Functional Organization of the Human Body, Body Fluids and Homeostasis

Vocabulary flashcards covering human body organization, fluid compartments, ion composition, water balance regulation, and homeostatic feedback mechanisms based on lecture slides.

Cell

The basic structural and functional unit of the human body.

Cell Structure

A cell consisting of a surrounding plasma membrane, cytoplasm, nucleus, and organelles such as mitochondria and ribosomes.

Mitochondrion

A cellular organelle where cellular respiration takes place and energy is produced.

Ribosomes

Cellular organelles that serve as the primary sites where proteins are synthesized.

Body Fluids

Solutions of water containing organic molecules and inorganic molecules/ions, accounting for about 60-65% of total body weight (40-42 L in a 70 kg adult).

Intracellular Fluid (ICF)

The fluid located inside cells, constituting 2/3 of total body fluids (approximately 28 L in a 70 kg adult).

Extracellular Fluid (ECF)

The fluid located outside cells, also known as the internal environment, constituting 1/3 of total body fluids (approximately 14-15 L in a 70 kg adult).

Plasma

The extracellular fluid component contained inside blood vessels, amounting to about 3-3.5 L.

Interstitial Fluid (IF)

The extracellular fluid component present in between cells and lymph vessels, amounting to about 10-12 L.

Transcellular Fluid

The extracellular fluid component contained within specialized body cavities (e.g., cerebrospinal fluid), amounting to about 1 L.

Main Intracellular Cation

Potassium ($\text{K}^+$), present at a concentration of $140\,mmol/L$ in the ICF.

Main Intracellular Anion

Proteins, present at a concentration of $55\,mmol/L$ in the ICF.

Main Extracellular Cation

Sodium ($\text{Na}^+$), present at a concentration of $140\,mmol/L$ in the ECF.

Main Extracellular Anion

Chloride ($\text{Cl}^-$), present at a concentration of $115\,mmol/L$ in the ECF.

Ion Concentration Comparison (ICF vs. ECF)

A comparative overview showing high concentrations of $\text{K}^+$ and Proteins inside cells, and high concentrations of $\text{Na}^+$ and $\text{Cl}^-$ outside cells.

Water Balance

The maintenance of constant body water by matching daily water input ($2400\,mL/day$) with daily water output ($2400\,mL/day$).

Insensible Water Loss

Unconscious water loss from the body occurring through the skin and lungs, amounting to about $700\,mL/day$.

Thirst Center

A neural center activated by decreased blood volume or increased plasma osmolarity to trigger thirst sensation and increase water intake.

Antidiuretic Hormone (ADH)

The main factor synthesized in the hypothalamus and released by the posterior pituitary to decrease urine volume when blood volume decreases or plasma osmolarity increases.

Homeostasis

The physiological mechanisms that keep the internal environment constant to ensure normal cellular function.

Negative Feedback Mechanism

The most common regulatory mechanism where the body's response inhibits the original stimulus to maintain a constant internal environment.

Negative Feedback Loop Example (CO2 Regulation)

Elevated $\text{CO}_2$ level triggers chemoreceptors to induce hyperventilation, which washes out excess $\text{CO}_2$ and restores normal balance.

Positive Feedback Mechanism

A regulatory mechanism where the response amplifies or stimulates the original stimulus, disturbing homeostatic balance.

Positive Feedback Loop Example (Childbirth)

Cervical dilation during labor signals the brain to release oxytocin, which increases uterine contractions, leading to further cervical dilation and baby descent until delivery.