the digestion of fat primarily occurs in the small intestine.
where does the digestion of fat primarily occur?
small intestine
digestion of some fats can begin in the mouth where lingual lipase breaks down some short chain lipids into diglycerides. however fats are mainly digested in the small intestine. the presence of fat in the small intestine produces hormones that stimulate the release of pancreatic lipase from the pancreas and bile from the liver which helps in the emulsification of fats for absorption of fatty acids. complete digestion of one molecule of fat (a triglyceride) results a mixture of fatty acids, mono- and di-glycerides, as well as some undigested triglycerides, but no free glycerol molecules.





















































section::::breakdown into nutrients.:carbohydrate digestion.
digestion
the transfer of nitrogen and carbon as discussed above readily occurs through live pelotons, but it has been observed by kuga 2014 and rasumussen 2009 that large amount of carbon and nitrogen may also be taken up by the plant during the senescence and digestion of fungal pelotons. this process is called mycophagy. lysis of pelotons begins between 30 and 40 hours after contact and initial peloton formation within the majority of observed orchid plants. as mentioned above as pelotons are formed they are covered by a plant derived membrane, which eventually takes on the properties of endoplasmic reticulum surrounded by golgi apparatuses. the presence of these organelles is indicative of their purpose, which is thought to be the excretion of digestive enzymes into the interficial space between the peloton and the plant membrane to digest the fungal cells. once the fate of the peloton is decided, and degradation and digestion are to occur, a secondary membrane forms around the fungal peloton which is essentially a large vacuole which will allow the isolated degradation of the peloton. additionally peroxisomes accumulate within the digestive plant cells and undergo exosytosis into the newly formed vacuole, this process concentrates a plethora of enzymes such as uricases, chitinases, peptidases, oxidases and catalses within the vacuole facilitating the breakdown of the peloton. once degraded the fungal remnants are absorbed into the plant, transferring the nutrients and energy to the plant host. stable isotope imaging reveals that c13 and n15 applied to mycorrhizal hyphea webs was found to be readily transferred to the plant via fungal pelotons, leading to a disproportionate amount of these isotopes within the peloton containing plant cells and the peloton itself, but in senescencing pelotons the concentrations of these c13 and n15 containing compound was even more pronounced, and significantly higher than in live pelotons. this indicates that as plant pelotons start to senescence they are loaded with carbon and nitrogen nutritive compounds, hypothetically to be transferred to the plant during lysis. morphological changes in the hyphea further support this proposition, in that the last morphological change in the peloton before is collapses is a swelling, perhaps due to the increased nutritive compound load. once digestion is complete, reinfection of the digestive cell will occur shortly after and a new peloton will form, and eventually will be degraded. reinfection and digestion are a continuum and will cyclically occur throughout the entire life span of the cooperation. rasmussen 2009 differentiates two types of plant host cells which are involved in nutrient transfer, so called 'digestion cells' and so called 'host cells', 'digestive cells' apparently engage in dense hyphal peloton formation followed by a rapid digestion and subsequent reinfection, where as 'host cells' contain live hyphae pelotons, which will not be digested, or at least not as readily. rasmussen 2002 discusses an additional mode of nutrient transfer called pytophagy involving lysis of fungal cells but instead of lysing the entire fungal hyphae only the growing end is degraded releasing the contents of the fungal cytoplasm into the interfacial space between the plant and fungi membranes, where the plant can uptake the necessary compounds. there is little information on this mode of nutrient transfer and it is still speculative, and more research is needed.
orchid mycorrhiza