Animal Nutrition

We need to eat! Since we as animals cannot produce our own food, we must EAT it. Classifying organisms by what they eat…  Herbivores: eat autotrophs  Carnivores: eat other animals  Omnivores: eat both autotrophs and animals

Classifying Animals by HOW They Get Their Food Suspension feeders:  Sift small food particles from the water  Examples: clams, oysters, whales Substrate feeders:  Live on (or in) their food source  Example: leaf miners, eat their way through leaves Deposit feeders:  A type of substrate feeder  Eat partially decayed organic material in soil

Classifying Animals by HOW They Get Their Food Fluid-feeders  Suck nutrient-rich fluids from a living host  Example: mosquitoes, hummingbirds Bulk-feeders  Eat relatively large pieces of food  That’s us!

The 4 Stages of Food Processing 1.Ingestion The act of eating 2.Digestion The process of breaking down food into molecules small enough for the body to absorb This involves hydrolysis, which you should know well This has to occur in a specialized compartment… why??

The 4 Stages of Food Processing 3. Absorption  The animal’s cells absorb the small molecules broken down during digestion 4. Elimination  Undigested material passes out of the digestive compartment

Gastrovascular Cavities Gastrovascular cavities are the digestive systems in simple animals GCs have only one opening, and there is only one “part” of a GC

Digestion in Alimentary Canals Complex animals use alimentary canals, a digestive tube extending between two openings, a mouth and an anus  An “Entrance” and an “Exit” Food travels in one direction only Mouth = site of ingestion Anus = site of elimination

Alimentary Canals

The Mammalian Digestive System

Consists of:  Oral cavity (mouth)  Pharynx  Esophagus  Stomach  Small Intestine  Large Intestine Food moves through the digestive system by peristalsis, rhythmic waves of contraction by the smooth muscles

Oral Cavity The mouth Chewing cuts, smashes, and grinds food to facilitate swallowing Saliva is secreted into the mouth by the salivary glands  Saliva contains salivary amylase  This enzyme breaks down starch and glycogen into smaller pieces

Pharynx The pharynx is the intersection that leads to both the esophagus (digestive system) and the trachea (respiratory system) The epiglottis makes sure that food doesn’t enter the trachea

Esophagus The esophagus carries food from the pharynx into the stomach

Stomach Our stomachs are stretchy – they expand to fit our food! The inside of the stomach contains gastric juice, which has a pH of about 2  HCl – kills most bacteria swallowed with food - breaks down cells in meat and plant material  Pepsin – breaks down proteins Because the smooth muscle of the stomach and enzymes churn and break up your meal, the food becomes a nutrient broth known as acid chyme

Stomach The pyloric sphincter closes off the stomach from the small intestine, the next stop on our tour The pyloric sphincter lets in small amounts of acid chyme at a time

Small Intestine Most digestion and absorption occurs in the small intestine In humans, the small intestine is about 6 meters long  It’s called the “small intestine” because it has a small diameter

Small Intestine First section of the small intestine is the duodenum  responsible for digestion  Acid chyme enters from the stomach  Pancreatic enzymes (hydrolytic) enter  Bile (produced in the liver, stored in the gall bladder) enters Bile contains bile salts which aid in digestion and absorption of fats

Small Intestine Carbohydrates are broken down (digested) by amylases from the pancreas Proteins are broken down (digested) by trypsin DNA and RNA are broken down by nucleases Fats are broken down by bile salts from the liver and lipase

Small Intestine The digestion occurs in the duodenum The absorption of nutrients occurs in the jejunum and ileum  In order to be useful to an organism, the nutrients that have been broken down must be absorbed  The jejunum and ileum (sections 2 and 3 of the small intestine) are responsible for absorbing what the duodenum digested

Small Intestine The jejunum and ileum have a brush border  The jejunum and ileum have villi (that look like fingers) and microvilli  This gives them more surface area, which facilitates absorption of nutrients More doors = faster access

The Small Intestine

Large Intestine (Colon) The major function of the colon is to reabsorb water that entered the digestive system as a solvent The wastes of the digestive tracts are called feces, and they become more solid as they are moved along the colon  If it moves through too quickly, not enough water is reabsorbed  diarrhea  If it moves through too slowly, too much water is reabsorbed  constipation The waste is stored in the rectum until it can be eliminated through the anus

The Mammalian Digestive System

Evolutionary Adaptations Evolutionary adaptations of the digestive system exist among animals, primarily based on their diet Herbivores have less specialized teeth than do carnivores Herbivores have longer alimentary canals than carnivores…why??

Evolutionary Adaptations

Food is our Fuel Undernourished:  Someone whose diet is deficient in calories Malnourished:  Someone whose diet is missing one or more essential nutrients However, obesity is a more common dietary problem in America