CHAPTER 6: ADIPOSE TISSUE Flashcards
Connective tissue in which fat-storing cells or adipocytes.
typically found isolated or in small groups within loose or dense irregular connective tissue
Adipose Tissue
normally represents 15%-20% of the body weight in men, somewhat more in women.
Adipose Tissue
serving as storage depots for neutral fats, chiefly triglycerides (long-chain fatty acyl esters of glycerol), adipocytes function as key regulators of the body’s overall energy metabolism.
Adipose Tissue
(long-chain fatty acyl esters of glycerol)
triglycerides
specialize in concentrating triglycerides as lipid droplet(s), with other cells normally accumulating relatively little lipid.
Adipocytes
active cells metabolically, responding to both nervous and hormonal stimuli. They release hormones and various other important substances.
Adipocytes
Dominate connective tissue o found isolated or in small groups within loose or dense irregular connective tissue o active cells metabolically, responding to both nervous and hormonal stimuli. o release hormones and various other important substances and adipose tissue is now recognized as an endocrine organ at the center of nutritional homeostasis.
Adipocytes
2 TYPES OF TISSUE
White Adipose Tissue
Brown Adipose Tissue
common type specialized for fat storage, consists of cells each containing one large cytoplasmic droplet of whitish-yellow fat.
White Adipose Tissue
contains cells with multiple lipid droplets interspersed among abundant mitochondria, which helps give this tissue a darker appearance.
Brown adipose tissue
release heat and function to warm the blood.
Brown adipose tissue
Specialized for relatively long-term energy storage, adipocytes of white adipose tissue are spherical when isolated but are polyhedral when closely packed in situ.
WHITE ADIPOSE TISSUE
When completely developed, a white adipocyte is very large, between 50 and 150 μm in diameter, and contains a single huge droplet of lipid filling almost the entire cell.
WHITE ADIPOSE TISSUE
the single large droplet of triglycerides, white adipocytes are also called unilocular
White Adipocytes
the lipid is removed from cells by _____
XYLENE
adipocytes are often empty in standard light microscopy
UNILOCULAR
have a signet-ring appearance, with the lipid droplet displacing and flattening the nucleus against the cell membrane
White Adipocytes
produces hormone called _____ or “satiety factor” with target cells in the hypothalamus, o can store triglycerides
LEPTIN
triglycerides derived from three sources:
- Dietary fats brought to the cells via the circulation as chylomicrons
- Lipids synthesized in the liver and transported in blood with very low-density lipoproteins (VLDLs)
- Free fatty acids and glycerol synthesized by the adipocytes.
generate benign tumors called lipomas that are relatively common, although malignant adipose tumors (liposarcomas) occur infrequently. Fetal lipomas of brown fat are sometimes called hibernomas.
Unilocar Adipocytes
generate benign tumors called ____
lipomas
malignant adipose tumors
liposarcomas
Fetal lipomas of brown fat are sometimes called ___
HIBERNOMAS
Most _________ in a white adipocyte are near the peripheral nucleus, including mitochondria, a small Golgi apparatus, a few cisternae of RER, and free polyribosomes.
cytoplasmic organelles
peripheral nucleus, including ______
mitochondria, a small Golgi apparatus
The thin, submembranous layer of cytoplasm surrounding the lipid droplet contains ________________
cisternae of smooth ER (SER) and pinocytotic vesicles.
form a fine interwoven network that supports individual fat cells and binds them together
Reticular fibers
between adipocytes may not always be apparent in tissue sections.
microvasculature
The distribution of _____________ changes significantly through childhood and adult life and is partly regulated by sex hormones controlling adipose deposition in the breasts and thighs.
white adipose tissue
( (Gr. chylos, juice + micros, small)
are particles of variable size, up to 1200 nm in diameter.
Chylomicrons
formed from ingested lipids in epithelial cells lining the small intestine and transported in the blood and lymph.
Chylomicrons
They consist of a core containing mainly triglycerides, surrounded by a stabilizing monolayer of phospholipids, cholesterol, and several apolipoproteins.
Chylomicrons
Very Low Density Lipoprotein (VLDL)
smaller complexes (30-80 nm, providing a greater surface-to-volume ratio), of similar lipid and protein composition to chylomicrons, but are synthesized from lipids in liver cells.
Very Low Density Lipoprotein (VLDL)
In adipose tissue both _____________ are hydrolyzed at the luminal surfaces of blood capillaries by lipoprotein lipase, an enzyme synthesized by the adipocytes and transferred to the capillary cell membrane.
chylomicrons and VLDLs
Levels of circulating lipoproteins are routinely measured in clinical tests for blood lipids, after fasting to allow depletion of chylomicrons. Varying levels of apoproteins and triglycerides in the complexes allow their categorization according to density, from VLDL to high-density lipoprotein (HDL).
Very Low Density Lipoprotein (VLDL)
stimulates glucose uptake by adipocytes and accelerates its conversion into triglycerides, and the production of lipoprotein lipase.
Insulin
released in the adrenal gland and by postganglionic sympathetic nerves in adipose tissue activates a hormone-sensitive lipase that breaks down triglycerides at the surface of the stored lipid droplets.
Norepinephrine
Scientific name for LEPTIN
16KDA polypeptide hormone
a “satiety factor” with target cells in the hypothalamus, other brain regions, and peripheral organs, which helps regulate the appetite under normal conditions and participates in regulating the formation of new adipose tissue.
