Ch 13/14 Cardiovascular Physiology (Day 3) Flashcards
Functional Model of CV System
diagram
- single, closed loop
- valves in veins and heart assure one way-flow
- each side of heart functions as interdependent pump
- systemic arteries: pressure reservoir (maintains blood flow during ventricular relaxation
- arterioles: site of variable resistance (adjustable diameters, where biggest drop in pressure occurs)
- capillaries: gas exchange between blood and cells/tissues
- post capillary venues: exchange and support leukocyte adhesion and emigration (site of most inflammation)
- systemic veins: expandable volume reservoir
Distribution of Blood in Body at Rest
- know that lungs get 100% of blood output –> distributed to right and left heart
- kidneys get approx 20% from every heartbeat
- skeletal muscle approx 20% –>altered during exercise, redistributed
controlled by diameter of the arterioles
Velocity of Blood Flow
see diagram
- velocity of blood flow depends on total cross-sectional area
- highest in aorta (smaller cross-sectional area)
- total blood flow in system in same in aorta as rest of system, even though velocity drops
Blood Vessel Structure
- all have layer of endothelial cells, barrier
- arteries have TONS of elastic tissue, thick
- veins have less, more collapsable
- no fibrous tissue in arterioles or capillaries
- capillaries are just single layer of endothelial tissue = greater diffusion
- arterioles have LOTS of smooth muscle
–>see diagram
Elastic Arteries
closer to the heart; stretch as blood is pumped into them and recoil when ventricles relax
Muscular Arteries
farther from the heart; have more smooth muscle in proportion to diameter; also have more resistance due to smaller lumen
Arterioles
20−30 µm in diameter; provide the greatest resistance; control blood flow through the capillaries
Ventricular Contraction
- ventricle contracts
- semilunar valve opens. blood ejected from ventricles –> arteries
- aorta and arteries expand and store pressure in elastic walls
Ventricular Relaxation
- isovolumic ventricular relaxation
- semilunar valve shuts, preventing back flow into ventricle
- elastic recoil fo arteries sends blood forward into rest of circulatory system
systemic circulation pressures
Pressure waves created by ventricular contraction travel into the blood vessels. Pressure in the arterial side of the circulation cycles, but the pressure waves diminish in amplitude with distance and disappear at the capillaries.
pulse pressure
pulse pressure = systolic pressure - diastolic pressure
- ->reflects amount of blood that heart is able to pump
- high BP = low pulse pressure
mean arterial pressure
MAP = diastolic pressure + 1/3 (pulse pressure)
pre capillary sphincters
can close off capillaries in response to local signals
blood flow to capillaries regulated by:
- vasoconstriction/vasodilation of arterioles
- precapillary sphincters
Capillaries
- smallest vessels: 7-10 µM diameter; have thinnest walls (single layer of flattened endothelial cells supported by basal lamina)
- No smooth muscle, no elastic tissue reinforcement facilitates exchange, as does the large aggregate surface area
- Thin walls and huge total surface area –> diffusion distance from lumen to tissue cells is small
- Plasma and cells exchange materials across thin capillary walls
- Capillary density related to metabolic activity of cells in the tissue (more active = more capillaries, ex. the heart)
Continuous Capillaries
Adjacent ECs close together [ex. muscles, heart, skin, adipose tissue & CNS]
–>very little leakage
-Transcytosis may be ONLY mechanism for exchange within CNS—blood-brain barrier
Fenestrated Capillaries
Pores in vessel wall [ex. kidneys, intestines & endocrine glands]
Basement membrane: mucoprotein which restricts passage of large molecules (especially proteins)
Discontinuous (Sinusoidal) Capillaries
Gaps between cells [ex. bone marrow, liver & spleen; allow the passage of proteins, cells]
–>leakage possible
Capillary Exchange
- Exchange between plasma and interstitial fluid via paracellular pathway or endothelial transport
- Small dissolved solutes and gases move by diffusion, depending on lipid solubility and concentration gradient
- Larger solutes and proteins move mostly by vesicular transport and by bulk flow—mass movement in response to hydrostatic or osmotic pressure gradients
Filtration
fluid movement out of capillaries
- Caused by hydrostatic pressure (pressure of fluid against vesicle wall)
- Net filtration at arterial end (fluid pushed out of the system)
Absorption
fluid movement into capillaries
- Net absorption at venous end (fluid back into the vesicle)
- Caused by colloid osmotic pressure
Capillary Beds
- pressure drop across
- arteriole side (net filtration)/venule side (net absorption)
- by the time we get to venous end, net volume of fluid flow is back towards reabsorption
–>see diagram
Starling Forces
Net Driving Force = (PH-PT) – σ(πC-πT)
PH = capillary hydrostatic pressure, PT = tissue hydrostatic pressure
πC = capillary oncotic pressure, πT = tissue oncotic pressure,
σ = reflection coefficient
π = colloid osmotic pressure = oncotic pressure (osmotic pressure due to proteins)
- When NDF > 0 Filtration
- When NDF
What is the equation for net pressure?
net pressure = hydrostatic pressure (PH) - colloid osmotic pressure (π)
Hydrostatic Pressure
forces fluid out of capillary
Colloid Osmotic Pressure
of proteins within capillary pulls fluid into the capillary
Veins
t-Most of the total blood volume
- Lower pressure (2 mmHg compared to 100 mmHg average arterial pressure)
- Thinner walls than arteries = less elastic, larger lumen; collapse when cut
- need help to return blood to heart
What helps veins return blood to heart?
–skeletal muscle pumps: contraction of muscles surrounding veins help force blood towards heart
–venous valves: ensure one-way directional flow (pooling = high BP)
–breathing: diaphragm flattens upon inhalation: increases abdominal pressure compared with thoracic pressure, also moving blood –> hear
Lymphatic System
- Returns fluid and proteins to circulatory system [lymphatic endothelium has very porous junctions, and so is much “leakier” than vascular endothelium]
- Transports absorbed fat from intestines –> blood
- Serve as filter for pathogens
- Produces & houses lymphocytes for the immune response
Thoracic trunk/right lymphatic trunk
formed from merging lymphatic ducts; deliver lymph into right and left subclavian veins
Lymph ducts
formed from merging capillaries
- Similar in structure to veins
- Lymph is filtered through lymph nodes
- when blocked –> edema
Lymphatic Capillaries
- smallest; found within most organs
- interstitial fluids, proteins, microorganisms, and fats can enter.
Edema
–> fluid buildup
Two main causes:
1. Inadequate drainage of lymph
- Filtration far greater than absorption
- -Increase in capillary hydrostatic pressure
- -Decrease in plasma protein concentration
- -Increase in interstitial proteins
- -Increased permeability
