ANATOMY AND PHYSIOLOGY IN NURSING
CHAPTER 13 : BLOOD VESSELS AND THE CIRCULATION
1st SEMESTER I SY. 2022-2023
LECTURER: MS. LEAH
BLOOD VESSELS
TRANSCEND BY: ALEYA
Major arteries
Blood Vessels
form a network more complex than an instate highway
system.
Carry blood to within two or three cell diameters of nearly
all the trillions of cells that make up the body.
2
classes:
1. Pulmonary vessels – transport blood from the right
ventricle, through the lungs, and back to the left
atrium.
2. Systemic vessels - transport blood from the left
ventricle, through all parts of the body, and back to
the right atrium
Pulmonary and Systemic Vessels constitute the Circulatory
System.
FUNCTIONS OF THE CIRCULATORY SYSTEM
1. Carries blood. Blood vessels carry blood from the heart
to almost all the body tissues and back to the heart.
2. Exchanges nutrients, waste products, and gases with
tissues. Nutrients and oxygen diffuse from blood vessels
to cells in all areas of the body. Waste products and
carbon dioxide diffuse from the cells, where they are
produced, to blood vessels.
3. Transports substances. Hormones, components of the
immune system, molecules required for coagulation,
enzymes, nutrients, gases, waste products, and other
substances are trans- ported in the blood to all areas of
the body.
4. Helps regulate blood pressure. The circulatory system
and the heart work together to maintain blood pressure
within a normal range of values.
5. Directs blood flow to tissues. The circulatory system
directs blood to tissues when increased blood flow is
required to maintain homeostasis.
Blood flow through circulatory system
GENERAL FEATURES OF BLOOD VESSEL STRUCTURE
Three main types of blood vessels:
1. Arteries
carry blood away from the heart
usually the blood is oxygenated
three categories: (1) elastic arteries, (2) muscular
arteries, or (3) arterioles.
2. Capillaries
blood flows from the arterioles into capillaries.
It is where exchange of substances such as O2,
nutrients, CO2, and other waste products occurs
between the blood and the tissue fluid.
3. Veins
blood flows into veins from the capillaries.
These vessels carry blood toward the heart:
Usually, the blood is deoxygenated
Increase in diameter and decrease in number as
they progress towards the heart and their walls
increase in thickness
Veins may be classified from smallest to largest:
(1) venules, (2) small veins, or (3) medium or
large veins.
BLOOD VESSEL WALL
Blood Vessel walls consist of three layers, or tunics.
From inner to outer wall, tunics are:
1. Tunica intima
innermost layer, consists pf an endothelium,
composed of simple squamous epithelial cells, a
basement membrane, and a small amount of
connective tissue
in muscular arteries, it contains a layer of thin
elastic connective tissue
2. Tunica Media
Middle layer, consist of smooth muscle cells
arranged circularly around the blood vessel.
It also contains variable amounts of elastic and
collagen fibers, depending on size and type of
vessel
In muscular arteries, a layer of elastic connective
tissue forms the outer margin of the tunica
media.
3. Tunica Adventitia
Composed of dense connective tissue adjacent
to tunica media
The tissue becomes loose connective tissue
toward the outer portion of the blood vessel wall.
VEINS
Blood flows from capillaries into venules and from venules
into small veins.
Venules
have a diameter slightly larger than that of capillaries
and are composed of endothelium resting on a
delicate connective tissue layer.
Small veins are slightly larger in diameter than
venules.
All three tunics are present in small veins. The tunica
media contains continuous layer of smooth muscle
cells and the connective tissue of the tunica adventitia
surround the tunica media.
Veins that have diameters greater than 2mm contain valves.
ARTERIES
1. Elastic Arteries
the largest-diameter arteries and have the
thickest walls
compared to other arteries, a greater portion of
their walls is composed of elastic tissue, and a
smaller portion of smooth muscle
examples: aorta and pulmonary trunk
2. Muscular Arteries
Medium-sized and small arteries
The walls of medium-sized arteries are relatively
thick compared to their diameter.\medium-sized
arteries are frequently called distributing
arteries.
