Flashcards in Physiology Deck (90):
Multi-unit vs unitary smooth muscle
multi-unit - fiber operate individually (have nerve fiber running between them)
Unitary - smooth muscle cells adhere and contain gap junctions to allow simultaneous contraction
What excites skeletal muscle vs smooth muscle?
Skeletal muscle - ACh
Smooth muscle - ACh (excitatory/inhibitory), NE/Epi (inhibit GI, excite vasculature), NO (inhibitory)
How do neurotransmitters reach smooth muscle?
through varicosities - swelling along the axon that release NTs
Describe differences in contraction between skeletal muscle and smooth muscle?
Skeletal muscle has faster cycling and myosin/actin attached for less time; high ATP demand
Smooth muscle has slower cycling and myosin/actin attached for more time; less ATP demand
How does Ca enter smooth muscle cytosol?
through plasma membrane (Ca L type channels or ligand activated Ca channels) or through SR
Describe how Ca is released from the SR
incoming Ca triggers ryanodine receptors (RYRs) on SR or NT/hormone can trigger PLC to convert PIP2 to IP3 which will react w/ receptor on SR
What does Ca in the cytosol do?
It binds reversibly to calmodulin (CaM)
What steps are involved in smooth muscle contraction?
CaM-Ca complex activates MLCK; phosphorylated MLCK allows myosin and actin to bind
What is smooth muscle contractile strength proportional to?
Intracellular Ca levels
What is responsible for smooth muscle relaxation?
myosin phosphatase -> removes phosphate from myosin to make it inactive
Describe the latch mechanism?
actin and myosin still latched after removal of phosphate; cell continues to generate active tension without use of ATP
What is RMP of smooth muscle?
-50 to -60 mv
Slow waves vs spike potentials
Slow waves - waves of partial depolarization that sweet along smooth muscle
Spike potentials - true APs that elicit muscle contraction; found on tope of slow waves
What can cause smooth muscle activity?
hormones, NT, mechanical stretch
Active tension vs passive tension
Active tension = muscle contraction
Passive tension = stretching of the muscle cell membrane
What allows smooth muscle to have longer active tension and less passive tension?
Dense bodies (aka adheren junctions) attached to myosin/actin fibers and rearrange to reduce passive tension
What is considered normal HDL?
< 40 mg/dL in men; < 50 mg/dL in women
What is considered normal LDL?
< 100 mg/dl in people w/ low CV risk
< 70 mg/dl in people w/ high CV risk
What are the criteria for metabolic syndrome?
3 or more of the following:
Waist circumference > 102 cm in men (40 inches) and >88 cm in women (35 inches)
Serum triglycerides > 1.7 mmol/l
Blood pressure > 130/85
HDL cholesterol < 40 mg/dl in men; < 50 mg/dl in women
Serum glucose > 115 mg/dl
What are 3 things that people should avoid eating?
foods that contain trans fats, processed meats, and sugar sweetened beverages (SSBs)
What does dietary approaches to stop HTN (DASH) recommend for daily Na intake?
< 2300 mg/day; recommends < 1500 mg/day
What is the recommended amount of exercise?
150 minutes per week of moderate aerobic exercise
What is normal MAP?
93.3 mmHg (approximately 100 mmHg)
MAP is regulated by what to things?
baroreceptor reflex and renin-angiotensin-aldosterone system (RAAS)
What are the detectors for the baroreceptor reflex?
mechanoreceptors - respond to changes in arterial pressure (through stretch receptors on vessel wall)
chemoreceptors - respond to changes in PO2, PCO2, and pH
What are the afferent neural pathways for the baroreceptor reflex?
carotid sinus through the glossopharyngeal nerve (CN IX)
aortic sinus through the vagus nerve (CN X)
Describe each of the following: nucleus of tractus solitarius (NTS); Dorsal motor nucleus of vagus & nucleus ambiguous; Rostral ventrolateral medulla
nucleus of tractus solitarius (NTS - receives and coordinates afferent signals from carotid and aortic sinuses
Dorsal motor nucleus of vagus & nucleus ambiguous - parasympathetic activity w/ CV function (inhibitory)
Rostral ventrolateral medulla - sympathetic activity w/ CV function
What is the control center for the baroreceptor reflex?
