Vasculature & Intro to Respiration - Study Notes

Intrinsic vs Extrinsic Regulation of Blood Flow (Autoregulation)

• Goal: reroute blood to tissues that need it most during different activities (rest vs. exercise). Example: skeletal muscle blood flow can increase >10× from rest to exercise.
• Brain blood flow: remains about rac{dQ}{dt} ext{(blood flow)} o ext{constant} \, \approx 750\ \text{mL/min}.
• Autoregulation concepts:
  • Intrinsic (local) controls operate right in/near the tissue.
  • Extrinsic controls act from outside the tissue (often nervous system, hormones).
  • Local controls can be overridden or modulated by extrinsic inputs.
• Long-term autoregulation (angiogenesis): tissue growth (e.g., increased mass) requires new blood vessels; angiogenesis = genesis of blood vessels; takes weeks to months.
• Brain exception: relatively constant perfusion; other tissues adapt more with metabolic demand.
• Context: these controls determine where blood goes during activity and how quickly that redistribution happens.

Local Controls: Myogenic and Metabolic

• Myogenic controls (local): smooth muscle response to stretch; automatic contraction in response to stretch to resist further stretch (no external nervous input required).
• Metabolic controls (local): chemical conditions produced by tissue metabolism regulate blood flow.
  • Active tissues (e.g., skeletal muscle during exercise) consume O₂, produce CO₂, generate H⁺ (acid), and alter other metabolites.
  • General pattern in active tissues: low O₂, high CO₂, high acidity (low pH). These changes promote vasodilation to increase blood flow to the tissue.
  • Gas exchange and metabolism are tied together: the same chemical signals that promote blood flow also facilitate O₂ unloading from hemoglobin in active tissues.
• Key metabolic conditions to know (for vasodilation):
  • Low O₂ concentration
  • High CO₂ concentration
  • High acidity (low pH)
  • Often accompanies these: high K⁺ (especially with acidity), though the main three are O₂, CO₂, and H⁺.
• Important note on chemical mediators (not all tested on exam):
  • Prostaglandins, adenosine, nitric oxide can promote vasodilation but may not be asked about in detail.
  • Endothelins are not a focus for this course/exam (scratch them out in your notes).
• Active tissues and these local factors are central to the controls of blood flow during respiration and exercise.

Extrinsic Controls: Neural and Hormonal

• Extrinsic vasodilation factors:
  • Reduced sympathetic tone (neural): lowering vasoconstrictor signals causes dilation.
  • ANP (atrial natriuretic peptide): a hormonal vasodilator that can reduce blood pressure by relaxing vessels.
• Extrinsic vasoconstriction factors:
  • Neural: increased sympathetic tone causes vasoconstriction.
  • Angiotensin II: potent vasoconstrictor (also influences fluid balance).
  • Antidiuretic hormone (ADH, vasopressin): primarily promotes kidney water reabsorption, but can contribute to vasoconstriction at certain levels.
  • Epinephrine and norepinephrine: potent vasoconstrictors (especially via α-receptors); can also cause vasodilation in some beds via β-receptors depending on tissue.
• Practical takeaway: for exam prep, focus on the list of vasodilators (low O₂, high CO₂, high acidity; plus ANP and reduced sympathetic tone) and vasoconstrictors (Ang II, ADH, EPI/NE, increased sympathetic tone).
• Big-picture: these factors can act locally or systemically to adjust tissue perfusion according to needs and hormonal status.

Factors Governing Blood Flow Velocity in the Vascular Bed

• Velocity of flow depends on the total cross-sectional area of the vessels in a region.
• Conceptual rule: more vessels spread out flow, the slower the velocity; fewer vessels in a given area increase velocity.
• Typical pattern:
  • Fastest flow in the aorta and large arteries (closer to the heart).
  • Slowest flow in capillary beds (to allow exchange with tissues).
  • Velocity increases again as flow moves into venules, veins, and back to the heart.
• Analogy used in lecture: water in a pipe network spreading across many tiny outlets slows down (more surface area to fill).
• Practical implication: capillaries are the site of exchange due to slow flow and high surface area.

Capillary Exchange: How Substances Move Between Blood and Tissues

• Goal: move nutrients, gases, and wastes across capillary walls to/from tissues.
• Four main mechanisms for crossing the capillary wall: 1) Diffusion through the membrane (lipid-soluble substances): pass directly through phospholipid bilayer.
  • Examples: triglycerides, fatty acids, cholesterol.
    2) Diffusion through intracellular clefts (water-soluble substances).
    3) Diffusion through fenestrations (water-soluble substances).
  • Note: 2) and 3) are essentially the same mechanism; fenestrations allow small, water-soluble molecules to pass if present.
    4) Transport via vesicles or caveolae (large substances): proteins or other large solutes.
• The big picture figure (capillary forces) shows two opposing forces:
  • Arterial (upstream) end: hydrostatic pressure drives fluid out of capillaries into surrounding tissue.
  • Venous (downstream) end: oncotic/osmotic pressure (primarily due to plasma proteins like albumin) pulls water back into capillaries.
• Key numbers to remember:
  • Arterial end hydrostatic pressure: P_{hydro} \,\approx\, 35\ \text{mmHg}. This pushes fluid out of capillaries into tissues.
  • Venous end oncotic (osmotic) pressure: P_{osmotic} \,\approx\, 26\ \text{mmHg}. This draws water back into the capillaries.
• Net filtration/reabsorption:
  • The arterial end pushes fluid out more than the venous end reabsorbs it, leading to a net outward movement of fluid.
  • The excess (~9 mmHg) is returned via the lymphatic system.
• Lymphatics:
  • Return excess tissue fluid to circulation and provide a route for immune cells (primarily T cells; occasional B cells).
  • If lymphatic vessels are damaged or blocked (e.g., by tumor), edema can occur in the affected area.
• Practical takeaway: think of capillary exchange as a balance between hydrostatic forcing outward and oncotic pulling inward; lymphatics mop up the surplus fluid.

