health help ?????

Question

______vessels provide a low pressure blood reservior through which blood returns to the heart.
A.exchange
B.capacitance
C.resistance
D.distribution

Answer 1

4. Capacitance vessels.
After capillary beds blood is collected in venules which are tributaries of veins. These vessels provide a low pressure blood reservoir through which blood returns to the heart. Veins have the same basic histological structure as arteries, but tend to be greater in cross sectional area at any given level, because of slower flow rate. For the same reason arteries are often accompanied by paired veins, vena combatants.

Answer 2

The arteries and arterioles take blood from the heart to the capillaries . The materials in the blood come out t the cells at this level, and the blood goes into venules and then to veins back to the heart. There is low pressure in the vein system.
Exchange occurs at the capillaries.
Distribution is by the arteries.
There is some resistanc to back flow in veins due to valves.
I do not know why capacitance is an answer.
So if I had to pick an answer it would be resistance, but it does not make alot of sense.

Answer 3

· The blood vessels form the “plumbing system” by which oxygen and nutrients are delivered to your cells, and wastes (CO2, etc) are removed.

PART 1: BLOOD VESSEL STRUCTURE AND FUNCTION
· Arteries à arterioles à capillaries à venules à veins
· The capillaries provide the site of gas, nutrient and waste exchange with the cells
· Altogether, we have about 60,000 miles of blood vessel plumbing in our bodies!

Structure of Blood Vessel Walls
· Arteries and veins have three distinct layers (Tunics; Figure 19.1) surrounding the lumen (the location of the blood)
· Tunica interna
o Slick, low friction, simple squamous endothelium that lines the lumen
o Subendothelial loose connective tissue in vessels >1mm diameter.
· Tunica media
o Circularly arranged smooth muscle cells and sheets of elastin
o Thickest layer in arteries – correlated with their role in maintaining blood pressure and circulation
o Regulated by sympathetic vasomotor nerve fibers, and chemical stimulation
§ What’s the definitions and differences between vasoconstriction and vasodilation?


· Tunica externa
o Loosely woven collagen fibers that protect and reinforce the vessel, and anchor it to surrounding tissue. What role do these fibers play during blood clotting?

o Infiltrated with nerve fibers, lymphatic vessels and in larger vessels, elastin fibers.

Arterial system (Figure 19.2)
Elastic (Conducting) Arteries
· Thick-walled, near heart (e.g. aorta)
· Low resistance to flow – hence “conducting”
· Highly elastic – absorb pressure changes, expand/recoil passively as heart beats

Muscular (Distributing) Arteries
· Thickest tunica media of any vessels
· Most active in vasoconstriction

Arterioles
· Primary role – regulation of blood flow to capillary beds
· Controlled by neural stimuli and local chemical influences

Capillaries
· Microscopic, walls consist of only tunica interna (one cell thick)
· Lumen just large enough for RBCs to pass through in single file
· Pericytes on the outer surface stabilize their walls
· Types of capillaries (Figure 19.3) – vary in degree of permeability of the endothelium
o Continuous – most common; abundant in skin and muscles
§ Relatively tight cell-cell junctions (called intercellular clefts)
§ Limited movement of fluids and solutes
o Fenestrated – found wherever active capillary absorption or filtration occurs
§ Cells have may oval pores (fenestrations)
§ Endocrine organs, kidneys, small intestine. What processes happen in each of these locations that makes fenestrated capillaries good to have?


o Sinusoids – highly modified, leaky capillaries
§ Found only in liver, bone marrow, lymphoid tissues and some endocrine organs
§ Large, irregular lumens; fenestrated cells
§ Intercellular clefts large enough for WBCs, and other cells to pass through
· Capillary beds – interwoven networks consisting of two vessels (Figure 19.4)
o Vascular shunt – a “detour” for the blood when precapillary sphincters are closed
o True capillaries – location of gas/nutrient exchange
§ Precapillary sphincter – ring of smooth muscle fibers that act as a valveto regulate flow to an individual capillary
o Nervous stimulation and local chemical levels affect degree of blood flow through the capillary bed at any given time

Venous system
Venules
· Smallest veins, formed when capillaries unite
· Relatively porous/”leaky”; WBCs pass through readily

Veins
· Three distinct tunics, but thinner walls and larger lumens than similarly sized arteries
· Larger lumens allow more blood to be held (65% of body’s blood is in veins at any given time) – often referred to as blood reservoirs. Also, larger lumens provide less resistance to blood flow
· Lower blood pressure so thinner walls OK
· Veins of limbs have one-way valves (see Figure 19.1) to keep blood flowing even against gravity
· Varicose veins – veins whose walls, over time, have become stretched and floppy. Direct cause is faulty valves that prevent proper blood return to the heart. So, blood collects within the veins. May be caused initially due to genetic factors, or prolonged physical conditions that restrict return blood flow.

