Exam 2

Question 1

Describe the process of antagonistic innervation, and be able to imagine a diagram.

Answer 1

When a muscle is stretched, the spindle apparatus is activated, sending a signal through the dorsal root ganglion to the spinal cord. One branch of the axon synapses directly w/ alpha motoneuron innervating agonist muscle, while the other synapses with an interneuron and then with a motor neuron that inhibits action of the antagonist muscle.

Question 2

List the steps in the knee jerk reflex, and be able to imagine a diagram.

Answer 2

1) The patellar ligament is stretched, stretching the tendon and quadriceps femoris muscle.
2) The spindle apparatus is stretched, distorting its central region which stimulates dendritic endings of sensory neurons
3) APs are conducted by afferent (sensory) nerve fibers into the spinal cord on the dorsal roots of the spinal nerves
4) Sensory neuron synapses directly with the alpha motoneuron in the ventral horn gray matter of the spinal cord.
5) Efferent (motor) nerve impulses in the axons of the alpha motoneurons in the ventral roots of the spinal nerves are conducted to the ordinary (extrafusal) muscle fibers, and thus to the whole muscle.
6) Contraction of the muscle relieves the stretch of its spindles, thus decreasing activity in the spindle afferent nerve fibers.

Question 3

List the steps in the crossed-extensor reflex, and be able to imagine a diagram.

Answer 3

1) Pain on the bottom of one foot stimulates the sensory neuron to send a signal to the spinal cord.
2) Sensory neuron synapses with interneurons in the ipsi- and contralateral spinal cord, which cause the flexor of the injured foot to contract and the extensor to relax, while the flexor of the noninjured foot relaxes and the extensor contracts.

Question 4

List and describe the layers in the structure of skeletal muscles (not cellular).

Answer 4

Epimyseum - protective sheath around skeletal muscles, made up of connective tissue proteins; extends into the body of the muscle and subdivides into columns
Perimysium - the connective tissue sheaths surrounding fascicles
Fascicles - the columns created by the epimysium
Muscle fibers - a muscle cell with elongated shape; many in each fascicle
Endomysium - the thin connective tissue layer surrounding the sarcolemma of muscle fibers; the basement membrane (basal lamina)

Question 5

Describe the structure of skeletal muscle fibers.

Answer 5

Sarcolemma - membrane
Myofibrils - subunits that extend in parallel rows from one end to the other, organelles are relegated to the narrow sarcoplasm spaces in the cell
Myofilaments - smaller structures found within myofibrils
Thick filaments - found in dark A bands, made of myosin
Thin Filaments - found in light I bands, made of actin

Question 6

What is a spindle and how does it work?

Answer 6

spindle - specialized neuron within extrafusal muscle fibers

-stim when tendon is stretched, leading to depolarization and AP

Question 7

What is a motor unit?

Answer 7

A motor unit consists of a somatic motor neuron, which originates in the ventral horn of the gray matter of the spinal cord, it’s axon, which exits the spinal cord through the ventral root, and all of the muscle fibers that the axon’s branches innervate.

Question 8

How are graded contractions produced in skeletal muscles?

Answer 8

Graded contractions of whole muscles are created by variations in the number of motor units that are activated. Smaller motor units are activated by lower levels of stimulation, and large motor units are recruited as needed. Different motor units are activated by rapid, asynchronous stimulation → summation of contractions.

Question 9

What is the significance of a large or small innervation ratio?

Answer 9

• Fine motor control is achieved through a smaller axon to muscle fiber ratio (innervation ratio), seen in the fingers and eyes
• Larger motor units sacrifice fine control to achieve greater muscle power

Question 10

Describe the structure of the motor end plate.

Answer 10

The specialized region of the sarcolemma at the neuromuscular junction; folded to increase surface area.

Question 11

Describe the process of motor neurons synapsing on sarcolemma.

Answer 11

1) Each muscle fiber receives a single axon from a motor neuron.
2) Depol. of motor neuron axon terminal → release of ACh from 100 synaptic vesicles across the synapse.
3) ACh binds to several thousand nicotinic receptors in motor end plate.
4) Binding opens ions channels, producing an end plate potential (depol.) leading to APs and contraction.