Vasoconstriction – contraction of smooth
muscle in blood vessels that decreases blood
vessel diameter and blood flow.
Vasodilation – increases blood vessel diameter
and blood flow.
3. Arterioles
Transport blood from small arteries to capillaries.
They are the smallest arteries in which 3 tunics
can be identified.
Tunica media of arterioles consist of only one or
two layers of circular smooth muscle cells/
Small arteries and arterioles are adapted for
vasodilation and vasoconstriction.
CAPILLARIES
Pre-capillary sphincters
A smooth muscle cells that regulates blood flow
through capillary networks
These are located at the origin of the branches of the
capillaries and by contracting and relaxing, regulate
the amount of blood flow through various sections of
the network.
Valves – ensure that blood flows toward the heart but not in
the opposite direction. Each valve consists of folds in the
tunica intima that form 2 flaps. These valves are similar in
shape and function to the semilunar valves of the heart.
BLOOD VESSELS OF THE PULMONARY CIRCULATION
Pulmonary Circulation – is the system of blood vessels that
carries blood from the right ventricle of the heart to the lungs
and back to the left atrium of the heart.
Pulmonary trunk – a short vessel where the blood from the
right ventricle is pumped into. The pulmonary trunk then
branches into the right and left pulmonary arteries, which
extend to the right and left lungs.
Right and Left Pulmonary Arteries – carry deoxygenated
blood to the pulmonary capillaries in the lungs, where the
blood takes up O2 and releases CO2.
Pulmonary veins (four) – exit the lungs and carry the
oxygenated blood to the left atrium.
BLOOD VESSELS OF THE SYSTEMIC CIRCULATION: ARTERIES
Systemic Circulation
is the system of blood vessels that carries blood from
the left ventricle of the heart to the tissues of the body
and back to the right atrium.
Oxygenated blood from the pulmonary veins passes
from the left atrium into the left ventricle and from the
left ventricle into the aorta.
Arteries distribute blood from the aorta to all portions
of the body.
AORTA
All arteries of the systemic circulation branch directly or
indirectly from the aorta.
Aorta – usually considered in three parts:
(1) ascending aorta
(2) the aortic arch
(3) descending aorta: thoracic aorta and abdominal
aorta
1. Ascending Aorta – part of the aorta that passes
superiorly from the left ventricle. The right and left
coronary arteries arise from the base of the
ascending aorta and supply blood to the heart.
2. Aortic Arch – the aorta arches posteriorly and to the
left as “aortic arch”
Three major arteries which carry blood to the head and
upper limbs, originate form the aortic arch:
1. Brachiocephalic artery
2. The left common carotid artery
3. The left subclavian artery
*there is no brachiocephalic artery on the left side of the body.
Left Common Carotid Artery – transports blood to the left
side of the head and neck.
Left Subclavian Artery – transports blood to the left upper
limb.
The common carotid arteries extend superiorly along each
side of the neck to the angle of the mandible, where they
branch into internal and external carotid arteries.
The base of each internal carotid artery is slightly dilated to
form carotid sinus.
Carotid Sinus – contains structures important in monitoring
blood pressure (baroreceptors).
3. Descending Aorta – longest part of the aorta. It
extends through the thorax and abdomen to the upper
margin of the pelvis.
External carotid arteries – have several branches that supply
the structures of the neck, face, nose, and mouth.
Thoracic Aorta – the part of the descending aorta
that extends through the thorax to the diaphragm.
Internal carotid arteries – pass through carotid canals and
contribute to the cerebral arterial circle (Circle of Willis).
Abdominal Aorta – the part of descending aorta that
extends from the diaphragm to the point at which it
divides into two common iliac arteries.
Cerebral Arterial Circle
Arterial Aneurysm – a localized dilation of an artery
that usually develops in response to trauma or
congenital weakness of the artery wall.
