Biology Chapter on Homeostasis and Cells

Study Notes

Homeostasis is the body's process of maintaining a stable internal environment despite external changes.
This internal balance is crucial for proper cell, organ, and system function.
Claude Bernard is considered the "Father of Physiology."

Cells are the basic structural units of a multicellular organism.
Cells specialize during development, becoming specialized for specific functions.
Cell differentiation is the transformation of unspecialized cells into specialized cells.
Cells are classified into four major categories:
- Muscle cells
- Neurons
- Epithelial cells
- Connective tissue cells
Multiple tissue types combine to form organs.
Organs work together as organ systems.
Atoms -> Molecules -> Macromolecules -> Organelles -> Cells -> Tissues -> Organs -> Organ Systems -> Organism

Total body fluid is approximately 60% of total body weight.
Intracellular fluid (ICF) is found inside the cells, comprising approximately 40% of total body fluid.
Extracellular fluid (ECF) is found outside cells, making up approximately 20% of total body fluid.
- Plasma/ Intravascular fluid: ~ 5% of ECF
- Interstitial fluid: ~ 15% of ECF
- Transcellular fluid: ~ <1% of ECF (e.g., cerebrospinal fluid, synovial fluid)
A 70-kg adult man has roughly 42 liters of total body water.

Extracellular fluid (plasma) has high levels of sodium (Na+), chloride (Cl-), and bicarbonate (HCO3-).
The osmolarity of extracellular fluid is 290 mosm/L.
Intracellular fluid has high levels of potassium (K+), magnesium (Mg2+), and phosphates.
The osmolarity of intracellular fluid is 290 mosm/L.

Homeostatic mechanisms maintain stable internal conditions.
Disruptions in homeostasis can cause health issues like diabetes, high blood pressure and heatstroke.
Stress can disturb homeostasis.
Chronic stress can impair the immune system function and increase the risk of other diseases.

Temperature regulation: The body maintains a core temperature of 37°C (98.6°F) through sweating and shivering.
Fluid balance: The body manages water and ion levels through urine production regulated by hormones.
- Kidneys excrete waste and regulate water and electrolyte levels.
Blood glucose regulation: Hormones (insulin and glucagon) regulate blood glucose levels.
High blood sugar can lead to diabetes.
pH balance (acid-base balance): The body keeps the blood pH near 7.4.
Set point concept: The parameters kept stable by homeostasis (e.g., body temperature, blood sugar, blood pressure).
Homeostasis and stress mechanisms are involved in maintaining body health

Homeostasis employs negative feedback mechanisms to counteract deviations from the set point.
If body temperature rises, the body will initiate processes like sweating to reduce temperature.

Positive feedback mechanisms amplify a change to a particular set point.
During childbirth, the release of the hormone oxytocin causes uterine contractions to become stronger.

Hormones: Chemical messengers that regulate functions.
- Examples include insulin (lowers blood sugar), glucagon (raises blood sugar), adrenaline (increases heart rate & energy), and aldosterone (controls water & salt balance).
Neurotransmitters: Chemical messengers in the nervous system.
- Examples include dopamine, serotonin, and acetylcholine.
Cytokines: Proteins involved in immune responses.
- Examples include interleukin, tumor necrosis factor (TNF).
Electrolytes: Ions essential for water balance, nerve signaling, and muscle function.
- Sodium (Na+), potassium (K+), and calcium (Ca2+) are examples.