A&P II Chapter 20 blood vessels

Blood vessels functions?

Transport and distribute blood through the body.

Deliver oxygen, nutrients, and hormones to cells and carry away carbon dioxide and wastes

Return blood to the heart

How many layers do most blood vessels have?

Most have 3 layers, except for the smallest vessels.

What are the three layers of blood vessels

The Tunica interna(innermost layer)

Tunica media(Middle layer)

Tunica externa(Outermost layer)

What makes up the Tunica interna and what does it do?

The endothelium, basement membrane and internal elastic lamina. Surrounds lumen, in direct contact with blood.

What makes up the Tunica media and what does it do?

Smooth muscle and external elastic lamina. Stretch and recoil, and changes diameter of lumen through vasoconstriction and vasodilation.

What makes up the tunica externa and what does it do?

Elastic and collagen fibers. Anchors vessels to surrounding tissue.

Function of arteries?

Carry oxygenated blood away from the heart.

Elastic arteries

Close to the heart. Have highly elastic walls to accommodate the surge of blood and project blood onward when ventricles are relaxing.

Muscular arteries

Have lots of smooth muscle in the tunica media for greater vasoconstriction and dilation to adjust blood flow to various regions of the body

Anastomoses

Form alternate route of blood flow to body part through collateral circulation

Abundant microscopic vessels are?

From small arteries branching from muscular arteries. They deliver blood to capillaries.

Tunics change

Thin tunica interna with fenestrated(small pores) internal elastic lamina.

Tunica media with one or two layers of smooth muscle

Metarteriole

Tapers toward junction with capillary.

Precapillary Sphincter(Single muscle fiber) at junction regulates blood flow through capillary bed by regulating resistance

Also affects blood pressure

Capillaries are?

Networks of microscopic vessels. They connect outflow of the heart through arteries and return to heart through veins.

Capillary bed

10 to 100 capillaries come from a single metarteriole

Blood flow is controlled by the precapillary sphincters in metarteriole.

Throughfare channel is?

The distal end of capillary bed with no smooth muscle. Provides a direct route to the venule.

Autoregulation?

Tissues automatically adjust blood flow to match its metabolic demands.

Types of capillaries?

Continuous

Fenestrated

Sinusoids

Continuous capillaries description

Endothelial cells form continuous tubes

intercellular clefts between adjacent cells allow only a few substances to move across, such as in blood-brain barrier.

Fenestrated capillaries description

Endothelial cells have many fenestrations(small pores). Allows greater exchange of materials, such as in kidneys for filtration.

Sinusoid capillaries description

Endothelial cells with large fenestrations, incomplete basement membrane, and large intercellular clefts. Allows all components of blood to pass through.

Capillary exchange

Movement of substances between blood and interstitial fluid.

Methods of Capillary exchange

Diffusion:

Across endothelial cell membranes - Gases and lipid soluble

through intercellular clefts or fenestrations - water soluble

Transcytosis: Pinocytic vesicles

What are the influences on capillary exchange

Filtration: capillary blood pressure pushes fluid out of capillary into interstitial fluid

reabsorption: Blood colloid osmotic pressure(due to plasma proteins) pulls fluid into capillary bed

Where does filtration occur? Where does reabsorption occur?

Greater arteriole end

Greater venule end

Most capillaries reunite to form venules

Thin walls that do not maintain shape.

Merge to form veins.

-Close to capillary, very porous, function as exchange of nutrients and wastes and movement of white blood cells from blood stream into inflamed or infected tissue.

-Acquire thicker walls as enlarge, with no exchange.

In some parts of the body, blood passes from one capillary bed into another, instead of a venule.

-known as portal system

-portal vein connects the two capillary beds

(hepatic - Liver )(hypophyseal - Hypothalamus/pituitary)

Veins do what?

transport deoxygenated blood from tissues back to the heart.

Difference between walls of veins and walls of arteries?

Veins have thinner tunica interna and media than arteries. They lack elastic lamina.

(This leaves them unable to withstand high pressure)

what are valves in the vein and what do they do?

Flap like cusps of tunica interna.

They prevent backflow of blood segments in vein.

What is a Vascular sinus.

Vein with thin endothelial wall, such as coronary sinus.

