Chapter 14 Blood vessels, blood flow, blood pressure
As blood enters capillary beds, velocity of blood flow __________
Decreases
When the resistance increases blood flow _______
Decreases
What are sinusoids? What type of cells do they have?
Large blood filled spaces that function in the exchange of substances between blood and tissue Have phagocytes
Describe fenestrated capillaries
Large pores that allow for rapid diffusion of small water soluble substances
Vein anatomy
Larger diameter than arteries but walls are only half as thick Walls contain smooth muscle, elastic and fibrous connective tissue Contain one-way valves that permit blood flow toward the heart but prevent it from flowing back to organs/tissues (only in peripheral veins not central veins)
Capillaries contain _______ walls
Leaky
What condition occurs when MAP is less than normal? Higher than normal?
Less: hypotension Higher: hypertension
what type of muscle do arterioles have? What does this allow?
Lined with smooth muscle that can relax/contract allowing resistance of blood flow to be regulated
The Aorta has ____ resistance
Little
Hormonal control of MAP
Long term Regulates blood volume
Blood pressure in veins is significantly ________than arteries
Lower
Mean arterial pressure equation
MAP = SV x HR x TPR
How to calculate mean arterial pressure
MAP= (SP+ (2DP))/3 MAP= CO x TPR
Describe the continuous capillaries
Most common type of capillaries Contain intracellular clefts (narrow spaces between tight junctions of continuous capillary endothelial cells) Highly permeable to water soluble substances with small molecular size and lipid soluble substances
Net filtration pressure formula
NFP= filtration pressure - absorption pressure (Pcap + Piif) - (Pif- picap)
What are four intrinsic mechanisms to regulate blood flow? What do they do
Nitric oxide: vasodilation Prostacyclin: Vasodilation Adenosine: vasodilator in coronary arteries Endothelin 1: vasoconstrictor
Does the parasympathetic nervous system innervate arteriolar smooth muscle? Is there any exceptions?
No except in external genitalia vasodilation
What happens in arterioles With increased sympathetic nerve activity
Norepinephrine binds to alpha adrenergic receptors (vasoconstriction) Increase TPR Increase MAP
What is interstitial osmotic pressure? What does it usually favor?
Osmotic force exerted by proteins in the interstitial fluid Favors filtration
Calloid osmotic pressure (oncotic pressure)
Osmotic pressure that is exerted by proteins
In the systemic circuit what are the formulas for pressure gradient
P= pressure in aorta- pressure in vena cava P= MAP- CVP
In the pulmonary circuit what is the formula for pressure gradient
P= pulmonary arterial pressure- pulmonary venous pressure
Describe discontinuous capillaries
Serve as a transition from fenestrated capillaries to sinusoids Found in areas where proteins and cells must cross the endothelium
arterioles function
Serves as passageway for blood to enter capillaries where exchange between blood and tissue takes place
Neural control of mean arterial pressure
Short term Regulates CO and TPR Managed through negative feedback control Controlled by integration center (cardiovascular control center) of the medulla oblongata
What are the three types of exchange across capillary walls
Simple diffusion Transcytosis Mediated transport
Describe simple diffusion
Small solutes (lipid and water soluble) move across capillary walls by simple diffusion Lipid soluble solutes diffuse across the plasma membrane of endothelial cells Water soluble solid to diffuse through water filled pores between endothelial cells
Venule anatomy
Smaller than arterioles with thinner walls that contain little or no smooth muscle
Describe the anatomy of capillaries
Smallest blood vessels Thin walls consisting of a single layer of endothelial cells with pores between them (allows for small diffusion)
The _________ muscle in the walls of veins contract or relax in response to input from the ___________nervous system and certain chemical agents
Smooth Sympathetic
What are precapillary sphincters? How are they controlled?
