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2015 NURS1004 Week 11 Blood vessels & Blood
pressure Part I, II & III Lecture notes prepared by
Didy Button
Refer to Martini et al., 2015, Fundamentals of
anatomy and physiology, 10th edn, PearsonBenjamin Cummings, San Francisco. p. 750-759, 760765, 770-775, 779-784, 789-793, 801. OR
Martini 20102 9th ed. p 708-717, 718-723, 728-732,
736-740, 748-749, 758. Part III p. 639- 646,650-652,
653-657, 660-664. OR International 9th ed 2014 . p
788-797, 798-803, 808- 812, 816-820, 828-829, 838.
Part III p 715-722, 726-728, 729-734, 736-741.
Blood Vessels and Circulation
Vasodilation The relaxation of arterial smooth
muscle Enlarging the lumen & BP goes down
Vasoconstriction and Vasodilation
Afterload on heart
Peripheral blood pressure
Capillary blood flow
From heart to capillaries, arteries change
From elastic arteries
To muscular arteries
To arterioles
Arteries Carry blood away from heart
Arterioles Are smallest branches of arteries
Capillaries Are smallest blood vessels & is the location
of exchange between blood and interstitial fluid
Venules Collect blood from capillaries
Veins Return blood to heart
Elastic Arteries Also called conducting arteries
Large vessels (e.g., pulmonary trunk and aorta)
The Largest Blood Vessels attach to heart
Pulmonary trunk Carries blood from right ventricle
To pulmonary circulation
Aorta Carries blood from left ventricle to systemic
Arterioles Are small Have little or no tunica externa
Have thin or incomplete tunica media
Capillaries: The Smallest Blood Vessels Have small
diameter and thin walls Chemicals and gases diffuse
across walls
Muscular Arteries Also called distribution arteries
Are medium sized (most arteries) Tunica media has
many muscle cells
Artery Diameter
Small muscular arteries and arterioles
Change with sympathetic or endocrine stimulation
Constricted arteries oppose blood flow
Resistance (R)
Resistance vessels - arterioles
The Structure of Vessel Walls have three layers
Tunica intima (Inner Layer)
Tunica media (Middle Layer)
Tunica externa (Outer Layer)
Capillaries Are smallest vessels with thin walls
Microscopic capillary networks permeate all active
tissues Capillary function Location of all exchange
functions of cardiovascular system Materials diffuse
between blood and interstitial fluid
Differences between Arteries and Veins
Arteries and veins run side by side
Arteries have thicker walls and higher blood pressure
Collapsed artery has small, round lumen (internal
space) Artery lining folds
Arteries more elastic
Capillary Structure
Endothelial tube, inside thin basement membrane
No tunica media No tunica externa Diameter is
similar to red blood cell
Vein has a large, flat lumen
Vein lining contracts, artery lining does not
Veins have valves
Arteries Elasticity allows arteries to absorb pressure
waves that come with each heartbeat
Contractility Arteries change diameter
Controlled by sympathetic division of ANS
Vasoconstriction The contraction of arterial smooth
muscle by the ANS & BP goes up
Continuous Capillaries
Have complete endothelial lining Are found in all
tissues except epithelia and cartilage
Functions of continuous capillaries
Permit diffusion of water, small solutes, and lipidsoluble materials
Block blood cells and plasma proteins
Specialised Continuous Capillaries
Are in CNS and thymus
Have very restricted permeability
For example, the blood–brain barrier
Fenestrated Capillaries
Have pores in endothelial lining
Permit rapid exchange of water and larger solutes
between plasma and interstitial fluid
Are found in: Choroid plexus Endocrine organs
Kidneys Intestinal tract
Sinusoids (Sinusoidal Capillaries)
Have gaps between adjacent endothelial cells
Liver, Spleen, Bone marrow, Endocrine organs
Permit free exchange of water and large plasma
proteins between blood and interstitial fluid
Phagocytic cells monitor blood at sinusoids
Capillary Beds (Capillary Plexus)
Connect one arteriole and one venule
Precapillary Sphincter guards entrance to each
capillary Opens and closes, causing capillary blood to
flow in pulses
Thoroughfare Channels