Lacking smooth muscle so unable to alter its diameter.

Venous return

Volume of blood flowing back to the heart through systemic veins.

Limited pressure remaining from heart pump.

(Venous return) Skeletal muscle pump info?

Skeletal muscle compression pushes blood through valve closer to heart, “milking.”

Valves further away close as some blood is pushed back against it.

(Venous return) Respiratory pump info?

during inhalation the diaphragm moves downward, decreasing pressure in thoracic cavity and increasing pressure in abdominal cavity; blood flows into decompressed veins and into right atrium.

Blood distribution

At rest, 64% of blood volume is in systemic veins and venules.

13% systemic arteries and arterioles

9% pulmonary vessels

7% heart

7% systemic capillaries

Blood reservoir.

-Blood can be diverted quickly as need arises

-Brain stem sympathetic impulses can vasoconstrict veins, allowing greater blood volume to flow to skeletal muscles as needed during increased activity

-Similar mechanism during hemorrhage, to counteract blood loss and associated decrease in blood volume and pressure

Blood flow in any given tissues

-Varies with blood pressure gradient and resistance

-In all systemic vessels is equal to cardiac output

Blood pressure

Hydrostatic pressure exerted by blood on blood vessel walls.

• Generated by ventricular contraction

• Measured in mm Hg

Highest at aorta and falls progressively, with fluctuations disappearing at the capillaries

influenced by cardiac output, blood volume, and vascular resistance.

Systemic blood pressure

highest arterial pressure during systole(< The phase when the heart contracts to pump blood out)

Diastolic blood pressure

Lowest arterial pressure during diastole.(< the heart muscle relaxes and blood flows in and refills chambers)

Vascular resistance

Opposition to blood flow due to friction between blood and walls of blood vessel

• An increase decreases blood flow and increases blood pressure

Factors affecting vascular resistance

• Size of lumen - Higher resistance as vasoconstrict

• Blood viscosity - higher resistance as ratio of blood cells and proteins increase

• total blood vessel length - higher resistance if longer

Systemic vascular resistance(SVR)

• total peripheral resistance from all systemic vessels

• slight change in arteriole diameter has large effect

BP regulation

Cardiovascular center in medulla oblongata

• In addition to regulating stroke volume(SV) and heart rate(HR), also regulates blood pressure and blood flow to specific tissues

Autonomic sympathetic and parasympathetic

neural regulation

• baroreceptor reflex - baroreceptors monitor blood pressure

• Chemoreceptor reflex - chemoreceptors monitor chemical composition of blood

Hormones

• Alter cardiac output, systemic vascular resistance, and total blood volume

Autonomic regulation of BP

Input from sensory receptors, cerebral cortex, limbic system and hypothalamus

output regulates heart rate, contractility and blood vessel diameter

Autonomic sympathetic regulation of BP

• Cardiac accelerator nerves increase rate and force of heat contraction, that increases BP

• vasomotor nerves maintain resting smooth muscle tone in blood vessel walls and stimulation of veins results in constriction and movement from venous blood reservoirs, that increases BP

Autonomic parasympathetic regulation of BP

Vagus nerves decrease heart rate, that decreases BP

(Neural regulation of BP)Baroreceptor reflexes

• Carotid sinus receptors - initiate reflex to regulate BP in brain

• aortic arch receptors - initiate reflex to regulate systemic BP

• BP fall - receptor fewer impulses to cardiovascular center, decreased parasympathetic and increased sympathetic impulses increase BP

(Neural regulation of BP) Chemoreceptor reflexes

• Carotid bodies and aortic bodies

• detect drop in O2, increase in CO2, or increase in H+(acidic)

• increased sympathetic impulses increase BP to drive gas exchange through the lungs

(Hormone reg of BP) Renin-angiotensin-aldosterone system

• Stimulates increased systemic vascular resistance and increased reabsorption of sodium and water to increase blood volume, thus increase BP

(Hormone reg of BP) Epinephrine and norephinphrine

• Stimulates increased rate of force of heart contraction and vasoconstriction of some arterioles and veins to increase BP, but vasodilation of arterioles in skeletal muscles

(Hormone reg of BP) Antidiuretic hormone

Stimulates vasoconstriction to increase BP

(Hormone reg of BP)Atrial natriuretic peptide

Stimulates vasodilation and loss of salt and water in urine to decrease BP.