Question 12

Describe the bands present in skeletal muscle.

Answer 12

A band - dark bands where thick filaments extend through and thin filaments overlap sides
I band - light bands containing only thin filaments
H band - the light region in the center of A bands due to lack of overlapping thin and thick filaments
Z line - dark vertical lines within I bands

Question 13

What is a sarcomere and what is it’s function?

Answer 13

In skeletal and cardiac muscle, one sarcomere is the distance from Z line to Z line. Forms the basic subunit of muscle contraction - actin filaments are pulled over myosin filaments, shortening the sarcomere. Z lines are attached to titin filaments that run through the myosin.

Question 14

What is a crossbridge?

Answer 14

Parts of the myosin protein that extend out toward the actin filament in arm-like projections and terminate in globular heads.

Question 15

What are the steps of the crossbridge cycle?

Answer 15

1) ATP binds to site on globular head.
2) Cross bridge hydrolyzes ATP into ADP and Pi → Pi binds → conformational change
3) Actin binds to globular head, ADP and Pi remain bound.
4) Pi is released from the cross bridge → conformational change → power stroke
5) ATP is released, and a new ATP molecule binds, and is hydrolyzed, breaking the previous actin bond.

Question 16

How is muscle contraction regulated?

Answer 16

1) Muscle relaxed, tropomyosin protein blocks myosin binding sites on actin
2) When Ca++ concentration rises, binds to troponin
3) Conformational change which moves troponin, attached to tropomyosin, out of the way
4) Power strokes continue as long Ca++ is bound to troponin

Question 17

What are the steps of Excitation-contraction coupling in skeletal muscles?

Answer 17

1) Somatic motor neuron releases ACh into the synaptic cleft
2) ACh binds to nicotinic receptors in the sarcolemma
3) Binding opens voltage-gated Na+ channels in the sarcolemma, propagating the AP along the transverse tubules
4) Stimulates the opening of the voltage-gated calcium channels in the t-tubules
5) This mechanically opens the calcium release channels in the terminal cisternae, releasing calcium into the sarcoplasm.
6) Ca++ in the sarcoplasm binds to troponin, allowing cross bridges to form.

Question 18

What are the cellular components involved in excitation-contraction coupling?

Answer 18

Sarcoplasmic reticulum - modified ER, interconnected sacs and tubes surrounding each myofibril.
Terminal cisternae - expanded portions of the SR near the T-tubules
T tubules - narrow membranous “tunnels” formed from and continuous with the sarcolemma; separate the terminal cisternae

Question 19

What are the steps in muscle relaxation?

Answer 19

1) When neural stimulation stops, calcium release channels close
2) Calcium is transported back up its concentration gradient into the lumen of the sarcoplasmic reticulum by sarcoplasmic/endoplasmic reticulum Ca2+ ATPase pumps (SERCA pumps)
* ATP is required for muscle relaxation as well as contraction

Question 20

What is the ideal resting length for striated muscle fibers?

Answer 20

2.0-2.25 µm - when the force (tension) required to prevent the muscle from shortening (flexing) is maximal

Question 21

What occurs when the muscle fibers are too short at rest?

Answer 21

Force generated by muscle contraction declines due to:

1) development of opposing forces (fluid pressure of the sarcoplasm)
2) double overlap of thin filaments might interfere with cross bridges
3) abutting of myosin against Z-disks may deform the myosin

Question 22

What occurs when the muscle fibers are too long at rest?

Answer 22

Force generated by muscle contraction declines due to less possibility for interaction between myosin and actin

Question 23

What is a twitch, and how does it relate to summation?

Answer 23

The quick contraction and relaxation of a muscle, in response to being stimulated by a single electrical shock of sufficient voltage; if a second shock is quickly delivered, it will piggyback on the first twitch (summation)

Question 24

How do incomplete and complete tetanus differ?

