Blood vessels Flashcards
What are the 2 main parts of the circulatory system?
Heart → function = pumping the blood
Vasuclar system → afferent (arteries) and efferent (veins) blood vessels
What are lymphatic vessels?
How do they start?
What are some of their important features?
Lymphatics are an anastomotic network of vessels that start as blind capillaries which converge into larger lymphatic vessels and drain into large veins
Features:
- Removed and recycle tissue fluid (lymph)
- Begin as open-ended lymph “capillaries”
- Very thin endothelium, with no occluding junctions
- No basement membrane, or partial
- Small/large lymphatic vessels can have valves (folds of endothelium) to allow unidirectionnal flow
- Large lymphatics have smooth muscle cells in their walls
What is the lymph composed of?
Lymph is formed by plasma enriched with immunoglobulins and lymphocytes produced by the lymphatic organs
What are, in order, the different types of arteries and veins
Heart
Large veins // Large (elastic) arteries
Medium/small size veins (muscular veins) // Muscular arteries
Venules // Arterioles
Post capillary venules // metarterioles
Capillary network
*each level runs in parallel → can be seen in same plan of section side by side
What are the different parts of the muscular arteries and its characteristics?
Intimar:
- Endothelium (gap and tight junctions)
- Sub-endothelial layer (thin)
- IELM (internal Elastic Limiting Membrane)
Media:
- 4 - 10 layer of smoothe muscle cells + collagen type III (reticular fibers) + proteoglycans
Adventitia:
- Dense irregular CT sometimes with vasa vasorum
What are the different parts of the medium/small size veins and their characteristics?
Intima:
- Endothelium (gap and tight junctions)
- Sub-endothelial layer
- NO IELM
Media:
- Incomplete layer ~2 of smooth muscle cells (CT in between the cells)
Adventitia:
Dense irregular CT with oy without vasa vasorum
*collapsed shape
What stain does the ILEM have affinity with?
Acidophilic → interacts with eosin → bright pink
What are the different parts of the large elastic arteries and their characteristics?
Intima:
- Well developed
- Endothelium → endocytic vesicles, gap and tight junctions
- Sub-endotheliual layer → thin
- IELM → fenestrated, is the 1st layer of elastic membrane before the media
Media:
- Alternance of smooth muscle cell layers and elastic membrane layers
- Rich in collagent type III and chondroitin SO4 proteoglycans
Adventitia:
- Dense irregular connective tissue rich in elastic fibers and collagen type I
- Contains vasa vasorum
What are the different parts of the large veins and their characteristics?
Intima:
- Endothelium
- CT and diffuse small muscle cells
Media:
- 5 layer or less of smooth muscle cells (no elastic membrane in alternance)
- CT and collagen within the layers
Adventitia:
- Often thickest layer
- Dense irregular CT + vasa vasorum
What are the different parts of arterioles and their characteristics?
Intima:
- Endothelium (gap + tight junctions)
- Subendothelial (thin-absent)
- no IELM, small elastic fibers
Media:
- 1 - 2 layers of smooth muscle cells
Adventitia:
- Thin without vasa vasorum
- Composed of connective tissue fibers/fibrils + fibrocytes
*Diamter = 0.5mm or less
*regular round shape
What are the different parts of venules and their characteristics?
Intima:
- Endothelium (with gap and tight junctions)
- No IELM, no Sub-endothelium
Incomplete media
- Pericytes may be present
Thin Aventitia
*Collapsed appearance, irregular shape
0.2mm to 20 um
What are metarterioles and postcapillary venules?
A capillary network is found between metarterioles (branch point of capillaries) and postcapillary venules (merge point of capillaries)
Why do some venules appear white and some red? Some collapsed and some not?
It depends on the method of preparation of the tissue slice
Red → Fixation by immersion bc RBCs are still there (more round?)
White → Fixation by perfusion which removed the blood (more collapsed?)
What is the precappillary sphincter?
It is the site at which the arteriole banches into capillaries → smooth muscle cells form pre-capillar ysphincter to regulate blood flow in the capillary network
*where the metarterial is located
What are AV anastomosis?
Where are direct connections between arterioles and venules (pre → post capillaries)
When there is a leak in the capillaries, the metarteriole can contract to restrain circulation through the capillaries and blood can go direclty to the venules (capillary shunt) by AV anastomosis
What is the average diameter of a capillary?
7-8um diameter
just enough for RBC to pass (7umm diameter)
What is the volume and flow of blood in the capillaries compared to the aorta?
Volume of capillaries = 800 times larger than in aorta
Flow in capillaries = 0.3 mm/sec (VERY SLOW) → allows metabolic echange with tissues
Flow in aorta = 320 mm/sec
*Capllaries are like a lake within a flowing river
What are 5 different functions of the capillaries?
- Exchange
- Nutrition
- Thermoregulation
- Blood pressure regulation
- Inflammation
How do the metarterioles react in cold/hot temperatures?
