Ch 20   Blood Vessels                                                          

FLOWCHART: Types of blood vessels (ARTERIES – VEINS - CAPILLARIES)

Heart  >  Elastic (conducting) arteries  >  Muscular (distributing) arteries  >  Arterioles (resistance vessels) >  Capillaries > Venules > Veins > Heart

            Lymph vessels > Veins

Three Tunics (layers) of Blood Vessels

Tunica intima (interna) –`

 

Tunica media –

 

Tunica externa –

 

Comparison of structure of three tunics in Arteries, Veins, Capillaries – see Fig. 20.1(a)

Artery – thicker wall (thicker tunica media, thicker elastic fibers); narrower lumen

           

Vein – thicker tunica externa; wider lumen; valves

           

Capillaries – tunica intima only

Other Comparisons of Arteries and Veins:

Microscopic structure of Arteries and Veins  - see Fig. 20.1(b); Fig. 20.2

Types of Arteries:

            Elastic (conducting)                                        Muscular (distributing)

•                                                                       •

                       

•                                                                       •

                       

•                                                                       •

                       

•                                                                       •

                       

•                                                                       •

                       

•                                                                       •

            Arterioles (resistance vessels)                      Veins

•                                                                       •

                       

•                                                                       •

                       

•                                                                       •

                       

•                                                            •

              

Capillaries

•  size

                       

•  structure

                       

•  general functions

                       

•  special functions

General anatomy of a capillary bed – “microcirculation”

terminal arteriole

                               

precapillary sphincters

                                   

metarteriole

                                   

thoroughfare channel

                                   

true capillaries

                                   

postcapillary venule 

                                   

“open” vs “closed” capillary beds

          

 Types of Capillaries

Continuous –

                       

Common; in most organs – muscles, skin, brain, spinal cord

                           

Mostly tight junctions

                      

Some intercellular clefts – gaps for small molecules

                           

Pericytes

                

Fenestrated -

                     

High rates of exchange – intestines, glands, kidneys, joints

                          

“Fenestrations" or "windows” pass small molecules

                 

Sinusoid –

                           

Liver, bone marrow, spleen

                     

Wide, leaky capillary; irregular shape

                           

Clefts wide open; extensive exchange of large molecules

                

Special Example: “BBB” or Blood-Brain Barrier

                     

Impermeable complex of brain capillaries and associated astrocytes

                          

Continuous capillaries with complete tight junctions

                          

No clefts, no fenestrae, no caveoli

                          

Have special transport mechanisms for select substances

                    

Substances which pass through freely:

                         

Breaking the BBB

                 

Tissues and organs which do not have capillaries:

                          How are they nourished?      

MAJOR BLOOD VESSELS OF THE BODY                       

Pulmonary Circulation

            

Large vessels that enter and leave the heart –

                 

Oxygen-poor -  Pulmonary trunk > pulmonary arteries

                                              

Superior and inferior vena cava

                                              

Coronary sinus - receives blood from coronary veins

                     

Oxygen-rich  -  Aorta

                                    

Coronary arteries   

                                             

Pulmonary veins

Systemic Circulation – see Overview Fig. 20.8

HANDOUT: Some large ARTERIES of the human body

(10) Aorta

Ascending –

                       

Coronary arteries

             

Aortic Arch -

             

Descending –

                      

Thoracic

                      

Abdominal

Branches of Aortic Arch – arteries to the neck, brain and arm

(7)

(8)

(9)

Arteries that supply the brain –

(1)

(2)

Arteries of the upper limb and thorax –

(8)

(2)  (11)  (12)

(13)

Radial

Ulnar

Volar arch

Digital arteries

Celiac Trunk and branches –

(3)

      left gastric

      common hepatic

      splenic

Other branches of the abdominal aorta –

(5)

(4)

(14)

(15)

*Three major (unpaired) vessels supply the digestive tract – celiac trunk, superior mesenteric and inferior mesenteric. The portal system drains these organs.

Arteries of the pelvis and lower limb –

(6)

(17)

(16)

(19)

(18)

Popliteal

Anterior and posterior tibial

Fibular

Plantar arch

Digital arteries

Veins have thin walls and carry blood under low pressure. How does blood return to the heart?

1.

           

2.

           

3.

The “skeletal muscle pump” –

Anastomoses -

Refer to HANDOUT: Some large VEINS of the human body

Veins from the brain drain into dural sinuses.

Superior sagittal sinus

Transverse sinus

Internal jugular vein

Venous drainage of the head, neck and brain –

(1)

(2)

(10)

(11)

Veins of the thorax and upper limb –

(3)

External & Internal Jugulars > Subclavian > Brachiocephalic > Superior Vena Cava

The Azygos System_

(13)

Veins of the Upper Limb -

            Deep set:

(4)

                       

(6)

                       

(8)

                       

(9)

            Superficial set:

(5)

                       

(7)

                       

Median cubital

Tributaries of the Inferior Vena Cava  (12)

Hepatic

           

Renal

           

Lumbar

           

Gonadal

Veins of the Pelvis and Lower Limb –

            Deep set:

(16)

                       

(17)

                       

(18)

                       

(20)

            Superficial:

(19)

Portal system

Definition:

Veins of the hepatic portal system –

(14)

(15)

In-Class Exercise on the Portal System

What is the hepatic portal system and why is it important?

Where is the blood?

Pulmonary circuit?        Heart?       Arteries?      Veins?       Capillaries?