Circulation components and control
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Circulation: Components and Control. Vessels, Blood, Blood Pressure, Regulation, Heart Disease, Clotting. AP Biology Unit 6. Blood Flow through Vessels. Arteries (and arterioles) Thick, muscular walls Walls also contain collagen and elastic fibers (make them stretchable)

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Circulation: Components and Control

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Circulation components and control

Circulation: Components and Control

Vessels, Blood, Blood Pressure, Regulation, Heart Disease, Clotting

AP Biology

Unit 6

Blood flow through vessels

Blood Flow through Vessels

  • Arteries (and arterioles)

    • Thick, muscular walls

    • Walls also contain collagen and elastic fibers (make them stretchable)

    • Can be constricted or dilated

Slide 2 of 23

Blood flow through vessels1

Blood Flow through Vessels

  • Veins (and venules)

    • Thinner walls

    • one-way valves to prevent blood from flowing backwards

    • Blood in veins is moved by the contractions of skeletal muscles around them (“milking”)

Slide 3 of 23

Blood flow through vessels2

Blood Flow through Vessels

  • Capillaries

    • Thin walls (usually one cell layer thick)

    • Permeable to water, ions, other small molecules

    • Blood flows slowly through them (red blood cells often have to travel single file)

    • Every cell in the body is close to at least 1 capillary

Slide 4 of 23



  • Capillaries must exchange materials between the blood and the interstitial fluid

  • Blood pressure and osmotic pressure drive the movement of molecules into and out of capillaries

    • Blood pressure forces water and solutes out (on the artery side)

    • Osmotic pressure (due to the proteins left in the capillaries) causes water to flow back into the capillaries by osmosis

Slide 5 of 23



  • How does the structure of each type of vessel support its function?

    • Arteries– thick walls can withstand pressure from heart pumping blood

    • Veins- valves help prevent backflow since the heart is too far away to provide forward pressure (to push the blood back to the heart)

    • Capillaries- very thin walls allow for easy exchange with the interstitial fluid

Slide 6 of 23

Blood pressure

Blood Pressure

  • Blood pressure = the force being applied to the blood vessel walls (from blood).

  • 2 phases of the cardiac cycle

    • Systole = when the heart muscle is contracting

    • Diastole = when the heart muscle is relaxed (between contractions)

Slide 7 of 23

Blood pressure1

Blood Pressure

  • Systolic Pressure = pressure in arteries when heart contracts

  • Diastolic Pressure = pressure in arteries between contractions

Slide 8 of 23



  • Giraffes need higher blood pressure. Why?

  • Since they are taller, they need more pressure to get the blood all the way to the top of their bodies

Slide 9 of 23

Control of circulation

Control of Circulation

  • Heart rate is controlled by

    • Nerve impulses sent to SA and AV Nodes

    • Hormones (adrenaline/epinephrine)

    • Body temperature

    • Oxygen requirements due to exercise

Slide 10 of 23

Control of circulation1

Control of circulation

  • The opening of sphincters leading to capillary beds is controlled by

    • Nerve impulses

    • Hormones

    • By controlling these sphincters, blood can be directed to specific parts of the body under stressful conditions

Slide 11 of 23

Control of circulation2

Control of Circulation

  • The Lymphatic System also plays a role in controlling circulation

    • Maintains fluid levels so blood pressure can remain constant

    • Lymph = fluid (like interstitial fluid, high in water and other nutrients)

    • Filters body fluids before allowing them to flow back into the circulatory system

    • Fluids flow out and into capillaries via blood pressure and osmotic pressure

Slide 12 of 23



  • From what part of the Digestive System did lymph flow from?

    • Small intestines (lacteals in the villi)

Slide 13 of 23

Components of blood

Components of blood

  • Plasma

    • Water, nutrients, proteins, ions, etc.

  • Cellular Components

    • Red blood cells (carry oxygen)

    • White blood cells (immune function)

    • Platelets (clotting)

Slide 14 of 23

Differentiation of blood cells

Differentiation of Blood Cells

  • Blood cells (RBC, WBC and platelets) all develop from stem cells in the red bone marrow.

  • Erythropoietin (EPO) is a hormone that promotes the production of erythrocytes (RBC)

    • Synthesized in the kidneys

Slide 15 of 23



  • When the body is not receiving enough O2, what will happen to EPO levels?

    • They increase to create more RBC to carry O2

  • If a patient is anemic (low iron levels in the blood), why might the doctor prescribe synthetic EPO?

    • Iron is the central part of hemoglobin that carries oxygen in RBC

Slide 16 of 23



  • How would taking synthetic EPO help with athletic performance?

    • Having more red blood cells would improve oxygen transport abilities  more endurance

Slide 17 of 23

Blood clotting

Blood clotting

  • Platelets begin the clotting reaction

    • damage in the blood vessel wall exposed collagen fibers

    • Platelets stick the collagen release substances to make other platelets sticky

  • Clotting factors = released by platelets to activate enzymes needed for clotting

Slide 18 of 23

Blood clotting1

Blood Clotting

  • STEPS:

  • Platelets adhere to the damaged region and become sticky release clotting factors

  • Clotting factors cause Prothrombin (inactive) to become Thrombin (active)

  • Thrombin causes Fibrinogen (plasma protein) to become fibrin (active form)

  • Fibrin forms threads that help seal the damaged area up

Slide 19 of 23

Cardiovascular disease

Cardiovascular Disease

  • Atherosclerosis = narrowing of arteries due to plaque build up

    • plaque deposits as a result damage to the vessel lining

    • Plaque desposits narrow the pathway for blood to flow

    • If the plaque is ruptured it will also cause clotting to occur– blocks pathway of blood

Slide 20 of 23

Cardiovascular t disease

Cardiovascular t Disease

  • Atherosclerosis can lead to heart attack or stroke

    • Heart attack – blockage in the arteries that supply the heart with blood

    • Stroke = blockage in an artery in the brain

Slide 21 of 23

Heart disease and cholesterol

Heart Disease and Cholesterol

  • Cholesterol travels in the blood (plasma)

  • Low Density Lipoproteins (LDLs) are associated with cholesterol deposits in arteries = “bad” cholesterol

  • High Density Lipoproteins (HDLs) appear to reduce cholesterol deposition = “good” cholesterol

  • What seems to matter is the ratio of HDL to LDLs in your blood

Slide 22 of 23

Cholesterol and lifestyle choices

Cholesterol and lifestyle choices

  • While there is a genetic component to cholesterol levels, lifestyle choices also influence it

    • Exercise increases HDL levels

    • Smoking increases LDL and lowers HDL levels

Slide 23 of 23

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