blood vessels ii Flashcards
cardiac output
CO = SV * HR
- normal = 5-5.5 L/min
- determined by venous return and neural/hormonal controls
- resting heart rate maintained by cardioinhibitory center via parasympathetic vagus nerves
- during stress, cardioacceleratory center increases heart rate and stroke volume via sympathetic stimulation (ESV decreases and MAP increases)
- stroke volume controlled by venous return (EDV)
short term vs long term control of BP
Short
-neural and hormonal controls –> counteract fluctuations in BP by altering peripheral resistance and CO
Long
-renal regulation –> counteracts fluctuations in blood pressure by altering blood volume
Neural controls for short term BP maintanence
- if low BP, vessels constrict except those to heart and brain (affects MAP)
- alter blood distribution to organs in response to specific demands
Neural controls operate via reflex arcs, involving: baroreceptors, cardiovascular center of medulla, vasomotor fibers to heart and vascular smooth muscle, sometimes chemoreceptors and higher brain centers
CV center
- clusters of sympathetic neurons in medulla oversee changes in CO and blood vessel diameter
- consists of cardiac centers and vasomotor center
- Vasomotor center sends steady impulses via sympathetic efferents to blood vessels –> moderate constriction called vasomotor tone
- recieves input from baroreceptors, chemoreceptors, and higher brain centers
Baroreceptors
- location
- response to increased BP
-located in carotid sinuses, aortic arch, and walls of large arteries in neck/thorax
increased BP stimulates baroreceptors to increase input to vasomotor center
- inhibts vasomotor and cardioacceleratory centers, causing arteriolar dilation and venodilation
- stimulates cardioinhibitory center
- decreases BP
Baroreceptor
- response to decreased BP
- example
- Reflex vasoconstriction –> increased CO –> increased BP
- when you stand, baroreceptors of carotid sinus reflex protect blood to brain; in systemic circuit as whole, aortic reflex maintains BP
- Baroreceptors don’t do shit if altered blood pressure is sustained
Chemoreceptor reflexes (short term BP maintenance)
- location
- how the alter BP
- in aortic arch and large arteries of neck
- detect increase in CO2 of drop in pH/O2
- Increased BP by signaling cardioacceleratory center to increase CO; or signaling casomotor center to increase vasoconstriction
Higher Brain Centers (short term maintenance of BP)
-where?
how?
- reflexes in medulla
- hypothalamus and cerebral cortex can modify arterial pressure via relays to medulla
- hypothalamus increases BP during stress
- Hypothalamus mediates redistribution of blood flow during exercise and changes in body temp
Hormonal control (short term BP maintenance) -how?!?!?!?!?
Cause increased BP
- epinephrine and norepinephrine from adrenal gland –> increased CO and vasoconstriction
- angiotensin II stimulates vasoconstriction
- High ADH causes vasoconstriction
Cause lowered BP
-ANP causes decreased blood volume by antagonizing aldosterone
Renal regulation (long term BP maintenance)
- why kidneys?
- 2 methods
- baroreceptors quickly adapt to chronic high or low BP so they’re ineffective
- long term mechanisms control BP by altering blood volume via kidneys
Kidneys regulate arterial blood pressure:
- direct renal mechanism
- indirect renal (RAA) mechanism
Direct Renal mechanism
alters blood volume independently of hormones
- increased BP or blood volume causes elimination of more urine, reducing BP
- Decreased BP or blood volume causes kidneys to conserve water, and BP rises
Indirect Renal Mechanism
The RAA mechanism
- low arterial BP causes kineys to release renine
- Renin changes angiotensinogen into angiotensin I
- ACE from lungs turnse angiotensin I into angiotensin II
- Angiotensin II causes vasoconstriction and the release of aldosterone and ADH; and triggers thirst
Monitoring Circulatory efficiency
- vital signs: pulse, BP, respiratory rate, body temp
- Pulse: pressure wave caused by expansion and recoil of arteries
- radial pulse: @ wrist- routinely used
- Pressure points where arteries are close to body surface (can be compressed to stop blood flow)
Measuring systemic arterial BP
- auscultatory method uses a sphygmomanometer
- pressure increased in cuff until it exceeds systolic pressure in brachial artery
- pressure released slowly and examiner listens for sounds of Korotkoff with a stethoscope
systolic pressure vs Diasolic pressure (when measuring BP)
Systolic: usually less than 120 mm Hg and is the first sound as blood starts to spurt through artery
Diastolic: usually less than 80 mm Hg and is last sound before artery is no longer constricted
what causes variation in BP?
- transient elevations occur during changes in posture, physical exertion, emotional upset, and fever
- age, sex, weight, race, mood, and posture also alter BP
Hypertension and pre hypertension
Hypertension = high BP
-sustained arterial pressure of 140/90 or higher (some ppl use 135/85)
Prehypertension = elevated values, but not in hypertension range
- may be transient adaptations
- often persist in obese ppl
What’s wrong with prolonged hypertension?
