Digestion

Types of Ingestion

Fluid Feeding: suck nutrients through liquid of a living host, eg mosquitos and ticks (doesn't have to be blood)

Substrate Feeding: animal lives on or in food, eg caterpillars and worms

Bulk Feeding: eat relatively large pieces of food, longer processes to break down food

Filter Feeding: animals that strain food from their surroundings (very basal animals)

4 Basic Steps of Food Processing

Absorption

Digestion (mechanical and chemical)

Elimination (excretion)

Ingestion

Digestive Compartments

Extracellular

Intracellular

food vacuoles fuse with lysosomes--> brings food into contact with hydrolytic enzymes, allows digestion to occur safely within a compartment

Hydrolysis of food happens when cell engulfs food particle by phagocytosis or pinocytosis (liquids)

Very few animals (such as sponges) digest all food this way

Food vacuoles are the simplest digestive compartments

Alimentary Canal

Gastrovascular Cavity

Have to eat simple (easy to break down) food

Simple animals with simple body plans/adaptations

Single opening for both ingestion and excretion

Digestion and distribution of nutrients from same location

specific compartments for digestion, storage, and absorption

2 openings, one for ingestion and one for excretion

carried out in stepwise fashion--> can ingest food while other food is still being digested or absorbed

Complete digestive tract

Human Digestion

Small Intestine

Stomach

Large Intestine

Oral Cavity (mouth)

saliva aids chemical digestion:

food moves down pharynx and esophagus towards stomach

chewing is the first stage of mechanical digestion

enzyme amylase breaks down carbs

protects mouth against abrasions, neutralizes acids, contain antimicrobial properties

first stage of chem digestion

Churns to aid digestion--> liquid churned called chyme

Why doesn't HCl Acid digest stomach itself?

Gastric juices--> first major stage of chemical digestion

Pepsin breaks peptide bonds of proteins

HCl denatures proteins

various structures in place to prevent this: gastric inactive until released into lumen, mucus from gastric glands protect stomach lining, stomach gets a new layer of epithelial cells every 3 days, sphincters on both ends of stomach restrict gastric juices to just the stomach cavity

Trick question--> It does!

Duodenum

Jejunum and ileum

Small in diameter but long in length, ~6m or 25 ft!

chemical digestion is largely completed here

Digestive juices come from pancreas (alkaline neutralizes stomach acid), liver (makes bile to digest lipids), and gallbladder (stores bile)

First leg of small intestine leads from stomach

Fats are hydrolyzed, recombined into triglycerides, and travel to lymphatic system, then to heart. If needed in body, go to heart to be distributed out

Capillaries and veins transport nutrients to liver for regulation/conversion, and then to heart

Beginning of water recovery

Villi and microvilli increase surface area

liver decides when/where nutrients are released

also makes sure toxins are not released back into body

Rectum--> storage of waste

Colon--> reabsorption of water completed

Anus--> excretion of waste

Cecum--> used for fermentation. Not large in humans but large in herbivores

longest transit time for digestion--> 12-24 hours

bacteria that can digest cellulose, can produce vitamins, improve immune function

Digestion differs with diet

Herbivores have a large cecum relative to carnivores because they need bacteria to help digest plant material

Different combination of teeth for different food sources

Carnivores: sharp for tearing

Different sized digestive tracts also relate to diet

Herbivores: dull for grinding