Biology 221 Anatomy & Physiology II TOPIC 4 Circulatory

1
TOPIC 4Circulatory System Blood Flow, Blood
Pressure Capillary Dynamics
Biology 221 Anatomy Physiology II
Chapter 20 pp. 727-747
E. Lathrop-Davis / E. Gorski / S. Kabrhel
2
Blood Flow

• volume of blood flowing through a vessel, an
  organ, or the entire circulation in a given
  period
• Measured in ml/min
• To entire system
• blood flow (BF) cardiac output (CO)
• relatively constant at rest
• To specific organ or tissue, flow varies with
  demand

3
Blood Flow Controlling factors

• BF ?P / R
• directly proportional to blood pressure gradient
  (?P) between two points
• inversely proportional to peripheral resistance
  (R)
• resistance is more important in controlling local
  flow

4
Resistance to Blood Flow

• a measure of the amount of friction blood
  encounters as it passes through vessels
• Peripheral resistance (PR) is resistance in
  peripheral vessels accounts for most resistance
  in system
• Resistance is inversely proportional to flow
• Think About It If something is directly related
  to resistance, what affect will it have on blood
  flow? What about things that are inversely
  related to resistance?

5
Resistance to Blood Flow

• Sources of resistance include
• blood viscosity thickness of blood
• directly proportional to resistance
• affected by number of blood cells
• blood volume directly proportional
• dehydration ? decreases volume ? decreases
  resistance
• water retention ? increases volume ? increases
  resistance
• total blood vessel length directly proportional
• angiogenesis - formation of new blood vessels
• fat and tumors lead to angiogenesis

6
Resistance to Blood Flow

• blood vessel diameter inversely related to
  resistance main source of resistance
• inversely proportional to resistance
• increased diameter ? decreased resistance
• varies as inverse of radius to 4th power (1/r4)
• i.e., double radius ? resistance decreases to
  1/16 original PR
• controlled at small arterioles in response to
  neural and chemical controls
• controlled overall by sympathetic vasomotor tone
• sudden decrease in size of lumen (e.g., due to
  partial blockage) creates turbulence ? increases
  resistance

7
Blood Pressure (BP)

• force per unit area exerted on the wall of a
  blood vessel by its contained blood
• In common usage, blood pressure usually refers
  to blood pressure in systemic arteries near heart
• Pressure gradient keeps blood flowing
• Measured in mm Hg (millimeters of mercury)

8
Blood Pressure (cont)

• Varies through vascular system
• Highest and most variable in aorta and other
  elastic arteries - Why?
• Decreases through arterioles and capillaries
• Lowest in venae cavae

Fig. 20.5, p. 729
9
Arterial Blood Pressure

• Varies with
• age
• gender
• weight
• stress level
• mood
• posture
• physical activity

10
Arterial Blood Pressure

• Depends on
• compliance (distensibility) of elastic arteries
• stroke volume
• Rises during ventricular systole, decreases
  during diastole
• systolic pressure (Ps) - pressure in arteries
  during ventricular systole
• diastolic pressure (PD) -pressure in arteries
  during ventricular diastole

11
Systolic and Diastolic Pressures

• Systolic pressure (Ps) 110-120 mm Hg
• semilunar valves open and blood is ejected
• compliance of elastic arteries decreases pressure
  needed to eject blood into arteries
• increased stroke volume (amount ejected) ?
  increased pressure
• Diastolic pressure (PD) 70-80 mm Hg
• occurs when the semilunar valves are closed
  because the heart is in diastole
• elastic recoil of arteries contributes to
  continued pressure ? movement of blood

12
Pulse Pressure (PP)

• difference between systolic (PS) and diastolic
  (PD) pressures PP PS PD
• increased by increased stroke volume (SV) during
  exertion
• increased by arteriosclerosis (loss of elasticity
  requires much more pressure to force blood into
  vessels during systole)

13
Mean Arterial Pressure (MAP)

• average pressure in main arteries
• heart spends more time in diastole
• therefore, MAP diastolic pressure (PD) (pulse
  pressure PP divided by 3)
• MAP PD (PP /3)

14
Measuring Pulse

• palpation of pulse points (pressure points)
• pulse can be felt at major arteries
• count number of pulsations felt
• pulse decreases strength away from heart
• Think About It Where would you expect pulse to
  be strongest?

