Adipose Tissue (Exam 2)

Adipocytes of white fate are typically what size and shape?

Very large cells; Singlet-ring appearance

FAs are released from white adipocytes by ________. When does this happen?

Lipase; When nutrients are needed

Beige adipocytes:

'Multi-locular' fat droplets *High in mitochondrial content *UCP1 upon activation Function: -Adaptive thermogenesis -Regulation of nutrient homeostasis

Brown adipocytes:

'Multi-locular' fat droplets *High in mitochondrial content *UCP1 Function: -Adaptive thermogenesis -Regulation of nutrient homeostasis

Fat cell differentiation lasts through ________.

Adolescence

White adipose tissue is subdivided into _____________ by partitions of connective tissue.

Incomplete lobules

White adipocytes:

'Unilocular' fat droplet Function: -Lipid storage -Production of endocrine hormones regulating nutrient homeostasis, food intake, CV function, & inflammation. -Tissue regeneration

Adipocytes =

**Most abundant cell in adipose tissue** -Specialized cells that are derived from mesenchymal stem cells through adipogenesis. -Active cells (metabolically) that respond to neuron and hormonal stimuli

Fibroblasts, macrophages, and other cells typically comprise about how much of the total cell # in white adipose tissue?

half total cell #

In mature white adipocytes, the droplet is so large that it displaces what? -The cells are said to have a ____________ appearance, because the lipid is washed away during sample preparation.

the nucleus and remaining cytoplasm to the cell periphery. -signet-ring appearance *Specialized for long term energy storage *Shape: spherical, but polyhedral when packed *Large: 50-150 in diameter

Different cell types contribute to the cellular architecture of adipose tissue:

-Adipocyte~Functionally making important contributions to systemic metabolic homeostasis. -Adipocyte precursor cells (Pre-adipocyte) -Vascular endothelial cells -Immune cells (Macrophages, T-cells) -Fibroblasts **All of these combines give rise to a tissue with remarkable flexibility in respect to expansion/contraction widely optimizing the ability if the tissue to act as an endocrine organ->influencing systemic lipid homeostasis

Adipocytes express ____________, which catalyzes the conversion of steroids to estrogens.

-Cytochrome P-450 aromatase -Risk of breast cancer or endometrial cancer -Obese women more prom to these diseases -TX: black aromatase

Functions of adipocytes:

-Key regulators of the body's overall energy metabolism (Store energy) -Capable of producing hormones to influence energy intake, s.a. leptin (central hormone) -Convert chemical energy to heat

Differentiation of mesenchymal stem cells to form white adipose tissue:

-MSCs differentiate as progenitor cells into pre-adipocytes. -Pre-adipocytes developing within the lateral plate mesoderm of the embryo. -Produce large # of white adipocytes and smaller # of beige adipocytes.

White adipose tissue structure: -Most cytoplasmic organelles are near the __________. -Contains these organelles: -Cytoplasm ~ -Calveolae

-Peripheral nucleus -Contains: Golgi cmplx, mitochondria, small amt RER, free ribosomes -Cytoplasm in the thin rim contains SER and pinocytotic vesicles. -Calveolae are important for lipid trafficking and formation of large triglyceride storage droplet.

Function of brown adipocytes:

-Produce heat by non-shivering thermogenesis -In newborns, nerve impulses liberate norepi into brown AT -Neurotransmitter activates hormone-sensitive lipase of adipocytes, promoting hydrolysis of triglycerides to FAs and glycerol. -Liberated FAs are quickly metabolized, with a consequent incr in O2 consumption and heath prod., raising the temp within the tissue.

Distribution of white adipose tissue:

-Subcutaneous fat (80% total body fat; layer of WAT under the skin) -Intraabdominal fat (20% total body fat) -Around major joints (Knees) -Pads in palms and soles *Distribution of WAT changes significantly thru lifetime. ~regulation by 6 hormones (ex. Women's breasts and thighs)

Adult adiposity vs. adolescent adiposity

Adult->hypertrophy~incr. the size of existing adipocytes Adolescent->hyperplasia~both incr. in size and # of cells

___________ obesity is very often associated with age-related metabolic changes and may involve reduced activity of the hormone-sensititve lipases of adipocytes.

Adult-onset obesity -Leading to less effective fat mobilization out of the cells

_______________ comprises up to 5% of the newborn body weight by smaller amounts in adults.

Brown adipose tissue

Brown adipose tissue structure: -Shape and size -Organelles -Packing

Cells are polygonal and generally smaller than white adipocytes -Lipid droplets and central spherical nuclei (compared to large and peripheral nucleus in white AT) -Abundant mitochondria (cytochrome pigment) -Receive direct sympathetic innervation->Reg metabolic activity

Obesity of characterized as a state of ____________.

Chronic mild inflammation

Proliferation of progenitor cells diminishes by ________, and adipose tissue increases mainly by ......

Late gestation; Filling of existing adipocytes until around age 10

_____________ is a polypeptide hormone with target cells in the hypothalamus that is released mainly from white adipocytes and helps regulate eating behavior.

