Regents Biology

38.2 – Animal Nutrition Human Digestion

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Objectives §  Distinguish intracellular from extracellular digestion §  Examine how the digestive system evolves across the

phyla §  Identify the components of the human digestive system

and discuss their functions §  Explain how “form fits function” by citing specific

examples from the digestive system

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Nutritional Requirements §  Animals are heterotrophs §  need to feed for

-  fuel (for production of ATP) -  raw materials (carbon source for synthesis) -  essential nutrients (stuff animals cannot make) -  elements (N, P, Fe, Na, K, Ca, etc.)

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Animals http://www.youtube.com/watch?

feature=player_embedded&v=wd-QnKlfZHI

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Processing Food §  Cavity -  digest food inside

specialized cells -  nutrients diffuse into

other cells §  Gastrovascular

cavities §  Intracellular digestion

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§  Digestive tracts -  many invertebrates and all

vertebrates -  digest food in a tube -  food moves in 1 direction -  extracellular digestion

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Path of Food §  Specialized structures -  breaks food down 1 step at a time -  no need for eating all the time!

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Mouth §  mechanical digestion -  teeth break up food

§  chemical digestion (saliva) -  amylase digests starch -  mucus protects soft lining of

digestive system -  buffers neutralizes acid to

prevent tooth decay -  anti-bacterial chemicals

kill bacteria that enter mouth with food

All that in spit!

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Swallowing (& not choking)

§ Esophagus -  epiglottis closes trachea (windpipe)

when swallowing -  involuntary muscle contractions to move

food along (peristalsis)

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§  Stomach -  hydrochloric acid -  kills bacteria -  activates pepsin à

digests protein -  no carbohydrate

digestion! Why? -  chyme squirts into

small intestine thru pyloric valve

-  can store ~2 L of food!

Inside the Stomach http://www.youtube.com/watch?

v=-U5JyODRVng

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§  caused by stress? §  most caused by

bacterial infection of stomach (H. pylori bacteria)

§  Treatment?

Ulcers

inflammation of stomach

inflammation of esophagus

Colonized by H. pylori

Free of H. pylori

white blood cells

cytokines

inflammatory proteins (CagA)

cell damaging proteins (VacA)

helper T cells

neutrophil cells

H. pylori

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Small Intestine §  Duodenum -  digestive enzymes enter From pancreas: -  amylase digest

carbohydrates -  trypsin digest proteins -  lipase, bile from liver

digest lipids -  nutrients move into body

cells by diffusion and active transport

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Absorption in Small Intestines §  villi and microvilli (finger-like projections) §  Form fits function?

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Absorption by Small Intestines

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Small Intestine

Ascending Colon

Liver

Gallbladder

Stomach

Descending Colon

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Pancreas, Liver, Gallbladder §  Pancreas produces -  enzymes that

digest all 4 types of biomolecules

-  hormones to regulate blood sugar levels

-  sodium bicarbonate to neutralize stomach acids. Why?

§  liver produces bile to break up fats §  gallbladder only stores bile

Inside the Human Body http://www.youtube.com/

watch?v=hDrxUizBPEI&list=PL76D4

ADE71CF274A1

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§  ~9 L of water is used every day in digestive juices

§  need to reabsorb water! §  > 90% of water reabsorbed! §  not enough water reabsorbed? §  too much water reabsorbed? §  reabsorb by diffusion

Large Intestines (Colon)

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You’ve got company! §  E. coli digests cellulose,

produces vitamins (K and B) §  generate gases (methane,

hydrogen sulfide)

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small intestines §  breakdown food - proteins - starch - fats

§  absorb nutrients

Stomach §  kills germs §  break up food §  digest proteins §  store food

Mouth §  break up food §  digest starch §  kill germs §  moisten food

Pancreas §  produce enzymes §  digest proteins, starch

Liver §  produces bile §  stored in gall bladder §  break up fats

large intestines absorb water

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Appendix

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Rectum §  last section of large intestines §  eliminate what’s left over

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Different diets, different bodies §  adaptations of herbivore vs. carnivore?