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REGULATION OF
BLOOD FLOW
Biology 20 – Unit D: Human Systems
Section 10.3 (pg. 328-335)
Cardiac Output
• Cardiac Output: The amount of blood that flows (is
pumped) from the heart each minute
• Amount of blood pumped from right side = amount of
blood pumped from left side
Stroke Volume
• Stroke Volume: The quantity of blood pumped with each
beat of the heart = ~70 mL/beat (resting)
Cardiac Output = Stroke Volume x Heart Rate
Cardiac Output = 70 mL/beat x 70 beats/min
Cardiac Output = 4900 mL/min
Cardiac Output Calculation
1. What’s your weight
in kg? (lbs x 0.45)
2. What’s your heart
rate?
3. Come up and tell me
Question 1
What is Cardiac Output?
(a) volume of blood that is pumped with each heart beat
(b) volume of blood that is pumped by the heart each
minute
(c) The number of times the heart contracts per minute
(d) The number of times the sinoatrial node stimulates the
heart
Blood Pressure
• The force of the blood on the walls of the arteries
• Measured by a sphygmomanometer
• Gauge measures the pressure exerted by the blood
during ventricular contraction
• Bladder increases until a low-pitched sound can be
detected – systolic blood pressure
• Bladder is deflated even more until sound disappears –
ventricular relaxation – diastolic blood pressure
Blood Pressure
• Measured in mmHg (mm of Mercury)
• Systolic pressure/Diastolic pressure
= Pressure in Arteries/pressure in Veins
• Normal = 90/60 – 140/90; Average = 120/80
• Example of High Blood pressure = 160/100
• Hypertensive
• Example of Low Blood pressure = 80/50
• Hypotensive
Blood Pressure
• Systolic = pressure in arteries
• BP = Systolic/Diastolic
• Diastolic = pressure in veins
• BP = 120/80 (Normal)
Question 2
True or False. Pressure increases as blood
flows away from the heart.
Blood Pressure
• Depends on:
1. Cardiac output (as cardiac output increases,
blood pressure increases and vice versa)
2. Arteriolar resistance (diameter of arteriole is
regulated by smooth muscle)
• Constriction closes the opening - reduces blood flow
through the arteriole and increases blood pressure
= vasoconstriction
• Arteriole dilation increases blood flow and decreases
blood pressure = vasodilation
• Responds to neural and hormonal controls
Blood Vessel Regulation
• Diameter of arterioles adjusts in response to metabolic
products such as
• Glucose by-products (in the break down of glucose)
• Carbon dioxide
• Lactic acid
• Causes relaxation of arterioles  dilation  blood flow
(increase of oxygen) increases
• How the body maintains equilibrium
Hypertension
• High blood pressure
• Increased resistance to blood flow
• Could cause vessels to weaken and rupture
• Body increases the amount of connective tissue – leading
to hardened/less elastic arteries.
• Diet is mainly responsible
• E.g. too much salt  higher blood pressure
• Heart Attack/Stroke!
Hypotension
• Low blood pressure
• Reduces your capacity to transport blood  and oxygen
• Adjusted by the sympathetic nerves
Blood Vessel Regulation
• Vasoconstriction: the narrowing of blood
vessels/arterioles (less blood to tissues)
• Increases blood pressure
• Caused by a nerve impulse that contracts smooth muscle
• Less O2 to tissues
• Vasodilation: the widening of blood vessel/arterioles
(more blood to tissues)
• Decreases blood pressure
• Relaxation of smooth muscle
• Helps you release excess heat
Blood Pressure Regulation
• Autonomic nervous system (controls motor nerves that
regulates the diameter of arterioles;
unconscious/involuntary) – medulla oblongata in the
brain
• Parasympathetic –
decelerates heart
beat
• Sympathetic –
accelerates heart
beat
Question 3
A blood pressure regulator in the brain is called the
_____________ ______________.
(don’t worry about spelling)
Blood Pressure Regulation
• Blood pressure receptors
are called baroreceptors
are located in the aorta
and the carotid artery
Baroreceptors
sense
increased
blood pressure
Heart rate
decreases
Nerve
transmits
signals to
medulla
oblongata
Vagus nerve
transmits
inhibitory
signal to
sinoatrial
node
What happens when blood pressure
drops…?
Nervous System
Parasympathetic
Sympathetic
Blood Vessels/Arterioles
Dilate (widen)
constrict (narrow)
Blood Pressure
Decreases
Increases
Cardiac Output
Increases
Decreases
Question 4
• When a someone becomes hypertensive, the body tries
to regulate itself by
• Stimulating the ________________ nervous system
• Causing arterioles to ________________
• Which ______________ blood pressure
• And _____________ their cardiac output.