Which sinus has a higher threshold for activation?
Aortic sinus; carotid bodies will fire up to 200mmHg and not below 40-60mmHg
What is the relationship between stretch and firing rate?
decreased stretch (MAP) = decreased firing
increased stretch (MAP) = increased firing rate
What effect does the firing of baroreceptors have on the nervous system?
parasympathetics = increased firing rate (decrease HR and indirect vasodilation through NO release)
sympathetics = decreased firing rate (constriction of arterioles and veins, increased HR and contractility)
What is renin secreted by and in response to what?
secreted by juxtaglomerular (JG) cells in response to drop in BP; release stimulated by B1 receptor
What is the function of renin?
causes angiotensinogen (from liver) to covert to angiotensin I (inactive)
What coverts angiotensin I to angiotensin II?
angiotensin converting enzyme (ACE) in the lungs and kidneys; angiotensin II is active
What is the function of angiotensin II?
causes secretion of aldosterone from adrenal cortex; leads to Na and H20 retention and increased blood volume; stimulates secretion of antidiuretic hormone (vasopressin)
What receptors does angiotensin II bind?
AT1 receptors on arterioles; causes global vasoconstriction
What receptors does vasopressin bind to?
V1 receptors (smooth muscle) and V2 receptors (collecting ducts); increases TPR and water retention
What secretes ANP, BNP, and CNP? What is their function?
secreted by heart by excessive preload of atria and ventricles; protects against over dilation or overstretching of cardiac chambers
In what way will the vascular function curve shift during hemorrhage?
shifts to the left; CO and RA pressure both decrease
Describe the body's reaction to hemorrhage
carotid sinus firing (baroreceptor) decreases; HR and contractility increase; unstressed volume (veins) decreases; TPR increases; production of renin, angiotensin II, aldosterone, Epi, and ADH increase
Describe the body's reaction to increased blood volume
increased preload; increased secretion of ANP; decrease ADH secretion and renal vasodilation
Describe the body's reaction to exercise
increased sympathetics (B1); increased HR and contractility; increased venous return
In what type of vessels would you find alpha 1 adrenergic receptors?
What affects velocity of flow?
cross sectional area
larger diameter = slower velocity; velocity is slowest at capillaries to allow gas exchange
In which vessels in compliance the greatest?
greatest in veins compared to arteries; compliance = how far vessel will distend (opposite of elasticity)
How does arteriosclerosis affect MAP?
plaques in arterial wall decrease diameter and compliance (increase SBP, pulse pressure, and MAP)
How does aortic stenosis affect MAP?
narrowing of aortic valve (SBP, pulse pressure, and MAP all decrease)
What is autoregulation?
maintenance of constant blood flow in face of changing arterial pressure
What is active hyperemia?
blood flow to organ proportional to metabolic activity (flow increases to exercising muscles)
What is reactive hyperemia?
increased blood flow in reaction to period of decreased blood flow (heart after ischemic event)
Describe each of the following as natural constrictors/dilators: histamine, bradykinin, 5-HT, prostacyclin, thromboxane A2, Angiotensin II, vasopressin, NO
histamine - dilation
bradykinin - dilation
5-HT - constrictor
Prostacyclin - dilation
thromboxane A2 - constrictor
Angiotensin II - constrictor
vasopressin - constrictor
NO - dilator
What is an important factor in coronary circulation?
metabolic control -> using vasoactive metabolites from hypoxia
What is an important factor in cerebral circulation?
metabolic control -> uses vasoactive metabolites CO2 and H+ for active and reactive hyperemia
What is an important factor in renal circulation?
metabolic control -> myogenic, tubuloglomerular feedback)
What is an important factor in skeletal muscle circulation?
metabolic control during exercise; sympathetics during rest
What is an important factor in skin circulation?
sympathetics -> temperature regulation via alpha 1 during vasoconstriction
Factors that affect Ca release from SR
size of inward Ca current during phase 2 and amount of Ca previously stored in SR
What type of inotropic effect does the sympathetic nervous system have? Which receptors?
