how does our digestive system function?

digestive system pathology

Some molluscs exhibit a radula which is like a tongue that's covered in tiny teeth called denticles they use to scrape algae off rocks or drill through the shell of its dinner. 

step 1:
​glycolysis

kerb cycle

      Porifera

     Cnidaria

monomers are used to build polymers...
polymers are broken down into monomers

Some Cnidarians have evolved symbiotic relationships with algae. Coral ecosystems are maintained by these symbiotic associations. Coral is a living cnidarian polyp that builds a limestone structure around itself from calcium minerals, CO2 and H2O. The structure remains after the cnidarian dies so another polyp can move in and add to the structure. These limestone formations become coral reefs.

triglyceride (lipid) = polymer 

gluten intolerance/
​celiac disease

IBS

 glycogenolysis = liberation of glucose from a polysaccharide (glycogen)
 gluconeogenesis = production of glucose from non-glucose sources like amino acids and fats

intestinal polyps

cellular respiration
catabolizes glucose and anabolizes ATP

Cnidarians exhibit cnidocytes with nematocysts on the surface of their tentacles used for capturing prey which is then brought into the gastrovascular cavity (coelenteron) through its single opening.

electron ​ transport chain

Cnidarians perform extracellular digestion. Enzymes released into the gastrovascular cavity break down the food and endoderm cells lining this cavity absorb the nutrients. Cnidarians have an incomplete digestive system with only one opening used as both a mouth and an anus.

Parasitic flatworms called Cestodes (tapeworms) have no digestive tract. they just absorb nutrients from the host across the body wall.

stomach ulcers

ATP produced

         annelids

enzymatic digestion of polymers

Ruminants (sheep/cows etc)
eat a lot (!) of roughage so they have evolved digestive systems that allow them consume tons of cellulose. Ruminants use their lower teeth/tongue/lips (they don't have upper incisors) to tear and chew their food. A ruminant's stomach has 4 chambers and contains microbes that break down and ferment cellulose.
This fermentation results in copious amounts of gas...
Cattle are the No. 1 agricultural source of greenhouse gases worldwide. One cow produces
220 pounds of methane/year. Methane 28X more impactful re global climate change than CO2. Beef (cattle) production accounts for 15% of the world's greenhouse gas emissions.
Maybe eat less cow?? 

Nematodes may feed by inserting a rigid straw like structure called a stylet into their food source and sucking in food.
Others feed by gulping food whole through a mouth opening. They may exhibit rasping or crushing projections that grind their food like teeth. You can tell what a nematode eats by looking at its mouth.
Some nematodes are parasitic. They bore into arthropods and release bacteria that kill their host, allowing the worm to feed on the decaying tissue.
Others cause trichinosis and filariasis. 

2 pyruvates (3C each)
​broken down 
6CO2 produced
H carried to next step

Glucose for cellular respiration comes from sugars and starches you eat AND can be made from other sources when glucose is not available.

lipid metabolism

accessory organs:
the liver

nutrient absorption and processing

Arthropods have a complete digestive system including the foregut which
delivers food into the body, the midgut which releases enzymes to digest and absorb food, and the hindgut which moves waste out of the tract.  The foregut and hindgut are lined with chitin which is molted with the rest of the skeleton. Only the midgut lacks this chitinous lining. The digestive tract varies greatly in structure, depending upon the diet and feeding mode of the animal. Insects exhibit structures called gastric caece which increase the surface area for enzyme secretion. 

 Echinoderms have a relatively simple digestive system with a mouth, stomach, intestine and anus. The mouth is often on the underside and the anus on the topside of the animal. Sea stars have 2 stomachs, the cardiac stomach and the pyloric stomach. They can push the cardiac stomach out of its mouth to engulf prey or to squeeze it between 2 shells. Starfish can force open a bivalve with suction disks on the underside of its body. Then it  secretes enzymes to digest they prey which lets them hunt prey that are much larger than its mouth. 

ATP produced

cirrhosis

digestive adaptations
in the phyla of
​Kingdom Animalia

polymer 

flatworms have a digestive system with only a single opening into the digestive cavity. marine flatworms have digestive cavities that branch into all parts of the body. Flatworms exhibit both extracellular and intracellular digestion.
Enzymes in the gut reduce the size of the food particles then the partially digested material is phagocytized by cells lining the gut. Feeding occurs using a pharynx which is a long, tubular mouthpart that extends from the body, surrounds the food, and sucks it into the gut cavity. 