Branches of Aorta
Vertebral Arteries
branch from the subclavian arteries and pass to the
head through the transverse foramina of cervical
vertebrae.
Branches of the vertebral arteries supply blood to the
spinal cord, as well as to the vertebrae, muscles and
ligaments in the neck.
Basilar Artery
it is formed when the vertebral arteries unite within
the cranial cavity.
It is located along the anterior, inferior surface of the
brainstem.
Gives off branches that supply blood to the pons,
cerebellum, and midbrain.
It also forms right and left branches that contribute to
the cerebral arterial circle.
Arteries of Head and Neck
ARTERIES OF THE HEAD AND NECK
Brachiocephalic Artery – the first vessel to branch from the
aortic arch. This extends a short distance and then branches
at the level of the clavicle to form the right common carotid
artery.
Right Common Carotid Artery – transports blood to the right
side of the head and neck.
Right Subclavian Artery – transports blood to the right upper
limb.
ARTERIES OF THE UPPER LIMBS
ABDOMINAL AORTA AND ITS BRANCHES
Axillary artery – the subclavian artery located deep to the
clavicle becomes the axillary artery in the axilla (armpit).
Branches of abdominal aorta can be divided into two groups:
Brachial artery – when the axillary artery extends into the arm,
it is referred to as brachial artery.
The brachial artery branches at elbow to form ulnar artery and
the radial artery.
Radial artery – one of the most commonly used for taking a
pulse (wrist). Both Radial Artery and Ulnar Artery supply blood
to the forearm and hand.
Arteries of the Upper Limb
1. Visceral Arteries
3 major unpaired branches:
a. Celiac trunk - supplies blood to the stomach,
pancreas, spleen, upper duodenum, and liver.
b. Superior Mesenteric Artery - artery supplies
blood to the small intestine and the upper portion
of the large intestine
c. Inferior Mesenteric Artery - supplies blood to the
remainder of the large intestine
3 paired branches:
a. Renal Arteries - supply the kidneys
b. Suprarenal Arteries - supply the adrenal glands
c. Testicular Arteries - supply the testes in males;
Ovarian Arteries - supply the ovaries in females.
2. Parietal Arteries – supply the diaphragm and abdominal
wall
a. Inferior Phrenic Arteries - supply the diaphragm
b. Lumbar Arteries - supply the lumbar vertebrae
and back muscles
c. Median Sacral Artery - supplies the inferior
vertebrae
ARTERIES OF THE PELVIS
THORACIC AORTA AND ITS BRANCHES
Branches of thoracic aorta can be divided into two groups:
1. Visceral Arteries – supply blood to the thoracic organs,
including esophagus, trachea, pericardium and part of the
lung.
2. Parietal Arteries – supply blood to thoracic wall, and
include the posterior intercostal arteries, which arise
from the thoracic aorta and extend between the ribs. They
supply the intercostal muscles, vertebrae, the spinal cord,
and the deep muscles of the back.
Superior Phrenic Arteries – supply the diaphragm.
Internal Thoracic Arteries - are branches of the subclavian
arteries. They descend along the internal surface of the
anterior thoracic wall and give rise to branches called the
anterior intercostal arteries.
Anterior Intercostal Arteries - extend between the ribs to
supply the anterior chest.
Major arteries of the head and thorax
The abdominal aorta divides at the level of the fifth lumbar
vertebra into two common iliac arteries. Each common iliac
artery extends a short distance and then divides to form an:
1. External iliac artery - enters a lower limb
2. Internal iliac artery - supplies the pelvic area
Visceral branches of the internal iliac artery - supply organs
such as the urinary bladder, rectum, uterus, and vagina.
Parietal branches of the internal iliac artery - supply blood to
the walls and floor of the pelvis; the lumbar, gluteal, and
proximal thigh muscles; and the external genitalia.
Major Arteries of Abdomen and Pelvis
face, and neck. The internal jugular veins join the
subclavian veins on each side of the body to form the
brachiocephalic veins.
