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Flashcards in Module 10: Special Senses Deck (313)
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61

Heat-Generating Mechanisms when the Body is Too COLD

• Vasoconstriction (PHSC stimulation)
• Piloerection
• Increase in thermogenesis
• Shivering
• Decrease sweating

62

Heat-Losing Mechanisms when the Body is Too HOT

• Vasodilation of skin blood vessels (PSHC [Posterior Hypothalamic Sympathetic Center] inhibition) - increase in diameter of blood vessel causing increase in blood flow thereby more heat release to the skin
• Sweating (1 deg C increase)
• Decrease in heat production

63

(Thermogenesis)
Shivering

• Shivering center- dorsomedial portion of posterior hypothalamus
• Maximum shivering can increase heat production to 4-5x normal

64

(Thermogenesis)
Sympathetic chemical excitation

• Epinephrine and Norepinephrin can increase rate of cellular metabolism
• Chemical thermogenesis is affected by amount of brown fat

65

(Thermogenesis)
Thyroxine effect

• Increase in rate of cellular metabolism

66

What is the role of fat and skin in terms of regulation of body temperature?

• Fat is the insulator and the skin is the radiator system

67

• More powerful system of body temperature control

Behavioral Control of Body Temperature

68

• Secondary to pyrogens increase >> prostaglandins >> increases set point temperature
• May also be secondary to brain lesions

Fever

69

• Increased set point temperature makes the brain think that the body is cold despite presence of fever

Chills

70

• Tissue damage secondary to excessive heat
• you may have dizziness, loss of consciousness

Heatstroke

71

• May cause frostbite (common in digits and ears)
• Can be used for preserving body organs

Exposure to cold

72

AT DIFFERENT ALTITUDES… (1)

• Alveolar PO2 decreases as altitude increases
- Carbon dioxide and water vapor dilutes oxygen in the alveoli

• Arterial oxygen saturation decreases as altitude increases
- Depends if you are breathing air or breathing pure oxygen
- When breathing pure oxygen, most of the space in the alveoli formerly occupied by nitrogen becomes occupied by oxygen

73

AT DIFFERENT ALTITUDES… (2)

• Unacclimatized person usually can remain conscious until O2 saturation falls to 50%
- When breathing air, the ceiling is 23 000 feet
- When breathing pure oxygen, the ceiling is about 47 000 ft

74

• Most Important Effect of high altitude
• judgment, memory, motor movements are affected

Decreased Mental Proficiency

75

Effect of High Altitude (At 12,000 Feet)

- Drowsiness
- Lassitude
- Mental and muscle fatigue
- Headache
- Nausea
- Euphoria

76

Effect of High Altitude (At 18,000 feet and 23,000 Feet)

At 18,000 feet : twitchings/seizures

At 23,000 feet: coma and death after

77

MECHANISMS FOR ACCLIMATIZATION TO LOW PO2

• Increased Pulmonary Ventilation
• Polycythemia
• Increase Diffusing Capacity of Oxygen
• Increased Vascularity of the Peripheral Tissue
• Increased Ability of Cells to Use Oxygen Despite Low PO2

78

Increased Pulmonary Ventilation

• After a few minutes at high altitudes à respiratory rate increases by 1.65x
• After a few days —> respiratory rate increases by 5x
• Respiratory alkalosis develops—> renal compensation occurs to bring plasma pH back to normal

79

• Hematocrit, Blood Volume and HgB increases
• Increases the enzyme BPG mutase which increases 2,3 BPG (Shift to the Right of the O2-HgB Dissociation Curve)

Polycythemia

80

Increased Diffusing Capacity Of Oxygen

• Up to 3x the normal
• Mechanisms
- Increased pulmonary capillary blood volume
- Increased lung volume
- Increased pulmonary arterial BP

81

Increased Vascularity Of The Peripheral Tissues

• Cardiac Output increases by 30% immediately but tapers off after Hct increases
• Growth of increased numbers of systemic circulatory capillaries in the nonpulmonary tissues

82

Increased Ability Of Cells To Use Oxygen Despite Low PO2

• Increased cell mitochondria and cellular oxidative enzymes

83

What are the changes seen in natural acclimatization?

• Decreased Body Mass, Increased Chest Size
• Larger Hearts and Lungs
• Better O2 delivery (increased HgB, better O2 utilization)

84

What are the manifestations of acute mountain sickness?

• Acute Cerebral Edema
hypoxia -> cerebral vasodilation -> fluid leakage in the blood vessel -> edema

• Acute Pulmonary Edema
hypoxia -> pulmonary vasoconstriction (not all vessels constrict) -> increased capillary pressure in unconstricted vessels -> fluids are pushed outside -> edema

85

What are the manifestations of chronic mountain sickness?

• Pulmonary Vasoconstriction leading to R-sided heart failure
- increase pressure in lungs will lead to pulmonary HTN causing increase pressure in the right ventricle there by causing Right sided heart failure

86

Body in sitting position in an airplane is subject to

• Linear Acceleration
• Centrifugal Acceleration

87

• a unit of force equal to the force exerted by gravity
• used to indicate the force to which a body is subjected when it is accelerated

G Force

88

• Pilot pushed against his seat
• More dangerous
• Blood shunted to the Lower Extremities
• +6 to +10G -> blackouts, LOC, death
• +20G -> Vertebral Fracture

Positive G

89

• Pilot pushed against his seatbelt
• Less dangerous
• Blood shunted to the Head
*May result in “red-out” of the eyes and transient psychotic disturbances
• -20G -> death

Negative G

90

• the constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration
• A skydiver would reach terminal velocity due to air resistance in 12 seconds, with a speed of 175 feet per second

Terminal Velocity