positive (increased contractility); faster rate of relaxation (twitch is shorter allowing for more time refilling); B1 receptors
What is phospholamban?
protein that regulates SERCA in SR -> when phosphorylated, stimulates SERCA resulting in greater uptake of Ca into SR
What type of inotropic effect does the parasympathetic nervous system have? Which receptors?
negative (decreased contractility); ACh decreases inward Ca during plateau phase; muscarinic receptors
What is the relationship between HR and contractility?
increased HR = increased contractility -> less time between contractions means less Ca released from cell
What effect do cardiac glycosides have on contractility? What is an example?
positive inotropic effect; Digoxin (increases contractility but not HR)
Why is there a relationship between CO and right atrial pressure?
EDV depends on venous return which determines RA pressure
Describe the cardiac function curve
as venous return increases, RA pressure increases; volume of blood LV ejects as CO equals volume it receives as venous return (up to certain point)
Describe vascular function curve
inverse relationship between venous return and RA pressure -> the lower pressure gradient in RA, the higher the gradient between systemic arteries and RA and greater venous return
What is the length-tension relationship in cardiac muscle? What is the sweet spot of sarcomeric length? Is it usually reached?
as pressure/filling of LV increases, greater tension is generated; sweet spot is 2.2-2.3 micrometers; resting beats don't reach sweet spot (heart greatly resists stretch)
Relationship between venous return and contractility
increased venous return = more filling = greater contraction
What is preload?
left ventricular end-diastolic volume
What is afterload?
pressure required to eject blood (open aortic valve); generally equal to aortic artery pressure (increases w/ increased systemic pressure)
What is stroke volume? What is the normal value?
volume of blood ejected by ventricle w/ each beat; usually about 70 ml
What is end diastolic volume (EDV)?
ventricular volume right before contraction
What is end systolic volume (ESV)?
ventricular volume right after contraction
What is ejection fraction?
What is the normal value?
fraction of EDV ejected in each stroke volume (how much blood is left in ventricle w/ each contraction); usually about 55%
What is cardiac output? What is the normal value?
total volume of blood ejected by ventricle per minute; usually about 5 L/min
Describe the Frank-Starling Relationship
volume of blood ejected by ventricle depends on volume present at end of diastole (more blood present, the harder the heart will contract)
What happens to pressure volume loop if preload increases?
more venous return = more blood volume; greater EDV; after load and contractility remain the same
What happens to pressure volume loop if afterload increases? When would you see this occur?
greater pressure is needed to open aortic valve; reduced SV and reduced EF%; would see w/ aortic stenosis or HTN
What would happen to pressure volume loop if contractility increases? When would you see this occur?
increased SV and increased EF% (less blood left in the heart); would see w/ adrenergic stimulation
Sympathetic influence on troponin I
phosphorylation of troponin I is inhibitory - when inhibited, troponin C (opening up actin and myosin) is more efficient; increased CO
Define each of the following: volume work, pressure work, minute work, stroke work
volume work = CO
pressure work = aortic pressure
minute work = CO x aortic pressure
stroke work = area within pressure volume loop (performed by LV)
Which requires more O2 consumption: pressure work or volume work?
pressure work -> LV must work harder than RV b/c systemic pressure greater than pulmonary pressure
What does it mean when the cardiac function curve moves left?
increased isotropy, increased HR, decreased afterload
What does it mean when the cardiac function curve moves right?
decreased isotropy, decreased HR, increased afterload
What will shift the vascular function curve right (up)?
increased blood volume or decreased compliance
What will shift the vascular function curve left (down)?
decreased blood volume or increased compliance
What does increased TPR do to the cardiac/vascular function curve?
shifts both curves down; cardiac to the right and vascular to the left
What does decreased TPR do to the cardiac/vascular function curve?
shifts both curves up; cardiac to the left and vascular to the right
What will occur to the relationship between CO and venous return w/ heart failure?
decreased inotropy; decreased vascular compliance; increased blood volume; increased systemic vascular resistance (SVR)
What does a (+) and (-) force mean w/ the Starling forces?
(+) means fluid is flowing out of the capillary; (-) means fluid is flowing into the capillary