ARTERIES OF THE LOWER LIMBS
The external iliac artery in the pelvis becomes the femoral
artery in the thigh.
Brachiocephalic veins - join to form the superior vena
cava.
The femoral artery extends down the thigh and becomes the
popliteal artery in the popliteal space.
Popliteal Artery - the posterior region of the knee. It branches
slightly inferior to the knee to give off the anterior tibial artery
and the posterior tibial artery, both of which give rise to
arteries that supply blood to the leg and foot.
o
o
The anterior tibial artery - becomes the dorsalis pedis
artery at the ankle.
The posterior tibial artery - gives rise to the fibular
artery, or peroneal artery, which supplies the lateral
leg and foot.
The femoral triangle
located in the superior and medial area of the thigh.
Its margins are formed by the inguinal ligament, the
medial margin of the sartorius muscle, and the lateral
margin of the adductor longus muscle.
A pulse in the femoral artery can be detected in the
area of the femoral triangle. This area is also
susceptible to serious traumatic injuries that result in
hemorrhage and nerve damage.
The femoral triangle is an important access point for
certain medical procedures as well.
Passing through the femoral triangle:
1. Femoral artery
2. Femoral vein
3. Femoral nerve
VEINS OF THE UPPER LIMBS
The veins of the upper limbs can be divided into deep and
superficial groups.
1. Deep Veins - carry blood from the deep structures of the
upper limbs, follow the same course as the arteries and
are named for their respective arteries. The only
noteworthy deep veins are the brachial veins, which
accompany the brachial artery and empty into the axillary
vein.
2. Superficial veins - carry blood from the superficial
structures of the upper limbs and then empty into the
deep veins.
Major superficial veins:
o Cephalic vein - empties into the axillary vein
o Basilic vein - which becomes the axillary vein, are
Median cubital vein - connects the cephalic vein or its
tributaries with the basilic vein. Although this vein varies in
size among people, it is usually quite prominent on the
anterior surface of the upper limb at the level of the elbow, an
area called the cubital fossa, and is often used as a site for
drawing blood.
VEINS OF THE THORAX
Three major veins return blood from the thorax to the superior
vena cava:
1. right brachiocephalic veins
2. left brachiocephalic veins
3. azygos vein.
Blood returns from the anterior thoracic wall by way of the
anterior intercostal veins.
Anterior Intercostal Veins - empty into the internal thoracic
veins, which empty into the brachiocephalic veins.
Blood from the posterior thoracic wall is collected by
posterior intercostal veins.
BLOOD VESSELS OF THE SYSTEMIC CIRCULATION: VEINS
The deoxygenated blood from the tissues of the body returns
to the heart through veins.
Superior Vena Cava – returns blood from the head, neck,
thorax, and upper limbs to the right atrium of the heart, and
the inferior vena cava returns blood from the abdomen, pelvis,
and lower limbs to the right atrium
Posterior Intercostal Veins - empty into the azygos vein on
the right and the hemiazygos vein or the accessory
hemiazygos vein on the left.
Hemiazygos and Accessory Hemiazygos Veins - empty into
the azygos vein, which empties into the superior vena cava.
VEINS OF THE ABDOMEN AND PELVIS
•
VEINS OF THE HEAD AND NECK
External and Internal Jugular Veins - the two pairs of major
veins that collect blood from the head and neck.
•
1. The external jugular veins - are the more superficial of the
two sets. They carry blood from the posterior head and
neck, emptying primarily into the subclavian veins.
•
2. The internal jugular veins - are much larger and deeper.
They carry blood from the brain and the anterior head,
Blood from the posterior abdominal wall returns toward
the heart through ascending lumbar veins into the azygos
vein. Blood from the rest of the abdomen and from the
pelvis and lower limbs returns to the heart through the
inferior vena cava.
The gonads (testes or ovaries), kidneys, adrenal glands,
and liver - are the only abdominal organs outside the
pelvis from which blood empties directly into the inferior
vena cava.
