BLOOD VESSELS
There are 100,000 miles of blood vessels.
With the exception of hyaline cartilage (which is avascular), no cell is more than a few
cell diameters away from a blood vessel, so they can get oxygen, nutrients, remove waste.
Arteries get smaller and thinner and are then called arterioles.
Arterioles get smaller and thinner until they are just one cell thick. At this point, they are
called capillaries, and this is where the oxygen exchange takes place. Capillaries then get
larger as they take waste products away from the cells in the capillary bed and head back
to the heart; now they are called venules. As venules get bigger, they are called veins
until they return to the heart. From the heart the blood is pumped to the lungs to get more
oxygen. During this trip, they get smaller again until they are capillaries, then they get the
oxygen from the lungs and drop off the waste products (carbon dioxide). Then the blood
returns to the heart to get pumped out to the body again.
All blood vessels (except the smallest) look similar.
1. TUNICA (“Coat”) INTIMA
a. ENDOTHELIUM: simple squamous epithelium. Allows for smooth
flow of blood. Similar to endocardium.
b. SUBENDOTHELIUM: loose fibrous connective tissue.
2. TUNICA MEDIA
a. SMOOTH MUSCLE (allows vasoconstriction). Allows blood to be
directed to parts of body.
b. ELASTIC FIBERS: within smooth muscles. Allows blood vessels to
return to normal size, and to stretch during systole.
3. TUNICA ADVENTITIA (TUNICA EXTERNA): dense fibrous connective tissue
which thins out to loose fibrous connective tissue.
a. Protects the blood vessel (strong)
b. Gives vessel strength for shape
c. Anchors vessel to surrounding tissue; loosens with age.
Lumen – central blood-filled space of a vessel
These layers are thick, so they need their own vascular supply: VASO VASORUM
(blood vessel for a blood vessel) to supply the oxygen. The endothelium layer does not
need this because it’s in direct contact with the blood, but the subendothelium needs it.
TYPES OF ARTERIES
ARTERIES carry blood away from the heart. Arteries have a smaller lumen than
veins of similar size. Arterial walls are thicker than venous walls. Arteries have more
elastin than veins. Arteries have no valves because the blood pressure in arteries is
high enough that there is no backflow of blood. There are two types of large arteries:
a. ELASTIC ARTERIES: largest, closest to heart. Has to take the full
force of the systolic contraction; compensates by expanding a lot. There
of lots of elastic fibers in the tunica intima as well. Does blood flow
during diastole? Yes; elastic arteries return to original size, pumps blood.
This is another pump besides the heart.
b. MUSCULAR ARTERIES: with the exception of a few elastic arteries,
every other names or visible artery in a body is a muscular artery. They
range in size from 1/3mm on up. The difference is the size of the tunica
media. Thick ones are muscular arteries. Function is to distribute blood,
and help control which regions of the body get blood. When you are
exercising, you want the blood from the GI system to go to muscles.
When your hands are cold, you don’t want more blood going there or
you’ll lose heat; therefore, the vessels will constrict in the hands. Dilation
is just lack of constriction.
ARTERIOLES (microscopic; these are the smallest). Large ones look like muscular
arteries. Small ones only have two layers: endothelium and tunica media. One of the
characteristics of an arteriole is that when it contracts, the lumen closes completely.
ANEURYSM
A sac-like outpouching of an artery
– Can rupture at any time; in aorta or brain can cause death within a few
seconds.
– Symptoms: Swelling or throbbing (asymptomatic in brain)
Some common locations for aneurysms include:
– Aorta
– Brain
– Leg
– Intestine (mesenteric artery aneurysm)
– Splenic artery aneurysm (can form during pregnancy)
Causes:
– Defect in part of the artery wall
– High blood pressure (abdominal aortic aneurysms)
– Congenital (present at birth)
Usually not detected except by an angiogram.
Treatment: surgical repair
The Ovation Abdominal Stent Graft System
Aneurysms can be repaired through open surgery or less invasively with
endograft repair using a stent graft otherwise known as an endograft.
Endografts feature a tube typically made of plastic material that is supported by a
metal frame or stent. They are compressed into a delivery catheter, inserted into
the femoral artery of the leg and then threaded into position in the weakened
portion of the artery where they are released. Once released, the endograft
expands against the wall of the aorta to redirect blood flow away from the
aneurysm.
How to Recognize a Stroke (“STROKE”)
S * Ask the individual to SMILE.
T * Ask the person to TALK and SPEAK A SIMPLE SENTENCE
(Coherently; i.e. It is sunny out today)
R * Ask him or her to RAISE BOTH ARMS.
O * Open the mouth and stick out the tongue
K * Keep them comfortable and still
E * Get EMERGENCY help (911)
If one side of the body responds differently than the other side, or if they
have trouble with the task, call 911.
Important:
You don’t have enough blood to go around; you only have 5 liters for 100,000 miles of
blood vessels. At any given time, most blood vessels will be closed (except at lungs).