Direct capillary connections between arterioles and
venules Controlled by smooth muscle segments
Collect blood from capillaries in tissues and organs
Return blood to heart
Are larger in diameter than arteries have thinner
walls than arteries have lower blood pressure
Venules Very small veins Collect blood from
Medium-sized veins Thin tunica media and few
smooth muscle cells Tunica externa with longitudinal
bundles of elastic fibers
Large Veins Have all three tunica layers Thick tunica
externa Thin tunica media
Venous Valves
Folds of tunica intima
Prevent blood from flowing backward
Compression pushes blood toward heart
The Distribution of Blood
Heart, arteries, and capillaries
30–35% of blood volume
Venous system
1/3 of venous blood is in the large venous networks
of the liver, bone marrow, and skin
Capacitance of a Blood Vessel
The ability to stretch
Relationship between blood volume and blood
Veins (capacitance vessels) stretch more than arteries
Venous Response to Blood Loss
Vasomotor centers stimulate sympathetic nerves
Systemic veins constrict (venoconstriction)
Veins in liver, skin, and lungs redistribute venous
Total Capillary Blood Flow
Equals cardiac output is determined by:
Pressure (P) and resistance (R) in the cardiovascular
Part II of Lecture starts here
Pressure (P)
The heart generates P to overcome resistance
The Pressure Gradient (P)
Circulatory pressure
The difference between:
Pressure at the heart
And pressure at peripheral capillary beds
Flow (F)
Is proportional to the pressure difference (P)
Divided by R
Measuring Pressure
Blood pressure (BP)
Arterial pressure (mm Hg)
Capillary hydrostatic pressure (CHP)
Pressure within the capillary beds
Venous pressure
Pressure in the venous system
Circulatory Pressure
∆P across the systemic circuit (about 100 mm Hg)
Circulatory pressure must overcome total peripheral
R of entire cardiovascular system
Vascular Resistance
Due to friction between blood and vessel walls
Depends on vessel length and vessel diameter
Adult vessel length is constant
Vessel diameter varies by vasodilation and
R increases exponentially as vessel diameter
R caused by molecules and suspended materials in a
Whole blood viscosity is about four times that of
Arterial Blood Pressure
Systolic pressure
Peak arterial pressure during ventricular systole
Diastolic pressure
Minimum arterial pressure during diastole
Abnormal Blood Pressure
Normal = 120/80
Abnormally high blood pressure
Greater than 140/90
Abnormally low blood pressure
Elastic Rebound
Arterial walls Stretch during systole
Rebound (recoil to original shape) during diastole
Keep blood moving during diastole
Venous Pressure and Venous Return
Determines the amount of blood arriving at right
atrium each minute
Low effective pressure in venous system
Venous Pressure and Venous Return
Low venous resistance is assisted by:
Muscular compression of peripheral veins
Compression of skeletal muscles pushes blood
toward heart (one-way valves)
The respiratory pump
Thoracic cavity action
Inhaling decreases thoracic pressure
Exhaling raises thoracic pressure
Capillary Pressures and Capillary Exchange
Vital to homeostasis
Moves materials across capillary walls by:
Diffusion : Movement of ions or molecules
From high concentration
To lower concentration
Along the concentration gradient
Filtration ; Driven by hydrostatic pressure
Water and small solutes forced through capillary wall
Leaves larger solutes in bloodstream
Reabsorption : The result of osmotic pressure (OP)
Blood colloid osmotic pressure (BCOP)
Equals pressure required to prevent osmosis
Caused by suspended blood proteins that are too
large to cross capillary walls
Interplay between Filtration and Reabsorption
Net hydrostatic pressure: Forces water out of
Net osmotic pressure: Forces water into solution
Both control filtration and reabsorption through
Capillary Exchange
At arterial end of capillary:
Fluid moves out of capillary
Into interstitial fluid
At venous end of capillary:
Fluid moves into capillary
Out of interstitial fluid
Tissue Perfusion
Blood flow through the tissues
Carries O2 and nutrients to tissues and organs
