Chapter 19 The Cardiovascular System: Blood Vessels G.R. Pitts, J.R. Schiller, and J. F. Thompson - PowerPoint PPT Presentation

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Chapter 19 The Cardiovascular System: Blood Vessels G.R. Pitts, J.R. Schiller, and J. F. Thompson


Chapter 19 The Cardiovascular System: Blood Vessels G.R. Pitts, J.R. Schiller, and J. F. Thompson Use the video clip: CH 19 - Anatomy of the Blood Vessels for a ... – PowerPoint PPT presentation

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Title: Chapter 19 The Cardiovascular System: Blood Vessels G.R. Pitts, J.R. Schiller, and J. F. Thompson

Chapter 19 The Cardiovascular System Blood
VesselsG.R. Pitts, J.R. Schiller, and J. F.
Use the video clip CH 19 - Anatomy of the
Blood Vessels for a review of vessel structure
Vessel Structure
  • Structure/function relationships change as one
    moves through the cardiovascular tree
  • Tunic thickness and composition of the three
    layers are variable

Capillary Beds
  • Flow regulated by smooth muscle valves
  • Metarterioles
  • from arterioles to venules through capillary bed
  • allows flow through capillary bed w/out flow
    through caps
  • True capillaries
  • pre-capillary sphincter
  • ring of smooth muscle
  • open/close to control flow
  • regulated by chemicals
  • intermittent vasomotion, open for flow 5-10 times
    each minute

  • Allow exchange of nutrients and wastes between
    the blood and the tissue cells
  • Capillary structure simple squamous epithelium
  • basal lamina - connective tissue
  • endothelial cells
  • Details of structure determine specific functions
  • 3 types continuous, fenestrated, sinusoidal

Vascular Anastomoses
  • Arterial Anastomoses
  • - provide collateral supply to some organs and
    tissues, e.g., skeletal muscles
  • Arteriovenous Anastomoses
  • - thoroughfare channels
  • Venous Anastomoses
  • - most common, e.g., deep and superficial veins
    in limbs and head

Vessel Structure - Histology
Vein Artery
Vein Artery
Varicose Veins
Vessel Structure/Function
  • At rest
  • 60 of blood volume is located in veins and
  • venous system serves as reservoirs for blood
  • particularly veins of the abdominal organs and
    the skin
  • ANS regulates volume distribution
  • vasoconstriction
  • vasodilation
  • diverts blood to areas with increased metabolic

Spleen 1L
Compare to Cardiac Output figures
Blood Distribution at Rest
? 0.75 L/min
CO 5 L/min
Blood Distribution -- Exercise
Using cardiac reserve
CO 25 L/min
Heavy Exercise
? 20 L/min
? 0.75 L/min
CO 5 L/min
Physiology of Circulation
  • Flow ?P/R
  • or CO MAP/R
  • MAP mean arterial pressure
  • higher pressure to lower pressure with decreasing
    resistance (R)
  • Blood pressure
  • pressure of the blood on the vessel wall
  • measure the pressure of a volume in a space
  • systole/diastole - 120/80 (mm Hg)
  • BP falls progressively from the aorta to
    essentially 0.0 mm Hg at the right atrium (RA)

Physiology of Circulation
  • Resistance - opposes blood flow because of the
    friction produced by the vessel walls
  • Factors that affect resistance (R)
  • (1) resistance (R) is proportional to viscosity
    ?V ? ?R
  • thickness of the blood
  • e.g., dehydration, elevated plasma proteins,
    polycythemia (?RBCs), leukemias (?WBCs)
  • (2) resistance (R) is proportional to vessel
  • obesity increases the route lengths within
    connective tissue
  • (3) resistance (R) is inversely proport. to
    vessel width
  • decrease the radius by 1/2 and R increases by 16X
  • most important in vessels that can change their
    size actively
  • changes in diameter affect flow
  • vessel wall drag blood cells dragging against
    the wall
  • laminar flow layers of flow

Physiology of Circulation
  • Systemic Vascular Resistance (SVR) Total
    Peripheral Resistance (TPR)
  • all vascular resistance is offered by the
    systemic vessels
  • which vessels change size?
  • resistance is highest in arterioles
  • largest pressure drop is in the arterioles
  • Relationship of the radius to resistance in the
    arterioles is due to smooth muscle

Systemic Blood Pressure
  • Arterial Blood Pressure
  • Pulsatile in arteries due to the pumping of the
  • Systolic/diastolic values
  • Pulse pressure systolic (minus) diastolic
  • Q- What does the Windkessel effect have on pulse
  • Q- What is the effect of hardening of the
    arteries on pulse pressure?