The internal iliac veins return blood from the pelvis and
join the external iliac veins from the lower limbs to form
the common iliac veins. The common iliac veins combine
to form the inferior vena cava.
Major Veins
Major Veins of the Abdomen and Pelvis
Veins of the Head and Neck
Liver - is a major processing center for substances absorbed
by the intestinal tract.
As such, blood from the capillaries within most of the
abdominal viscera, such as the stomach, intestines,
pancreas, and spleen, drains through a specialized portal
system to the liver.
Portal System - is a system of blood vessels that begins and
ends with capillary beds and has no pumping mechanism,
such as the heart, in between.
Hepatic Portal System - begins with capillaries in the viscera
and ends with capillaries in the liver.
Veins of the Upper Limb
Major vessels of the hepatic portal system:
1. splenic vein
2. superior mesenteric vein
Inferior mesenteric vein - empties into the splenic vein.
The splenic vein carries blood from the spleen and pancreas.
The superior and inferior mesenteric veins carry blood from
the intestines. The splenic vein and the superior mesenteric
vein join to form the hepatic portal vein, which enters the
liver.
Veins of the Head and Neck
Blood from the liver flows into hepatic veins, which join the
inferior vena cava. Blood entering the liver through the
hepatic portal vein is rich in nutrients collected from the
intestines, but it may also contain a number of toxic
substances that are potentially harmful to body tissues.
Within the liver, nutrients are taken up and stored or
modified, so that they can be used by other cells of the body.
Also, within the liver, toxic substances are converted to
nontoxic substances. These substances can be removed
from the blood or carried by the blood to the kidneys for
excretion.
Other veins of the abdomen and pelvis include the renal
veins, the suprarenal veins, and the gonadal veins.
•
•
Renal Veins – carry blood from the kidneys
Suprarenal Veins – drain the adrenal glands.
•
•
Testicular Veins - drain the testes in males
Ovarian Veins - drain the ovaries in females
VEINS OF THE LOWER LIMBS
•
Deep veins - follow the same path as the arteries and are
named for the arteries they accompany.
•
Superficial veins - consist of the great and small
saphenous veins.
o Great Saphenous Vein - originates over the dorsal
and medial side of the foot and ascends along the
medial side of the leg and thigh to empty into the
femoral vein.
o Small Saphenous Vein - begins over the lateral side
of the foot and joins the popliteal vein, which
becomes the femoral vein. The femoral vein empties
into the external iliac vein.
This turbulence produces vibrations in the blood and
surrounding tissues that can be heard through the
stethoscope. These sounds are called Korotkoff sounds, and
the pressure at which the first Korotkoff sound is heard is the
systolic pressure.
As the pressure in the blood pressure cuff is lowered still
more, the Korotkoff sounds change tone and loudness. When
the pressure has dropped until the brachial artery is no longer
constricted and blood flow is no longer turbulent, the sound
disappears completely. The pressure at which the Korotkoff
sounds disappear is the diastolic pressure. The brachial
artery remains open during systole and diastole, and
continuous blood flow is reestablished.
The systolic pressure is the maximum pressure produced in
the large arteries. It is also a good measure of the maximum
pressure within the left ventricle. The diastolic pressure is
close to the lowest pressure within the large arteries. During
relaxation of the left ventricle, the aortic semilunar valve
closes, trapping the blood that was ejected during ventricular
contraction in the aorta. The pressure in the ventricles falls to
0 mm Hg during ventricular relaxation. However, the blood
trapped in the elastic arteries is compressed by the recoil of
the elastic arteries, and the pressure falls more slowly,
reaching the diastolic pressure.
PRESSURE AND RESISTANCE
The values for systolic and diastolic pressure vary among
healthy people, making the range of normal values quite
broad. In addition, other factors, such as physical activity and
emotions, affect blood pressure values in a normal person.
A standard blood pressure for a resting young adult male is
120 mm Hg for the systolic pressure and 80 mm Hg for the
diastolic pressure, commonly expressed as 120/80.