LEPTIN
are transported by blood and lymph from the intestine and liver in lipoprotein complexes known as chylomicrons (Chylo) and VLDLs.
Triglycerides
In the capillary endothelial cells of adipose tissue, these complexes are partly broken down by _____________, releasing free fatty acids and glycerol. The free fatty acids diffuse from the capillary into the adipocyte, where they are reesterified to glycerol phosphate, forming triglycerides that are stored in the lipid droplet until needed.
lipoprotein lipase
stimulates the cyclic AMP (cAMP) system, which activates hormone-sensitive lipase to hydrolyze the stored triglycerides to free fatty acids and glycerol.
Norepinephrine
Although______________ associated with different organs appears histologically similar, differences in gene expression have been noted between visceral deposits (in the abdomen) and subcutaneous deposits of white fat. Such differences may be important in the medical risks of obesity; it is well established that increased visceral adipose tissue raises the risk of diabetes and cardiovascular disease, whereas increased subcutaneous fat does not.
white adipose tissue
differentiate as progenitor cells for all types of connective tissue, including preadipocytes.
Mesenchymal stem cells
developing within the lateral mesoderm of the embryo produce large number of white adipocytes (forming white adipose tissue) and a smaller number of so-called beige adipocytes with cytological features and gene expression patterns of both white and brown adipocytes.
Preadipocytes
are unilocular, with one large lipid droplet occupying most of the cytoplasm. The white adipocyte is usually much larger than that shown here in relation to the other cell types.
White Adipocytes
differentiate from another population of preadipocytes located in paraxial embryonic mesoderm and remain multilocular (having many small lipid droplets) with numerous mitochondria (not shown here).
Brown Adipocytes
Brown Adipocytes
differentiate from another population of preadipocytes located in ___________________and remain multilocular (having many small lipid droplets) with numerous mitochondria (not shown here).
paraxial embryonic mesoderm
Preadipocytes
developing within the _________ of the embryo
lateral mesoderm
contains cells with multiple lipid droplets interspersed among abundant mitochondria, o develops from mesenchyme.
BROWN ADIPOSE TISS
contains brown adipocyte which release heat and function to warm the blood.
BROWN ADIPOSE TISSUE
surrounded by a thin external lamina containing type IV collagen
BROWN ADIPOSE TISSUE
constitutes 2%-5% of the newborn body weight, located mainly in the back, neck, and shoulders, but it is greatly reduced during childhood and adolescence.
BROWN ADIPOSE TISSUE
BROWN ADIPOSE TISSUE
found only in scattered areas, especially around the kidneys, adrenal glands, aorta, and mediastinum. (adults)
greatly reduced during childhood and adolescence o color is due to both the very abundant mitochondria (containing cytochrome pigment) scattered among the lipid o amount is maximal relative to body weight at birth
BROWN ADIPOSE TISSUE
very abundant mitochondria (containing ________ pigment)
cytochrome
contain many small lipid inclusions and are therefore called multilocular
Brown Adipocytes
Brown Adipocytes
contain many small lipid inclusions and are therefore called _______
multilocular
small lipid droplets, abundant mitochondria, and rich vasculature
Brown Adipocytes
often closely packed around large capillaries
produce heat by nonshivering thermogenesis
number increases during cold adaptation
Brown Adipocytes
often closely packed around large capillaries
produce heat by nonshivering _______
thermogenesis
are slightly smaller and characteristically contain many small lipid droplets and central spherical nuclei. If the lipid has been dissolved from the cells, as shown here, the many mitochondria among the lipid spaces are retained and can be easily discerned.
Brown Adipocytes
emerge earlier than white fat during fetal development.
Brown adipocytes
ending that releases norepinephrine to stimulate mitochondrial production of heat, the principal function of brown adipose tissue.
sympathetic nerve
The physiology of brown fat is best understood from studies of the tissue in hibernating species.
BROWN ADIPOCYTES
As in white fat, this neurotransmitter activates the hormone-sensitive lipase of adipocytes, promoting hydrolysis of triglycerides to fatty acids and glycerol.
BROWN ADIPOCYTES
Liberated fatty acids of multilocular adipocytes are not released but are quickly metabolized, with a consequent increase in O2 consumption and heat production. This raises the temperature within the tissue and warms the locally circulating blood, which then distributes the heat throughout the body
BROWN ADIPOCYTES
- White adipocytes are derived developmentally from what precursor cells?
c. Mesenchymal cells
- What are the relatively large particles formed in the intestinal epithelial cells and rich in ingested lipids?
b. Chylomicrons
3.What substance, released from the adrenal gland and some autonomic neurons, increases lipolytic activity in white adipocytes?
c. Norepinephrine
- What is the most important form of lipid storage in both white and brown adipocytes?
e. Triglycerides
- Important target cells of leptin are found in which organ?
d. Hypothalamus
- The hormone-sensitive lipase in the cells of adipose tissue acts primarily on what substrate?
d. Triglycerides
- Applied to adipocytes, the term “multilocular” refers to which of the following?
a. The large number of small cytoplasmic lipid droplets
- Fully differentiated white adipocytes are large cells, typically having diameters of approximately what size?
c. 100 μm
