Lecture 8 Flashcards
Describe micro-circualtion?
The blood comes through an arteriole, it then goes through terminal arteriole, then there is a metarteriole (discontinuous layer of smooth muscle - less control of the diameter). It could then go through the capillary bed. Once you get into the papillary bed you cannot control the diameter of the lumen. There are pre-capillary sphincters - which contract and relax to allow blood to flow through 20x a minute (think about demand - CO2 conc drives this). It then heads out through the bed and to a post-capillary venue which has a coat (pericytes). Another route is to go through a thoroughfare channel (skips the capillary bed). If you have not got huge demand then majority of the blood will flow through the channel, if there is hug demand then the pre-capillary sphincters will be relaxed and the blood will flow right through the capillary bed. Another route is to go from an arteriole to a venue - arteriovenous shunt. This is just an insurance policy for situations of high demand.
What are examples of arteriovenous shunts?
Digestion - increase of blood flow will have opening of sphincters.
Exercise - increase of blood flow.
Cold/extreme heat - shunt large volume of blood i.e. flushing.
Erectile function - large volume of blood.
Describe capillaries?
Have an internal diameter of 8-10microm. Their walls are made up of endothelium with a basement membrane but no CT or muscle. There are 3 types of capillaries:
- Continuous.
- Fenestrated.
- Sinusoids.
Describe continuous capillaries?
Extremely strict, tightly regulated i.e. blood brain barrier. The only way you can get things across is through pinocytosis. Very selective.
Describe fenestrated capillaries?
Might allow certain things through, mostly found in endocrine glands (or places where you need ion, fluid exchange and peptides but not plasma proteins or cells) e.g. kidneys.
Describe sinusoids?
Wide capillaries. Need the travelling of large proteins and cells. Might find in the bone marrow. Allows large volume of fluid exchange and proteins (100-1000nm wide).
Describe venules?
There is SM, CT and three layers. Post-capillary venues can be relatively wide. There are pericytes. Very thin walled. Like big collecting pools, and low pressure vessels. Small change in pressure huge change in volume. Can be very leaky. If there is an allergic response, the venues can cause oedema. Muscular venues are large venues and may have up to two layers of smooth muscle in TM. Their lumen is bigger than arterioles (large lumen due to greater volume of blood in their).
Describe veins?
60% of volume is in the venous system. High capacitance to hold large volumes due to muscles. Low pressure system (less muscles than arteries and bigger lumen). Due to less structural component in the muscular wall they have collapsed profile. The valves have an intimal lining fold. For every 136cm of a column of fluid will generate a pressure of 100mmHg. The skeletal muscles contract and push the blood up towards the heart.
Describe Varicose Veins?
Can cause some discomfort and achy legs. More common in women and increase with family history. The veins valves do not meet. So the veins become tortuous and swollen.
Describe Venous Thrombosis?
When the blood becomes slower and thicker. Virchow’s triad.
Describe lymphatic capillaries?
Small diameter, and help to maintain interstitial fluid. Can transport blood plasma as well as WBC. They sit all around the capillary bed and the fluid drains one way. It works on a gradient - nothing comes out of the lymph system. Very thin walled vessels and quite leaky (very thin endothelial cells). If there is swelling in the interstitial fluid, it will pull on the anchoring filaments (on the vessel) this will open the cleft to allow more fluid into the vessel (these clefts allow cells through i.e. cancer cells).
Describe larger lymphatic vessels?
Most tissues will have lymphatic vessels. The contraction of the SM wrapped around the vessel allows the fluid to move. The vessels lead to lymph nodes. Secondary tumours may establish there. The lymph system goes to the thoracic duct, and via the right duct will enter the right subclavian vein and then enter back into the systemic circulation.