Pulse is?

Alternate expansion and recoil of an artery wall after each contraction of the left ventricle.

Tachycardia

rapid heart rate

Bradycardia

slow heart rate

Pulse pressure is?

The difference between systolic pressure and diastolic pressure.

(Circ Routes) How many routes are blood vessels organized in?

Two

(Circ routes)Pulmonary circulation

• Carries oxygen poor blood from right ventricle to the air sacs of the lungs

• Returns oxygen rich blood to the left atrium

(CIrc routes) Systemic circulation

• Carries oxygen rich blood from the left ventricle to systemic capillaries throughout the body(except to air sacs of lungs)

• returns oxygen poor blood to the right atrium

Major systemic arteries

• Ascending aorta

  • Right and left coronary arteries

• Arch of the aorta

  • Brachiocephalic trunk

  • left common carotid artery

  • left subclavian artery

• Thoracic aorta

  • Branches to thoracic aorta, passing through diaphragm

• Abdominal aorta

  • Branches to abdominal organs

  • common iliac arteries supply pelvis and lower limbs

Major systemic Veins

• Superior vena cava

  • from head: dural venous sinus, internal jugular, external jugular, and vertebral veins

  • Upper limbs: superficial and deep veins

  • Thorax: azygos system

• Inferior vena cava

  • Hepatic portal vein: Collects from splenic and superior mesenteric veins

  • Hepatic vein

  • Lower limbs: superficial and deep veins

Hepatic portal circulation

• Directs venous blood from gastrointestinal organs and spleen into the hepatic portal vein of liver before it returns to the heart

  • enables the liver to utilize nutrients and detoxify harmful substances in the blood

Splenic vein

Drains the spleen stomach and large intestines

Superior mesenteric vein

drains the small intestine, large intestine, stomach, and pancreas

Hepatic veins

Drain the liver

What layer of an artery contains the lumen?

Tunica interna

What layer of an artery contains smooth muscle?

Tunica media

What layer anchors a blood vessel to surrounding tissue?

Tunica externa

What structure surrounds the lumen and contacts the blood?

Endothelium

What structure is found inside the lumen of a vein?

Valve

What type of blood vessel has only an endothelial layer?

Capillary

What happens to elastic arteries when the ventricles contract?

They stretch

What happens to elastic arteries when the ventricles relax?

They recoil

Where are precapillary sphincters located?

At capillary entrances

What happens to capillary blood flow when precapillary sphincters relax?

It increases

What happens to capillary blood flow when precapillary sphincters contract?

It decreases

What vessel provides a direct route from a metarteriole to a venule?

Thoroughfare channel

Where is the thoroughfare channel located relative to the capillary bed?

At the distal end

What structure allows substances to cross a continuous capillary between endothelial cells?

Intercellular clefts

What structure allows increased exchange in a fenestrated capillary?

Fenestrations

What type of capillary has large openings and an incomplete basement membrane?

Sinusoid

Where does filtration occur more strongly in the capillary bed?

Arteriole end

Where does reabsorption occur more strongly in the capillary bed?

Venule end

Where does filtered fluid move during capillary filtration?

Into interstitial fluid

Where does reabsorbed fluid move during capillary reabsorption?

Into the capillary

Where do most capillaries drain?

Venules

What vessels merge to form veins?

Venules

Where are venous valves located?

Inside veins

What is the direction of blood flow through a venous valve?

Toward the heart

What happens to a vein when the skeletal muscle pump compresses it?

Blood moves toward the heart

During inhalation, where does blood move from decompressed veins?

Right atrium

Where is most blood volume stored at rest?

Systemic veins and venules

What happens to blood pressure as blood moves away from the aorta?

It decreases

Where is systemic blood pressure highest?

Aorta

Where do blood-pressure fluctuations disappear?

Capillaries

What happens to blood pressure when systemic vascular resistance increases?

It increases

What happens to blood flow when vascular resistance increases?

It decreases

What happens to arterial diameter during vasoconstriction?

It decreases

What happens to blood pressure when cardiac output increases?

It increases