What are the functions of the blood circulatory system?
- Deliver O2 and nutrients to tissues
- Remove CO2 and other waste products from tissues
- Transport cells of the immune system
- Distribute chemical messengers (e.g. hormones) Temperature regulation
What are the functions of the lymphatic system?
- Drain extracellular fluid (lymph) from the tissues, to the blood circulatory system
- Immunological screening via passage through the lymph nodes
What are the 3 layers that form the common structure of blood vessels?
1. Tunica Intima – internal
2. Tunica Media - intermediate
3. Tunica Adventitia - outer
the dilatation of blood vessels, which decreases blood pressure.
Function of the endothelium?
- Actively involved in mediating the exchange of small molecules between the interstitial fluid and blood plasma and restrict the transport of macromolecules
- Assists the migration of lymphoid cells to and from tissues.
- Clotting regulation
What is the tunica intima composed of ?
- A layer of endothelial cells lining the vessel’s inner surface including the basal lamina
- In larger vessels, a subendothelial layer of loose connective tissue that may contain a few smooth muscle cells which tend to be organised longitudinally.
- An internal elastic lamina lies beneath the subendothelial layer which is well developed in muscular arteries
What is the Tunica Media composed of ?
- Concentric layers of helically arranged smooth muscle cells
- Variable amounts of elastin and proteoglycans (depending on the vessel size)
- In arteries the media is separated from the intima by an internal elastic lamina and from the adventitia by an external lamina.
What is the Tunica Adventitia composed of ?
- Longitudinally orientated (type 1) collagen and elastic fibres
- The adventitia gradually becomes continuous with the enveloping connective tissue of the organ through which the vessel is running. The adventitia is often the most prominent coat in veins
Where does most of the blood pressure regulation occur?
What are the final branches of the arterial system?
Which vessels lack the intimal, medial and adventitial layers that are present in the rest of the circulatory system?
What are the smallest vessels in the circulatory system?
What are capillary pericytes?
Pericytes are capillary support cells that are found wrapped around the vessel in close contact with the basal lamina of the vessel.
What are the 4 types of capillaries?
2. Fenestrated with diaphragm
3. Fenestrated without diaphragm
Why are valves necessary in vessels?
They prevent backflow of blood in vessels.
Venous blood flow is driven by a combination of contraction of the smooth muscle wall of the vessel and contraction of surrounding skeletal muscle. Valves are necessary to prevent backflow of blood.
What are varicose veins? and what is the cause?
Varicose veins are swollen and enlarged veins – usually blue or dark purple – that usually occur on the legs. They may also be lumpy, bulging or twisted in appearance.
Varicose veins develop when the small valves inside the veins stop working properly.
In a healthy vein, blood flows smoothly to the heart. The blood is prevented from flowing backwards by a series of tiny valves that open and close to let blood through.
If the valves weaken or are damaged, the blood can flow backwards and collect in the vein, eventually causing it to be swollen and enlarged (varicose).
walls are thinner in veins than in arteries
What does the blood circulatory system consist of??
what is this??
Left: muscular artery
Right: Elastic artery
describe the intima, media and adventitia in elastic arteries
Tunica Intima: Of all the types of arteries, the elastic arteries have the thickest intima with connective tissue displaying a longitudinal orientation and an internal elastic lamina present.
Tunica Media: In elastic arteries contains layers of concentrically arranged elastic fibres. There are smooth muscle fibres between the elastin, along with proteoglycans. The elastin provides the resilience to smooth out the pressure wave.
Tunica Adventitia: Underdeveloped and contains elastic and collagen fibres.
function of elastic arteries?
The aorta and its largest branches (brachiocephalic, common carotid, subclavian, common iliac)
Conduct the blood away from the heart and distribute it to the medium sized arteries.
They receive blood from the heart at high pressure but this is intermittent and therefore they must stabilize the flow by extending during systole and recoiling during diastole.
Vasa Vasorum ??