Fig. 20.11, p. 737
15
Measuring Blood Pressure

• Auscultatory method
• sphygmomanometer
• brachial artery usually used
• Korotkoff sounds sounds heard as blood moves
  through partially blocked artery
• normally, 120/80 (for a healthy, young male)
• varies with age, sex, physical condition, gender,
  weight, stress, mood, posture

16
Capillary Blood Pressures

• Pressure in capillaries
• Pressure drops from 35-40 mm Hg (at arterial
  end) to 17-20 mm Hg (at venous end)
• Lower pressure helps prevent breakage of
  capillary walls decreases fluid loss to tissues

Fig. 20.5, p. 729
17
Venous Blood Pressures

• Low, steady pressure
• Venous return supported by
• valves prevent backflow
• varicose veins (see Topic 3 Blood Vessels)
• respiratory pump changes in thoracic and
  abdominal pressures during breathing
• during inspiration thoracic pressure decreases
  and abdominal pressure increases, thus pushing
  blood from the abdominal vessels (inferior vena
  cava inferior to the diaphragm) into the thoracic
  part of the inferior vena cava

18
Venous Blood Pressures (cont)

• muscular pump
• milking by skeleltal muscle promotes return
• prolonged inactivity or prolonged contraction
  causes blood to pool (may allow clots to form)

19
Maintaining Blood Pressure

• Blood pressure (BP) varies directly with
• Cardiac output (CO see Topic 2)
• controlled by cardiac centers in medulla
  oblongata
• cardioacceleratory center (CAC) ? sympathetic
  outflow
• cardioinhibitory center (CIC) ? parasympathetic
  outflow
• Think About It What is the relationship between
  HR and BP?

Fig. 20.7, 20.8
20
Maintaining Blood Pressure

• Peripheral resistance (PR) - pressure varies
  directly with resistance
• Think About It What is the relationship between
  blood vessel diameter and BP?
• Blood volume (BV) - BP varies directly with BV
• Think About It What is the relationship between
  CO and BV?

Fig. 20.7, 20.8
21
Short-Term Control of Resistance

• Based on controlling blood vessel diameter
• Mechanisms include neural and chemical controls
• Goals
• alter distribution to meet demands of various
  organs/tissues
• maintain overall MAP through vasomotor tone

Fig. 20.8, p. 733
22
Neural Control of Resistance

• Vasomotor center (VMC) controls vasomotor tone
• located in medulla oblongata (as part of
  cardiovascular center)
• maintains vasomotor tone in all vessels
• vasomotor fibers are part of the sympathetic
  division of the ANS (for the most part)

23
Neural Control of Resistance

• Vasomotor fibers
• most use norepinephrine (NE) as their
• increased activity ? vasoconstriction ? increased
  BP
• fibers to vessels serving skeletal muscle use ACh
• increased sympathetic activity ? vasodilation ?
  increased flow to skeletal muscle (generally
  little importance to overall BP)
• Reflexes initiated by baroreceptors or
  chemoreceptors integrated in medulla oblongata
  (reticular formation See AP I Unit 6 - Brain)

24
Baroreceptor-initiated Reflexes

• Baroreceptors (pressoreceptors) present in
  carotid sinus, aortic arch, most other elastic
  arteries of neck and thorax
• Increased BP stimulates baroreceptors
• ? increased afferent impulses inhibit vasomotor
  center
• ? decreased sympathetic outflow ? vasodilation
• Afferent impulses from baroreceptors also go to
  CIC in medulla and increase parasympathetic
  outflow to heart also inhibit CAC, thus
  decreasing sympathetic outflow
• Prolonged hypertension causes baroreceptors to
  reset to higher pressure

25
Chemoreceptor-initiated Reflexes

• Chemoreceptors located in aortic arch and large
  arteries of neck
• Connected to CAC and vasomotor center by afferent
  fibers
• Respond to oxygen (O2), pH (hydrogen ion), carbon
  dioxide (CO2) levels
• decreased O2 or pH, or increased CO2 ? increases
  impulses to CAC and vasomotor center ? increased
  sympathetic outflow
• increased heart rate and vasoconstriction ?
  increased BP ? helps move blood through system
  faster ? gets blood to lungs faster

26
Influence of Higher Brain Centers on Vasomotor
Tone

• Cerebral cortex and hypothalamus connected to
  cardiovascular center (cardiac centers CAC and
  CIC and vasomotor center) in medulla oblongata
• Hypothalamus threats initiate fight-or-flight
  response mediated by hypothalamus ? increased
  sympathetic outflow (CAC and vasomotor center)
• hypothalamus directs changes in flow during
  activity and to control body temperature
• Cerebral cortex bio-feedback - person learns to
  relax, increasing parasympathetic outflow and
  decreasing sympathetic, resulting in decreased
  blood pressure

