Download Chapter 16 * The Endocrine System

Chapter 19 – Blood Vessels and
Circulation
Types of blood vessels
• Arteries
– Carry blood away from the heart
– Branch into smaller vessels called arterioles
• Capillaries
– Smallest vessels
– Form beds in tissues/organs
– Where diffusion occurs
• Veins
– Carry blood back to heart
– Venules – small veins from capillary beds
• Converge to form larger veins
Vessel walls
• With the exception of capillaries, vessels have 3 layers/tunics
surrounding the central lumen
• Tunica intima/interna
– Endothelium – simple squamous epithelium continuous with the
endocardium of the heart
– Tends to be convoluted in large arteries
• Tunica media
– Smooth muscle and elastin fibers
• Can alter lumen size
– Vasodilation – muscle relaxes/lumen enlarges
– Vasoconstriction – muscle contracts/lumen decreases
– Thicker in arteries
• Tunica externa or adventitia
– Loose connective tissue and collagen
– Large vessels have small vessels within externa called vasa vasorum
Vessel walls
Arterial system
• Elastic/conducting arteries
– Largest in diameter
• Aorta and major branches
– Large amount of elastic fibers
• Expand and recoil
• Muscular arteries
– Relative to size, largest tunic
media
– Ability to vasocontrict
• Arterioles
– Few elastic fibers
– Diameter controls amount of
blood delivered to capillary
beds
Capillaries
• Consist only of tunica intima
and basement membrane
– Continuous – endothelium is
complete
• Prevents loss of blood cells
and proteins
– Fenestrated – contains pores
• Allows for movement of small
proteins
• Choroid plexi, GI tract for
absorption, kidneys,
endocrine system
• Forms beds – network of
capillaries
Capillary microcirculation
• Blood from arteriole to
venule
• Terminal arteriole →
metarteriole → true
capillaries → thoroughfare
channel → post capillary
venule
• Precapillary sphincter
– Band of smooth muscle at
metarteriole/capillary
junction
– When contracted, blood
bypasses capillary bed
– Blood goes directly from
metarteriole to thoroughfare
channel
Venous system
• Venules
– Very porous, like capillaries
• Veins
– Walls are thinner and
lumens are larger as
compared to same size
artery
– Relatively little smooth
muscle
• Large veins tend to collapse
in histological preparation
– Externa is the largest layer
Venous system cont
• Since veins are exposed to
relatively low pressure:
– Veins contain valves
• Prevents backflow of blood due to
gravity
– Skeletal muscles “milk” veins
• Contraction of muscles close to
veins help move blood through
the vessel
– Abdominal pressure differences
due to breathing
• Abnormalities
– Varicose veins
• Poor circulation causes valves to
become leaky
• Veins stretch out and become
floppy
– Usually superficial veins that
have little support from
underlying tissues
• Hemorrhoids – varicose veins of
anal veins
Vascular anastomoses
• Where multiple vessels unit
• Arterial anastomoses
– Arteries that supply same area merge
– Provides alternate blood supply
• Venous anatomoses
– More common than aterial
Disorders
• Atherosclerosis
– Lipid deposits on arterial
walls
– Can cause restriction or
blockage of blood flow
• Arteriosclerosis
– Decreased elasticity
“hardening of arteries”
– Affects proper blood
flow
Circulation physiology
• Blood flow
– Volume of blood that passes through a specific point
of a vessel in a specific time
• ml/min
• Blood pressure
– Force per unit exerted by blood on vessel wall
• mm Hg
– Usually refers to arterial pressure
– Pressure gradient – pressure difference is required for
blood to flow
Circulation physiology cont
• Resistance
– Opposition to flow; measures friction the blood
encounters
– Influenced by:
• Blood viscosity
• Blood vessel length
– Longer the vessel = greater resistance
• Blood vessel diameter
– Blood next to the wall flows more slowly
• F = ∆P/R
– F = flow; ∆P = pressure difference; R = resistance
– As pressure increases, flow increases
– As pressure decreases, flow decreases
Systemic blood pressure
• Vessel pressure is highest in
the aorta and decreases to
zero in right atrium
– Blood flows from region of
high pressure to low
• Blood pressure is measured
in arteries – exposed to
highest pressure
• Systole – ventricular
contraction
– ~120mm Hg
• Diastole – ventricular
relaxation
– ~80mm Hg
Maintaining blood pressure
• Hormonal control (discussed during endocrine
system)
• Baroreceptors – detect pressure changes
– Located in aortic arch, carotid arteries, and large
head/neck arteries
– When relaxed, the medulla oblongata sends
signals to vessels for vasoconstriction, which
increases pressure
– When stretched, medulla doesn’t send signal –
causes vasodilation, which decreases pressure
Baroreceptors
Maintaining blood pressure cont
• Chemoreceptors – detect changes in
respiratory gases
– Increases in carbon dioxide is detected by aortic
arch and carotid sinuses
• Vasocontriction causes an increase of blood pressure,
which increases blood flow
– Gets to respiratory system to unload carbon dioxide more
quickly
– Decrease of carbon dioxide causes vasodilation –
causes slower flow
Chemoreceptors
Pulse
• Surges of pressure in an
artery
• Pulse rate should equal
the heart rate (beats
per minute)
– Apical pulse – actual
heartbeat count
– BIG difference = pulse
deficit
• Felt with fingers (do not
use thumb)
Blood pressure
• Pressure from blood against the vessel walls (arteries)
– Reported as diastolic pressure over systolic pressure
• Measured with a sphygmomanometer
– Inflation blocks bloodflow through brachial artery
– Pressure of cuff gradually reduced to allow partial flow
• Sounds of Korotkoff – tapping sound of blood flowing
back into artery
– First appears at systole
• Blood spurting into artery
– Sound disappears when artery is no longer compressed
• Diastole
Blood pressure alteration
• Hypertension
– >140 systole; >90
diastole
– To pump against
increased pressure,
heart works harder
• Myocardium increases
(especially LV), heart
ultimately weakens
• Hypotension
– <100 systole
Circulatory shock
• Blood vessels inadequately filled; abnormal
blood flow
• Hypovolemic
– Significant blood loss
• Vascular
– Poor circulation due to extreme vasodilation
• Anaphylactic – allergies; septic – infection
• Cardiogenic
– Heart not pumping (myocardial infarction)
Arteries
Arteries
Arteries
Veins
Veins
Veins