Animal Nutrition
Digestion: ingesting large amounts of some minerals can upset homeostatic balance and impair health
Ex. Excess instake of salt -> high blood pressure; often due to sodium hidden in processed foods
- Recommended sodium uptake for Canadians 19-30 yo: 1.5g per day
- Typical male Canadian consumes >4g per day; women 2.8g per day
Ex. Excess iron-> liver damage
Dietary Deficiencies
Malnutrion: diet has too much or too little of critical nutrients
Undernutrition: shortage of an essential nutrient/caloric intake
Deficiencies in Essential Nutrients
● Insufficient intake of essential nutrients can cause deformities, disease, and death
Ex. cattle, deer, and other herbivores may develop fragile bones if they graze on plants growing in soil that lack phosphorus
- Some grazing animals obtain missing nutrients by consuming concentrated sources of salt or other minerals
● Carnivores: spiders adjust for dietary deficiencies by switching to prey that restores nutritional balance
Deficiencies in Energy Intake
● When an animal doesn’t consume adequate energy- body uses up stored carbs and fat, then begins breaking down its
proteins for fuel
- Muscles become smaller, and the brain may become protein-deficient
- If energy intake remains less than energy expenditures, the animal will experience irreversible damage/death
● In sub-Saharan Africa, where the AIDS epidemic has crippled rural and urban communities, approx 200 million
children and adults cannot obtain enough food
Methods used to study human nutrition
● Several researchers who discovered vitamins a century ago used themselves as subject animals
● Insight into human nutrition comes from epidemiology: study of human health and disease at the population level
Present: researchers rely on the study of genetic defects that disrupt food uptake, storage, or use
- Ex. genetic disorder hemochromatosis causes iron build-up in absence of any abnormal iron consumption or
exposure
- Disorder is common and easy to treat; drawing blood regularly removes enough iron from the body to restore
homeostasis
The main stages of food processing: ingestion, digestion, absorption, and
elimination
Ingestion: eating or feeding
- Strategies for extracting resources from food differ widely
Digestion: food is broken down into molecules small enough for the body
to absorb
Mechanical digestion (chewing) precedes chemical digestion
- breaks food into smaller pieces, increasing the surface area
,available for chemical processes
● Chemical digestion is necessary because animals cannot directly use the proteins, carbohydrates, nucleic acids, fats,
and phospholipids in food- molecules are too large to pass through membranes and enter cells
- When large molecules in food are broken down into their components, animals can use the smaller molecules
to assemble the large molecules it needs
Ex. Fruit flies and humans have diff diets, however, both convert proteins in their food to the same 20 amino acids from
which they assemble all of the proteins specific to their species
Hydrolysis: bonds broken + addition of water, covalent bond- mediated by enzymes that are specialized to attack different
macromolecules; polysaccharides and disaccharides are split into simple sugars; proteins are broken down into amino
acids; and nucleic acids are cleaved into nucleotides and their components
- Enzymatic hydrolysis releases fatty acids and other components from fats and phospholipids
Absorption: animal cells take up (absorb) small molecules such as amino acids and simple sugars
Elimination completes the process as undigested material passes out of the digestive system
Digestive compartments
Intracellular digestion: hydrolysis of food inside vacuoles, begins after a cell engulfs solid food by phagocytosis or liquid
food by pinocytosis
Food vacuoles: hydrolytic enzymes break down food— simplest digestive compartments
● Newly formed food vacuoles fuse with lysosomes, containing hydrolytic enzymes
● This fusion of organelles brings food in contact with the enzymes, allowing digestion to occur safely within a
compartment enclosed by a protective membrane
- A few animals, such as sponges, digest their food entirely by this intracellular mechanism
Extracellular digestion: breakdown of food in compartments that are continuous with the outside of animal’s body
● Having one or more extracellular compartments for digestion enables an animal to devour much larger pieces of
food than can be ingested by phagocytosis
● Many animals with relatively simple body plans have a digestive compartment with a single opening
- Gastrovascular cavity (pouch), functions in digestion and the distribution of nutrients throughout the body
● The carnivorous cnidarians uses its tentacles to stuff captured prey through its mouth into its gastrovascular cavity
- Specialized gland cells of the hydra’s gastrodermis, the tissue layer that lines the cavity, secrete digestive
enzymes that break the soft tissues of the prey into tiny pieces
- Other cells of the gastrodermis engulf these food particles, and most of the hydrolysis of macromolecules
occurs intracellularly, as in sponges
- After a hydra has digested its meal, undigested materials that remain in the gastrovascular cavity, such as
exoskeletons of small crustaceans, are eliminated through the same opening food entered
- Many flatworms also have a gastro-vascular cavity with a single opening .
