Exchange in, and control of, the peripheral circulation Flashcards
What are the key processes of capillary-tissue exchange?
Diffusion – Passive movement of gases, nutrients, and wastes (e.g., O₂, CO₂).
Filtration – Movement of fluid out of capillaries due to hydrostatic pressure.
Reabsorption – Movement of fluid into capillaries due to oncotic (colloid osmotic) pressure.
Transcytosis – Transport of larger molecules (e.g., proteins) via vesicles.
What is the blood-brain barrier (BBB), and why is it important?
The BBB is a selective barrier formed by tight junctions in brain capillary endothelial cells, preventing large or harmful substances from entering the brain while allowing glucose, O₂, and CO₂ to pass.
What are Starling forces, and how do they influence oedema?
Hydrostatic pressure (Pc) pushes fluid out of capillaries.
Oncotic (colloid osmotic) pressure (πc) pulls fluid into capillaries.
Imbalance (e.g., high hydrostatic pressure, low oncotic pressure) leads to oedema (excess interstitial fluid).
How does the lymphatic system prevent oedema?
It drains excess interstitial fluid and returns it to circulation via the thoracic duct, preventing fluid buildup.
What is Poiseuille’s Law, and why is it important in blood flow regulation?
Poiseuille’s Law states that blood flow (Q) is proportional to vessel radius (r⁴).
Small changes in radius cause large changes in resistance (R = 1/r⁴).
Vasoconstriction → ↑ resistance, ↓ flow.
Vasodilation → ↓ resistance, ↑ flow.
What is active hyperaemia?
Increased blood flow in response to increased metabolic activity (e.g., muscles during exercise).
What is pressure autoregulation?
The ability of organs (e.g., brain, kidneys) to maintain constant blood flow despite changes in arterial pressure.
What is reactive hyperaemia?
Increased blood flow after a period of ischemia (e.g., after removing a tourniquet).
What happens during the injury response in blood vessels?
Vasoconstriction – Limits blood loss.
Platelet plug formation – Platelets aggregate at the injury site.
Coagulation cascade – Clotting factors generate fibrin, stabilizing the clot.
Vasodilation & inflammation – Promotes healing via immune cell recruitment.
What are the main factors affecting arteriolar tone?
Neural – Sympathetic NS (vasoconstriction via α1 receptors), Parasympathetic NS (vasodilation in some tissues).
Hormonal – Adrenaline, angiotensin II (vasoconstriction), ANP (vasodilation).
Local – Nitric oxide (vasodilation), endothelin (vasoconstriction), metabolic demand (CO₂, H⁺, lactate → vasodilation).
What are the dominant factors controlling cardiac blood flow?
Metabolic demand (mainly adenosine & hypoxia causing vasodilation).
What are the dominant factors controlling cerebral blood flow?
Autoregulation & CO₂ levels (↑CO₂ → vasodilation, ↓CO₂ → vasoconstriction).
What are the dominant factors controlling pulmonary blood flow?
Hypoxic vasoconstriction (↓O₂ → constriction to redirect blood to well-oxygenated areas).
What are the dominant factors controlling renal blood flow?
Autoregulation via myogenic & tubuloglomerular feedback mechanisms.
