Why did humans start cooking their food? Food historians, archaeologists, and paleontolgists do not have exact an answer due to the age of the evidence.
The apoA-IV gene gene symbol: The gene is composed of only three exons and encodes a protein of 46 kDa, derived from a amino acid precursor protein. Intestinal synthesis of apoA-IV increases in response to ingestion and absorption of fat and it is subsequently incorporated into chylomicrons and delivered to the circulation via the lymphatic system.
Intestinal apoA-IV Following the consumption of fat, the intestinal absorption of the lipid content stimulates the synthesis and secretion of apoA-IV. The increased production of apoA-IV by the small intestine in response to lipid absorption is the result of enhanced transcription of the apoA-IV gene in intestinal enterocytes.
The precise signal for this increase in intestinal transcription is the formation and secretion of chylomicrons. It has been shown that neither digestion, uptake, or the re-esterification of absorbed monoglycerides and fatty acids to form triglyceride is the inducing signal for apoA-IV transcription.
This was conclusively demonstrated in experiments showing that the intestinal absorption of only myristic acid or long-chain fatty acids is sufficient to stimulate the lymphatic transport of both chylomicrons and apoA-IV.
However, it is still unclear whether different types of triglyceride those containing either saturated, monounsaturated, or polyunsaturated fatty acids are equally effective in stimulating the secretion of apoA-IV. Although it is known that chylomicrons serve as the inducing signal for apoA-IV transcription and secretion, the precise mechanism by which the transcriptional enhancement is effected is currently undetermined.
What is known is that an intact vagal innervation from the CNS to the gut is not necessary since vagotomy does not affect intestinal apoA-IV synthesis in response to lipid absorption. Leptin is a peptide synthesized and secreted by adipocytes whose principle effects result in decreased food intake and increased energy expenditure.
The levels of circulating leptin increase in response to the consumption of a high-fat diet and are directly correlated to the amount of fat stored in adipose tissue. The level of apoA-IV transcription has been shown to be reduced within 90 minutes of ingesting a high fat meal and this reduction is a result of increased leptin secretion.
Although numerous studies have demonstrated a negative correlation between leptin levels and apoA-IV expression, the mechanism by which this effect is exerted is not fully understood.
There are leptin receptors in the gut and, therefore, leptin binding to these receptors could lead to direct effects on intestinal enterocytes. Given that circulating leptin levels increase as an individual becomes more obese it is likely that leptin is involved in the attenuation of the intestinal apoA-IV response to lipid ingestion.
Although the initial response to consumption of a high-fat diet is increased plasma apoA-IV levels, this increase disappears over time. This finding makes it tempting to speculate that the autoregulation of apo AIV in response to chronic high fat feeding is related to the elevation of circulating leptin.
Direct infusion of lipid into the ileum results in increased expression of ileal and jejunal apoA-IV, whereas, infusion of lipid into the duodenum only results in increased jejunal apoA-IV expression. These results strongly suggest that a signal is released by the distal gut during active lipid absorption which is capable of stimulating apoA-IV synthesis in the proximal gut.
A strong candidate for this signal is the ileal peptide PYY. To determine if PYY is indeed involved in increased apoA-IV expression experiments were performed in rats involving intravenous injections of physiological doses of PYY.
These experiments showed that PYY infusion does indeed result in significant stimulation of jejunal apoA-IV synthesis and lymphatic transport in fasting animals.
Further experiments demonstrated that the stimulation of jejunal apoA-IV synthesis by PYY is the result of effects on translation of the mRNA as opposed to increased transcription of the gene since the levels of the mRNA were unaltered but synthesis of the protein was markedly stimulated.
Whereas fat absorption-mediated increases in apoA-IV expression do not require vagal innervation, the responses to PYY do involve the vagal nerve. The presence of apoA-IV in the hypothalamus, a site intimately involved in regulating energy homeostasis, suggests that the effects exerted on appetite by apoA-IV may be due to direct hypothalamic synthesis and secretion.
Experiments in rodents, aimed at determining the role of apoA-IV in hypothalamic functions, clearly demonstrated a role for this apolipoprotein in feeding behaviors.
Blocking apoA-IV actions by central injection of antibodies to the protein results in increased food consumption, even during the light phase when rodents normally do not eat. Additional studies have shown that apoA-IV is involved in inhibiting food intake following the ingestion of fat.
Infusion of lymph fluid that contains chylomicrons results in markedly suppressed food intake during the first 30 min of administration. However, it is not the lipid content of the chylomicrons that is responsible for the suppression of food intake since infusion of a mixture of triglycerides and phospholipids does not exert the same effect.
If apoA-IV is removed from chylomicrons prior to infusion, via the use of specific antibodies, there is no observed effect on food intake. If apoA-IV itself is infused, the level of suppression of food intake is the same as that seen with infusion of fatty lymph fluid containing chylomicrons. The plasma levels of apoA-IV in humans adapt in response to prolonged consumption of fat.
Chronic consumption of a high-fat diet initially results in significantly elevated plasma apoA-IV levels. However, the increased level disappears over time. Conversely, on a low-fat diet, intestinal apoA-IV gene expression is sensitive to fasting and lipid feeding, being low during fasting and high during lipid absorption.This guide serves to provide both a guided, extended reading list on analyzing social inequality (or stratification) and the syllabus for a graduate course based on the core of this extended reading list (over articles are included below).
I can understand phrases and the highest frequency vocabulary related to areas of most immediate personal relevance (e.g. very basic personal and family information, shopping, local area, employment).
Ever since he related the exploits of his journey to the empire of the great khan in the late thirteenth century, Marco Polo and his stories have been the subjects of speculation, fascination, and skepticism. Medieval fare. The study of Medieval culture and cuisine is a complicated and facinating topic.
There is plenty of information available, from comprehensive academic sources to simple children's books. Marco Polo changed the world by writing a book about his travels from Venice to the court of Kublai Khan in China. His account of his journeys inspired other adventurers, such as the explorer Christopher Columbus, who always carried a copy of Polo's book.
Maps he brought back helped to develop. Marco is also very important to the play as he is very respectful towards Eddie to begin with. Marco is willing to do any work to support his family as he is very proud of his wife and he is grateful to Eddie for his help and for giving him the opportunity to live in his home and work down the docks.