Fat tissue is an energy storage depot for most large mammals . Its main task is to store energy in the form of triglycerides through the process of lipogenesis that occurs in response to excess energy and mobilize energy through the process of lipolysis in response tefhadap energy shortage . In normal circumstances , these two processes strictly regulated . Fat tissue is a connective tissue has the function as a fat storage in the form of triglycerides .
In mammals , fatty tissue found in 2 forms : white adipose tissue and brown adipose tissue . Existence , depending on the number and distribution of species .
White fat tissue has three functions , namely thermal insulation , mechanical bearings , and most importantly as a source of energy . Subcutaneous fatty tissue that lies directly beneath the skin , is retaining heat for the body , because it has a conductivity of 1/3 compared with other tissues depends on the ability to withstand the heat of a thick layer of fat . Fat tissue also coat the inside of organs and acts as a protective organ .
Brown fat tissue serves to retain body heat ( thermogenesis ) . The main function of adipose tissue is for energy storage in the form of triglycerides and release it as free fatty acids and glycerol which is a source of energy derived from fat .
The human body is divided into two interrelated parts , the materials required for energy ( fat and glycogen ) and water .
Actual composition of the human body is much more complex and consists of four kinds of composition :
Atomic composition
From the standpoint of atomic composition , body weight throughout life is an accumulation of 6 main elements , namely : oxygen , carbon , hydrogen , nitrogen , calcium , and phosphorus . Less than 2 % of body weight composed of sulfur , potassium , sodium , chloride , magnesium and 40 other elements that are nonnal present in an amount less than I0 grams .
Molecular composition .
Elements are divided into molecular components that can be grouped into five broad categories , namely : fat , protein , glycogen , water , and minerals . Molecular level is practically often divided into: fat and fat -free mass . Another model is the division according to fat , sof lean tissue , and bone mineral . Molecular composition of cells that compose the basis for the functional .
Cellular composition .
Cellular composition consists of 3 components : cells , extracellular fluid and solid extracellular part . Subdivided cell mass over fat ( molecular components ) and parts of the metabolically active body cell mass . So that in the end will consist of body cell mass , extracellular fluid and solid extracellular .
Network Composition and Organ .
Cells to form tissues and organs , such as adipose tissue , skeletal muscle , bone , skin , heart , and other visceral organs . Tissues and organs will form the human body is a combination of 5 components of the body , namely the atomic , molecular , cellular , tissue , and organ and the body as a whole
Fat tissue morphology and development
Droplets of fat in fat tissue can be shaped unilocular and / or multilokular .
Unilocular cells constitute a large lipid droplets , which will push the cell nucleus to the plasma membrane so that the cell would resemble a ring . Unilocular cells are characteristic of white adipose tissue and have a variety of sizes ranging from 20-200 microns . Mitochondria are mainly found on the outskirts of a thicker cell cytoplasm near the cell nucleus . Cells do not have large fat droplets smaller intracellular organelles . Multilokular cells are generally obtained in brown fat cells contain many smaller droplets .
Fat Distribution Network
Fat accumulation is determined by the balance between fat synthesis ( lipogenesis ) and fat breakdown ( lipolysis - the oxidation of fatty acids ) . In addition to the two factors, other factors that also affect is unknown.
Factors associated with an increased risk of disease is excess visceral fat rather than subcutaneous fat in the body .
Fat metabolism
Understanding of the nutritional , hormonal , and particularly transcriptional regulation of lipogenesis has been growing rapidly . Lipogenesis is stimulated by a high-carbohydrate diet , but also can be inhibited by the presence of polyunsaturated fatty acids and by fasting .
The effect partly mediated by hormones that can inhibit ( such as growth hormone , leptin ) or stimulate ( such as insulin ) lipogenesis .
Sterol regulatory element binding protein - 1 is an important mediator of the pro - labor or anti - lipogenic lipogenic several hormones and nutrients . Another transcription factor associated with lipogenesis is peroxisome proliferator - activated receptor y .
Both of these transcription factors are attractive targets for pharmacological intervention in disorders such as hypertriglyceridemia and obesity
lipogenesis
Lipogenesis should be distinguished from that adipogenesis is a process of differentiation of pre - adipocytes into mature fat cells . Lipogenesis is the process of fat deposition and fatty acid synthesis involves the process and then the synthesis of triglycerides in the liver that occurs in the cytoplasm and mitochondria and regional adipose tissue . Energy derived from fat and exceed the needs of the body are stored in fat tissue . Similarly, the energy derived from carbohydrates and protein derived from food can be stored in fat tissue
Fatty acids , in the form of triglycerides and fatty acids bound to albumin derived from food intake or fat synthesis in the liver
Triglycerides are formed from chylomicrons or lipoproteins will be hydrolyzed into glycerol and free fatty acids by the enzyme lipoprotein lipase ( LPL ), which is formed by adipocytes and secreted into the endothelial cells adjacent to it ( adjacent ) .
