Adipose Tissue Anatomy/Histology

what percentage of body weight in a healthy individual is white adipose tissue?

10%

where do you want white adipose tissue, generally speaking?

subcutaneous

What is the development of brown adipocytes?

- In paraxial mesoderm, skeletal myogenic progenitor stem cell differentiates to become a preadipocyte - Similar to the white adipocyte, the early brown lipoblast cell accumulates lipid droplets as multiple, individual droplets - Unlike the white adipocyte, the brown adipocyte remains multilocular

What is the histo of brown adipose?

- abundant mitochondria, gives brown color - small lipid inclusions, multilocular - smaller ad more central nucleus - richly vascularized

What are the uses of triglycerides?

- added to adipose when food intake exceeds energy expenditure - outlined to produce energy/heat when energy expenditure exceeds food intake

What is the 3rd type of adipocyte?

- beige adipocytes - under basal conditions expresses markers similar to white adipose, but under sympathetic stimulation and/or cold expresses UCP-1 - located in subcutaneous depots of white adipose tissue

How can you treat leptin deficiency?

- effective treatment for mongenic leptin deficiency causes of obesity - not effective for more complex forms of obesity

What is transdifferentiation of adipocytes in animals?

- exposure to cold temps white adipose being converted to brown adipose to generate body heat - positive energy balance, brown adipose can transform into white to increase triglyceride storage

What happens when leptin is secreted?

- inhibits insulin secretion from pancreatic beta cells - in leptin-resistant overweight individuals, leptin doesn't inhibit insulin secretion, resulting in hypersecretion of insulin and hypersecretion of leptin

What is adipose tissue?

- loose CT composed of lipid-filled cells that are surrounded by collagen fibers, blood vessels, fibroblasts, and immune cells - has endo fxn and is now recognized as the largest endocrine organ in the body

What is leptin?

- peptide hormone secreted in a circadian rhythm manner by white adipose (but also skeletal muscle, intestine, brain, joints, and bone) - Functions as circulating satiety factor limiting food intake, stimulates metabolic rate, stimulates weight loss.

What happens in the development of the lateral mesoderm?

- perivascular mesenchymal stem cells differentiate to become preadipocytes - preadipocytes accumulate lipid droplets as multiple, individual droplets - multiple lipid droplets fuse to form one large lipid droplet

What is leptin deficiency?

- rare AR mutation leading to severe obesity beginning first few months of life - normal weight at birth; but constantly hungry and quickly gain WT - Also has hypogonadotropic hypogonadism with delayed or absent puberty

What does UCP-1 do in humans?

- responsible for adaptive thermogenesis response -- stimulated by changes in external environment -- cold stimulates glucose utilization by increased expression of glucose transporters - increase brown fat during winter - heat produced by metabolism of lipid in brown adipose is nonshivering thermogenesis

What is adiponectin?

- secreted by adipose tissue and circulates at high concentration in serum - Decreased levels in obesity, DM II, CAD, dyslipidemia -- Used as a marker for metabolic syndrome

What does adiponectin do in skeletal muscle?

- stimulates fatty acid oxidation in skeletal muscle -- decrease FA levels

How does leptin regulate BW?

- weight gain results in increase adipose, which in turn leads to increase in leptin secretion - leptin acts in hypothalamus as well as other brain locations to decrease food intake and increase energy expenditure

What are the general themes for adiponectins in vascular sm muscle?

1. Decreases proliferation 2. Decreases migration 3. Increases differentiation

what are the immune effects of leptin?

1. increase NK 2. promote activation of granulocytes/macrophages 3. increase T/B cells 4. promotes inflammatory T helper cells 5. activates B cell cytokine secretion

what are general themes for adiponectins role in the endothelial cells?

1. increase survival 2. increse differentiation 3. increases migration 4. decreases moncyte adhesion

what are the effects of adiponectin in the liver?

1. increases insulin sensitivity 2. inhibits gluconeogenesis 3. inhibits accumulation of ceramide 4. indirectly inhibits liopogenesis by increasing beta oxidation

What are locations of white adipose tissue?

1. subcutaneous fascia -- provides thermal insulation from cold -- considered to be "good" white fat 2. CT under skin of abdomen, butt, axilla, thigh, and mammary gland 3. cushions -- palms and soles -- visceral pericardium -- orbits surround eyeballs 4. visceral fat -- "bad" fat -- greater omentum, mesentery, and retroperitoneal space (kidneys, BM, fills spaces between tissues)

What are the general themes for adiponectins role in macrophages?

1.Reduces foam cell formation 2.Decreases inflammatory response

What are other fxns of leptin?

1.bone metabolism 2.regulation of reproduction 3.regulation of vascular function 4.inflammation/infection/ immune system

What are the 3 main fxns of leptin?

1.energy expenditure 2.food intake 3.hormone regulation

Where are receptors located for leptin?

CNS, adipocytes, pancreatic beta cells, muscle cells, gonads, and endothelial cells

what neurotransmitter stimulates lipolysis and hydrolysis of triglycerides and the expression of UCP-1?

NE

during what diagnostic test for tumors can brown adipose give false positive findings?

PET scans - usually brown adipose is bilateral and symmetrical

what class of endocrine secretions does white adipose secrete?

adipokines which includs hormones, GFs, and cytokines

where is brown adipose tissue mainly located in the newborn?

back, neck, shoulders

what adipose tissue increases in pheochromocytoma due to increased secretion of epinephrine and norepinephrine?

brown adipose

what are the 2 types of adipose tissue?

brown and white

in what 6 regions is brown adipose found in the adolescence?

cervical, axillary, paravertebral, mediastinal, sternal, abdominal

white adipose tissue is said to have this appearance on histological examination?

chicken wire

what are the 5 functions of white adipose tissue?

energy homeostasis, adipogenesis, steroid metabolism, angiogenesis, immune responses

what are the effects of adiponectin in adipose tissue?

glucose uptake, adipogenesis, inhibition of lipolysis

what hormone induces secretion of leptin and then goes on to inhibit its secretion?

insulin

where is brown adipose found in adults?

kidneys, adrenal glands, aorta, mediastinum

what environmental factor can lead to hypoleptinemia?

malnutrition

what innervation do brown adipocytes receive that regulated their metabolic activity? What does brown adipose do during this time?

sympathetic - generates heat, offset the heat loss from newborn's high surface to mass ratio and helps prevent lethal hypothermia

adipose stores excess energy as lipid droplets in the form of what?

triglycerides

what is exclusively expressed in brown adipose tissue in the inner mitochondrial membrane and allows protons to bypass ATP synthase allowing for the release of chemical energy as heat?

uncoupling protein 1