Are you using your legs now? When your legs run low on oxygen, the vessels there will
open up again. Are you using your brain now? I hope so! The vessels there will be
open. When your leg falls asleep, there is pressure on an artery which stops the blood
flow. When the nerves are deprived of oxygen, they tingle.
SOME COMMON ARTERIES
Femoral artery: good place to take a pulse since it is superficial, but that also makes it
susceptible to injury.
The circle of Willis is a loop of arteries around the pituitary gland and the optic chiasma;
common area for stroke, in which case it causes blindness.
CAPILLARIES
Smallest blood vessels; they are found everywhere
These are the only sites of nutrient, gas exchange, and waste exchange in the
cardiovascular system.
– Diameter from 8–10 µm
Diameter is similar to an erythrocyte
Red blood cells pass through single file
They only have an endothelium.
Site-specific functions of capillaries
In the lungs – oxygen enters blood, carbon dioxide leaves
In the small intestines – receive digested nutrients
In endocrine glands – pick up hormones
In the kidneys – removal of nitrogenous wastes
CAPILLARY PERMEABILITY
Intercellular clefts – gaps of unjoined membrane
– Small molecules can enter and exit
Three types of capillaries
– Continuous – most common
– Fenestrated (“window”) – have pores
– Discontinuous (Sinusoids) – have very large gaps
CAPILLARY BED:
2. CAPILLARIES: These are are the only sites of nutrient, gas exchange, and
waste exchange in the cardiovascular system. They are the smallest vessels; 810µ; about the size of an erythrocyte. They are the simplest; only have an
endothelium. They are found everywhere. There are three main types:
a. CONTINUOUS CAPILLARIES: found in all organs of body, made of
simple squamous epithelium. They have intracellular clefts, the function
of which is essential for plasma to leak out and bathe each cell with
Extracellular fluid, which is rich in oxygen and nutrients. Erythrocytes
and platelets don’t fit through, but leukocytes can squeeze through so they
can enter and leave the blood vessels as needed.
b. FENESTRATED CAPILLARIES (“window”). These have a lot more
leakage because there are more holes. Found in areas where lots of fluids
need to be moved back and forth (synovial membrane, small intestine).
c. DISCONTINUOUS CAPILLARIES (sinusoidal capillaries). These
have a big gap in the capillary. What can go in and out here? Anything,
including erythrocytes. These are found in red bone marrow. Why?
That’s where RBCs are made, and they need to enter the circulation by
way of sinusoidal capillaries. These capillaries are also found in the liver
and spleen, where red blood cells are destroyed.
CAPILLARY BEDS
A network of continuous capillaries supply individual cells with oxygen, nutrients, blood, etc.
At the start of each capillary, there is a small muscle: PRE-CAPILLARY SPHINCTER,
which controls the flow of blood to individual capillaries. ARTERIOLES direct the blood
flow to the specific tissue. Pre-capillary sphincters direct the blood flow to specific cells. If
one cell is starving, the capillary next to it will open. The sphincter opens and closes
depending on the needs of individual cells.
Blood always flows to those cell and tissues that need it. There is not enough blood to go
around. Are continuous capillaries truly continuous? No, because plasma leaks in and
out of capillaries and are eventually reabsorbed into the veins. They drop off nutrients,
pick up CO2 waste, etc.
3. VEINS: A vein carries blood to the heart. There are 2 varieties.
a. VENULE: this is the smallest. It takes blood from the capillary to the
vein.
b. VEIN: takes blood to the heart.
i. Thinner walls (less pressure here)
ii. Larger lumen (blood moves more slowly)
iii. Skeletal muscle pushes on the vein to move the blood uphill.
iv. Need valves in veins
All veins are much thinner than arteries. There is no pressure in veins, so they don’t
need thick walls. Blood moves slowly through veins, so lumen has to be bigger than an
artery.
How does blood get uphill back to the heart? Veins need valves. Veins are
the only BLOOD vessels that have valves (although LYMPH vessels also
have valves). Valves in veins allow blood to move in only one direction.
What pushes the blood? The muscle of the body constrict, squeezes the
vessels. This is a type of blood pump.
BLOOD PUMPS
1. The heart
2. Elastic arteries
3. Muscles constricting the veins
CLINICALLY SIGNIFICANT VEINS
Great Saphenous vein is often used to bypass a damaged coronary artery in coronary
bypass surgery. It is the most likely vein to become varicose anyway.
Facial vein: squeezing pimples, and nose piercings in the “danger triangle” of the face
can spread infection through the facial vein into the dural sinuses of the brain.
Renal vein: oxygen poor, but contains the lowest concentration of nitrogen waste.
Veins that are rich in oxygen and nutrients:
Umbilical vein
Hepatic Portal vein
Pulmonary vein
VARICOSE VEINS:: incompetent valves in a vein
The valves become incompetent:
They can’t close all the way because too much fluid has built up in them and the
lumen has stretched too wide.
