Cardiovascular System
Blood Vessels
Anatomy of Blood Vessels
 Arteries carry blood from the heart to
the tissues
Anatomy of Blood Vessels
 Arterioles are small arteries that
connect to capillaries
Anatomy of Blood Vessels
 Capillaries are the site of substance
exchange between the blood and body
tissues
Anatomy of Blood Vessels
 Venules connect capillaries to larger
veins
Anatomy of Blood Vessels
 Veins convey blood from the tissues back
to the heart.
Arteries
1.
2.
3.
Tunica interna (intima) – innermost
Tunica media – middle layer
Tunica externa – outer layer
Tunica Intima

1.
2.
Composed of;
simple squamous epithelium
(endothelium)
Internal elastic membrane
Tunica Media

Rich in smooth muscle and elastic fibers
Tunica Media

Maintains elasticity and contractility
Tunica Externa

Rich in elastic and collagen fibers
Functional Properties of Arteries
1.
2.
Elasticity
Contractility
Elasticity

Due to the elastic tissue in the tunica
intima and media
Elasticity

Allows arteries to accept blood under
great pressure from the contraction of the
ventricles
Contractility

Due to the smooth muscle in the tunica
media
Contractility

Allows arteries to increase or decrease
lumen size
Contractility

Sympathetic stimulation of alpha 1
receptors on cutaneous arteries causes
vasoconstriction
Contractility

Sympathetic stimulation of beta 2
receptors on arteries supplying skeletal
muscle causes vasodilation
Elastic Arteries

Elastic Arteries – Large arteries with more
elastic fibers and less smooth muscle
Elastic Arteries

Example: aorta, sublcavian, and
pulmonary arteries
Elastic Arteries

Also called conducting arteries
because they conduct blood from the
heart to medium sized arteries
Muscular or distributing arteries

Medium sized and have a large amount of
smooth muscle and distribute blood to
various parts of the body
Muscular or distributing arteries

Examples: brachial, femoral, and popliteal
arteries
Arterioles

Very small arteries that deliver blood to
capillaries
Capillaries

Connect arterioles and venules
Capillaries

Microcirculation – flow of blood through
the capillaries
Capillaries

Capillaries are found near almost every
cell in the body
Capillaries

Function – Permit the exchange of
nutrients and wastes between the blood
and tissue cells
Capillaries

Composed of a single layer of cells
(endothelium) and a basement membrane
Capillaries

1.
2.
Two types;
Continuous
Fenestrated
Capillaries

Continuous –
composed of
endothelial cells that
form a continuous
tube that contains
gaps between cells
called intercellular
clefts
Capillaries

Fenestrated capillaries
– plasma membrane
contains small pores
Capillaries

Materials can cross the blood capillary
walls in four ways
Capillaries
Four Ways;
1. Intercellular clefts
2. Trancytosis using pinocytic vesicles
3. Diffusion
4. Fenestrations
Intercellular clefts

Open in response to histamine (released
during inflamation) making capillaries
more leaky
Intercellular clefts

This allows fluid and wbc, and antibodies
to go from the bloodstream to the site of
infection
Pinocytosis

Large fats cross via pinocytosis
Diffusion

Water, CO2, and O2 cross capillaries by
diffusion
Fenestrations

Allow small molecules such as water and
electrolytes to get into the urine
Fenestrations

Prevent large proteins and red cells from
getting into the urine
Sinusoids

Discontinuous
capillaries
Sinusoids

Present in the liver
Sinusoids

Allow large molecules such as protein and
bilirubin to get from the bloodstream into
hepatocytes
Venules

They are small vessels that are formed
from the union of several capillaries
Venules

Merges to form veins
Venules

Drain blood from capillaries into veins
Veins

Contain 60% of our blood volume
Veins

Consist of the same three tunics as
arteries
Veins

Have a thinner tunica intima and media
Veins

Thicker tunica externa
Veins

Thinner walled than arteries due to less
elastic tissue and smooth muscle
Veins

Low pressure systems
Veins

Contain valves to prevent backflow
Veins

Squeezing of the veins by muscles and
inspiration promote venous return
Venous Return

The volume of blood returning back to the
heart from the systemic veins
Veins

Vascular sinuses – veins with very thin
walls with no smooth muscle to alter their
diameter

Example: Coronary sinus
Anastomoses

Union of the branches of two or more
arteries supplying the same region
Anastomoses

Provide alternate routes for blood to reach
a tissue or organ
Anastomoses

Collateral circulation is the alternate flow
of blood to a body part through an
anastomosis
Anastomoses

