Md1 Histology Block3 Circulatory 2

Front 1

____ /____/_____ 3ct are devoid of capillaries.

Back 1

epidermis
cornea of the eye
cartilage

Front 2

Capillaries

is regulated by vessels with

Back 2

smooth muscle in their wa

Front 3

A metarteriole is a vessel that emerges from an arteriole, traverses the capillary network, and empties into a

Back 3

venule

Front 4

The proximal portion of metarterioles are surrounded by

Back 4

scattered smooth muscle

Front 5

The distal portion of a metarteriole has no smooth muscle cells and is called a

Back 5

oughfare channel.

Front 6

True capillaries emerge from arterioles or metarterioles and are not on direct flow route from a

Back 6

arteriole to venule.

Front 7

At their sites of origin, there is a ring of smooth muscle called a

Back 7

precapillary sphincter that controls the flow of blood entering a true capillary

Pic info

Hint 7

Front 8

Capillaries

are composed of a single layer of

Back 8

endothelial cells

Front 9

Capillaries

a few mitochondria
rough endoplasmic reticulam
Junctions of the zonula occludens type are present

Back 9

.

Front 10

Capillaries

________ proximity to that of the endothelial cell. The pericytes have a great potential for transformation into other cells and thus are undifferentiated cells.

Back 10

pericytes

info

Hint 10

At various locations along capillaries and small venules, there are mesenchymal cells with long cytoplasmic processes that partially surround the endothelial cells. These are called pericytes or perivascular cells.

Front 11

Capillaries

can be grouped into 3 types depending on the structure of the endothelial cell and the presence or absence of a basal lamina.

Back 11

continuous
fenestrated
sinusoidal

Hint 11

Front 12

***Nm the type of structure

Back 12

Nm the type of structure

Hint 12

Nm the type of structure







fenestrated
continuous
sinusoidal

Front 13

Few or no vesicles
. in the central nervous system

Back 13

Continuous capillaries

Hint 13

Continuous capillaries

In most regions there is a narrow gap between opposed cell membranes, which contains some electron dense material, but in some regions, the opposed cell membranes fuse to form tight junctions (e.g. in the central nervous system).

Few or no vesicles are encountered in the continuous capillaries of the central nervous system. This feature accounts for the existence of the blood-brain barrier.

Front 14

A continuous basal lamina is present.
What type of vessel

Back 14

2. Fenestrated (Type II or Visceral) Capillaries

Front 15

Fenestrated capillaries are found in tissues where =

Back 15

rapid interchange of substances

Front 16

rapid interchange of substances is required
What vessel type

Back 16

Fenestrated Capillaries

Front 17

These have

1 tortuous path and a greatly enlarged diameter (30-40µm), which slows the circulation of blood.
2 endothelial cells form a discontinuous layer and are separated from one another by wide spaces.
3 multiple fenestrations (no diaphragm) in the endothelial cell wall
4 the presence around the wall of the cells with phagocytic activity (macrophages)
5 absence of a continuous basal lamina.

Back 17

3. Sinusoidal Capillaries

Front 18

Sinusoidal Capillaries

have 5ct points

Back 18

1 tortuous path and a greatly enlarged diameter (30-40µm), which slows the circulation of blood.
2 endothelial cells form a discontinuous layer and are separated from one another by wide spaces.
3 multiple fenestrations (no diaphragm) in the endothelial cell wall
4 the presence around the wall of the cells with phagocytic activity (macrophages)
5 absence of a continuous basal lamina.

Front 19

The sinusoidal capillaries are found mainly in

Back 19

liver
hematopoietic organs
bone marrow
spleen
found in the adrenal cortex
adenohypophysis
endocrine glands

Front 20

Have these types of capillaries? =

liver
hematopoietic organs
bone marrow
spleen
found in the adrenal cortex
adenohypophysis
endocrine glands

Back 20

The sinusoidal capillaries

Front 21

Functions of Capillaries

Capillaries perform at least 3ct important functions. They serve as
=

Back 21

a selective permeability barrier
a synthetic and metabolic system
a nonthrombogenic container for the blood.