PHYSIOLOGY OF CIRCULATION
PULSE PRESSURE
Blood Pressure
is a measure of the force blood exerts against the
blood vessel walls.
In arteries, blood pressure values go through a cycle
that depends on the rhythmic contractions of the
heart.
When the ventricles contract, blood is forced into the
arteries, and the pressure reaches a maximum value
called the systolic pressure.
When the ventricles relax, blood pressure in the
arteries falls to a minimum value called the diastolic
pressure.
The standard unit for measuring blood pressure is
millimeters of mercury (mm Hg).
For example, if the blood pressure is 100 mm Hg, the
pressure is great enough to lift a column of mercury
100 mm.
The difference between the systolic and diastolic pressures
is called the pulse pressure.
In people who have arteriosclerosis, the arteries are less
elastic than normal.
Ejection of blood from the left ventricle into the aorta
produces a pressure wave, or pulse, which travels rapidly
along the arteries.
CAPILLARY EXCAHNGE
Health professionals most often use the auscultatory method
to determine blood pressure.
A blood pressure cuff connected to a sphygmomanometer is
wrapped around the patient’s arm, and a stethoscope is
placed over the brachial artery. The blood pressure cuff is
then inflated until the brachial artery is completely blocked.
Because no blood flows through the constricted area at this
point, no sounds can be heard through the stethoscope. The
pressure in the cuff is then gradually lowered. As soon as the
pressure in the cuff declines below the systolic pressure,
blood flows through the constricted area each time the left
ventricle contracts. The blood flow is turbulent immediately
downstream from the constricted area.
Edema, or swelling, results from a disruption in the normal
inwardly and outwardly directed pressures across the
capillary walls.
CONTROL OF BLOOD FLOW
The body’s MAP is equal to the cardiac output (CO) times
the peripheral resistance (PR), which is the resistance to
blood flow in all the blood vessels:
MAP = CO × PR
Because the cardiac output is equal to the heart rate (HR)
times the stroke volume (SV), the mean arterial pressure is
equal to the heart rate times the stroke volume times the
peripheral resistance (PR):
MAP = HR × SV × PR
Thus, the MAP increases in response to increases in HR, SV,
or PR, and the MAP decreases in response to decreases in HR,
SV, or PR. The MAP is controlled on a minute-to-minute basis
by changes in these variables. Mechanisms are also activated
to increase the blood volume to its normal value.
BARORECEPTOR REFLEXES
NERVOUS AND HORMONAL CONTROL OF BLOOD FLOW
Nervous control of blood flow is carried out primarily through
the sympathetic division of the autonomic nervous system.
Sympathetic nerve fibers - innervate most blood vessels of
the body, except the capillaries and precapillary sphincters,
which have no nerve supply.
The vasomotor center - continually transmits a low frequency
of action potentials to the sympathetic nerve fibers that
innervate blood vessels of the body.
As a consequence, the peripheral blood vessels are
continually in a partially constricted state, a condition called
vasomotor tone.
Baroreceptor reflexes
activate responses that keep the blood pressure
within its normal range.
Baroreceptors respond to stretch in arteries caused
by increased pressure.
They are scattered along the walls of most of the
large arteries of the neck and thorax, and many are
located in the carotid sinus at the base of the internal
carotid artery and in the walls of the aortic arch.
Action potentials travel from the baroreceptors to the
medulla oblongata along sensory nerve fibers
A sudden increase in blood pressure stretches the
artery walls and increases action potential frequency
in the baroreceptors.
A sudden decrease in blood pressure results in a
decreased action potential frequency in the
baroreceptors.
regulate blood pressure on a moment-to-moment
basis.
Vasomotor Tone
Changes in vasomotor tone will alter blood flow as
well as blood pressure.
An increase in vasomotor tone causes blood vessels
to constrict further and blood pressure to increase.
A decrease in vasomotor tone causes blood vessels
to dilate and blood pressure to decrease. Nervous
control of blood vessel diameter is an important way
that blood pressure is regulated.
