Animal Digestion

Gazelle and Python

How do animals get their food?

filter (suspension) feeding substrate feeding

fluid feeding bulk feeding

Eating a balanced diet What happens if an animal’s diet is

missing an essential nutrient? deficiency diseases

scurvy — vitamin C (collagen production) rickets — vitamin D (calcium absorption) blindness — vitamin A (retinol production) anemia — vitamin B12 (energy production)

Digestion System DiversityIntracellular Digestion• food particles

engulfed by phagocytosis

• food vacuoles fuse with lysosomes containing hydrolytic enzymes

• Example: sponges

Extracellular Digestion• the breakdown of food

particles outside of cells

• occurs in compartments that are continuous with the outside of the animal’s body

• Examples: hydra, worms, insects, humans

intracellulardigestion

Digestive System Diversity

Animals, such as hydra, with simple body plans have a single opening pouch called the gastrovascular cavity that functions in both digestion and distribution of nutrients.

extracellulardigestion

Digestive System Diversity

Everybody’s got one!

More complex animals, such as humans, have a digestive tube, the alimentary canal, with two openings, a mouth and an anus.

stomachkills germs break up fooddigest proteinsstore food

small intestinesbreakdown food

- proteins- starch- fats

absorb nutrients

pancreasproduces enzymes to digest proteins & carbs

liverproduces bile

- stored in gall bladderbreak up fats

large intestinesabsorb water

mouthbreak up foodmoisten food digest starchkill germs

Digestive Organ Review

Maintaining Homeostasis

• Interactions between certain organs help to regulate homeostasis.

• Example: • After stomach mechanically breaks

down food, enzymes are produced by the stomach and small intestine to chemically digest them into nutrients.

• These nutrients are absorbed by the small intestine and eventually delivered to cells.

Maintaining Homeostasis: Stomach• Functions

disinfect foodHCl = pH 2

kills bacteriabreaks apart cellsComponents of HCl are

produced by parietal cells

chemical digestionExample: pepsin

enzyme breaks down proteinschief cells secrete pepsinogen

activated by HClBut the stomach is made out of protein!What stops the stomach from digesting itself?

mucus secreted by stomach cells protects stomach lining

Ooooooh!Zymogen!

Maintaining Homeostasis:Small intestine

Function chemical digestion

digestive enzymes absorption through villi & microvilli:

finger-like projections increase surface area for absorption over 6 meters! small intestine has huge surface area = 300m2

(~size of tennis court) most nutrients are absorbed across the

epithelium of the small intestine Structure

3 sections duodenum = most digestion jejunum = absorption of nutrients & water ileum = absorption of nutrients & water

Duodenum

1st section of small intestines acid food from stomach mixes with

digestive juices from accessory glands:

pancreas liver gall bladder

Accessory Organ: Pancreas

Digestive enzymes peptidases

trypsin trypsinogen

chymotrypsin chimotrypsinogen

carboxypeptidase procarboxypeptidase

• pancreatic amylase Buffers

reduces acidity alkaline solution rich in

bicarbonate (HCO3-) buffers acidity of material from

stomach Explain how this is a molecular example of structure-function theme.

Explain how this is a molecular example of structure-function theme.

small intestines

Accessory Organ: Liver Digestive System Functions

produces bile bile contains bile saltso stored in gallbladder until neededo break up and absorb fats in the duodenum

act like detergents to breakup fats

Circulatory System ConnectionCirculatory System Connectionbile contains colors from old red blood cells collected in liver =iron in RBC rusts & makes feces brown

bile contains colors from old red blood cells collected in liver =iron in RBC rusts & makes feces brown

Evolutionary Adaptations of Vertebrate Digestive Systems

specialization in teeth length of digestive system number & size of stomachs

Digesting cellulose How well you digest cellulose

governs life strategy of herbivores

bond between the sugars governs digestibility

starch

cellulose

Cowcan digest cellulose well; no need to eat supplemental sugars

Gorillacan NOT digest cellulose well; must supplement with sugar source, like fruit

Cowcan digest cellulose well; no need to eat supplemental sugars

Gorillacan NOT digest cellulose well; must supplement with sugar source, like fruit

Mutualistic Adaptations

Ruminantsadditional mechanical digestion by chewing food multiple times after mixing it with enzymes

How can cows digest cellulose efficiently? symbiotic bacteria in stomachs help digest cellulose-

rich meals rabbit vs. cow adaptation: eat feces vs. chew cud

ruminantcaprohagy

liver

pancreas

liver

Example: Regulation of Blood Sugar

blood glucose level(90 mg/100 mL blood)

insulin

body cells take

up glucose from blood

liver storesglucose asglycogen

reducesappetite

glucagon

pancreas

liver releasesglucose

triggershunger

high

low

Maintaining Homeostasis through Feedback

Is this a negative or positive feedback

system?

Is this a negative or positive feedback

system?

Homeostatic Imbalance

Diabetes mellitus• caused by a deficiency of insulin or a

decreased response to insulin • marked by elevated blood glucose

levels