Systemic Blood Pressure
  • Capillary Blood Pressure
  • relatively low blood pressure
  • low pressure is good design for capillaries
  • capillaries are fragile - high pressure would
    tears them
  • capillaries are very permeable - high pressure
    forces a lot of fluid out

Systemic Blood Pressure
  • Venous return
  • the volume of blood flowing back to heart from
    systemic veins
  • depends on pressure difference from beginning of
    venules (16 mmHg) to heart (0 mmHg)
  • any change in right atrial (RA) pressure changes
    venous return

Venous Return/Valves
  • Assistance for venous return
  • skeletal muscles act as pumps
  • contracting muscles squeeze veins
  • force blood back to the heart
  • valves prevent back flow
  • respiratory pump
  • inhaling causes a lowered pressure in the
    thoracic cavity
  • primarily to pull air into the lungs
  • helps to draw blood into thorax via pulmonary

Velocity of Blood Flow
  • Velocity of blood flow - inversely proportional
    to the total cross sectional area (CSA) of
  • Aorta
  • total CSA 3-5 cm2
  • velocity 40 cm/sec
  • Capillaries
  • total CSA 4500-6000 cm2
  • velocity 0.1 cm/sec
  • Vena Cava
  • total CSA 14 cm2
  • velocity 5-20 cm/sec

Capillary Function
  • Capillary Function
  • site of exchange between blood and tissues
  • delivery of nutrients and removal of wastes
  • slow flow allows time for molecules to diffuse
  • Mechanisms of nutrient exchange
  • diffusion - O2, CO2, glucose, AA's, hormones,
    electrolytes -- diffuse down gradients
  • lipid soluble molecules can pass through cell
    membrane easily
  • water soluble molecules generally require
    transport mechanisms to enter/exit cells

Capillary Function
  • Fluid movement
  • Fluid diffuses out and is reabsorbed across the
    capillary walls
  • Starlings law of the capillaries
  • Forces driving the movement of fluid
  • Hydrostatic pressure capillary (HPc)
  • Hydrostatic pressure interstitial fluid (HPif)
  • Osmotic pressure capillary (OPc)
  • Osmotic pressure interstitial fluid (OPif)
  • Net filtration pressure (NFP) is the net effect
    of all four forces at any point along the

Net Filtration Pressure (NFP)
  • NFP (HPC - HPIF) - (OPC - OPIF)
  •        Pushing forces - Pulling forces
  • On average, 85 of fluid entering the tissues on
    the arteriole side is reabsorbed on venous end

Maintaining Blood Pressure Short Term
Mechanisms - CNS
  • Neural Control - Cardiac Centers in medulla
  • Vasomotor center
  • medullary area dedicated to control of blood
  • sends sympathetic output to blood vessels
  • Vasoconstricts or vasodilates as needed
  • Vasomotor tone - normal amount of
    vasoconstriction or vasodilation
  • ANS can vary the vasomotor tone which varies the
    delivery of blood to particular regional
    capillary beds
  • receives sensory input from different sources
  • baroreceptors (blood pressure)
  • chemoreceptors (O2, CO2, H, HCO3-)

Maintaining Blood Pressure Short Term
Mechanisms - CNS
  • Baroreceptor initiated reflex
  • located at carotid sinuses and aortic arch
  • monitors blood pressure
  • regulates the activity of the sympathetic nervous
    system (vascular tone)

Maintaining Blood Pressure Short Term
Mechanisms - CNS
  • Chemoreceptor initiated reflexes
  • Carotid bodies, aortic bodies
  • Monitor changes in indicator chemicals (O2, CO2,
    H, HCO3-)
  • ? CO2, ? H, ? O2 (stresses) result in ?
    sympathetic activity and ? BP

Maintaining Blood Pressure Short Term
Mechanisms - CNS
  • Influence of higher brain centers (areas above
    medulla) - cortex and hypothalamus
  • not involved in minute-to-minute regulation
  • influence vasomotor center depending on
  • temperature changes
  • stressful emotional situations

Maintaining Blood Pressure Short Term
Mechanisms - Chemicals
  • Renin - Angiotensin - Aldosterone
  • Renin/ACE
  • enzymes from kidney/lung
  • catalyze formation of Angiotensin I/II
  • Angiotensin II
  • vasoconstrictor
  • stimulates ADH, thirst
  • stimulates aldosterone release for Na H2O
  • why/how would these things affect blood pressure?

