Physiology of Cell, Body Fluids & Homeostasis – Lecture Notes

Pre-Reading Strategy

Read assigned textbook pages before each lecture for easier comprehension and bring questions to class.

Physiology

The study of how biological systems function, integrating biochemistry, anatomy, physics, and cell biology.

Nucleus

The nucleus contains DNA and is the site of transcription, not translation. Mutations can lead to genetic disorders.

Mitochondrion

The 'powerhouse' of the cell, where aerobic respiration and oxidative phosphorylation occur. It has its own circular maternal DNA.

Electron Transport Chain (ETC)

A series of protein complexes in the inner mitochondrial membrane where electrons from NADH and FADH\_2 are passed, ultimately reducing oxygen to H\_2O, and a proton gradient is generated to drive ATP synthesis.

ETC Uncouplers

Uncouplers like 2,4-DNP and thermogenin dissipate the proton gradient across the inner mitochondrial membrane, leading to heat production instead of ATP synthesis.

Rough Endoplasmic Reticulum (RER)

Ribosome-studded ER that synthesizes secretory and membrane proteins; abundant in salivary glands.

Smooth Endoplasmic Reticulum (SER)

ER without ribosomes that synthesizes lipids and steroids, and detoxifies drugs; prominent in the liver and adrenal cortex.

Golgi Apparatus

Organelle responsible for post-translational modification (e.g., glycosylation), sorting, and packaging proteins, and producing lysosomes.

I-cell disease

A genetic disorder where lysosomal enzymes are secreted into the plasma due to a missing M6P tag, resulting from a Golgi apparatus defect.

Lysosome

Acidic vesicle within the cell responsible for waste breakdown. Malfunction leads to lysosomal storage disorders.

Peroxisome

Organelle involved in β-oxidation of very-long-chain fatty acids and generates H\_2O\_2. Defects cause Zellweger syndrome.

Microtubules

The largest components of the cytoskeleton, involved in vesicle transport, cilia, and the mitotic spindle. Defects can cause primary ciliary dyskinesia.

Tay-Sachs disease

An autosomal recessive lysosomal storage disease characterized by GM2 ganglioside accumulation, 'onion-skin' lysosomes, and a cherry-red macula, usually without hepatosplenomegaly.

Total Body Water (TBW)

Approximately 60% of total body weight in a standard reference male (e.g., 42 L for a 70 kg individual).

60-40-20 Rule

A guideline stating that TBW is 60% of body weight, intracellular fluid (ICF) is 40% BW, and extracellular fluid (ECF) is 20% BW.

Osmolarity

The concentration of solute particles per liter of solution, which drives water movement across membranes.

Isotonic

Extracellular fluid concentration is equal, leading to no net water shift into or out of cells.

Hypotonic ECF

Extracellular fluid has lower osmolarity, causing water to enter cells and leading to cell swelling.

Hypertonic ECF

Extracellular fluid has higher osmolarity, causing water to exit cells and leading to cell shrinkage.

Starling Forces

The balance between filtration (fluid leaving capillaries) and reabsorption (fluid entering capillaries) in capillary exchange, governed by hydrostatic and oncotic pressures.

Edema

Fluid accumulation in the interstitial space due to filtration greatly exceeding reabsorption. Causes include increased capillary hydrostatic pressure (CHF) or decreased capillary oncotic pressure (nephrotic syndrome).

Hemorrhage

Loss of isotonic volume, resulting in decreased ECF volume but unchanged osmolarity. Activates the RAS and vasopressin systems.

Dehydration (Sweating, Fever, Diarrhea)

Loss of water greater than salt (hypertonic loss). Leads to decreased ECF volume and increased ECF osmolarity, causing water to shift from ICF to ECF, shrinking both compartments.

Isotonic IV Fluid

Intravenously administered solution of 0.9% NaCl, having no osmolar shift and increasing only the ECF compartment (plasma + interstitial fluid).

Hypotonic IV Fluid

Intravenously administered solution (e.g., 0.45% NaCl, D5W) that causes water to shift into cells, increasing ICF and posing a risk of cerebral edema.

Hypertonic IV Fluid

Intravenously administered solution (e.g., 3% NaCl) that causes water to shift out of cells into the ECF, decreasing ICF and increasing ECF volume, used to treat hyponatremia and cerebral edema.

Homeostasis

The physiological process of maintaining internal constancy (e.g., temperature, pH, ions, glucose, BP) through feedback loops.

Negative Feedback

A regulatory mechanism that opposes the initial stimulus, bringing the system back to a set point (e.g., blood glucose regulation by insulin/glucagon, body temperature regulation).

Positive Feedback

A regulatory mechanism that amplifies the initial stimulus to completion (e.g., childbirth, blood clotting).

Hypertonic Dehydration

Condition of a marathon runner experiencing fatigue, dry mucosa, oliguria, tachycardia, and hypotension after a hot race without water intake; characterized by water loss greater than salt loss.

Albumin

The main protein responsible for capillary oncotic pressure, which pulls fluid into the capillaries.