Physiology of Cell, Body Fluids & Homeostasis – Lecture Notes

Reading Plan & Resources

• Pre-Reading Strategy
  • Read assigned textbook pages before each lecture for easier comprehension.
  • Bring questions from the reading to class for clarification.
• Texts Mentioned
  • Netter’s Physiology (required): concise, high-yield.
  • Costanzo Physiology (recommended): detailed, student-friendly.
  • Dr. Thomas will post a chapter/page cross-reference list for every lecture.
• Supplemental Uploads
  • Extra handout on oxidative phosphorylation already posted on Blackboard.
  • Future uploads: practice questions, study guides, PDF copies of slides, additional Starling-force examples.

Instructor Background

• Dr. Jessica Thomas
  • B.S. Chemistry, minor Mathematics – Alabama State University (Montgomery native).
  • Ph.D. Neuroscience – University of Iowa.
  • Post-doctoral training – Vanderbilt University.
  • Currently teaches & conducts research at Meharry Medical College.
  • Contact: prefers text for fastest response; flexible Zoom/on-campus meetings; no fixed office hours (toddler schedule!).

Course & Assessment Logistics

• First half of Physiology taught by Dr. Thomas.
• Quizzes: clinical-style and factual questions; practice sets provided ahead of time.
• Study guide = list of concepts (all quiz questions pulled directly from slides).
• Class email list being assembled for students lacking Blackboard access.

Scope of Today’s Lecture

• Physiology overview (functions & mechanisms).
• Core cell biology review: organelles & clinical correlations.
• Body-fluid compartments & tonicity.
• Starling forces in capillary exchange.
• IV fluid types & clinical decision rules.
• Homeostasis & feedback loops.

Physiology: Definition & Disciplinary Links

• Study of how biological systems function.
• Integrates biochemistry, anatomy, physics (gradients, pressure), and cell biology.
• Foundation for understanding pathophysiology (disease = disrupted normal function).

Cell Structure & Function

• Why important? All drugs, toxins, diseases act at the cellular level.

Nucleus

• Contains DNA; site of transcription, not translation.
• Nuclear envelope regulates RNA export.
• DNA mutations ⇒ genetic disorders.
• Central dogma: \text{DNA} \;\xrightarrow{\text{transcription}}\;\text{RNA} \xrightarrow{\text{translation}} \text{Protein} plus reverse transcription by viral enzymes.

Mitochondrion

• “Powerhouse”: site of aerobic respiration & oxidative phosphorylation.
• Own circular maternal DNA → disorders preferentially affect high-energy tissues (brain, muscle).
• Electron-transport chain (ETC):
  • Electron donors: \text{NADH} (→ Complex I) & \text{FADH_2} (→ Complex II).
  • Oxygen = final electron acceptor → H_2O.
  • Proton gradient across inner membrane drives ATP synthase.
  • Yield: 1\;\text{NADH} \Rightarrow 2\;\text{ATP},\; 1\;\text{FADH}_2 \Rightarrow 1.5\;\text{ATP} (board figure).
  • ETC inhibitors/uncouplers:
  • Complex IV: cyanide, CO → ↓ATP, cell death.
  • ATP synthase: oligomycin (unused clinically).
  • Uncouplers: 2,4-DNP, thermogenin (brown fat) → heat production.

Endoplasmic Reticulum (ER)

• Rough ER (ribosome-studded)
  • Synthesizes secretory & membrane proteins.
  • Abundant in salivary glands, other secretory epithelia.
• Smooth ER (no ribosomes)
  • Synthesizes lipids & steroids, detoxifies drugs.
  • Prominent in liver & adrenal cortex.

Golgi Apparatus

• Post-translational modification (glycosylation, tagging), sorting, packaging.
• Produces lysosomes.
• I-cell disease: missing \text{M6P} tag → lysosomal enzymes secreted into plasma.

Lysosome

• Acidic vesicle for waste breakdown.
• Malfunction → lysosomal storage disorders (e.g., Tay-Sachs).

Peroxisome

• β-oxidation of very-long-chain fatty acids; generates H2O2.
• Defect → Zellweger syndrome (↑ VLCFA, hypotonia, seizures, cranio-facial dysmorphisms).

Cytoskeleton

• Microtubules (largest): vesicle transport, cilia, mitotic spindle.
• Microfilaments (actin): motility, muscle contraction (details in muscle lecture).
• Intermediate filaments: structural support (e.g., keratin, neurofilaments).
• Microtubule defect → primary ciliary dyskinesia (infertility, chronic infections, situs inversus).

High-Yield Organelle–Disease List (memorise)

• Tay-Sachs – lysosome (GM2 ganglioside accumulation; “onion-skin” lysosomes; cherry-red macula; NO hepatosplenomegaly).
• Gaucher, Niemann-Pick, Pompe, etc. – various lysosomal enzymes.
• Zellweger – peroxisome (↑ VLCFA, neonatal death).
• I-cell disease – Golgi tagging failure.
• ETC inhibitor toxicities as above.