● Most animals have a digestive tube extending between two openings, a mouth and an anus: complete digestive
tract/alimentary canal
- Food moves along alimentary canal in a single direction, tube can be organized into specialized
compartments that carry out digestion and nutrient absorption stepwise
, - Animals w/ alimentary canal can ingest food while earlier meals are still being digested
Because most animals, including mammals,
have an alimen-tary canal, we can use the
mammalian digestive system as
an example of the general principles of food
processing
In mammals, the digestive system consists
of the alimentary canal and various
accessory glands that secrete
digestive juices through ducts into the canal
Accessory glands of the mammalian digestive system: 3 pairs of salivary glands, the pancreas, the liver, and gallbladder
● Food is pushed along the alimentary canal by peristalsis, alternating waves of contraction and relaxation in the
smooth muscles lining the canal
● At some of the junctions between specialized compartments, the muscular layer forms ringlike valves (sphincters)
acting like draw-strings to close off the alimentary canal, sphincters regulate the passage of material between compartments
The Oral Cavity, Pharynx, and Esophagus
● Ingestion and the initial steps of digestion occur in the mouth, or oral cavity
● Mechanical digestion begins as teeth cut, mash, and grind food, making it easier to swallow, increasing its SA
- Presence of food stimulates a nervous reflex that causes the salivary glands to deliver saliva through ducts to
the oral cavity
- Saliva may also be released before food enters the mouth, triggered by a learned association between eating
and the time of day, a cooking odour, or another stimulus
- Saliva initiates chemical digestion while also protecting the oral cavity
● Salivary amylase hydrolyzes starch (glucose polymer from plants) and glycogen (glucose polymer from animals) into
smaller polysaccharides and the disaccharide maltose
- Much of the protective effect of saliva is provided by mucus: viscous mixture of water, salts, cells, and
slippery glycoproteins (carbohydrate-protein complexes) called mucins
- Mucus in saliva protects the lining of the mouth from abrasion and lubricates food for easier swallowing
- Additional components of saliva include buffers, which help prevent tooth decay by neutralizing acid, and
antimicrobial agents, which protect against
bacteria that enter the mouth with food
● Tongue aids digestive processes by evaluating ingested
material and then enabling its further passage
● When food arrives at the oral cavity, tongue distinguishes
which foods should be processed further
Digestion: ingesting large amounts of some minerals can upset homeostatic balance and impair health
Ex. Excess instake of salt -> high blood pressure; often due to sodium hidden in processed foods
- Recommended sodium uptake for Canadians 19-30 yo: 1.5g per day
- Typical male Canadian consumes >4g per day; women 2.8g per day
Ex. Excess iron-> liver damage
Dietary Deficiencies
Malnutrion: diet has too much or too little of critical nutrients
Undernutrition: shortage of an essential nutrient/caloric intake
Deficiencies in Essential Nutrients
● Insufficient intake of essential nutrients can cause deformities, disease, and death
Ex. cattle, deer, and other herbivores may develop fragile bones if they graze on plants growing in soil that lack phosphorus
- Some grazing animals obtain missing nutrients by consuming concentrated sources of salt or other minerals
● Carnivores: spiders adjust for dietary deficiencies by switching to prey that restores nutritional balance
Deficiencies in Energy Intake
● When an animal doesn’t consume adequate energy- body uses up stored carbs and fat, then begins breaking down its
proteins for fuel
- Muscles become smaller, and the brain may become protein-deficient
- If energy intake remains less than energy expenditures, the animal will experience irreversible damage/death
● In sub-Saharan Africa, where the AIDS epidemic has crippled rural and urban communities, approx 200 million
children and adults cannot obtain enough food
Methods used to study human nutrition
● Several researchers who discovered vitamins a century ago used themselves as subject animals
● Insight into human nutrition comes from epidemiology: study of human health and disease at the population level
Present: researchers rely on the study of genetic defects that disrupt food uptake, storage, or use
- Ex. genetic disorder hemochromatosis causes iron build-up in absence of any abnormal iron consumption or
exposure
- Disorder is common and easy to treat; drawing blood regularly removes enough iron from the body to restore
homeostasis
The main stages of food processing: ingestion, digestion, absorption, and
elimination
Ingestion: eating or feeding
- Strategies for extracting resources from food differ widely
Digestion: food is broken down into molecules small enough for the body
to absorb
Mechanical digestion (chewing) precedes chemical digestion
- breaks food into smaller pieces, increasing the surface area
,available for chemical processes
● Chemical digestion is necessary because animals cannot directly use the proteins, carbohydrates, nucleic acids, fats,
and phospholipids in food- molecules are too large to pass through membranes and enter cells
