artery arteriole capillary venule vein · adenosine increase blood flow to match metabolism hypoxic...
Post on 07-Oct-2020
2 Views
Preview:
TRANSCRIPT
-
1
Learning Objectives:
Explain how capillary perfusion is regulated
Eplain how the elasticity of arties affects diastolic pressure
Describe the theory of sphygmomanometry
Calculate mean arterial pressure and pulse pressure
QUIZ/TEST REVIEW NOTES
SECTION 1 BLOOD FLOW/CONTROL OF BLOOD PRESSURE
[VASCULATURE] CHAPTER 15
I. STRUCTURE OF VESSELS
ARTERY VEIN
Walls Thick, Low Compliance (not
very collapsible), High Recoil
(very stretchable)
Thin, High Compliance (very
collapsible), Low Recoil (not
stretchable)
Inner Diameter Small Larger
Pulse Pressure Greatest Pressure Least Pressure
Valves None Yes
Miscellaneous 65% of blood volume is held in
the veins except during exercise
a. General Characteristics of blood vessels a. Compliance and Recoil
Compliance: How easily the wall can collapse
Recoil: How easily the wall can stretch Arteries No Compliance/Yes Recoil
Veins Yes Compliance/No Recoil
Blood leaving the left side of the heart (oxygenated) enters systemic arteries where there is expandable elastic regions; where pressure produced contraction of left ventricle is stored in
the elastic walls of arteries and slowly released through elastic recoil
Artery Arteriole Capillary Venule Vein
-
2
This mechanism maintains continuous driving pressure for blood flow during the time when ventricles are relaxing
Blood flow through any level of circulation is equal to CO (If cardiac output is 5L/min by heart, it will be 5L/min in all other systemic capillaries)
>Blood Vessels Contain Vascular Smooth Muscle<
- Smooth muscle in vessels is known as vascular smooth muscle
- Vasoconstriction: Narrows the diameter of vessels lumen
- Vasodilatation: Widens the diameter of vessels lumen
b. Exchange Between the Blood and Interstitial Fluid Takes Place in the Capillaries a. General characteristics
Smallest vessels in the cardiovascular system Site of exchange between blood and interstitial fluid Site of exchange also for nutrients, waste, and water Lack smooth muscle and elastic/fibrous tissue reinforcement Walls contain only flat layer of endothelium one cell thick supported on basal lamina
(acellular matrix/basement membrane)
- Pericytes are contractile cells that surround the capillaries forming mesh like outer layer between endothelium of capillaries and interstitial fluid
- Pericytes contribute to tightness of capillary permeability; more perictyes the less leaky the capillary
2 MAIN TYPES OF CAPILLARIES:
(1) Continuous Capillaries: Endothelia cells are joined to one another with leaky
junctions;
(2) Fenestrated Capillaries: Large pores that allow high volumes of fluid to pass
rapidly; found primary in kidney/intestine
b. Microcirculation through capillary beds
- Capillary density is directly related to the metabolic activity of a tissue cell (Muscles/Glands have highest density)
- Blood cells pass single file; one at a time - Cell junctions between endothelia cells account for leakiness of
capillary
- 3 Liters of fluid pushed out of capillaries every day - HYDROSTATIC PRESSURE
(1) Lateral pressure component of blood flow that pushes fluid out through the capillary pores
(2) Decreases along the length of the capillary as energy is lost to friction
-
3
o Bulk Flow: Mass movements of fluid between blood and interstitial fluid
o Absorption: If direction of bulk flow is into the capillary o Filtration: If the direction of bulk flow is out of the
capillary
II. MEASURING BLOOD PRESSURE a. Blood Pressure
- Pressure created by ventricular contraction is the driving force for blood flow throughout the cardiovascular system
- By sustaining the driving pressure for blood flow during ventricular relaxation (diastole) the arteries create continuous blood flow through
the blood vessels
- Four factors affecting resistance Radius blood vessels Viscosity of blood Length of system Friction between blood vessels
b. Systemic Blood pressure is Highest in Arteries and Lowest in veins
Blood pressure is highest in arteries and decreases through circulatory system Decrease occurs because energy is lost as a result of flow resistance
a. VENTRICLE Systolic [WORKING] pressure - Maximal pressure created by ventricular systole causing a pressure
wave that moves ten times faster then the blood itself
- Highest pressure occurrence in the Aorta because of left ventricle systole [120mm Hg]
b. VENTRICLE Diastolic [RESTING] pressure - Arterial pressure during ventricular diastole - Ventricle pressure falls near [0mm Hg] but diastolic pressure in large
arteries remains relativity high because of their ability to capture and
store energy in their elastic walls
c. Pulse pressure - Rapid pressure increase that occurs when left ventricle pushes blood
into aorta is called the PULSE (pressure wave)
-
4
- Pressure wave deceases over distance because of friction and eventually disappears at the capillaries
- Pulse Pressure: Measure of the strength of the pressure wave; defined as systolic pressure minus diastolic pressure
PP = Systolic – Diastolic
Areas where pulse pressure is present Left Ventricle Artery
Arteriole
Areas where there is no pulse pressure present Capillaries
Venules
Right Ventricle
- Holding your arm straight down for a couple minutes
causes the veins in the back of your hand to stand out as
they fill with blood
- More evident in older people whose subcutaneous C.T.
