5 Types Vasa Vasorum, of Blood Blood vessel of the blood

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5 Types Vasa Vasorum, of Blood Blood vessel of the blood

Transcript Of 5 Types Vasa Vasorum, of Blood Blood vessel of the blood

Blood Vessels & Hemodynamics
“Hemo” = blood, “Dynamics” = power Forces involved in circulating blood throughout the body
5 Types of Blood Vessels
1.  Arteries: carry blood away from the heart
2.  Arterioles: very small arteries 3.  Capillaries: tiniest vessels. allow exchange of substances between blood and body tissues
4.  Venules: very small veins 5.  Veins: carry blood back to the heart

What do Blood vessels do?
•  Adjust velocity & volume of blood flow
•  Transport & exchange of substances absorbed from the outside world & those produced by the deepest, tiniest tissues of our bodies
–  Eg O2, CO2, nutrients, cellular metabolic wastes, hormones etc.
Vasa Vasorum, Blood vessel of the blood vessel
•  Larger blood vessels require smaller blood vessels to supply oxygen and nutrients to their smooth muscle tunica media
•  Vasa Vasorum means ‘blood vessels of the blood vessels’
–  Small vessels located within larger vessels

Arteries and Veins have 3 Tunics (Coats)
1.  The Tunica Interna (intima), also called the endothelium. The innermost layer is only 1-cell thick and made of flat cells.
2.  The Tunica Media has smooth muscle cells + Elastic fibers for regulating the diameter of the lumen
3.  The Tunica Externa is made of collagen + elastic fibers. This outermost covering contains nerves, vasa vasorum, and anchors the vessel to the surrounding tissue
Blood vessel types and functions

Elastic = Conducting Arteries Muscular = Distributing Arteries Resistance Arterioles
Largest arteries:ELASTIC ARTERIES
•  Have the largest diameter, but their walls are relatively thin. Examples: the aorta or pulmonary artery
•  They function as a PRESSURE RESERVOIR:
–  They stretch when the ventricle pumps blood into them.
–  ** when the ventricles relax, they recoil, propelling blood forward
•  Also called conducting arteries because they conduct blood from the heart to the medium-sized arteries

Elastic lamellae

•  Layers of elastic fibers in the tunica media, elastic lamellae, make elastic arteries able to stretch & RECOIL which maintains diastolic blood pressure.

•  Elastic fibers give arteries high compliance, the ability to stretch in response to pressure without tearing

Systolic and Diastolic Pressure
•  Initial blood pressure is generated by contraction of the Left Ventricle & CO (eg. 120mm Hg)
•  Systolic BP: the highest pressure attained in the arteries during systole
•  Diastolic BP: the lowest arterial pressure during diastole
•  BP falls progressively with distance from left ventricle. BP is 0 at Right ventricle


Blood Pressure generation

‘Blood Pressure’ refers to the Hydrostatic pressure exerted by blood on the wall of a blood vessel

Blood Pressure depends on: 1.  Cardiac Output 2.  Vascular Resistance 3.  Total Blood Volume

Blood Pressure = Cardiac Output x Resistance

•  The elastic vessels cushion the pulsations generated by the heart

Checking BP & Pulse

•  Pulse: stretch & recoil of elastic arteries create the wave •  Heart rate creates the rate
–  Normal: 70-80 bpm –  Tachycardia: >100 bpm –  Bradycardia: < 50 bpm
•  BP cuff & stethoscope:. Cut off circulation to the arm with a BP cuff. listen for Karotkoff sounds as you release and reduce the pressure in the cuff –  First sound heard = systolic BP, Last sound heard = diastolic BP

Pulse Pressure vs Mean Arterial Pressure (MAP)
•  The difference between systolic & diastolic pressure is called the pulse pressure
•  The average of the systolic and diastolic pressures is called the mean arterial pressure
Medium sized Muscular Artery
•  Capable of great vasoconstriction / vasodilation to adjust vessel pressure & thus rate of blood flow
•  Muscular arteries have more smooth muscle, fewer elastic fibers in the tunica media

