+ 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 Histology of the blood vessels the microscopic structure of the wall of the blood vessels including: a. Elastic arteries. Extra notes: Gray b. Muscular (medium-sized) arteries. Important notes: Red c. Medium-sized veins. d. Blood capillaries. + BLOOD VESSELS Arteries: Veins: - Elastic artery. - Venules. - Muscular (distributing) - Small veins. Blood capillaries. (medium-sized) artery. - Medium-sized veins. - Arterioles. Large veins. STRUCTURE OF BLOOD VESSELS The wall of blood vessel is formed of three concentric layers: Tunica Tunica intima Tunica adventitia (interna) media (externa) + GENERAL STRUCTURE OF BLOOD VESSELS wall of blood vessels Outermost layer NOTE: Composed of connective tissue Intermediate layer Is the innermost layer Tunica: a containing (3 layers) The thickest layer (4 layers) general term for a Composed of: Composed of: VASA VASORUM: membrane and other structures (blood vessels supplying other 1- Smooth muscles. blood vessels) that line and •ENDOTHELIAL CELLS: 2- Elastic fibers. Arteries, supplies TM and TA, Veins = cover •Simple squamous epithelium large veins from the arteries, small veins from anastomosies 3- Type III collagen (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 Media Tunica Tunica Intima Tunica •INTERNAL ELASTIC LAMINA: 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: aorta, common carotid a., subclavian a., common iliac a, pulmonary Trunk. MICROSCOPIC STRUCTURE: - Endothelium. 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. Smooth muscle 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 VEIN 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. Pericytes: (protective cells) Continuous blood Capillaries Sinusoidal blood capillaries A- with diaphragms capillaries ■ Have processes. B- without diaphragms ■ Share the basal lamina 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 glomerulus. Red bone marrow, nervous T., C.T. pancreas liver (to discharge and endocrine macrophages and dead cells etc), glands. spleen 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. Capillary b. Fenestrated capillaries b. Arteriole c. Sinusoidal capillaries c. Venule d. AV anastomoses d. Elastic artery 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. Tunica externa 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. Metarteriole 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 d. AV anastomoses --Team histology. 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 occur? Hazim Bajri a. Capillary b. Arteriole For any question or suggestion: c. Venule [email protected] d. Elastic artery e. Muscular artery .