lipgenesis

generally what is lipogenesis

adipose tissue hypertrophy

lipogenesis hypertrophy

triglyceride accumulation in adipocytes

depending on developmental stage, triglycerides can form into…

multilocular or unilocular droplets

2 stages of lipogenesis

1. synthesis: creation of FA chains

2. esterification: FA stuck to glycerol backbone

triglycerides are too…

big to pass between endothelium of blood vessel walls to leave circulatory system and entire adipocytes

bird lipogenesis

most lipogenesis occurs in liver

• adipocytes mainly for triglyceride storage- not insulation, protection, or heat

mammal lipogenesis

• most lipogenesis occurs within adipocytes

• some occurs in liver

in monogastrics…

most fatty acids derived directly from diet

what are the 2 sources of fatty acids

1. TG from diet via circulatory system

2. adipocytes can synthesize FAs= de novo synthesis

TG from diet through..

• directly from small intestine - mammals

• indirectly through liver - birds and somewhat mammals

de novo synthesis from…

• from glucose in monogastrics

• from acetate in ruminants

adipose tissue depots develop roughly in what order

1. visceral

2. subcutaneous

3. intermuscular

4. intramuscular

visceral depot

visceral fat specific to organ

mesenteric visceral fat

associated with intestines

abdominal/omentum visceral fat

thin sheet overlying stomach and nearby organs

• caul or lace fat

perirenal visceral fat

associated with kidneys

leaf fat visceral fat

• mammals: thoracic cavity and ribs

• poultry: abdominal fat pad overlying intestines

subcutaneous depot

fat ‘membrane’ under skin

3 layers of subcutaneous depot

1. outer - insulation

2. middle - thickest; metabolically active

3. inner- thinnest

• in lean animals, may not be present

most abundant depot in pigs

intermuscular depot

around and between groups of muscles

intermuscular depot is associated with…

epimysium

• seam fat

  • most abundant fat depot in sheep and cattle

  • typically what consumers trim off

intramuscular depot

within muscle

• associated with perimysium

• marbling with meat cuts

adipose tissue homeostasis

dynamic metabolic response to nutritional status, activity level, stress, ambient temperatures

• requires shifting between lipogenesis and lipolysis

brown fat

brown adipocytes

• more and larger mitochondria than white

• express special protein that uncouples oxidation from ATP formation → release heat

brown fat is important for…

survival during neonatal period for many species

• NOT pigs or birds

brown fat is present..

in much lower proportions in adults