This document summarizes key aspects of panniculus, or subcutaneous fat. It discusses the structure and functions of adipose tissue, including its role in insulation, energy storage, and as an endocrine organ. The embryological development of brown and white fat is described. Histologically, adipocytes have a signet ring appearance with a large lipid vacuole displacing the nucleus. Adipose tissue is highly vascularized and innervated. The processes of adipogenesis and lipogenesis are outlined. Fat deposits in various internal organs in addition to subcutaneous fat. Adipose tissue secretes hormones like adiponectin and leptin that regulate metabolism and energy homeostasis.
2. Introduction
Occurs almost universally over the body
surface, between the skin and deep fascia
Absent from eyelids and male genitalia
It varies in thickness with the race, age,
sex, endocrine and nutrtional status
In a normal person, fat constitutes 10% of
body weight
3. Functions
Acts as an insulating layer
Protective cushion
Thermogenesis
Store of readily available energy
Major endocrine organ
Provides support and has cosmetic function
(contours of face)
4. Embryology
Pre – adipocyte appears in the mesenchyme at 14th
week of fetal life
Pre – adipocyte terminally differentiate into either
brown adipocyte or white adipocyte
Development of brown fat begins at the 20th week
of gestation, reaches maximum at birth
5. Brown fat
It is multilocular and metabolically
very active with many mitochondria
Surrounded by a greater capillary network than
white fat ( partly responsible for the brown
colour), such that heat can be rapidly tranferred
into the circulation
Most prominent in neck and upper thorax of fetus
Adults have supraclavicular areas of brown fat
6. Histology of adipocytes
Have a diameter upto 100 microns
Mature fat cell has a characteristic signet ring
appearance, because the oval nucleus is displaced to a
side by a single, large, intracellular, fat containing
vacuole, which is surrounded by perilipin
7. Arranged in lobules, which are separated by
interlobular septa
Each lobule consists adipocytes, stromavascular
tissue being macrophages, fibroblasts, mast cells,
pericytes, endothelial cells and pre-adipocytes
8. Blood, nerve and lymph supply
BLOOD - Fat tissue has an abundant blood supply, each
lobule being supplied by a terminal arteriole running
along the septa
Then breaks up to form capillaries
LYMPH - Also contains a rich lymphatic plexus
These lymph vessels penetrate deep fascia and drain
into regional lymph nodes
NERVE - Innervated by noradrenergic fibres of
sympathetic nervous system and para sympathetic
fibres
9. Adipogenesis
It refers to the recruitment from multipotent
stem cells in the mesenchyme and stromavascular
tissue, and proliferation of pre adipocytes
followed by their differentiation into mature fat
cells
-Glucocorticoids -
growth hormone and
-insulin, stimulate cells to terminally
differentiate, but after a certain size, growth
occurs through hyperplasia rather than
hypertrophy
10. Energy homeostasis
Catabolism and anabolism of fat depends on
-nourishment, endocrine and nervous activity
Insulin inhibits hydrolysis and breakdown of
triglycerides, conserving the energy store
Adipose tissue in vitro has a metabolic rate similar
to a kidney and half that of liver
13. Fat as an organ
Apart from the subcutaneous fat,
20% of fat tissue occurs internally,
in mediastinal and retroperitoneal
tissues, mesentry, marrow and
other individual organs including
blood vessels
In view of the recent obesity
epidemic, increase in the upper
body and visceral fat are
associated with an increase
cardiovascular and metabolic risks
15. Adiponectin
Protein with structural similarity to collagen and C1q
Has autocrine/paracrine effects locally and endocrine
effects distally
Promotes pre adipocytes to become mature fat cells
with increase in size
Serum adiponectin levels are lower with weight gain
and higher with weight loss
Also exerts anti inflammatory properties
16. Leptin
Adipokine involved in energy homeostasis
Structural homology similar to other
cytokine proteinssuch as TNF alpha and IL-6
Exerts main effect via satiety centres