They might be asymptomatic or they may be painful (phlebitis).
Treatment:
Laser can be used to seal off the distal end of the vein. It will close off.
Sclerosing agents (alcohol or saline) injected around the vein can be used to do
the same thing.
Large painful veins can be surgically removed (vein stripping)
EDEMA
If the veins are varicose for a long time, plasma may leak out into the tissues,
causing edema.
Edema means swelling anywhere in the body (including from an injury or from
hanging your legs down too long like when on an airplane), but it frequently
occurs from incompetent veins in the legs.
There are two types of edema:
Pitting
Non-pitting
Pitting edema is when you can push your finger into the skin and it leaves behind your
print when you remove it.
This type is less serious; it tends to be better in the morning since the legs have
been horizontal all night.
It will improve if a pressure bandage is applied.
Treatment of pitting edema
Ace wrap
In the foot or leg always wrap from base of toes all the way to below the knee.
Don’t leave a hole at the heel.
In the hand, always wrap from the base of fingers to wrist before the end of the
elbow
Support hose (don’t use the kind with the open heel; edema will push out of that
area)
Jobst Intermittent Compression
– A machine is used to inflate air in a bag around the leg. The air pressure is
increased and decreased every few minutes to milk the edema out. Patient
goes in for therapy several times a week.
Non-pitting edema is hardened tissue that does not leave your fingerprint.
It is just as bad in the morning as it is at the end of the day.
This is more severe because it does not go away easily.
HELPFUL TIP for everyone:
Buy your shoes at the end of the day when your feet are the most swollen.
Wear new shoes around the house for two hours to make sure they don’t hurt.
Diabetic people need to have someone else examine their feet after wearing a new
pair of shoes for two hours. Check for redness and blisters that they might not see
or feel.
VENOUS STASIS ULCERS
Might occur after the formation of varicose veins, when plasma has leaked out
into the tissues, causing edema.
Acid products from the blood plasma (sugar, carbon dioxide, etc) can eventually
erode all the way to the skin.
Common in diabetics.
Treatment must address sugar levels, vein problem, and the open wound.
PHLEBITIS: inflammation of a vein
Inflammation of a vein
Usually in the legs.
When phlebitis is associated with the formation of blood clots (thrombosis),
usually in the deep veins of the legs, the condition is called Deep Vein
Thrombophlebitis (DVT).
Signs and Symptoms of DVT
Redness (erythema) and warmth with a temperature elevation of a degree or more
above the baseline
Pain or burning along the length of the vein
Swelling (edema)
Vein being hard, and cordlike
Need to go to the emergency room if all symptoms are present
SPIDER VEINS
Small superficial veins become varicose and do not function properly.
Cause an unsightly appearance but are not dangerous.
Injections of alcohol or saline into the vein will sclerose them (scar them shut).
A laser can also be used to do the same.
After treatment, macrophages will eventually phagocytize them and they will
disappear.
Polidocanol (don’t need to know for exam)
A sclerosant, an irritant injected to treat varicose veins. It causes fibrosis inside
varicose veins, occluding the lumen of the vessel, and reducing the appearance of
the varicosity.
The FDA has approved it for veins up to 3 mm in diameter.
It works by damaging the cell lining of blood vessels, causing them to close and
eventually be replaced by other types of tissue.
Tissue Necrosis
Necrosis = dead
Caused by infection, toxins, or trauma
Almost always detrimental and can be fatal
Peripheral Vascular Disease (PVD)
Refers to the obstruction of large arteries, frequently in the lower extremity.
Usually caused from atherosclerosis (fatty plaques).
Symptoms
– Claudication: pain, weakness, numbness, or cramping in muscles due to
decreased blood flow
– Sores, wounds, or ulcers that heal slowly or not at all
– Change in color (blueness or paleness) or temperature (coolness) when
compared to the other limb
– Diminished hair and nail growth on affected limb and digits (shiny,
hairless skin)
RESTLESS LEG SYNDROME (don’t need to know for exam)
This is NOT a blood vessel disease. It is a neurological condition that is characterized by the
irresistible urge to move the legs.
You have a strong urge to move your legs which you may not be able to resist. The need to move
is often accompanied by uncomfortable sensations. Some words used to describe these sensations
include: creeping, itching, pulling, creepy-crawly, tugging, or gnawing.
Your RLS symptoms start or become worse when you are resting. The longer you are resting, the
greater the chance the symptoms will occur and the more severe they are likely to be.
Your RLS symptoms get better when you move your legs. The relief can be complete or only
partial but generally starts very soon after starting an activity. Relief persists as long as the motor
activity continues.
Your RLS symptoms are worse in the evening especially when you are lying down. Activities that
bother you at night do not bother you during the day.
Treatment
Medicines: (don’t need to know for exam)
– Ropinirole (Requip)
– Pramipexole (Mirapex)
– Other drugs approved for other conditions:
Dopaminergic agents
Sleeping aids
Anticonvulsants
Pain relievers