Transcript Human Physiology

Aims
• Regulation of vascular tone.
• Capillaries
• Readings; Sherwood, Chapter 10
Vascular Tone
• The state of arteriole resistance that is established
by the arteriolar smooth muscle.
– Normally under a slightly constricted state
• Smooth muscle cells undergo self-induced
contractile activity due to ___________________
potentials.
Sherwood’s Human Physiology 10-10
Vasoconstriction
• Increased contraction of circular smooth muscle cells in
arteriolar wall.
• Results in:
– Increased resistance.
– __________________________ flow.
• Due to:
–
–
–
–
–
–
Increased myogenic activity.
Increased oxygen.
Decreased carbon dioxide.
Increased sympathetic stimulation.
Vasopressin, Angiotensin II
Cold
Sherwood’s Human Physiology 10-10
Vasodilation
• Decreased contraction of circular smooth muscle cells in
arteriolar wall.
• Results in:
– Decreased resistance.
– _________________ flow.
• Due to:
–
–
–
–
–
–
Decreased myogenic activity.
Decreased oxygen.
Increased carbon dioxide.
Decreased sympathetic stimulation.
Histamine release
Heat
Sherwood’s Human Physiology 10-10
Regulation of Vascular Tone
• Intrinsic (local) Controls
– Important in distribution of cardiac output
• Chemical influences
• Physical influences
• Extrinsic Controls
– Important in blood pressure regulation
• Neural influences
• Hormonal Influences
Regulation of Vascular Tone
• Intrinsic (local) Controls
• Chemical Influences
•
•
•
•
•
•
•
Oxygen
Carbon Dioxide
Blood pH
Blood Osmolarity
Adenosine
Prostaglandins
Histamine
Regulation of Vascular Tone
• Intrinsic (local) Controls
• Physical Influences
– Heat or Cold application
– Myogenic response to stretch
Regulation of Vascular Tone
• Extrinsic Controls
• _____________________ Nervous System
– Mainly vasoconstrictor nerve fibers
(norepinephrine).
• Most potent in kidneys, gut, spleen, and skin.
• Less potent in skeletal muscle and brain.
– Very few vasodilator fibers (epinephrine).
• Unlikely to play an important role in normal
circulation.
• Fainting due to emotional distress.
Regulation of Vascular Tone
• Extrinsic Controls
• Hormonal System
– Norepinephrine and epinephrine from the
adrenal medulla
• Support sympathetic nervous stimulation.
– Vasopressin and Angiotensin II
• Potent vasoconstrictors
• Play important role in maintaining blood pressure
during hemorrhage.
Regulation of Vascular Tone
• Extrinsic Controls
• Adrenergic Receptors
– 1 (vasoconstriction)
– 2 (vasodilation)
Sherwood’s Human Physiology Table 10-4
Response to Exercise and Fright
• Stimulate sympathetic system and inhibit
parasympathetic system.
– Almost all arterioles are constricted. (increase
peripheral resistance)
• Increases arterial pressure.
– Veins are constricted.
• Displaces blood from large peripheral blood vessels
toward the heart.
• Result in heart beating stronger. (increasing stroke
volume)
– Autonomic nervous system stimulates heart rate.
Response to Exercise and Fright
• Exercise causes local O2
depletion.
– Resulting in local
vasodilation
• Elevated BP and local
vasodilation = great
supply for skeletal
muscle.
Sherwood’s Human Physiology 10-12
Summary of Regulation
Sherwood’s Human Physiology 10-14
Veins are Volume Reservoirs
• Veins serve as ________
resistance passageways
to return blood to the
heart.
• Additionally, they serve
as a blood reservoir.
– Thinner walls and less
smooth muscle than
arteries.
Sherwood’s Human Physiology 10-28 (10-27 6th Edition)
Veins Have Valves
• Valves prevent
backward blood
movement.
• When valves no longer
function properly you
get varicose veins.
– Allows for the pooling
of blood and swelling of
the vein.
Sherwood’s Human Physiology 10-33 (10-32 6th Edition)
Venous Pump
• Gravity forces blood to pool in the lower
extremities.
– Thus pressure in the lower veins is greater
than that of the higher veins.
• The venous pump or muscle pump pushes
blood up from the lower extremities.
– Utilizing muscle contraction and valves to
ratchet blood upward.
• Thus, when walking the blood pressure in
leg is 25mm instead of 90mm
Guyton’s Textbook of Medical Physiology 15-10
Capillaries
Capillaries make up most of
the total cross-sectional area
of blood vessels (600 m2).
