Capillaries and Veins Flashcards
How big are capillaries?
Microscopic
What do capillaries connect?
Arterioles to venules, endothelium, and basement membrane
Where aren’t there capillaries?
cornea, lens, epidermis, cartilage
Where are there few capillaries?
Tendons and ligaments
Where are there lots of capillaries?
brain/nervous tissue; endocrines system; kidneys
What are the three kinds of capillaries?
Continuous capillaries
Fenestrated capillaries
Sinusoid capillaires
Where are continuous capillaries found?
Found in most tissue, eg skeletal muscle
Describe the basement membrane of a continuous capillary. How are the endothelial cells held together?
Basement membrane forms a continuous ring around capillary
Endothelial cells are held together by tight junctions
What special structure is found in the endothelial cells of continuous capillaries?
intercellular clefts
How big is the intercellular cleft in a continuous capillary? What can pass through it? Where aren’t they?
~4 nm wide
Glucose and other small solutes can get through the clefts
The capillaries in the brain do not have these clefts- because of blood brain barrier
What is a fenestrated capillary and why is it named as such?
These endothelial cells have filtration pores (windows),
How big are the windows in a fenestrated capillary, and what covers them?
~20-100 nm, often spanned by a glycoprotein membrane
Where are fenestrated capillaries found?
Found in kidneys, endocrine glands, small intestine
Describe the basement membrane of a fenestrated capillary
surrounds the fenestrated capillaries
Where are sinusoid capillaries found?
Found in liver, bone marrow, spleen
What does a sinusoid capillary look like?
There are spaces in between the endothelial cells
Basement membrane in incomplete or absent
Why do sinusoid capillaries have space between the endothelial cells?
These spaces allow things like albumin, clotting factors, etc to get into the blood (from the liver/marrow/spleen where they are produced)
What are the three specialized structures in the capillary bed?
Metarteriole
Thoroughfare channel
Precapillary sphincter
Where is the metarteriole?
Short, 1st section of the thoroughfare channel to venule, when an arteriole gives off a branch to a capillary bed area
What surrounds the met metarteriole?
Has isolated smooth muscle fibers around this short section
Where is the thoroughfare channel?
Longer section, from metarteriole to venule
Is the continuation of the metarteriole, capillaries come off this part
Where does the thoroughfare channel go? What can it act as?
Will empty to a venule- Sometimes acts as a shunt, if precapillary sphincters are closed
How many capillary beds come off the thoroughfare channel?
Usually 10-100 capillary beds are supplied off this channel
What is the pre capillary sphincter?
Smooth muscle wrapped around the beginning of a capillary bed
What does the pre capillary sphincter do?
Autoregulation: if theres plenty to O2, will slow blood flow for a short time
__of the body’s capillaries are shut down at any given time, because there’s not enough ______ to fill everything.
¾
Blood
Several _____ unite to form a venule
capillaries
Will a vein ever be as thick as an artery?
No
How many layers does a vein have? Which is the thickest?
3
Tunica adventitia
How to veins prevent back flow? Where are these structures located?
Have valves to prevent the backflow of blood, only on tunica intima
What two “pumps” allow for veinous return?
Skeletal Pump
Respiratory Pump
What is the skeletal pump?
In the legs when the skeletal muscle contracts, blood is pushed up towards the heart
What is the respiratory pump?
During respiration, the diaphragm flattens and moves downwards, this decreases pressure in the thoracic cavity, increases pressure in abdominal cavity, and blood will flow to an area of lower pressure- returning to the thoracic cavity
What is hemostasis?
Cessation of bleeding
What is a thrombus?
A blood clot that develops in the luminal wall of a blood vessel
What is a thrombosis?
Clotting in an unbroken blood vessel
What is hemophilia?
A genetic disorder, clotting is diminished or absent
What is an embolus?
“A mass” A substance that is carried in the blood and obstructs a blood vessel
eg an air bubble, a blood clot, a fat globule
What is an aneurysm?
A sac formed by the dilation of a wall of an artery or vein
What are the “layers” of blood flow called?
Laminar flow
Describe laminar flow
Blood in the middle of an artery flows faster than blood near the walls, due to friction
The diameter of a vessel has a powerful influence on blood flow velocity
In addition to laminar flow, what also impacts blood flow?
Viscosity and peripheral pressure
What does MAP stand for?
Mean arterial pressure
What is MAP?
Pressure that propels blood to tissues
A measure of stress on blood vessels
Since diastole lasts longer than systole, it’s not just an average of the two
How is MAP determined?
MAP = Diastolic pressure + ⅓( Pulse Pressure) Pulse pressure: Systolic-Diastolic MAP = Diastolic pressure + ⅓(Systolic-Diastolic)
What is hypertension?
Abnormally high BP
Chronic resting BP higher than 140/90 mmHg
What is atherosclerosis?
Tearing of endothelium due to pressure, causes lesions that lead to lipid deposits along the walls of vessels
What is hypotension?
Chronic systolic pressure below 100mmHg
What is net filtration/reabsorption pressure?
The difference between fluids entering/exiting capillaries
What is hydrostatic pressure?
Fluid filters out of the arterial end of a capillary
The physical force exerted by blood against the capillary wall
What is colloidal osmotic pressure?
Fluid osmotically reenters at the venous end of capillary
Albumins primarily responsible for re entry of fluid back into capillary
How, where, and in what percents is fluid reabsorbed?
Capillaries reabsorb 85% of fluid they filter, remaining 15% absorbed/returned by lymphatic system
