Medical Physiology Block 8 Week 1

Question 1

Define homeotherms.

Answer 1

species that do regulate internal body temperature

Are relatively stable over a broad range of ambient conditions

Question 2

Describe the components regulating human internal body temperature.

Answer 2

Components of the system: thermal sensors, afferent pathways, and integration system in the CNS, efferent pathways, and target organs that control heat generation and transfer (skeletal muscle shivering, dissipation of heat through skin, and dissipation of heat through sweat glands)

Question 3

When is body temperature lowest? highest? why?

Answer 3

3-6 AM; 3-6 PM

Entrained by light-dark cues to a 24-hour cycle

Question 4

How is body temperature changes in a postovulatory women?

Answer 4

raised by half a degree Celsius

Question 5

Why do infants have difficulty controlling body temperature?

Answer 5

cannot shiver or sweat

Question 6

Why do the elderly have difficulty controlling body temperature?

Answer 6

weakened sensation, decreased metabolism, and reduced ability to dissipate heat

Question 7

Which hormones increase metabolic rate?

Answer 7

thyroxine and epinephrine

Question 8

Why is the skin an ideal location for heat transfer to the environment?

Answer 8

large surface area

Question 9

Describe heat transfer by radiation.

Answer 9

occurs between the skin and solid bodies in the environment

Question 10

Describe heat transfer by conduction. Is this a major factor in humans?

Answer 10

occurs when the body touches a solid material of different temperature

NO

Question 11

Describe heat transfer by evaporation.

Answer 11

is proportional to the water vapor pressure gradient between skin and environment

Question 12

Is the rate of heat exchange greater or smaller in water compared to air?

Answer 12

greater

Question 13

What happens to the temperature gradient and water vapor gradient in windy conditions (increased air velocity)

Answer 13

With forced air movement (wind), the cooler “ambient” air replaces the air overlying the skin more rapidly (increased heat exchange)

Increased air velocity over the skin increases the effective vapor pressure gradient between skin and the overlying air because of the faster movement of water vapor away from the skin

Question 14

Describe the body’s sensors for temperature.

Answer 14

Free nerve ending distributed over the entire skin surface are specialized sensory neurons that provide the CNS with information about the body’s thermal condition

Body core sensors are at high densities in the preoptic area and anterior hypothalamus (important for sensing increases in internal temperature during exercise)

Warm receptor fibers are very sensitive to an acute rise in skin temperature but deactivate at higher temperatures

Question 15

How does the body increase heat dissipation?

Answer 15

With a moderate heat load, the autonomic response primarily increases the heat transfer rate from core to skin by increasing cutaneous blood flow

However, when the heat load is sufficiently great, the autonomic nervous system also activates the eccrine sweat glands, which secrete sweat on the skin surface, thus elevating the partial pressure of water vapor there and promoting increased evaporation

Question 16

How does the body preserve or increase heat production?

Answer 16

When a cold stress is sufficiently great, the physiological response includes increasing heat production by involuntary, clonic, rhythmic contraction and relaxation of skeletal muscle (shivering); in addition to vasoconstriction of cutaneous vessels

Question 17

What innervates the sweat gland?

Answer 17

sympathetic nervous system (Ach)

Question 18

Describe internal body temperature during exercise.

Answer 18

Steady-state core temperature is slightly elevated during exercise (persists as long as exercise continues)

The slight initial drop in core temperature at the onset of exercise is caused by flushing out of blood from the cooler peripheral circulation when the muscle and skin beds vasodilate

Mean skin temperature decreases during exercise because of the increased evaporative cooling of the skin caused by sweating

Question 19

Why does the steady-core body temperature rise during exercise?

Answer 19

Consequence of the initial imbalance between rates of heat production and dissipation.

Question 20

What is the defense mechanism for preventing hypothermia when immersed in cold water?

Answer 20

A thick layer of insulating fat retards heat loss to the water and postpones or even prevents hypothermia during prolonged exposures

Question 21

How does heat transfer change when ambient temperature is greater than 30 degrees Celsius?

Answer 21

When ambient temperature reaches the mid-30s (ºC), evaporation becomes the only effective avenue for heat dissipation.

Question 22

How does heat transfer change when exposed to high humidity?

Answer 22

high ambient humidity reduces the skin-to-environment gradient for water vapor pressure and thus reduces evaporation

Question 23

Describe fever.

