Histology of Adipose Tissue

Question 1

What are the main functions of adipose tissue?

Answer 1

Adipose tissue is a type of specialized connective tissue with several functions:
* Stores fat for energy use
* Provides insulation from the cold
* Provides padding around organs
* Brown adipose can generate heat for newborns
* Releases hormones like leptin and estrogen (synthetic organ)

Question 2

What cell types make up adipose tissue?

Answer 2

Adipose tissue is mainly adipocytes but the tissue also contains:
* Fibroblasts
* Vascular endothelial cells
* Macrophages

Question 3

Each adipocyte is surrounded by a thick, specialized ECM called the _

Answer 3

Each adipocyte is surrounded by a thick, specialized ECM called the basal lamina

Question 4

The basal lamina surrounding the adipocytes contains type _ collagen

Answer 4

The basal lamina surrounding the adipocytes contains type IV
* The basal lamina supports adipocytes, which are otherwise susceptible to injury because of the scanty cytoplasm

Question 5

Differentiate between white adipose tissue and brown adipose tissue

Answer 5

White adipose tissue stores fat for energy needs

Brown adipose tissue generates body heat by metabolizing fat

Question 6

Both white and brown adipose tissue stores fat in organelles called _

Answer 6

Both white and brown adipose tissue stores fat in organelles called lipid droplets
* Each white adipocyte has one lipid droplet
* Brown adipocytes have many lipid droplets

Question 7

What do white adipocytes look like?

Answer 7

Each white adipocyte contains a central lipid droplet containing fat; this pushes the cytoplasm and nucleus to the periphery of the cell
* Cell can increase 20-fold in diameter
* Stored fat is mainly in form of triglycerides and cholesterol esters

Question 8

What do brown adipocytes look like?

Answer 8

Brown adipocytes are smaller than white, they have multiple smaller lipid droplets per cell
* More abundant cytoplasm
* Nucleus is in the center
* Brown color comes from high quantity of mitochondria

Question 9

White adipocytes have a remarkable ability to expand and store energy in the form of TG in the adipose tissue and liver; however, white fat is associated with _ and _

Answer 9

White adipocytes have a remarkable ability to expand and store energy in the form of TG in the adipose tissue and liver; however, white fat is associated with heart attacks and strokes

Question 10

The main fat storage hormone is _

Answer 10

The main fat storage hormone is insulin
* It gets released from the islet cells of the pancreas
* Then binds to white adipose cell receptors
* And it inactivates lipase to promote fat storage

Question 11

If higher fat mass leads to higher leptin, then why don’t we lose our appetite when we gain weight?

Answer 11

Leptin resistance at the receptor level

Question 12

Explain the involvement of cytokines in obesity

Answer 12

Adipocytes contribute to a state of inflammation by secreting cytokines and inflammatory modulators like plasminogen, activator inhibitor 1, monocyte chemoattractant protein 1, TNFa, IL-6, and IL-8
* Macrophages in the adipose tissue also releases pro-inflammatory cytokines

Question 13

Leptin binds to _ in the brain and acts to _

Answer 13

Leptin binds to the hypothalamus in the brain and acts to reduce hunger and stimulate satiety

Question 14

Fat mobilization is caused by the following hormones:

Answer 14

Fat mobilization is caused by the following hormones: epinephrine, norepinephrine, glucagon, growth hormone, cortisol
* These activate lipase to cause breakdown from TG –> fatty acids + glycerol
* Fatty acids then get used by muscle and cardiac tissue for energy
* Glycerol is taken up by the liver to make new glucose

Question 15

List some common sites of white fat deposition

Answer 15

Subcutaneous fat: located beneath the skin
Visceral fat: located around visceral organs (intra-abdominal)
Breast fat: in breast tissue
Marrow fat: in bone marrow
Ectopic fat: abnormal deposition in the muscles, heart, liver, pancreas

Question 16

Subcutaneous fat is located in the _ layer of the skin; subcutaneous fat is not related to heart disease and stroke and may actually be protective

Answer 16

Subcutaneous fat is located in the hypodermis layer of the skin; subcutaneous fat is not related to heart disease and stroke and may actually be protective
* Sex hormone differences make premenopausal women more likely to have subcutaneous fat around the hips, thighs, buttocks

Question 17

Visceral fat is located inside the _ and is associated with _

Answer 17

Visceral fat is located inside the intra-abdominal region and is associated with insulin resistance, metabolic syndrome, type 2 diabetes
* Men are more likely to have this central obesity
* After menopause women’s fat moves from subcutaneous –> visceral and increases cardiovascular risk

Question 18

Marrow fat is adipose tissue that resides in the _ , interspersed with the hematopoietic cells

Answer 18

Marrow fat is adipose tissue that resides in the bone marrow , interspersed with the hematopoietic cells
* These adipocytes are derived from mesenchymal stem cells

Question 19

Why does ectopic fat occur if fat should not normally be inside muscle cells or in the liver?

Answer 19

1. When white adipocytes get too big for their blood supply, they release biochemical signs of stress (ie cytokines) –>
2. Immune cells are called in –> induce more cytokine production and inflammation
3. Cytokines interfere with insulin signaling and increase lipolysis
4. Induces a redirection of FFA towards peripheral tissues like muscle, liver, pancreas, heart

Fatty deposition below epicardium, fibrosis next to myocardium

Question 20

Fatty infiltration of the liver is called _

Answer 20

Fatty infiltration of the liver is called hepatic steatosis

Question 21

Brown fat produces endogenous heat in a process called _

Answer 21

Brown fat produces endogenous heat in a process called thermogenesis
* Brown fat is most abundant in newborn babies (5% of their body weight)
* The little brown fat that we have as adults is around the neck, shoulders, vertebrae, over the kidneys

Question 22

How does brown fat differ from white fat?

Answer 22

1. Brown adipocytes have multiple lipid droplets for fat storage
2. More mitochondria to generate heat
3. Capillary supply is rich to carry the heat to the body

Question 23

Heat generation (of brown fat) is accomplished by a unique mitochondrial membrane protein called _

Answer 23

Heat generation (of brown fat) is accomplished by a unique mitochondrial membrane protein called mitochondrial uncoupling protein 1 (UCP1)
* Normally the movement of protons across the mitochondrial membrane would generate ATP (oxidative phosphorylation)
* In brown adipocytes, this special mitochondrial membrane protein instead converts the proton movement to heat

Question 24

Obesity is generally defined as _ body fat percentage in men and _ in women

Answer 24

Obesity is generally defined as > 25% body fat percentage in men and >33% in women

Question 25

Obesity in adults is defined as a BMI greater than or equal to _

Answer 25

Obesity in adults is defined as a BMI greater than or equal to 30

Question 26

The research gold standard of measuring totaly percent body fat is _

Answer 26

The research gold standard of measuring body fat is underwater weighing
* Whole-body displacement plethysmography, DEXA, bioelectrical impedance analysis, anthropomorphic techniques are other methods

Question 27

To measure subcutaneous fat we can use _ or _

Answer 27

To measure subcutaneous fat we can use skinfold thickness or ultrasound