Answer 24

Incomplete tetanus - when stimuli are given in rapid succession, the twitches summate to produce a sustained but jerky muscle contraction
Complete tetanus - when stimuli are given even faster, a smooth, sustained contraction is produced; muscle will gradually lose its ability to maintain the contraction and fatigue

Question 25

What is the force-velocity curve and how does it relate to the different types of contractions?

Answer 25

A curve that shows the relationship of force vs. velocity of muscle shortening. The greater the force, the slower muscles shorten. A contraction is isotonic when the length of the muscle changes as it strains against the load, and isometric when the muscle length is constant.

Question 26

What processes in muscles require energy?

Answer 26

Myosin-ATPase in the sarcomere (cross bridge cycle) and SERCA pumps

Question 27

How do muscles obtain energy at rest?

Answer 27

aerobic respiration of fatty acids

Question 28

How do muscles obtain energy during exercise?

Answer 28

- aerobic and anaerobic respiration of blood glucose (incrs uptake due to GLUT-4 insertions into membrane), muscle triglyceride, plasma fatty acids, and muscle glyocgen - glucose from Cori cycle (gluconeogenesis in the liver) - O2 from myoglobin stores

Question 29

What is the function of phosphocreatine?

Answer 29

During exercise, donates phosphate to ADP so that muscle ATP levels don't fall During rest, creatine (produced in liver and kidneys) is phosphorylated by ATP

Question 30

What part of the body is likely to have a lot of slow-twitch (type 1) fibers, and why?

Answer 30

- The leg muscles, and other muscles that can sustain contraction for long periods of time. - Slow-twitch fibers take longer to reach their maximum tension, but fatigue less easily due to being richly supplied with myoglobin, hemoglobin from capillaries, many mitochondria, and aerobic respiratory enzymes; also called red fibers

Question 31

What part of the body is likely to have a lot of fast-twitch (type 2) fibers, and why?

Answer 31

- The extraoccular muscles of the eyes, and arm muscles, that need to be able to respond quickly. - Fast-twitch fibers take a short time to reach their maximum tension, but fatigue more easily due to fewer capillaries, less mitochondria, and less myoglobin; adapted to metabolize glycogen anaerobically; also called white fibers

Question 32

What would lead to the development of either type IIA or type IIX muscle fibers?

Answer 32

Endurance training exercise would lead to increase in type IIA fast oxidative fibers and a decrease in type IIX fast glycolytic fibers. This occurs due to increased mitochondria and slow myosin ATPase isoenzyme.

Question 33

How might the VO2max and the lactate threshold differ in a couch potato vs a trained athlete?

Answer 33

VO2max is the maximum rate of O2 metabolism, and the lactate threshold is the percentage of VO2max at which there is a significant rise in blood glucose. Endurance athletes have higher VO2max, and their lactate threshold is a higher percentage of their VO2max. In addition, they produce less lactate.

Question 34

What is the process by which muscles adapt to endurance training?

Answer 34

Increased oxidative capacity through increased number of mitochondria, increased myoglobin (O2 storage), increased speed and efficiency of oxygen uptake, elevated intracellular triglycerides with ability to oxidize them.

Question 35

Where in the body can smooth muscle be found? What is it's general function?

Answer 35

Blood vessels, bronchioles, stomach, uterine tubes, other lumens. Function is primarily constrictions of lumens and rhythmic contractions; controlled by autonomic nervous system

Question 36

How does the structure of smooth muscles differ from skeletal muscles?

Answer 36

Smooth muscles do not have sarcomeres. Instead, actin filaments are attached to the cell membrane or dense bodies. Myosin proteins are stacked vertically so that long axis is perpendicular to the thick filament, myosin heads can form cross bridges with actin all along the length of the thick filaments.

Question 37

Why is unique smooth muscle structure vital to its function?

Answer 37

smooth muscles must be able to contract even when they are greatly stretched

Question 38

What is the difference between single and multi-unit smooth muscles?