Leptin

Unilocular adipocytes can generate benign tumors called ____________. Malignant tumors called __________ occur infrequently.

Lipomas; Liposarcomas -Fetal lipomas of brown fate sometime called Hibernomas

Adipocytes of brown AT are typically smaller than those of white fat and contain primarily how many lipid droplets? How does this affect the organelles?

Many small lipid droplets in cytoplasm -Contains many mitochondria and a central nucleus

Leptin mediates its effects by.....

Mediates its effects by binding to specific leptin receptors (ObRs) expressed in the brain as well as in peripheral tissues (reg of neuroendocrine func/immune func/metabolism)

The lipolytic effect of glucagon in adipose tissue is _______ in humans.

Minimal ~Indirect effect thru insulin -Insulin inhibits the hormone-sensitive lipase, and also stimulates enzymes for lipid synthesis (lipogenic influence)->Formation of triglycerides from FFAs for storage

Brown adipose tissue:

Multilocular AT -Amt of brown is less than white at all ages. -Reaches max amt at birth -Adults ~ Found only in scattered areas, esp around kidneys, adrenal glands, aorta, neck and shoulders -Develops from MSCs, but involves pre-adipocytes in a diff embryonic location (paraxial mesoderm) than white fat. (white=lateral plate meso)

Leptin resistance leads to, or maintains, ______________.

Obesity -Chronically high circulating leptin levels -Insufficient receptors (ObRs) -Biological condition~Brain does not respond to leptin, despite adequate fat stores. Fat cells produce even more leptin.

White fat cells each contain primarily how many lipid droplets? What does this cause?

One large lipid droplet (unilocular) -Causes the nucleus and remaining cytoplasm to be pushed agains the plamalemma

Leptin:

Produced primarily by white adipose tissue and levels are (+) correlated proportionate) with the amt of body fat. ->Decr. leptin levels, incr appetite -Serves as a gauge for energy reserves and directs the CNS to adjust food intake and energy expenditure.

Adrenocorticotropic hormone (ACTH) ~

Released by the anterior pituitary gland, stimulates adipocytes to release FFAs (lipolytic influence)

White adipose tissue: ___________ form a fine interwoven network that supports individual fat cells.

Reticular fibers -Includes small blood vessels near adipocytes that provide nutrition.

Functions of adipose tissue:

Serve as: -Storage depots for neutral fats -Regulator of metabolic homeostasis -Insulator (subcutaneous fat tissue provides thermal reg) -Structure supporter (areas w mechanical stress, holding organs in place) *Releases a large # of hormones, cytokines, and ECM proteins (adipokines)

Lipid storage and mobilization:

-Triglygerides from dietary fats are transported from the intestine and liver in lipoprotein cmplxs(chylomicrons) and VLDLs. -In the capilary endothelial cells, these cmplxs are broken down by lipoprotein lipase, releasing free FAs and glycerol. -FFAs diffuse from the capillary into the adipocyte, where they are re-esterfied to form triglycerides. (stored in lipid energy droplet for energy later) -Norepi released in adrenal gland activates a hormone-sensitive lipase that break down triglycerides at the surface of the stored lipid droplets (lipolytic influence) -FFAs diffuse across the membranes of the adipocyte and the capillary endothelium, and bind the protein albumin in blood for transport thru body.

Adipocytes store lipids from 3 sources:

1. Dietary fats packaged as lipoprotein complexes known as chylomicrons in intestine 2. Triglycerides produced in the liver and circulating as VLDLs (v low density lipopoteins) 3. Fatty acids synthesized locally

3 types of adipocytes:

1. White adipocytes 2. Brown adipocytes 3. Beige adipocytes

Adipose tissue represents ____% of body weight in men.

15-20%

Brown adipose tissue constitues _____% of the newborn body weight.

3-5% ~ Back, neck, shoulders -Decreases through adolescence

Adipsoe tisse =

A connective tissue that is specialized to store fuel (energy) ~ Fat

What predisposes an individual to obesity in later life?

Increased # of adipocytes during childhood -Incr risk

Rather than ATP synthesis, what happens to the FAs released in adipocytes of brown fat?

FAs are metabolized in the mitochondria of these cells for thermogenesis, rather than ATP synthesis, using UCP-1.

In lipid storage and mobilization, hormone-sensitive lipase is stimulated by _________.

Growth hormone (lipolytic effect)

Lipids are mobilized from adipocytes by ________________ activated by _______________.

Hormone-sensitive lipase; Norepinephrine

Brown adipose tissue: -Inner mitochondrial membranes have greatly upregulated levels of the _____________________.

Transmembrane uncoupling protein-1 (UCP-1) -UPC1 permits the flow of protons from the intermembranous space to the matrix without passing thru ATP synthase complxs.

What kinds of fats are well-developed before birth?

Visceral and subcutaneous

_________________ is found in many organs throughout the body, typically forming about 20% of the body weight in adults.

White adipose tissue

What is the most abundant type of adipose tissue?

White adipose tissue ~ Unilocular adipose tissue

Humans are born with stores of _______ adipose tissue, which begin to accumulate by the ____ week of gestation.

White; 14th