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Flashcards in Module 6: Cardiovascular Deck (237)
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2 Major factors that affect Pulse Pressure

1. Stroke Volume
2. Compliance – total distensibility of the arterial tree

*The greater the SV - the greater the amount of blood that must be accommodated in the arterial tree with each heartbeat therefore the greater the pressure rise during systole and fall during diastole – greater PP

*Less compliant arterial system – greater the rise in pressure
Ex. Arteriosclerosis (arteries less elastic – non compliant – increase PP 2x as normal


Factors that maintain normal ABP

1. Total Peripheral Resistance – the resistance offered by the
- Arterioles which have great capacity to change radius
- Blood Viscosity – imparted firstly by RBC and secondly by plasma proteins

2. Cardiac Output
- Stroke Volume
- Heart Rate


Determinants of Arterial Blood Pressure

1. Physical Factors or Fluid Mechanical Characteristics
- fluid volume (blood volume)
- static elastic characteristics (compliance of arterial system)

2. Physiological Factors
- cardiac output (stroke volume X heart rate)
- total peripheral resistance


Basis for ABP measurement: turbulent flow of blood KOROTKOFF’S SOUNDS:

1. Thud or tapping sound
2. Tapping sound + bruit (murmuring quality)
3. Loud snapping sound
4. Muffled, dull, softer sound
5. Complete disappearance of sound


Methods of Measuring Blood Pressure

A. Direct Method

B. Indirect Method
1. Auscultatory Method
2. Palpatory Method
increased pressure ----------- HYPERTENSION
decreased pressure ----------- HYPOTENSION


thin-walled lined with a single layer of endothelial cells, which are surrounded by a basal lamina




1. Lipid soluble substances (O2 and CO2) cross the capillary wall by dissolving in & diffusing across the endothelial cells
2. H2O soluble substances (ions) cross the capillary either
a. Through water-filled clefts (spaces) between the endothelial cells or
b. Through large pores in the wall of some capillaries (ex. Fenestrated caps)


Not all capillaries are perfused with blood at all times. Instead, there is __ of capillary beds – depending on the metabolic needs of the tissues.

o This selective perfusion is determined by the degree of dilation or constriction of the arterioles and pre-capillary sphincters (smooth muscle bands that lie before the capillary)
o The degree of dilation or constriction is in turn, controlled by the: sympathetic innervation of the vessel smooth muscle and by Vasoactive metabolites produced in the tissues

selective perfusion


Structure of capillary wall

• lined by single layer of endothelial cells
• surrounded by very thin basement membrane
• total thickness = 0.5 micrometer
• diameter = 4 to 9 micrometers
• endothelial cells, basement membrane
• (-) smooth muscle and (-) elastic tissue
• tight junctions, fenestrations (pores), intercellular cleft and and pericytes
• Total area exceeds 6300 m2 and 1 µm thick


Types of Capillaries

- Continuous capillaries
- Fenestrated capillaries
- Sinusoidal capillaries


- the rate of filtration at any point along the capillary depends upon the balance of forces called Starling’s Forces across the capillary wall.

Capillary Fluid Shift


Starling’s Forces

1. Total Filtration Pressure
- Capillary Hydrostatic Pressure
- Tissue Colloid Osmotic Pressure

2. Total Absorption Pressure
- `Plasma Colloid Osmotic Pressure
- Tissue Hydrostatic Pressure


The __ in the capillaries tends to force fluid and its dissolved substances through the capillary pores into the interstitial spaces.

hydrostatic pressure


osmotic pressure caused by the plasma proteins (called __) tends to cause fluid movement by osmosis from the interstitial spaces into the blood. This osmotic pressure exerted by the plasma proteins normally prevents significant loss of fluid volume from the blood into the interstitial spaces.

colloid osmotic pressure


Starling’s Forces

1. The CAPILLARY PRESSURE (PC), which tends to force fluid outward through the capillary membrane.

2. The INTERSTITIAL FLUID PRESSURE (Pif), which tends to force fluid inward through the capillary membrane when Pif is positive but outward when Pif is negative.

3. The CAPILLARY PLASMA COLLOID OSMOTIC PRESSURE (Πp), which tends to cause osmosis of fluid inward through the capillary membrane.

4. The INTERSTITIAL FLUID COLLOID OSMOTIC PRESSURE (Πif), which tends to cause osmosis of fluid outward through the capillary membrane.


If the sum of these forces-the net filtration pressure-is positive, there will be a __ across the capillaries.

net fluid filtration


If the sum of the Starling forces is negative, there will be a __ from the interstitial spaces into the capillaries.

net fluid absorption



1. Intercellular cleft – a thin-slit channel between adjacent endothelial cells called “slit-pores”
2. Plasmalemmal vesicles – which coalesce to form vesicular channels all the way through the endothelial cells


- most __ permit only molecules with radius less than 3 – 6 mm to pass through vessel wall
- allowed to pass through small pores
*water, inorganic ions, glucose, amino-acids, water-soluble solutes

- not allowed to pass through
*serum albumin, globular proteins, blood cell components

- lipid soluble molecules (O2 and CO2) pass through lipid components of endothelial cell membrane



Porosity of capillaries NOT the same in all organs (Brain and Spinal Cord)

Have continuous tight junctions between endothelial cells. Thus only the smallest water-soluble molecules pass through (H2O, O2 and CO2)


Porosity of capillaries NOT the same in all organs (Capillaries in cardiac and skeletal muscles)

- have low porosity to water and small water-soluble substances


Porosity of capillaries NOT the same in all organs (Liver and GIT)

Liver – the clefts between endothelial cells wide open. So, almost all dissolved substances of plasma (plasma proteins) can pass from blood to liver tissues

GIT – midway between liver and muscles


Porosity of capillaries NOT the same in all organs (Glomerular tuft of kidneys and Spleen and Bone Marrow Capillaries)

Glomerular tuft of kidneys – numerous small oval windows (fenestrae) penetrate all the way through endothelial cells. Only plasma protein cannot pass.

Spleen and Bone Marrow Capillaries – large pores


- main determinant of transcapillary exchange
- force exerted by the blood against the walls of capillaries
- pushing pressure – pushes fluid from capillary to interstitium

Capillary Hydrostatic Pressure (CHP)


Capillary Hydrostatic Pressure (CHP): Normal Values

arteriolar end - 35 mm Hg
venular end - 15 mm Hg
average CHP - 25 mm Hg


- normal THP: -7 to 1 mm Hg
- pushing pressure – pushes fluid from interstitium back to the capillaries and veins through the lymphatic system

Tissue (Interstitial) Hydrostatic Pressure (THP)


- normal PCOP: 25 mmHg
- also known as Osmotic Pressure of Plasma Proteins (OPPP) and Oncotic pressure
- exerted by the plasma proteins (particularly albumin)
- pulling pressure – pulls fluid from interstitium to capillaries

Plasma Colloid Osmotic Pressure (PCOP)


- normal TCOP: 7 – 8 mm Hg
- exerted by plasma proteins that leaked through the capillary wall and go into the interstitium
- pulling pressure – pulls fluid from capillaries to interstitium

Tissue (Insterstitial) Colloid Osmotic Pressure (TCOP)


Circulatory Adjustments are effected by:

1. Altering the output of the heart – CO
2. Changing the diameter of the resistance vessels – TPR
3. Altering the amount of blood pooled in the capacitance vessels


Caliber of Arterioles adjusted or effected by:

1. autoregulation
2. locally produced Vasodilator Metabolites
3. subs secreted by Endothelium
4. systematically produced by circulating vasoactive subs (Hormones)
5. the nerves that innervate the arterioles (Neural)