Pathway 13-8-3 Local and Humoral Control of Blood Flow + Lymph FLUID DRAINAGE

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Questions and Answers

What is the primary function of endothelin-1 in the dental pulp microvascular bed?

Modulates shear forces on endothelial cells

Reduces pulpal blood flow through close intraarterial infusions (correct)

Regulates blood flow in response to LOCAL tissue demands

Which substance is likely released from ischemic tissue and plays a significant role in vasodilation?

Angiotensin II

Adenosine (correct)

DOPA

Epinephrine

What effect does angiotensin II have on pulpal blood vessels?

Acts as a vasodilator in response to hypoxia

Induces vasodilation through AT1 receptors

Enhances nitric oxide release

Exerts a vasoCONSTRICT basal tone (correct)

Which of the following substances are involved in the vasodilatory process in pulpal vessels?

Prostacyclin and NO Signup and view all the answers

How do the shear forces from blood flow affect the endothelial cells in pulpal vessels?

Enhance the synthesis of nitric oxide Signup and view all the answers

What is the significance of interstitial fluid accumulation in tissues?

It helps in maintaining fluid balance. Signup and view all the answers

Why is it difficult to distinguish between blood and lymphatic vessels in tissues?

Standard microscopic techniques lack specific lymphatic markers. Signup and view all the answers

Which lymphatic marker is known to be expressed by lymphatic endothelial cells?

Vascular endothelial growth factor receptor-3 (VEGFR-3) Signup and view all the answers

What challenge is associated with identifying lymphatic vessels in dental pulp?

Contradictory results from different studies. Signup and view all the answers

⭐️What conclusion can be drawn regarding the lymphatic supply in pulp tissue?

No draining lymphatic vessels are present in the pulp. Signup and view all the answers

What regulates fluid transport between blood vessels and interstitial space in tissues?

Colloid osmotic (COP)and hydrostatic pressures Signup and view all the answers

Which tissues are exceptions to the presence of lymphatic vessels?

Tooth pulp Signup and view all the answers

What percentage of extracellular fluid in dental pulp is located outside the vascular system?

60% Signup and view all the answers

What is the range of interstitial fluid pressure measured in the pulp?

6 to 10 mm Hg Signup and view all the answers

What implication does a high colloid osmotic pressure (COP) in the pulpal interstitial fluid suggest?

Ineffective drainage of plasma proteins OR normal permeability of pulpal vessels to plasma proteins is relatively high Signup and view all the answers

Which two transport methods are proposed for excess interstitial fluid in the pulp?

Transport to the apical part or blood vessel reabsorption Signup and view all the answers

What does the measurement of interstitial fluid volume in pulp reveal?

A significant extracellular fluid proportion in interstitial space Signup and view all the answers

Why is the drainage of interstitial fluid from the pulp challenging?

Lack of lymphatic vessels in the pulp Signup and view all the answers

Study Notes

Local Control of Blood Flow

Endothelin-1, found in the lining of pulpal blood vessels, can reduce blood flow when directly applied, but does not affect the resting vascular tone
The lining of pulpal blood vessels releases vasodilators like prostacyclin and nitric oxide (NO) to regulate blood vessel tone
NO normally provides a vasodilating effect on pulpal vessels
The force of blood flow against the vessel lining helps regulate the release of NO
Adenosine, released from tissues experiencing lack of oxygen, helps regulate blood flow in response to low oxygen levels in the pulp
When applied from the outside of the vessel wall, adenosine causes pulpal vessels to dilate

### Humoral Control of Blood Flow

Humoral control of blood flow in the dental pulp relates to the influence of substances circulating in the blood on blood vessels
Angiotensin II, produced by the renin-angiotensin system, normally constricts pulpal blood vessels
Receptors for angiotensin II (AT1 and AT2) have been found in rat pulp
Epinephrine, released from the adrenal medulla, constricts pulpal blood vessels by activating alpha-adrenergic receptors, similar to the effect of norepinephrine released from nerve fibers
Dihydroxyphenylalanine (DOPA) also constricts pulpal arterioles when applied directly to the blood vessels

Fluid Drainage in Tissues

Interstitial fluid, the fluid surrounding the cells, is normally regulated by filtration from blood vessels.
During inflammation, increased filtration can lead to fluid accumulation.
Lymphatic vessels are responsible for draining excess interstitial fluid back into the blood vessels.
Lymphatic system also plays a key role in transporting captured antigens and presenting them in lymph nodes.

Lymphatic Vessel Presence in Dental Pulp

The existence of lymphatic vessels in the dental pulp has been a subject of debate due to difficulty in distinguishing them from blood vessels using conventional microscopy.
Several lymphatic markers, including vascular endothelial growth factor receptor (VEGFR-3), have been used to identify them.
Studies using VEGFR-3 showed its expression in both human and mouse pulp tissue, but using multiple lymphatic markers is recommended for definitive identification.
VEGFR-3 has also been found on blood vessels and various immune cells, making it less specific to lymphatic vessels.
Other studies have failed to find lymphatic markers in the dental pulp, and one study observed LYVE-1 staining in pulp immune cells, but not in vascular structures.
Similar observations were made in the lymphatic system of the mouse head, where lymphatic vessels were identified in the mandibular canal.
Research in rats has identified lymphatic vessels in the mandibular canal, starting from below the molars.
Based on the available evidence, it can be concluded that the dental pulp is not supplied with draining lymphatic vessels.

Fluid Exchange in Dental Pulp

Fluid transport between blood vessels and interstitial space in dental pulp is influenced by:
- Colloid osmotic pressure (COP) in plasma and interstitium
- Hydrostatic pressure in plasma and interstitium
- Properties of the capillary membrane
Unlike most tissues, dental pulp lacks lymphatic vessels, meaning excess interstitial fluid is not transported back to circulation through this route.
Dental pulp has an average interstitial fluid volume of 0.6 ± 0.03 mL/g wet weight, representing 60% of extracellular fluid.
Interstitial fluid pressure in dental pulp ranges from 6 to 10 mm Hg, although higher values have been reported.
Pulpal COP is relatively high, reaching 83% of plasma COP, suggesting either high pulpal vessel permeability to plasma proteins or ineffective protein drainage.
Due to the lack of lymphatic vessels, excess interstitial fluid and proteins are transported out of the pulp via two possible mechanisms:
- Flow of fluid towards the apical part of the pulp and out of the apex.
- Reabsorption of fluid into pulpal blood vessels alongside transport of protein-rich fluid towards the apex.

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