Structure and Function of Blood Vessels Flashcards
Explain the principles of angiogenesis
The sprouting of new capillaries from pre-existing vessels
The process of angiogenesis is controlled by chemical signals in the body. Some of these signals bind to receptors on the surface of normal endothelial cells. When VEGF endothelial growth factors bind to their receptors on endothelial cells, signals within these cells are initiated that promote the growth and survival of new blood vessels. Other chemical signals, called angiogenesis inhibitors, interfere with blood vessel formation.
List some pro-angiogenic factors
VEGFA
Hypoxia
FGF2
Angiopoietins
PDGF
IGF
MMPs
Intergrins
List some anti-angiogenic factors
Angiostatin
Thrombospondin
PEDF
Endostatin
Soluble FLT1
What is the importance of angiogenesis in fetal and post natal development
Metabolically active tissue needs to be “close” to a capillary for gaseous exchange
Explain angiogenesis in adults
Limited in adults
Principally in female reproduction i.e. uterine/ovarian changes and placental development
List pathology of angiogenesis
Wound healing
Skin / heart disease
Tumour development
i.e mammary tumor development
Explain how angiogenesis occurs in repsonse to hypoxia
Cellular responses to hypoxia are mainly regulated by the activation of transcription factors called hypoxia-inducible factors (HIFs)
When O2 levels are low, levels of HIF increase
HIF transactivates target genes such as vascular endothelial growth factor (VEGF-A).
Endothelial cells exposed to the highest VEGF-A concentration become tip cells
Endothelial cell tip secretes proteolytic enzymes, which digest a pathway through the ECM for the developing sprout
Define Vasculogenesis
Formation of blood vessels from endothelial progenitor cells
i.e. angioblasts issued from the mesoderm during embryogenesis.
Describe the concept of a vascular tree
The blood is sent “in parallel”: each tissue receives fresh blood from the heart and not from other tissues
The vascular tree is split in two parts:
1- The systemic circulation
2- the pulmonary circulation
Briefly outline the systemic circulation of the vascular tree
Blood leaves the left ventricle highly oxygenated and under high pressure
This blood is spread throughout the organs excluding the lungs
It is then returned to the right ventricle poorly oxygenated and under low pressure
Briefly outline the systemic circulation of the vascular tree
Blood leaves the right ventricle poorly oxygenated and under high pressure
This blood is received by the lungs
The blood returns to the Left atrium highly oxygenated but under low pressure
Explain theportal system and describe its advantage
Portal system:
A few organs are connected “in series” they obtain their blood “second hand” from the venous outflow of another organ. This is called portal system
i.e. Liver receiving blood from digestive tract via hepatic portal vein
Portal system main advantage
To transport a solute from one place to the other without dilution in the general circulation.
Describe how the portal system varies between species
Hepatic portal vein in all vertebrate:
From the GI to the Liver.
Filter newly absorbed compounds
Renal portal vein in all vertebrate-not mammals (birds)
From the hind limbs to kidney
Resorb salt, water…
Explain the function of anastomosis
Special circulations which form a bridge between arteries if one becomes blocked so that the organ is able to still receive a collateral supply of blood to mitigate necrosis
Explain the function of anastomosis
Special circulations which form a bridge between arteries if one becomes blocked so that the organ is able to still receive a collateral supply of blood to mitigate necrosis
Describe how a vascular tree can vary between species
Differences in aortic arches
i.e. mammals have left aortic arch whereas birds have a right aortic arch
Difference in subclavian placement
i.e. Mammals L & R branches off aorta and aortic arch whereas birds branches off of common carotid
Outline the main functions of blood circulation
To transport gases to and from organs and tissues (E.g. CO2 & O2)
To deliver nutrients (e.g. digested food)
To remove waste (e.g. by products of cellular metabolisms)
To communicate (e.g. insulin)
To maintain the cardiac output pressure (e.g. erectile tissues)
To maintain a constant temperature (for warm blood animals)
Explain how blood is distributed throughout tissues of the body according to their physiological purpose
Generally during rest the GI systems, kidneys and skeletal muscle and brain will receive the majority of blood (Digestion and excretion are priorities)
However, during exercise the Gi system, brain and kidneys blood supply drops significantly within similar range of the bones and skin. Whilst skeletal muscle receives a large increase in blood (80-85%) to support the metabolising tissues. Exercise is the priority
Describe the principal components of a vascular system and their function
Delivery system: arteries and arterioles
- High pressure
- ~15% blood volume
Exchange system: capillaries
- Intermediate pressure
- ~5% blood volume
Return system: venules and veins
- Low pressure
- ~80% blood volume
- (reservoir of blood)
Describe the microscopic structure of veins & arteries and describe their properties
Endothelium
Tunica intima (or interna)
smooth muscles, collagen, elastin
Internal elastic lamina
elastin
Tunica media
smooth muscles, collagen, elastin
External elastic lamina
elastin
Tunica adventitia (or externa)
collagen, elastin
Outline the structure of aorta
High levels of elastin and collagen which damp the oscillating cardiac output when blood leaves.
