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Home , Precapillary sphincter, Tunica externa, Tunica intima, Tunica media

Anatomy Lecture Objectives Chapter 19

Chapter 19 - Vascular System

A. categories and general functions:

1. - carry away from

2. - allow exchange of materials between blood and tissue fluid

3. - return blood to heart

B. wall structure - most walls have 3 layers

lumen = space inside vessel

1. / tunica interna

- simple squamous e.

subendothelial layer - loose c.t. ()

2.

a. - cells circularly arranged

controlled by ANS and chemical factors

constriction (smooth muscle contracts) decreases blood flow and increases systemic blood pressure

dilation (smooth muscle relaxes) increases blood flow and decreases systemic blood pressure

b. elastic c.t.

3. tunica adventitia /

c.t. attaches vessel to surrounding structures

nourish outer part of vessel wall

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Anatomy Lecture Objectives Chapter 19

C. arteries

1. elastic (conducting) - large arteries near heart ( and major branches) conduct blood to muscular arteries low resistance tunica media = circular sheets with few smooth m. cells recoil maintains blood pressure during diastole

2. muscular - middle-sized arteries, distal to elastic arteries distal to elastic arteries tunica media very thick; much smooth m. and some elastin regulate blood flow to organs have an internal and an external elastic lamina

3. - smallest arteries tunica media contains smooth m. only diameter controlled by ANS and chemical messengers diameter determines blood flow and blood pressure

D. capillaries

wall consists of endothelium and basal lamina (no tunica media or externa) 8 to 10 mm in diameter join and branch to form beds cells are joined at spots around perimeter by tight junctions and desmosomes intercellular clefts are spaces between cells

1. types

a. fenestrated capillaries (high permeability) have fenestra (openings) in endothelial cells some fenestra are covered by a membrane, others are not also have intercellular clefts found in small intestine, synovial joints, kidney

b. continuous capillaries intercellular clefts but no fenestra most common type

c. sinusoids wide, leaky capillaries, usually fenestrated fewer cell junctions allow passage of large particles found in bone marrow, spleen, liver

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Anatomy Lecture Objectives Chapter 19

d. low-permeability capillaries

2. capillary beds

metaarteriole thoroughfare channel

capillaries

- smooth m. cell wrapped around origin of capillary controls blood flow through capillaries when sphincter is closed, blood is diverted to thoroughfare channel sphincter controlled by autoregulation (local control, not nervous system)

E. veins

have thinner walls than arteries for the same diameter (larger lumen) act as capacitance vessels - store extra blood (65%) low pressure tunica adventitia thicker than tunica media venous valves prevent backflow

F. a vascular anastomosis occurs when vessels join midstream

anastomoses provide alternate pathways (collateral channels)

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Anatomy Lecture Objectives Chapter 19

G. circulatory routes

1. pulmonary circuit: right ventricle to to left atrium pressure supplied by right ventricle low pressure system takes low oxygen blood (75% saturated) to lungs and brings high oxygen (98% saturated) blood back to heart

right ventricle

pulmonary semilunar valve

pulmonary trunk

left and right pulmonary arteries

lobar arteries (3 R, 2 L) take blood to lobes

pulmonary capillaries

pulmonary veins (superior and inferior, L and R)

left atrium

2. systemic circuit: left ventricle to body to right atrium pressure supplied by left ventricle high pressure system takes O2 to tissues and removes CO2 distributes nutrients from digestive tract to body collects wastes and takes them to kidney for excretion

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Anatomy Lecture Objectives Chapter 19

a. circulatory pathways of the brain (cerebral arterial circle, circle of Willis)

anterior communicating a.

anterior cerebral a.

internal carotid a.

posterior communicating a.

posterior cerebral a.

basilar a.

vertebral a.

cross section of neck:

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Anatomy Lecture Objectives Chapter 19

b. hepatic portal circulation

portal system = two capillary beds in series, joined by veins or arteries

capillaries of small intestine, part of large intestine and stomach

superior mesenteric

capillaries of spleen, stomach and pancreas

splenic vein

capillaries of distal large intestine and rectum

inferior mesenteric vein

hepatic portal vein

liver

liver sinusoids

hepatic veins

inferior vena cava

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Anatomy Lecture Objectives Chapter 19

c. fetal circulation

placenta = organ formed from extra-embryonic membranes and endometrium to exchange materials between fetal and maternal blood

umbilical vein from placenta

fetal liver

hepatic portal vein

ductus venosus

inferior vena cava

right atrium foramen ovale left atrium

right ventricle left ventricle

pulmonary trunk ductus arteriosus aorta

lungs

internal iliac a.

umbilical a. to placenta

adaptations:

1) to bypass the fetal liver ductus venosus - allows some umbilical vein blood to go through the fetal liver but diverts most of it directly into the inferior vena cava

2) to bypass the non-functional fetal lungs a. foramen ovale – opening in interatrial septum that allows blood to go from the right atrium directly into the left atrium b. ductus arteriosus – vessel that connects pulmonary trunk and aorta

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