Download PP Chapter 19-Blood Vessels

Blood Vessels
Chapter 19
Biology 2122
Blood Vessels
Three types of blood vessels:
arteries, veins and capillaries
Arteries -- arterioles ---
capillary beds -- venules --- veins
Tunica interna
– contains endothelium (simple
squamous) which is in direct contact
with the blood
Tunica media
– mostly circular, smooth muscle and
elastin sheets
Tunica externa
– Collagen fibers
– Contains nerve fibers, lymph vessels,
and in large veins elastin fibers
– Very large vessels contain vasa
vasorum which are small blood vessels
that nourish the external cell wall
Structure - Tunics
Types of Arteries
Elastic arteries
• have thick walls and are located
close to the heart
– Aorta and branches of aorta
• Diameters from 2.5 cm to 1.0 cm
– ‘Conducting arteries’
• Elastin
– Arteriosclerosis
Muscular arteries
– ‘distributing arteries’ which move
blood into organs
• Diameter 1.0 – 0.3 cm
– Thickest tunica media
Arteries-Capillaries
Arterioles
– smallest diameters (0.3 cm or less)
– Large - all three tunica’s
– Smaller - lead to capillary beds
Capillaries
– thin walls- only tunica intima
• Exchange
– Endothelial cells
– Pericytes
– Diameter is 8-10 microns
1. Continuous – skin and muscles
– uninterrupted endothelial lining
– joined by tight junctions – incomplete
2. Fenestrated
– ‘fenestrations’
3. Sinusoids – leaky
– found in liver, bone marrow, lymph
tissue and some endocrine organs
– irregular and have fenestrations
– fewer tight junctions
– allows for blood cells and larger
particles to pass
Capillary
Types
Flow from arterioles to venules ‘microcirculation’
Blood will pass through either:
– Metarteriole straight through to the
venule via a thoroughfare channel (shunt)
– True capillaries to outer tissue areas
Capillary Beds
Percapillary sphincters (smooth muscle)
– When opened, blood flows through the true
capillaries; blood exchange at the tissue site
Structure of Veins and Venous System
Venules
– small (8-100 microns in diameter)
– Postcapillary venules
Veins have three tissues but the
tunica media contains very little
smooth muscle and elastin
• Externa
• Vena cava
• 65% of blood supply
• Blood pressure in the veins is lower than in the
arteries
• Contain ‘valves’ to help move blood back to the
heart
Varicose veins
Venous sinuses
Anastomoses
Merging of vascular channels
– Organs or body regions receive blood from more than one artery
Form ‘anastomoses’ which form alternate pathways called collateral channels for
blood to reach a region of the body
– Collateral pathways
Carbon Dioxide
Angiogram
Venous Anastomosis
Kidney Stenosis
Physiology of Circulation
Dynamics of Blood Circulation:
1. Relationship between flow, pressure and
resistance
2. Blood Pressure
3. Regulation of Blood Pressure
4. Imbalances
Blood Flow, Pressure and Resistance – Important
Terminology
Blood Flow
– volume of blood flowing through a vessel, organ or entire
circulation at a given time (equal to CO)
Blood pressure (BP)
– force per unit area exerted on a vessel wall by blood (expressed in
mmHg); refers to ‘systemic BP’ near the aorta and large arteries
near the heart
Resistance
– opposition to blood flow
– Caused by friction in vessels and most is encountered away from
the heart in the peripheral parts of the body
Blood viscosity:
– Viscosity is proportional to resistance
– Greater the viscosity the greater the resistance
Blood vessel length
– the greater the length the greater the resistance (constant)
Blood vessel diameter
– the smaller the diameter the greater the resistance
Relationship
Flow = ΔP/R
Systemic
Blood
Pressure
• The closer to the ‘pump’ the greater the BP
– Aorta > Veins
• Blood flow is ‘immediately’ opposed by
resistance.
