Approximately 37 trillion cells in the human body.
Over 200 different types of cells in humans, each with specific functions.
Human cells are animal cells containing specific structures (organelles).
Important Cell Structures
Nucleus: Contains genetic material for protein production and cell functions.
Cell Membrane: Made of phospholipids (a type of fat), protecting the cell by regulating the entry and exit of substances.
Cytoplasm: The area where many chemical reactions occur, including the initial steps of glucose breakdown.
Mitochondrion/Mitochondria: The energy-forming site in the cell (ATP production from glucose and fats).
Cells have multiple mitochondria, varying in number depending on cell function.
Adipocytes: Fat Storage Cells
Adipocytes are cells specialized for storing fat (triglycerides).
Adipose tissue is formed when many adipocytes come together.
Adipocytes have a unique, almost perfectly spherical shape, unlike most cells.
They are large in size, even in lean individuals.
A large lipid droplet in the middle stores triglycerides, pushing other organelles to the side.
Adipose Tissue Structure
Adipocytes are held together by a mesh of collagen fibers, forming bag-like structures.
Collagen is a protein that provides structural support.
Fat Storage Mechanisms
Two ways to store excess fat:
Adding triglycerides into existing adipocytes, causing them to grow larger.
Synthesizing new adipocyte cells to store triglycerides.
The number of adipocytes in an average adult is about 50 billion, but varies among individuals.
Once new adipocytes are formed, they persist for a long time and do not disappear quickly.
The method of fat storage depends on where the triglyceride is stored in the body.
Study on Overeating (2010)
A study with 28 healthy adults in their late 20s examined the effects of overeating.
Participants gained an average of 4 kg over eight weeks.
Nearly 3 billion new fat cells formed in the legs, but not significantly in the abdomen.
Weight gain in legs and buttocks involves new fat cell formation, while the abdomen uses existing cells.
This difference may explain why it's harder to lose weight from the legs and buttocks.
Adipocyte Lifespan and Turnover
Adipocytes do not disappear when you lose weight; they shrink as triglycerides are used for energy (released as carbon dioxide).
Adipocytes have a finite lifespan and die after about ten years.
During this period, they grow and shrink repeatedly.
Weight loss during this time reduces the need for new fat storage, leading to fewer new adipocytes formed when old ones die.
All fat cells in the body are renewed within a ten-year period.
In obesity, the death rate of fat cells can be 30 times higher due to inflammation of adipose tissue.
This inflammation is caused by the inelastic collagen mesh surrounding enlarged adipocytes.
Prevention of weight gain is better than trying to cure it due to potential complications.
Fat Deposits in the Body
Two main fat deposits:
Subcutaneous Fat: Located under the skin, covering the entire body.
Visceral Fat: Surrounds internal organs, providing protection against shock.
Smaller fat deposits are also found in other areas.
Apple vs. Pear Shaped Bodies
Apple Shaped Bodies: Excessive fat stored in the abdominal region (mostly visceral fat).
Pear Shaped Bodies: Fat stored around the buttocks and legs (mostly subcutaneous fat).
Apple shaped bodies are less healthy due to the hormonally active visceral fat, which releases hormones that can cause inflammation, heart disease, and diabetes.
Visceral fat protects internal organs, but too much is harmful.
Subcutaneous fat releases hormones, but to a lesser extent than visceral fat.
Other Fat Deposits
Fat pads under the balls of feet (heels) protect against impact when walking.
Fat deposits in knee joints aid in walking.
Fat in baby cheeks fills space between jaw muscles, aiding the sucking mechanism for milk.
Types of Adipose Tissue
White Adipose Tissue (WAT): For energy storage (triglycerides).
Releases stored fat during starvation, fasting, or exercise for energy.
Brown Adipose Tissue (BAT): Primarily for producing heat (thermogenesis).
Shivering heat production (muscle contraction).
Non-shivering heat production (BAT).
BAT is important for maintaining body temperature at 37 degrees Celsius.
Distribution and Structure
WAT is present throughout life and is the largest volume of adipose tissue.
BAT was initially thought to be mainly in infants but is also found in adults in smaller amounts.
WAT is distributed throughout the body, including subcutaneous and visceral regions.
BAT is mainly found around the collarbone and chest area.
WAT has a large lipid droplet, pushing organelles aside.
BAT has multiple small lipid droplets and contains many mitochondria to break down fats for heat production.
Brown Fat and Heat Production
High concentration of mitochondria in brown fat gives it a brownish appearance due to iron content.
Babies are born with more brown fat to maintain body temperature.
Animals that hibernate also have large amounts of brown fat.
Exposure to cold weather activates brown fat.
Mechanism of Heat Production
Glucose and fatty acids are broken down to make energy in the form of ATP through respiration.
Brown fat makes some ATP but also produces heat energy.
Brown fat cells need to break down more fatty acids to make the required ATP, resulting in heat production.
Brown fat helps use up more stored fat, aiding in weight loss.
Brown fat is associated with lower BMI and lower body fat percentage.
Recent Discoveries
Beige Adipocytes: Display characteristics of both brown and white adipocytes.
Emerge within subcutaneous white adipocytes.
Formation can be induced through diet, exercise, pre/post-biotics, pharmaceutical agents, and adipokines.
Seem to have a protective effect against obesity.
Pink Adipocytes: Found only in rodents so far.
Originate from subcutaneous adipocytes.
Occur during late pregnancy or lactation in female mice.
Have an epithelial cell appearance with villi.
Adipokines: Signaling Molecules
Adipokines are signaling molecules (e.g., hormones) produced by adipose tissue.
They can have local effects on adipose tissue or travel to other parts of the body.
Involved in inflammation, metabolic pathways, insulin sensitivity, and immune function.
Leptin
Leptin is a hormone produced by the OB gene.
Acts as an appetite suppressant, signaling the brain to indicate fullness.
Empty fat cells secrete less leptin; full fat cells secrete more.
In obesity, leptin is highly expressed, but the body may become resistant to its effects.
Leptin binds to leptin receptors on the cell surface, targeting the brain, central nervous system, liver, and pancreas.
Congenital leptin deficiency (CLD) results in constant hunger and morbid obesity.
Synthetic versions of leptin can treat CLD, but do not work for obese individuals without the mutated gene due to leptin resistance.
Weight Loss Methods
Liposuction: Removes subcutaneous fat, but does not provide the health benefits of natural weight loss (decreased blood fat, insulin levels).
Does not remove harmful visceral fat.
Weight Loss Pills: Require careful understanding of the mechanism of action and potential side effects.
DNP (2,4-Dinitrophenol): An example of a dangerous weight loss drug that was discovered in the early 1900s.
It uncouples ATP production, leading to a dangerous increase in body heat.
Leads to death, blindness and organ failure.
The drug was taken off the market once they found out these detrimental health effects, and it was made illegal to sell.
Body Mass Index (BMI)
BMI is a measure of body fatness based on weight and height, invented in the early 1800s. BMI=Height(m)2Weight(kg)
Indicates if a person is underweight, at a healthy weight, overweight, or obese.
Does not account for gender, age, or muscle mass.
In Australia, two-thirds of adults are overweight or obese (67% in 2017-2018).
Fat storage location is important for assessing disease risk.
BMI is not always accurate, especially for elite athletes, classifying some as overweight.
More accurate ways to assess body fat include skin fold thickness, underwater weighing, and dual-energy X-ray absorptiometry (DEXA), but these are time-consuming and expensive.