Carries CO2 and wastes away
Is affected by:
Cardiac output
Peripheral resistance
Blood pressure
Cardiovascular Regulation Changes Blood Flow to a
Specific Area
At an appropriate time
In the right area
Without changing blood pressure and blood flow to
vital organs
Controlling Cardiac Output and Blood Pressure
Causes immediate, localized homeostatic
Neural mechanisms
Respond quickly to changes at specific sites
Endocrine mechanisms
Direct long-term changes
Autoregulation of Blood Flow within Tissues
Adjusted by peripheral resistance while cardiac
output stays the same
Local vasodilators accelerate blood flow at tissue
Low O2 or high CO2 levels
Low pH (acids)
Nitric oxide (NO)
High K+ or H+ concentrations
Chemicals released by inflammation (histamine)
Elevated local temperature
Neural Mechanisms
Cardiovascular (CV) centers of the medulla oblongata
Cardiac centers
Cardioacceleratory center increases cardiac output
Cardioinhibitory center reduces cardiac output
Vasomotor Center
Control of vasoconstriction
Reflex Control of Cardiovascular Function
Cardiovascular centers monitor arterial blood
Baroreceptor reflexes
Respond to changes in blood pressure
Chemoreceptor reflexes
Respond to changes in chemical composition,
particularly pH and dissolved gases
Baroreceptor Reflexes
Stretch receptors in walls of:
Carotid sinuses (maintain blood flow to brain)
Aortic sinuses (monitor start of systemic circuit)
Right atrium (monitors end of systemic circuit)
For example, Adrenaline and Noradrenaline from
adrenal medullae stimulate cardiac output and
peripheral vasoconstriction
Antidiuretic Hormone (ADH)
Released by neurohypophysis (posterior lobe of
Elevates blood pressure
Reduces water loss at kidneys
ADH responds to: Low blood volume
High plasma osmotic concentration
Circulating angiotensin II
Lecture Part III starts here
Blood components and Coagulation
A fluid medium (blood)
•Is specialized fluid of connective tissue
•Contains cells suspended in a fluid matrix
•Transports materials to and from cells
•Oxygen and carbon dioxide
•Immune system components
•Waste products
Baroreceptor Reflexes
When blood pressure rises, CV centers: decrease
cardiac output
Cause peripheral vasodilation
When blood pressure falls, CV centers:
Increase cardiac output
Cause peripheral vasoconstriction
Important Functions of Blood
Transportation of dissolved substances
Regulation of pH and ions
Restriction of fluid losses at injury sites
Defense against toxins and pathogens
Stabilization of body temperature
Chemoreceptor Reflexes
Peripheral chemoreceptors in carotid bodies and
aortic bodies monitor blood
Central chemoreceptors below medulla oblongata:
Monitor cerebrospinal fluid
Control respiratory function
Control blood flow to brain
Whole Blood
•Fluid consisting of:
•Dissolved plasma proteins
•Other solutes
•Formed elements
•All cells and solids
Chemoreceptor Reflexes
Changes in pH, O2, and CO2 concentrations
Produced by coordinating cardiovascular and
respiratory activities
CNS Activities and the Cardiovascular Centers
Thought processes and emotional states can elevate
blood pressure by:
Cardiac stimulation and vasoconstriction
Hormones and Cardiovascular Regulation
Hormones have short-term and long-term effects on
cardiovascular regulation
Three Types of Formed Elements
1. Red blood cells (RBCs) or erythrocytes
•Transport oxygen
2. White blood cells (WBCs) or leukocytes
•Part of the immune system
3. Platelets
•Cell fragments involved in clotting
Three General Characteristics of Blood
1. 38C (100.4F) is normal temperature
2. High viscosity
3. Slightly alkaline pH (7.35–7.45)
•Blood volume (liters) = 7% of body weight
•Adult male 5 to 6 liters
•Adult female 4 to 5 liters
•Makes up 50–60% of blood volume
•More than 90% of plasma is water
•Extracellular fluids
•Interstitial fluid (IF) and plasma
•Materials plasma and IF exchange across capillary
•Small solutes
Plasma Proteins
Albumins (60%)
Globulins (35%)
Fibrinogen (4%)
•Albumins (60%)
•Transport substances such as fatty acids, thyroid
hormones, and steroid hormones
•Globulins (35%)
•Antibodies, also called immunoglobulins
