{{more citations needed, date=December 2022 Fat globules (also known as mature lipid droplets) are individual pieces of intracellular fat in human

cell biology Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living an ...

. The lipid droplet's function is to store energy for the organism's body and is found in every type of adipocytes. They can consist of a

vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

droplet A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the end of a tube or other surface boundary, producing a hanging drop called a pendant drop. Dro ...

triglyceride A triglyceride (from '' tri-'' and '' glyceride''; also TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids. Triglycerides are the main constituents of body fat in humans and other vertebrates ...

, or any other

blood lipid Blood lipids (or blood fats) are lipids in the blood, either free or bound to other molecules. They are mostly transported in a phospholipid capsule, and the type of protein embedded in this outer shell determines the fate of the particle and its ...

, as opposed to fat cells in between other cells in an

organ Organ and organs may refer to: Biology * Organ (biology), a group of tissues organized to serve a common function * Organ system, a collection of organs that function together to carry out specific functions within the body. Musical instruments ...

. They contain a hydrophobic core and are encased in a

phospholipid Phospholipids are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...

monolayer membrane. Due to their hydrophobic nature, lipids and lipid digestive derivatives must be transported in the globular form within the cell, blood, and tissue spaces. The formation of a fat globule starts within the membrane bilayer of the

endoplasmic reticulum The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryote, eukaryotic cell, and has many other important functions such as protein folding. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for ...

. It starts as a bud and detaches from the ER membrane to join other droplets. After the droplets fuse, a mature droplet (full-fledged globule) is formed and can then partake in neutral lipid synthesis or

lipolysis Lipolysis is the metabolic pathway through which lipid triglycerides are hydrolysis, hydrolyzed into a glycerol and free fatty acids. It is used to mobilize stored energy during fasting or exercise, and usually occurs in Adipose tissue, fat adip ...

. Globules of fat are emulsified in the

duodenum The duodenum is the first section of the small intestine in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest p ...

into smaller droplets by

bile salts Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver in peroxisomes. Bile acids are conjugated with taurine or glycine residues to give anions called bile ...

during food digestion, speeding up the rate of digestion by the enzyme

lipase In biochemistry, lipase ( ) refers to a class of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; howe ...

at a later point in digestion. Bile salts possess

detergent A detergent is a surfactant or a mixture of surfactants with Cleanliness, cleansing properties when in Concentration, dilute Solution (chemistry), solutions. There are a large variety of detergents. A common family is the alkylbenzene sulfonate ...

properties that allow them to

emulsify An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Although ...

fat globules into smaller emulsion droplets, and then into even smaller

micelles A micelle () or micella () ( or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated colloidal system). ...

. This increases the surface area for lipid-hydrolyzing enzymes to act on the fats. Micelles are roughly 200 times smaller than fat emulsion droplets, allowing them to facilitate the transport of

monoglycerides Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two differe ...

and fatty acids across the surface of the

enterocyte Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells which line the inner surface of the small and large intestines. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase ...

, where absorption occurs. Milk fat globules (MFGs) are another form of intracellular fat found in the

mammary gland A mammary gland is an exocrine gland that produces milk in humans and other mammals. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in primates (for example, human ...

s of female mammals. Their function is to provide enriching

glycoprotein Glycoproteins are proteins which contain oligosaccharide (sugar) chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known a ...

s from the female to their offspring. They are formed in the endoplasmic reticulum found in the mammary epithelial lactating cell. The globules are made up of

triacylglycerols A triglyceride (from '' tri-'' and '' glyceride''; also TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids. Triglycerides are the main constituents of body fat in humans and other vertebrates a ...

encased in cellular membranes and proteins like

adipophilin Adipose differentiation-related protein, also known as perilipin 2, ADRP or adipophilin, is a protein which belongs to the perilipin (PAT) family of cytoplasmic lipid droplet (CLD)–binding proteins. In humans it is encoded by the ''ADFP'' gene. ...

and TIP 47. The proteins are spread throughout the ER membrane and fuse with the droplets before they are released from the ER. The ER releases the droplets into the

cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...

of the mammary epithelial lactating cell. While in the cytosol, proteins and polar lipids will coat the droplets and form various sizes of globules. MFGs can exist in various diameters ranging from 1 μm- 8 μm and even higher on rare occasions.

Bibliography

* Barisch, Caroline; Soldati, Thierry (2017-10-01). "Breaking fat! How mycobacteria and other intracellular pathogens manipulate host lipid droplets". Biochimie. Microbe and Host Lipids Gerli Meeting. 141: 54–61. doi:10.1016/j.biochi.2017.06.001. ISSN 0300-9084. * Heid, Hans W.; Keenan, Thomas W. (2005-03). "Intracellular origin and secretion of milk fat globules": 245–58. European Journal of Cell Biology. * Martini, Mina; Salari, Federica; Altomonte, Iolanda (2016-05-18). "The Macrostructure of Milk Lipids: The Fat Globules". Critical Reviews in Food Science and Nutrition. 56 (7): 1209–1221. doi:10.1080/10408398.2012.758626. ISSN 1040-8398. PMID 24915408. Cell biology

See also

Bibliography