Transcript Ch 15: Blood Flow and the Control of Blood Pressure

Ch 15:
Blood Flow and the Control
of Blood Pressure
Keypoints
1.
Blood pressure (BP) and Regulation
2.
Exchange at capillaries
3.
Lymphatic system
4.
Cardio-vascular diseases
Fig 15-2
Angiogenesis

Growth of new blood vessels – occurs
during
– Normal body maturation and growth
– Monthly re-growth of functional endometrium
– Wound healing
– Endurance training
– Cancer growth

Clinical implications: Promote or inhibit
angiogenesis with relevant cytokines
Blood Pressure
Pressure created by
ventricular contraction
is driving force for
blood flow
Fig 15-4
Pulsatile blood flow in arteries  Elastic
arteries expand and recoil for continuous
blood flow
Pulse wave disappears past arterioles
Blood Pressure (BP) Measurements

Ventricular pressure difficult to measure 
measure arterial BP

BP highest in the arteries – falls continuously
throughout systemic circulation

Read as “Systolic over diastolic”– normal value
 120 / 80 mm Hg

2003: New range for blood pressure readings
between 120/80 and 139/89 “Prehypertension”

Diastolic pressure in ventricle: ? mm Hg
BP Estimated by Sphygmomanometry
Auscultation of brachial artery with
stethoscope in cubital fossa
Based on effects of
laminar flow vs.
turbulent flow
Principles of Sphygmomanometry
Cuff inflated until brachial artery compressed
and blood flow stopped
kind of sound?
Compare to Fig 15-7
Slowly release pressure in cuff:
turbulent flow
Pressures at which . . .
. . . sound (= blood flow) first heard:
. . . sound disappeared:
CD
Animation
Cardiovascular
System:
Measuring
Blood Pressure
Mean Arterial Pressure

Sometimes useful to have single value for
driving pressure: Mean Arterial Pressure
MAP = Diastolic P + 1/3 Pulse Pressure
(for 60 -80 bpm)

MAP for 120/80 = ?

MAP closer to diastolic pressure – why?
MAP influenced by

Cardiac output

Peripheral resistance
(role of arterioles  see Ch14)
most common cause of hypertension

Total blood volume

Blood distribution
Figs 15-8 & 10
BP too low:

Driving force for blood flow unable to
overcome gravity

O2 supply to brain 

Symptoms?
Shock
= generalized circulatory failure

Hypovolemic shock  volume loss
(dehydration, blood loss, burns)

Distributive shock  loss of vascular tone
(anaphylactic, septic, toxic)

Cardiogenic shock  pump failure
Dissociative shock  inability of RBC to deliver
O2 (CO poisoning)
Cell damage due to inadequate perfusion
Signs and symptoms?
Management ?

BP too high:

Weakening of arterial walls lead to
Aneurysms  Risk of rupture &
hemorrhage
 Cerebral
 Rupture
hemorrhage
of major artery
Exchange at the Capillaries

Capillaries are anatomically designed for
exchange
Fig 15-16

Capillary blood flow: Greatest total cross
sectional area  Velocity ?

Most cells within ____ µm of capillary – why?

Direct correlation between # of caps and
metabolic needs of tissue

Three types of exchange of molecules across
the barrier
Methods of Capillary Exchange
1. Paracellular diffusion
2. Transendothelial transport
(transcytosis) – some diffusion
3. Bulk flow: mass movement of H2O
and dissolved solutes as result of
hydrostatic or osmotic pressure
 Filtration – flow direction out of caps
 Absorption – flow direction into caps
Two Forces Regulate
Capillary Bulk Flow
Hydrostatic P: lateral
component of fluid
flow
 Osmotic P: due to
solute difference
(main solute difference due to?)

Mostly:
Net filtration at arterial end
 Net re-absorption at venous end

Fig 15-18
Fluid Exchange
= Pcap + cap
cap = 25 mmHg

 

Fig 15-18
3) Lymphatic System
Close functional
association with
three other systems
1.
2.
3.
Lymphatic System Functions
 Return
filtered fluid & proteins
to circulatory system (anatomical
design!) – Fig 15-18
 Transfer
fat from small intestine
to circulatory system
 Trap
and deal with
pathogens
Edema
Due to disruption of capillary exchange
2 major causes:
1.
Blockage of lymph drainage
– Cancer & fibrotic growth
– Pathogens
2.
Capillary filtration > absorption
– Venous pressure  due to right / left
heart failure
– Plasma protein concentration  due to
liver failure or severe malnutrition
(Kwashiorkor)
Right or Left Heart Failure?
Alveolar Flooding
Sweden
Kroniskt invalidiserande lymfödem (2,1 liter) i höger
arm sedan 8 år.
Kwashiorkor
Regulation of Blood Pressure

Reflex control: Baroreceptor Reflex = 1o
homeostatic control for BP

Baroreceptors = stretch
sensitive ______receptors
in aorta and carotid artery

Medullary CVCC integrates
neural control
Cardiovascular System:
CD
Animation Blood Pressure Regulation
Fig 15-22
Additional Control of BP

Arterial chemoreceptors activated by
O 2

Cerebral cortex
– emotional responses such as blushing &
fainting  vasovagal response

Integration with Kidney function
Orthostatic hypotension normally
triggers Baroreceptor reflex
Cardiovascular Disease (CVD)

Account for ~ 1/2 of deaths in US –
most common: CAD or CHD

Uncontrollable & controllable risk factors

Gender, age, genetics

Cigarette smoking, obesity, high BP,
high cholesterol, DM
Cigarette Smoking:

Nicotinic cholinergic receptors stimulate
sympathetic neurons at ?
 Vasoconstriction
 Risk

& BP 
for atherosclerosis 
Carbon monoxide (myocardium extracts most of
O2 brought to it under resting conditions)
Atherosclerosis
Changes in artery walls start with
lipid deposits
Macrophage ingests LDL-cholesterol
Fatty streaks just under endothelial lining of
larger arteries
Macrophage paracrines attract smooth muscle
cells
Fig 15-24
Smooth muscle cells proliferate
 stable plaques vs. vulnerable plaques
Cerebral and coronary thrombi and emboli  ?
Role of Elevated Cholesterol in
Development of Atherosclerosis

Lipids insoluble in plasma  lipoproteins

Chylomicron
, VLDL to adipose
to muscle & adipose cells
cells

2 main types of cholesterol carriers:
HDL to liver
vs.
LDL to body cells
Essential Hypertension
the end