Transcript Veins

Anatomy
Chapter 11 Part II – Blood Vessels
Blood Vessels
Blood circulates inside blood vessels forming a closed transport system called the
vascular system. As the heart beats the blood is propelled into the large arteries
leaving the heart. As it moves through the body it enters smaller arterioles
which feed the capillary beds of the tissues. Capillary beds drain into venules
which empty into veins that empty into the right atria of the heart.
Arteries carry blood away from the heart and veins drain the tissues and return
the blood to the heart. The capillary beds serve the needs of the body cells.
Arteries are depicted red to indicate
the oxygen-rich blood and veins are
depicted blue to indicate
oxygen-depleted blood.
Microscopic anatomy of blood vessels
The walls of blood vessels are called tunics.
• Tunica intima – lines the lumen
• Tunica media – smooth muscle, elastic
• Tunica externa - fibrous connective tissue
Scanning electron micrograph of an
artery and a vein in cross section.
Capillaries are found between
arteries and veins in the
circulatory pathway. Capillaries
are composed of tunica intima
only, allowing for diffusion
between the blood and the body
cells.
Structural differences between arteries, veins, and capillaries:
Artery walls are thicker than veins – media
is heavier. Arteries are closer to the heart
and must be able to expand as blood is
forced into them. Artery walls are strong
and stretchy to take pressure changes.
Veins are farther from the heart where the
pressure is low. The walls are thinner, lumen
is larger, and there are valves present to
prevent backflow of blood.
Capillary beds are our
microcirculatory system.
Skeletal muscle activity
enhances venous blood
flow. Inhalation drops
the pressure in the
thorax allowing large
veins near the heart to
expand and fill.
Gross Anatomy Blood Vessels
Major arteries of the systemic system:
• Aorta – largest artery (garden hose)
• Ascending aorta – upward from heart;
coronary arteries that serve the heart
• Aortic arch – arches left, downward into
thorax following the spine
 Brachiocephalic trunk – splits into the
R. common carotid and R. subclavian
 L. Common carotid – branches to L.
internal carotid and L. external carotid
to serve the brain, skin of head and
neck
 L. Subclavian artery – serve part of
brain, arm, and the forearm
• Thoracic aorta – passes through diaphragm
into abdominal cavity
 Intercostal arteries – muscles of
thorax walls
 Bronchial arteries – lungs
 Esophageal arteries – esophagus
 Phrenic arteries – diaphragm
Major arteries of the systemic circulation.
Major arteries of the systemic system:
• Abdominal aorta –
 Celiac trunk – first branch of abdominal
aorta: stomach (gastric), spleen (splenic),
liver (hepatic)
 Superior Mesenteric artery – small
intestine, first half of colon
 L. and R. Renal arteries – kidneys
 L. and R. Gonadal arteries – gonads;
ovaries or testes
 Lumbar arteries – heavy muscles of
abdomen and trunk walls
 Inferior Mesenteric arteries – second half
of colon
 L. and R. Common iliac arteries – pelvic
organs (internal iliac), thigh (external iliac
to femoral ), leg, foot (anterior and
posterior tibial)
Major arteries of systemic circulation.
Major Veins of the Systemic Circulation:
Veins are more superficial and some are
easily palpated on the body surface. Most
deep veins follow the same course of the
major arteries. Veins converge on the
venae cavae, which enter the right atrium
of the heart. Veins draining the head and
arms empty into the superior vena cava
and those draining the lower body empty
into the interior vena cava.
Veins draining into the superior vena cava:
named in a distal to proximal direction.
 Radial and ulnar veins – drain the
forearm, are (brachial vain), and empty
into axillary region
 Cephalic vein – drains lateral aspect of
the arm, empties into axillary vein
 Basilic vein – drains medial aspect of arm,
empties into brachial vein
 Subclavian vein – blood from arm
through axillary vein; skin, muscles of
head through external jugular
 Vertebral vein – drains posterior part of
the head
 Internal jugular vein – drains the dural
sinuses of the brain
 Brachiacephalic vein – receive venous
blood from subclavian, vertebral, and
internal jugular; all join to from the
superior vena cava
 Azygos vein – single vein that drains the
thorax and enters the vena cava just
before it enters the heart
Veins draining into the inferior vena cava:
returns blood from below the diaphragm.
 Anterior and posterior tibial and fibular
veins – drain the leg, (calf and foot);
posterior tibial popliteal vein at the knee
and femoral vein at the thigh, then
external iliac at pelvis
 Great saphenous veins – longest vein in
the body; receive superficial drainage of
the leg
 Common iliac (R. and L. ) vein –
formed from the union of external and
internal iliac veins (drains pelvis); join to
form inferior vena cava, ascends into
abdominal cavity
 R. Gonadal vein – drains right ovary
and right testicle; L. gonadal vein
empties into left renal vein
 L. and R. Renal veins – drain the
kidneys
 Hepatic portal vein – single vein that
drains the digestive tract organs, carries
blood through the liver before systemic
circulation
 L. and R. Hepatic veins – drains the
liver
Special Circulations
Hepatic portal circulation – veins drain
the digestive organs and delivers the
blood to the liver through the hepatic
portal vein. The liver processes
substances (nutrients – glucose, fat,
protein) before they enter the systemic
circulation.