(FYI) Pulse pressure: young vs old
•  As we age, vessels become harder and more dilated.
•  The can no longer cushion the wave
•  So, both pulse pressure and pulse wave velocity increase
Changes Vessel Diameter
SMOOTH MUSCLE allows artery to contract or dilate, changing vessel diameter
•  Vasoconstriction: a decrease in lumen diameter –  Sympathetic innervation
•  Vasodilation: an increase in lumen diameter –  Parasympathetic (ACh), NO, H+, lactic acid
•  Vasospasm: constriction of an artery when it’s damaged to reduce blood loss

•  The great vasoconstriction or vasodilation, determines the distribution, or % of blood that goes to the various parts of the body
•  Muscular arteries are also called distributing arteries
1.  Arterioles Regulate RESISTANCE TO BLOOD FLOW –  Resistance is due to friction between blood & blood vessel wall –  Sympathetic nerves in the tunica externa constrict vessels –  More sympathetic constriction, more friction, more resistance to flow
2.  Arterioles Regulate blood flow into capillaries –  The terminal portion of an arteriole is called the “metarteriole” –  Each metarteriole has various precapillary sphincters which control blood flow into capillaries

HEMODYNAMICS: factors affecting Blood Flow
•  Blood Flow (mL/min) = volume of blood flowing through any tissue in a given period of time
•  Total Blood Flow = Cardiac Output (CO) –  Volume of blood circulating through the systemic (or pulmonary) vessels each minute. –  CO = heart rate (HR) x stroke volume (SV)
•  Distribution of CO depends on: 1.  Pressure differences •  blood flows from high to low pressure. greater pressure difference= greater blood flow 2.  A Vessel’s resistance to blood flow •  The higher the resistance, the smaller the blood flow
1.  Elastic or Conducting arteries
–  Pressure reservoir. Maintains diastolic /constant flow
2.  Muscular or Distributing arteries
–  Distribute blood to organs (%) –  Regulate rate of blood flow (mL/min)
3.  (Resistance) Arterioles
–  Regulate resistance to blood flow –  Regulate flow of blood into capillaries
4.  Arteriolar Capillaries
–  Exchange vessels

Capillary Beds & Metabolic Activity

Section 2

•  Capillary beds: 10-100 capillaries arise from 1 metarteriole •  Throughfare channel: the distal end of a metarteriole can bypass a capillary bed •  Usually only a small part of a capillary network is full. but, when a tissue is active
(i.e. contracting muscle), the entire network fills with blood •  Tissues with high metabolic activity eg muscles, liver, kidneys, nervous system
have more capillaries •  Tissues with lower metabolic activity eg tendons, ligaments have less capillaries •  No capillaries in a few tissues, such as cornea, lens of the eyes, and cartilage
VELOCITY of Blood Flow Slows at branched capillaries

•  The “Microcirculation of the body” refers to blood flow through 1) metarterioles 2) capillaries and 3) postcapillary venules
•  Capillaries connect arterioles to venules. Metarterioles contract and relax spontaneously.

•  Velocity (cm/sec) depends on branching:
–  When an artery branches, cross sectional area increases, so velocity of flow decreases
–  When venules merge to form a vein, cross sectional area decreases so velocity increases
–  Thus blood flow is slowest at capillaries which is good for exchange of materials
•  Circulation time: time it takes 1 drop of blood to go from R atrium, to pulmonary & systemic circulation and back to R atrium - Normally 1 min at rest

•  Vasomotion: the spontaneous, intermittent contraction & relaxation of metarterioles creates intermittent blood flow through capillaries
1. CONTINUOUS –  Endothelial cells form a continuous tube except for intercellular clefts •  Found in brain, lungs, skeletal & smooth muscle
2. FENESTRATED (‘windowed’) –  The plasma membrane has fenestrations or pores •  Found in kidneys, villi of small intestine, choroid plexus in brain, endocrine glands
3. SINUSOID –  Wider, more winding –  Large fenestrations and an incomplete basement membrane –  Protein & RBCs can pass •  Found in red bone marrow, liver, spleen, anterior pituitary

