A&P 2: EXAM 2: Blood vessels

indirect mechanism: RAAS *SLIDE 65*

(The renin-angiotensin-aldosterone mechanism) - Decreased arterial blood pressure causes release of renin from kidneys - Renin enters blood and catalyzes conversion of angiotensinogen from liver to angiotensin I - Angiotensin-converting enzyme (especially from lungs) converts angiotensin I ---> angiotensin II Angiotensin II acts in 4 ways to stabilize arterial BP and ECF: 1.Stimulates aldosterone secretion 2. Causes ADH release from posterior pituitary 3. Triggers hypothalamic thirst center to drink more water 4. Acts as a potent vasoconstrictor - increases BP by increasing resistance.

compare and contrast veins, arteries and capillaries both structurally and fuctionally

*arteries*: run deep. muscular carry blood from the heart towards tissues of organs. elastic are low resistance, blood flows continuously; contains all 3 layers (tunica intima - endothelium, thick tunica media, thinner tunica externa,). *arterioles*: 0-3 mm-um, resistance vessels *veins*: run deep & superficial. return vessels that take deoxygenated blood back to the heart, has all three layers that are thin; blood reservoirs & can accomodate large blood volumes; valves to prevent backflow. *venous valves*: prevent the backflow and found in limbs where gravity opposesw upward flow (absent in thoracic and abdominal cavities). *venous sinuses* : flattened veins, composed of endothelium *venules*: united capilaries that allow for fluid and WBC leak *capillaries*: made of only tunica intima (8-10 um), form capillary networks that increase surface area for diffusion EXCEPT FOR: tendons and ligaments, cartilage and epithelium (nearby connective tissue blood vessels); avascular cornea and lens (acqueous humor). beds function to allow passage of fluids, solutes, and gases.

define blood pressure and differentiate between systolic and diastolic pressure

*blood pressure*: force exerted on a vessel wall, typically refers to systemic arteriol BP at large arteries near the heart. *systolic*: 120 mmHg. pressure exerts against artery wall during ventricular systole/contraction. *diastolic*: 80 mmHg. pressure exerted against artery wall during ventricular diastole/relaxation. top # systolic, bottom # diastolic

Renal control (long term): direct renal mechanism *SLIDE 65*

- alters blood volume independantly of hormones - increased blood volume or BP causes elimination of more urine thus reducing BP - decreased blood volume or BP causes kidneys to conserve water and BP rises

Explain how vascular resistance is regulated by the autonomic nervous system

- baroreceptors sense pressure and send signals to the medulla oblongata - the integrating center that interprets the signals. - effectors (act in response to stimulus): heart, arterioles, veins. - sympathetic nervous system promotes vasoconstriction of arterioles in most areas, increases heart function and venomotor tone (stiffness) - parasympathetic promotes vasodilation in some areas but is not important in influencing TPR; reduces heart rate

hydrostatic pressure

- force exerted by a fluid pressing against a wall ; capillary blood pressure. - HP in capillaries is HPc, which is higher at arterial end than venous end. it tends to force fluids through capillary walls which leaves behind cells and most proteins. - BP is opposed by interstitial fluid hydrostatic pressure (HPif). - there is HP of interstitial fluid but is slight because lymphatic vessels take that fluid away

colloid osmotic pressure

- oncotic pressure in the capillary: OPc. 26 mmHg , doesn't vary significantly from one end of capillaries to another - is a force opposing HPc because its created out of everything that can't move out via HPc, such as large nondiffusable molecules like plasma proteins - is basically sucking fluid back into vessels via osmosis

Briefly describe the structure and function of each of the following circulatory routes: systemic, pulmonary, coronary, cerebral, hepatic portal, and fetal. Include and unique features where appropriate*

1. systemic: provides functional blood supply to all body tissues - delivers o2, nutrients, other substances while carrying away co2 and other wastes. freshly oxygenated blood returning from pulmonary circuit is pumped out of left ventricle into aorta - from here blood can take various routes. 2. pulmonary: pathway is short. low pressure is needed to propel blood through vesssels. the autoregulatory mechanism is OPPOSITE: low pulmonary o2 levels cause vasoconstriction & high levels promote dilation. functions only to bring blood into close contact with the alveoli so that gases can be exchanged - doesnt directly serve the metabolic needs of body tissues. 3. coronary: aortic pressure/pumping activity of ventricles infleunce movement of blood through smaller vessels of coronary circulation. exercise: coronary vessels dilate and blood flow increases 3/4x. 4. *above question* 5: hepatic portal: veins that drain the digestive viscera empty into hepatic portal vein and transports venous blood into liver before it moves into the systemic circulation via the hepatic veins. 2 capillary beds connected together is a portal system. the portal system serves to carry blood from the digestive organs to the liver (the blood contains nutrients, potential toxins, microorganisms that liver filters prior to returning it to systemic circulation) 6. fetal: fetal shunts bypass nonfunctional lungs (foramen ovale & ductus arteriosus). ductus venosus bypass liver. umbilical veins/arteries circulate blood between fetal circulation & placenta where gas & nutrient exchanges occur with mother's blood

discuss blood pressure as it relates to CO and resistance

CO (blood flow) is directly related to pressure gradient. if pressure gradient increases, CO increases.... as well as SV. CO is inversely proportional to resistance. increased viscosity = increased resistance. increased length = decreased resistance. decreased radius= increased resistance. if resistance increases, CO decreases.