Smooth muscle that surrounds capillaries on the arteriolar end that regulate blood flow through capillaries Affected by local control Increase in metabolites relax sphincters and increase blood flow through capillaries
What are four factors that affect venous pressure
skeletal muscle pump, respiratory pump, blood volume, venomotor tone
What Instruments are used to measure blood pressure
sphygmomanometer and stethoscope
Pulse pressure formula
systolic pressure - diastolic pressure
Blood pressure formula
systolic/diastolic
What makes up microcirculation
arterioles, capillaries, venules
myogenic response
A change in vascular resistance that occurs in response to stretch of blood vessels Does not require actions of sympathetic nerves, hormones, other chemical agents
What happens upon standing that makes a person feel dizzy
A drop of MAP and increase in hydrostatic pressure upon standing (orthostatic hypotension) may cause a person to feel dizzy because of decrease in blood flow to the brain
Edema
A shift in fluid from plasma to interstitial fluid that causes swelling of tissues
Describe blood volume as it relates to venous pressure
An increase in blood volume produces an increase in venous pressure and MAP A decrease in blood volume produces a decrease in venous pressure and MAP
What happens when there is an increase in Venomotor tone
An increase in venomotor tone promote a rise in CO and MAP
Where are Arterial baroreceptors (aka sinoaortic baroreceptors)
Aortic arch and carotid sinus of carotid arteries
Arterial end of capillaries is for ________ while venous end is for ________
Arterial end filtration Venous end reabsorption
What type of vessel has the largest pressure drop because of its high resistance
Arterioles
What type of vessels provide the greatest resistance to blood flow?
Arterioles
________ contribute to 60% of TPR
Arterioles
what happens in arterioles When Eppinette friend secreted from the adrenal medulla in response to sympathetic activity binds to Alpha receptors? Binds to beta-2 receptors?
Binding to alpha receptors causes vasoconstriction Binding to beta to receptors activates CAMP which causes vasodilation and decreased resistance of blood flow
What are the 4 Starling forces?
Capillary hydrostatic pressure (Pcap) • interstitial fluid hydrostatic pressure (Pif) • capillary osmotic pressure (piCAP) • Interstitial fluid osmotic pressure (piif)
_______ hydrostatic pressure and _______ Osmotic pressure favor filtration
Capillary hydrostatic pressure and interstitial fluid osmotic pressure
Total peripheral resistance
Combined resistance of all the blood vessels within the systemic circuit
What does venules connect? What is their function?
Connect capillaries to veins Exchange between blood and interstitial occurs in capillaries and small venules
Vasomotion
Contraction and relaxation of precapillary sphincter's
What does venomotor tone
Degree of tension exerted by smooth muscles in walls of vein
Capillary hydrostatic pressure
Favors filtration Equal to the blood pressure in capillaries Blood pressure decreases as blood flows from the arteriolar end of the capillary to the Venule end
Capillary osmotic pressure
Favors reabsorption Does not change his blood flows from one end of the capillary to the other
Interstitial fluid hydrostatic pressure
Favors reabsorption Is usually low
Filtration and absorption in capillary walls
Filtration: fluid moving from blood to interstitial fluid Absorption: fluid moving from interstitial fluid to blood
How to calculate Oregon blood flow
Flow= P/ organ resistance Flow= MAP/ organ resistance
flow rate formula
Flow= P/R
Osmotic pressure
Force exerted on water by non-permeating solutes
The systemic circuit has _______ resistance
Greater
Veins have _______ compliance
High (A large increase in blood volume is required for a large increase in pressure)
What end of a capillary is NFP higher? Lower?
Higher at arteriolar end Lower at venule end
active hyperemia
Increase in blood flow following an increase in metabolic activity (observed during exercise)
Changes associated with increased metabolic activity causes ________ while changes associated with decreased metabolic activity causes ________
Increased metabolic activity causes vasodilation Decreased metabolic activity induces vasoconstriction
Describe the process of the respiratory pump when you inhale
Inhale -> diaphragm pulls downward and rib cage expands -> lowers pressure in thoracic cavity and raises pressure in abdominal cavity -> pressure gradient that promotes the movement of blood from abdominal veins to central veins -> increasing blood flow toward the heart
What are meta-arterioles? What are their functions
Intermediate between arterioles and capillaries Serve as shunts by directly connecting arterioles to venules
_______ hydrostatic pressure and _______ Osmotic pressure favor absorption
Interstitial fluid hydrostatic pressure and capillary osmotic pressure
What does intrinsic controls use to regulate blood flow? What does extrinsic control use to regulate MAP?