Vascular Anastomoses
· Locations where blood vessels interconnect.
· Arterial Anastomoses: Alternate pathways (collateral channels) by which blood flow may reach organs – important if one path becomes blocked due to normal movement (e.g. around a joint) or due to a clot
PART 2: PHYSIOLOGY OF CIRCULATION

Blood Flow, Blood Pressure and Resistance
Blood Flow – volume thru vessel, organ, etc in a given period (ml/min)
· Under resting conditions, relatively constant considering whole body circulation
· In individual organs, flow varies widely, depending on their immediate needs

Blood Pressure (BP) – force per unit area exerted on a vessel wall by the blood within it. Usually expressed in units of: mm Hg
· BP is the driving force that keeps blood flowing through the CV system

Resistance – a measure of the amt of friction encountered by blood as it flows thru the vessels. Three important sources:
· Blood viscosity – how “thick” is the blood?
· Vessel length – longer = higher resistance.
· Vessel diameter – smaller diameter = increased resistance.
· Some thoughts:
o Which vessels have the least resistance? The most?

o How do vasoconstriction and vasodilation alter resistance?

o How would gaining weight change resistance in our bodies?

Systemic Blood Pressure
· In a closed system, the closer you are to the pump, the higher the pressure. So, where would our BP be highest? Why? (see Figure 19.5)

Arterial BP
· Related to: (1) ability of vessels near heart (i.e. aorta) to stretch (2) how much blood is forced into them at a given time
· Systolic pressure – the peak pressure (~120 mm Hg)
· Diastolic pressure – the elastic walls of the aorta recoil, forcing continued blood flow to tissues even as left ventricle is refilling (~70-80 mm Hg)
o These numbers give you the standard BP reading: “120 over 80”, etc.
· When you feel your “pulse” what are you actually feeling?

Capillary BP
· Entering BP ~40 mm Hg; exiting to venules ~20 mm Hg
· Low pressure desirable because:
o High BP would rupture capillaries
o Low BP still sufficient for transfer of fluids and solutes across capillary walls – this flow helps to continually flush and clean the intercellular fluids

Venous BP
· Steady and changes little as the heart beats (~20 mm Hg)
· This pressure is generally too low to bring all your blood back to the heart, so there are two other mechanisms that are important:
o Respiratory “pump” – pressure changes in the thoracic cavity as we breath
o Muscular “pump” – as skeletal muscles contract during movement they squeeze blood through the deep veins. The one-way valves in the veins force blood to flow to the heart (Figure 19.6). What would this mean for a person who stands relatively still for long periods of time at work? (e.g. a hairdresser, assembly line worker)

Maintaining BP
· Homeostatic mechanisms constantly regulate CO, peripheral resistance, and blood volume in order to maintain BP

Short-term mechanisms: Neural controls
· Mediated by nervous system and bloodborne chemicals
· Counteract BP changes by altering peripheral resistance
· Respond to immediate blood flow demands:
o Redirect blood to skeletal muscles during exercise
o Priority flow to heart and brain during stress/injury
· Vasomotor center of medulla oversees changes in vessel diameter – arterioles are almost always in a state of slight vasoconstriction, the vasomotor tone. This can be thought of as similar to muscle tone in skeletal muscles.
· How does the vasomotor center monitor BP?
o Baroreceptors – pressure sensitive receptors that monitor arteriole BP and stretch
§ Particularly good for acute changes in BP; e.g. standing up quickly after having been lying down
o Chemoreceptors – monitor blood [O2], [CO2], and pH
o Higher brain centers – e.g. hypothalamus signals the medulla during fight-or-flight response