27
Short-Term Chemical Control of Resistance

• Chemicals that act on vessels, heart or blood
  volume
• Norepinephrine (NE from adrenal medulla) ?
  vasoconstriction
• Epinephrine (epi from adrenal medulla)
• vasoconstriction, except in skeletal and cardiac
  muscle
• nicotine (in tobacco) stimulates sympathetic
  ganglionic neurons and adrenal medulla
• also increases heart rate and strength of
  contraction

28
Short-Term Chemical Controls (cont)

• Antidiuretic hormone (ADH a.k.a., vasopressin
  released from neurohypophysis see AP I Unit
  11- Endocrine System)
• stimulates water reabsorption
• at high levels, causes vasoconstriction
• Angiotensin II (see AP I Unit 11 - Endocrine
  and AP II Topic 10 - Urinary System)
• produced from angiotensinogen in response to
  renin from kidney
• causes intense vasoconstriction
• stimulates secretion of ADH and aldosterone (long
  term control)

29
Short-Term Chemical Controls (cont)

• Atrial natriuretic peptide (ANP from atria of
  heart) antagonizes aldosterone and causes
  general vasodilation
• Alcohol
• inhibits ADH secretion
• depresses vasomotor center
• Inflammatory chemicals cause vasodilation
• histamine, prostacyclins, kinins and others
• released during inflammatory response

30
Short-Term Chemical Controls (cont)

• Endothelium-derived factors affect vascular
  smooth muscle
• endothelin potent vasoconstrictor, released in
  response to low blood flow
• nitric oxide (NO) vasodilator released in
  response to high blood flow causes systemic and
  local vasodilation

31
Long-Term Control of Resistance Renal Regulation

• Regulates blood volume (BV)
• Blood volume important to venous pressure,
  venous return, EDV, SV, CO
• Control
• direct renal control
• indirect renal control

32
Direct Renal Control

• Increased BP ? increased filtration ? increased
  water loss ? decreased BV
• Decreased BP ? decreased filtration ? decreased
  water loss ? increased BV

Fig. 20.9, p. 735
33
Indirect Renal Control

• Renin-angiotensin pathway
• Decreased BP ? juxtaglomerular cells of kidney
  tubules secrete renin ? enzymatic cascade ?
  converts angiotensinogen to angiotensin I ?
  angiotensin II
• Kidney also releases renin in response to
  sympathetic impulses
• Angiotensin II
• stimulates aldosterone secretion
• stimulates ADH secretion
• causes vasoconstriction

Fig. 20.9, p. 735
34
Blood Pressure Disorders Hypotension

• Systemic systolic BP lt 100 mm Hg
• Orthostatic hypotension drop in BP on rising
  from sitting or laying common in the elderly
• Chronic hypotension long-term depression in BP
• possible causes poor nutrition, Addisons
  disease, hypothyroidism
• Acute hypotension rapid drop in BP
• most often due to hemorrhage
• sign of circulatory shock

35
Blood Pressure Disorders Hypertension

• Long-term elevation of arterial pressure gt 140/90
• Results in damage to heart, kidneys, brain
  (stroke), blood vessels overall
• Primary hypertension
• 90 of all cases
• no clearly identifiable cause
• Secondary hypertension
• 10 of cases
• cause is identified

36
BP Disorders Primary Hypertension

• possible causes
• diet high in Na, saturated fat, cholesterol low
  in K, Ca2, Mg2
• obesity, heredity, age
• stress, smoking
• treatment
• changes in diet, weight loss, exercise, stress
  management
• antihypertensive drugs diuretics, beta-blockers,
  calcium-channel blockers

37
BP Disorders Secondary Hypertension

• causes
• excess renin secretion
• arteriosclerosis
• hyperthyroidism
• Cushings disease
• treatment aimed at cause

38
Changes in Blood Distribution During Exercise

• Total increases from 5,800 ml/min at rest to
  17,500 ml/min during exercise
• Brain flow remains relatively steady (750
  ml/min)
• Skeletal muscle, heart flow increases
  dramatically to supply oxygen and nutrients and
  remove wastes
• Skin flow increases for heat loss
  (thermoregulation)
• Kidney flow decreases (decreases urine output)
• Abdominal organs flow decreases (redirected to
  skeletal muscle heart)
• Other flow decreases (redirected to skeletal
  muscle heart)

Fig. 20.12, p. 738
39
Tissue Perfusion

• Blood flow through tissues
• Varies with need of tissue
• Functions
• 1) delivery of oxygen nutrients, removal of
  wastes
• 2) gas exchange in lung
• 3) absorption of nutrients from gut
• 4) urine production in kidney

