Pericytes and the Blood-Brain Barrier

Questions and Answers

What is a characteristic function of precapillary sphincters in true capillaries?

They facilitate the exchange of gases and nutrients.

They maintain the structural integrity of the capillary.

They contract or relax to regulate blood entry. (correct)

They operate independently of metarterioles.

How does blood flow through capillaries when precapillary sphincters are closed?

Blood flow is halted completely in the capillary network.

Blood flows continuously into the capillaries.

Blood is diverted back to the arteries.

Blood flows directly from metarterioles to post capillary venules. (correct)

What role do tight junctions play in capillaries?

They support the rhythmic contraction of muscle fibers.

They regulate the permeability of the capillary walls. (correct)

They prevent the formation of basal lamina.

They promote nutrient absorption from surrounding tissues.

What structural feature is often observed in the nuclei of capillary cells?

They are typically curved to fit the tubular structure. Signup and view all the answers

What distinguishes the structural variation in capillaries across different organs?

Variations depend on the specific metabolic needs of the organs. Signup and view all the answers

What is the primary function of capillaries in the circulatory system?

They facilitate the exchange of nutrients and waste. Signup and view all the answers

Which type of capillary has pores that allow for increased permeability?

Fenestrated capillaries Signup and view all the answers

What is the average diameter of capillaries, which allows blood cells to transit one at a time?

4 to 10 μm Signup and view all the answers

What role do pericytes play in the structure of capillaries?

They assist in regulating blood flow and capillary stability. Signup and view all the answers

In which situation is blood flow to capillary beds maximally efficient?

When blood is shunted away by contracted sphincters. Signup and view all the answers

How is blood oxygenation characterized as it moves through the capillaries?

Blood enters well oxygenated and leaves poorly oxygenated. Signup and view all the answers

What is not a characteristic of continuous capillaries?

They contain large intercellular clefts. Signup and view all the answers

What is a common clinical condition associated with capillary dysfunction?

Diabetic microangiopathy Signup and view all the answers

Which characteristic is specific to fenestrated capillaries when compared to other types of capillaries?

They contain large perforations without diaphragms. Signup and view all the answers

What role do pericytes play in the maintenance of the blood-brain barrier?

They help maintain endothelial tight junctions. Signup and view all the answers

What is a consequence of the larger diameter of fenestrated capillaries?

Slower blood flow through the capillaries. Signup and view all the answers

What physiological change occurs in pericytes following tissue injury?

They proliferate and differentiate into smooth muscle cells. Signup and view all the answers

Which of the following organs does NOT typically contain fenestrated capillaries?

Lungs Signup and view all the answers

In diabetic microangiopathy, what is the primary effect on capillaries?

Diffuse thickening of capillary basal laminae. Signup and view all the answers

How do fenestrated capillaries differ structurally from continuous capillaries?

They contain discontinuous endothelial cells with holes. Signup and view all the answers

What is a key function of capillaries in relation to pericytes?

Capillaries facilitate molecular exchange between blood and tissue fluid. Signup and view all the answers

What role do pericytes play in relation to fenestrated capillaries?

They provide structural support. Signup and view all the answers

Which of the following features allows fenestrated capillaries to be more permeable than continuous capillaries?

Large openings within the endothelial cells. Signup and view all the answers

How do pericytes respond to vasoactive agents like histamine?

By altering the permeability of the endothelial barrier. Signup and view all the answers

What type of vascular structure is often found along continuous capillaries and postcapillary venules?

Pericytes. Signup and view all the answers

Which cell type is included in the pericyte population and is vital for tissue regeneration?

Mesenchymal stem cells Signup and view all the answers

Fenestrated capillaries are primarily known for which of the following functions?

Selective filtration of plasma components. Signup and view all the answers

What is a major consequence of hyperglycemia on capillary function?

Reduced metabolic exchange across blood vessels. Signup and view all the answers

What structure is primarily disrupted in diabetic microangiopathy?

The capillary basal laminae Signup and view all the answers

What is the primary function of pericytes in relation to capillaries?

They regulate blood flow by dilating or constricting capillaries. Signup and view all the answers

What structural characteristic allows for greater exchange across endothelial layers?

Fenestrations in the endothelial cells. Signup and view all the answers

Which component do pericytes secrete that supports their function?

Extracellular matrix (ECM) components. Signup and view all the answers

What is a distinguishing feature of progressively larger collecting venules?

They contain a recognizable tunica media with smooth muscle layers. Signup and view all the answers

Which proteins are primarily found in the cytoskeletal network of pericytes?

Myosin, actin, and tropomyosin. Signup and view all the answers

How do pericytes interact with endothelial cells?

Through long cytoplasmic processes that partially surround them. Signup and view all the answers

What effect do pericytes have on the blood flow of red blood cells?

They regulate blood flow by contracting or dilating capillaries. Signup and view all the answers

Which statement accurately describes the relationship between pericytes and basal lamina?

Pericytes produce a basal lamina that can fuse with endothelial cells. Signup and view all the answers

Study Notes

Capillaries Overview

Capillaries are the smallest blood vessels, with an average diameter of 4 to 10 μm and a wall thickness of only 0.25 μm.
They facilitate nutrient, waste, O2, and CO2 exchange through their endothelial structure.
Blood enters capillary beds in a pulsatile manner due to the contraction of precapillary sphincters.

Types of Capillaries

Continuous Capillaries:
- Composed of a single layer of endothelial cells forming a tube.
- Characterized by tight junctions and few gaps, allowing selective permeability.
Fenestrated Capillaries:
- Contain pores (fenestrations) around 80 nm in diameter, enhancing exchange capabilities.
- Found in organs like the liver, spleen, some endocrine glands, and bone marrow.
- Possess a discontinuous basal lamina and larger diameters (30-40 μm), which slow blood flow.
Discontinuous Capillaries:
- Have large openings with a discontinuous endothelial layer, permitting maximal substance interchange.

Pericytes

Mesenchymal cells located alongside continuous capillaries and postcapillary venules.
Involved in maintaining the endothelial blood-brain barrier within the CNS.
Regulate blood flow by contracting or dilating capillaries, with a significant role in tissue regeneration after injuries.

Venules

Formed from the convergence of postcapillary venules into larger collecting venules.
As they increase in size, they develop tunica media with smooth muscle layers, termed muscular venules.
Facilitate the collection of blood from capillaries and act as sites for material exchange and white blood cell migration into tissues.

Clinical Application

Diabetic Microangiopathy:
- A consequence of hyperglycemia in diabetes leading to diffuse thickening of capillary basal laminae.
- Impairs metabolic exchange, notably affecting the kidneys, retina, skeletal muscle, and skin.

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Description

This quiz explores the role of pericytes within the central nervous system and their importance in maintaining the endothelial blood-brain barrier. It also discusses their functions, including collecting blood from capillaries and responding to vasoactive agents after tissue injuries.