What is the importance of arteries that
anastomose?
Anastomoses

Occlusion of an end artery interrupts the
blood supply to a whole segment of an
organ, producing necrosis of that segment
Blood Pressure

Pressure exerted on the walls of a blood
vessel
Blood Pressure

In a clinical sense, it refers to pressure in
arteries
Blood Pressure

BP=CO X TPR
Blood Pressure

Systolic and Diastolic fluctuations in the
pressure are only seen in the arteries and
arterioles
Systolic Pressure

Peak pressure in the arteries with each
cardiac cycle during ventricular contraction
Systolic Pressure

Due to the stroke volume being ejected
into the aorta
Diastolic Pressure

Lowest pressure in the arteries with each
cardiac cycle
Diastolic Pressure

Force of blood recorded during ventricular
relaxation
Blood Pressure

Young adult male = 120/80 mm Hg (8-10
mm Hg less in a young adult female)
Resistance

1.
2.
3.
Depends on three variables;
Blood viscosity
Vessel length
Blood Vessel Radius
Blood Viscosity

Increased viscosity increases resistance
Vessel length

Increased length increases resistance
Blood Vessel Radius

Increased radius decreases resistance
Systemic vascular resistance

Total peripheral resistance (TPR)
Systemic vascular resistance

All of the vascular resistance offered by
systemic blood vessels
Mean Arterial Pressure

MAP = Diastolic Pressure X 1/3(systolic
pressure – diastolic pressure)
Mean Arterial Pressure

MAP = CO X TPR
Mean Arterial Pressure
Factors that increase BP
 increase SV
 increase HR
 constrict the blood vessels (increases
resistance)

Mean Arterial Pressure
Factors that decrease BP
 Decrease CO
 Dilate the arteries

Cardiovascular Center

A group of neurons in the medulla that
regulate heart rate, contractility, and blood
vessel diameter
Cardiovascular Center

CV receives input from higher brain
regions and sensory receptors
(baroreceptors and chemoreceptors)
Cardiovascular Center

Sympathetic impulses along
cardioaccelerator nerves increase heart
rate and contractility
Cardiovascular Center

Parasympathetic impulse along vagus
nerves decrease heart rate
Cardiovascular Center

The sympathetic division also continually
sends impulses to smooth muscle in blood
vessel walls via vasomoter nerves
resulting in a moderate state of tonic
vasoconstriction
Neural Regulation of Blood Pressure
Baroreceptors
 Chemoreceptors

Baroreceptors

Pressure-sensitive sensory neurons that
monitor stretching of the walls of blood
vessels
Baroreceptors
If blood pressure falls, the baroreceptor
reflexes;
 accelerate heart rate
 increase force of contraction
 promote vasoconstriction

Baroreceptors
If pressure increases above normal, the
reflexes cause;
 decrease in sympathetic tone
 increase in parasympathetic tone

Hormonal Regulation

Renin leads to the formation of
angiotensin II
Hormonal Regulation

1.
2.
Angiotensin II causes;
Vasoconstriction
Secretion of aldosterone, which leads to
sodium and water retention
Hormonal Regulation

Epinephrine and norepinephrine increase
CO and cause vasoconstriction
Hormonal Regulation

ADH causes water retention and a little
vasoconstriction
Hormonal Regulation

Nitric oxide from the endothelial cells
causes vasodilation
Hormonal Regulation

Cortisol keep our arteries sensitive to
vasoconstricting hormones
Shock

Is an inadequate CO that results in failure
of the CV system to deliver adequate
amounts of O2 and nutrients to meet the
metabolic needs of body cells
Shock
Could result in;
 dysfunction of cellular membranes
 abnormal cellular metabolism
 cellular death
Types of Shock

5 main types
Hypovolemic Shock

Due to decreased blood volume
Cardiogenic Shock

Due to poor heart function
Vascular Shock

Due to inappropriate vasodilation
Obstructive Shock

Due to obstruction of blood flow
Neurogenic shock

Due to decreased sympathetic outflow
Homeostatic Response

Activation of renin-angiotensin-aldosterone
system
Homeostatic Response

Secretion of ADH
Homeostatic Response

Activation of the sympathetic division of
the ANS
Circulatory Routes
Systemic
 Pulmonary
 Hepatic Portal
 Fetal

Hepatic Portal Circulation

Collects blood from the veins of the
pancreas, spleen, stomach, intestines and
gallbladder and directs it into the hepatic
portal vein of the liver before it returns to
the heart
Hepatic Portal Circulation

Enables nutrient utilization and blood
detoxification by the liver