Histology of Blood Vessels Flashcards
(44 cards)
The circulatory system consists of…
* heart
* vascular system (afferent and efferent blood vessels)
What are the functions of these structures?
Heart: Pumps blood
Afferent vessels (veins): Convey metabolism waste products and CO2 to the heart
Efferent vessels (arteries): Conduct nutrients and O2 to tissues
Describe the lymphatic network
Blind capillaries (tubules) converge into larger lymphatic vessels that drain into large veins
What is the lymph?
Fluid conducted by the lymphatic system, formed by plasma enriched with immunoglobins and lymphocytes produced by the lymphatic organs.
Name the types of vessels the blood moves through as it moves away from the heart
Heart
Large (elastic) arteries
Muscular arteries
Arterioles
Metarterioles
Capillary network
Post capillary venules
Venules
Medium/small (muscular) veins
Large veins
Heart
What are the 3 distinct layers of the wall of arteries and arterioles?
Intima
Media
Adventitia
The adventitia or arteries and arterioles often merges with…
dense or loose connective tissue surrounding the vessels
Do walls of veins and venules have equivalent layers to those in arteries and arterioles?
Yes but they are difficult to identify and their borders are often poorly defined
Describe the anastomosing (interconnected, web-like) microvasculature
Metarterioles are small vessels that connect arterioles to the capillary
network.
Postcapillary venules are small veins that collect blood from the capillary network.
The capillary network is located between the metarterioles and postcapillary venules and is the site of gas, nutrient and waste exchange.
Describe the capillary wall
- Simple squamous endothelium with tight junctions sitting on a basement membrane and surrounded by reticular fibres.
- Support is provided by vimentin filaments within the endothelial cells.
- Absent or minor adventitia
How does the cross-sectional area of the aorta compare to that of the capillary network? How does the flow compare?
The total cross-sectional area of the capillary network is 800 times larger than that of the aorta.
The flow in capillaries is 0.3mm/sec compared to 320mm/sec in the aorta (i.e. much slower in capillaries).
Name two substances that increase the permeability of the capillaries.
Histamine
Bradykinin
Other than gas and nutrient exchange, name 3 other roles of the capillaries
- thermoregulation
- regulation of blood pressure
- inflammation
Describe the classification of capillaries
Capillaries are classified based on their permeability.
- Impermeable capillaries
* continuous capillaries - Permeable capillaries
* fenestrated capillaries
* sinusoid capillaries
Describe continuous (impermeable) capillaries
- Contain trans-endothelial channels
- Contain pinocytic vesicles
- Do not contain fenestrations (have tight junctions between endothelial cells with few or no gaps, creating a continuous lining)
- Present in nervous tissue, skeletal, cardiac and smooth muscle, skin, lungs and lymphatic organs
Describe fenestrated (permeable) capillaries
- Contain trans-endothelial channels
- Contain pinocytic vesicles
- Contain fenestrations (pores) with diaphragms
- Enable larger particles and solutes to pass through the capillary wall, like albumin
- Present in intestinal mucosa, pancreas, salivary glands, endocrine glands and renal glomerulus of the kidney
What is the endothelium? What are its 3 primary functions?
The endothelium is a thin layer of specialized cells that line the interior surface of blood vessels, lymphatic vessels and the heart.
- Permeability
- Metabolic function
- Production of vasoactive substances
What is the “permeability” function of the endothelium?
The endothelium has selective permeability, allowing it to control the movement of substances between the bloodstream, lymphatic system and surrounding tissues.
What are the 2 metabolic functions of the endothelium?
- Conversion of angiotensin I to angiotensin II (a hormone that regulates BP)
- Inactivation of vasoconstrictive and pro-inflammatory molecules: bradykinin (a potent stimulator of smooth muscle contraction) and serotonin, prostaglandins, norepinephrine, etc.
Name two vasoactive substances produced by the endothelium and their effects.
Endothelin (vasoconstrictive)
Nitric oxide (relaxing factor, vasodilation)
What is desquamation? What can it lead to?
Desquamation is when endothelial cells get detach and peel off the endothelial lining of blood vessels. This process can trigger fibrin aggregation by attracting platelets and result in the formation of thrombi.
Describe the mechanism of action of endothelin
Endothelin released by endothelial cells will bind endothelin receptors on nearby smooth muscle cells. This leads to an increase in calcium ions in the muscle cell, causing it to contract.
Therefore, endothelin has vasoconstrictive effects of blood vessels.
Describe the mechanism of action of nitric oxide
Nitric oxide released by endothelial cells activates an enzyme called guanylyl cyclase, which increases the levels of cGMP. cGMP reduces calcium levels in the muscle cells, causing it to relax. Therefore, nitric oxide has vasodilative effects on blood vessels.
What is another name for fibrin? Briefly describe its function
Factor Ia
Fibrin is formed by the action of thrombin on fibrinogen as a result of the coagulation cascade. Fibrin combines with platelets to form a hemostatic plug (blood clot) over a wound in the blood vessels.
What is an atherosclerotic plaque?
A buildup of fatty deposits and cholesterol in the walls of arteries. It can lead to endothelial injury and trigger blood clot formation, causing an occlusion of the blood vessels.
