Cardiovascular Autoregulation, Vasoconstriction, and Blood Flow Control in Physiology

What are the effects of Angiotensin II?

Vasoconstriction via AT1 receptors + RAAS activation

What does ADH (vasopressin) do?

V1 receptors: Vasoconstriction; V2 receptors: ↑ Water reabsorption

What are the effects of ANP?

"Vein relaxation, ↑ HR, ↓ water reabsorption"

How does epinephrine affect vessels?

α₁ receptors: Vasoconstriction; β₂ receptors: Vasodilation

What is autoregulation?

Intrinsic ability of organs to maintain constant blood flow despite changes in perfusion pressure

What vessels are primarily affected by autoregulation?

Arterioles

What triggers myogenic autoregulation?

Vessel stretch → ion channel activation → MLCK → constriction

What happens with ↑ arterial pressure?

Vasoconstriction to protect capillaries

What happens with ↓ arterial pressure?

Vasodilation to maintain flow

What triggers metabolic autoregulation?

↑ Metabolic demand vs. oxygen delivery

Name key vasodilating metabolites.

"CO₂, H⁺, adenosine, ATP, lactate, K⁺"

What causes flow-mediated dilation?

↑ Shear stress → endothelial NO release → vasodilation

What is active hyperemia?

↑ Blood flow with ↑ metabolic rate

What is reactive hyperemia?

↑↑↑ Flow after occlusion due to metabolite buildup

What do histamine and bradykinin do?

Vasodilation → redness; ↑ Capillary permeability → edema; ↓ BP (slightly)

What happens in anaphylaxis?

Systemic mediator release → severe hypotension

What regulates cerebral blood flow?

Myogenic autoregulation + CO₂ levels

What is the cerebral autoregulation range?

50-150 mmHg

What happens below 50 mmHg in cerebral circulation?

Ischemia risk

What happens above 150 mmHg in cerebral circulation?

Risk of vessel rupture

What crosses the blood-brain barrier?

"Water, CO₂, O₂, lipid-soluble drugs, glucose (via transporters)"

What does NOT cross the blood-brain barrier?

"Charged substances, proteins, lipid-insoluble drugs"

What is CSF made from?

Filtered plasma with selective transport

What is the function of CSF?

Cushions brain and CNS

What happens if CSF absorption is impaired?

Hydrocephalus

What regulates coronary flow?

Hypoxia

When does LV perfusion occur?

During diastole

Why is tachycardia risky for LV?

Shortened diastole → ↓ perfusion → ischemia

What controls skin blood flow?

Sympathetic system (α₁ receptors)

What is the main function of skin circulation?

Temperature regulation

What happens with cold exposure?

Vasoconstriction → pale fingers

What happens with trauma?

Histamine release → vasodilation

What is unique about pulmonary response to hypoxia?

Vasoconstriction (opposite of systemic)

Why does pulmonary hypoxic vasoconstriction happen?

Redirects blood to ventilated lung areas

What are pulmonary artery and vein characteristics?

Arteries: Deoxygenated blood; Veins: Oxygenated blood

What cardiovascular changes occur in pregnancy?

"↑ Blood volume (↓ Hct), ↓ SVR, ↓ BP, ↑ CO (↑ HR + SV), ↑ Clotting factors"

What crosses the placenta?

"IgG, O₂, CO₂, glucose, ions, water, urea, creatinine, some drugs"

What does NOT cross the placenta?

"RBCs, immune cells, some drugs"

What fetal structures bypass lungs?

Ductus arteriosus & foramen ovale

What causes DA closure after birth?

↓ Prostaglandins

What regulates renal blood flow?

Sympathetic + RAAS + autoregulation

What type of autoregulation is used in kidneys?

Myogenic + tubuloglomerular feedback

What controls skeletal muscle flow at rest vs. exercise?

Rest: Sympathetic (α₁); Exercise: Metabolic regulation

How much can skeletal muscle flow increase during exercise?

Up to 50-fold

What is the hepatic portal system?

GI veins → liver → heart

What regulates splanchnic flow?

Catecholamines (SNS)

What is the function of the lymphatic system?

Returns interstitial fluid to cardiovascular system

What drives lymph flow?

"External pressure, smooth muscle contractions, one-way valves"

Where does lymph drain?

Thoracic duct → subclavian veins

What happens after lymph node excision?

Chronic edema risk