Body-Fluid Compartments

• Human ≈ 60\% water, 40\% solids.
• Standard reference male 70\;\text{kg} \Rightarrow 42\;\text{L} total body water (TBW).
• Rule 60-40-20:
  • 60\% of body weight = TBW.
  • 40\% BW = intracellular fluid (ICF).
  • 20\% BW = extracellular fluid (ECF).
  • ECF split: \frac{3}{4} interstitial fluid, \frac{1}{4} plasma.
• Variations: men > women, infants > elderly (fat ↓ TBW).

Osmolarity & Tonicity

• Osmolarity = solute particles per liter solution; drives water movement.
• Isotonic: equal osmolarity → no net water shift.
• Hypotonic (ECF ↓ osmolarity): water enters cells → swelling.
• Hypertonic (ECF ↑ osmolarity): water exits cells → shrinkage.

Starling Forces & Capillary Exchange

• Balance between filtration (fluid leaves capillaries) and reabsorption (fluid enters capillaries).
• Starling equation (conceptual): \displaystyle Jv = Kf \big[(Pc - Pi) - \sigma(\pic - \pii)\big]
  • P_c = capillary hydrostatic pressure (pushes out).
  • P_i = interstitial hydrostatic pressure (pushes in).
  • \pi_c = capillary oncotic (albumin) pressure (pulls in).
  • \pi_i = interstitial oncotic pressure (pulls out).
  • Positive J_v → net filtration; negative → net reabsorption.

Clinical Correlations

• Edema = filtration ≫ reabsorption.
  • Causes: ↑Pc (CHF), ↓\pic (nephrotic syndrome, liver failure, hemorrhage), ↑ capillary permeability (inflammation), lymphatic obstruction.
• Hemorrhage: isotonic volume loss (↓ ECF volume, same osmolarity) → activates RAS, vasopressin.
• Dehydration (sweating, fever, diarrhea): hypertonic loss (water > salt).
  • ↓ ECF volume, ↑ ECF osmolarity → water shifts from ICF to ECF; both compartments shrink.

Intravenous (IV) Fluids: Composition & Effects

Quick Fluid-Shift Summary (Board Table)

• Hemorrhage: ICF = same, ECF ↓, \text{osm} = same.
• Dehydration: ICF ↓, ECF ↓, \text{osm} ↑.
• Isotonic infusion: ICF same, ECF ↑, \text{osm} same.
• Hypotonic infusion: ICF ↑, ECF ↑, \text{osm} ↓.
• Hypertonic infusion: ICF ↓, ECF ↑, \text{osm} ↑.
• Edema: plasma → interstitium (↑ interstitial volume, no ICF change).

Homeostasis & Feedback Loops

• Goal: maintain internal constancy (temperature, pH, ions, glucose, BP).
• Components: sensor → control center (usually hypothalamus) → effector.
• Negative Feedback (most common)
  • Blood glucose (insulin vs. glucagon).
  • Body temperature (sweating, vasodilation; shivering, vasoconstriction).
  • Blood pressure (baroreceptor reflex → HR & vessel tone adjustments).
• Positive Feedback (amplify to completion)
  • Childbirth: stretch → oxytocin → uterine contractions → more stretch.
  • Blood clotting: platelet activation cascade.
  • Drug addiction (reward-loop potentiation, though long-term receptor down-regulation complicates).

Case Study: Marathon Runner

• Presentation: fatigue, dry mucosa, oliguria, tachycardia, hypotension after hot race w/ no water.
• Diagnosis: hypertonic dehydration (water ≪ salt).
• Primary disturbed compartment: ECF first, then compensatory water shift causes both ECF & ICF shrinkage.
• Management: hypotonic or isotonic fluids depending on serum Na⁺ and neuro status (avoid hypertonic saline).
• Starling perspective: ↓ plasma volume → ↓P_c, ↑ oncotic pull → fluid re-entry until volume restored.

Common Student Q&A Highlights

• Why isotonic solutions cause no net water movement? Equal osmolarity between compartments.
• Albumin = main determinant of \pi_c; low albumin → edema/filtration.
• Dialysis removes solutes directly from blood; not a classic Starling variable.
• Practice questions, Zoom reviews, & office meetings will precede each quiz.

Practical Study Tips

• Master organelle functions + hallmark diseases; expect straight recall questions.
• Drill Starling variables: associate each pressure with direction (filter vs. absorb) & location (capillary vs. interstitium).
• Memorize IV-fluid table & when to choose each clinically.
• Work textbook end-of-chapter questions; compare to posted practice sets.
• Use Costanzo for deeper explanations if Netter feels too brief.