Overview
This lecture explores the roles and importance of fat (adipose tissue) in human survival, physiology, and evolution, including its types, functions, and differences across age and sex.
What is Fat (Adipose Tissue)?
- Fat, or adipose tissue, is a type of connective tissue located beneath the skin and around organs.
- At the microscopic level, adipose tissue is made of adipocytes—cells that store fat as triglycerides.
Functions of Fat
- Stores energy for times of food scarcity, crucial for early human survival.
- Provides insulation to reduce heat loss.
- Produces heat (thermogenesis), especially in infants.
- Cushions and protects internal organs.
- Acts as an endocrine organ by secreting hormones.
Evolutionary Importance
- Fat storage enabled humans to survive famines and fuel long hunts.
- Human ancestors' higher body fat may have contributed to increased brain size.
- Energy reserves in fat were essential for reproductive success, especially in females.
Differences in Body Fat: Males vs. Females
- Healthy males typically have 10-15% body fat; females 20-25%.
- Estrogen promotes fat storage in females, especially on hips, thighs, and breasts.
- Fat reserves in females support pregnancy and breastfeeding, requiring extra calories.
- Low body fat in females can disrupt menstrual cycles, signaling insufficient reserves for pregnancy.
Types and Locations of Fat
- Fat is categorized by color: white fat (most adult fat) and brown fat (abundant in infants).
- White fat insulates the body, prevents heat loss, and stores energy.
- Brown fat generates heat (non-shivering thermogenesis) via specialized mitochondria.
- Infants have more brown fat to stay warm since they can't shiver effectively.
- By location: subcutaneous fat (under the skin) and visceral fat (around organs).
- Both subcutaneous and visceral fat are mainly white fat and secrete hormones.
Hormonal and Metabolic Functions
- Fat tissue secretes hormones like leptin (regulates hunger), adiponectin (improves insulin sensitivity), and estrogen (via aromatase enzyme).
- Also produces cytokines, signaling molecules involved in inflammation.
Key Terms & Definitions
- Adipose tissue — connective tissue that stores fat.
- Adipocyte — fat cell storing triglycerides.
- Triglyceride — fat molecule made of one glycerol and three fatty acids.
- White fat — insulates, stores energy, and cushions organs.
- Brown fat — produces body heat, especially in infants.
- Subcutaneous fat — fat located under the skin.
- Visceral fat — fat surrounding internal organs.
- Thermogenesis — production of heat by the body.
Action Items / Next Steps
- Watch the next video focusing on the health effects of excessive fat and why it leads to health problems.