Fig. 20.12, p. 738
40
Velocity of Blood Flow

• Inversely related to total cross-sectional area
  of blood vessels to be filled
• Branching of arteries increases cross-sectional
  area
• Velocity lowest in capillaries
• allows time for exchange between blood and tissue
• Increases as capillaries rejoin to form venules
  and venules join to form veins

Fig. 20.13, p. 739
41
Autoregulation of Blood Flow

• Local (intrinsic) regulation of blood flow
• blood vessels serving tissues adjust to meet
  needs of tissue
• if blood flow is inadequate ? tissue metabolism
  decreases ? cell death
• Long-term autoregulation ? increase in number and
  size of blood vessels angiogenesis
• Short-term autoregulation 2 mechanisms of
  control
• metabolic control response to chemical needs of
  tissue
• myogenic control response to stretch

42
Metabolic Control of Blood Flow

• Maintains proper chemical environment for cells
• Causes relaxation (vasodilation) of precapillary
  sphincter to increase blood flow
• Important vasodilating chemicals include
• nitric oxide (NO)
• attaches to hemoglobin in lungs as O2 is loaded
• released at capillaries as O2 is released
• inflammatory chemicals (histamine, kinins)

43
Metabolic Control (cont)

• active hyperemia - due to chemicals changes
  associated with hard-working tissues
• decreased oxygen and/or other nutrients
• products of metabolic activity increased K,
  adenosine, lactic acid, H (decreased pH)

44
Myogenic Control of Blood Flow

• Maintains relatively steady flow to tissues in
  spite of changes in overall BP
• Response of vascular smooth muscle to stretch
• increased stretch ? vasoconstriction ? decreased
  flow
• decreased stretch ? vasodilation ? increased flow
• Reactive hyperemia
• dramatic increase in blood flow following removal
  of blockage
• results from
• stretching of arteriole upstream from blockage,
  and
• accumulation of wastes in tissue

45
Capillary Dynamics

• Movement across capillary is based on gradients
• Solute gradient (diffusion)
• Water gradient (osmosis)
• Pressure gradient (hydrostatic pressure)

Fig. 20.14, p. 742
46
Diffusion

• small water-soluble molecules pass between
  endothelial cells through small clefts
  (desmosomes are loose cell junctions)
• lipids and lipid-soluble (non-polar) materials
  diffuse directly through the lipid bilayer of the
  endothelial cells
• Osmosis
• special form of diffusion in which solvent
  (water) moves across membrane (diffusion of
  water)
• moves toward area of higher solute concentration
  (lower water concentration)

47
Bulk Fluid Flow

• Moves fluids and dissolved substances through
  capillary walls together using the following
  forces
• Hydrostatic Pressure
• physical pressure exerted by a fluid in an
  enclosed space
• fluids and dissolved substances move from areas
  of high to areas of low hydrostatic pressure
• Osmotic Pressure
• pull exerted on solvent by solute in solution
• solution with more solute has greater osmotic
  pressure

48
Forces Moving Fluid OUT Of Capillary

• i.e., moving fluid INTO interstitial space
• Capillary hydrostatic pressure HPc
• also called capillary blood pressure (or blood
  hydrostatic pressure)
• pushes fluid out of capillary
• 35 mm Hg at arterial end of capillary (average)
• 17 mm Hg at venous end of capillary (average)
• Interstitial fluid osmotic pressure OPif
• proteins in interstitial fluid exert osmotic
  pressure on plasma
• pulls fluid out of capillary into tissues
• BUT, normally very little protein present in IF
  average value is 1 mm Hg

49
Forces Moving Fluid INTO Capillary

• Interstitial fluid hydrostatic pressure (HPif)
  physical pressure pushing interstitial fluid into
  the capillary
• ranges from slightly negative to slightly
  positive
• 0 mm Hg is generally used in equations
• fluid removed by lymphatic system
• Capillary osmotic pressure (OPc) - pressure due
  to presence of large, nondiffusible molecules
  (e.g., plasma protein) that draws fluid into the
  capillary from the interstitial fluid
• average value is 26 mm Hg
• little change along capillary from arterial to
  venous end

50
Net Filtration Pressure

• Sum of all hydrostatic and osmotic forces acting
  on fluids as they move through capillary walls
• Can be seen as difference between forces moving
  fluid out of capillary and forces moving fluid
  into it
• net filtration pressure (NFP)
• sum of outward forces sum of inward forces
• HPc OPif - HPif OPc