has lost elasticity
- Then raising your hand above your head so gravity
assists venous flow causes bulging veins to disappear - This is example of venous return to the heart aided by
skeletal muscle pump and respiratory pump; which
contain internal one-way valves to ensure blood passing
the valve cannot flow backward
d. Sphygmomanometry - The measuring of arterial blood pressure in the radial artery of an arm
using an instrument consisting of an inflatable cuff and a pressure
gauge (sphygmus, pulse + manometer, instrument for measuring
pressure of fluid) - Cuff is inflated to higher then systolic pressure to cut off blow flow - Pressure gradually released until pumping noise of systolic flow can be
heard as thumping sound from radial artery, called Korotkoff Sound First Korotkoff sound is the systolic pressure
-
5
Diasoltic Pressure
1/3 (Systolic Pressure -Diasotlic Pressure)
MAP
Point where Korotkoff sound disappears is the diastolic pressure
c. Arterial Blood Pressure Reflects the Driving Pressure for Blood Flow (MAP: Mean Arterial Pressure)
a. MAP - Ventricular pressure is difficult to measure so it is customary to assume
that arterial blood pressure reflects ventricular pressure
- MAP represents driving pressure, “blood pressure” created by the pumping action of the heart
- MAP is closer to diastolic pressure than to systolic pressure because diastole lasts twice as long as systole
HYPOTENSION: Blood pressure falls to low, driving force of blood will be unable to
overcome gravity (dizzy/faint)
HYPERTENSION: Chronically elevated pressure; vessel walls may weaken and rupture
CEREBRAL HEMORRHAGE: If rupture occurs in brain; “stroke”
b. Cardiac Output and Peripheral Resistance Determine MAP
- Arterial pressure is a balance between flow into the arteries and blood flow out of the arteries
More blood in then out: Increase MAP (blood collects in arteries) More blood out then in: Decrease MAP (no blood in arteries)
-
6
- Peripheral Resistance: Influences blood flow out of the arterioles; Definition: Resistance to flow offered by the arterioles; how much
resistance blood has to fight against to move through arterioles
- Most cases of hypertension are believed to be caused by increased peripheral resistance without changes in C.O
c. Changes In Blood Volume Affect Blood Pressure - If blood volume increases blood pressure increases - If blood volume decreases blood pressure decreases
- Adjustments for increased blood volume are primarily the responsibility of the kidneys;
o If blood volume increases the kidneys excrete excess water in urine
o If blood volume decreases the kidneys cannot restore lost fluid
III. Resistance in the Arterioles - Arterioles are the main site of variable resistance in the systemic
circulation and contribute more then 60% of total resistance - Resistance in arterioles is variable because of large amounts of smooth
muscle
-
7
- Arteriolar resistance in influence by both systemic and local control mechanisms
1. Sympathetic Reflexes: Mediated by C.N.S. – maintain MAP and govern blood distribution for homeostatic needs
2. Local Control Of Arteriolar Resistance: Matches tissue blood flow to metabolic needs of the tissue;
3. Hormones: Regular salt and water excretion by Kidneys – influence blood pressure by acting directly
on arterioles and altering autonomic reflex control
- BELOW: Table that lists chemicals that mediate arteriolar resistance by producing vasoconstriction or vasodilatation that influence blood flow at tissue level
CHEMICAL PHYSIOLOGICAL ROLE SOURCE TYPE
Vasoconstrictors
Norepinephrine (α
receptors)
Baroreceptor reflex
Sympathetic neurons Neurotransmitter
Vasopressin Increase blood pressure in
hemorrhage
Posterior pituitary Neurohormone
Angiotensin II Increase blood pressure Plasma hormone
Vasodilators
Epinephrine (β2
receptors)
Increase blood flow to
skeletal muscle, heart,
liver
Adrenal Medulla Neurohormone
Alpha Antagonists - - -
Nitrates (NO) Paracrine mediator Endothelium Paracrine
Adenosine Increase blood flow to
match metabolism
Hypoxic cells Paracrine
↓O2↑CO2↑ H+↑
K
+ Increase blood flow to
match metabolism
Cell metabolism Paracrine
Histamine Increase blood flow Mast Cells Paracrine
b. Myogenic Autoregulation Automatically Adjusts Blood Flow - Vascular smooth muscle has ability to regulate its own state of
contraction, process called Myogenic Autoregulation
