Summary of "Cardiovascular | Microcirculation"

Summary of Scientific Concepts and Phenomena in Microcirculation

Terminal arterial: The small artery feeding into the capillary bed.
Meta-arterial: Branches off the Terminal arterial and gives rise to True capillaries.
True capillaries: Smallest blood vessels (10-100 per capillary bed) where gas and nutrient exchange occurs.
Thoroughfare channel: A vessel that connects the Meta-arterial to the post-capillary venule, allowing blood to bypass True capillaries.
Vascular shunt: Combination of Meta-arterial and thoroughfare channel; an example of an arteriovenous anastomosis.
Post-capillary venule: Drains blood from the capillary bed.

Rings of smooth muscle around True capillaries that regulate blood flow into capillaries.
Controlled by sympathetic nervous system and local chemical signals.
Constriction blocks blood flow; dilation allows blood flow to tissues.

Capillary hydrostatic pressure (HPc): Pushes fluid out of capillaries (~35 mmHg arterial side, ~17 mmHg venous side), dependent on systolic blood pressure.
Capillary osmotic pressure (OPc): Pulls fluid into capillaries (~25 mmHg), mainly due to plasma proteins like albumin.
Interstitial fluid hydrostatic pressure (HPif): Pushes fluid into capillaries (~0 mmHg, usually negligible).
Interstitial fluid osmotic pressure (OPif): Pulls fluid out of capillaries (~1 mmHg), due to small solutes in interstitial fluid.

On arterial side: NFP ≈ (HPc + OPif) - (OPc + HPif) = (35 + 1) - (25 + 0) = +11 mmHg → net fluid out (filtration).
On venous side: NFP ≈ (17 + 1) - (25 + 0) = -7 mmHg → net fluid in (reabsorption).

Loss of plasma proteins (e.g., albumin) in conditions like Nephrotic syndrome reduces OPc → increased filtration → edema.
Lymphatic vessel blockage (e.g., cancer, lymphoma) impairs drainage → increased interstitial hydrostatic pressure → edema.

Arterial anastomosis: Connections between arteries (e.g., Circle of Willis in the brain, coronary circulation, joints).
Venous anastomosis: Connections between veins (most common, e.g., median cubital vein connecting basilic and cephalic veins in the arm).
Arteriovenous anastomosis: Direct connections between arteries and veins bypassing capillaries (vascular shunts).

A key arterial anastomosis in the brain formed by internal carotid arteries, anterior and posterior communicating arteries, vertebral arteries, basilar artery, and cerebral arteries.
Provides collateral blood flow to protect brain tissue in case of arterial blockage.
Clots in some arteries (e.g., middle cerebral artery) can still cause stroke despite anastomosis.

Skeletal muscle during exercise:
- Increased CO2, H+ (from lactic acid), and low pH cause vasodilation of arterioles.
- Relaxation of smooth muscle in tunica media increases blood flow (active hyperemia).
Brain:
- Regulated by mean arterial pressure (MAP).
- High MAP → vasoconstriction (myogenic mechanism) to protect fragile cerebral vessels.
- Low MAP → vasodilation to maintain perfusion and prevent syncope.
Lungs:
- Unique regulation: low oxygen partial pressure causes vasoconstriction of pulmonary arterioles to divert blood to better-ventilated areas.
Gastrointestinal tract (GIT), skin, kidneys:
- Under sympathetic stimulation (e.g., stress, fight or flight), vasoconstriction reduces blood flow to these less vital organs.
- Blood is shunted to vital organs like brain, heart, and skeletal muscles.

A pathological condition where arteries connect directly to veins without capillaries.
Causes high-pressure arterial blood to flow directly into veins, risking vessel rupture and hemorrhage.
Commonly found in the brain.
Treated by Embolization therapy to prevent rupture.