Blood pressure is the highest and has the largest range within the aorta
Systolic pressure (max pressure in aorta when the heart contracts and ejects blood into the aorta from the left ventricle) 120mmHg
Diastolic pressure (min pressure in aorta when the heart is relaxing before ejecting blood into the aorta from the left ventricle) 80mmHg
Outline the structure and function of arteries
Have a thick outer layer of longitudinal collagen and elastic fibers to avoid leaks and bulges. They have a thick wall, which is essential to withstand the high pressures.
They also have thick layers of circular elastic fibres and muscle fibres to help pump the blood through after each contraction of the heart.
In addition the narrow lumen maintains the high pressure inside the arteries.
Outline the structure and function of the arterioles
Composed of smooth muscle cells
They contract which diminishes the radius of the arterioles (contraction allows regulation in blood pressure between arteries and capillaries).
They provide resistance to blood flow
(hypertension - too much will damage capillaries and could lead to heart failure)
Outline the structure and function of the capillaries
Contain no collagen or elastin
Have relatively low blood pressure due to fragility and permeability
Three types:
-Continous
-Fenestrated
-Discontinuous sinusoid
Mechanisms of nutrient exchange:
-diffusion - O2, CO2, glucose, hormones, electrolytes – diffuse down [ ] gradients
-lipid soluble molecules can pass through cell membrane easily (drugs/therapeutics)
-water soluble molecules generally require transport mechanisms to enter/exit cells
Describe continuous capillaries
Continuous lining of endothelial cells except for clefts between cells
Found in the majority of the body
Describe fenestrated capillaries
Fenestration are no true holes, but rather where the cell membrane is compressed to permit greater fluid transmission
Found in glomerular capillaries in the kidney
Describe discontinuous sinusoid’s capillaries
Some wider intercellular gaps permit increased exchange with surrounding tissues
Found in liver, bone marrow, lymphoid tissue, some endocrine glands
Outline the structure and function of the veins
High levels of collagen but low levels of elastin
This is because blood does not flow in pulses and so the vein walls cannot help pump the blood on.
Veins also have thin walls which allows the near by muscles to press against them so that they become flat. This helps the blood to be pushed forwards towards the heart.
There is only a thin outer layer of longitudinal collagen and elastic fibres as there is low pressure inside the vein and so little chance of bursting.
A wide lumen is needed to accommodate the slow flowing blood due to the low pressure. They have valves to prevent blood pooling at extremities
Describe the process of venous return
Depends on pressure difference between venules and RA (changes in RA pressure changes venous return)
Smooth muscles contraction in tunica media
Inspiration, lower diaphragm/ abdominal compression
Existence of venous valves
Skeletal muscles
Gavitations (upper parts of the body)
Outline the structure and function of tunica intima
-innermost layer of veins/artery
-exposed to the blood
-made of simple squamous
-provides a smooth inner lining that normally repels platelets and blood cells.
Outline the structure and function of tunica media
-the middle layer of arteries/veins.
-thickest
-made of smooth muscle, collagen,sometimes elastic tissue depending if its a vein or artery
Outline the structure and function of tunica externa
-outermost layer of arteries/veins.
-consists of loose connective tissue
-anchors the vessels and provides passage for small nerves, lymphatic vessels, and smaller blood vessels.
-the inner half are nourished by diffusion from blood in the lumen.
Explain the effect of changing vessel diameter on vascular resistance