Respiratory System: Overview and Unit Two Transition

• Respiratory system functions in tandem with the cardiovascular system: it delivers O₂ to blood, removes CO₂ from blood, and moves gases through the blood to tissues.
• Four respiratory processes:
  • Pulmonary ventilation: breathing; moving air into and out of the lungs.
  • External respiration: gas exchange between air in the lungs and the blood (across the alveolar-capillary membrane).
  • Internal respiration: gas exchange between blood and tissues (systemic capillaries).
  • (Ongoing theme: interplay with circulation for gas transport.)
• Basic anatomy focus for this unit:
  • Air enters primarily through the nasal cavity, goes through the pharynx (throat), larynx, trachea, bronchial tree, and into the lungs.
  • Lungs are asymmetric: right lung has 3 lobes; left lung has 2 lobes (cardiac notch present on left due to heart).
• Upper vs lower respiratory system:
  • Upper: nasal cavity and pharynx (air filtration, warming, humidification; includes oral pharynx and nasopharynx).
  • Lower: begins at the larynx and includes the trachea, bronchi, and lungs.
• Lower respiratory division is functionally split into two zones:
  • Conducting zone: moves air, no gas exchange; supported by cartilage to keep airways open (cartilage in the walls; trachea with a horseshoe-shaped cartilage; back wall containing soft tissue and trachealis muscle).
  • Respiratory zone: where gas exchange occurs (alveolar region).
• Key anatomical features (narrative highlights from lecture):
  • Pharynx regions: nasopharynx, oropharynx (oral pharynx), and laryngopharynx (leads to larynx).
  • Epiglottis: a flap-like structure that covers the glottis during swallowing to prevent food from entering the airway; choking hazard linked to the sharp right-angle between the mouth and esophagus.
  • Larynx (voice box): houses vocal cords/folds; vibration of these folds produces sound; glottis is the opening between folds.
  • Trachea: reinforced by cartilage rings (horseshoe); the back wall is fibromuscular and contains the trachealis muscle which can adjust tension; this helps accommodate swallowing by preventing tracheal collapse.
  • Mucus escalator: mucus-producing glands and ciliated cells line the airway; cilia move mucus upward to keep airway clear.
  • Primary, secondary, and tertiary bronchi: branching into progressively smaller airways to reach all lobes.
• Important clinical note (aspiration): if a foreign object is inhaled, it is more likely to lodge in the right main bronchus due to its more vertical orientation compared with the left.
• The right vs left lung anatomy is linked to heart position (left chest cavity) and heart notch on the left lung.
• Terminology recap:
  • Upper respiratory tract infection typically involves nose/pharynx; lower tract infections involve structures below the larynx.
  • Conducting zone vs respiratory zone distinction is essential for understanding where gas exchange occurs.
• Quick advisory from the lecturer: respiration is not as “hard” conceptually, but it introduces gas pressures and chemistry (e.g., more chemistry than previously). Expect focus on gas pressures, volumes, and movement of air in the next sessions.

Key Connections and Implications

• Interdependence of systems:
  • Cardiorespiratory integration: blood flow redistribution supports tissue metabolism; gas exchange supports cellular respiration.
  • Local vs extrinsic control principles apply across organ systems, not just vasculature.
• Real-world relevance:
  • Understanding capillary exchange helps explain edema and the role of the lymphatic system.
  • Knowledge of airway anatomy and choking mechanisms informs first-aid and clinical assessments.
• Ethical/philosophical note (implicit): appreciating how homeostatic mechanisms balance regional needs under varying conditions highlights the importance of maintaining systemic health to prevent local failures (e.g., edema, impaired ventilation).

Quick Reference: Summarized Figures and Numbers

• Brain perfusion: ext{Q}_{ ext{brain}}
  ightarrow ext{about }750\ \text{mL/min}
• Capillary hydrostatic pressure (arterial end): P_{hydro} \approx 35\ \text{mmHg}
• Capillary osmotic (oncotic) pressure (venous end): P_{osmotic} \approx 26\ \text{mmHg}
• Net fluid movement: arterial end favors filtration/outflow; venous end favors reabsorption, with lymphatics returning the excess (~9 mmHg equivalent).
• Capillary transport mechanisms: diffusion through membranes; diffusion through clefts or fenestrations; vesicular transport (caveolae).
• Gas exchange processes: Pulmonary ventilation, External respiration, Internal respiration; nasal cavity to bronchi to alveoli; upper vs lower respiratory tract; conducting vs respiratory zones.
• Equations to remember:
  • Gas transport and reactions (carbon dioxide hydration): \ce{CO2 + H2O
• Anatomical landmarks to recall:
  • Epiglottis, vocal cords, glottis; trachea with C-shaped cartilage and soft posterior wall (trachealis);
  • Right main bronchus more vertical; lobes: right 3, left 2; cardiac notch on left lung.

study prompts / quick questions

• What are the four main processes of respiration and how do they differ?
• Which factors most strongly drive vasodilation in active tissues? What about vasoconstriction?
• How does the lymphatic system help prevent edema in capillary exchange?
• Why is the right main bronchus more likely to receive aspirated material?
• How do the hydrostatic and oncotic pressures drive fluid movement across capillaries, and what happens to the excess fluid?