Answer 38

Single-unit - numerous gap junctions between adjacent cells, welded together electrically → behave as a single unit; pacemaker activity, some cells receive neural stimulation and stimulate other cells in the mass; intrinsic (myogenic) electrical activity in response to stretch; most smooth muscles Multiunit - few gap junctions, cells must be stimulated individually by nerve fibers; ciliary muscles in eyes

Question 39

How are smooth muscles innervated?

Answer 39

NTs are released from bulges on autonomic nerve fibers called varicosities. The entire surface of smooth muscle cells contains NT receptors; synapses "en passant"

Question 40

Describe the mechanism of excitation-contraction coupling in smooth muscles.

Answer 40

1) Depolarization of the plasma membrane during APs (when Na+ channels are open) causes voltage-gated Ca2+ channels in the transverse tubules to open (graded, the greater the depolarization, the more open) 2) Ca2+ crosses the sarcolemma through the channels, and combines with calmodulin 3) The calmodulin-Ca2+ complex combines with and activates myosin light-chain kinase (MLCK) 4) MLCK catalyzes the phosphorylation of myosin light chains, which are a component of cross bridges 5) This is a regulatory event in smooth muscle cells, and allows myosin to bind to actin and produce a contraction * contraction strength and duration are dependent on degree of light-chain phosphorylation, which is dependent on relative activities (speeds) of MLCK and MLCP

Question 41

Describe the mechanism of muscle relaxing in smooth muscles.

Answer 41

1) Relaxation occurs following closing of Ca2+ channels and the reduction of calcium by SERCA pumps 2) When calcium is reduced in the sarcoplasm, calmodulin dissociates from the MLCK 3) Phosphate groups that were added to myosin are removed by myosin light-chain phosphatase (MLCP), inhibiting cross bridge formation

Question 42

How would you characterize smooth muscle contractions? Why?

Answer 42

Smooth muscle contractions are slow and sustained; slow because myosin ATPase is slower in smooth muscles, and sustained because they can enter latch state, in which they hydrolyze less ATP than normal.

Question 43

What are the three main functions of the circulatory system?

Answer 43

1) Transportation of oxygen, absorbed nutrients, and waste products throughout the body 2) Regulation through transport of hormones, and of temperature through diverting blood to deeper vessels in cold. 3) Protection from damage (clotting) and pathogens (white blood cells).

Question 44

What are the components of the blood?

Answer 44

55% plasma (liquid w/water and solutes) | 45% formed elements (leukocytes and erythrocytes)

Question 45

What solutes are present in the plasma?

Answer 45

Na+ and other ions, hormones, enzymes, antibodies, and plasma proteins such as albumins, alpha, betta and gamma globuins, and fibrinogen.

Question 46

Describe the structure and function of erythrocytes.

Answer 46

red blood cells; transport oxygen and carbon dioxide - flattened, biconcave discs; lack nuclei and mitochondria - contain 280 million molecules of hemoglobin

Question 47

Describe the structure and function of leukocytes.

Answer 47

white blood cells; aids in defense against infection by microorganisms - contain nuclei and mitochondria - can move in an amoeboid fashion —> can squeeze through pores in capillary walls and move to site of infection (diapedesis or extravasation)

Question 48

Describe the structure and function of thrombocytes.

Answer 48

platelets; actually fragments of large bone marrow cells called megakaryocytes - lack nuclei, but are capable of amoeboid movement - survive for 5-9 days before being destroyed by the spleen or liver - clotting function - secrete growth factors which are important in maintaining the integrity of blood vessels

Question 49

What is the progression of erythropoiesis and where does it take place?

Answer 49

Takes place in the bone marrow. 1) Erythropoietin binds to membrane receptors on Hematopoietic stem cells 2) cells divide and differentiate, producing erythroblasts 3) erythroblasts become normoblasts 4) normoblasts expel nuclei and become reticulocytes 5) reticulocytes then change into mature erythrocytes

Question 50

How is erythropoiesis regulated?

Answer 50

Through erythropoietin, a hormone secreted from the kidneys in response to decreased blood oxygen; stimulates production of red blood cells; injections significantly improve aerobic performance

Question 51

What prevents clotting of the blood when there is no injury?

