food-getting techniques to one of 4 strategies:
filter small organisms or particles of organic debris from water, by means of cilia, mucous-lined "nets," or other structures
swallow organic-rich sediments and other types of deposited material
suck or lap up fluids
what the majority of animals are. they seize and manipulate chunks of food by using jaws, teeth, beaks, or special toxin-injecting organs
the taking in of food
the breakdown of food into small enough pieces to allow for absorption
the uptake of nutrients
the disposal of wastes
where digestion takes place. also called the alimentary canal or gastrointestinal (GI) tract. It begins at the mouth and ends at the anus
Digestive tracts come in 2 general designs:
-incomplete digestive tracts
-complete digestive tracts
Incomplete Digestive Tracts
have a single opening through which food is ingested and wastes are eliminated. the mouth opens into a chamber, called a gastrovascular cavity, where digestion takes place
-e.g., phylum Cnidaria (jellyfish, corals, anemones) and phylum Platyhelminthes (flatworms)
Complete Digestive Tracts
have two openings - they start at the mouth and end at the anus. occur in most bilateral animals
Complete digestive tracts have 3 advantages:
-animals can feed on larger pieces of food
-chemical and physical processes can be separated within the canal, so that they occur independently of each other and in a prescribed sequence
-material can be ingested and digested continuously
Where does digestion begin?
in the mouth, starting with the tearing and crushing activity of teeth during chewing
What must be broken down during digestion?
Each of the 3 types of macromolecules - carbohydrates, lipids, and proteins
Where are the small molecules absorbed?
in the small intestine, along with water, vitamins, and ions
Where is more water absorbed?
in the large intestine, producing feces that eventually exit the body at the anus
the most important catalyst in the breakdown of carbohydrates
secreted in the tongue, beings the breadown of lipids
in the mouth, release water and glycoproteins called mucins
What happens when mucins contact water?
they form a slimy substance called mucus
a muscular tube connecting the mouth and stomach
a wave a muscle contractions that propels the esophagus to the stomach
an automatic reaction to a stimulus - that is stimulated by the act of swallowing
a tough, muscular pouch bracketed on both ends by valves called sphincters
What happens after eating?
muscle contractions in teh stomach result in churning that mixes and breaks down the food mechanically
Hydrochloric Acid (HCl)
the predominant acid in the stomach
contains hydrochloric acid and the enzyme pepsin to begin the digestion of proteins
contain an inactive pepsin precursor called pepsinogen, which is converted to active pepsin by contact with the acidic environment of the stomach
Secretion of a protein-digesting enzyme in inactive form is important:
it prevents destruction of proteins in the cells where the enzyme is synthesized
the source of HCl in gastric juice
secrete mucus, which lines the gastric epithelium and protects the stomach from damage by HCl
a 6m long tube that partially digested food passes into from the stomach.
-the food mixes with secretions from the pancreas and liver and begins to move through the tube
At the end of the small intestine:
digestion is complete and most nutrients, including water, has been absorbed
Why does the small intestine have an enormous surface area?
for absorption of nutrients due folding and to projections called villi, which in turn have projections called microvilli
Why do nutrients pass quickly from epithelial cells into the body's transport systems?
because each villus contains blood vessels and a lymphatic vessel called a lacteal
enzymes in the small intestine that digest polypeptides to amino acids
How are proteases synthesized?
in inactive form by the pancreas, transferred through the pancreatic duct to the small intestine, and activated there
an enzyme that activates the pancreatic enzymes
nucleases and pancreatic amylase
digest the RNA and DNA in food
continues the digestion of carbohydrates that began in the mouth
2 general principles apply to nutrient absorption by epithelial cells of small intestine:
-it is highly selective; the plasma membranes of microvilli are responsible for bringing specific nutrients into the cell
-it is active; it requires an expenditure of ATP to bring nutrients into the epithelium against a concentration gradient
breaks certain bonds present in complex fats and results in the release of fatty acids and other small lipids
enter the small intestine as large globules that must be broken up (empulsified) before digestion can begin
How does emulsification result?
from the action of small lipids called bile salts, which are synthesized in the liver and secreted in a complex solution called bile, which is stored in the gallbladder
What happens when bile enters the small intestine?
it raises the pH and emulsifies the fat into small globules
pancreatic lipase breaks bonds in the complex fats, resulting in the release of fatty acids and other small lipids (monoglycerides)
After the monoglycerides and fatty acids are released by lipase activity:
they eneter the epithelial cells attached to a protein named fatty-acid binding protein
protein-coated globules which diffuse into small lymph vessels called lacteals
an outpocketing of the digestive tract located at the start of the large intestine
What is the cecum called in humans?
the appendix; it is dramatically reduced in size and functions against invading bacteria and viruses
What is the primary function of the large intestine?
to compact wastes that remain and absorb enough water to form feces
main section of the large intestine
Where are the feces held?
in the rectum, the final part of the large intestine, until they can be excreted
experience abnormally high levels of glucose in their blood
How is diabetes caused?
by problems with a hormone called insulin
produced in the pancreas when blood glucose levels are high.
cells in the pancreas secrete this hormone when blood glucose levels fall too much
the synthesis of glucose from non-carbohydrate compounds
Type I Diabetes Mellitus
people who do not synthesize insulin
Type II Diabetes Mellitus
have defective versions of the insulin receptor
Body Mass Index
calculated by weight(kg) divided by height(m) squared