Internal layers of larger vessels are too thick to be sustained by simple diffusion of nutrients from the blood. They therefore require blood vessels to run within their vessel walls (vasa vasorum).
describe the intima, media and adventitia in muscular arteries
Intima: Thinner than elastic arteries .
Media: Up to 40 layers of smooth muscle and some elastin and proteoglycans are present. It is usually between 1cm and 0.5cm in diameter
Adventitia: Collagen and elastic fibres present as well as fibroblasts and fat cells.
describe the intima, media and adventitia in
Intima: Very thin and lacks internal elastic lamina.
Media: 1-5 layers of smooth muscle cells
Adventitia: Very thin
functions of arterioles?
Final branches of the arterial system
Important regulators of blood distribution to the capillaries.
The small lumen allows the vessel to be closed to generate resistance to blood flow which is the major determinant of blood pressure.
functions of capillaries?
Smallest vessels of the circulatory system.
Specialised for diffusion of substances across their wall. • Structurally, they lack the intimal, medial and adventitial layers present in the rest of the circulatory system.
Thinnest walls of all the blood vessels, a low blood flow and a large surface area.
They are the major site of gaseous exchange, permitting the transfer of oxygen from blood to tissues and carbon dioxide from tissues to blood. Fluids containing large molecules pass across the capillary wall in both directions.
what is this?
Continuous Capillary ??
Found in the brain, muscle, thymus, bone and lung.
Transport substances through the cytoplasm by diffusion and pinocytosis.
Endothelial cells are held together by tight junctions and the basal lamina is continuous.
Fenestrated Capillary ???
Endothelial cell has many fenestrations with or without diaphragms and a continuous basal lamina.
Present in tissues involved in fluid transport (intestinal villi, choroid plexus and the glomerular capillaries).
Discontinuous Capillary ??
Gaps are larger than fenestrated capillaries and the basal lamina is discontinuous.
Found in tissues where there is a need for a close association of blood and the parenchyma
(e.g. liver and spleen).
what is the Venous System ??
Blood from capillaries enters a system of venules (10-25μm) which initially are very similar to capillaries but have more pericytes.
Post capillary venules drain into larger venules (20-50 μm) in which the pericyte layer becomes continuous and surrounding collagen fibres appear.
As the collecting vessels becomes larger the pericytes are replaced by smooth muscle and and an adventitia becomes identifiable. These muscular venules (50-100 μm) drain into veins.
Veins vary in size from less than 1mm to 40mm in diameter. The lumen of veins is large but the walls are thin and usually look collapsed in histological sections. As with arteries their structure depends on size.
structure of veins?
Small Veins (up to 1mm)
There is a more clearly defined muscular coat than muscular venules.
Medium Veins (1 to 10mm)
There is evidence of a discontinuous internal elastic membrane. The adventitia is well developed.
The intima is well developed with collagen and elastic fibres. As is the adventitia.
characteristics of Veins ??
Arteries vs. Veins ??
Veins have a highly distensible wall resulting in an irregularly shaped lumen histologically
Walls are thinner in veins than in arteries
Valves present in Veins
Summary of Venous and Arterial Architecture
The Lymphatic Vascular System ??
Lymphatic capillaries originate in tissue as thin blind-ended vessels consisting of a single layer of endothelium without fenestrations, junctional complexes or a basal lamina
Lymphatics act as a drainage system removing surplus fluid from the tissue spaces
Like veins, valves are present to maintain flow in one direction
On its way to larger vessels the fluid passes through lymph nodes to allow antigen processing by the immune system
The larger vessels have muscular walls and pump the lymph into the main channels -the thoracic duct or the lymphatic duct from where it enters the blood vascular system
Role of Lymphatics in Digestion ??
Lacteal- lymphatics in the small intestine which aid in the absorption of certain fats
Chyle- a milky fluid consisting of lymph and emulsified fats
do lymph vessels contain red blood cells?