•Transport globulins (small molecules): hormonebinding proteins, metalloproteins, apolipoproteins
(lipoproteins), and steroid-binding proteins
•Fibrinogen (4%)
•Molecules that form clots and produce long,
insoluble strands of fibrin
SerumLiquid part of a blood sample In which
dissolved fibrinogen has converted to solid fibrin
Other Plasma Proteins
•1% of plasma
•Changing quantities of specialized plasma proteins
•Peptide hormones normally present in circulating
•Insulin, prolactin (PRL), and the glycoproteins
thyroid-stimulating hormone (TSH), folliclestimulating hormone (FSH), and luteinizing hormone
Origins of Plasma Proteins
•More than 90% made in liver
•Antibodies made by plasma cells
•Peptide hormones made by endocrine organs
Red blood cells (RBCs)
•Make up 99.9% of blood’s formed elements
•The red pigment that gives whole blood its color
•Binds and transports oxygen and carbon dioxide
Red blood cell count - the number of RBCs in 1
microliter of whole blood
•Male: 4.5–6.3 million
•Female: 4.2–5.5 million
Structure of RBCs
•Small and highly specialized discs
•Thin in middle and thicker at edge
Life Span of RBCs
•Lack nuclei, mitochondria, and ribosomes
•Means no repair and anaerobic metabolism
•Live about 120 days
•Hemoglobin (Hb)
•Protein molecule that transports respiratory gases
•Normal hemoglobin (adult male) 14–18 g/dL
whole blood (adult female)12–16 g/dL whole
Hemoglobin Function
•Carries oxygen
•With low oxygen (peripheral capillaries)
•Hemoglobin releases oxygen
•Binds carbon dioxide and carries it to lungs
•Forms carbaminohemoglobin
RBC Formation and Turnover
•1% of circulating RBCs wear out per day
•About 3 million RBCs per second
•Hemoglobin Conversion and Recycling
•Macrophages of liver, spleen, and bone marrow
•Monitor RBCs
•Engulf RBCs before membranes rupture (hemolyze)
Hemoglobin Conversion and Recycling
•Phagocytes break hemoglobin into components
•Globular proteins to amino acids
•Heme to biliverdin
Breakdown of Biliverdin
•Biliverdin (green) is converted to bilirubin (yellow)
•Is excreted by liver (bile)
•Jaundice is caused by bilirubin buildup
•Converted by intestinal bacteria to urobilins and
RBC Production
•Occurs only in myeloid tissue (red bone marrow) in
•Stem cells mature to become RBCs
19-3 Red Blood Cells
Blood Typing
Surface Antigens
•Are cell surface proteins that identify cells to
immune system
•Normal cells are ignored and foreign cells attacked
•Blood Types
•Are genetically determined
•By presence or absence of RBC surface antigens A, B,
Rh (or D)
Four Basic Blood Types
1.A (surface antigen A)
2.B (surface antigen B)
3.AB (antigens A and B)
4.O (neither A nor B)
•Antigens on surface of RBCs
•Screened by immune system
•Plasma antibodies attack and agglutinate (clump)
foreign antigens
Blood Plasma Antibodies
•Type A
•Type B antibodies
•Type B
•Type A antibodies
•Type O
•Both A and B antibodies
•Type AB
•Neither A nor B antibodies
•The Rh Factor
•Also called D antigen
•Either Rh positive (Rh) or Rh negative (Rh)
•Only sensitized Rh blood has anti-Rh antibodies
Cross-Reactions in Transfusions
•Also called transfusion reaction
•Plasma antibody meets its specific surface antigen
•Blood will agglutinate and hemolyze
•Occur if donor and recipient blood types not
Testing for Transfusion Compatibility
•Performed on donor and recipient blood for
•Without cross-match, type O is universal donor
White Blood Cells (WBCs)
•Also called leukocytes
•Do not have hemoglobin
•Have nuclei and other organelles
•WBC functions:
•Defend against pathogens
•Remove toxins and wastes
•Attack abnormal cells
•Most WBCs in:
•Connective tissue proper
•Lymphatic system organs
•Small numbers in blood
•5000 to 10,000 per microliter
Four Characteristics of Circulating WBCs
1.Can migrate out of bloodstream
2.Have amoeboid movement
3.Attracted to chemical stimuli (positive chemotaxis)
4.Some are phagocytic
•Neutrophils, eosinophils, and monocytes
White Blood Cells
•Also called polymorphonuclear leukocytes
•50–70% of circulating WBCs
•Pale cytoplasm granules with:
•Lysosomal enzymes
•Bactericides (hydrogen peroxide and superoxide)
Very active, first to attack bacteria
