Physiology and Immunology: Homeostasis

Study Notes

Physiology is the study of the function of living systems, including molecules, cells, organs, organ systems, and organisms.
Homeostasis is the regulation of internal conditions to maintain a stable state, such as temperature and pH.
Homeostatic regulation allows organisms to function in a variety of environments. For example, ectotherms become sluggish in cold temperatures, while endotherms maintain stable temperatures.
Homeostasis requires energy.
Many homeostatic processes are controlled by hormones released into the bloodstream.
Homeostasis is crucial for regulating body pH (7.365) and blood glucose levels.
Insulin and glucagon regulate blood glucose in mammals, maintaining levels relatively constant even after extended periods of fasting.
Insulin is secreted by beta cells in the pancreas.

All homeostatic control systems contain three interdependent components:
- A receptor senses a stimulus that deviates from the normal range.
- A control center (often the brain) sets the range at which a variable is maintained.
- An effector makes necessary adjustments.
Positive feedback mechanisms accelerate change, while negative feedback mechanisms maintain a stable internal environment.
Blood pressure regulation is an example of negative feedback: blood vessels sense high pressure and signal to the brain, which in turn reduces heart rate and dilates blood vessels, bringing pressure back to normal.
Hypothalamus monitors temperature and adjusts body temperature via mechanisms like sweating or shivering.

Blood is a fluid connective tissue that transports essential materials (e.g., nutrients, oxygen) and removes waste products.
Blood plasma is mostly water and contains proteins, glucose, electrolytes, carbon dioxide, and other molecules.
Blood contains:
- Erythrocytes (red blood cells) carrying oxygen
- Leukocytes (white blood cells) part of the immune system
- Thrombocytes (platelets) involved in clotting
Blood performs various functions, including delivering oxygen and nutrients to tissues and removing waste.

Blood vessels sense pressure changes and send signals to the brain to adjust blood pressure appropriately.
Factors like food deprivation can reset the metabolic set point, resulting in a decrease in metabolism and a slower, more manageable rate of weight loss.
Exercise can increase the metabolic demand and impact this process.

Homeostatic imbalance occurs whenever there is a disruption of homeostasis.
This can have serious consequences, such as illness and ultimately death.
Some diseases resulting from imbalances include diabetes, dehydration, hypoglycemia, hyperglycemia, gout, and diseases resulting from toxins in the bloodstream.
Imbalances can also result in age-related physiological changes.

The immune system protects against disease and pathogens (e.g., viruses, worms).
Innate immunity, present from birth, involves mechanical, chemical, and biological barriers.
Adaptive immunity, found in vertebrates, has memory and depends on the recognition of specific antigens.
Lymphocytes (e.g., B cells and T cells) are crucial to adaptive immunity.
- B cells produce antibodies that recognize specific antigens, while
- T cells destroy infected cells or activate other immune cells.
Immunological memory is maintained by memory cells.
Passive immunity can be transferred across the placenta or in breast milk.
Active immunity is acquired after exposure to a pathogen or via vaccinations.

Inflammatory infiltration is a crucial first defense response during infection.
Cells such as phagocytes and leukocytes migrate to the affected area to engage with the pathogen.
In addition, cytokines are released to attract and activate other immune cells.
Inflammatory infiltration is accompanied by effects like redness, swelling, heat, and pain.