• Steepest Drop = Arterioles
– Highest resistance
Arterial Blood Pressure
Determined by the elastic properties of BV in this circuit
Blood Flow
– from left side of heart to the aorta, this is the peak of pressure called ‘systolic
pressure’ (120 mmHg)
Closing of the aortic semilunar valve
•
•
this prevents blood from reentering the heart
the walls of the aorta recoil which helps to maintain adequate pressure on the reducing
blood volume to keep blood flowing forward in small vessels
– diastolic pressure (70-80 mmHg)
Pulse Pressure
– Difference between systolic and diastolic pressures
Mean Arterial Pressure
– MAP = diastolic + pulse pressure/3
– Important: moves blood to and through the tissues!
Capillary and Venous Blood Pressures
BP drops in the capillaries to 40-20 mmHg
– Desirable because they are thin and fragile and very
permeable so low pressures are adequate for
forcing fluids out
Venous pressure is constant (around 20 mmHg)
Blood flow is increased due to large lumens, and
valves
Even with the two factors above, this is not
enough to cause proper flow
– Respiratory pump (pressure changes in ventral
body cavity) in which breathing squeezes the BV’s
and causes blood flow
– Muscular pump and the contraction of muscles
Short-term control of Blood Pressure
Neural Controls - Counteract immediate flucuations in BP
–
–
–
–
Maintain MAP
Alters distribution of blood to tissues
operate via reflex arcs (baroreceptors and chemoreceptors)
Changes in BP diameter – vasomotor centers (medulla)
• Cardiac center (cardiovascular center) controls CO and BV diameter
– Vasomotor tone
1. Baroreceptors
– carotid sinuses-internal carotid arteries; aortic arch; walls of large
arteries of neck and thorax
– Arterial BP rises------- stretched (impulses to vasomotor center)
• Promotes reduction in BP
2. Chemoreceptors
– Aortic arch; large arteries of neck
– CO2 rise --- pH falls ----- cardioacceleratory center -- CO
increased
Neural Controls
Chemoreceptors
Controls of BP
1. Adrenal medulla
– releases NE and E which enhance the Sympathetic response via
vasoconstriction of BVs
2. Antidiuretic hormone or ADH
– is produced by the hypothalamus and stimulates the kidney to conserve
water. When BP falls, more ADH is released and causes strong
vasoconstriction action
3. Angiotensin II
– renin an enzyme released by the kidneys which causes the release of
Angiotensin II which causes vasoconstriction increasing BP.
Long Term – Renal Control
– Control via altering blood volume
– Direct renal mechanism
– Indirect renal mechanism
• Renin-angiotension mechanism
Role of the Kidneys
Hypertension
•
Transient – normal increases during illness, physical exertion
•
Persistant – caused by obesity, genetics
– Obese people have longer BVs compared to thinner
•
Can be ‘asymptomatic’ for years and can lead to heart failure, vascular disease, renal
failure, stroke
– Heart is forced to pump against greater resistance which will enlarge the myocardium which
will eventually weaken the heart (becomes flabby and ineffective
– Causes small tears in the endothelium and accelerates atherosclerosis
•
Primary hypertension (90% of people) caused by the factors on page 732; Secondary
hypertension (10%) caused by identified causes like renal failure, excessive renin,
athrosclerosis
–
–
–
•
Animation
Stroke
Stroke II
Hypotension or low blood pressure
– In elderly people when standing or sitting due to slow response of sympathertic nervous
system
– Chronic situations may be caused by poor diets, anemia causing low blood volume
Difference in blood flow at rest compared to exercise
Blood Flow- Tissue Perfusion
• Flow of blood to tissues is an exact amount to that
particular tissue (gas exchange, body tissues, digestion)
dependent on the function
• At rest, brain (13%); heart (4%); kidneys (20%);
abdominal organs (24%); skeletal muscles (20%)
• During exercise more is shunted to skeletal muscles and
shunted away from digestive organs
Capillary Exchange
Diffusion of Molecules Across Capillary Membranes
– Lipid-soluble (gases) through lipid bilayer of plasma membranes
– Small water-soluble (sugars, amino acids)
• Intercellular capillary clefts
• Fenestrations
– Larger molecules (proteins)
• Pinocytotic vesicles
Fluids move via Bulk Flow
– Hydrostatic pressure
– Colloid osmotic pressure
– Hydrostatic – Osmotic pressure interactions
Capillary Exchange
1. Nutrient
Exchange Animation
2. Fluid
Exchange
Capillary Exchange of Gases and Nutrients
Circulatory Shock