Adipose Tissue premed II

FAT CELLS(ADIPOCYTES)

ADIPOSE TISSUE

A Specialty Connective Tissue

• Adipose connective tissue cells are specialized for fat storage and do not form ground substance or fibers.

• On prepared slides, adipose tissue appears somewhat like a fish net with white spaces connected together in a network.

• The cytoplasm and nucleus have been pushed to one side by a single, large, fat-filled vacuole that occupies the center of the cell.

HISTOLOGIC STRUCTURE:Unilocular adipose tissue in isolation is spherical.When they are packed together it is polyhedral.

Since lipid droplets are removed by alcohol and xylol used in routine histologic techniques, each cell appears in standard microscope preparations as a thin ring of cytoplasm sorrounding the vacuole left by the dissolved lipid droplet.--------------SIGNET RING PRESENTATION.

These cells have eccentric and flattened nuclei. The rim of the cytoplasm that remains after removal of the stored triglycerides(neutral fats) may rupture and collapse distorting the tissue structure.

Function of Adipose Tissue

• Largest repository of energy in the body– Triglycerides– 9.3kcal/g

• Contributes to thermal insulation– Important for temperature regulation

• Fills spaces between structures/protects– Between organs– Aids fit of valves in heart– Pads of fat protect heels, palms

How Fat is Used in Adipose Cell

• Fatty acid + glycerol move into cell from capillary.

• Sympathetic stimulation (NE) and Ep from adrenal gland stimulate adipose cell:– Release fatty acid, glycerol– Used as a source of energy

Adipose Dynamics

FFAGlycerol

(insulin)

Glu

capillary

triglyceride

nucleus

Glycerol

FFA

NE

Ep

LIVER

capillary

Fatty acids cross the following layers in order:

In passing from the capillary endothelium into the adipose cell.

(1)Capillary endothelium>>>>>> (2) capillary basal lamina>>>>>(3) connective tissue ground substance>>>>>>(4)adipocyte basal lamina>>>(5) adipocyte plasma membrane.

(2)The movement of FA across the cytoplasm into the lipid droplet is incompletely understood but may utilize specific carrier proteins.

Route of FFA to Adipose Tissue

• Capillary endothelium• Basal lamina• CT ground substance• Adipocyte basal lamina• Adipocyte plasma membrane

Development of Fat Tissue

Differences between uni and multilocular

Colour of brown fat (multilocular fat) is due to:

(1)Large no of blood capillaries in this tissue.

(2) numerous mitochondria (containing coloured cytochromes in the cells).

(3)Multilocular fat compared to unilocular which is present throughout the body, multilocular is limited in its distribution(because it is more abundant in hibernating animals,)it was one time called hibernating gland .

Adipose Tissue

Multilocular(Brown Fat)

Unilocular

Distribution of Adipose Tissue In a human newborn, multilocular adipose tissue constitutes 2—5% of the body weight and is distributed as shown. The black areas indicate multilocular adipose tissue; shaded areas are a mixture of multilocular and unilocular adipose tissue.

Adipose Tissue

Adipose Tissue

Location: Subcutaneous

• hyperplastic and hypertrophic obesity• lipomas

Hypertrophic obesity:Obesity in adults may result from an excessive accumulation of fat in unilocular tissue cells that become larger than usual.

Hyperplastic obesity: an increase in the no of adipocytes causes hyperplastic obesity.More prevalent in child hood obesity.

TUMORS OF ADIPOSE TISSUE:

Unilocular adipocyte can generate very common benign tumors called lipomas.Malignant adipocyte –derived tumors (liposarcomas) are among the more common tumors of connective tumors of the multilocular adipose cells (hibernomas)are relatively rare.