10.3 Regulation of Blood Flow

Page 328- 335

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Cardiac Output

• Definition:

– Amount of blood that flows from the heart per minute

• Generally, the amount of blood pumped from the right side = the left side

• Two factors affect cardiac output:

1. Stroke volume

2. Heart rate

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Cardiac Output 1. Stroke volume:

– The quantity of blood pumped with each beat of the heart

– The stronger the heart contraction, the greater the stroke volume

– ~70 mL of blood/beat

2. Heart rate:

• Number of times the heart beats per minute

Cardiac output = stroke volume x heart rate

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Cardiac Output

• On average, a 70 kg person will have to pump ~ 5 L of blood each minute

• Cardiac output is a basis for comparing individual fitness

– Lower heart rates may indicate higher stroke volumes, and therefore stronger hearts

• Heart rate can vary throughout the day

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Cardiac Output Example

Person Stroke Volume (mL/beat)

Heart rate (beats/min)

Cardiac Output (Stroke Volume x heart volume)

Tom 50 100 5000mL = 5 L

Lee 100 50 5000mL = 5 L

• Lee’s lower heart rate indicates a higher stroke volume so Lee is in better shape.

• Strong hearts can pump greater volumes of blood with each beat.

• This is why athletes often have low heart rates

• Weak hearts have to pump more often for the same amount of blood.

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Blood Pressure

• Definition:

– The force of the blood on the walls of the arteries

• Measured with a sphygmomanometer

– We will go over how to do this in a mini demo…

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Blood Pressure

• Normal systolic blood pressure is 120 mmHg

• Normal diastolic pressure is 80 mmHg

• Blood pressure is given as systolic over diastolic blood pressures (ex. 120/80)

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Blood Pressure

• Depends on two factors:

1. Cardiac output – increases in cardiac output will increase blood pressure

2. Arteriolar resistance – when arteries are constricted or smaller in diameter because of plaque can result in reduced blood flow, and therefore increase in pressure

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Regulation of Blood Pressure

• Blood pressure receptors are located in the walls of the aorta and carotid arteries (found on either side of the neck)

• When pressure gets too high, a nerve message travels to the medulla oblongata (the blood pressure regulator in the brainstem) – Sympathetic nerve impulses are decreased

– Parasympathetic nerve impulses are increased

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Regulation of Blood Pressure

• Low blood pressure is regulated without the pressure receptors

– Sympathetic nerves will be stimulated when blood pressure is low causing the arterioles to constrict increases blood pressure

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Stresses…

Exercise:

• Exercise is a stress, therefore the sympathetic nervous system is stimulated

• The sympathetic nerves stimulate the adrenal glands, which then release epinephrine (adrenaline)

• Epinephrine stimulates the release of red blood cells from the spleen

• Increased numbers of red blood cells aids in oxygen delivery

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Stresses… • Sympathetic nerves also stimulate

increased heart rate (moving more oxygen faster to cells) and breathing rate (getting more oxygen to the red blood cells)

• Epinephrine also causes vasodilation of arterioles leading to the heart, brain and muscles and vasoconstrict blood vessels leading to the kidneys, stomach and intestines

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Stresses…

Maintaining body temperature:

• Thermoregulation:

– Maintenance of body temperature within a range that enables cells to function efficiently

• To maintain the temperature, the body increases cellular respiration when in a cold environment

• When the brain senses the body is too hot, it sends a message to the hypothalamus (in the brain) to initiate the sweat glands to start sweating

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Stresses…

• Evaporation of perspiration from the skin causes cooling (endothermic)

• The blood vessels of the skin are also dilated, causing more blood to flow to the skin, and therefore cool

• The opposite idea occurs when your brain senses you are too cold

• Shivering also increases temperature by increasing cellular respiration by the muscles continuously contracting

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Stresses… Hypertension:

• High blood pressure

• Caused by increased resistance to blood flow increased blood pressure

• To fix the problem, the body attempts to compensate by increasing the support provided by connective tissues hardening of the arteries

• A heart attack or stroke can be the first indication that anything is wrong

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Regulation of Blood Flow (Homeostasis)

• Answer questions 1-4 on page 332.

• Answer questions 1 – 3, 6 – 8, 11, 12, 15 on page 335.

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10.4 Capillary Fluid Exchange

Page 336-339

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Capillaries

• Estimated that nearly every tissue of the body is within 0.1 mm of a capillary

• Provide cells with oxygen, glucose and amino acids

• Exchange between blood and extracellular fluid (ECF)

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Capillaries • Two forces regulate the movement of

water between the blood and ECF:

1. Fluid pressure

– 35 mmHg at artery end and 15 mmHg at the vein end

– Lower pressure in the ECF

– Therefore movement of water from the high pressure capillary to the low pressure ECF filtration (of small particles)

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Capillaries 2. Osmotic pressure

– Osmotic pressure draws water back into the capillary due to large proteins and molecules in the blood absorption

Osmotic pressure 25 mmHg Fluid pressure 35 mmHg Absorption -10 mmHg

Osmotic pressure 25 mmHg Fluid pressure 15 mmHg Absorption 10 mmHg

Water moves out Water moves in 20

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Upset of the Balance

• Hemorrhage (excessive bleeding) – Decrease of blood decreases

blood pressure – Lower fluid pressure but

normal osmotic pressure

• Starvation – Often display tissue swelling

(edema) – Plasma proteins used as

energy – Causes low osmotic pressure,

thereby decreasing absorption – More water enters the tissue

spaces than is pulled back into the capillaries, causing swelling

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Lymphatic System • Extra proteins and fluid filtered out of the

blood and are not reabsorbed are returned to the circulatory system via the lymphatic system

• Lymph is a fluid similar to blood plasma

• Carried in open-ended lymph vessels similar to veins

• Lymph is eventually returned to the venous system

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Lymphatic System

• Lymph nodes – enlargements located at intervals along the lymph vessel – House white blood cells

that filter out any bacteria by phagocytosis

– Filter damaged cells and debris from the lymph

– Store lymphocytes (white blood cell that makes antibodies)

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& Recall in digestive tract:

Lymphoid Organs

• Spleen

– Blood reservoir

– Release red blood cells in response to low blood pressure or when blood oxygen drops

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• Thymus Gland

– Where T cells mature (more on this in next chapter)

Nucleus Medical Art. "Anatomy of the Thymus Gland and Surrounding Structures." SMART Imagebase. 3 Apr 2009 10:20 EDT. Nucleus Medical Art. 7 Dec 2009 29

Your Task

• Textbook questions pg 337 #1-3

• Textbook questions page 339 #1-7

• Finish up review assignment

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