Baroreceptor Effects on Blood Pressure
REGULATION OF ARTERIAL PRESSURE
Mean arterial blood pressure (MAP) - is slightly less than the
average of the systolic and diastolic pressures in the aorta
because diastole lasts longer than systole. The mean arterial
pressure changes over our lifetime. MAP is about 70 mm Hg
at birth, is maintained at about 95 mm Hg from adolescence
to middle age, and may reach 110 mm Hg in a healthy older
person.
CHEMORECEPTOR REFLEXES
Chemoreceptor reflexes - respond to changes in blood
concentrations of O2 and CO2, as well as pH.
Carotid bodies - are small structures that lie near the carotid
sinuses.
Aortic bodies - lie near the aortic arch.
These structures contain sensory receptors that respond to
changes in blood O2 concentration, CO2 concentration, and
pH. Because they are sensitive to chemical changes in the
blood, they are called chemoreceptors. They send action
potentials along sensory nerve fibers to the medulla
oblongata. There are also chemoreceptors in the medulla
oblongata.
HORMONAL MECHANISM
1. Adrenal Medullary Mechanism
Stimuli that lead to increased sympathetic
stimulation of the heart and blood vessels also cause
increased stimulation of the adrenal medulla.
The adrenal medulla responds by releasing
epinephrine and small amounts of norepinephrine
into the blood. Epinephrine increases heart rate and
stroke volume and causes vasoconstriction,
especially of blood vessels
in the skin and viscera. This leads to an increase in
blood pressure. Epinephrine also causes vasodilation
of blood vessels in
skeletal muscle and cardiac muscle, thereby
increasing the supply of blood flowing to those
muscles and preparing the body for
physical activity
2. Renin-Angiotensin-Aldosterone Mechanism
In response to reduced blood flow, the kidneys
release an enzyme called renin into the circulatory
system.
Renin acts on the blood protein angiotensinogen to
produce angiotensin I.
Another enzyme, called angiotensin-converting
enzyme (ACE), found in large amounts in organs,
such as the lungs, acts on angiotensin I to convert it
to its most active form, angiotensin II.
Angiotensin II – is a potent vasoconstrictor. Thus, in
response to reduced blood pressure, the kidneys’
release of renin increases the blood pressure toward
its normal value.
Angiotensin II
Angiotensin II also acts on the adrenal cortex to
increase the secretion of aldosterone.
Aldosterone acts on the kidneys, causing them to
conserve Na+ and water.
As a result, the volume of water lost from the blood
into the urine is reduced.
The decrease in urine volume results in less fluid loss
from the body, which maintains blood volume.
Adequate blood volume is essential to maintain
normal venous return to the heart and thereby
maintain blood pressure.
3. Antidiuretic Hormone Mechanism
When the concentration of solutes in the plasma
increases or when blood pressure decreases
substantially, nerve cells in the hypothalamus
respond by causing the release of antidiuretic
hormone (ADH), also called vasopressin from the
posterior pituitary gland.
ADH acts on the kidneys and causes them to absorb
more water, thereby decreasing urine volume. This
response helps maintain blood volume and blood
pressure. The release of large amounts of ADH
causes vasoconstriction of blood vessels, which
causes blood pressure to increase
4. Atrial Natriuretic Mechanism
A peptide hormone called atrial natriuretic is
released primarily from specialized cells of the right
atrium in response to elevated blood pressure.
Atrial natriuretic hormone causes the kidneys to
promote the loss of Na+ and water in the urine,
increasing urine volume. Loss of water in the urine
causes blood volume to decrease, thus decreasing
the blood pressure.
EFFECTS OF AGING ON THE BLOOD VESSELS
Atherosclerosis – a type of arteriosclerosis results from the
deposition of material in the walls of arteries that forms
plaques. The material is composed of a fatlike substance
containing cholesterol. The fatty material can eventually be
dominated by the deposition of dense connective tissue and
calcium salts.