Answer 23

Fever is caused by the action of circulating cytokines called pyrogens, where are low-molecular weight polypeptides produced by cells of the immune system

Fever begins when heat production temporarily exceeds heat dissipation
.
Modulated by interleukins and production of prostaglandins (E2)

Question 24

What is the bodies response to a fever when a patient is in a warm environment? cold?

Answer 24

If fever strikes when the patient is in a warm environment in which the cutaneous vessels are dilated, the response will be to vasoconstrict to decrease heat loss

If the patient is in a cold environment the cutaneous vessels are already constricted, so the response will be to shiver

Question 25

What is the difference between warm-blood and cold-blooded animals?

Answer 25

Warm-blooded creatures, like mammals and birds, try to keep the inside of their bodies at a constant temperature. They do this by generating their own heat when they are in a cooler environment, and by cooling themselves when they are in a hotter environment.

Cold-blooded creatures take on the temperature of their surroundings. They are hot when their environment is hot and cold when their environment is cold.

Question 26

What is the difference between endothermy and ectothermy?

Answer 26

endothermy: a warm
-blooded animal that controls its body
temperature by producing its own heat
through metabolism

ectothermy: an animal that relies on external environment for temperature control instead of generating
its own body heat (cold-blooded)

Question 27

What is the heat balance equation?

Answer 27

Heat production (metabolism - work done) - heat losses (radiation, convection, evaporation)

Question 28

What is the Van’t Hoff rule?

Answer 28

For every 10 degree Celsius increase/decrease in temperature, the reaction rate is doubled/halved.

Question 29

What is the energy source for muscle contraction for a 1.5 minute run?

Answer 29

Nonoxidative breakdown of carbohydrates from glycogen breakdown and oxidative breakdown of fat and glucose

Question 30

What is VO2 max?

Answer 30

Maximal aerobic power/maximal oxygen consumption

Question 31

What is the fuel source for low intensity exercise (less than 30% VO2 max)? high intensity (greater than 70% VO2 max)?

Answer 31

fats; carbohydrates

Question 32

What is fatigue?

Answer 32

decrease in the number of active cross bridges formed and the force produced per cross bridge (decreased force of contraction)

Question 33

What is central fatigue?

Answer 33

reduced excitatory input to motor control centers in the brain and spinal cord; reduced output to alpha and gamma motor neurons

Question 34

What is peripheral fatigue?

Answer 34

impairments in initiation and propagation of muscle action potentials; depleted substrates for energy metabolism and accumulation of lactate

Question 35

Describe peripheral fatigue caused by high frequency stimulation.

Answer 35

caused by continuous firing of action potentials during intense exercise

sodium entry and potassium exit exceed ability of sodium/potassium pump (inactivation of voltage gated sodium channels)

recovery is rapid

Question 36

Describe peripheral fatigue caused by low frequency stimulation.

Answer 36

caused by prolonged, moderate intensity exercise

calcium release from SR falls, which decreases intracellular calcium

recovery requires several hours

Question 37

During the first 2-3 minutes of an aerobic activity, prior to the ability to consume enough oxygen to totally meet the energy needs, the difference in the energy requirement and the energy supplied by the aerobic systems is called?

Answer 37

oxygen deficit

Question 38

What is oxygen debt?

Answer 38

the extra volume needed to restore the energetic system

Question 39

How are athletes and sedentary people different in terms of oxygen uptake (VO2 max)?

Answer 39

athletes have higher oxygen consumption prior to beginning exercise

a sedentary person will reach VO2 max quicker than an athlete during exercise

An elite/trained athlete will have a higher resting O2 consumption, a higher VO2 max and is able to reach this at a higher intensity than an untrained person

Question 40

Describe blood flow during exercise

Answer 40

decrease in blood flow to kidney, liver, and GI tract

increased blood flow to working skeletal muscle

oxygen uptake by the muscle depends on blood flow and oxygen contraction

redistribution of blood depends on metabolic rate and exercise intensity

convective delivery rate = cardiac output x arterial oxygen content

Question 41

How does cardiac function change with exercise?

Answer 41

heart rate increases with exercise intensity and reaches a new steady state (changes dependent on intensity)

stroke volume increases but plateaus because: increased heart rate decrease stroke volume but increased contractility, preload, and decreased afterload all increase stroke volume

mean arterial pressure increases because: cardiac output increases and total peripheral resistance slightly decreases as a consequence of muscle vasodilation

Question 42

What is rete mirabile?

