Blood Vessels Peripheral Circulation

Question 1

Types of Blood Vessels

Answer 1

Arteries—carry blood away from the 
heart 
•  Capillaries—smallest blood vessels 
– The site of exchange of molecules between 
blood and tissue fluid 
•  Veins—carry blood toward the heart

Question 2

Types of blood vessels

Answer 2

  Elastic arteries (diameter 1 - 2.5 cm)
conduct blood
•  Muscular arteries (diameter 0.3 mm – 1.0cm)
distribute blood
•  Arterioles (diameter 10 µm to 0.3 mm)
•  Capillaries (diameter from 8–10 µm)
•  Venules (diameter from 8–100 µm)
•  Veins

Question 3

Three layers (tunics) of arteries

Answer 3

Lumen: central blood-filled space of a vessel
•  Tunica intima:
– Endothelium composed of simple
squamous epithelium
– Subendothelial layer
– Internal elastic membrane
•  Tunica media: sheets of smooth muscle and
elastic fibers, and external elastic membrane
• Contraction—vasoconstriction
• Relaxation—vasodilation
•  Tunica externa—composed of collagen fibers

Question 4

Elastic Arteries for conducting blood

Answer 4

•  The largest arteries
•  Diameters range from 2.5 cm to 1 cm
•  Includes the aorta and its major branches
•  Sometimes called conducting arteries
•  High elastin content dampens surge of blood pressure
•  Vasa vasorum: network of small blood vessels which supply
large vessels

Question 5

Muscular arteries for distributing blood

Answer 5

Lie distal to elastic arteries 
•  Diameters range from 
1 cm to 0.3 mm 
•  Includes most named 
arteries 
•  Tunica media is thick 
•  Unique feature: internal 
and external elastic 
membranes that dampen 
the pulsatile pressure 
produced by the heartbeat

Question 6

Arterioles

Answer 6

Smallest arteries 
•  Diameters range from 0.3 mm to 10 µm 
•  Larger arterioles possess all three tunics 
•  Diameter of arterioles controlled by: 
• Local factors in 
the tissues 
• Autonomic 
nervous system

Question 7

Capillaries

Answer 7

Smallest blood vessels with diameter 8–10 µm
•  Red blood cells pass through in single file
•  Site-specific functions of capillaries include:
• Lungs: oxygen enters blood, carbon
dioxide leaves blood
• Small intestines: receive digested
nutrients
• Endocrine glands: pick up hormones
• Kidneys: remove of nitrogenous wastes

Question 8

Poorly vacularized tissues

Answer 8

•  Tendons and ligaments—poorly 
vascularized 
•  Epithelia and cartilage—avascular 
– Receive nutrients from nearby 
connective tissue

Question 9

Capillary beds

Answer 9

•  Networks of capillaries running through

tissues

Question 10

Precapillary sphincters

Answer 10

•  Regulate the flow of blood to tissues
•  When relaxed, the precapillary sphincters are
open and the blood runs through the true
capillaries
•  When constricted, the precapillary sphincters
are closed and the blood runs through the
metarteriole thoroughfare channel and
bypasses true capillaries

Question 11

Types of capillaries

Answer 11

•  Continuous capillaries: lowest permeability;
form the blood brain barrier
•  Fenestrated capillary: large fenestrations
(pores) increase permeability in small
intestines and kidneys
•  Sinusoidal capillary: most permeable with
wide open intercellular clefts in bone marrow,
liver and spleen

Question 12

Continuous capillaries

Answer 12

Most common type
•  Relatively low permeability
•  Found in skin, muscle, blood brain barrier
•  Capillaries have complete tight junctions of endothelial
cells which prevent functional intercellular clefts
•  Vital molecules pass through via highly selective
transport mechanisms
•  Not a barrier against oxygen, carbon dioxide, and some
drugs (e.g. anesthetics) so these pass through the
blood brain barrier
•  The lowest permeability continuous capillary is in the
CNS and forms the blood brain barrier

Question 13

Pericytes

around continuous capillary

Answer 13

•  Contractile cells that wrap around 
endothelial cells 
•  Embedded in basement membrane of 
endothelial cells and communicate with 
and help sustain endothelial cells

Question 14

Fenestrated capillaries

Answer 14

Large fenestrations (pores) result in 
increased permeability 
•  Found in kidneys & small intestine

Question 15

Summary of Routes of
Permeability into and out of
capillaries

Answer 15

•  Direct diffusion through endothelial cell
membranes
•  Through pinocytotic vesicles
•  Through fenestrations
•  Through intercellular clefts (especially
in sinusoidal capillaries)

Question 16

Sinusoidal capillaries

Answer 16

• Most permeable capillaries
• Wide open intercellular clefts (gaps of unjoined membrane through which small molecules can enter and exit)
• Usually fenestrated
• Incomplete basement membrane
• Have a large diameter and twisted course
• Occur in bone marrow, liver, and spleen

