Central blood-containing space in the vessel
innermost tunic, contains the endothelium (the simple squamous epithelium that lines the lumen of all vessels)
middle tunic, mostly circularly arranged smooth muscle cells and sheets of elastin
lumen diameter decreases as the smooth muscle contracts- allows more blood flow
lumen diameter increases as the smooth muscle relaxes - decreases blood flow
outermost layer of a blood vessel wall, composed largely of loosley woven collagen fibers that protect and reinforce the vessel, and achor it to surrounding structure
In larger vessels, the tunica externa contains a system of these tiny blood vessels
Thick-walled arteries near the heart (the aorta and its major branches) They are also known as pressure reservoirs aka: conducting arteries
deliver blood to specific body organs (sometimes called distributing arteries)
smallest of the arteries-lumen diameter ranging from 0.3mm down to 10 Um
smallest blood vessels
smooth muscle-like cells that stabilize the capillary wall and help control capillary permeability
abudant in skin and muscles, these are the most common and have intercellular clefts (least permeable capillary)
gaps of unjoined membrane that are large enough to allow limited passage of fluids and small solutes
riddled with oval pores, or fenestrations and increase permeability (fenestra=window)
highly modified, leaky capillaries found only in the liver, bone marrow, spleen, and adrenal medulla.most permeable capillary
remove and destroy any bacteria (can be found in sinusoid capillaries)
interweaving networks that connect arteriole and venule
flow of blood from an arteriole to a venule (through a capillary bed)
What are the two types of vessels that a capillary bed consists of?
1. Vascular Shunt
2 True capillaries
short vessel that directly connects the arteriole and venule at opposite ends of the bed
actual exchange vessels; number 10-100 per capillary bed
an arteriole that divides into capillaries.
vessel structurally intermediate between an ateriole and a capillary (continuous with the thoroughfare channel)
intermediate between a capillary and a venule (connects with the metarteriole)
joins with the thoroughfar channel and then drains the capillary bed
surrounds the root of each true capillary at the metarteriole and acts as a valve to regulate blood flow into the capillary
Capillaries unite to form venules; extremely porous (like capillaries)
venules join to form veins; walls are always thinner and their lumens larger than those of corresponding arteries, however, veins are usually collapsed and their lumens appear slitlike
capacitance vessels & blood reservoirs
AKA VEINS; with their large lumens,&thin walls, veins can accomodate a fairly large blood volume.
How much blood supply can veins hold?
up to 65% of the body's blood supply at any time (although they are usually only partially filled)
formed from fold sof the tunica intima, prevent blood from flowing backward
veins that are toruous and dilated because of incompetent (leaky) valves
highly specialized, flattened veins with etremely thin walls composed only of endothelium
blood vessels that form special interconnections
most organs receive blood from more than one arterial branch, and arteries supplying the same territory often merge, forming arterial anastomoses
What do anastomoses provide?
altenbate pathways, called collateral channels (helps blood to reach a given body region)
meterteriole-thoroughfare channel shunts of capillary beds that connect arterioles and venules
veins that interconnect much more freely than arteries, and are very common
the volume of blood flowing through a vessel, or an organ
Blood pressure (BP)
the force per unit area exerted on a vessel wall by the contained blood (exptressed in mm Hg)
opposition to flow and is a measure o the amt of friction blood encounters as it passes through vessels
most friction is encountered in the peripheral (systemic) circulation, well away from the heart, this is the term we use
related to the thickness or "stickiness" of the blood
Total Blood Vessel Length
relationship betwn total blood vessel length and resistance is straightforward: the longer the vessel, the greater the resistance
Blood Vessel Diameter:
Blood vessel diameter changes frequently and significantly alters peripheral resistance (think of a river: water runs rapidy in the center, but slower on the sides)
What is the relationship formula for Flow, Pressure, and Resistance?
∆P= difference in blood pressure betwn two points in circulation
The pressure peak generated by ventricular contraction
How much does the systolic pressure average in adults?
averages 120 mm Hg
aortic valves close, preventing blood from flowing back into the heart. during this time aortic pressure drops to its lowest level
What is the average diastolic pressure in healthy adults?
70 to 80 mm Hg
difference between the systolic and diastolic pressures
Mean Arterial Pressure (MAP)
the pressure that propels the blood to the tissues.
MAP=diastolic pressure+ pulse pressure/3
What are the three functional adaptations that are critically important to venous return?
1. The muscular Pump
2. The respiratory pump
3. Sympathetic Venoconstriction
What vessel has the greatest drop in Blood pressure?
consists of skeletal muscle activity: as skeletal muscles surrounding the deep veins contract and relax, they "mil" blood toward the heart
moves blood up toward the heart as pressure changes in the ventral body cavity during breathing
reduces the volume of blood in the veins-the capacitance vessels
consists of the cardiac centers and the vasomotor center that controls the diameter of blood vessels
controls diameter of blood vessels
vasomotor center transmits impulses at the fairly steady rate along sympathetic efferents
arterioles are almost always in a state of moderate constriction
when arterial blood pressure rises, it activates baroreceptors. These inhibit (or bar) to the vasomotor and cardioacceleratory centers
What are the threemechanisms that bring about a decrease in blood pressure?
