Chapter 12, Part 1 – Blood vessels!

Ch. 12, Part 1: Blood Vessels and Circulation!

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Major Vessel Types! Arteries carry blood away from the heart! •  Higher pressure vessels! •  Thick wall compared to lumen size! Capillaries allow exchange between blood and extracellular fluid (ECF)! •  Medium pressure vessels! •  Simple squamous endothelium! Veins carry blood towards the heart! •  Lower pressure vessels! •  Thin wall compared to lumen size! 2!

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Chapter 12, Part 1 – Blood vessels!

Blood Flow DIRECTION Defines Vessel Type! Figure 12.7d!

Arteries! Capillaries!

Veins!

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Blood Vessel Structure "

Know:! Tunica interna! Tunica media! Tunica externa!

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" Figure 12.2"!

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Chapter 12, Part 1 – Blood vessels!

Arteries - General Properties! A. Carry blood AWAY from the heart! B. Elasticity - Stretch and recoil! C. Contractility! •  Vasoconstriction = ↓ vessel diameter! •  Vasodilation (vasodilatation) = ↑ vessel diameter! Contractility affects resistance to blood flow through blood vessels and therefore:! •  Overall (systemic) blood pressure! •  Blood flow through capillaries! 5!

Capillaries (Exchange Vessels)! Connect arterioles to venules! ! Exchange of gases (O2, CO2), nutrients, waste products between blood and tissues occurs here.! Factors influencing capillary exchange:! •  Wall is thin so diffusion distance is small! •  MANY capillaries exist: there is a large surface area for exchange.! •  Blood velocity is low (slow) in capillaries so there is time for exchange to occur.!

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Chapter 12, Part 1 – Blood vessels!

Surface Area and Blood Velocity " Figure 12.5!

Arterial! end!

Venous! end! 7!

Veins Contain Most of the Body’s Blood! Carry blood TOWARDS heart! Act as a blood reservoir! •  Most of your blood is in your veins at any one time.! Small and medium-size veins have valves.! NOTE: The definitions of “artery” and “vein” have NOTHING to do with the amount of oxygen in the blood they each carry. The definitions are based ONLY upon the DIRECTION of blood flow.! 8!

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Chapter 12, Part 1 – Blood vessels!

Venous Valves! Valves prevent backflow towards capillaries due to gravity! Skeletal muscle pump! •  Blood forced in one direction towards heart (see next slide)! •  Can’t flow backwards due to valves!

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Figure 12.6 Venous Valves

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Figure 12.6!

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Chapter 12, Part 1 – Blood vessels!

Blood Pressure! Blood pressure is a hydrostatic pressure =! = pressure exerted by blood against the walls of a blood vessel! 1.  e.g. heart pumps blood → ↑ hydrostatic pressure on walls of vessel! 2.  e.g. gravity pulls on blood → ↑ hydrostatic pressure on walls of vessel (e.g. in ankles)! ! Fluid moves from higher to lower pressure! 11!

Arterial Blood Pressure! Blood pressure (BP) is the pressure exerted by blood against the wall of a vessel.! Systolic (blood) pressure = maximum pressure generated during ventricular contraction! Diastolic (blood) pressure = minimum pressure at end of ventricular relaxation! Pulse pressure = systolic - diastolic pressure! ! BP reported as: "systolic pressure : 120mmHg ! " " " "diastolic pressure "80mmHg! 12!

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Chapter 12, Part 1 – Blood vessels!

Mean Arterial Pressure (MAP)! An index of “average” blood pressure! Factors affecting MAP:!

MAP = CO x PR! CO = cardiac output (e.g. liters of blood per minute)! CO = heart rate (HR) X stroke volume (SV)! PR = total peripheral resistance (to blood flow)! If PR goes up, what happens to MAP?! If HR goes up, what happens to MAP?! If SV goes up, what happens to MAP?!

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Blood Pressures Along the Systemic Circuit "! The Big Picture: ! ! BP decreases ! on the way back to the heart. If it didn’t, blood wouldn’t flow in the direction it does!!!

(F.H. Martini 2004)

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Chapter 12, Part 1 – Blood vessels!

Resistance (to Blood Flow)! Resistance impedes Flow through a tube.! Flow through a tube is inversely proportional to resistance. If resistance increases, flow decreases.! !

Flow α "

1

"α

" resistance"

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"vessel radius4!

" blood viscosity x tube length!

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Resistance α 1 α "blood viscosity x tube length! " " " flow " "vessel radius4 "! 15!

Peripheral Resistance (to Blood Flow)! The major factor determining resistance to flow through a blood vessel is vessel radius (r) because this variable is raised to the 4th power.! Examples:! If r = 1, then r4 = 1; If r = 2, then r4 = 16! So…! Doubling vessel radius decreases resistance by 16x.! Doubling vessel radius therefore increases flow by the same 16x.! How might this effect your blood pressure in daily life?! 16!

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Chapter 12, Part 1 – Blood vessels!

Capillary Exchange - General Features! Depends upon processes of:! •  Diffusion! •  Filtration! •  Reabsorption! ! Slightly more fluid leaves from the arterial end of a capillary than re-enters at the venous end of a capillary! !

The excess tissue fluid (ECF) is returned to the circulation by the lymphatic system! 17!

Filtration of Fluid and Small Solutes! •  Filtration = movement of water and solutes across a semipermeable membrane in response to hydrostatic pressure! •  Solute movement depends on solute size! •  Think of making coffee with a drip coffeemaker! Large proteins do not easily exit the capillary by filtration.!

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Chapter 12, Part 1 – Blood vessels!

Reabsorption of Fluid and Small Solutes! Reabsorption is the result of osmosis! ! Water moves in response to osmotic pressure! Osmotic pressure is proportional to the number of particles in solution! •  Plasma proteins trapped in the blood create blood colloid osmotic pressure! •  These proteins tend to pull water INTO capillaries by osmosis! •  “Water follows salt” Ch. 3, Part 1! 19!

Net Filtration and Reabsorption! Roughly 24 l/day moves out of capillaries! Roughly 20 l/day returned into capillaries! •  So roughly 4 liters day must be returned to circulation via lymphatic vessels! 20!

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Chapter 12, Part 1 – Blood vessels!

Edema: Excess Accumulation of ECF! Accumulation of excess tissue fluid (ECF) is called edema.!

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Lymphatic System! Structure:! •  Lymph: extracellular fluid (interstitial fluid) that has entered …! •  Lymphatic vessels! •  Lymphoid tissues and organs! Contain many lymphocytes! Functions! •  Return ECF to blood! •  Transport fats from small intestine to blood! •  Defense against disease! 22!

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Chapter 12, Part 1 – Blood vessels!

Lymphatic System! Tonsils! ! Right lymphatic duct! ! Thymus! ! Thoracic duct! ! Spleen!

Lymph returns to the blood at the subclavian veins.!

! Lymph vessels! ! Lymph nodes! 23!

Lymph Capillaries! Different than blood capillaries because these:! •  Begin as a blind end! •  Have larger diameters! •  Have thinner walls! •  Composed of endothelial cells that are not tightly bound together - act as one-way valves!

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Chapter 12, Part 1 – Blood vessels!

Lymph Capillaries and Drainage!

Large Lymphatics! •  Larger ones have valves, prevent backflow of lymph! •  Merge to form lymphatic trunks! Largest:! •  Thoracic duct and right lymphatic duct empty into 25! subclavian veins!

Some Lymphatic Organs and Their Functions! Tonsils!

Thymus!

Spleen ! Peyer’s patches! • 

Lymph nodes!

Keep bacteria from breaching the intestinal wall! 26!

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