Intrinsic control uses metabolites that regulate blood flow Extrinsic controls use the ANS and hormones to regulate mean arterial pressure
arteriolar tone
Partial vasoconstriction of arterioles due to inherent contractile activity of smooth muscle
How to calculate hydrostatic pressure gradient
Pcap- Pif
perfusion pressure. What happens to blood flow and arterial pressure if perfusion pressure increases?
Pressure gradient that drives blood flow through a given organ or tissue If perfusion pressure increases blood flow increases and arteriolar pressure rises
Arterial baroreceptors
Pressure in aortic arch and carotid sinus
What is the Function of capillaries
Primary site where exchange of nutrients and waste products occur between blood and tissues
Describe transcytosis
Proteins are selectively transported across endothelial cells Requires energy Uses endocytosis and exocytosis
Describe mediated transport
Receptor mediated Certain solutes are transported across endothelial cells by mediated transport in the brain
A decrease in oxygen and increase in CO2 causes ________ of arteriolar smooth muscle
Relaxation
What are Starling forces?
The forces that drive the movement of fluid into an out of capillaries
What vessel is the volume Reservoir
Veins are the volume reservoir (blood reservoir) due to high compliance
The pulmonary and systemic circuit have different or the same pressure gradient
The pressure gradient is smaller in the pulmonary circuit because the pulmonary arterial pressure is lower than aortic pressure
What is the respiratory pump
The rise in thoracic pressure drives the forward movement of blood from the central veins to the heart, thereby promoting increased venous return and CO (increase in venous pressure)
The pulmonary and systemic circuit have different or the same flow
The same
What are the largest veins
Vena cavae
How does long-term regulation of blood pressure occur
Through blood volume regulation
In vasculature, what is the tunics intima, túnica media, and túnica externa
Tunica intima: internal elastic membrane endothelial layer Tunica media: external elastic membrane made of sheets of smooth muscle and loose connective tissue Tunica externa: smooth muscle in veins made of collagen and elastic fibers
How is turbulence caused? What does turbulent blood flow cause?
Turbulence is caused when pressure inside the artery is higher than pressure outside of it which forces the vessels to open and causes turbulent blood flow into the artery through a narrow opening. Causes audible vibrations (korotkoff sounds)
A decrease in metabolic activity causes a decrease in CO2 and increase in oxygen which causes _______ of arterioles
Vasoconstriction
What is vasoconstriction? What is vasodilation?
Vasoconstriction: decrease in vessel radius Vasodilation: increase in vessel radius
What two hormones cause vasoconstriction and increase MAP in arterioles
Vasopressin (ADH) Angiotensin II
What are the three main factors affecting blood flow
Vessel radius (as radius decreases, resistance increases) Vessel length (longer vessels have greater resistance) Blood viscosity (as viscosity increases resistance increases)
What happens when NFP is positive? When it's negative?
When NFP is positive filtration occurs. When NFP is negative absorption occurs.
What happens when arterial pressure rises and arteries expand
When arterial pressure rises -> arteries expand (stretching their walls and sensory endings of the baroreceptors within them) -> induces depolarization -> triggers action potentials conducted to CNS via baroreceptor axons
What is the skeletal muscle pump
When skeletal muscles contract, they press against veins traveling between them, which raises the venous pressure of blood Increased pressure -> forces distal valves to close -> prevents blood from flowing backward -> forces proximal valves to open -> allows blood to flow toward the heart
Baroreceptors
a type of sensory receptor neuron in blood vessels and the heart that respond to changes in pressure within the cardiovascular system
Venus pooling
accumulation of blood in the veins
________ are pressure reservoirs. Which means they have _____ compliance.
arteries Low compliance ( A small increase in blood volume causes a large increase in blood pressure)
What are the three types of capillaries
continuous, fenestrated, sinusoidal (discontinuous)
Arteries have ______ blood pressure
highest
reactive hyperemia
if blood supply cut off then restored, flow increases above normal
What happens when there's an increase in venous pressure
increase in venous pressure enhance venous return -> increases end diastolic volume -> increases stroke volume -> increases CO -> increases MAP