Answer 51

1) Endothelium separates platelets from collagen in the blood vessels 2) Endothelium secretes vasodilators that act on platelets to inhibit aggregation 3) Cell membrane of epithelial cells contains enzyme that breaks down ADP (released by platelets and promotes aggregation) in the blood to AMP and Pi 4) Fibrinogen is a soluble protein in the blood

Question 52

How is the platelet plug formed after injury?

Answer 52

1) damage to the endothelium → collagen fibers are exposed 2) glycoproteins in platelet's plasma membrane bind to them 3) everything is further bound by von Willebrand’s factor (produced by endothelial cells) and binds to collagen and proteins 4) when platelets stick to collagen, they degranulate as their secretory granules release ADP and thromboxane A2 (platelet release reaction) 5) these chemicals recruit more platelets and make them sticky so that they adhere to the platelets already stuck 6) second layer of platelets also undergoes platelet release reaction, leading to the formation of a platelet plug at the site of the injury 7) Platelet plug is further strengthened by meshwork of insoluble fibrin fibers. 7) in activated platelets, phosphatidylserine becomes exposed on the surface, and anchors factor VIII and factor V complexes to the platelet surface, increasing thrombin formation

Question 53

What is the pathway that leads to fibrin activation?

Answer 53

1) Tissue factor exposed when blood vessel injured 2) Cascade of clotting factor activations 3) Thrombin converts fibrinogen in the plasma to fibrin

Question 54

What are the immediate responses to blood vessel injury?

Answer 54

1) local vasoconstriction 2) plasma plug formation 3) factor activation cascade to produce fibrin

Question 55

What are some common anticoagulants and their mechanisms of actions?

Answer 55

Heparin - activates antithrombins Warfarin - blocks activation of vitamin K, which is needed for conversion of glutamate to substance more effective at bonding with Ca++, which is needed for activation of clotting factors. Aspirin - blocks cyclooxygenase, which blocks a pathway to fibrin. Tissue plasminogen factor (TPA) - activates plasmin which breaks down fibrin holding clots together

Question 56

What kind of blood normally flows through arteries?

Answer 56

deoxygenated, except pulmonary

Question 57

What kind of blood normally flows through veins?

Answer 57

oxygenated, except pulmonary

Question 58

What is the basic structure of arteries and veins?

Answer 58

tunica externa - outermost layer of arteries and veins; composed of connective tissue tunica media - middle layer of arteries and veins; composed of smooth muscle tunica interna - innermost layer of arteries and veins; composed of 1) an inner-most simple squamous epithelium, 2) the basement membrane (glycoproteins) and 3) a layer of elastic fibers (elastin)

Question 59

How does the structure of arteries and veins differ?

Answer 59

1) arteries have more muscle, and therefore appear more rounded in cross section 2) many veins have valves

Question 60

How does blood flow through veins if they have no vascular resistance?

Answer 60

Blood passes between skeletal muscles (skeletal muscle pump) which push blood toward the heart as they contract - one-way flow is ensured by venous valves, which only open toward the heart. - increased cardio activity in linked with increased venous return - breathing causes the diaphragm to increase abdominal pressure, squeezing abdominal veins

Question 61

What are the different types of capillaries, and where in the body might they be found?

Answer 61

continuous capillaries -those in which adjacent epithelial cells are closely joined together, preventing passage of most molecules; found in muscles, lungs, adipose tissue, and the brain fenestrated capillaries - those characterized by wide intercellular pores covered by a layer of mucoprotein which restricts entry of molecules that would otherwise be able to pass (proteins); found in kidneys, endocrine glands, and intestines discontinuous capillaries - those in which distance between endothelial cells is so great that the capillaries look like cavities in the organ; found in bone marrow, liver, and spleen.

Question 62

What are the functions of the lymphatic system?

Answer 62

1) transports interstitial fluid back to blood 2) transports absorbed fat from the small intestine to the blood 3) it’s cells – lymphocytes – provide immunological defense

Question 63

What are the components of the lymphatic system and their functions?

