Blood Vessels

What is the role of the heart?

to pump blood

What are efferent vessels?

the arteries which conduct oxygen and nutrients to the tissues which diffuse out through the capillary network

What are afferent vessels?

the veins which convert CO2 and waste (the product of metabolism of the tissues) to the heart

What is an example of a large elastic artery?

aorta

What is the system for the circulation of blood?

heart → large elastic artery → muscular arteries → arterioles → metarterioles → capillary network → post capillary venule → venues → medium/small vein → large veins

What the differences between arteries and veins? how can you tell them apart?

*in cross section:

• artery - large potion of media, more circular due to thicker wall*

• vein - smaller media, more cylindrical due to thinner wall*

**in longitudinal section

• artery may not be seen, still larger media 

• vein has little to no media, also looks more collapsed

Compare muscular artery vs vein

• both have intima (containing endothelium → squamous simple epithelium)

  • Intima in artery contains Internal Elastic Lamina (IELM)

  • artery also contains sub-endothelial layer

• both have media (smooth muscle cells) 

  • artery has more layers of smooth muscle cells 

• adventitia → dense irregular CT

  • possibly both contains vasa vasorum

What is the vasa vasorum?

small blood vessels within a blood vessel

describe the characteristics of the muscular artery

• media contains 4+ layers of smooth muscle

• should see intima, media with IELM, adventitia

• circular  

describe the characteristics of the muscular vein

• incomplete media of smooth muscle 

• collapsed lumen

• adventitia present 

describe an elastic artery

• you get alternation between smooth muscle cells and elastic membranes in the media

describe large vein

• media contains few layer of smooth muscle cells (scattered)

• no elastic membranes 

• lumen often contain blood cells as well 

• no IELM

Describe arterioles

• media contains 1-2 smooth muscle cells

• circular

• very small in size

describe a venule

• absent media

• collapsed lumen

• lumen stains very pink due to blood vessels sometimes

• fibrocytes

What is the volume of the capillaries?

800 times larger than the aorta 

What is the flow in the aorta compared to the capillaries?

Aorta: 320 mm/sec

capillaries: 0.3 mm/sec

What is the function of the capillaries?

1. Exchange of gases

2. Nutrition 

3. Thermoregulation (more blood going in = warmer)

4. BP regulation 

5. Inflammation 

What happens if blood volume decreases?

durring hemorrhage the body senses the decrease in blood pressure and the sphincter on the metarteriole closes → blood enters into post capillary venules 

describe the classification of capillaries according to permeability

permeable: 

• fenestrated 

• sinusoids 

impermeable or continuous

reticular fibres are collagen type..

3

What junctional complexes are found between the epithelial cells of the capillaries?

Zonula Occludens (tight and gap junctions)

What cell is found to support post capillary venules?

Pericyte

Where are sinusoids found?

in the liver

describe the characteristics of sinusoids

they do not have tight junctions (the cells are completely separated)

surrounded by reticular fibres

fluids flow well because there are no junctions

What is the difference between impermeable and fenestrated capillaries?

Both: 

• have tight junctions

• Plasma lema vesicles (do endo and exocytosis → molecules less than 90 A pass through)

Impermeable:

• transendothelial channels (small water soluble molecules only and they can open and close)

• Clatherin coated vesicles (similar to other vesicle)

• Found in nervous, skeletal, cardiac, smooth muscle, skin, lungs, lymphatic organs

Fenestrated

• big openings that look like rings (fenestrations/pores → molecules bigger than 90 A pass through)

• found in pancreas, salivary glands, endocrine glands, glomerulus of kidney

What diffuses freely through all capillaries?

Lipid soluble substances

How is the capillary system divided?

the arterial end → hydrostatic pressure is high and osmotic pressure low

venous end → hydrostatic pressure low and osmotic pressure high (due to proteins)

Describe the lymphatic vessels

• they are channels within connective tissue containing lymph

• very thin endothelial cells (not occluding and gap junctions)

• no basement membrane associated with endothelium

• Endothelial cells are anchored to the connective tissue fibres (type 1 and 3 collagen, elastic fibres) 

• large lymphatic vessels have smooth muscle cells in their walls 

What is the function of the endothelium?

1. permeability 

2. metabolic function (convert angiotensin 1 → 2, can also inactivate bradykinin which stimulates smooth muscle contraction)

3. endothelial cells can also inactivate serotonin, prostaglandins, norepinepherine

4. production of vasoactive substances (can’t tell muscle cells to contract or relax) → endothelin (constriction)

5. Anti-thrombogenic function

How does Endothelin work?

endothelin released into endothelial cells → binds to its receptor in smooth muscle cell → causes calcium to increase → contraction 

calcium also activates myosin light chains → contraction of smooth muscle cell

What does nitric oxide do?

relaxing factor

nitric oxide synthase catalyzes a reaction → nitric oxide produced → acts on enzyme → enzyme generates cyclic GMP from GDP → vasodilation → relaxation

describe the Anti-thrombogenic function of endothelial cells

during injury connective tissue is exposed → has thrombin → thrombin acts on fibrinogen → generates fibrin → helps blood clot 

there is also an accumulation of platelets that helps with clotting 

What is atherosclerosis?

the accumulation of cholesterol in the artery (between intima and media)

Damage to the arterial wall → LDL cholesterol enters the wall and becomes oxidized → macrophages come in forming a fatty streak → lipids and smooth muscle build up, creating a fibrous plaque → decreased blood flow