Download Homeostasis and Blood Flow

Homeostasis and Blood Flow
The Circulatory System
Cardiac Output

Cardiac output is defined as the amount of
blood that flows from the heart per minute.

Typically, unless some dysfunction occurs, the
blood pump on the right side of the heart will
equal the amount pumped on the left side.

Cardiac output is affected by:
 Stroke
Volume
 Heart Rate
Stroke Volume

Stroke volume is the quantity of blood
pumped with each beat of the heart.

The stronger the heart contractions, the
greater the stoke volume.

70mL of blood per beat leave each
ventricle (at rest).
Heart Rate

Heart Rate is
the number of
time the heart
beats per minute.
Determining Cardiac Output:
Cardiac Output = stroke volume X heart rate
70mL/beat X 70 beats/min= 4900ml/min (the cardiac output)

Larger individuals pump more blood per minute;
therefore, have a larger cardiac output.

Heart rate increases during exercise; meet demands.
Comparing Individual Fitness
Levels
Person
Stroke
Volume
Heart
Rate
Cardiac
Output
Tom
50
100
5L
Lee
100
50
5L
“Why do two people with the
same body mass have
different heart rates?”
Comparing Individual Fitness
Levels

Lee’s lower heart rate
indicates a higher stroke
volume. Strong heats can
pump greater volumes of
blood with each beat.

This is why athletes have
low heart rates.
Lance Armstrong



In all, during those three weeks in
July, Armstrong spent eighty-six
hours, seventeen minutes, and
twenty-eight seconds on the bike.
Lance Armstrong's heart is almost a
third larger than that of an average
man. During those rare moments
when he is at rest, it beats about
thirty-two times a minute —slowly
enough so that a doctor who knew
nothing about him would call a
hospital as soon as he heard it. (When
Armstrong is exerting himself, his
heart rate can edge up above two
hundred beats a minute.)
Physically, he was a prodigy.
Blood Pressure

Blood Pressure is the force of blood on
the walls of the arteries.

Measured with a sphygmomanometer



Measuring blood pressure
Cuff is pumped until it closes off blood flow. A
stethoscope is placed below the cuff and air is
slowly released until a low-pitch sound is
detected. The sound is caused by blood entering
the artery. The gauge measures the pressure
exerted by blood entering the ventricle during
contraction (systolic blood pressure)
Cuff is then deflated more until the sound
disappears. This is when the ventricle is in
relaxation and the atrium is filling (diastolic
blood pressure)
Blood Pressure

Normal blood pressure for
young adults:




systolic blood pressure: 120mmHg
(millimeters of mercury)
Diastolic blood pressure: 80mmHg
It would be reported as: 120/80
Blood pressure depends on:



Cardiac Output
Arteriolar Resistance
YouTube - Effects of High Blood
Pressure on your Body
2 Factors of Blood Pressure

Cardiac Output increase in output will cause an
increase in blood pressure.

Arteriolar Resistance the diameter of the
arterioles. Constriction of smooth muscles reduces
the blood flow, and leaves more blood in the
arteries = higher blood pressure.
Muscle can relax and cause the opposite.

What Do The Smooth Muscles Of
The Arterioles Respond To?
Neural and Hormonal Controls.
 Metabolic Products (ex. Products of the breakdown of

glucose)
 Insufficient
Oxygen lactic acid produced.
 Sufficient Oxygen CO2 and H2O
 Accumulation of CO2 and lactic acid causes the
relaxation of smooth muscles (dilation). This results
in an increase in blood flow and the delivery of more
O2.
Homeostasis and Arteriolar
Dilation

More metabolic products
in most active tissues
dilation  more
nutrients and oxygen to
tissues in need.

Metabolic products
minimal in less active
tissues  constriction 
less nutrients and
oxygen.
Hypertension

Hypertension (a.k.a. high blood
pressure) is caused by an increase
resistance to blood flow, which results
in a increase in blood pressure.

High blood pressure causes weakening
of the blood vessels (may rupture).

The body attempts to compensate by
increasing support provided by
connective tissues. This leads to hard
and less elastic arteries.

Artery rigidity causes an even greater
increase in blood pressure and further
vessel weakening.
Causes of Hypertension


Hereditary
Diet (primary factor)

Susceptible if:


Too much salt can lead to an
increase in blood pressure.
“silent killer”; heart attack
or stroke are usually your
first indications.
Regulation of Blood Pressure



There are blood pressure receptors in
the walls of the aorta and carotid
arteries (in neck)  sensitive to high
blood pressures.
When bp exceeds acceptable levels,
the receptors respond by sending a
message to the medulla oblongata, the
bp regulator in the brainstem.
Sympathetic (stress) nerve impulses
are decreased and parasympathetic
(relaxation) nerve impulses increased.
Medulla Oblongata

Decreased Sympathetic Nerve
Impulse:



Arterioles dilate
Increasing the outflow of blood
from the artery
Stimulated Parasympathetic
Nerve Impulse:



Heart rate decreased
Stroke volume decreased
This slows the movement of blood
into the arteries, lowering bp.
Response to Exercise

In stress, the sympathetic nerves stimulate
the adrenal glands. The hormone
epinephrine (adrenaline) is released from
the adrenal gland and travels in the blood
to other organs in the body.

Epinephrine:




stimulate the release of red blood cells from the
spleen aids in oxygen delivery.
Increase heart rate (faster oxygen transport).
breathing rate (blood contains higher levels of
O2).
Increase removal of waste from tissues.
Vigorous Exercise Accelerates the
heartbeat in 2 ways:
1.
As cellular respiration
increase, so does CO2 levels.
This stimulates receptors in the
aorta and carotid arteries 
medulla oblongata  heart.
2.
As muscle activity increases,
the muscle pumps more blood
back to the right atrium.
Stretch receptors M.O.
heart
Regulating Body Temperature




Thermoregulation is the
maintenance of body temperature
within a range that enables cells
to function efficiency.
We can maintain temp.
regardless of surroundings.
Increases cell respiration to
generate heat.
Average body temp: 37 degrees
Celsius.

Extremities can vary up to four
degrees from core.
Human thermoregulation
Protecting Against Excessive Heat

When sensors in the brain detect a
rise in temp, in coordination with
the hypothalamus, a nerve impulse
is sent to the sweat glands.

The evaporation of perspiration
from the skin causes cooling ( loss
of water and salts).

Impulse is also sent to the blood
vessels in the skin to dilate
blood looses heat to the skin.