Blood Vessels and Circulation. 2 Some embryology first There are at first six pairs of aortic...

Blood Vessels and Circulation

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Some embryology first

There are at first six pairs of aortic arches

In fish these are connected to the gills

They undergo a transformation in mammals Birds use the right

arch of the fourth pair Mammals use the

left arch of the fourth pair

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Ventral (anterior) view

Full set of arches develops,but not all present at the same time; (beforetransformation)

Transformation :4th through 7th

weeks: some persist,some atrophy

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Right common carotid a ------------------------------.Right subclavian a. --------------------------Brachiocephalic trunk-----------------------------------

4th arches become: Left side: aortic arch Right side: brachiocephalic trunk

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What the aortic arches become…

Right common carotid a ---------------------------.Right subclavian a. ---------------------------Brachiocephalic trunk-------------------------------

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3 Major types of blood vessels

Body RA RV Lungs LA LV Boby

1.Arteries2.Capillaries 3.Veins

Arteries carry blood away from the heart-”branch,” “diverge” or “fork”

Veins carry blood toward the heart-”join”, “merge,” “converge”

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General characteristics of vessels

Three layers (except for the smallest)1. Tunica intima - AKA intima

2. Tunica media – smooth muscle

3. Tunica externa - AKA adventitia

Lumen is the central blood filled space

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Intima is endothelium (simple squamous epithelium)

Tunica media: layers of circular smooth muscles Lamina (layers) of elastin and collagen internal and external Thicker in arteries than veins (maintain blood pressure)

Smooth muscle contraction: - vasoconstriction

Smooth muscle relaxation: - vasodilation

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Adventitia (t. externa) – longitudinally running collagen and elastin for strength and recoil

15“muscular” middle sized artery

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Arteries Carry blood away from the heart From biggest to smallest, these are the categories:

1. Elastic 2. Muscular 3. Arterioles (then these to capillaries)

Pressure diminishes along the route

1. Elastic arteries: act as conduits 2.5-1 cm diameter Expand with surge

of blood from heart contraction Recoil from heart relaxation, which aids movement of blood Elastin is thick in media:

dampens the surge of blood pressure

Aorta and its branches

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Arteries continued

2. Muscular arteries: act as distributing arteries

Middle sized .3mm-1cm Changes diameter to

differentially regulate flow to organs as needed

Internal as well as external elastic lamina

Most of what we see as “arteries”

From these we measure blood pressure

Tunica media larger in proportion to the lumen, thus “muscular”

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Arteries continued

3. Arterioles Smallest: .3mm-10um Only larger ones have all 3 layers Send blood into capillaries

Tunica media has only a few layers of smooth muscle cells

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Capillaries

Heart arteries capillaries veins heart

Capillaries are smallest blood vessel 8-10um Just big enough for a single file of erythrocytes (RBCs) Composed of:

single layer of endothelial cells surrounded by a membrane

General Function Oxygen and nutrient delivery to tissues CO2 and nitrogenous waste (protein break-down product)

removal

Types of Capillaries

1. Continuous – has virtually no “gaps” open in its walls (e.g., blood-brain barrier)

2. Fenestrated – numerous “pores” in the endothelium (e.g., intestinal lining, kidneys, endocrine glands)

3. Sinusoids – modified “leaky” capillaries (e.g., liver, spleen, bone marrow)

Continuous Capillaries

Figure 19.3a

Fenestrated Capillaries

Figure 19.3b

Sinusoids

Figure 19.3c

Capillary Beds

A microcirculation of interwoven networks of capillaries, consisting of: Vascular shunts – thoroughfare channel

connecting an arteriole directly with a venule True capillaries – 10 to 100 per capillary bed,

capillaries branch off and return to the thoroughfare channel

Capillary Beds

Blood Flow Through Capillary Beds

Precapillary sphincter Cuff of smooth muscle that surrounds each

true capillary Regulates blood flow into the capillary

Blood flow is regulated by vasomotor nerves and local chemical conditions

Capillary Beds

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Veins

From smallest to large:Capillaries venules veins heart

Veins are larger than arteries Tunica externa is thicker

But…blood pressure is lowered at capillaries, so the walls of veins are much thinner There is less elastin

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Special features of veins

Valves Prevent backflow Most abundant in legs (where

blood has to travel against gravity)

Muscular contraction Aids the return of blood to heart in

conjunction with valves

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Exercise helps circulation (because muscles contract and squeeze blood back to the heart)

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Vascular anastomoses (shunts)

Alternative pathways or connections between blood vessels

Protect organs from being supplied by just one route Poor anastomoses & therefore vulnerable: central

artery of retina, kidneys, spleen, bone diaphyses

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Angiogram

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Major Arteries

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Systemic Veins

3 major vessels enter Right Atrium: SVC (superior vena cava) IVC (inferior vena cava) Coronary sinus

Many veins are very superficial (unlike arteries)

Venous plexuses (networks of anastomoses and parallel veins) are very common

Head and hepatic portal systems are unusual

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Vein overview

Note that unlike the arteries, the veins have a brachiocephalic on the right and left sides

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Leg veins Names similar to

arteries Femoral becomes

external iliac after crossing under inguinal ligament

External iliac joins with internal iliac to form common iliac vein

_________used for grafting in coronaryartery bypass grafts: is the longest vein in the body

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Vascular System (Blood vessels of the body)

Two circulations Systemic Pulmonary

Arteries and veins usually run together Often nerves run with them Sometimes the systems do not have bilateral

symmetry In head and limbs, most are bilaterally symmetrical

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Pulmonary Circulation

Pulmonary trunk branches Right and left pulmonary arteries Division into lobar arteries

3 on right 2 on left

Smaller and smaller arterioles, into capillaries surrounding alveoli Gas exchange

Pulmonary system pressure is only 1/6 of systemic blood pressure

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Pulmonary Circulation

After gas exchange blood enters venules Larger and larger into Superior and Inferior

Pulmonary veins Four Pulmonary Veins empty into left atrium

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In lungs

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Systemic Circulation Oxygenated blood to body Leaves LV through Ascending Aorta

Only branches are the 2 coronary arteries to the heart Aortic Arch has three arteries branching from it:

1. Brachiocephalic trunk, has 2 branches: Right common carotid a. Right subclavian a.

2. Left common carotid a.3. Left subclavian a.

Ligamentum arteriosumconnecting to pulmonary a.

remember aortic arches…

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Hepatic portal system Picks up digested nutrients from stomach & intestines

and delivers them to liver for processing and storage Storage of nutrients Detoxification of toxins, drugs, etc.

Two capillary beds Route: artery to capillaries of gut to hepatic portal

vein to liver’s capillaries to hepatic vein to IVC

Tributaries of hepatic portal vein:-superior mesenteric vein-splenic vein-inferior mesenteric vein

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Assignment - Some Diseases

Atherosclerotic cardiovascular disease Cerebrovascular disease Coronary artery disease (CAD) Peripheral vascular disease (PVD)

Affecting veins Chronic venous insufficiency Deep venous thrombosis (DVT)

Aneurysms Portal hypertension Hypertension

Blood Vessels and Circulation. 2 Some embryology first There are at first six pairs of aortic...

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