misc. math equations

MAP = CO X Systemic vascular resistance CO = HR x SV MAP = HR X SV X SVR SVR = MAP/CO (not determined by either of these variables)

Explain the importance of mean arterial pressure to the overall functioning of the cardiovascular system

MAP is maintained by altering blood vessel diameter which alters resistance (ex: if blood volume drops, all vessels constrict except those to heart and brain). decreased diameter = increased resistance. can also alter blood distribution to organs in response to specific demands.

Define Peff /NFP*

NFP (net filtration pressure): the total of all the forces acting on the capillary bed; drives fluid out of the capillary. must consider what is happening at the arterial side (out of circulation) and at the venous side (into circulation). -indicates final direction of fluid movement - NFP = (pressures that promote filtration) - (pressures that promote reabsorption) outward pressures (HPC AND OPif) minus inward pressures (HPif and OPc). (HPc+OPif) - (HPif + OPc) - more fluid enters the tissue than returns, resulting in a net loss of fluid from the circulation of ~1.5 mL/min. lymphatic vessels pick up this fluid/any leaked proteins and return it back to vascular system -filtration: arteriolar end. reabsorption: venous end. *diagram* Peff: blood flow through body tissues; filtration pressure that determines which way fluid will flow.

Explain how blood flow through capillaries in skeletal muscle and the brain is regulated

Skeletal muscle: in red (slow oxidative) fibers capillary density and blood flow are greater. resting skeletal muscles receive 1L blood/minute and only 25 % of capillaries are open until exercise. during exercise norepi causes vasocinstriction of vessels of reservoirs and diverst blood away from them and to the skeletal muscles. local controls override sympathetic vasoconstriction & blood flow to skeletal muscles can increase . brain: cerebral blood flow is regulated precisely (blood has to go to the nuerons that are most active at any given time). vasodilation is in response to declining pH and rising CO2 levels. as MAP declines capillaries in the brain will always dilate to ensure adequate brain perfusion. when rising cerebral vessels constrict and protect smaller vessels. MAP below 60 mmHg = fainting. above 160 mmHg = edema (increase in brain capillary permeability)

Define total peripheral resistance and indicate how resistance is affected by the length of vessels, by the viscosity of the blood and by the radius of the vessels

TPR: opposition to flow; the amount of friction blood encounters with vessel walls. for the most part, resistance occurs in smaller arteries, arterioles, and capillaries; small changes in the radius of these vessels is what changes resistance. tpr = systematic vascular resistance = resistance = resistance to blood flow offered by all of the systemic vasculature (excluding pulmonary). blood viscosity increase = tpr increase length = constant diameter/radius =The smaller the radius, the more contact between blood and vessel walls, thus greater the friction and resistance. decrease in radius = increase resistance

Explain methods by which blood pressure is controlled and regulated in the body either via regulation of CO or blood vessel radius

Three factors regulate BP (or MAP): cardiac output (CO), peripheral resistance (R), blood volume. only in pathophysiological or diseased states does one variable change; the other variables cant compensate for the change resulting in a hypertension or hypotension CO = SV X HR X R --> if one fails the other has to make up for what is lost resistance is altered inversely by diameter. for example... if diameter increases, resistance decreases, and BP decreases

Describe the roles of the vasomotor center, baroreceptors, and chemoreceptors in blood pressure regulation

VASOMOTOR CENTER: (cardiovascular center of brain) cardioinhibitory & cardioacceleratory centers. sends steady impulses via sympathetic efferents called vasomotor fibers to blood vessels which cause continuous moderate constriction called vasomotor tone. BARORECEPTORS: 1. MAP is high - located in carotid sinuses, aortic arch, and walls of large arteries of neck and thorax - increased BP stimulates baroreceptors to increase input to vasomotor center - inhibits vasomotor and cardioacceleratory centers by shutting off things that constrict vessels and increase HR - stimulates cardioinhibitory center 2. trigger MAP decrease by vessel dilation (vasodilation: decreased output from vasomotor center causes dilation; arteriolar vasodilation: reduces PR, MAP falls; venodilation: shifts blood to venous resorvoirs which decreases venous return and CO) 3. also triggers MAP decrease by decreasing CO - Impulses to cardiac centers inhibit sympathetic activity and stimulate parasympathetic activity which reduces HR and contractility; CO decrease decreases MAP 4. if MAP is low... - reflex vasoconstriction is initiated that increases CO and BP (ex: a person stands and BP falls/triggers *carotid sinus reflex* which ensure enough blood to brain, and *aortic reflex* which maintains BP in systemic circuit - Baroreceptors are ineffective if altered BP is sustained CHEMORECEPTORS - located in carotid artery and aortic arch - detect increase in CO2, or drop in pH/o2 - increase BP by signaling cardioacceleratory center to increase CO, or signaling vasomotor center to increase vasoconstriction

