WEEK 2 Flashcards
WHAT Two sounds are associated with closing of heart valves?
First sound (LUB ~ S1) AND Second sound (DUB ~ S2)
when does First sound (LUB ~ S1) occur?
occurs as atrioventricular valves close
what does First sound (LUB ~ S1) signify?
signifies the beginning of systole (ventricles contracting and pumping blood)
auscultation points of First sound (LUB ~ S1)
auscultation points are between the left 5th and 6th ribs (L)
when does Second sound (DUB ~ S2) occur?
occurs when semilunar valves close at the beginning of ventricular diastole (relaxed and filling with blood)
auscultation points of Second sound (DUB ~ S2)
auscultation points are between 2nd and 3rd ribs (L & R)
Arteries functions
carry blood away from the heart
branch and diverge as they form smaller vessels
carry oxygenated blood (except for pulmonary arteries- which carry deoxygenated blood)
blood flow order of arterioles, capillaries and arteries.
arteries —>arterioles —>capillaries
Veins function
carry blood toward the heart
join, merge and converge into larger vessels
have valves
carry deoxygenated blood(except for pulmonary veins (which carry oxygenated blood)
blood flow order for veins, capillaries, venules
capillaries—>venules—>veins
Three main layers found in all arteries
Tunica Intima/Interna (innermost layer), Tunica Media (middle layer), Tunica Externa (outermost layer)
Tunica Intima/Interna (innermost layer) Contacts ….
Contacts the vessel lumen
Tunica Intima/Interna (innermost layer) consists of
consists of endothelium (↓fluid friction)
the basement membrane and the internal elastic lamina
what is Tunica Media (middle layer) innervated by?
Innervated by the sympathetic nervous system – e.g. ↑ stim. = vasoconstriction and ↓ stim. = vasodilation (due to the recoil of the wall)
what does Tunica Media (middle layer) consist of?
consists of a muscular layer and external elastic lamina
what does Tunica Externa (outermost layer) consist of?
connective tissue.
larger arteries contain vasa vasorum (small blood vessels that supply tunica externa) contain nerves which pass to the tunica media
Tunica Externa (outermost layer) provides
provides anchorage and protection
what artery is the closest to the heart?
Elastic artery
functions of Elastic artery:
delivers blood to regions
largest lumen diameter (~ low resistance)
more elastic
act as pressure reservoirs: expand and recoil as blood is ejected from the heart blood flows smoothly rather than in a pulsatile manner.
Elastic artery examples
e.g. Aorta, Pulmonary trunk, etc.
Muscular Artery delivers
delivers blood to organs
Muscular Artery consists of
more smooth muscle in tunica media (which means more active in vasoconstriction and less distensible)
Muscular Artery examples
e.g. brachial arteries, radial arteries, femoral arteries, etc
Arteriole delivers
delivers blood to tissues
Arteriole consists of
very small lumen
what determines Arteriole’s blood flow to capillaries
arteriole diameter determines blood flow to capillaries (constriction causes tissues to be by-passed (shunting) and dilation increase flow to capillary bed)
Arteriole examples
e.g. kidney arterioles, brain arterioles, pulmonary arterioles, etc.
Capillaries are
the smallest blood vessels
capillaries deliver
deliver blood to tissues and cells
lumen is just big enough for a
single erythrocyte to pass along
Capillaries consists of
consists of a single layer of tunica intima (endothelium and basement membrane), which does not contain smooth muscle
most tissues have a rich capillary supply except for…
most tissues have a rich capillary supply (except for tendons, ligaments, cartilage and epithelium)
main function of capillaries
main function is to exchange O2, CO2, nutrients, hormones, etc., between blood and interstitial fluid
types of Capillaries
3 structurally different types: continuous, fenestrated and sinusoidal
Continuous capilaries are
most common and least permeable
Continuous capilaries are abundant in
skin and muscles
endothelial cells provide an uninterrupted (“continuous”) lining for
Continuous capilaries
in continuous capilaries there are tight…
tight junctions between cells
small gaps called intercellular clefts which allow limited passage of fluids and small solutes
…….. are more permeable than continuous capillaries
Fenestrated capillaries
endothelial cells contain
endothelial cells contain fenestrations (pores)
Fenestrated capillaries are found…..
found wherever active capillary absorption or filtrate formation occurs such as; small intestine ~ nutrients, endocrine organs ~ hormones into bloodstream and kidneys ~ filtration of blood(pores are constantly open.
