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Home , Arteriole, Elastic artery, Internal elastic lamina, Tunica externa, Tunica intima

+ Motivational Corner:

Mistakes are proof that you are trying.

Objectives: By the end of this lecture, the student should be able to identify and describe of the vessels the microscopic structure of the wall of the blood vessels including:

a. Elastic . Extra notes: Gray b. Muscular (medium-sized) arteries. Important notes: Red c. Medium-sized .

d. Blood .

+ BLOOD VESSELS

Arteries: Veins: - Elastic . - . - Muscular (distributing) - Small veins. Blood capillaries. (medium-sized) artery. - Medium-sized veins. - . Large veins.

STRUCTURE OF BLOOD VESSELS The wall of is formed of three concentric layers:

Tunica Tunica adventitia (interna) media (externa) + GENERAL STRUCTURE OF BLOOD VESSELS wall of blood vessels

Outermost layer NOTE: Composed of

Intermediate layer Is the innermost layer Tunica: a containing (3 layers) The thickest layer (4 layers) general term for a

Composed of: Composed of: : membrane and (blood vessels supplying other other structures 1- Smooth muscles. blood vessels) that line and •ENDOTHELIAL CELLS: 2- Elastic fibers. Arteries, supplies TM and TA, Veins = cover •Simple squamous large veins from the arteries, small veins from anastomosies 3- Type III (reticular

•SUBENDOTHELIAL LAYER: fibers). •loose C.T. They are small arterioles in tunica 4- Type I collagen. adventitia and the outer part of

. Tunica Media Tunica Tunica Intima Tunica •: fenestrated elastic sheet. They are more prevalent in the

NB: Large muscular arteries Adventitia Tunica walls of veins than arteries – why? have external elastic lamina, Venous blood contains less oxygen separating the tunica media and nutrients than arterial blood. from the tunica adventitia + ELASTIC ARTERIES Examples: , common carotid a., subclavian a., common iliac a, pulmonary Trunk.

MICROSCOPIC STRUCTURE:

- . it consists of:

A. Fenestrated (openings

for nutrition) elastic Much thinner membranes (sheets) than T.M. -Subendothelial (lamellae): C.T. It is the main It is composed of component of T.M. loose C.T. - Internal elastic B. In between, there are:

lamina: 1. cells. Contains vasa T. Media T. T. Intima T. 2.Collagen fibers (type I vasorum → send (not prominent) collagen). T. Adventitia T. branches to the 3. Reticular fibers (type (indistinct) III collagen). outer part of T.M. 4. Elastic fibers. + MUSCULAR ARTERIES (Medium-sized artery) Examples: brachial, ulnar, renal. MICROSCOPIC STRUCTURE:

- Endothelium. (Thicker than T. Adventitia or similar in thickness).

Loose CT

- Subendothelial Components: C.T. layer. A- Smooth muscle cells (SMC): are the predominant component. - Internal elastic lamina: B- In between there are:

•Elastic fibers. T. Media T. T. Intima T. •Type III collagen fibers.

Is prominent. •Type I collagen fibers. Adventitia T.

Displays an C -External elastic lamina: undulating surface. may be identifiable. + VALVES OF VEINS MEDIUM-SIZED Valve of a vein is composed of Thickness of the wall: thinner than the accompanying artery. 2 leaflets Each leaflet has a thin fold of

the T. Intima.

usually forms Thinner than Thicker than valves. T. Adventitia T. Media COMPONENTS:

NO internal Rich in vasa ■Endothelium

Consists of: vasorum ■Core of C.T. T. Media T. T. Intima T. elastic • Fewer SMCs.

T. Adventitia T. lamina • Types I & III Collagen fibers. + BLOOD CAPILLARIES Diameter: usually 8-10 µm.

MICROSCOPIC STRUCTURE: Types of blood capillaries: 1. Single layer of squamous endothelial cells. 2. Basal lamina: surrounds the external Fenestrated blood surface of the endothelial cells. 3. : (protective cells) Continuous blood Capillaries Sinusoidal blood capillaries capillaries ■ Have processes. A- with diaphragms ■ Share the basal lamina B- without diaphragms of the endothelial cells.

Pericytes around here + TYPES OF BLOOD CAPILLARIES:

CONTINUOUS BLOOD FENESTRATED BLOOD FENESTRATED BLOOD SINUSOIDAL CAPILLARIES CAPILLARIES CAPILLARIES WITH CAPILLARIES DIAMETER: IRREGULAR DIAPHRAGMS WITHOUT DIAPHRAGMS (30-40 µM). (DICONTINUOUS) MICROSCOPIC No pores or The walls of their The walls of their - Their endothelial cells fenestrae in their endothelial cells endothelial cells have fenestrae (wide) STRUCTURE: without diaphragms. walls. have pores have pores - They possess (fenestrae). (fenestrae). discontinuous endothelial NO GAPS cells. - They possess These pores are These pores are discontinuous basal covered by NOT covered by lamina. diaphragm. diaphragm. - Macrophages may be (diaphragm acts like a located in or along the valve) outside of the endothelial wall. (Reticular fibers hold the cells together) DISTRIBUTION: In muscles, In intestine, In renal . Red bone marrow, nervous T., C.T. pancreas liver (to discharge and endocrine macrophages and dead cells etc), glands. and certain endocrine glands. + + MCQs 1- Which of the following is a distinct structure found 5- At what level of the vascular tree does gas specifically in the liver, spleen, and bone marrow? exchange occur? a. Continuous capillaries a. b. Fenestrated capillaries b. c. Sinusoidal capillaries c. d. AV anastomoses d. e. Venous sinus e. Muscular artery

2- What do you call the simple squamous epithelium that 6- Which layer in an artery is primarily smooth

D - lines the blood vessels? muscle? 8

a. Epithelioid tissue C - a. Tunica intima 7

b. Mesothelium b. Tunica media

B -

c. Endothelium c. 6

A -

d. Transitional d. All of the above 5

A - e. Pseudostratified e. None of the above 4

D -

3- What is a thoroughfare which is a an intermediate 7- Which of the following constitutes the 3

C -

between an arteriole and capillary? microvascular bed of a tissue? 2

C - a. Metcapillary a. Capillaries 1 b. Metartery b. Capillaries and arterioles c. Metvenule c. Capillaries, arterioles, and post capillary venules d. d. Capillaries, arterioles, post capillary venules, and veins e. None of the above e. Capillaries, arterioles, post capillary venules, veins, and arteries 4- In which structure are things moved across the Done by: Thanks for checking epithelium via pinocytotic vesicles? 8-What is a direct route between arteries and veins Areeb AlOgaiel our work, Good a. Continuous capillaries called? luck! b. Fenestrated capillaries a. Continuous capillaries Edited by: c. Sinusoidal capillaries b. Fenestrated capillaries Shadn Alomran --Team histology. d. AV anastomoses c. Sinusoidal capillaries e. Venous sinus d. AV anastomoses Team leaders: e. Venous sinus Areeb AlOgaiel 5- At what level of the vascular tree does gas exchange Hazim Bajri occur? a. Capillary b. Arteriole For any question or suggestion: c. Venule [email protected] d. Elastic artery e. Muscular artery