3.1.1. Physical Properties and Histology of the Circ. Flashcards
What do we call the specialized epithelium lining the interior of the heart, blood vessels, and the lymphatics?
The endothelium
Which ventricle in the heart contains more muscle and why?
The Left Ventricle (LV) contains more muscle because it pumps against higher pressures.
In what manner does the heart contract? (is it like preistalsis, or do the muscles line up to squeeze in a certain way)
What does this accomplish?
The hear contracts in a spiral manner (like wringing out a wet hand towel).
This helps the heart to increase the amount of blood moved with each pump.
What do we call the amount of blood actually ejected from the LV?
The ejection fraction (in %)
In general, are the atria more or less muscular than the ventricles?
Generally, they are less muscuar
What 3 layers of cardiac tissue are present in the heart?
Epicardium (outer most)
Myocardium (central, muscle)
Endocardium (innermost)
Do cardiac cells function as a syncytium?
If not, how do they pump synchronously?
They are not a syncytium.
Myocardium pumps as one unit because the cells are connected by gap junctions, allowing chemical and electrical stimuli to travel along a long line of cells as if it were one large cell.
Valves in our vasculature contain what material instead of muscle?
Dense Connective Tissue (Dense CT)
What are the functions of the SA (sinoatrial) and AV (atrioventricular) nodes?
These are the sites of pacemaker cells in the heart, which tell myocytes when to contract.
Both nodes have a “preset” pace (AV is actually slower than SA)
The SA node sets the basal rhythm
AV node functions to slow the electrical stimulus from the SA node so that the atria and ventricles do not pump at the same time.
How is the electrical stimulus sent throughout the heart?
OR
What structures does it go through in what order?
(ECG correlate, from https://www.youtube.com/watch?v=RYZ4daFwMa8)
Starts at SA node
Travels across the atria (P wave)
Hits the AV node and slows (P-R segment)
Moves from AV to the bundle of His in the interventricular septum (Q)
Travels up Purkinje fibers (R and S)
Ventricles repolarize (T wave)
What three layers are vessels comprised of in the circulatory system?
Tunica (L. tunic = layer):
Intima (luminal)
Media(middle)
Externa/Adventitia (outside of vessel)
The tunica intima of vessels is lined by what cell type?
Endothelium
Properties of endothelium change based upon which vessel you are in
What does the tunica media typically contain?
Is the tunica media larger in arteries or veins?
Smooth Muscle (especially in arteries)
This layer is thicker in arteries than in veins because of the extra smooth muscle.
What does the tunica adventitia contain?
What is special about the tunica adventitia of the Vena Cava?
Typically connective tissue, along with the nervi vasorum and the vasa vasorum
The tunica adventitia of the Vena Cava contains smooth muscle (it’s the only vessel with smooth muscle in the adventitia)
Source: Mr. Jones (and meee)
Histologically, what are two differences between veins and arteries?
Arteries have a thicker wall than veins
Veins will typically appear flattened, whereas arteries will keep their rounded appearance
What are two histological differences between arteries and veins in the tunica intima?
The endothelium will appear wavy in arteries due to muscle constriction, where as the vein endothelia will appear smooth
You may find an internal elastic membrane in arteries, but this is absent in veins
Name some differences between the Tunica Media of veins and arteries
Tunica Media (TM)
Arteries
- Normally the thickest layer in arteries
- Smooth muscle cells and elastic fibers predominate (the proportions of these vary with distance from the heart)
- External elastic membrane present in larger vessels
Veins
- Normally thinner than the tunica externa
- Smooth muscle cells and collagenous fibers predominate
- Nervi vasorum and vasa vasorum present
- External elastic membrane absent
Name some differences between veins and arteries in the tunica adventitia
Tunica Externa (TE) / Adventitia
Arteries
- Normally thinner than the tunica media in all but the largest arteries
- Collagenous and elastic fibers
- Nervi vasorum and vasa vasorum present
Veins
- Normally the thickest layer in veins
- Collagenous and smooth fibers predominate
- Some smooth muscle fibers
- Nervi vasorum and vasa vasorum present
Why are the largest arteries called “elastic arteries”?
Because they contain elastin bundles and layers
Allows for the reboud of these vessels against changes in blood pressure (may expand then contract to translate BP changes)
What are the four valves of the heart?