Sinusoidal capillaries is the most …
permeable and has modified, leaky capillaries
Sinusoidal capillaries lumen shape
large, irregular-shaped lumens
in sinusoidal capillaries endothelial cells contain….
endothelial cells: contain large fenestrations (pores), have fewer tight junctions and have larger intercellular clefts
Sinusoidal capillaries allows for….
large molecules and RBCs to pass through
Sinusoidal capillaries are found….
only in the: liver, bone marrow, spleen, adrenal medulla
what are capillary beds?
Capillaries do not function independently they form networks called capillary beds
what is microcirculation
The flow of blood from an arteriole to a venule is called the microcirculation
Sinusoidal capillaries Consists of two types of vessels
Consist of two types of vessels: vascular shunt/meta-arteriole: directly connects the arteriole and venule. AND true capillaries: where the exchange actually takes place.
Blood flow in Sinusoidal capillaries is regulated by…
Blood flow is regulated by pre-capillary sphincters
what is Capillary exchange
Capillary exchange is the movement of fluid and dissolved materials in and out of a capillary
The capillary wall is …..membrane meaning….
The capillary wall serves as a semipermeable membrane –> does not allow blood cells and plasma proteins to move through (selectivity based on size of particles)
3 Layers of the capillary wall:
endothelial cells for lipid soluble substances: substances pass directly through the endothelial cells, includes; respiratory gases, alcohol, amino acids, sugars, etc
fenestrations (pores) in endothelial cells in fenestrated capillaries for larger and water soluble substance
intercellular clefts between endothelial cells for water soluble substances
why cant capillary exchange occur through simple diffusion
While capillary exchange could occur through simple diffusion (movement down a concentration gradient), this process would be very slow. Instead, fluid is forced to move in and out of the capillaries (carrying dissolved substances) – this transport mechanism is called bulk flow
what is Bulk flow
Bulk flow occurs in response to action of opposing forces (pressures)
Two steps in bulk flow: – filtration of fluid through the capillary walls into the interstitial space and – reabsorption of fluid into the capillary blood.
what is Filtration in bulk flow
Filtration is a selective movement of material into interstitial fluid through the capillary walls, that acts as a filter, it is directed outwards – promoted by blood hydrostatic pressure (the force exerted by a fluid pressing against a capillary wall)
what is reabsorption in bulk flow
Reabsorption is movement of material from interstitial fluid into capillaries – directed inwards. Promoted by blood colloid osmotic pressure (the force opposing hydrostatic pressure, contributed by proteins that cannot move through the capillary wall, such molecules are close to the capillary and draw water towards themselves).
Difference between blood hydrostatic pressure and blood colloid osmotic pressure is
Difference between blood hydrostatic pressure and blood colloid osmotic pressure is filtration pressure – it determines if fluid is moving from capillaries into interstitial space or in the opposite direction.
How do the pressures drive fluid flow across a capillary?
Net filtration occurs at the arteriolar end of a capillary
lymphatic system role in fluids
During capillary exchange a large amount of fluid move out into the interstitial space
The lymphatic system functions to reabsorb the fluids which have leaked into interstitial spaces (spaces between cells) and return it to blood circulation
Three main layers are found in all veins
Tunica Intima/Interna (innermost layer): contacts the vessel lumen, consists of endothelium (↓ fluid friction) and basement membrane, contain valves (except for venules)
Tunica Media (middle layer): innervated by the sympathetic nervous system, e.g. ↑ stim. = venoconstriction ↓ stim. = venodilation (due to the recoil of the wall), consists of a muscular layer
Tunica Externa (outermost layer): connective tissue, provides anchorage and protection, larger veins contain vasa vasorum (small blood vessels that supply tunica externa), contain nerves which pass to the tunica media
when are Venules formed
formed when capillaries unite
venule lumens
very small lumens
venules are extremely …
extremely porous (more like capillaries than veins), fluid and leukocytes (WBCs) move in and out easily
venules example
e.g. kidney venules, brain venules, pulmonary venules, etc.
