A&P II Chapter 19

What are the 3 main layers that make up the walls of blood vessel? Innermost to outer.

Tunica intima

Tunica media

Tunica externa

Why are vascular anastomoses important?

They help connect blood vessels to each other 

What is the tunica intima?

Innermost endothelium.

- Simple squamous epithelium lining lumen of all vessels.

- Slick surface reduces friction

- Capillaries ONLY have endothelium layer.

What is tunica media?

Middle layer.

- Smooth muscle and elastic fiber layer.

- Regulated by SNS.

- Bulkiest layer responsible for maintaining blood flow and BP.

What does tunica media also control pertaining to lumen?

- Vasoconstriction: decreases lumen diameter

- Vasodilation: increases lumen diameter

What is the tunica externa other name?

Tunica adventitia.

What is the tunica externa?

Outermost layer of a blood vessel.

- Mostly loose collagen fibers that protect and reinforce wall

- Anchors blood vessel to surrounding structures

- Has associated nerve fibers and lymphatic vessels

Elastic arteries function?

conduct blood from the heart to the medium-sized vessels

Elastic arteries important characteristic?

Contains smooth muscles

What is elastic arteries also called?

Conducting arteries

Muscular arteries function?

distribute blood to body organs.

What is muscular arteries also called?

distributing arteries

Muscular arteries important characteristic

Contains more smooth muscle and less elastic tissue  

What is Aterioles function

It changes the diameters, which changes the resistance to the blood flow. 

Aterioles is also called

resistance arteries

What is an important ateriole characteristic?

Contains one layer of smooth muscle

Continuous capillary

• the least permeable  

• Most common (most found in the skin, muscles, and CNS) 

• Associated with pericytes 

• Found in the blood-brain barrier (BBB), no intercellular cleft 

• Only has tight junction

Fenestrated capillary  

• Has large fenestrations (pores) that increase permeability  

• It occurs in areas of active filtration (kidney) or absorption (small intestine) and areas of endocrine hormone secretion. 

• (remember Swiss cheese) 

• Covered in a very thin layer of condensed extracellular glycoproteins.

Sinusoid Capillary 

• The most permeable and occurs in limited locations 

• Location-like liver, bone marrow, spleen, and adrenal medulla  

• Has an incomplete basement membrane 

• Have intercellular cleft and fenestrations 

• Few tight junctions 

• Macrophages in lining to capture and destroy foreign invaders

How does the structure of veins help return blood to the heart?

- Large-diameter lumens lower resistance to blood flow

- Venous valves

- Venous sinuses

What are venous valves?

Prevent backflow of blood; most abundant in veins of limbs

What are vascular anastomoses?

Interconnections of blood vessels.

What is resistance? (Total peripheral resistance: TPR).

Opposition to blood flow

3 important sources of resistance?

1. blood viscosity

2. total blood vessel length

3. blood vessel diameter (GREATEST INFLUENCE ON RESISTANCE!!)

What is mean arterial pressure? (MAP)

Pressure that propels blood to tissues.

MAP = diastolic blood pressure + (pulse pressure / 3)

What is the relationship between MAP and cardiac output, stroke volume, and heart rate?

As SV and/or HR increase, CO increases, and MAP increases (varies directly) 

What is the relationship between MAP and blood volume?

Blood volume directly varies CO, so BV also directly varies BP 

What is the relationship between MAP and blood vessel resistance (R) (vasoconstriction/vasodilation)?

BP varies directly with R; anything that increases R will also increase MAP 

What are the two pressures that have an influence on the bulk flow of fluid?

Hydrostatic pressure (HP) and Capillary Colloid osmotic pressure (oncotic pressure, OP)

Capillary Colloid osmotic pressure (oncotic pressure, OP)

Opposes capillary hydrostatic pressure by providing “sucking” pressure

Hydrostatic pressure (HP)-

Force exerted by fluid pressing aganist wall.

What are short-term mechanisms that control blood pressure?