Every cell is within 0.01 cm
of a capillary.
Contain only about 5% of
total blood volume at any
given time.
Very slow velocity of blood
flow (distance/time).
Sherwood’s Human Physiology 10-16
Blood Flow through Capillaries
Same volume flows from A1-B1 as flows from
A2-B2 in 1 minute (= flow rate), but the distance
from A1-B1 > A2-B2 (velocity of flow).
Sherwood’s Human Physiology 10-17
Capillary lumen size
• Capillaries have lumens about 7 mm but can be
as small as 3.5mm.
• Barely big enough for erythrocytes (about 8
mm) to squeeze through.
Sherwood’s Human Physiology 10-15
Capillary Regulation of Blood Flow
• Capillaries branch off of metarterioles.
• At this location the capillary is circled by a smooth
muscle cell forming the precapillary sphincter.
• Regulates whether the capillary is open or closed.
• O2 Dependent.
Sherwood’s Human Physiology 10-19
Capillaries are the site of fluid and
nutrient exchange
• Capillaries prime function is _____________
exchange
•
•
•
•
Intercellular clefts.
Plasmalemmal vesicles.
Vesicular channels
Fenestrations
Sherwood’s Human Physiology 10-18
Diffusion Through Membranes
• Lipid soluble substances pass right through the endothelial cell.
– O2 & CO2
Sherwood’s Human Physiology 10-18
Intercellular Clefts
• Intercellular cleft
– Water filled pore.
– 6-7 nm wide
• Small water-soluble
substances pass
through these pores.
– Ions Na+ and K+
– Glucose
– Amino acids
Sherwood’s Human Physiology 10-18
Plasmalemmal Vesicles
• Lipid insoluble
proteins are moved
across by vesicular
transport.
– Non-plasma
proteins.
– Plasma proteins
are usually
unable to leave
the circulation.
Sherwood’s Human Physiology 10-18
Vesicular Channels
• Vesicles coalesce
to form channels
that go
completely
through the
endothelial cell.
Adopted from Ganong’s Review of Medical Physiology
Similar to Guyton’s Textbook of Medical Physiology 16-2
Specialized Capillaries
• Fenestrations
– Numerous small oval
windows which pass
through the
endothelial cell.
– Found in the kidney.
– Responsible for
filtration in the
glomeruli.
Adopted from Ganong’s Review of Medical Physiology
Similar to Guyton’s Textbook of Medical Physiology 16-2
Specialized Capillaries
• In the liver sinusoids the intercellular clefts
are very large.
– Resulting in almost all dissolved substances
including plasma proteins can pass from the
blood to the liver tissue.
• In the _________________ the intercellular
clefts do not exist due to tight junctions
between endothelial cells.
– Resulting in only small molecules such as
water, CO2 and O2 can pass from the blood to
this tissue.
Interstitial Fluid
• Makes up 80% of the ECF while the plasma
makes up the remaining 20%.
• Gel of _________________ and Proteoglycans.
• Collagen fiber bundles.
• Free fluid vesicles.
• Free fluid.
Sherwood’s Human Physiology 10-21 5th Edition only & Guyton’s Textbook of Medical Physiology 16-4
Exchange of Solutes
• Solutes will diffuse __________________ their
concentration gradients during capillary-cell exchange.
• Also leave capillaries via bulk flow which is most
important in maintaining plasma volume.
Sherwood’s Human Physiology 10-22 (10-21 6th Edition)
Forces Influencing Bulk Flow
• Capillary hydrostatic pressure
– Forces fluid out of the capillaries.
• Interstitial fluid hydrostatic pressure
– Usually forces fluid into the capillaries.
• Plasma colloid osmotic pressure
– Causes osmosis driving fluid into the capillary.
• Interstitial fluid colloid osmotic pressure
– Causes osmosis driving fluid out of the capillaries.
Guyton’s Textbook of Medical Physiology 16-5
Exchange of Solutes
Sherwood’s Human Physiology 10-24 (10-23 6th Edition)
Next Time
• Lymphatic system.
• Blood composition
– Erythrocyte production
• Reading; Sherwood, Chapter 10
Objectives
1. Describe the function and properties of blood
vessels and their regulation.
1. Distensibility and Compliance
2. Pulsatility
3. Vascular Tone (vasoconstriction &
vasodilation)
2. Describe the structure and function of veins.