•Engulf and digest pathogens
•Removing granules from cytoplasm
•Defensins (peptides from lysosomes) attack
pathogen membranes
•Release prostaglandins and leukotrienes
•Form pus
Eosinophils (Acidophils)
•2–4% of circulating WBCs
•Attack large parasites
•Excrete toxic compounds
•Nitric oxide
•Cytotoxic enzymes
•Are sensitive to allergens
•Control inflammation with enzymes that counteract
inflammatory effects of neutrophils and mast cells
•Are less than 1% of circulating WBCs
•Accumulate in damaged tissue
•Release histamine
•A cut triggers vascular spasm that lasts 30 minutes
•Three Steps of the Vascular Phase
1.Endothelial cells contract and expose basement
•Dilates blood vessels
•Release heparin
•Prevents blood clotting
membrane to bloodstream
•2–8% of circulating WBCs
•Are large and spherical
•Enter peripheral tissues and become macrophages
•Engulf large particles and pathogens
•Secrete substances that attract immune system cells
and fibrocytes to injured area
•20–30% of circulating WBCs
•Are larger than RBCs
•Migrate in and out of blood
•Mostly in connective tissues and lymphoid organs
•Are part of the body’s specific defense system
The Differential Count and Changes in WBC Profiles
•Detects changes in WBC populations
•Infections, inflammation, and allergic reactions
Three Steps of the Vascular Phase
2. Endothelial cells
•Release chemical factors ADP, tissue factor, and
•Release local hormones, endothelins
•Stimulate smooth muscle contraction and cell
3. Endothelial plasma membranes become “sticky”
•Seal off blood flow
The Platelet Phase
•Begins within 15 seconds after injury
•Platelet adhesion (attachment)
•To sticky endothelial surfaces
•To basement membranes
•To exposed collagen fibers
•Platelet aggregation (stick together)
•Forms platelet plug which closes small breaks
•Platelet Phase
•Activated platelets release clotting compounds
Myeloid Stem Cells
•Produce all WBCs except lymphocytes
•Lymphoid Stem Cells
•Lymphopoiesis - the production of lymphocytes
1.Adenosine diphosphate (ADP)
2.Thromboxane A2 and serotonin
3.Clotting factors
4.Platelet-derived growth factor (PDGF)
5.Calcium ions
•Cell fragments involved in human clotting system
•Nonmammalian vertebrates have thrombocytes
(nucleated cells)
•Circulate for 9–12 days
•Are removed by spleen
•2/3 are reserved for emergencies
The Coagulation Phase
•Begins 30 seconds or more after the injury
•Blood clotting (coagulation)
•Cascade reactions
•Chain reactions of enzymes and proenzymes
•Form three pathways
•Convert circulating fibrinogen into insoluble fibrin
Three Functions of Platelets
1.Release important clotting chemicals
2.Temporarily patch damaged vessel walls
3.Reduce size of a break in vessel wall
•Is the cessation of bleeding
•Consists of three phases
1.Vascular phase
2.Platelet phase
3.Coagulation phase
The Vascular Phase
13 Clotting Factors
•Also called procoagulants
•Proteins or ions in plasma
•Required for normal clotting
Three Coagulation Pathways
1.Extrinsic pathway
2.Intrinsic pathway
3.Common pathway
•The Extrinsic Pathway
•Begins in the vessel wall
•Outside bloodstream
•Damaged cells release tissue factor (TF)
•TF + other compounds = enzyme complex
•Activates Factor X
•The Intrinsic Pathway
•Begins with circulating proenzymes
•Within bloodstream
•Activation of enzymes by collagen
•Platelets release factors (e.g., PF-3)
•Series of reactions activates Factor X
The Common Pathway
•Where intrinsic and extrinsic pathways converge
•Forms enzyme prothrombinase
•Converts prothrombin to thrombin
•Thrombin converts fibrinogen to fibrin
Calcium Ions, Vitamin K, and Blood Clotting
•Calcium ions (Ca2+) and vitamin K are both essential
to the clotting process
Clot Retraction
1.Pulls torn edges of vessel closer together
•Reducing residual bleeding and stabilizing injury site
2.Reduces size of damaged area
•Making it easier for fibrocytes, smooth muscle cells,
and endothelial cells to complete repairs
•Slow process of dissolving clot
•Thrombin and tissue plasminogen activator (t-PA)
•Activate plasminogen
•Plasminogen produces plasmin
•Digests fibrin strands
D Button 2015