Front 22

Info

Permeability of capillary walls varies with the size and charge of the permeating molecules and with the structure of the endothelial cell.

Back 22

Interpreting results of physiologic experiments, researcher have postulated the existence of two sizes of pores in the capillary walls. The smaller pores are thought to have a diameter of 9-11 nm and the larger pores a diameter of 50—70 nm.

Hint 22

Selective permeability:
Capillaries (and postcapillary venules) are often referred to as exchange vessels.
These allows selective movements of small and large molecules from blood to tissues and from tissues to blood.
Small hydrophilic and hydrophobic molecules e.g. oxygen, carbon dioxide, glucose, amino acids and electrolytes can diffuse or are actively transported across the plasma membrane.

Front 23

Functions of Capillaries

Three possible morphologic equivalent to these ‘physiologic pores’ are

Back 23

intercellular junctions and clefts between neighboring endothelial cells

fenestral diaphragms in fenestrated capillaries

large number of pinocytotic vesicles thought to cross the endothelial cells of most capillaries.

Front 24

Functions of Capillaries

Back 24

The intercellular junctions are now believed to be the morphologic counterpart of the small pores postulated by physiologic studies.

The large pores of the physiologist is almost certainly represented by the fenestrae or pinocytotic vesicles of endothelial cells.

Small molecules, water and soluble proteins are transported by pinocytotic vesicles.
Large molecules are transported through fenestrations

Some specific molecules e.g. low-density lipoproteins, cholesterol, transferrins are transported via receptor mediated endocytosis which uses endothelial specific surface receptors.

Front 25

Clinical Note: In abnormal state such as inflammation or injection of snake or bee venom, capillary and postcapillary venular permeability is

Back 25

greatly increased.

Front 26

diapedesis

Back 26

Leukocytes may leave the bloodstream by passing between endothelial cells and entering the tissue spaces

Front 27

Opening of these junctions seems to be mediated by locally liberated pharmacologically active substances, such as =
2ct

Back 27

histamine
bradykinin

Front 28

Functions of Capillaries

. Metabolic Functions: Capillary endothelium 6ct

Back 28

1 Synthesizes substances that modulate blood flow and vascular resistance by secretion of vasoconstrictors (endothelin, angiotensin-converting enzyme) and vasodilators (Endothelial derived relaxation factor and nitric oxide).
2 Regulates immune response by controlling interaction of lymphocytes with endothelial surface by expression of adhesion molecules and their receptors and by the secretion of interleukin IL-1, IL-6 & IL-8. Leukocyte migration from blood to tissue is also regulated by adhesion molecules formed by endothelial cells (Selectins, integrins, CD marker molecules).
3 Synthesizes basal lamina as well as glycocalyx.
4 Converts angiotensin-I to angiotensin-II
5 Inactivates by conversion of bradykinin, serotinin, prostaglandins, norepinephrines, thrombin, etc, to biologically inert compound.
6 Modifies lipoproteins by oxidation.

Front 29

Functions of Capillaries

3. Nonthrombogenic Function:
4ct

Back 29

-Platelets do not normally adhere to intact endothelium.

- due, in part, to the ability of endothelial cells to release prostacyclin (prostaglandin I2) a powerful inhibitor of platelet aggregation

-endothelial lining is disrupted, underlying collagen of basal lamina is stimulus for clot formation.
-Anticoagulants (thrombomodulins & others)
synthesized by endothelial cells.

Hint 29

-Platelets do not normally adhere to an intact endothelium.

-This is due, in part, to the ability of endothelial cells to release prostacyclin (prostaglandin I2) which is a powerful inhibitor of platelet aggregation and thus thrombus (clot) formation.

-If the endothelial lining is disrupted, the underlying collagen of the basal lamina is an important stimulus for clot formation.
-Anticoagulants (thrombomodulins & others) are also synthesized by endothelial cells.