Answer 63

lymph - contains interstitial fluid, proteins, extraverted leukocytes, microorganisms, absorbed fat lymphatic capillaries - smallest vessels of lymphatic system; composed of endothelial cells with wide junctions → many elements can enter to become lymph lymph ducts - lymphatic vessels; walls similar to veins and include valves; movement is a result of peristaltic wave (pacemaker cells that initiate action potentials associated with Ca++ influx, rate increases as stretch increases); empty into thoracic duct or right lymphatic duct, to be drained into the right and left subclavian veins, respectively lymph nodes - before return to cardiovascular system, lymph filtered through these; contain phagocytic, pathogen removing cells, and germinal centers, which produce lymphocytes

Question 64

How are cardiac muscles similar to and different from skeletal muscles?

Answer 64

Cardiac muscles are striated, and have sarcomeres, but they are shorter, more branched, and intertwined; tubular structure; connected by intercalated discs (desmosomes + gap junctions)

Question 65

What is the mechanism of excitation-contraction coupling in cardiac muscle?

Answer 65

1) Action potential opens voltage-gated sodium channels, depolarizing the cell 2) Voltage-gated Ca++ channels in the T-tubules are opened in response to the depolarization 3) Ca++ that enters the cell from the T-tubules interacts with the Ca++ release channels in the SR to release more calcium (calcium-induced calcium release)

Question 66

Describe the pathway of systemic circulation.

Answer 66

Left ventricle → aortic valve → aorta → arteries → capillaries → veins → superior/inferior vena cava → right atrium

Question 67

Describe the pathway of pulmonary circulation.

Answer 67

Right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary arteries → lungs (gas exchange) → pulmonary veins → left atrium → mitral valve → left ventricle

Question 68

What prevents backflow through the heart valves?

Answer 68

The valves only open in the direction they are supposed to open, and they open only when the pressure behind them is higher than the pressure in front of them. If ventricular pressure is too high, there is a risk that the AV valves will evert. Normally prevented by papillary muscles connected to valves by chordae tendonae.

Question 69

Where do APs in the heart begin?

Answer 69

In the pacemaker cells of the sinoatrial (SA) node; located in the right atrium near the superior vena cava

Question 70

What are the other pacemaker regions of the heart?

Answer 70

The AV node, the bundle of His, and the purkinje fibers, normally suppressed because the SA node has a faster depolarization rate

Question 71

Describe the steps in the pacemaker potential.

Answer 71

1) Pacemaker cells have RMPs at -60mV 2) When cell reaches -60mV, HCN channels are activated by the hyperpolarization, and Na+ enters the cell, slowly depolarizing 3) At a threshold, voltage-gated Ca++ open leading to the upward phase of the AP 4) Repolarization is produced by opening of voltage-gated K+ channels

Question 72

Describe the pathway through which the electrical activity is conducted in the heart.

Answer 72

SA node → sinoatrial conduction pathways → atrial myocardium → AV node → bundle of His → Purkinje fibers → ventricular myocardium (inner endocardium to outer epicardium)

Question 73

What causes the delay between atrial contraction and ventricular contraction?

Answer 73

The traveling of the action potential, especially the slow velocity at which it moves through the AV node.

Question 74

What does the P wave of an ECG correspond to?

Answer 74

Depolarization and contraction of the atria

Question 75

What does the QRS wave of an ECG correspond to?

Answer 75

Depolarization and contraction of the ventricles; followed by the closing of the AV valves and the first sound

Question 76

What does the T wave of an ECG correspond to?

Answer 76

Repolarization of the ventricles (outer epicardium to inner endocardium); followed by closing of the semilunar valves and second heart sound

Question 77

Describe the steps of the myocardial cell AP.

Answer 77

1) Myocardial cells have RPs at -85mV 2) When depolarized by pacemaker potential, there is rapid sodium influx through voltage gated fast Na+ channels 3) As K+ slowly leaks out of the cell, Ca++ enters the cell, elongating the AP into a plateau → begins excitation-contraction coupling thru Ca++ induced Ca++ release 4) K+ gates open, Ca++ gates close, repolarization

Question 78

What prevents graded contractions in cardiac muscle?