- can cause heart failure, vascular disease, renal failure, and stroke
- heart must work harder –> myocardium enlarges, weakens, and becomes flabby
- also accelerates atherosclerosis
Primary/ Essential Hypertension
- 90% of hypertensive conditions
- No underlying cause identified (risks = heredity, diet, obesity, age, diabetes mellitus, stress, and smoking)
-no cure, but can be controlled (reduce salt, fat, and cholesterol intake; increase exercise, lose weight, stop smoking; antihypertensive drugs)
Secondary Hypertension
- less common
- due to identifiable disorders including obstructed renal arteries, kidney disease, and endocrine disorders (e.g. hyperthyroidism and Cushing’s syndrome)
-Treatment focuses on correcting underlying cause
Hypotension
- low BP
- Blood pressure below 90/60 mm Hg
- Usually not a concern unless it leads to inadequate blood flow to tissues
- often associated with long life and lack of cardiovascular illness
Tissue perfusion
- Delivery of O2 and nutrients to and removal of wastes from tissue cells
- gas exchange in lungs
- absorption of nutrients (digestion)
- urine formation (kidneys)
-Rate of Blood flow is just right to provide proper func.
velocity of blood flow
- changes as it travels through systemic circulation
- inversely related to total cross-sectional area
- fastest in aorta; slowest in capillaries; increases in veins
- slow capillary flow allows adequate time for exchange bt blood and tissues
Autoregulation
- what is it?
- how is it controlled?
- is it associated with MAP
- automatic adjustment of blood flow to each tissue relative to its varying requirements
- controlled intrinsically by modifying diameter of local arterioles feeding capillaries (independent of MAP which is controlled as needed to maintain BP)
- organs regulate own blood flow by varying resistance of own arterioles
2 types of autoregulation
metabolic controls
myogenic controls
Metabolic Autoregulation Controls
- what does it do
- what triggers it
- what do endothelins have to do with all this?
-vasodilation of smooth muscle in arterioles and precapillary sphincters; release of NO and/or inflammatory chems (vasodilators) from endothelial cells
occur in response to:
- declining tissue O2
- Substances from metabolically active tissues (H+, K+, adenosine, and prostaglandins) and inflammatory chemicals
Endothelins are vasoconstrictors which are usually balanced with NO, but if blood flow is inadequate, NO wins
Myogenic Autoregulation Controls
-Myogenic responses keep tissue perfusion constant depite most fluctuations in system pressure
- vascular smooth muscle responds to stretch:
1. Passive stretch (more intravascular pressure) promotes increased tone and vasoconstriction
2. Reduced stretch promotes vasodilation and increases blood flow to the tissue
long term autoregulation
-occurs when short term autoregulation can’t meet tissue nutritient needs
Angiogenesis
- # of vessels to region increases and existing vessels enlarge
- common in heart when coronary vessel occluded, or throughout body in people in high-altitude areas
3 types of movement of substances between blood in capillary and interstitial fluid
diffusion
transcytosis
bulk flow
Diffusion
- most important one
- substances move down concentration gradient (O2 and CO2)
- Get to/from capillary thru intracellular clefts, fenestrations, or through endothelial cells
Most plasma proteins cant cross except in sinusoids
BBB is supre tight
Transcytosis
- small quantity of material
- substances in blood plasma get pinocytized and/or leave via exocytosis
- important for large, lipid insoluble molecules that can’t get thru any other way
Bulk flow
- passice process in which larges of ions, molecules, or particles in a fluid move together in the same direction
- based on pressure gradient
- diffusion is more important for solute exchange
- bulk flow is important for regulation of relative volumes of blood and interstitial fluid
- filtration = from capillaries into interstitial fluid
- reabsorption = from intersitial fluid into capillaries
Net filtration pressure
- formula
- components
-balance of 2 pressures which promote filtration:
NFP = (BHP + IFOP) - (BCOP + IFHP)
Filtration:
- blood hydrostatic pressure (BHP) generated by pumping of heart (falls over capillary bed from 35-16 mmHg)
- Interstitial fluid osmotic pressure (IFOP) 1 mmHg
Reabsorption
- Blood colloid osmotic pressure (BCOP) about 36 mmHg bc blood plasma porteins wanna cross walls
- Interstitial fluid hydrostatic pressure (IFHP) close to 0 mmHg
Pressure at arterial end vs venous end?
How much of the fluid that’s filtered is reabsorbed?
What happens to the rest?
10 mmHg vs -9 mmHg
85%
-it enters lymphatic capillaries (3 L/day) and is eventually returned to blood
Vasomotion
- slow, intermittent flow
- reflects on/off opening and closing of precapillary sphincters
Capillary exchange of respiratory gases and nutrients
- diffusion down concentration gradients (O2 and CO2)
- lipid solubles diffuse
- water soluble pass through clefts and pores
- Big molecules (prots) are actively transported via pinocytosis or caveolae (lipid raft)
Blood flow in lungs
-autoregulatory mechanisms here
Pulmonary circuit
- short path
- arteries are more like veins (thin walls; big lumens)
- arterial resistance and pressure are low (24/10 mmHg)
- Autoregulatory mechanism opposite that in most tissues (low O2 causes vasoconstriction and vice versa)
Circulatory shock
- any condition in which blood vessels inadequately filled or blood can’t circulate normally
- results in inadequate blood flow to meet tissue need
Types of Circulatory shock
Hypovolemic shock - results from large scale blood loss
Vascular shock - results from extreme vasodilation and decreased peripheral resistance (allergies)
Cardiogenic shock - results when an inefficient heart can’t sustain adequate circulation (pump failure)