1. Arteriolar Vasodilation
3. Decreased Cardiac Output
decreased output from the vasomotor centers allows arterioles to dialte
decreased output from the vasomotor center also allows veins to dilate, which shifts blood to venous reservoirs. This decreases venous return and CO (cardiac output)
Decreased Cardiac Output
impulses to the cardiac centers inhibit sympathetic activity and stimulate parasympathetic activity, reducing heart rate and contractile force.
Carotid Sinus Reflex
protects the blood supply to your brain (these are from baroreceptors)
helps maintain adequate blood pressure in your systemic circuit as a whole
Adrenal medulla hormones
epinephrine, and norepinephrine goes to the blood; causing an increase in cardiac output and promoting generalized vasoconstriction
When blood pressure or blood volume are low the kidneys release renin. Renin generates Angiotensin II which stimulates intense vasoconstriction, promoting a rise in systemic blood pressure. It stimulates release of aldosterone and ADH
Atrial Natriuretic Peptide (ANP)
this leads to a reduction in blood volume and blood pressure (vasodilation)
Antidiuretic hormone (ADH)
stimulates kidneys to conserve water.
Direct Renal Mechanism
alters blood volume independently of hormones
through this the kidneys can also regulate blood pressure indirectly.Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II.
a hormone that enhances renal reabsorption of sodium
this is how clinicians assess the efficiency of a person's circulation by measuring pule and blood pressure
alternating expansion and recoil of arteries during each cardiac cycle allow us to feel a pressure wave
the pulse points on the body that are compressed to stop blood flow into distal tissues during hemorrhage
measure systemic arterial blood pressure indirectly in the brachial artery of the arm
What is the instrument used to measure blood pressure by the auscultatory method?
chronically elevated blood pressure
low blood pressure (below 90/60 mm Hg)
Primary and Secondary Hypertension
90% are Primary and only 10% are secondary. Primary hypertension is when there has been no underlying cause identified. Secondary Hypertension is when there is an identifiable condition.
What could cause chronic hypotension
addison's disease, hypothyroidism, sever malnutirition
Blood flow through body tissues
What is tissue perfusion involved in?
1. delivering oxygen and nutrients to tissue cells & removing wastes
2. exchanging gases in the lungs
3. absorbing nutrients from digestive tract
4. forming urin in kidneys
this is how each organ or tissue manage to get the blood flow it needs. The automatic adjustment of blood flow to each tissue in proportion to the tissue's requirements at any instant.
Nitric Oxide (NO)
powerful vasodilator which acts via a cyclic GMP second-messenger system.
the endothelium also releases potent vasoconstrictors, called endothelins, which are among the most potent vasoconstrictors known.
fluctuations in systemic blood pressure would cause problems for individual organs were it not for the myogenic responses of vascular smooth muscle.
refers to the dramatically increased blood flow into a tissue that occurs after the blood supply to the area has been temporarily blocked
Active or Exercise Hyperemia
when muscles become active, blood flow increases (hyperemia) in direct proportion to their greater metabolic activity
the on/off opening and closing precapillary sphincters in response to l local auto-regulatory controls
Capillary Hydrostatic Pressure (HPc)
tends to force fluids through capillary walls (a process called filteration) leaving behind cells and most proteins.
Interstitial fluid hydrostatic pressure (HPif)
blood pressure-which forces fluid out of the capillaries is opposed by the HPif acting outside the capillaries and pushing fluid in.
Capillary colloid osmotic pressure (OPc)
abundant plasma proteins in capillary blood (primarily albumin molecules) develop this.
New filteration pressure (NFP)
this considers all the forces acting at the capillary bed.
any condition in which blood vessels are inadequately filled and blood cannot circulate normally.
the most common form of circulatory shock:which result from large-scale blood or fluid loss.
blood volume is normal, but circulation is poor as a result of extreme vasodilation.
pump failure, occurs when the heart is so inefficient that it cannot sustain adequate circulation. (could be caused by heart attacks)
The endothelial lining of blood vessels is formed by mesodermal cells which collect in little masses
What are the conducting arteries?
Elastic Arteries are sometimes called this.
What are the distributing arteries?
Direct renal mechanism
alters blood volume independently of hormones
angiotesin II acts in 4 ways to stabilize arterial blood pressure and extracellular fluid volume. What are those ways?
1. stimulates adrenal cortex to secrete aldosterone; also stimulates sodium reabsorption by kidneys
2.prods posterior pituitary to release ADH; promotes more water reabsorption by kidneys
3. triggers sensation of thirst, by activating hypothalamic thirst center
4. potent vasoconstrictor, increasing blood pressure by increasing PR
What is the major player in controlling local vasodilation?
NO (Nitric Oxide), often this overrides sympathetic vasoconstriction when tissues need more blood flow
MAP is the same everywhere in the body. true/false?
Are capillary density and blood flow greater in red fibers, or white fibers?
red (slow oxidative) fibers
Blood will flow into occipital sinus into the ____ and turn into the brachialcephalic vein
blood in the circle of willis will flow into the _______ and then into the transverse sinus
Blood in the cephalic vein flows into the ________ and then into the basilic vein
median cubital vein
blood in the Great sa``phenous vein flows into the _____ and then into the iliac vein