Answer 78

Refractory period corresponds to long action potential; muscles cannot be stimulated again until they have relaxed

Question 79

Describe the pressure changes in the heart during the length of the cardiac cycle.

Answer 79

1) As ventricles contract, intraventricular pressure builds and the AV valves snap shut (first heart sound); phase of isovolumic contraction because no filling or ejection taking place 2) When pressure in the left ventricle exceeds pressure in the aorta, the aortic valve opens, allowing for ejection of blood from the ventricles (pressure maxes out at 120mmHg) 3) As pressure falls in the left ventricle (volume decrease), the aortic valve snaps shut (second heart sound) to prevent backflow 4) Pressure in the aorta and pressure in the left ventricle fall, to 80mmHg and 0mmHg respectively (isovolumic relaxation) 5) When pressure of the ventricles falls below the pressure of the atria, the AV valves open, resulting in the phase of rapid filling (diastole) 6) Atria contact to eject the last 20% of blood to end diastolic volume

Question 80

What equation can be used to calculate cardiac output?

Answer 80

Stroke volume * Cardiac Rate

Question 81

Why doesn't the heart beat at 90-11 bpm if thats the speed of the SA node?

Answer 81

Due to constant parasympathetic tone, the HR is slowed to ~70bpm. -Ach from vagus nerve endings bind to muscarinic receptors → opening of additional K+ channels in the membrane of pacemaker cells, slowing down the rate of depolarization

Question 82

How does the heart rate change in response to SNS activity?

Answer 82

It speeds up, due to Ep and NEp from adrenal medulla and sympathetic axons binding to ß-adrenergic receptors in the heart → stim. production of cAMP → acts on HCN and Ca++ channels in SA node to incrs. rate of depolarization Also increased strength of contraction.

Question 83

How do EDV, contractility, and stroke volume related? What law is involved?

Answer 83

Load put on ventricle prior to contraction (EDV) is directly proportional to stroke volume and contractility due to the Frank-Starling law. -The more the heart muscle stretches, the more forcefully it can contract producing a proportional stroke volume.

Question 84

How is total peripheral resistance related to stroke volume?

Answer 84

TPR or afterload (load that is put on ventricle once contraction has begun) is inversely proportional to stroke volume (for at least a few beats until the heart compensates w/contractility)

Question 85

How is venous return facilitated? (four ways)

Answer 85

1) higher pressure in venules and lower pressure near the vena cava, promoting return to the heart 2) sympathetic nerve activity stimulating smooth muscle in walls of the veins to decrease compliance 3) skeletal muscle pumps squeezing veins during muscle contraction 4) breathing → diaphragm puts pressure on the abdomen to squeeze abdominal veins

Question 86

Describe the mechanism of capillary/tissue fluid exchange.

Answer 86

passive process regulated by pressure changes 1) hydrostatic pressure is higher in the capillary than the interstitial fluid, and higher on the arterial side of the capillary than the venule side. 2) osmotic pressure asserted by plasma proteins is much higher in capillaries filtration = (hydrostatic in cap + osmotic in int) - (hydrostatic in int + osmotic in cap) - net positive → force out of cap - net negative → force into cap

Question 87

Describe the regulatory response that is initiated by dehydration or excessive salt intake.

Answer 87

Blood osmolality increases → osmoreceptors in hypothalamus → stimulates thirst and secretion of ADH from posterior pituitary → ADH increases water retention by the kidneys → increases blood volume and decreases blood osmolality through water retention and water intake (drinking)

Question 88

Describe the regulatory response that is initiated by low blood pressure and low blood flow to the kidneys.

Answer 88

Juxtaglomerular apparatus → secetes renin → converts angiotensinogen to angiotensin I → ACE converts angiotensin I to angiotensin II in the lungs → vasoconstriction (incrs BP), stim thirst center in hypothalamus, stim adrenal cortex to secrete aldosterone → salt and water retention by the kidneys

Question 89

Describe the regulatory response that is initiated by over or under stimulation of atrial stretch receptors.