Explain the relationship between vascular resistance and flow

blood flow is inversely proportional to peripheral resistance (R) in systemic circulation. if R increases, blood flow decreases. F= deltaP/R Resistance is a greater determinant in blood flow because it's more readily changed than pressure

Define hypertension and characterize it by symptoms and consequences

def: chronically elevated BP. characterized by: sustained increase in systolic pressure (above 140 mmHg) or diastolic pressure (above 90 mmHg). - "silent killer" - slowly strains the heart and damages the arteries - prolonged hypertension is the major cause of heart disease, vascular disease, renal failure, stroke - higher the pressure = greater the risk for serious problems - heart is forced to pump against greater resistance & must work harder; over time the myocardium weakens and its walls become flabby - hypertension ravages blood vessels and accelerates progress of atherosclerosis; vessels become blocked, blood flow to tissues becomes inadequate, vascular complications appear in brain, heart, kidneys, retinas of eyes

explain how blood flows via a pressure gradient

flows from regions of high pressure to regions of low pressure. high in arteries, lower in arterioles, lower in capillaries, lower in venules, lowest in vains. the closer you are to the heart, the greater the pressure on fluid. systemic BP is highest in aorta.

Explain Starling's Law of the Capillaries*

in short: is a hypothesis that states that the fluid movement due to filtration along the wall of a capillary is dependant on the balance between the hydrostatic pressure gradient and the oncotic pressure gradient across the capillary. at arteriole end: -Hydrostatic pressure (+33mmHg) > Osmotic pressure (-20mmHg) -hydrostatic pressure pushes fluid out of capillaries -osmotic pressure (due to plasma proteins) draws fluid into capillaries Net movement of fluid OUT of capillaries At venule end: -Hydrostatic pressure (+13mmHg) < Osmotic pressure (-20mmHg) -hydrostatic pressure still pushing some fluid out of capillaries -osmotic pressure draws fluid into capillaries Net movement of fluid INTO capillaries

discuss factors which affect blood pressure; cite examples

maintaining BP requires cooperation of heart, blood vessels, and kidneys. all supervised by brain. 3 main regulating factors: CO, periperal resistance, blood volume. BP varies directly with them; changes in one variable are compensated for by changes in other variables.

calculate pulse pressure & MAP given systolic and diastolic pressures

pulse pressure: systolic - diastolic MAP: diastolic + pulse pressure/3

Describe how cardiac output, resistance, MAP and blood flow change during exercise

resting skeletal muscle receives 1L of blood/minute and only 25% of capillaries are open until exercise. during rest: blood flow goes most towards abdominal organs, then kidneys, then skeletal muscles, then brain, then heart. during exercise: all of increased CO flushes into skeletal muscles as intrinsic autoregulatory controls dilate skeletal muscle arterioles. to maintain BP, the extrinsic controls act to decrease blood flow to kidneys and digestive organs

Define shock. List and describe several possible types of shock

shock - (circulatory) any condition in which blood vessels are inadequately filled and blood can't circulate normally. 1. hypovolemic - results from large scale blood or fluid loss and could lead to acute hemmorrhage, vomiting, diarrhea, extensive burns. blood volume drops rapidly & weak thready pulse is the first sign. intense vasoconstriction. blood pressure drops if blood loss continues. managing: replace fluid volume ASAP 2. vascular - blood volume is normal but circulation is poor as a result of extreme vasodilation. drop in peripheral resistance follows (rapidly falling BP). cause: loss of vasomotor tone due to anaphylaxis, neurogenic shock, septicemia. 3. cardiogenic - pump failure. heart is so inefficient that it cant sustain adequate circulation. cause: myocardial infarcations (heart attack)

Discuss the role of the capillary network (diagram)

the network is an interlaced network of capillaries between arterioles to venules. - blood arrives at 33 mmHg and then down to 17 mmHg when it leaves (higher pressure would rupture beds. also are highly permeable so low pressures are sufficient to filtrate substances into bloodstream) - nutrients such as O2, CO2, nutrients, and wastes all have to move between blood and interstitial fluid via diffusion*. each takes a different route. MOVEMENT 1. diffuse directly through endothelial membranes (lipid soluble molecules like respiratory gases) 2. pass through clefts (water soluble solutes) 3. active transport via pinocytotic vesicles or caveolae (ex: larger molecules like proteins) 4. movement through fenestrations (water-soluble substances) MOVEMENT OF FLUID: - forced out of clefts of capillaries at arterial end, most returns to blood at venous end (important in determining relative fluid volumes in blood and interstitial space) - bulk flow across capillary walls causes continuous mixing of fluid between plasma and interstitial fluid ; maintains interstitial environment direction and amount of fluid flow depend on two opposing forces... hydrostatic & colloid osmotic pressures

discuss the relationship between blood volume and blood pressure

they are directly proportional to each other - they increase and decrease together