PP23 Adipose Tissue Anatomy and Development 1

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PP23Adipose Tissue Anatomy and Development 1

• Chapter 2 pg 15-16
• ANS 3043
• University of Florida
• Dr. Michael J. Fields

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Functions

• Metabolic Energy Substrate
• Fat metabolism increases when nutrient intake is
  restricted
• Energy density is greater than that of
  carbohydrates and proteins (6-8x more energy
  dense than protein)
• Storage Lipids, Vitamins
• Protection of vital organs
• Physical support and insulation
• Maintenance of serum lipids
• Generation of heat Brown aidpose tissue
• Source of hormones

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Anatomical Location

• In order of development
• Visceral
• Perinephric fat surrounding kidneys, pelvis and
  heart (KPH)
• Omental or Mesenteric fat surrounding the GI
  tract
• Subcutaneous external fat under hide
• Intermuscular fat between muscles
• Intramuscular fat within muscle (marbling)
• Specifically with perimysium
• Species differences

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Structure

• Adipocyte fat cell that stores lipid
• Single cell or small groups of fat cells are
  normal constituents of connective tissue
• Adipose Tissue composed mostly of fat cells
  organized into lobules
• Site of fatty acid synthesis
• Also occurs to a limited extent in the liver
• Species dependent

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Structure

• Lobules of fat separated and supported by loose
  connective tissue called septa
• Septa carries blood vessels and nerves to adipose
  tissue
• Connective tissue within fat cells brings fat
  cells in contact with capillaries

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Types

• Brown Adipose
• Extensive vascularity gives it dark color
• Common in
• Neonates
• hibernating animals
• cold adapted animals
• Associated with non-shivering thermogenesis
• Fatty acids converted to HEAT in adipose tissue
• Due to uncoupling protein-1 allows uncoupling
  of oxidation from ATP formation

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Types

• Brown Adipose (cont.)
• For maintenance of body heat from immediately
  after birth to 7-10 days of age in neonates
• Non-functional in adults
• Initiated by arousal of hibernating animals
• Persists throughout the life of a hibernating
  animal

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Brown Adipose
Nucleus
Steroid/Lipid Metabolism
Protein Synthesis
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Brown Adipose in the Bovine
Highly developed mitochondria
L
M
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Types

• White Adipose Tissue
• Predominate fat in the body
• Long term energy storage
• Few cytoplasmic inclusions
• Poorly developed mitochondria

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White Adipose Cell
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White Adipose in the Bovine
L
N
L
Poorly developed mitochondria
Few cytoplasmic inclusions
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Fetal Origin

• Adipoblasts early form of fat cells
• Derived from mesenchymal cells
• Contain no lipogenic enzymes or lipid droplets
• Multiply and differentiate into pre-adipocytes
• Pre-adipocytes (hyperplasia)
• Contain some lipogenic enzymes and few lipid
  droplets
• Cell is destined to become an adipocyte by
  increasing size

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• Adipogenesis - origin, formation and development
  of adipose tissue (Fig 7.3)

Adult Development
Hyperplasia
Hypertrophy
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Fetal Origin

• Adipocyte (hypertrophy)
• Fat containing cell
• Increased lipogenic enzyme activity with
  accumulation of a large single droplet of lipid
• Fat deposition is a result of hypertrophy of
  adipocyte without hyperplasia
• Process is under molecular control
• Adipocyte differentiation is controlled by a
  series of transcriptional events
• May serve as an area to control adipocyte numbers
  in humans and animals

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Fetal and Postnatal Growth

• Fetal
• Preadipocyte hyperplasia is significant
• Ceases once adipoblasts turn into adipocytes
• Increased number of small adipocytes with little
  hypertrophy
• Initiation of vascularization of connective
  tissue associated with adipose

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Fetal and Postnatal Growth

• Postnatal (Fig 7.4 and 7.5)
• Recruitment of new fat cells with age and degree
  of fatness
• Fibroblast cells associated with connective
  tissue presumably differentiate into adipocytes
• Appears to be repeated phases of recruitment of
  fat cells resulting in a bimodal distribution of
  fat cells with increased fatness

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Backfat Increase in Pigs
More Smaller Cells
Larger Cells
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Age and Weight Effects

• As animals age, they fatten
• Recruitment of smaller adipocytes
• Adipocytes swell with fat
• Mean diameter of existing adipocytes increases
  with age and a new population is eventually
  recruited
• Loss of Weight
• Retained number of adipocytes
• Adipocytes shrink in size
• Next weight gain is even larger due to existing
  population of adipocytes and new recruitment

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Diet

• Sufficient energy in the diet causes adipocyte
  hypertrophy
• Increase in diameter and volume of fat cell
• Continued vascularization
• Increase in mass of adipose tissue due to
  increased adipocyte number and size

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Increase Fat
Increased Size Cell Number