Animal Nutrition Chapter 41

Animals are heterotrophs They eat for three reasons: To obtain fuel for cell processes To get carbon to build organic molecules To get nutrients they cannot make

Why do we eat? There is a homeostatic mechanism at work Blood glucose levels help determine when we should eat

1. After a meal, blood glucose levels rise. 2. This triggers the beta cells in the pancreas to make insulin 3. Insulin levels rise, making cells use available glucose 4. Blood glucose levels fall. 5. This triggers the alpha cells in the pancreas to make glucagon 6. Blood sugar levels rise as stored glucose is released into blood- stream

Animals feed in different ways Most are opportunistic feeders Carnivores, herbivores and omnivores

Feeding Adaptations Suspension feeders: sift food particles from the water Substrate feeders: live on their food source Fluid feeders: suck nutrient- rich liquid from host organisms Bulk feeders: eat large particles of food

Stages of Food Processing There are 4 stages you need to be familiar with

1. Ingestion The act of taking food into the body From

2. Digestion Process of breaking down food into particles small enough to absorb Achieved with enzymes

3. Absorption Molecules that have been broken down are absorbed by the digestive system Nutrients travel to blood stream to be distributed to whole body From

4. Elimination Waste products of digestion are expelled from the body Contains undigested parts of food

Digestion happens in specialized compartments Intracellular: Digestion occurs in food vacuoles Ex. paramecium Extracellular: Digestion occurs outside cells Is possible to eat larger food items this way Ex. Hydra eating Daphnia

Human Digestive Tract

Generalized Structure of the Tract Throughout the digestive tract, the general structure is like that shown at right

Mouth Mechanical digestion by teeth and tongue happens here Saliva secreted to lubricate food Salivary amylase to digest starches to smaller polysaccharides From

Swallowing and the esophagus Food is formed into a bolus-a ball of food and is pushed back by the tongue into pharynx Peristalsis moves bolus down esophagus to stomach

Stomach Mechanical and chemical digestion happen here— chyme produced pH of stomach is low to facilitate protein digestion by pepsin From

Cells of the stomach Chief cells: secrete pepsinogen Parietal cells: secrete HCl Pepsinogen is converted to pepsin in presence of HCl

Sphincters and the Stomach The stomach has two sphincters: Cardiac: controls food entrance into stomach Pyloric: controls food entrance into duodenum From stomach00.jpg

Small intestine: duodenum More than 6 m in length Majority of digestion and absorption takes place here Chyme mixes with bile, enzymes and secretions from duodenum, pancreatic secretions

What is secreted? Liver: produces bile Gall bladder: stores bile Pancreas: makes bicarbonate ions, lipase Duodenum: produces hydrolytic enzymes

Enzymes of digestion

Digestion of Fats Fats are hydrophobic, thus digestion is difficult Bile salts emulsify large fat particles into smaller globules Pancreatic lipase surrounds smaller globules and digests them

Absorption of Fats Glycerol and fatty acids are absorbed by epithelial cells Remade into fats, and mixed with cholesterol, then coated with special proteins Form small globules called chylomicrons absorbed by lacteals

Absorption of Nutrients The small intestine is lined with villi Each villus has capillaries and a lacteal Nutrients are absorbed and carried to the hepatic portal vein

Hepatic portal system Hepatic portal vein: Major blood vessel that goes to the liver The liver uses absorbed nutrients in the manufacture of other organic molecules

Large Intestine Responsible for water recovery and absorption Produces feces Mutualistic bacteria reside here

Rectum and anus Fecal matter is stored here until expelled through the anus To process an entire meal takes from hours in humans