- Absence of Autoregulation an increase in blood pressure increases blood flow through arteriole
-
8
- When smooth muscle fibers in wall arteriole wall stretch because of increased blood pressure the arteriole constricts
- Vasoconstriction increases resistance offered by arteriole, automatically decreasing blood flow through the vessel
Mechanism responsible for intrinsic response of vascular smooth muscle is stretch that opens gated Ca2+ channels
c. Paracrines Alter Vascular Smooth Muscle Contraction - Active Hyperemia: Process in which an increase in blood flow
accompanies an increase in metabolic activity
If blood flow to tissue is occluded (closed) O2 levels fall and metabolically produced Paracrines such as CO2/H
+ accumulate
Local hypoxia (low oxygen) causes synthesis of vasodilator NO causing significant vasodilatation
- Reactive Hyperemia: An increase in tissue blood flow following a period of low perfusion
d. Sympathetic Branch Controls Vascular Smooth Muscle - Most systemic arterioles are innervated by sympathetic neurons
(exception erection reflex penis/clitoris which indirectly by
parasympathetic)
- Tonically controlled and always actively regulating and maintain Myogenic tone of arterioles
- Norepinephrine binding to α-Receptors on vascular smooth muscles causes vasoconstriction
If sympathetic release of Norepinephrine decrease the arterioles dilate
Overall:
Metabolic Paracrines (adenosine, histamine, ATP) induce vasodilatation
Blood flow (perfusion) is matched to metabolic activity)
-
9
Flight or Fight Response Correlations to Sympathetic Control
β2-Receptors respond to epinephine by vasodilating; enhancing blood flow to the heart, skeletal msucles and liver, tissues that are active during flight-fight repsonse
α-Receptor causes vasoconstriction; increased sympathetic activity that
diverts blood from nonessential organs such as
G.I. tract to skeletal muscles, liver and heart
If sympathetic release of Norepinephrine increases the arterioles constrict
- Epinephrine from adrenal medulla binds with α-Receptors reinforcing vasoconstriction
Also binds to β2-Receptors on vascular smooth muscle on heart/liver/skeletal muscle arterioles
These sites are not innervated and respond only to excess/present epinephrine freely flowing in
circulation
Activation β2-Receptors causes vasodilatation
IV. Blood Distribution to Tissue - Distribution of system blood varies according to metabolic needs of
individual organs
Ex: Non-exercise Skeletal Muscles: 20%
Ex: Exercise Skeletal Muscles: 85%
- All arterioles receive blood at the same time from the aorta Flow through individual arterioles depends on
their resistance
Blood is diverted from high-resistance arterioles to lower-resistance arterioles
-
10
Total blood flow through all the arterioles of the body always equals
the C.O.
V. CAPILLARY EXCHANGE
a. Overview - Capillary density in tissue is directly related to metabolic activity of
cells tissue
- Tissues with high metabolic activity and high need for oxygen/nutrients and contain more capillaries per unit area
- Most capillaries in muscles and gland - Have thinnest walls of all blood vessels composed of single endothelial
cell on a basal lamina
- Diameter allows for blood to line up single filed to diffuse - Continuous Capillaries: Most common; joined to one another by leaky
junctions found in muscle, C.T., neural tissue (blood-brain barrier)
- Fenestrated Capillaries: Large pores to allow for high volumes of fluid to pass between plasma and interstitial fluid; primary in kidney and
intestine
b. Velocity Blood Flow is Lowest in Capillaries - Determinant for velocity of flow through capillaries is not diameter but
total cross-sectional area
- Least resistance of all arterial blood vessels - Opening of capillary beds decreases PR and MAP - Velocity of flow is inversely proportional to cross-sectional area
-
11
Hydrostatic Pressure
• Lateral pressure component of blood flow that pushses fluid out through capilary pores
• Capillary Hydrostatic Pressure decreases along the lenght of capillary as energy is lost to driction
•Water movement due to hydrostatic pressure will always be directed out of capillary due to low hdrostatic pressure in interstitial fluid
Osmotic Pressure
•Determined by a solute concentration of a compartment
•Main solute difference between plasma and interstitial fluid is due to proteins