Hydrogen's  electron completes a  series of redox rx. energy from these reactions
is used to generate ATP.
last reaction is H + O to form water

gut microbiome imbalance

hepatocytes are the cells along the cell plate

 protein digestion releases amino acids including 7 essential aa. All 20 amino acids are used to synthesize new proteins.
​when aas are catabolized, urea is released.

gut/brain connection

 Evolution of  Digestion in Kingdom Animalia

nematodes have a complete digestive systems. food enters through the mouth, is ground down in the pharynx, is digested in the gut, and is eliminated from the anus. A complete system (vs one with only one opening) allows them to take in food, digest food, and eliminate waste all at the same time.

Chordates have a one way digestive system that starts with a mouth and ends with an anus. Digestive organs include a mouth, stomach, intestines, and anus.
The complexity of digestive organs varies among species in the phylum.

movement of monomers into circulation

     chordates

Annelids exhibit a true coelom allowing for more efficient digestion because food can be pushed through the digestive tract by muscles.

 filariasis/elephantiasis 

Porifera are primarily filter feeders.
food particles (primarily microorganisms) floating in the water are captured by the choanocytes. Choanocytes, also called collar cells, generate a water current through the sponge permitting them to trap and ingest tiny food particles via phagocytosis. 

Bivalves exhibit a crystalline style which is a long rod of solidified mucus that
sticks into the stomach from an attached sac. the sac is lined with cilia that cause the style to rotate which winds in a stream of mucus with food stuck in it from the mouth and mixing up the contents of the stomach. 

glucose = monomer 

monomer 

glycerol and fatty acids = monomers 

accessory organs:
​the pancreas

Annelids like earthworms are heterotrophic, ingesting soil containing small invertebrates or dead and decaying organic matter. food enters the mouth, then its pharynx pushes the food into its esophagus then its passed into the gizzard. Their waste is called "casts" which are nutrient rich (nitrogen/phosphorus). 
​Leeches are parasitic annelids, sucking
blood from their host using anterior suckers.​They
secrete hirudin
which prevents
oagulation.

< urinary system

       mollusca

lipogenesis requires
​essential fatty acids

Sponges filter microscopic life and organic debris (detritus) which makes them detrivores. 
Some freshwater sponge may host endosymbionts like photosynthesizing algae and as such benefit from the symbionts photosynthetic efforts.

Carnivorous sponge thrive in the deep sea, capturing passively teensy crustaceans using sticky threads.

Parasitic  sponge attach to shells and coral, bore holes through them and then drain them of nutrients killing the animal. 

one glucose (6C) broken down
2 pyruvates produced (3C each)

Porifera exhibit intracellular digestion. 
Intracellular digestion is exhibited by animals without a digestive tract. Food is brought into the cell via phagocytosis/endocytosis for digestion then the vacuole containing the food fuses with a lysosome containing digestive (hydrolytic) enzymes.
Extracellular digestion is a process in which animals feed by secreting enzymes through the cell membrane onto the food.
With intracellular digestion, only chemical digestion can take place. With extracellular digestion, both chemical and mechanical digestion can occur and the food particle can be larger.

     platyhelminthes

deamination

ATP produced

Birds don't have teeth! Their digestive systems must be able to process unchewed food. Birds exhibit different shaped beaks that correspond to their diet ie insects/seeds/fruit.
Most birds fly so their metabolic rates are really high. They need to process food 
but also remain relatively lightweight. The stomach of a bird has two chambers.
The proventriculus is where gastric juices digest food before it enters the stomach proper and then the gizzard. The gizzard grinds down the food.

crohn's disease

amino acids = monomers 

           nematodes

 choanocyte

starch =  polysaccharide = polymer 

lactose intolerance

     echinoderms

diverticulitis

protein synthesis requires
​essential amino acids

   Mollusca is a highly diverse phylum which includes omnivorous grazers, herbivores, carnivorous scavengers and predators, and parasites. All molluscas exhibit a head, a foot and a visceral mass all covered with a mantle (pallium) that usually secretes the shell.  

The complexity and arrangement of the chordate gut differs. 
Is the animal aquatic? omnivorous? 
Some chordates have a single stomach, while others have multi-chambered stomachs. Birds have developed a digestive system adapted to eating food that isn't chewed. 

       arthropods

Arthropods may be parasites, carnivores, herbivores, detrivores, or filter feeders.  
This phylum usually exhibits paired appendages around the mouth which are
specialized depending on the lifestyle of the animal:
Aphids are adapted for piercing vegetation and sucking out plant juices.
Fiddler crabs use small claws to shovel sand into their mouths where a cluster of
hairs sift out organic matter.
Sand crabs use their antennae to filter plankton.
Tiny Copepods collect diatoms with specialized maxillae.
Spiders have fang like structures that to deliver poison.

 trichinosis 

polypeptide/protein = polymer