Short-term mechanisms: chemical controls
· Direct actions on vasomotor center, vessel smooth muscles, and the kidney (Table 19.2)
· These various chemicals promote changes in BP via:
o Vasoconstriction or vasodilation
o Changes in HR and contractility
o Changes in salt and water loss at the kidney

Long-term mechanisms: Renal Regulation
· BP is regulated long-term by changes in blood volume rather than by altering resistance in the arterioles/arteries
· Generally speaking: Increase blood volume = increased BP
· Kidneys release renin, which triggers angiotensin II formation (a vasoconstriction promotor), which in turn signals for adrenal cortex to produce aldosterone – both of which promote reabsorption of salt and water reabsorption by the kidneys (see Figure 19.9)

Monitoring Circulatory Efficiency
· Measurement of the body’s vital signs: BP, pulse, respiratory rate and body temp
· Pulse is the pressure wave created by the alternating expansion and recoil of arteries during each cardiac cycle
· BP was described earlier; most often measured by the auscultatory method
Alterations in BP
· Hypotension – lower than average systolic pressure (<100 mmHg); usually not a cause of concern, unless acute (a sign of circulatory shock – see below)
· Hypertension – high BP
o Transient hypertension is normal
o Chronic hypertension can have serious negative long-term effects on function of the heart and may lead to damaged arteries; also: heart failure, strokes, vascular disease, and renal failure
o Often linked to atherosclerosis (which is the precursor to arteriosclerosis)
o Factors believed to be involved: diet, age, race, heredity, stress, smoking

Blood flow through the body tissues: Tissue Perfusion
· Tissue perfusion is essential for:
o Delivery of oxygen and nutrients to cells, removal of wastes from them
o Gas exchange in the lungs
o Absorption of nutrients in the digestive system
o Urine formation in the kidneys

Velocity of blood flow
· Highest in the arteries, lowest in capillaries, intermediate in veins (see Figure 19.13)
· Why is a slow flow desirable in the capillaries?

Autoregulation: local regulation of blood flow
· Autoregulation is the automatic adjustment of blood flow to each tissue in proportion to the tissue’s requirements at any instant
· These controls are intrinsic – i.e. highly localized – and may be metabolic or myogenic
o Metabolic – e.g. declining nutrient or oxygen levels cause immediate vasodilation of the arterioles serving the capillary beds of the tissue in “need”
o Myogenic responses – BP changes stretch or relieve pressure on the vessel smooth muscle; the muscle responds by contracting or dilating to counteract the effects of BP change.

Blood flow in special areas – a few examples
· Skeletal Muscles – blood flow varies with activity and fiber type; At rest, only 25% perfusion; During activity, blood flow is redirected from digestive viscera and skin to the muscles
o Autoregulation is almost completely triggered by declining O2 levels – why would this be so?

· Brain – both metabolic and myogenic controls. Extreme BP changes can cause damage: fainting occurs when mean arterial BP is <60 mmHg, cerebral edema at >160 mmHg
· Skin – in addition to supplying skin cells with nutrients, flow to skin aids in temp regulation and provides a blood reservior

Blood flow through capillaries and capillary dynamics
· Oxygen, CO2, nutrients and wastes move by diffusion.
· Fluid movement – balance between hydrostatic pressure (forcing fluid OUT of capillaries) and colloid osmotic pressure (pulls fluid back into capillaries).
o Think of colloid osmotic pressure as a difference in solute concentrations between the blood and intercellular fluid that causes a net fluid movement into the capillary

Circulatory shock
· Any condition in which vessels are inadequately filled and blood can’t circulate normally – if chronic, this condition leads to cell death and organ damage
· Most common form is hypovolemic shock, which results from large-scale loss of blood

PART 3: CIRCULATORY PATHWAYS: BLOOD VESSELS OF THE BODY
· The details (names, locations) of major blood vessels will be covered in lab. Use the Figures/Tables on pages 744-766 as a reference when learning the vessel names.
· For the exam in lecture, recall the following:
o The heart is a double pump, serving both the pulmonary and systemic circulatory systems – each system has its own set of arteries, capillaries and veins
o Arteries run deep within the body, veins run both deep and superficial. Why is it a good idea for arteries to only be located deep?
D.distribution