chapter 15 physio

Mass flow in cardiovascular system

Blood flow driven by pressure gradients created by the heart

What drives blood flow

Pressure generated by ventricular contraction

What regulates resistance

Arteriolar smooth muscle (local + reflex control)

Baroreceptor reflex

Monitors arterial pressure to maintain brain and heart perfusion

Where exchange occurs

Capillaries and postcapillary venules

Total blood flow

Equal to cardiac output

Blood vessel composition

Smooth muscle, elastic tissue, connective tissue, endothelium

Vascular smooth muscle tone

Baseline level of contraction in vessels

Function of arteries

Act as pressure reservoir via elastic recoil

Function of veins

Hold majority of blood volume and expand easily

Where most blood is stored

Veins

Angiogenesis

Formation of new blood vessels

Blood pressure definition

Force exerted by blood on vessel walls

Where BP is highest

Arteries

Normal BP

~120/80 mmHg

Pulse pressure

Systolic − diastolic pressure

MAP (mean arterial pressure)

Driving force for blood flow

BP depends on

Cardiac output and peripheral resistance

Effect of ↑ blood volume

↑ blood pressure

Effect of ↓ blood volume

↓ blood pressure

How veins return blood

Valves + skeletal muscle pump + respiratory pump

Main site of resistance

Arterioles

Effect of radius on resistance

Small ↓ radius → large ↑ resistance

Vasoconstriction

↑ resistance, ↓ blood flow

Vasodilation

↓ resistance, ↑ blood flow

Local vasodilators

Nitric oxide, prostaglandins, adenosine, histamine

Low oxygen effect

Vasodilation

Endothelin function

Potent vasoconstrictor

Active hyperemia

Increased blood flow with increased metabolism

Reactive hyperemia

Increased flow after temporary blockage

Sympathetic control of arterioles

Tonic vasoconstriction

Norepinephrine effect

Vasoconstriction

Epinephrine α receptors

Vasoconstriction

Epinephrine β receptors

Vasodilation (heart, liver, muscle)

Flow relationship

Flow inversely proportional to resistance

What determines tissue blood flow

Arteriolar resistance

Cardiovascular control center

Medulla oblongata

Baroreceptors location

Carotid arteries and aorta

Sympathetic effects

↑ heart rate, ↑ contractility, vasoconstriction

Parasympathetic effect

↓ heart rate

Orthostatic hypotension

Drop in BP upon standing

Primary capillary exchange mechanism

Diffusion

Bulk flow

Movement of fluid due to pressure differences

Filtration

Fluid leaves capillaries

Absorption

Fluid enters capillaries

Colloid osmotic pressure

Pulls fluid into capillaries (due to plasma proteins)

Capillary types

Continuous, fenestrated

Blood-brain barrier

Tight continuous capillaries

Capillary blood flow

Slow for efficient exchange

Lymphatic system function

Returns excess fluid to circulation

Daily fluid loss to tissues

~3 L/day

Lymph flow mechanisms

Smooth muscle + valves + skeletal muscle pump

Edema

Excess interstitial fluid accumulation

Atherosclerosis

Plaque buildup in arteries

Hypertension

Chronic high blood pressure

Biggest CVD risk

Hypertension