Exchange in, and control of, the peripheral circulation Flashcards
What happens in capillary exchange?
It’s how nutrients, gases, and waste move between blood and tissues.
🛠️ Main methods:
Diffusion: movement from high to low concentration
Carrier-mediated transport: uses special proteins (e.g., glucose transporters)
Bulk flow: movement of fluid driven by pressure (like a sponge squeezing)
What is the blood-brain barrier (BBB)?
A special capillary system in the brain that only allows certain substances (like oxygen and glucose) to pass through.
🧠 Extra info: Protects the brain from harmful substances in the blood.
What are Starling forces?
They determine the net movement of fluid in or out of capillaries.
🧮 Two main forces:
Hydrostatic pressure (pushes fluid out)
Oncotic (osmotic) pressure (pulls fluid in)
📌 Imbalance can lead to oedema (fluid build-up).
What is the lymphatic system’s role?
It drains excess fluid from tissues and returns it to the bloodstream.
🛡️ Also helps in immune defense and prevents oedema.
What is oedema?
Swelling caused by too much fluid leaking into tissues.
🧾 Causes: Increased pressure in capillaries, low protein in blood, or blocked lymphatics.
Why are arterioles important?
They control how much blood flows into capillaries and affect blood pressure.
📉 More constriction = higher resistance = higher blood pressure
📈 More dilation = lower resistance = better blood flow
What is total peripheral resistance (TPR)?
The overall resistance to blood flow in the whole circulation.
🧮 TPR helps determine mean arterial pressure (MAP) along with cardiac output.
What is Poiseuille’s Law?
A formula that shows how resistance is affected by the radius of a blood vessel.
🔍 Small change in radius = big change in flow!
E.g., if radius halves, resistance increases by 16x.
What is active hyperaemia?
Increased blood flow to a tissue because it’s more active and needs more oxygen (like muscles during exercise).
What is pressure autoregulation?
When a tissue keeps blood flow steady even if blood pressure changes.
🧠 Important in the brain and kidneys to prevent damage.
What is the injury response in vessels?
When blood vessels dilate and become leaky after injury to bring immune cells and healing factors.
What controls arteriolar tone (tightness)?
Local factors: O₂/CO₂ levels, pH, nitric oxide
Neural control: Sympathetic nerves (using norepinephrine)
Hormonal control: Adrenaline/epinephrine, angiotensin
What controls blood flow to the heart (coronary circulation)?
Mostly local control — heart gets more blood when it works harder (active hyperaemia).
🫀 Nitric oxide and adenosine help dilate vessels.
What controls blood flow to the brain (cerebral circulation)?
Pressure autoregulation keeps brain blood flow stable, despite BP changes.
CO₂ levels are also a strong influence.
What controls blood flow to the lungs (pulmonary circulation)?
Blood goes to oxygen-rich areas of the lungs.
Low oxygen causes vasoconstriction to redirect flow.
What controls blood flow to the kidneys (renal circulation)?
Autoregulation maintains steady flow to filter blood.
Also influenced by hormones like renin and angiotensin.