Nervous system and hormones

- Alter blood pressure by changing total peripheral resistance or cardiac output

Neural control of cardiac output

What are long-term mechanisms that control blood pressure?

The Kidneys and it alters blood pressure by changing blood volume.

What are intrinsic controls on blood flow?

• Control is entirely from within the tissue or organ. 

• Uses paracrines or properties of muscle tissue. 

• Organs can regulate their own blood flow my adjusting their diameters of their own arterioles 

• Also known as autoregulation or local control. 

• NO nerve or hormonal input 

• 2 mechanisms: metabolic controls and myogenic controls 

What are extrinsic controls of blood flow?

• Control is from outside of the tissue or organ. 

• Acts on anterior smooth muscles to shunt blood from some areas to other areas where no blood flow is needed  

•  Uses nerves or hormones (ANS) 

• Maintains constant MAP. 

What is the blood flow in the Skeletal system?

At rest, makes up 20% total blood in body.

During muscle activity, blood flow increases due to increased metabolic activity.

At rest, myogenic and neutral mechanisms work together.

How is the blood flow in the brain?

It must be constant because neurons are intolerant of 
ischemia; brain can’t store nutrients so needs blood flow to provide nutrients 

Why does blood flow through the skin?

1.Supplies nutrients to cells (autoregulated in response to O2 needs)

2.Helps regulate body temperature (neurally controlled: extrinsic)

3.Provides a blood reservoir (neurally controlled: extrinsic)

Brachiocephalic trunk definition:

right-side branch that further branches into right common carotid artery and the right subclavian artery.

Common carotid arteries definition:

Each side has a different origin. Both ascend through lateral neck then divide into external and internal carotid arteries

Cerebral arterial circle (circle of Willis) definition:

arterial anastomosis in the central brain area. Formed by serval arteries supplying the brain. It equals blood pressure in the brain and provides alternate routes for blood to circulate through and reach brain tissue if another vessel is occluded 

Radial arteries definition:

Supplies lateral muscles of the forearm, wrist, thumb, and index finger.

- Clinically important pulse point near wrist.

Celiac trunk definition:

unpaired branch off aorta, has three important branches: common hepatic artery, splenic artery, and left gastric artery 

Femoral arteries definition:

Main arteries supplying the lower limbs. Has many branches supplying the upper limb thigh muscles. Near the knee it becomes the popliteal artery.

Popliteal artery definition:

Supplies knee region then splits into anterior and posterior tibial arteries of the lower leg.

Dorsalis pedis artery definition:

Supplies the ankle and dorsum of foot. Ends in the sole of the foot where it forms medial part of the plantar arch.

Mesenteric arteries definition:

A network of blood vessels that supply the small and large intestines

Subclavian arteries definition:

In addition to the head, its branches supply blood to the upper limbs 

Superior vena cava definition:

Receives blood draining from all areas superior to the diaphragm expect the heat wall. Drains into right atrium 

Inferior vena cava definition:

Receives blood draining from all areas inferior to the diaphragm. Drains to the right atrium

Medial cubital vein:

The superficial vein at the anterior aspect of the elbow that connects the cephalic and basilic veins. Often used to obtain blood

Internal jugular veins

Merge with subclavian veins. Largest vein draining the head and neck region. 

Hepatic portal system:

two connected capillary beds. Nutrient rich blood may also carry toxins and microbes coming from the digestive organs goes through the hepatic portal system. 

Azygos system:

Flanks vertebral column laterally.

Drains the intercostal muscles of the thorax and provides an accessory venous system to drain the abdominal wall.

Brachiocephalic veins:

help return blood from your head, neck, and arms back to your heart.  

Common iliac veins:

paired veins formed by the joining of the internal and external iliac veins. Drains blood from the pelvis and lower limbs into the distal end of the inferior vena cava 

Renal veins:

drain the kidneys and connect to IVC

Lumbar veins:

Several pairs of veins that drain posterior abdominal wall. Empty into IVC and azygos system 

Venous sinuses

flattened backflow of blood