Lab #7 - Human circulatory system physiology

Question 1

Myocardium

Answer 1

the muscles of the heart making up the middle and thickest layer of the heart wall

Question 2

Bradycardia

Answer 2

slow heart rate

Question 3

Tachycardia

Answer 3

heart rate of more than 100 beats per minute

Question 4

Myogenic

Answer 4

the ability of a muscle to contract reflexively without nervous stimulation. a myogenic heartbeat.

Question 5

Neurogenic

Answer 5

controlled by nervous tissue

Question 6

Systole

Answer 6

period of contraction of the ventricles of the heart that occur between the first and second heart sounds of the cardiac cycle pumping blood out

Question 7

Diastole

Answer 7

the phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood

Question 8

Baroreceptor

Answer 8

provides the brain with information pertaining to blood volume and pressure, by detecting the level of stretch on vascular walls. As blood volume increases, vessels are stretched and the firing rate of baroreceptors increases.

Question 9

Baroreflex

Answer 9

one of the body’s homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels

Question 10

Depolarization

Answer 10

Depolarization of the heart is the passage of electrical current through the heart muscle changing it from the resting polarized state to the depolarized. When the electrical signal of a depolarization reaches the contractile cells, they contract.

Question 11

Repolarization

Answer 11

Repolarization in the ventricles of the heart is a process allowing the muscle cells of the ventricles to regain their ability to depolarize again. Repolarization entails movement of the ions, which entered the cell during the depolarization phase of the cycle, to flow out of the cell. When the repolarization signal reaches the myocardial cells, they relax

Question 12

relate ECG waveforms to the normal mechanical events of the cardiac cycle, electrical activity (depolarization and repolarization) in the atria and ventricles, and activity within the cardiac pacemaker/conduction system.

Answer 12

• The electrical signals passing trough the heart can be detected by attaching electrodes to different points on the surface of the body
• The signals change in a regular pattern corresponding to the electrical signals that trigger the cardiac cycle, producing an ECG

Question 13

explain the physiology that underlies the response of the heart and peripheral components of the circulatory system to exercise.

Answer 13

• Moderate physical activity results in an increase in blood flow to the heart by 360%, to the muscles of the skin by 370% (increases loss of heat), and to the skeletal muscles by 1060%
• Flow is decreased to the digestive tract and liver by 60%, to the kidneys by 40%, and to the bone and most other tissues by 30%
• Only the blood flow to the brain remains unchanged
• These changes are the result of increased cardiac output and increased heart rate together with adjustments to the muscles in the arterioles supplying the various organs that are in immediate need of oxygenated blood

Question 14

explain the physiology of the heart and peripheral components of the circulatory system that are associated with the diving response.

Answer 14

• Blood pressure must be regulated carefully so that the brain and other tissues receive adequate blood flow, but it must not be so high that the heart is overburdened
• The diving reflex is an instant, and automatic reflex activated when our sensory receptors - carotid chemoreceptors - touch the water. When they detect wetness, the trigeminal nerve sends information to the brain, which immediately triggers bradycardia
• bradycardia is caused by selective peripheral vasoconstriction and significantly reduces the blood flow to the skin, gut and limbs. This automatic reflex makes sure that organs with a great need of oxygen such as the heart and brain get what they need.

Question 15

Describe the electrical conduction pathway that is responsible for initiating a heart contraction cycle, starting with the heart’s pacemaker.

Answer 15

• The pacemaker generates a wave of signals to contract’
• Signals are delayed in the region between the atria and the ventricles
• AV node cells are stimulated to produce a signal, which travels along the purkinje fibers to the bottom of the heart
• Signals spread from the bottom of the heart upward, causing the ventricles to contract

Question 16

Describe the effects of the autonomic nervous system on the ECG and overall heart activity.

Answer 16

Heart rate is controlled by the activity of the autonomic nervous system: the sympathetic (induces changes in ECG repolarization) and parasympathetic nervous systems increase and suppress heart rate.

Question 17

Explain the baroreceptor reflex.

Answer 17

One of the most important peripheral feedback loops within the autonomic nervous system. This reflex normally acts to ensure that ventral arterial blood pressure is maintained at a level appropriate for metabolic activities in the body, but that is not too high to cause rupture of arterial vessels or excess fluid leakage from the capillaries. Coordinates heart activity, arterial blood pressure and peripheral blood flow.