Blood Vessels and Lymphatics Flashcards
What is the function of capillary beds?
1- Exchange of tissue fluid, nutrients, oxygen and waste.
2- In inflammatory situations, cells can also be exchanged
What are the three layers present in blood vessels?
1- Tunica intima (innermost)
2- Tunica media (middle)
3- Tunica adventita (outermost)
Which vessels are mainly elastic?
Large arteries such as the aorta and pulmonary trunk as they are conducting arteries
Which vessels are mainly muscular?
Medium arteries such as the femoral, axillary and carotid arteries are muscular to control distribution and flow
Which vessels are thin-walled and often with valves?
Veins in order to store and return blood to the heart
When do muscular arteries dilate?
When a major artery to an area is occluded, smaller collateral muscular arteries enlarge to carry the needed blood to the ischaemic area
What do muscular arteries do when injured?
They contract to prevent haemorrhage
Give examples of muscular arteries.
1- Internal and external carotid in the neck
2- Axillary artery in UL
3- Femoral artery in LL
What is the difference between arteries proximally and distally?
1- Proximally arteries are elastic or mixed (elastic becoming muscular)
2- Distally arteries are muscular but gradually decrease in thickness and calibre
Describe the distribution of the UL arteries.
Subclavian > axillary > brachial > ulnar and radial
What is arterial anastomosis?
1- A connection between two arteries resulting in an extensive supply of blood vessels
2- E.g. Superficial and deep palmar arches
3- All joints have anastomoses around them
Describe the distribution of LL arteries.
Femoral > popliteal > anterior and posterios tibial > fibular
What is the relationship of the femoral artery with its vein and nerve?
The femoral artery lies between its vein and nerve, with the vein being most medial and the nerve most lateral.
What are venae comitantes?
1- Large arteries have venae comitantes, which are smaller separate veins which lie close to them
2- Arterial movement or pulsation encourages venous return
How are thrombi formed?
In arteries, plagues of atheroma may form leading to a thrombus and vascular occlusion.
What is the approximate diameter of arterioles?
~0.5mm
What is the approximate diameter of metarterioles?
Same diameter as capillaries (~5-10µm), but with only one layer of smooth muscle cells in their walls
What are capillaries?
1- Sites of exchange for CO2, O2, nutrients, hormones and tissue fluid
2- Present in virtually all tissues
3- Capillaries cannot contract as they do not have smooth muscles in their walls. However, the basal lamina splits to enclose pericytes which contract and constrict capillaries
What are pericytes?
1- Myoepithelial cells
2- Present in basal lamina of capillaries
3- Contract and constrict capillaries
What is the basic structure of capillaries?
1- Smallest vessels
2- Endothelial linings which are only one cell thick
3- Supported on a basal lamina
4- ~8µm in diameter
What are postcapillary venules?
1- Located just after capillaries, delivering to venules
2- Smallest venules
What are precapillary sphincters?
1- Sphincters which close or limit blood supply to organs and/or conserve oxygen
2- This does not apply to certain organs which must have their blood flow maintained e.g. brain, heart, lungs and kidneys
Describe the basic structure of the layers of veins and venules.
1- Tunica media is thin and often incomplete, with only a few smooth muscle fibres
2- As the vessel becomes thicker, the amount of muscle in the media increases and a thick tunica adventita develops
3- Tunica intima has a continuous endothelium with a thin basal lamina
What is diapedesis and how does it apply to venules?
1- Passage of leukocytes through walls of venules, which then escape into surrounding connective tissue
1- Passage of leukocytes through walls of venules, which then escape into surrounding connective tissue
1- Valve leaflets arise from tunica intima and are covered by endothelium
2- When the blood pressure proximal to the leafelets is greater than distally, the valves close, preventing backflow.
Describe the distribution of veins in the LL.
1- LL arteries, which are situated depply within the muscle compartments, are accompanies by venae comitantes
2- These converge to form the popliteal vein
3- Popliteal > femoral > external iliac > common iliac > inferior vena cava
4- Superficial veins: great long saphenous vein medially and small short saphenous vein laterally, both with many tributaries
How does venous blood flow in the LL?
1- Superficial to deep
2- Against gravity
3- Via perforators and then muscle pump, arterial pulsation and negative intrathoracic pressure
Describe the distribution of veins in the UL.
1- Arranged around arteries
2- Superficial system also present
3- Median cubital vein links cephalic and basilic veins across the front of the elbow joint, site of venipuncture
What does the superior vena cava drain?
Drains head, neck and upper limbs into the right atrium.
What does the azygos vein drain?
Drains thoracic wall into the superior vena cava.
What does the inferior vena cava drain?
Drains lower limbs, pelvic organs, kidneys and abdominal walls into the right atrium.
What is the hepatic portal vein?
1- Venous blood from the components of the GI tract and spleen does not return directly to the heart
2- Instead it forms the hepatic portal vein, which takes the venous blood through the liver before draining into the inferior vena cava
Give an example of another portal circulation.
1- Pituitary gland
2- Hypophyseal portal system
What is the lymphatic system?
1- A network of lymph nodes
2- Mops up interstitial tissue fluid, some of which ends up back in the circulation
3- Lymph capillaries are thin-walled, endothelial tubes
4- Superficial lymphatics are related to veins while deep lymphatics are related to arteries
Where are lymph nodes usually clustered?
Iliac and para-aortic lymph nodes
What are lymphocytes and where are they made and stored?
1- Protective cells of the body
2- Made and stores in the lymph nodes as well as the tonsils, thymus, spleen and intestinal wall
What are the three superficial, palpable lymph node collections?
1- Superficial inguinal and deep inguinal
2- Axillary
3- Superficial and deep cervical
Where can the superficial inguinal nodes be palpated?
Inferior to inguinal ligament and alongside the great saphenous vein in the groin
Where do the superficial inguinal nodes drain?
Drain into the deep inguinal nodes
Where can the deep inguinal nodes be palpated?
Alongside femoral vein
Where do the deep inguinal nodes drain?
External iliac lymph nodes
Where do inguinal nodes receive afferents/lymph drainage from?
1- LL 2- Buttock 3- External genitalia 4- Lower back 5- Abdominal wall bellow umbilicus
Where can the axillary nodes be palpated?
1- Axillary nodes are groupes in the axilla
2- Related to the axillary vein and artery
3- Lateral, deep to and medial to pectoralis minor (axillary nodes are arranged in many groups)
Where do axillary nodes receive afferents/lymph drainage from?
1- UL
2- Anterior and posterior thoracic walls
3- Upper abdominal wall above umbilicus
4- Breast
Where can superficial cervical lymph nodes be palpated?
Under the jaw, over parotid, behind ear or on the occipital bone (cervical nodes are arranged in many groups)
Where can deep cervical lymph nodes be palpated?
Alongside the internal jugular vein
What do the cervical lymph nodes drain?
Head and neck structures
What is the largest lymph vessel?
Thoracic duct
Where does the thoracic duct enter?
It enters the junction of the left subclavian, internal jugular veins at the level of the brachiocephalic vein