Vein (medium) formed when
Vein (medium)
formed when venules unite
vein (medium) lumens
large lumens
Vein (medium) function/role
accommodate large blood volume
under lower pressure than arteries
Vein (medium) possess
possess venous valves (folds of tunica intima), most abundant in the veins of the limbs, where upward flow is opposed by gravity
outer and middle layer of vein medium
thick tunica externa
thin tunica media
vein (medium) etc.
e.g. cephalic vein, saphenous vein, et
Vein (large) formed when
Vein (large) formed when medium sized veins unite
vein (large) lumens
large lumens
Vein (large) function/role
accommodate large blood volume
under lower pressure than arteries
parts of Vein (large)
thin tunica media
thick tunica externa, with vasa vasorum and nerve
examples of vein(large)
e.g. superior and inferior vena cava, portal vein, etc.
In fluid dynamics, fluid flows due to
differences in pressure between two points (pressure gradient)
pumping of the heart during systole
The pumping of the heart generates pressure intermittently during systole. Therefore, blood is forced out of heart (higher pressure) into the arteries (lower pressure)
Elastic arteries function during systole and diastole
Elastic arteries expand during systole and recoil during diastole (due to abundance of elastic tissue). Lessens fluctuations in blood pressure, maintains steady flow of blood throughout cardiac cycle and decreases stress on small arteries
which parts have have large portion of smooth muscle and why?
Muscular arteries and arterioles have large portion of smooth muscle. Control flow into capillary network via vasoconstriction and vasodilation.
Blood flow is ….
Blood flow is the volume of blood flowing through a vessel, an organ, or entire circulation in a given period
Blood flow (F) is enabled and opposed by ….
Blood flow (F) is enabled by blood pressure and is opposed by peripheral resistance (amount of friction the blood encounters)
blood flow formula
Three important sources of resistance:
- blood viscosity (“thickness” of the blood due to formed elements and plasma proteins), -total blood vessel length (depends on body weight, increased in obesity; the longer the vessel, the greater the resistance) and
-blood vessel diameter (the most important and variable factor; the wider the vessel the lower the resistance).
Supporting mechanisms of venous blood flow;
skeletal muscle pump and respiratory pump
how does skeletal muscle pump Support venous blood flow?
skeletal muscle pump: contraction of muscles exerts pressure on veins and valves direct blood towards the heart; normally no back flow
how does respiratory muscle pump Support venous blood flow?
respiratory pump: decreased thoracic pressure during inhalation draws blood into thoracic veins and the right atrium
what is Systemic Blood Pressure
The pumping action of the heart generates blood pressure (measured in millimetres of Mercury [mm Hg]) and blood flow
Systemic blood pressure is highest in…. and declines ……
Systemic blood pressure is highest in the aorta and declines throughout the pathway (is 0mm Hg in the right atrium). Blood pressure near the heart is pulsatile. The steepest drop occurs in arterioles (resistance vessels)
Systolic pressure is
Systolic pressure: pressure exerted during ventricular contraction
Diastolic pressure is
Diastolic pressure: lowest level of arterial pressure
Pulse pressure is
Pulse pressure: difference between systolic and diastolic pressure (e.g. Aorta ~ 120 – 80 = 40)
what is Mean arterial pressure (MAP)
pressure that propels the blood to the tissues; can be calculated as: MAP = diastolic pressure + 1/3 pulse pressure
Pulse pressure and MAP both decline ….
with increasing distance from the heart
Blood pressure depends on
Blood pressure depends on cardiac output and peripheral resistance (vasoconstriction ↑ pressure while vasodilation ↓ it)
relatively fast flow of blood (Hg) is…
Large pressure gradient (about 60 mm Hg) between Aorta and the arterioles, means relatively fast flow of blood
Venous Blood Pressure is
Venous Blood Pressure is Steady and changes little during the cardiac cycle
Venous Blood Pressure gradient..
Small pressure gradient (about 15 mm Hg) between venules and the terminal parts of the vena cavae, means relatively slow flow of venous blood.
Short-term neural and hormonal controls Counteract
Short-term neural and hormonal controls; Counteract fluctuations in blood pressure by altering peripheral resistance
Long-term renal regulation Counteracts
Long-term renal regulation; Counteracts fluctuations in blood pressure by altering blood volume
Neural controls of peripheral resistance:
maintain MAP by altering blood vessel diameter
alter blood distribution in response to specific demands (capillary sphincters)
operate via reflex arcs that involve; baroreceptors and/or chemoreceptors, (in carotid arteries and aortic arch), vasomotor centre in medulla/vasomotor fibres and vascular smooth muscle.
what are Baroreceptors
Baroreceptors: pressure-sensitive mechanoreceptors that respond to changes in arterial pressure and stretch. e.g. activation from ↑ aortic stretching –> vaso/venodilation to decrease BP