LPL activation by apoprotein C - II which was conceived by chylomicrons and lipoprotein ( VLDL ) . Free fatty acids then be taken up by adipocytes cells according to the degree of concentration by a transmembrane transport proteins .
When the free fatty acids into adipocytes already , it forms the fatty acid pool . This pool will contain fatty acids derived from both incoming and going out . ( Figure 1 ) .
Insulin is probably the most important hormonal factor affecting lipogenesis . lnsulin stimulates lipogenesis by increasing glucose uptake in adipose tissue via glucose transporter to the plasma membrane . Insulin also activates lipogenic and glycolytic enzymes through covalent modification ( Figure 2 ) . The effect is achieved by binding of insulin to insulin receptors on the cell surface tyrosine kinase that activates its work and improve downstream effects through tyrosine phosphorylation . Insulin also has long-term effects on lipogenic genes , possibly through the transcription factor Sterol Regulatory Element Binding Protein - 1 ( SREBP - I) ( Figure 2 ) . In addition , SREBP - 1 causes insulin increases
expression and action of the enzyme glucokinase , and as a result , increasing the concentration of glucose metabolites are considered to be a mediator of the effects of glucose on lipogenic gene expression .
Growth hormone ( growth hormone or GH ) dijaringan adipose lipogenesis decrease dramatically , resulting in a significant decrease in fat , and is associated with the addition of muscle mass . The effect is mediated through two pathways :
Growth hormone lowers insulin sensitivity resulting in down - regulation of fatty acid synthetase enzyme expression in adipose tissue . The mechanism is unclear , but GH may affect insulin signaling in the post - receptor level .
GH may decrease lipogenesis by way phosphorylate transcription factors Stat5a and 5b . Loss of Stat5a and 5b in knockout models memperlilhatkan decrease fat accumulation in adipose tissue . The mechanism by which Stat5 protein increases fat storage , still unknown
Leptin is a hormone associated with lipogenesis . Leptin is not only limit the storage of fat by reducing food intake , but also by affecting specific metabolic pathways in adipose and other tissues . Leptin -induced stimulation of glycerol from adipocytes , by stimulating fatty acid oxidation and inhibiting lipogenesis . The latter effect is achieved by down-regulation of gene expression associated with fatty acid and triglyceride synthesis , as described in the micro - anay oligonucleotide analysis .
Negative targets leptin others may SREBP - I, because this transcription factor may play a role in mediating the inhibitory effects of leptin on lipogenic gene expression .
Endocrine or autocrine factors associated with triglyceride synthesis after insulin , GH and leptin are Acylation Stimulating Protein ( ASP ) . ASP is a small peptide with C3adesArg , a product of factors komplernen C3 .
ASP is produced by adipose tissue and the possibility of an autocrine work . Several in vitro studies showed that ISP stimulates the accumulation of triglycerides in adipose cells . The accumulation occurs because there is an increased synthesis of triglycerides and adipose tissue lipolysis decreased at the same time .
Lipolysis .
Lipolysis is a process in which chemical decomposition and release of fat from fat tissue . Where the additional energy required lipolysis is the predominant process for lipogenesis process . Honnone Sensitive Lipase enzymes ( HSL ) will cause the hydrolysis of triglycerides into free fatty acids and glycerol .
The resulting fatty acids will enter into fatty acid pool , which will take place in the process of re - esterification , oxidation or fatty acid beta will be released into the blood circulation to be a substrate for skeletal muscle , cardiac muscle , and liver . Fatty acid will be formed into AIP through the process of oxidation and fatty acid beta will be taken out of the fat tissue through the blood circulation and has become a source of energy for a network that requires .
The hormone insulin will reduce the mobilization of fatty acids from fat tissue triglycerides by inhibiting the enzyme lipase . Mechanism of this inhibition occurs through a process of reduction of cyclic AMP which in turn will inhibit the cyclic AMP -dependent protein kinase . Suppression of lipolysis This will reduce the amount of fatty acids to the liver and peripheral tissues . With the reduction of fatty acids to the liver is reduced keto acid formation . isulin also will stimulate the use of these keto acids by peripheral tissue so it will not happen this acid accumulation in the blood .
Fat tissue as an endocrine gland
Adipocytes were previously known only as a storage triglycerides , now known to secrete several peptides with a variety of work that have some effect as the nature of the endocrine glands . Endocrine cells secrete hormones going for an effect that is located far away ( endocrine effects ) and also has the effect of local ( paracrine ) . Also, it can also have an effect on themselves ( autocrine ) . Experimental studies in animals suggest that hormones and cytokines produced adipocytes have an effect on the central nervous system , liver , muscle , and bone tissues as well as several other organs .
New discovery using genomic and proteomic approaches have identified novel adipocyte secretory factors whose function is not yet clear . Adipose tissue is too little or too much cause metabolic disorders such as insulin resistance . Central obesity is highly correlated with the onset of diabetes , hypertension , and cardiovascular disease .
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