MN04 - Obesity

What type of tissue is adipose tissue?

A specialized connective tissue.

What is the primary storage function of adipose tissue?

It stores fat (triacylglycerols).

How does adipose tissue contribute to insulation?

It reduces heat loss by providing thermal insulation.

How does adipose tissue protect organs?

It cushions and protects visceral organs.

Why is adipose tissue considered a synthetic organ?

It secretes hormones, cytokines, and growth factors.

Which hormones are secreted by adipose tissue?

Leptin and estrogen.

What immune mediators are secreted by adipose tissue?

Cytokines.

What types of cells are found in adipose tissue?

• Adipocytes

• Fibroblasts

• Vascular endothelial cells

• Macrophages

What are adipokines?

Pro-inflammatory proteins secreted by adipocytes.

Approximately how many adipokines have been identified?

More than 50.

What is the defining structural feature of white adipose tissue (WAT)?

A single large central lipid droplet.

How does the lipid droplet affect the cell structure in WAT?

It pushes the cytoplasm and nucleus to the periphery.

How much can adipocytes increase in size?

Up to 20× their diameter depending on fat storage.

What hormone level is high in WAT?

Leptin.

What protein level is low in WAT?

UCP1 (uncoupling protein 1).

What are the main distribution sites of WAT?

• Subcutaneous fat

• Visceral fat

• Other: mammary gland, bone marrow, ectopic sites

In which population is brown adipose tissue most abundant?

Newborns.

What is the primary function of BAT?

Active thermogenesis (heat production).

What is the structure of BAT adipocytes?

Smaller cells with multiple small lipid droplets.

Why does BAT appear brown?

High number of mitochondria.

What hormone level is low in BAT?

Leptin.

What protein level is high in BAT?

UCP1.

Where is BAT located in adults?

• Shoulders and neck

• Around vertebrae

• Around kidneys

How much BAT is present in adults?

Minimal.

What enzyme does insulin repress in fat metabolism?

Hormone-sensitive lipase (HSL).

What enzyme does insulin induce to promote fat storage?

Diacylglycerol acyltransferase.

What process does insulin promote in adipose tissue?

Lipogenesis.

Which hormones stimulate lipolysis?

Glucagon and epinephrine.

How do glucagon and epinephrine stimulate fat breakdown?

By activating HSL.

What systems regulate appetite?

Hormonal and neural gastrointestinal inputs.

What happens when the stomach is empty?

Orexigenic signals are sent to the hypothalamus to increase appetite.

What happens when the stomach is full?

Anorexigenic signals are sent to the hypothalamus to induce satiety.

What is the main orexigenic hormone?

Ghrelin.

Where is ghrelin secreted from?

Gastric cells.

When is ghrelin released?

Before meals.

What is the function of ghrelin?

Stimulates appetite and increases food intake.

How does ghrelin act on the brain?

It stimulates the hypothalamus.

What neuropeptides does ghrelin increase?

• Agouti-related protein (AgRP)

• Neuropeptide Y (NPY)

When are ghrelin levels increased?

During starvation, fasting, and weight loss.

Where is leptin produced?

Fat cells (adipocytes).

What determines leptin secretion?

Amount of fat stored.

What is leptin’s effect on appetite?

Decreases appetite and increases energy expenditure.

What pathway does leptin stimulate?

Proopiomelanocortin (POMC).

What pathway does leptin inhibit?

Neuropeptide Y (NPY).

Where is adiponectin produced?

Adipocytes.

What does adiponectin do to glucose metabolism?

Decreases hepatic gluconeogenesis.

What does adiponectin do to fat metabolism?

Increases fatty acid oxidation.

Where is CCK produced?

Enteroendocrine cells of the duodenum and jejunum.

What is the primary role of CCK?

Aids digestion and contributes to satiety.

Where is PYY produced?

Intestinal L cells.

When is PYY released?

After a meal.

What does PYY do to appetite?

Decreases appetite.

How does PYY affect ghrelin?

Directly inhibits ghrelin secretion.

What is GLP-1’s role in appetite?

Suppresses hypothalamic feeding centers.

Which hormone does GLP-1 work closely with?

CCK.

How stable is body weight in most individuals?

Relatively stable over time.

What percentage of body fat is influenced by heredity?

5–40%.

What percentage of fat distribution is genetically determined?

~50%.

What is an example of a genetic mutation affecting weight?

Leptin mutation.

What dietary environmental factor contributes to obesity?

Increased access to high-carb, high-fat, energy-dense foods.

What lifestyle factor contributes to obesity?

Sedentary behavior.

What energy imbalance contributes to obesity?

Energy intake greatly exceeding energy expenditure.

What role do epigenetic changes play in obesity?

They influence gene expression related to metabolism and fat storage.

What is obesity (OB)?

A chronic, multifactorial disorder of body weight regulation characterized by excess body fat accumulation.

How many people worldwide are overweight or obese?

Over 1 billion.

How has adult obesity prevalence changed since the 1980s?

Increased by 27%.

How has childhood obesity prevalence changed?

Increased by 47%.

What trend is seen in high-income countries?

Plateau since early 2000s.

Where is obesity increasing most rapidly?

Urban areas in low- and middle-income countries.

What is the obesity prevalence in the U.S.?

41.9% (2017).

Which group has the highest obesity prevalence?

Non-Hispanic Black adults (49.9%).

Which age range has the highest obesity prevalence?

Ages 40–59

44.3%.

What behavioral factors contribute to primary obesity?

• Overeating

• High-fat/high-calorie diet

• Infant feeding patterns

• Binge eating

• Sedentary lifestyle

What genetic factor contributes to primary obesity?

Inherited tendencies.

How does aging contribute to obesity?

Lower basal metabolic rate and reduced activity.

What hormonal resistance contributes to obesity?

Leptin resistance.

What endocrine disorders cause secondary obesity?

• PCOS

• Hypothyroidism

• Growth hormone deficiency

• Cushing syndrome

What medications can cause obesity?

• Insulin

• Antipsychotics

• Antidepressants

• Antiseizure medications

What genetic syndrome causes obesity?

Prader-Willi syndrome.

What is BMI measured in?

kg / m².

What are BMI limitations?

Does not account for body composition, ethnicity, sex, race, or age.

What is waist hip ratio (WHR) used for?

Assess fat distribution.

What defines upper-body obesity?

Fat distribution pattern influencing health risk.

What is abnormal WHR in women?

>0.8.

What is abnormal WHR in men?

>1.0.

What does ultrasound measure?

Thickness of fat tissue.

What is skinfold testing?

Pinch test to estimate fat.

What is bioelectrical impedance?

Estimates body composition.

What happens to TAG storage in obesity?

Increased storage → adipocyte enlargement.

How much do adipocytes enlarge?

2–3× increase in size.

What happens with prolonged overnutrition?

Preadipocytes differentiate into new adipocytes.

What defines obesity at cellular level?

Hypertrophy + hyperplasia.

How many adipocytes can obese individuals have?

Up to 5× normal number.

What happens to adipocyte number after weight loss?

Number remains the same; size decreases.

How do visceral adipocytes differ from subcutaneous?

• Larger

• More efficient at TAG storage

• Slower fatty acid mobilization

What percentage of people regain weight after weight loss?

>80%.

What explains weight regain after weight loss?

Genetic fat mass “set point” hypothesis.

What lipid abnormalities occur in obesity?

Low HDL, high TAG.

What glucose abnormality occurs in obesity?

Insulin resistance.

What liver condition occurs in obesity?

Hepatic steatosis (fat accumulation).