Question 17

Venules and veins

Answer 17

•  Conduct blood from capillaries toward the
heart
•  Blood pressure is much lower than in arteries
•  Smallest veins—called venules
– Diameters from 8–100 µm in venules
– Smallest venules—called postcapillary
venules
•  Venules join to form veins
•  Tunica externa rich in collagenous tissue is
the thickest tunic in veins

Question 18

Mechanisms to help move venous blood

Answer 18

•  Valves in some veins 
particularly in limbs 
•  Skeletal muscle 
press against vein 
walls and help pump 
blood toward the 
heart

Question 19

Vascular Anastomoses

Answer 19

  Vessels interconnect to form vascular 
anastomoses 
– Organs receive blood from more than one 
arterial source 
•  Neighboring arteries form arterial 
anastomoses 
– Provide collateral channels 
•  Veins anastomose more frequently than 
arteries

Question 20

Vasa Vasorum

Answer 20

-Vessels of vessels
-network of small blood vessels
which supply large vessels
•  Tiny arteries, capillaries, and veins
nourish outer region (tunica externa) of
large vessels
•  Inner half of large vessels receive
nutrients from luminal blood

Question 21

Pulmonary Circulation

Answer 21

• Pulmonary trunk leaves the right ventricle, divides into right and left pulmonary arteries and carries de-oxygenated blood to lungs
• Superior and inferior pulmonary veins carry oxygenate blood into the left atrium

Question 22

Systemic arteries

Answer 22

Carry oxygenated blood away from the
heart
•  Aorta—largest artery in the body

Question 23

The Aorta 1

Answer 23

Ascending aorta—arises from the left 
ventricle 
– Early branches form coronary arteries 
•  Aortic arch—lies posterior to the 
manubrium and has these branches: 
• Brachiocephalic trunk: right common 
carotid and right subclavian branch off 
this 
• Left common carotid 
• Left subclavian artery

Question 24

The Aorta 2

Answer 24

Descending aorta—continues from the
aortic arch
– Thoracic aorta—in the region of T5–T12
– Abdominal aorta—ends at L4
•  Divides into right and left common iliac
arteries

Question 25

Common Carotid Arteries

Answer 25

``` Located in the anterior triangle of the neck •  Two branches of the common carotid artery – External carotid artery – Internal carotid artery ```

Question 26

External carotid artery branches

Answer 26

*   Superior thyroid artery *   Lingual artery *   Facial artery *   Occipital artery *   Superficial temporal artery *   Posterior auricular *   Maxillary artery

Question 27

Internal carotid artery branches

Answer 27

Ophthalmic artery •  Anterior cerebral artery •  Middle cerebral artery

Question 28

Cerebral artery circle

Answer 28

•  The cerebral artery circle forms a loop around the pituitary gland and optic chiasm and unites the brain’s anterior and posterior blood supplies which are provided respectively by the internal carotid (anterior blood supply) and vertebral arteries (posterior blood supply)

Question 29

Cerebral artery circle

Answer 29

•  Vertebral arteries extend off subclavian artery and supply blood to posterior brain •  Vertebral arteries merge to form the unpaired basilar artery which ascends along ventral midline of brain stem and at border of the pons and midbrain it divides into a pair of posterior cerebral arteries •  Posterior communicating arteries connect the posterior cerebral arteries to the middle cerebral arteries anteriorly •  The anterior cerebral arteries extend off the middle cerebral arteries and are connected by the anterior communicating artery

Question 30

Arteries of the arm

Answer 30

``` Subclavian artery enters the axilla as the axillary artery •  Axillary artery becomes the brachial artery at the inferior border of teres major muscle ```

Question 31

Arteries of forearm and hand

Answer 31

Brachial artery divides into radial artery and ulnar artery which transition into superficial and deep palmar arches and digital arteries

Question 32

Arteries of the Abdominal Aorta

Answer 32

``` Inferior phrenic •  Celiac trunk •  Superior mesenteric •  Suprarenal (adrenal) •  Renal •  Gonadal (testicular or ovarian) •  Inferior mesenteric •  Common iliac ```

Question 33

The Celiac Trunk its main arterial branches supply viscera in the superior part of the abdomen

Answer 33

•  Three main branches of the celiac trunk are the left gastric, splenic, and common hepatic arteries. •  The celiac trunk and its branches send arteries to the stomach, liver, gallbladder, pancreas, spleen, and duodenum

Question 34

Superior & Inferior Mesenteric Arteries

Answer 34

•  From the superior mesenteric artery, arteries extend to the jejunum, ileum, and the proximal half of the colon (cecum, appendix, ascending colon, and part of the transverse colon) •  From the inferior mesenteric artery, arteries extend to the distal half of the colon (2nd half of the transverse colon, descending colon, sigmoid colon, and rectum)

Question 35

Artery branches off the internal iliac

Answer 35

*   Gluteal *   Obturator *   Internal pudental *   Vesical *   Uterine

Question 36

Arteries of the Pelvis and Lower Limbs

Answer 36