Answer 89

1) stimulate reflex tachycardia (incrs SNS activity) 2) inhibit ADH activity 3) Secrete Atrial Natriuretic Peptide, a hormone that stimulates increased sodium excretion

Question 90

Describe the regulatory response that is initiated by over or under stimulation of baroreceptors in the carotid sinus and the aortic arch.

Answer 90

Baroreceptors → vasomotor and cardiac control centers in the medulla → PNS and SNS axons to the heart and blood vessels (cardiac output and total peripheral resistance)

Question 91

What is the Valsalva maneuver?

Answer 91

Attempting forceful exhalation while preventing air escape, as when pooping. Raises intrathoracic pressure → compresses thoracic veins → reduces venous return (EDV, SV, CO, BP) → baroreceptor reflex raises HR Upon breathing, thoracic pressure falls → increases CO further briefly before venous return improves and raises aortic pressure → normal CO restored through baroreceptor reflex

Question 92

What law relates rate of flow to vascular resistance, length of vessel, viscosity of blood, and radius of vessel?

Answer 92

Poiseuille's Law - -resistance to flow is directly proportional to pressure difference, length of vessel, and viscosity of blood -resistance to flow is inversely proportional to radius of vessel rate of flow (Q) = (∆Pr4 (π))/(ηL(8))

Question 93

What is the physical mechanism by which blood flows through the blood vessels?

Answer 93

Rate of blood flow is proportional to pressure difference between one end of tube and other, flows towards lower pressure

Question 94

What does the total peripheral resistance refer to?

Answer 94

The sum of all the vascular resistances within the systemic circulation

Question 95

What would the effect of massive vasodilation in a large organ be?

Answer 95

- decreased total peripheral resistance which would decrease mean arterial pressure - compensatory mechanisms, such as increased cardiac output and vasoconstriction in other areas

Question 96

How is blood flow regulated by the autonomic nervous system?

Answer 96

sympathetic - cAMP → HCN channels → incrs. HR and contractility (CO) - cholinergic fibers → arterial skeletal muscles → incrs flow to muscles in emergency - adrenergic sympathetic fibers → NEp to alpha-adrenergic receptors (resting tone/constant vasoconstriction) parasymp - cholinergic nerve endings in genitals, digestive tract and salivary glands, produce vasodilation

Question 97

How is blood flow regulated intrinsically?

Answer 97

Myogenic - changes in arterial pressure are detected by stretch receptors in arteries and compensated for by the blood vessels in the brain and kidneys (BP up, vasoconstrict; BP down, vasodilate) Metabolic - promotion of local vasodilation prompted by changes in the chemical environments sensed by arterial chemoreceptors (O2 down, pH of tissue down, CO2 up, K+ up → vasodilate) Paracrine - endothelium of tunica interna produces endothelins to contract and adenosine, nitric oxide, and prostaglandins to dilate

Question 98

What system regulates coronary blood flow during fight-or-flight?

Answer 98

Sympathetic - coronary arteries have beta adrenergic receptors; in fight or flight → adrenal medulla promotes Ep release → vasodilation

Question 99

How is resting vasoconstriction in the coronary arteries produced?

Answer 99

Coronary arteries have alpha adrenergic receptors; at rest adrenergic sympathetic fibers release NEp to activate alpha-adrenergic receptors → to produce vasoconstriction

Question 100

How is blood flow to the heart intrinsically regulated during exercise?

Answer 100

Heart consumes O2 more quickly producing metabolic environment of high CO2, low O2, high K+, high paracrine regulators like nitric oxide, adenosine, and prostaglandins → signals organ that needs more oxygen to produce vasodilation

Question 101

Why does HR increase upon inhalation?

Answer 101

When you breathe in, intrathoracic pressure becomes more negative, increasing venous return → atrial stretch receptors → incrs HR through increased sympathetic nerve activity