• Pressure created by protein presence is known as colloid osmotic pressure
c. Diffusion and Transcytosis Exchange - Diffusion rate is determined by concentration gradient between plasma
and interstitial fluid
- Transcytosis: Transport of large molecules including selected proteins across endothelium
d. Filtration and Absorption by Bulk Flow - Bulk Flow: Mass movement of fluid between blood and interstitial
fluid as result of hydrostatic or osmotic pressure gradients
Movement into the capillary: absorption
Movement out of the capillary: filtration which is caused by
hydrostatic pressure that forces fluid out of capillary through
cell junctions]
- Most capillaries show net filtration from arterial end to net absorption at venous end
STARLING FORCES the regulators of bulk flow through capillaries
-
12
• Carotid Artery
• Aortic Arch
Baroreceptors
•Medullary Cardiovascular Control Center
• Integrating Center
Medulla Oblongata •Autnomic Neurons
• Sympathetic
• Parasympathetic
Efferent Pathway
VI. REGULATION OF BLOOD PRESSURE a. Baroreceptor Reflex Primary Homeostatic Control for Blood Pressure
- CNS coordinates reflex control of blood pressure - Main integrating center is the medulla oblongata - Stretch-sensitive mechanoreceptors known as baroreceptors are located
in walls of carotid arteries and aorta where they measure blood flow to
the brain (carotid baroreceptors) and body (aorta baroreceptors)
[carotid and aorta = tonically regulated] (always firing)
- Baroreceptor reflex
Primary reflex pathway for homeostatic control of blood pressure
Increased blood pressure in arteries stretches baroreceptors membrane, firing rate of receptor then increases
Decreases blood pressure in arteries decreases firing rate
Changes in CO and Peripheral resistance occur within two heartbeats
EFFECTORS Sympathetic EFFECTORS Parasympathetic
SA/AV Node Increase HR; Adrenergic β1
Receptors
SA/AV Node Decrease HR: Cholergenic
[mACH] receptors;
Ventricles Increases Contraction; β1
Receptors
Arterioles and Veinules Vasoconstriction;
increase peripheral resistance; α-receptors
-
13
b. Orthostatic Hypotension Triggers Baroreceptor Reflex - When you are lying flat gravitation forces are disturbed evenly up and
down your body and blood is distributed evenly
- When you stand up gravity causes blood to pool in lower extremities causing an instantaneous decrease in venous return
C.O falls from 5L/min to 3L/min causes decrease in blood pressure; this decrease due to standing is known as orthostatic hypotension
Orthostatic hypotension triggers the Baroreceptor reflex
Carotid and aortic baroreceptors respond to the fall by decreasing their firing rate; with diminished input into the cardiovascular
control center sympathetic activity increases and parasympathetic
decreases
RESULT: Heart rate and force of contraction increases while arterioles and veins constrict
RESULT: Increased C.O. and increased Peripheral Resistance increase MAP and restore it to normal within 2 heart beats
-
14
Problem
•CAD (Coronary Artery Disease) Inflamatory Disease
•Stenosis/Ischemia: Increased blood pressure
Rapid Response
•AP Baroreceptors (Increase signals to brain)
•Sympathetic Stimulation (β1 SA/β1 Contractile/α Ssytemic Arterioles/β2 of Arterioles and skeletal muscle, liver, and coronary artiers)
• Parasympathetic: Slow down heart rate
Slow Response
•1. Elevated MAP stretches heart
•2. Artrial natriuretic peptide (ANP) hormone
•3. Enhanecd water loss at kidneys
•4. Decreases MAP
Receptor Adapation
• FAILURE of Homeostasis
•a. Tonic barorecepotrs slowly adapt
•b. Reduce AP freuqency to CVCC
•c. High MAP is can be misread as normal by CVCC
Case Study: Hypertension
Problem
•CHF (Chronic Heart Failure)
• Insufficient CO to maintain flow; not sufficient MAP
Role of Chonric Hypertension
•Results from Uncontrolled Hypertension
•1. Failure of Left Ventricle (resulting in Pulmonary Edema; excess blood and fluid in lungs)
•2. Increased Afterload
•3. Increased preload stretch causing enlargement of the ventricles (leads to incompentence of valves)
Treatments
•1. Diuretics and low salt diet
•2. Positve inotropic agents (to increase beat/more force)
•LVAD
•Heart replacement
Case Study: Congestive Heart Failure
-
15
Case Study: Hypervolemia1. Shock 2. Overhydration
• Fainting
• Tachycardia
• Cold clamy skin
• Low urine output
top related