Lecture 17 - Circulation Flashcards
What are the 3 pre-capillary resistance vessels?
- Arterioles
- Metaarterioles
- pre-capillary Sphincters
What are the exchange vessels?
Capillaries
What are the post-capilalry resistance vessels?
Venules
What are the main characteristics that allow Capillaries to have great blood flow?
- Low velocity
- Intermittent (some open/closed)
- Direction (pressure gradient)
- NOT UNIFORM
- Rouleuax formation
Why do meta-arterioles not exchange CO2/O2 ?
- contain vascular smooth muscle, therefore contribute to pre-capillary resistance
What kind of cells are capillaries made up of?
ENDOTHELIAL cells
Most resistance is on the pre or post-capillary side? Why is this?
- Pre - capillary
2. Post-capillary side has little smooth muscle & cannot control resistance much (4:1 ratio)
Why is velocity of capillaries so LOW?
Large cross-sectional area
What is the Rouleaux formation? How is this related to sickle cell anemia?
- RBC’s lineup on an angle to allow optimal O2/CO2 exchange
2. Sickle cells do not have Rolex formation and thus POOR O2/CO2 exchange
Transcapilalry Fluid exchange: What are two determinants of pressure INSIDE capillaries?
Outside?
- Plasma Oncotic Pressure
- Capillary Hydrostatic Pressure
Outside:
- Tissue Oncotic Pressure
- Interstitial Hydrostatic Pressure
Why is the movement of fluid crucial for healthy tissue?
- wash away metabolites, carry glucose, nutrients, proteins
Describe the relation between hydrostatic & oncotic pressure on the:
- Arteriole Side
- Venule Side
- Capillaries
Arteriole:
Hydrostatic > Oncotic
- fluid OUT(filtration)
Venule:
Hydrostatic < Oncotic
- fluid IN (absorption)
Capillaries:
Hydrostatic > Oncotic
- fluid moves out at the pre-capillary and moves in at the post-capillary (as you move across the capillary bed)
If hydrostatic pressure is 32, and oncotic pressure is 25 which direction is fluid moving?
Fluid moving OUT
(net force is 7 mmHg out)
- net filtration out (which occurs in the arteries)
Is the hydrostatic pressure in the following areas high or low?:
- Glomerulus
- Lungs - alveoli
- Lymphatics
- HIGH hydrostatic pressure - pushing fluid OUT (filtration)
- LOW hydrostatic pressure (fluid in- to keep alveoli dry & prevent fluid in interstitum aka pulmonary edema)
- low Hydrostatic pressure so fluid moves IN
Where does extra fluid go that is washed out of the interstitium? Where is it shunted from here?
Lymphatic System
- shunts blood to the RIGHT side of the heart
What is of greatest importance for oncotic force & determines Oncotic pressure in the CAPILLARIES?
ALBUMIN
- exerts a high hydrostatic pressure
51% concentration but exerts 65% of the plasma oncotic pressure
What is the affect of Albumin on the cell?
- positively charged so it attracts CHLORIDE (-)
- which retains SODIUM
and increases the osmotic force by retaining more WATER
What exerts a large effect on capillary HYDROSTATIC pressure? Why?
- VENULES
- Has low post-capillary resistance
arteries have HIGH pre-capillary resistance so the hydrostatic pressure is low
- less moving out, less to contribute to Hydrostatic pressure
Determine the Capillary hydrostatic pressure based on the pre/post-capillary resistance ratio:
- decrease pre/post resistance
- Increase pre/post resistance
- INCREASE hydrostatic pressure
2. DECREASE hydrostatic pressure
What occurs if the Left Ventricle does not contract & fluid backs up into the Pulmonary veins?
PULMONARY EDEMA
- high hydrostatic pressure pushing fluid OUT which seeps into the alveoli
What occurs if there is an increase in Afterload on the Left Ventricle and blood backs up all the way to the Right Atrium?
- backs up to Vena Cava (IVC, SVC)
PORTAL HYPERTENSION!!
- CIRRHOSIS OF THE LIVER
also: increased venous pressure in the viscera & patient gets ASCITES - accumulation of fluid in abdomen & ankles
What is a common problem that occurs after Right Heart Failure?
Pulmonary Hypertension
- no pulmonary edema since this is on the ARTERIAL side (not venous)
What endothelial derived mediators function to VASODILATE? Vasoconstrict?
- Prostacyclins
- EDRF
- Nitric Oxide
- Metabolites
Constrict:
Endothelin!
- activates PLC to release IP3 and increase Calcium
Describe the following of lymphatics:
- Flow of tissue fluid back to the heart
- Mechanism of control
- structure
- Where the collecting vessels end
- UNIDIRECTIONAL
- VALVES
- non-fenestrated endothelium (no smooth muscle & little basal lamina)
- return to SUBCLAVIAN on the right side of the heart