Arterial supply of the brain and Circle of Willis
A continuous blood supply to the brain is crucial.
A lack of blood for a few minutes, brain cells die.
The brain is supplied with two pairs of arteries –
internal carotid and vertebral arteries. Anterior
and posterior blood supplies are united by small
communicating arterial branches called the Circle
of Willis. This circle of vessels protects the brain
by providing more than one route for blood to
reach the brain tissue.
Fetal circulation –
The lungs and digestive system
of the fetus are not yet working.
All nutrients and excretory gas
exchanges occur through the
placenta. Nutrients and oxygen
move from the mother’s blood
into the fetal blood, and fetal
wastes move in the opposite
direction. The umbilical cord
contains three blood vessels; a
large umbilical vein and two
smaller umbilical arteries. The
vein carries nutrient and oxygen
rich blood to the fetus. The
arteries carry carbon dioxide
and wastes from the fetus to
the placenta.
Physiology of Circulation: can be assessed by measuring arterial pressure
and blood pressure
Arterial pulse – alternating expansion and
recoil of an artery that occurs with each beat of
the left ventricle. A pulse or pressure wave
travels through the entire arterial system.
Normally the pulse rate (pressure surges per
min.) equals the heart rate (beats per min.).
Pulse averages 70 to 76 beats per min. in a
normal resting person. It is influenced by
activity, postural changes, and emotions.
The pulse can be felt in any artery lying close to
the body surface by compressing the artery
against firm tissue. Routinely detected where
radial artery surfaces on the wrist.
Pressure points – used to measure pulse and
are compressed to stop the flow blood during
hemorrhage.
Vital signs – arterial pulse rate, blood
pressure, respiratory rate, and
temperature
Blood Pressure - the pressure blood exerts
against the inner walls of blood vessels and is
the force that keeps the blood circulating
between heart beats.
Blood pressure gradient – pressure is
highest in the large arteries, high pressure in
the arteries forces blood to continually move
into areas of lower pressure. Pressure
continues to drop throughout the pathway,
reaching zero at the vena cava. Blood flows
into arterioles, then capillaries, venules,
veins, and finally back to the vena cava. Blood
flows along a pressure gradient from high to
low pressure. Valves in the veins, skeletal
activity, and pressure changes in the thorax,
keep blood flowing.
Blood pressure in various areas
of the cardiovascular system.
Measuring Blood Pressure The heart alternately contracts
and relaxes causing an on/off
flow of blood into the arteries.
This causes the blood pressure
to rise and fall during each
beat. There are two arterial
measurements made:
Systolic pressure is the
pressure in the arteries at the
peak of ventricular
contraction, and diastolic
pressure, the pressure when
the ventricles are relaxing.
Blood pressure is reported in
millimeters of mercury (mm
Hg).
Auscultatory Method of measuring blood pressure
Measuring the blood pressure in the brachial artery.
Effects of Various Factors on Blood Pressure  Arterial blood pressure (BP) is directly
related to cardiac output (CO) and
peripheral resistance (PR): BP = CO X PR
 Peripheral resistance - friction;
viscosity, narrowing, atherosclerosis;
age, weight, time of day, exercise,
emotional state, drugs
 Neural factors – sympathetic
vasoconstriction; hemorrhage,
exercise, frightened
 Renal factors – osmoregulation;
renin; aldosterone
 Temperature –cold/ vasoconstriction,
heat/ vasodilation
 Chemicals – epinephrine, nicotine,
alcohol, histamine
 Diet – low sodium, low saturated fat,
low cholesterol help prevent
hypertension
Summary of factors causing and increase in
arterial blood pressure.
Variations in Blood Pressure
Normal adults at rest, should have a systolic pressure that varies between 110 and 140
mm Hg, and a diastolic pressure between 75 and 80 mm Hg. Blood pressure varies from
one person to another. Blood pressure varies with age, weight, race, mood, physical
activity, and posture.
Hypotension - low blood pressure. Generally a systolic pressure below 100 mm Hg –
individual differences and not usually cause for concern.
Hypertension – persistent high blood pressure; is pathological and defined as a condition
of sustained elevated arterial pressure of 140/90 or higher.
Capillary Exchange of Gases and Nutrients
Capillaries form an intricate
network among the body’s cells.
Diffusion takes place easily with
the cells. Substances exchanged
first diffuse through the interstitial
fluid.
Four routes in the capillary walls:
• Substances can diffuse directly
through if they are lipid soluble
(gases)
• Lipid soluble substances may
enter or leave by endocytosis or
exocytosis
• Limited passage allowed by
intercellular clefts – gaps or areas
of the plasma membrane not
joined by tight junctions
• Free passage of small solutes and
fluids is allowed by fenestrated
capillaries – found where
absorption is a priority or where
filtration occurs.
Substances exchanged
between blood and
cells must diffuse
through interstitial
fluid.
Substances diffuse to and
from the body cells
according to their
concentration gradients.