Regulating Body Temperature
• Thermoregulation: maintenance of body temperature
within a range that enables cells to function efficiently
• Consider the exchange of heat between the body and the
environment
What is normal body
temperature?
Question 5
Which of the following regulates a body that has become
too hot?
(a) Blood vessels dilate and shivering
(b) Blood vessels constrict and shivering
(c) Blood vessels dilate and sweating
(d) Blood vessels constrict and sweating
Thermoregulation
• Hypothalamus: a region of the brain that is responsible
for coordinating many nerve and hormone functions
Stimulus
Physiological
Response
Result
Decreased
Environmental
Temperature
• Constriction of blood • Heat is conserved
vessels in skin
• More head is
• Body hairs become
generated by
erect (goosebumps)
increased
• Hypothalamus
metabolism (skeletal
initiates shivering
muscle movement)
Increased
Environmental
Temperature
• Dilation of blood
vessels
• Sweating
• Heat is dissipated
Capillary Fluid Exchange
• Every tissue is within 0.1mm of a capillary
• Capillaries provide cells with oxygen, glucose, and amino
acids
• Fluid exchange between the blood and the surrounding
extracellular fluid
• Water passes through spaces between the capillary cells
• Fluid & Osmotic pressure influence water movement
• Water moves from an area of higher pressure to an area
of lower pressure
Precapillary Sphincters
Capillary Fluid Exchange
Question 6
When fluid pressure outside of a capillary is
greater than the fluid pressure inside a capillary,
the water moves
(a) into the capillary
(b) out of the capillary
(c) along side the capillary
(d) nowhere
The Lymphatic System
• Lymph: the fluid found in
lymph vessels that contains
some proteins that have
leaked through capillary
walls
• Leaked proteins drain from
the extracellular fluid (ECF)
and return to the circulatory
system by way of the
lymphatic system
• Lymph is transported in open-ended lymph vessels
(similar to veins)
• Low pressure return system uses muscle contractions
• Lymph is returned to the venous system
Lymph Nodes
• Are enlargements that house white blood cells that filter out any
bacteria
• Filter damaged cells and debris from the lymph and store
lymphocytes
• Red bone marrow is
where all types of blood
cells are produced
• White blood cells
• Spleen – has many blood
sinuses (each hold ~150mL
blood) – reservoir
Lymphoid Organs
Question 7
Which of the following does the lymphatic system NOT do?
(a) Return leaked protein to the circulatory system
(b) Houses white blood cells
(c) Transports lymph into open-ended lymph vessels
(d) Transports oxygen and carbon dioxide
Edema (a.k.a. Swelling)
Results when small blood vessels become
leaky and release fluid into tissues. The
fluid accumulates causing tissues to swell.
Response of the Circulatory System to
Exercise
• Go for a run!
• Oh no! Lactic acid buildup in your calf!
1. Sympathetic nerves stimulate the adrenal glands which
release epinephrine/adrenaline
2. Epinephrine travels through the blood and stimulates
the release of red blood cells from the spleen
3. Increased numbers of red blood cells aid in oxygen
delivery
4. Epinephrine and stimulation from sympathetic nerves
increases heart and breathing rates  higher levels of
blood and faster oxygen transport & wastes are
removed!
Summary
• Cardiac output is the amount of blood the heart can
pump each minute
• Blood pressure is the force of blood on the walls of the
arteries. It is measured as systolic and diastolic blood
pressure in millimetres of mercury (mmHg)
• Blood pressure is higher in vessels closer to the heart
• Increased cardiac output increases blood pressure. If
arteries are constricted, blood flow is slower and blood
pressure is higher
Summary
• Capillaries are associated with fluid exchange between
blood and extracellular fluid
• The movement of water between blood and the ECF is
regulated by fluid pressure and by osmotic pressure
• Water moves from an area of high fluid pressure, the
capillary, to an area of low fluid pressure, the ECF
• Proteins and dissolved minerals in the blood cause
fluid from the ECF to move into the blood by osmosis
Summary
• Proteins in the ECF are returned to the circulatory
system by the lymphatic system
• Lymph nodes house white blood cells that filter bacteria
• Red bone marrow is where all types of blood cells are
produced
• The spleen stores and purifies blood. The spleen
releases red blood cells in response to low blood
pressure or low oxygen levels in blood.