``` Internal iliac •  External iliac •  Femoral •  Popliteal •  Anterior tibial •  Posterior tibial •  Fibular •  Dorsalis pedis •  Plantar •  Plantar arch ```

Question 37

Systemic Veins

Answer 37

``` •  Three major veins enter the right atrium •  Superficial veins lie just beneath the skin •  Veins have valves which prevent the backflow of blood •  Multivein bundles—venous plexuses •  Unusual patterns of venous drainage – Dural sinuses – Hepatic portal system ```

Question 38

Venous supply into right atrium

Answer 38

``` Superior vena cava: returns blood from body regions superior to the diaphragm •  Inferior vena cava: returns blood from body regions inferior to the diaphragm •  Coronary sinus: returns blood from cardiac muscle ```

Question 39

Coronary sinus | supply into Right Atrium

Answer 39

Right atrium receives blood via the coronary sinus (large vein) in posterior part of coronary sulcus which receives blood from cardiac veins (great, middle, and small cardiac veins)

Question 40

Dural sinuses in brain

Answer 40

•  Venous channels found between dura mater and the brain •  Walls of the dural venous sinuses are lined with endothelium •  Internal jugular vein drains the dural venous sinuses

Question 41

Dural sinuses of Head & Neck

Answer 41

``` Dural sinuses – Superior and inferior sagittal sinuses – Straight sinus – Transverse sinuses – Sigmoid sinus – Cavernous sinus ```

Question 42

Veins of the Head and Neck

Answer 42

``` •  Venous drainage of head & neck into bracheocephalic vein: – Internal jugular – External jugular – Vertebral ```

Question 43

Deep Veins of the upper limbs which | follow path of companion arteries

Answer 43

```   subclavian •  axillary •  brachial •  radial •  ulnar vein •  deep palmar arch •  digital ```

Question 44

Superficial veins of the upper | limbs easily visible beneath skin

Answer 44

``` Cephalic •  Basilic •  Median cubital (common site to draw blood) •  Median antebrachial of the forearm ```

Question 45

Superficial Veins of Right Upper Limb

Answer 45

•  Form anastomese frequently •  Median cubital vein is used to obtain blood or administer IV fluids

Question 46

Veins of the Thorax

Answer 46

*   Azygos *   Hemiazygos *   Accessory hemiazygos *   Intercostal

Question 47

Veins of the Abdomen

Answer 47

``` Inferior phrenic •  Hepatic •  Suprarenal •  Renal •  Lumbar •  Gonadal (testicular or ovarian) ```

Question 48

Hepatic Portal System

Answer 48

A specialized part of the vascular circuit •  Picks up digested nutrients from the stomach and intestine and delivers nutrients to the liver for processing and storage

Question 49

Hepatic portal system

Answer 49

•  Series of vessels in which two separate capillary beds lie in between arterial supply and final venous drainage •  Capillary beds in the stomach and intestines receive digested nutrients and then drain into the hepatic portal vein •  Hepatic portal vein delivers nutrient-rich but oxygen poor blood to a second capillary bed (the liver sinusoids) through which nutrients reach liver cells for processing •  After passing through liver sinusoids, blood enters hepatic veins and then inferior vena cava thereby re-entering the general systemic circulation

Question 50

Superficial Veins of the Pelvis and | Lower Limbs

Answer 50

•  Small saphenous vein empties into popliteal vein which empties into femoral vein which empties into iliac vein •  Great saphenous vein empties into the femoral vein which empties into iliac vein

Question 51

Deep Veins of Pelvis & Lower Limbs

Answer 51

*   Iliac *   Popliteal *   Anterior tibial *   Fibular *   Dorsalis pedis *   Plantar *   Plantar arch *   Digital

Question 52

Disorders of the Blood | Vessels

Answer 52

•  Aneurysm: dilation of blood vessel wall which may burst •  Deep vein thrombosis (clot) of the lower limb •  Venous disease e.g., varicose veins •  Microangiopathy of small blood vessels e.g., with diabetes •  Arteriovenous malformation

Question 53

Atherosclerosis

Answer 53

•  Atherosclerosis with fat deposits inside arteries can begin in young people with consequences becoming evident in middle to old age •  Males have more atherosclerosis than females between ages 45–65 •  Females tend to experience heart disease and atherosclerosis later in life than males •  Atherosclerosis in coronary arteries can lead to ischemic heart disease