51
Net Filtration Pressure

• At arterial end
• out HPc 35mm Hg OPif 1 mm Hg
• in HPif 0 mm Hg OPc 26 mm Hg
• NFP 35mm Hg 1 mm Hg 0 mm Hg 26 mm Hg
• 10 mm Hg (flow OUT OF capillary at arterial
  end)

HPc 35 mm Hg
OPif 1 mm Hg
36 mm Hg OUT

Hpif 0 mm Hg
OPc 26 mm Hg

26 mm Hg IN
NFP (OUT-IN) 10 mm Hg OUT
52
Net Filtration Pressure

• At venous end
• out HPc 17 mm Hg OPif 1 mm Hg
• in HPif 0 mm Hg OPC 26 mm Hg
• NFP 17 mm Hg 1 mm Hg 26 mm Hg 0 mm Hg
• - 8 mm Hg (net flow INTO capillary at
  venous end)

HPc 17 mm Hg
OPif 1 mm Hg

18 mm Hg OUT
Hpif 0 mm Hg
OPc 26 mm Hg

26 mm Hg IN
NFP (OUT- IN) -8 mm Hg (IN)
53
Net Filtration Pressure

• Results is net LOSS of fluid from capillary to
  interstitial fluid
• 10 mm Hg loss at arterial end
• - 8 mm Hg gain at venous end
• 2 mm Hg net loss along length of capillary

54
Net Filtration Pressure

• Can also be seen as difference in hydrostatic
  pressures minus difference in osmotic pressures
• (HPc HPif) - (OPc OPif)
• Difference in hydrostatic pressures Net
  Hydrostatic Pressure
• NHP HPc HPif
• at arterial end 35mm Hg 0 mm Hg 35mm Hg
• at venous end 17mm Hg 0mm Hg 17mm Hg
• Difference in osmotic pressures Net Osmotic
  Pressure NOP OPc OPif
• 26 mm Hg 1 mm Hg 25 mm Hg
• normally does not change along length of capillary

55
Net Filtration Pressure

• At the arterial end
• NFP net hydrostatic presssure net osmotic
  pressure
• 35mm Hg 0mm Hg 26mm Hg 1mm Hg
• 35mm Hg 25mm Hg
• 10 mm Hg (fluid moves out of the capillary)

Fig. 20.15, p. 743
HPc 35 mm Hg
OPif 1 mm Hg
Hpif 0 mm Hg
OPc 26 mm Hg
56
Net Filtration Pressure

• At venous end
• NFP net hydrostatic presssure net osmotic
  pressure
• 17 mm Hg 0 mm Hg 26mm Hg 1mm Hg
• - 8 mm Hg (fluid moves into capillary)

Fig. 20.15, p. 743
HPc 17 mm Hg
OPif 1 mm Hg
Hpif 0 mm Hg
OPc 26 mm Hg
57
Edema

• Abnormal accumulation of fluid in tissues
• Predict the effect of the following on capillary
  dynamics (i.e., which way will fluid move, and
  why?)
• increased MAP
• venous obstruction
• leakage of plasma protein across into
  interstitial fluid as a result of an allergic
  reaction
• myxedema accumulation of glycoprotin in the
  interstitial fluid as a result of hypothyroidism
• decreased plasma protein production, due to
  protein malnutrition (kwashiorkor)
• destruction of lymphatic drainage channels as in
  filariasis (blockage of lymphatics by parasitic
  worms)

58
Circulatory Shock

• any condition in which blood vessels are
  inadequately filled and blood cannot circulate
  normally
• Results in decreased flow to tissues leading to
  cell death (necrosis)
• Signs
• rapid, but weak, heart beat (thready pulse)
• intense vasoconstriction
• sharp drop in blood pressure
• Treatment rapid replacement of fluids

59
Types of Circulatory Shock

• Cardiogenic Shock
• heart not able to pump enough blood
• often due to myocardial damage (multiple
  infarcts)
• Hypovolemic shock
• large scale loss of fluid
• most common type
• causes
• acute hemorrhage
• severe vomiting or diarrhea
• extensive burns

60
Types of Circulatory Shock

• Vascular shock extreme vasodilation resulting
  in decreased peripheral resistance
• anaphylaxis (anaphylactic shock) systemic
  reaction to allergen (e.g., bee sting)
• neurogenic shock failure of ANS (sympathetic)
  regulation (loss of vasomotor tone)
• septicemia systemic reaction to bacterial toxic
• prolonged exposure to heat (e.g., sunbathing)
  vasodilation of cutaneous vessels