2 groups:
atrioventricular valves
semilunar valves
Or in this order, from R to L:
Tricuspid, Pulmonary, Bicuspid (Mitral), Aortic
Pneumonic: Try (Tri) before you buy (bi/mitral)
What is important about the orientation of the valves in the heart?
The orientation of these valves allows blood to flow in one direction, and quickly halts blood flow in the opposite direction.
(Histologially, if it looks like you are looking at a bowl or cup, you are looking at it in the forward direction, or “as the blood flows”)
Learn to compare and contrast each type of vessel
Which vessels/structures allow for regulation of blood flow around capillaries?
Arterioles
Precapillary Sphincters (The SPHINCTERRRR says what?)
Venules
How many layers of muscle cells are present in arteriorles?
In small arteries?
1-2 muscle layers in arterioles
More than 2 in small arteries
Large arteries are…larger
What are pericytes and what do they do and where are they?
What they are:
specialized cells found w/in the basal lamina
What they do:
responsive to chemical signals (eg NO, synthesized by the E-NOS gene)
give rise to muscle and endothelium during injury
can be involved in the Dz process
Where they are:
sparsely located in/on capillaries & venules
________ _______ determines how circulation is regulated.
Local Control
Pressure is defined as…
Force exerted over an area
P = F/A
When talking about pressure in the cardiovascular system, what are we really talking about?
We are really talking about the DIFFERENCE in pressures
What are the big three “pressures” seen in the cardiovascular (CV) system?
Driving Pressure: difference in pressure between two points
Hydrostatic Pressure: Pressure due to gravity
Transmural Pressure: pressure exerted by fluid (blood) on the walls of vessels
(Mura = Latin for wall)
(BP = Circulatory pressure - atmospheric pressure)
What is flow?
The movement of a fluid (blood here) relative to a certain point
(In general, slower flow = better diffusion of nutrients, waste, oxygen, etc)
What is resistance?
What kinds of things create resistance?
Forces that, in general, oppose flow
Size of a vessel (both radius and length)
Friction (viscosity of fluid, “stickiness” of vessel wall)
Is arterial BP dependent or independent of Cardiac Output (CO)?
Typically, it is INDEPENDENT of CO
How is resistance related to the following:
Vessel Length?
Vessel Radius?
Blood Viscosity?
Resistance is directly proportional to vessel length and blood viscosity
Resistance is indirectly proportional to vessel radius to the fourth power
What is Poiseuille’s Equation?
R ~ (n)L/(r^4)
n = viscosity
L = length
r = radius
R = resistance
What are the three requirements of Poiseuille’s Equation?
- Blood is incompressible and newtonian (follows newtonian mechanics, i.e. newton’s laws)
- blood flow is laminar through a tube of constant circular cross-section (radius) and is substantially longer than its diameter
- There is no acceleration of fluid in the pipe (flow is constant and steady)
What kind of factors influence blood viscosity?
hematocrit
- positively-related to viscosity (increased # of RBCs → curvilinear increase in viscosity)
- strong determinant of viscosity, esp important in polycythemia
temperature
- inversely-related to viscosity (1 degree C decrease → blood becomes ~2% thicker)
flow rate
- low flow states w/in microcirculations (arterioles, capillary beds, venules) may promote increased molecular interactions b/w RBCs and plasma proteins
clotting
- kind of like letting Jell-O cool after you mix the hot water and gelatin…
What is laminar flow?
Turbulent flow?
Laminar = smooth flow
Turbulent flow = “messed up” flow
What are the clinical differences between laminar and turbulent flow?
With auscultation:
CANNOT hear laminar flow
CAN hear turbulent
Turbulent flow occurs in large arteries at branch points, in diseased & stenotic arteries, and across stenotic heart valves
What is the importance of a series versus parallel arrangment in blood flow?
Series arrangement
- seen in hepatic portal system and pulmonary circulation
- pulmonary: heart to lungs, then back to heart
- capillary beds lie one after another, but consequently see less pressure (heart, GI tract, liver, back to heart)
Parallel arrangement
- allows the body to regulate organ systems individually
- different organs can draw from the same pool of blood (w/the same BP)
What is pulse pressure?
Systolic - diastolic blood pressures
What is Total Peripheral Resistance (TPR)?
- R = ΔP / Q
- ΔP is the change in pressure across the ENTIRE SYSTEMIC circulation
- BP is measured immediately after exiting the left ventricle and within the right atrium
- Q is the flow rate through the vasculature (equal to the CO)