- When large molecules in food are broken down into their components, animals can use the smaller molecules
to assemble the large molecules it needs
Ex. Fruit flies and humans have diff diets, however, both convert proteins in their food to the same 20 amino acids from
which they assemble all of the proteins specific to their species
Hydrolysis: bonds broken + addition of water, covalent bond- mediated by enzymes that are specialized to attack different
macromolecules; polysaccharides and disaccharides are split into simple sugars; proteins are broken down into amino
acids; and nucleic acids are cleaved into nucleotides and their components
- Enzymatic hydrolysis releases fatty acids and other components from fats and phospholipids
Absorption: animal cells take up (absorb) small molecules such as amino acids and simple sugars
Elimination completes the process as undigested material passes out of the digestive system
Digestive compartments
Intracellular digestion: hydrolysis of food inside vacuoles, begins after a cell engulfs solid food by phagocytosis or liquid
food by pinocytosis
Food vacuoles: hydrolytic enzymes break down food— simplest digestive compartments
● Newly formed food vacuoles fuse with lysosomes, containing hydrolytic enzymes
● This fusion of organelles brings food in contact with the enzymes, allowing digestion to occur safely within a
compartment enclosed by a protective membrane
- A few animals, such as sponges, digest their food entirely by this intracellular mechanism
Extracellular digestion: breakdown of food in compartments that are continuous with the outside of animal’s body
● Having one or more extracellular compartments for digestion enables an animal to devour much larger pieces of
food than can be ingested by phagocytosis
● Many animals with relatively simple body plans have a digestive compartment with a single opening
- Gastrovascular cavity (pouch), functions in digestion and the distribution of nutrients throughout the body
● The carnivorous cnidarians uses its tentacles to stuff captured prey through its mouth into its gastrovascular cavity
- Specialized gland cells of the hydra’s gastrodermis, the tissue layer that lines the cavity, secrete digestive
enzymes that break the soft tissues of the prey into tiny pieces
- Other cells of the gastrodermis engulf these food particles, and most of the hydrolysis of macromolecules
occurs intracellularly, as in sponges
- After a hydra has digested its meal, undigested materials that remain in the gastrovascular cavity, such as
exoskeletons of small crustaceans, are eliminated through the same opening food entered
- Many flatworms also have a gastro-vascular cavity with a single opening .
● Most animals have a digestive tube extending between two openings, a mouth and an anus: complete digestive
tract/alimentary canal
- Food moves along alimentary canal in a single direction, tube can be organized into specialized
compartments that carry out digestion and nutrient absorption stepwise
, - Animals w/ alimentary canal can ingest food while earlier meals are still being digested
Because most animals, including mammals,
have an alimen-tary canal, we can use the
mammalian digestive system as
an example of the general principles of food
processing
In mammals, the digestive system consists
of the alimentary canal and various
accessory glands that secrete
digestive juices through ducts into the canal
Accessory glands of the mammalian digestive system: 3 pairs of salivary glands, the pancreas, the liver, and gallbladder
● Food is pushed along the alimentary canal by peristalsis, alternating waves of contraction and relaxation in the
smooth muscles lining the canal
● At some of the junctions between specialized compartments, the muscular layer forms ringlike valves (sphincters)
acting like draw-strings to close off the alimentary canal, sphincters regulate the passage of material between compartments
The Oral Cavity, Pharynx, and Esophagus
● Ingestion and the initial steps of digestion occur in the mouth, or oral cavity
● Mechanical digestion begins as teeth cut, mash, and grind food, making it easier to swallow, increasing its SA
- Presence of food stimulates a nervous reflex that causes the salivary glands to deliver saliva through ducts to
the oral cavity
- Saliva may also be released before food enters the mouth, triggered by a learned association between eating
and the time of day, a cooking odour, or another stimulus
- Saliva initiates chemical digestion while also protecting the oral cavity
● Salivary amylase hydrolyzes starch (glucose polymer from plants) and glycogen (glucose polymer from animals) into
smaller polysaccharides and the disaccharide maltose
- Much of the protective effect of saliva is provided by mucus: viscous mixture of water, salts, cells, and
slippery glycoproteins (carbohydrate-protein complexes) called mucins
- Mucus in saliva protects the lining of the mouth from abrasion and lubricates food for easier swallowing
- Additional components of saliva include buffers, which help prevent tooth decay by neutralizing acid, and
antimicrobial agents, which protect against
bacteria that enter the mouth with food
● Tongue aids digestive processes by evaluating ingested
material and then enabling its further passage
● When food arrives at the oral cavity, tongue distinguishes
which foods should be processed further