CAPILLARIES: Exchange Vessels
•  Have no tunica media, no tunica externa, no innervation - just endothelial cells & a basement membrane
•  Exchange vessels: Their primary function is to exchange substances between blood and interstitial fluid
Capillary Exchange
There are 3 ways to exchange substances between the blood & the
interstitial fluid: 1.  Diffusion (a) 2.  Transcytosis (b) 3.  Bulk flow (d,e

Capillary Exchange

•  Solutes can diffuse from high concentration to low concentration, crossing capillary walls through the: 1.  Lipid bilayer of Endothelial cell 2.  Intercellular clefts 3.  Fenestrations
•  Plasma Proteins normally cannot cross capillary walls
•  However, in sinusoid capillaries, proteins & even RBCs can cross. Eg, in the: –  Liver: plasma proteins cross fibrinogen & albumin –  Red marrow: RBCs cross
•  Blood-brain barrier has tight junctions that limit diffusion


•  Used to transport large, lipid-insoluble molecules that cannot cross the capillary walls in any other way
–  Eg insulin, antibodies
•  Substances from the blood plasma enter capillary endothelial cells by endocytosis and exit the other side, into the interstitial space, by exocytosis

Direction of movement of some substances
–  From Blood to ECF to Cells:
•  O2 •  Glucose •  Amino acids •  Hormones
–  From Cells to ECF to Blood:
•  CO2 •  Wastes
3. BULK FLOW: Filtration / Reabsorption
•  Due to pressure differences, FLUID with large numbers of ions, molecules, & particles dissolved in it, will cross the capillary. –  Movement occurs from high pressure to low pressure –  faster rate than diffusion
•  Diffusion is about specific solute & depends on concentration gradient
•  Bulk flow depends on pressure & is more about fluid with solutes in it.
•  Regulates relative volumes of blood and interstitial fluid
•  Filtration: flow from capillaries into interstitial fluid
•  Reabsorption: flow from interstitial fluid into capillaries

BULK FLOW: Osmotic & Hydrostatic Pressure
1.  Blood hydrostatic pressure (BHP) – pressure generated by pumping action of the heart
2.  Interstitial fluid osmotic pressure (IFOP) ≈ 1
1.  Blood colloid osmotic pressure (BCOP) - created by concentration of plasma proteins in suspension
2.  Interstitial fluid hydrostatic pressure (IFHP) ≈ 0
Starling’s Law Of The Capillaries
•  Nearly as much fluid is reabsorbed as was filtered
–  85% of the fluid that was filtered is then reabsorbed
–  Not 100% fluid returns because a few plasma proteins leave vessels into interstitial space
–  Remainder of fluid & proteins enter lymphatic capillaries (3L/ day) & is eventually returned to blood

Net Filtration Pressure
•  Indicates final direction of fluid movement •  Net Filtration Pressure (NFP) = (pressures that promote
filtration) - (pressures that promote reabsorption) –  Arterial end: net pressure out: 10mmHg so fluids tend to leave
Venous end: net pressure in: -7mm Hg so fluids tend to be absorbed
Bulk flow to Lymphatic circulation
•  Bulk flow creates interstitial fluid which then flows into the lymph and finally returns to the blood vessels

Section 3

Lymphatic circulation

EDEMA: Increased interstitial fluid


•  An abnormal increase in interstitial fluid volume occurs if there is:
–  Increased filtration of fluid & solutes out of capillary due to: •  Increased capillary permeability to plasma proteins •  increased blood pressure
–  Or, decreased reabsorption of fluid & solutes from ECF due to: •  Decreased # of plasma proteins in capillaries from liver disease, burns, malnutrition, kidney disease
•  Same three tunics as arteries: interna, media, externa –  Tunica externa is thickest layer
•  Thinner walls - so the lumen of vein is larger than the lumen of a comparable artery
•  Not designed to withstand high pressure
•  Many veins contain valves –  Valves are thin folds of the tunica interna –  Cusps point towards the heart –  Prevent backflow of blood
BloodPressureFluidArteriesBlood Flow