Chapter 21

Nutrition and Digestion

Humpback whale

• Can eat up to 2 tons of krill and fish in a day which allows them to harvest much more energy than they need

• In cold weather they migrate to breed in warmer waters

• They do not need to eat or hardly eat during these 4 months

Ways of ingesting food for animals

Ways of ingesting food for animals continued

• Suspension feeders: extract food from particles in fluid/ examples: humpback whale, clams, oysters

• Substrate feeders: live in or on their food source and eat their way through it/ example: earthworm

• Fluid feeders: obtain food by sucking nutient-rich fluids from a living host/ ex. mosquitoes

• Bulk feeders: ingest their food in large pieces/ example: grey heron

Food processing

1. ingestion: the act of eating 2. Digestion: breaking down food into smaller

pieces (physical and chemical)3. Absorption: the take up of the products of

digestion4. Elimination: undigested materials exit the

digestive tract

Specialized compartments of digestion

• Gastrovascular cavity: just a mouth• Alimentary canal: mouth and an anus• Pharynx: throat• Esophagus: tube that channels food• Crop: softens and stores food• Stomach: churn and grind food• Gizzard: churn and grind food• Intestine: chemical digestion and nutrient absorption• Anus: expels undigested food

Human digestion: the oral cavity

• Saliva is released before a bite is even taken

• Salivary glands release more than a liter of saliva a day

• A glycoprotein protects the soft lining of the mouth and lubricates food for easier swallowing

• Saliva contains salivary amylase which begins to breakdown the carbs the food

• Buffers neutralize the food to prevent tooth decay

• Mechanical and chemical digestion occur here

• Tongue: muscular organ that is covered in taste buds and pushes the bolus of food to the back of the oral cavity and into the pharynx

Oral cavity

• Blade like incisors (2): Used for biting

• Single pointed canine: used to rip apart food

• Premolars (2): grind and crush food

• Molars (3): grind and crush food

Food path continued

• Oral cavitybolus to the back of the oral cavity bolus down the pharynx down the esophagus by way of peristalsis

Stomach

• Secretes gastric juices made up of mucous, enzymes and strong acids/ pH of 2/ breaks apart the particles of food

• Pepsin begins the chem. Digestion of proteins/ breaks down large polypeptides into smaller polypeptides

• The stomach takes about 2-6 hours to empty after a meal

Small Intestine

• The rest of chemical digestion occurs here

• More than 6 m in length• Sources of digestive

enzymes in the sm intestine: pancreas, liver, gallbladder

• First 25 cm of sm intestine is the duodemnum

Digestion in the small intestine

• Starch (pancreatic amylase)maltose (maltase)monosaccharides

• Polypeptides (trypsin, chymotrypsin) smaller polypeptides (aminopeptidase, carboxypeptidase, dipeptidase) amino acids

• DNA and RNA (nucleases)nucleotides (other enzymes)N-bases, sugars and phosphates

• Fat (bile salts)fat droplets (lipase)fatty acids and glycerol

Absorption in the small intestine

• Use microvilli which are finger-like projections that increase surface area for absorption

• Some materials are absorbed through simple diffusion

Liver• Hepatic portal vein: the large

vessel that transport nutrients absorbed from the small intestine right into the liver

• Regulates the amount of glucose released into the blood

• Plays a large role in the body’s metabolism

• Aids in the digestion of fats• Detoxifies and modifies

substances

Large Intestine

• AKA colon• Reabsorbs water from

undigested foods• As water is absorbed

the remaining undigested materials remains a solid (feces)

• Feces is eliminated through the rectum