Ch. 13/14 Day 3 Flashcards
Functional Model of CV System
Closed system in series
Each side of heart functions as an independent pump
- Arterioles: sites of variable resistance
- -biggest drop in pressure occurs here - Capillaries: exchange between blood and cells
- Postcapillary venules: exchange and support leukocyte adhesion and emigration
- Systemic Veins: expandable volume reservoir
- Valves in veins and heart assure one-way flow around closed loop system
- Elastic Systemic Arteries: pressure reservoir; maintain blood flow during ventricular relaxation
How much cardiac output do the lungs get?
100% from every heartbeat
–distributed to left and right heart
How much of the cardiac output do the kidneys get?
~20% from every heartbeat
How much of the cardiac output does the skeletal muscle get?
~20% from every heartbeat
–can radically change during exercise
Velocity of Blood Flow
Slows down as it passes through smaller structures (arterioles, capillaries, venules).
Total blood flow over all those capillaries is basically equal to blood flow in a single aorta.
–blood flow is relatively constant throughout the whole system, but velocity drops down
Blood Vessel Structure
All blood vessels have endothelial layer
- Artery
- -tremendous amount of elastic tissue
- -lots of smooth muscle - Arteriole
- -lots of smooth muscle - Capillary
- -single layer of endothelial cells
- -no muscle since it’s an exchange vessel - Venule
- -fibrous tissue
- -no muscle since it’s an exchange vessel - Vein
- -collapsable (very little elastic tissue)
- -some smooth muscle
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
Resistance vessels
–control of BP
Ventricular Contraction
- Ventricle contracts
- Semilunar valve opens; blood ejected from ventricles flows into arteries
- Aorta and arteries expand and store pressure in elastic walls
Ventricular Relaxation
- Isovolumic ventricular relaxation
- Semilunar valve shuts, preventing flow back into ventricle
- Elastic recoil of arteries sends blood forward into rest of circulatory system
Pulse Pressure
Systolic pressure minus diastolic pressure
Reflects actual amount of blood that the heart has been able to pump
Mean Arterial Pressure
Diastolic pressure + 1/3 (pulse pressure)
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.
Capillary Blood Flow
Blood flow to capillaries is regulated by:
- -vasoconstriction and vasodilation of arteries
- -precapillary sphincters (can close off capillaries in response to local signals)
Exchange Function
Takes place in capillaries and postcapillary venules
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
Types of Capillaries
Continuous, Fenestrated, Discontinuous (sinusoidal)
Continuous Capillaries
Adjacent ECs close together (muscles, heart, skin, adipose tissue, and CNS)
–very little leakage (tight)
Have tight/close junctions
Transcytosis may be only mechanism for exchange within CNS—blood-brain barrier
Fenestrated Capillaries
Pores in vessel wall (kidneys, intestines, and endocrine glands)
–leakage possible
Have large pores
Basement membrane: mucoprotein which restricts passage of large molecules (especially proteins)
Discontinuous (sinusoidal) Capillaries
Gaps between cells (bone marrow, liver, and spleen; allow passage of proteins, cells)
–leaky vessel
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
Capillary Filtration
Fluid movement out of capillaries
Caused by hydrostatic pressure
Net filtration at arterial end –> fluid pushed out of system
Capillary Absorption
Fluid movement into capillaries
Net absorption at venous end –> fluid back into vesicle
Caused by colloid osmotic pressure
Starling forces and Transmicrovascular Exchange
of Fluid
Net Driving Force (NDF):
- when NDF > 0 Filtration
- -hydrostatic pressure greater than oncotic pressure - when NDF
Net Pressure Formula
Net Pressure = hydrostatic pressure minus colloid osmotic pressure
Veins
Most of the total blood volume is in veins
Lower pressure (2 mmHg compared to 100 mmHg average arterial pressure)
Thinner walls than arteries, larger lumen; collapse when cut
What helps blood in veins return to the heart?
Skeletal muscle pumps:
–contraction of muscles surrounding veins help force blood towards heart
Venous valves:
–ensure one-way directional flow
Breathing:
–diaphragm flattens upon inhalation: increases abdominal pressure compared with thoracic pressure, also moving blood –> heart
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 to blood
Serve as filter for pathogens
Produces and houses lymphocytes for the immune response
Thoracic Trunk and Right Lymphatic Trunk
Merging lymphatic ducts; deliver lymph into right and left subclavian veins (so fluid can be returned to heart)
Lymph Ducts
Formed from merging capillaries
Similar in structure to veins
Lymph is filtered through lymph nodes
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