Cold: Metarteriole relax → vasoconstriction to keep the blood for vital organs
- more blood flows through capillaries of vital organs → more heat brought to the tissue to prevent freezing (ex: red cheeks)
Hot: Metarteriole relax → more blood flows through capillaries → heat dissipation
What are the different type of capillaries?
Structural variations allow different levels of metabolic exchange
Permeable → Fenestrated vs Sinusoids
Impermeable/Continuous
*Impermeable and fenestrated look the same in a light microscope, need to see EM to find differences
What is the structure of permeable sinusoid capillaries?
*ex: SPLEEN, Liver
- Spindle shaped endothelial cells separated (no tight junctions between them, potentially gaps allowing passage of white and red blood cells)
- Cells are maintained by network of reticular fibers (type III collagen, fibrocytes)
- Larger irregular lumen
- No Basement Membrane
What are the common characteristics of fenestrated and impermeable capillaries?
- Zonula Occludens (tight junctions) connect the endothelial cells
- Gap junctions
- Both rest on a BM
- Plasmalemmal / Pinocytic vesicles shuttle proteins from lumen → CT
- Trans-endothelial channels (can open or close)
*Fenestrations → 80 nm in diameter + diaphragm (albumin may pass)
What are the differences between fenestrated and impermeable capillaries?
Fenestrated capillaries have fenestrations (80nm in diameter) within the endothelial cells, most them have diaphragms
*Albumin can pass through the fenestrations
Which of the following tissues have impermeable vs fenestrated capillaries?
- Nervous tissue
- Pancreas
- salivary glands
- muscle tissues
- skin
- lungs
- lymphatic organs
- renal glomerulus of kidney
- intestinal mucosa
Impermeable/continuous capillaries → nervous tissue, skeletal, cardiac, smooth muscle, skin, lung, lymphatic organs
Fenestrated capillaries → Intestinal mucosa, pancreas, salivary glands, endocrine glands, renal glomerulus of kidney
Which substances can go through which transport mechanisms from the lumen → CT of the capillaries ?
- Lipid soluble subtances (VitA) → diffuse freely through all capillaries
- Small water soluble molecules < 10Å and ions → trans-endothelial channels
- Molecules < 90Å → Pinocytic vesicles
- Molecules > 90Å → fenestrations
How do the hydrostatic pressure and osmotic pressure vary from metarteriole to postcapillary venule in the capillaries?
Arterial end → High Hydrostatic pressure, Low Osmotic pressure → loss of H2O
Venous end → Low Hydrostatic pressue, High Osmotic pressure → recovery of H2O
*Net liquid loss in the CT → drained through the lymphatic vessels
What are the characteristics of lymphatic vessels?
- No RBC
- Very thin endothelial cells → without occluding and gap junctions
- No Basement Membrane
- Endothelial cells anchored to the CT fibers (Type I and III collagen, elastic fibers in larger vessels)
- Valves → folds of the wall projecting in the lumen
- Large lymphatic vessels (ex: thoracic duct) have smooth muscle cells in their walls
What are the 4 main functions of Endotheliums?
1) Permeability
2) Metabolic function
3) Production of Vasoactive substances
4) Anti-thrombigenic function → Thrombi form from a cascade of events that produce fibrin from blood fibrinogen → grows to complete obstruction of local flow → Emboli can detach and obstruct distant blood vessel
How are Endothelium involved in metabolic functions?
- Conversion of Angiotensin I → Angiotensin II
- Inactivation of bradykinin (stimulator of smooth muscle contraction) and or serotonin, prostaglandins, norepinephrine, etc.
Which vasoactive substances are produced by the endothelium?
- Endothelin (vasoconstrictive):
- Binds to Endothelin receptor
- Receptor converts PIP → IP3
- Increase in intracellular Ca2+ in smooth muscle cells → Contraction - Nitric Oxide (relaxing factor)
How does blood clotting occur?
When damage to a blood vessel → platelets immediately adhere to cut edges → release chemicals that attract more platelets → platelet plug forms to stop external bleeding
Fibrin (Factor Ia) = fibrous, non-globular protein involved in blood clotting
Fibrin is formed by action of protease thrombin on fibrinogen which causes it to polymerize into fibrin
Fibrin + platelets forms hemostatic plug/clot over wound site
*Fibrinogen is secreted by hepatocytes
What is an atherosclerotic plaque?
Build up of fat in the artery wall → thins the lumen of the artery → can possibly rurpture the endothelium → exposes CT to protease thrombin → fibrin clot which blocks the blood vessel
What is the Thoracic duct and its function?
It is a Large lyphatic vessel
Empties into venous system at the junction of jugular and subclavian veins
Layer of smooth muscle in different blood vessels?
Elastic artery = 30-50
Muscular artery = 4-10
Arteriole = <4
Venule = none
Medium vein = incomplete
Large vein = 4-5
