L35: Adipose Tissue & Obesity

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Locule

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small cavity

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Adipose tissue

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usually reserved for large masses (grossly visible) of adipocytes

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Most loose connective tissue contains

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scattered clusters or adipocytes

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Adipocytes remain separated by

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a thin layer of matrix (ground substance & collagen) which includes numerous capillaries

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Adipose tissue comprised of several cell types

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Adipocytes, fibroblasts & preadipocytes, macrophages, epithelial cells

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Types of adipose tissue based on type of adipocytes contained

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White adipose tissue, brown adipose tissue, brown-like adipose tissue

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White Adipose Tissue (WAT)

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most common type of adipocyte - UNILOCULAR or white fat

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Each white fact cell contains

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one main fat droplet (95% of cell) surrounded by thin rim of cytoplasm

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WAT comprised of several cell types

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adipocytes, fibroblasts, preadipocytes, macrophages, epithelial cells

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Functions of WAT

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storage (for reserve E), thermoreg, cushioning (kidneys, behind eyeballs), endocrine & paracrine

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White adipocytes are __ cells

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secretory

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Secretory cells

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release many endocrine & paracrine factors commonly referred to as ADIPOKINES

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Adipokines

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Hormones (adiponectin, leptin, resistin, estrogen), cytokines (TNFa, IL-6)

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Endocrine factors

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allow adipocyte to regulate processes in peripheral tissues (liver) & CNS (hypothalamus)

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Paracrine factors

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impact neighboring adipocytes & other local cell types w/in adipose tissue

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Adipokines affect

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glucose & lipid metabolism, E homeostasis

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Brown adipose tissue

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individual brown fat cells contain numerous small lipid droplets (multilocular adipocytes). Numerous mitoch (confer brown), high rate metabolism

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Function of BAT

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E expenditure (FA oxidation), Thermogenesis: cold, nonshivering & diet induced

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BAT thermogenesis

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BAT store triglycerides w BAT uses for free FA oxidation. E prod during FFA ox released as heat w/o ATP prod. Thermogenic process vital for neonates exposed to cold

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Where do brown adipocytes come from?

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+ skeletal myocytes derive from common precursor cell - Myf5-positive lineage

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White adipocytes & brown adipocyte-LIKE cells

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from Myf5-negative lineage

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Brown adipocyte-LIKE cells

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appear in white fat deposits after adrenergic stimulation

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Who has BAT?

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Babies born with, located mainly around neck & large blood vessels of thorax cavity. Thermogenesis important to provide heat for neonate. Some adults have detectable amts, others lose. Greater prevalence in women, young, normal wt, normal glucose levels

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Essential fat

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Necessary for proper body functions of brain, nerve tissue, bone marrow, heart tissue, cell membranes. Adult male 3% body wt. Adult female 12-15% body wt. In females body fat necessary for reprod.

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Storage fat

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depot for excess E, quantity varies by individual.

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Total body fat recommendation male

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25% (>31% obesity)

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Total body fat recommendation female

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30% (>42% obesity)

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Subcutaneous body fat depot

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70-80% below surface of skin, in abs bw skin & outer ab wall. Less of health risk vs visceral fat, might be protective

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Cellulite (subcutaneous)

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dimpled look in skin due to small compartments that extrude into dermis. Contains glycoproteins that attract water.

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Visceral fat depots

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Inside ab cavity, packed in bw organs (stomach, liver, intestines, kidneys) & in apron of omentum. More related to classic obesity-related pathologies ie heart disease, cancer, stroke

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Ectopic fat

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deposition of triglycerides in non-adipose tissue cells that would typically contain only small amt. Thought to occur when adipose tissue dysfunctional. Impairs cell & organ function, assoc w insulin resistance & type II diabetes

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Adipose tissue dysfunction

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large adipocytes, secreting proinflammatory adipokines

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Generation of ectopic fat

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Excess E --> hyperplasia, hypertrophy & adipose tissue dysfunction --> ectopic fat storage. Unknown mech, potentially stress signals

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Hyperplasia

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inc in # adipocytes. Rate preadipocyte proliferation highest during first year of life & at prepuberty. Slows down during adolescence & remains constant during adult life when wt stable. Sensitive periods of adipose tissue dev. during childhood when adult adipose cell # established. Adult humans may preserve ability to form new adipocytes @ any age out of pool of dormant precursor cells.

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Childhood-onset obesity characterized by

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combo of both fat cell hypertrophy & hyperplasia

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Hypertrophy

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inc in amt of fat in each adipocyte - in adulthood-onset obesity, fat cell hypertrophy seems to be predominant

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Lipoatrophy - WAT size matters

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absence of fat tissue (depots) - severe hypertriglyceridemia. Type II diabetes usually occurs by adolescence.

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Ectopic fat

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lipid-filled liver, bright color of muscle indicative of lipid-filled myocytes

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Gynoid-type obesity (pear shape)

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lower body, fat cells seem to store fat more readily & lose less readily. Pre-menopausal women store adipose tissue preferentially below waist

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Android-type (apple shape)

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abdominal obesity, assoc w greater risk for metabolic disease, chronic inflammation, coagulation. Men tend to accumulate fat in visceral/ abdominal region.

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Prevalence of obesity

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400 mill adults world wide are obese, predicted 700 million by 2015

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Medical complications of obesity

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Pulmonary disease, nonalcoholic fatty liver disease, gall bladder disease, gynecologic abnormalities, osteoarthritis, skin, gout, idiopathic intracranial hypertension, stroke, cataracts, coronary heart disease, diabetes, dyslipidemia, hypertension, severe pancreatitis, cancer, phlebitis

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Medical complications of childhood obesity

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Psychosocial, pulmonary, gastrointestinal, renal, musculoskeletal, neurological, cardiovascular, endocrine

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How many obese adults are metabolically healthy?

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30%. 20-30% of normal wt people have metabolic abnormalities

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Control mech for body wt

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Phys reg of food intake: CNS controlled primarily in hypothalamus, stimuli.

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Theories - why are we so fat?

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Genes explain 25-40% of obesity

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Environmental factors

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food composition, sleep deprivation, maternal environment, gut microbiota, technology, processed foods, toxins, environmental temperature, drugs, personal relationships, emotional stress