Maintaining Blood Pressure Short Term
Mechanisms - Chemicals
  1. diverts blood from the skin and abdominal organs
    to the skeletal muscles
  2. increases heart rate, stroke volume and,
    therefore, cardiac output blood pressure
  • Adrenal medulla releases epinephrine and
    norepinephrine in coordination with activity from
    the Sympathetic Division of the ANS

Maintaining Blood Pressure Short Term
Mechanisms - Chemicals
  • Antidiuretic Hormone (ADH) or Vasopressin
  • osmoreceptors in hypothalamus trigger release
    from the neurohypophysis
  • ADH targets kidneys to retain water (ADH action
    is inhibited by alcohol)
  • ADH also stimulates vasoconstriction at high
  • why/how would this affect blood volume and

Maintaining Blood Pressure Short Term
Mechanisms - Chemicals
  • Atrial Natriuretic Peptide (ANP)
  • released from atrial cells in response to ?blood
    vol ? BP
  • stimulates vasodilation, ?Na and water loss,
    antagonizes Aldosterone, inhibits thirst
  • why/how would this affect blood volume and

Maintaining Blood Pressure Long Term Regulation
  • Renal mechanism
  • control blood volume
  • nervous control - ANS
  • hormones
  • regulation in the short term by adjusting blood
    pressure and adjusting blood flow to different
    capillary beds
  • regulation in the long term by adjusting blood
  • target the kidneys
  • ? BP, ? urine flow to ? BP
  • ? BP, ? urine flow to ? BP

Control of Blood Flow
  • Autoregulation (local control) - local automatic
    adjustment of blood flow to match specific local
    tissue metabolic needs
  • Physical changes
  • Warming - ? vasodilation
  • Cooling - ? vasoconstriction
  • Chemical changes in local tissues generate
    metabolic byproducts
  • vasodilators or vasoconstrictors
  • Myogenic control
  • smooth muscle controls resistance
  • ? stretch ? contraction ? stretch ? contraction

Blood Flow in Special Areas
  • Skeletal Muscle
  • fine tuned control with wide variation in rate of
  • brain directs the sympathetic division for NE
    release in response to the degree of muscular
  • a receptors - vasoconstriction
  • ß receptors - vasodilation
  • metabolic regulation in tissue
  • low O2 causes vasodilation, increasing flow
  • high O2 cause vasoconstriction, decreasing flow
  • Brain
  • minimal variation in rate of flow
  • minimal nutrient storage, so adequate flow must
    be maintained!
  • local metabolic changes adjust local

Blood Flow in Special Areas
  • Skin
  • adjusting rate of flow aids in temperature
  • controls skins capacity as a blood reservoir
  • sympathetic and local metabolic regulation
  • Lungs
  • low pressure (25/10 mm Hg), low resistance system
  • flow regulated by O2 availability in the lungs
  • high O2 ? vasodilation to increase flow
    opposite of muscle
  • low O2 ? vasoconstriction to decrease flow
    opposite of muscle
  • Heart
  • variable flow depending on metabolic/pumping
  • sympathetic and local metabolic regulation

Regulation of Blood Pressure
The CirculationLearn specific vessels and routes
in lab
The CirculationLearn specific vessels and routes
in lab
Hepatic Portal System
a portal system transfers venous blood from one
capillary bed to another capillary bed before the
blood is returned to the heart
  • HPS collects venous blood from five abdominal
    organs and routes the blood to the liver for
    specific processing of transported molecules
  • - stomach toxins (ethanol)
  • - small intestine nutrients, toxins
  • - large intestine nutrients, toxins
  • - pancreas insulin, glucagon
  • - spleen RBC breakdown products

Fetal Circulation
  • Umbilical veins bring oxygen and nutrients from
    the placenta to the liver and then to the heart
    of the fetus

Fetal Circulation
  • ductus venosus bypasses liver
  • 3 Right ? Left shunts
  • because oxygenated blood is derived from the
  • ductus arterious ? ligametum arteriosum
  • foramen ovale ? fossa ovalis
  • interventricular shunt ? no remnant

Circulatory Shocksudden dramatic loss in blood
pressureor sudden decrease in circulatory flow
  • Hypovolemic Shock
  • Acute hemorrhage (or other sudden fluid loss as
    from vomiting or diarrhea)
  • Vascular Shock
  • Loss of vasomotor tone as from anaphylaxis,
    neural malfunction, or poisons (septicemia)
  • Cardiogenic Shock
  • Loss of cardiac output due to heart failure

End Chapter 19
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