Answer 42

There is a network of blood capillaries between red swimming muscles (in a mackerel shark with a length of 1m, it has a surface of 4m²!), which acts as a heat exchanger. The heat created through muscle activity is transported by the blood in the vessels that takes oxygen-depleted blood to the gills. Blood vessels with thin walls and cold, oxygen-rich blood from the gills are running in the opposite direction along the heated vessels and are warmed this way.
Thus, heat is transferred to the blood flowing into the body, while the blood flowing towards the gills cools off already and cannot lose as much heat to the outer medium anymore. This principle of opposite streams is so efficient that hardly any body heat is lost through the gills

Question 43

How does exercise affect the lungs?

Answer 43

increased ventilation

Question 44

What converts chemical energy to mechanical work?

Answer 44

cross-bridge cycling and SERCA pump

Question 45

What is the size principle?

Answer 45

small motor units are recruited before larger motor units

Small motor neuron depolarizes rapidly and has high membrane resistance (however conduction velocity is low)

associated with type 1 fibers

Question 46

What is rate coding?

Answer 46

determinant of force is the frequency with which the muscle fibers are stimulated by their innervating axon.

Question 47

T/F: When a motor nerve reaches threshold to fire an action potential, all the muscle fibers it innervates contract

Answer 47

T

Question 48

What are muscle fibers classified by?

Answer 48

myosin heavy chain

Question 49

T/F: all of the muscle fibers a motor neuron innervates are the same fiber type?

Answer 49

T

Question 50

Which fiber type would be most beneficial to a marathon runner?

Answer 50

type 1

Question 51

The ability to generate force is proportional to what?

Answer 51

number and diameter of the fibers

Question 52

Describe anaerobic training paradigm.

Answer 52

Neural adaptations (4-6 weeks of program): increased motor unit activation, firing frequency, and firing synchronization; decrease in Golgi tendon organ inhibition; selective recruitment of type 2 fibers

Muscular adaptations (second month of training): hypertrophy, facilitation of fiber type transitions; increased enzyme and substrate concentration; tissue repair (satellite cells and down-regulation of myostatin)

Question 53

Describe muscle learning.

Answer 53

When learning a new skill, motions are uncoordinated (recruitment of antagonistic muscles)

Fatigue of the muscle will lead to recruitment of larger motor units to maintain energy resulting in loss of fine control (costly due to greater energy expenditure)

Question 54

T/F: For athletes with high intensity, short duration exercise, oxidative and glycolytic pathways are modes for replenishing phosphocreatine lost during the exercise period (improve lactate threshold)

Answer 54

T

Question 55

Describe parallel muscle fibers.

Answer 55

a muscle with a few long fibers in parallel with the axis of shortening produces rapid shortening but less tension

Question 56

Describe oblique muscle fibers.

Answer 56

a muscle with many short fibers at an angle to the axis of shortening produces slow shortening but more tension

Question 57

Which sweat glands contribute to temperature regulation?

Answer 57

eccrine

Question 58

Describe eccrine glands.

Answer 58

Eccrine sweat glands are tubules comprising a secretory coiled gland and a reabsorptive duct

The release of acetylcholine stimulates the muscarinic receptors on the acinar cells and causes them to secrete into the lumen a protein-free plasma-like fluid (PLC; a Na/K/Cl cotransporter mediates the uptake of chloride across the basolateral membrane, and the chloride exits across the apical membrane through a chloride channel; lumen-negative voltage drives sodium secretion through the paracellular pathway; osmotic gradient for water)

Duct cells reabsorb salt and water until the fluid reaches the skin surface through an opening (sweat pore)

water reabsorption is limited

Question 59

Describe acclimatization to heat.

Answer 59

Aldosterone mediates the ability to reabsorb sodium chloride

Question 60

Why are type IIb fibers ideal for sprinters?

Answer 60

fast contraction speed, large motor neuron size, and high anaerobic enzyme content

Question 61

What is an adaptation to aerobic exercise?

Answer 61

increase maximum heart rate, increase mitochondrial content, increase GLUT4 content, angiogenesis, and increase in acetylcholine release

Question 62

What is the Lorrain-Smith effect? Bert effect? Bean effect?

Answer 62

damage to tracheobronchial tree (inflammation, swelling, and reduced vital capacity); confusion, seizures, and LOC; necrosis and paralysis