Chapter 19: Blood Vessels

Arterial Blood pressure is caused by what two factors?

1. How much the elastic arteries close to the heart stretch or distend 2. By volume of blood forced into these vessels at any one time

Peripheral resistance

A measure of the amount of friction encountered by blood as it flows through the blood vessels

Vasa Vasorum

A network of small blood vessels that supply the walls of large blood vessels, such as elastic arteries and large veins.

Baroreceptors

A sensory nerve endings in the wall of the carotid sinus or aortic arch sensitive to vessel stretching

Tight Junctions

A specialized connection of two adjacent animal cell membraces such that the space usually lying between them is absent.

Venules

A very small vein, collects blood from capillaries

Intracellular Clefts

Allows the transportation of fluids and small solute matter through the endothelium

Circulatory Shock

Any condition in which blood vessels are inadequately filled and blood cannot circulate normally. Blood flow is inadequate to meet tissue needs. If circulatory shock persists, cells die and organ damage follows.

What are the 3 types of blood vessels?

Arteries, veins, capallaries

How does the Sympathetic Venoconstriction work?

As the layer of smooth muscle around the veins constricts under sympathetic control, venous volume is reduced and blood is pushed toward the heart.

How does the Respiratory pump work?

As we inhale, abdominal pressure increases, squeezing local veins and forcing blood toward the heart. At the same time, the pressure in the chest decreases, allowing thoracic veins to expand and speeding blood entry into the right atrium.

Microcirculation

Blood flows through a capillary bed from arterioles to venule

Vasomotor Center

Brain area concerned with regulation of blood vessel resistance.

Why are low capillary pressures desirable?

Capillaries are fragile and high pressures would rupture them and most capillaries are extremely permeable and thus even the low capillary pressure can force solute- containing fluids out of the bloodstream into the interstitial space.

Maintaining blood pressure is critical for cardiovascular system homeostasis. Its regulation involves what three key variables?

Cardiac output, peripheral resistance, and blood volume

What is the tunica externa made up of?

Composed of large loose woven collagen fibers

3 types of capillaries

Constriction, fenestrated, and sinusoid

What type of capillary have pericytes? And how does it use them?

Continuous capillaries use pericytes for pinocytosis to move fluids across and in the brain; epithelial cells do not have intercellular clefts so no fluid flows between the cells called blood brain barrier.

Pericytes

Contractile cells that wrap around the endothelial cells of capillaries and venues through the body

Name the type of artery that matches each description: major role in dampening the pulsatile pressure of heart contractions; vasodilation or constriction determines blood flow to individual capillary beds; have the thickest tunica media relative to their lumen size.

Elastic arteries play a major role in dampening the pulsatile pressure of heart contractions. Dilation or constriction of arterioles determines blood flow to individual capillary beds. Muscular arteries have the thickest tunica media relative to their lumen size.

What are the 3 types of arteries?

Elastic, muscular, and arterioles

What is the function of capillaries?

Exchange materials between blood and interstitial fluid

Venous Sinus

Flatten veins with very thin walls of endothelial cells

How are venous valves formed?

From folds of the tunica intima and resemble the semilunar valves of the heart

Fenestrated capillaries

Have large pores that increase permeability and occurs in areas with active filtration or absorption

In the systemic circuit, which contains more blood—arteries or veins—or is it the same?

In the systemic circuit, veins contain more blood than arteries

What kind of bleeding is bruising and where does it occur?

Internal; loose connective tissue

Muscular Pump

Involves muscles surrounding the deep veins contract & relax -- milking the blood toward the heart.

What regulates the amount of blood entering a capillary bed?

Local chemical conditions and arterioles vasomotor nerve fibers

What is the tunica media made up of?

Made up of smooth muscle and sheets of elastin that contracts

Respiratory Pump

Moves blood toward the heart as pressure changes in the ventral body cavity during breathing.

Capillary Beds are formed by:

Network of capillaries

Cardiogenic shock

Pump failure, occurs when the heart is so inefficient that it cannot sustain adequate circulation. Usually caused by myocardial damage, as might follow numerous myocardial infarctions.

Chemoreceptors

Receptor sensitive to various chemicals in solution.

Sympathetic Venoconstriction

Reduces the volume of blood in the veins the capacitance vessels

Muscular Arteries

Reliever blood to specific body organs; have the thickest tunica media of all the vessels; more active in vasoconstriction; less capable of stretching.

What type of epithelium does the Tunica Intima contain?

Simple squamous epithelium aka Endothelium of the tunica intima.

Precapillary Sphincter

Surrounds the root of each true capillary at the metarteriole and acts as a valve to regulate blood flow into the capillary. Made of smooth muscle fibers.

Vasomotor Fibers

Sympathetic nerve fibers that cause the contraction of smooth muscle in the walls of blood vessels, thereby regulating blood vessel diameter.

Capacitate vessels

The blood vessels that hold the major portion of intravascular blood volume

Vascular anastomoses

The connection of two normally divergent structures.

Vasoconstriction

The constriction of blood vessels which increase blood pressure

Vasodilation

The dilation of blood vessels which decreases blood pressure

Blood pressure

The force per unit area exerted on a vessel wall by contained blood, is expressed in mmHg

Pinocytosis

The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.

Describe the three layers that typically form the wall of a blood vessel, and state the function of each.

The innermost tunic is the tunica intima; it forms a slick surface that minimizes blood friction. The mid layer tunic is the tunica media; maintains blood pressure and continuous blood circulation by vasoconstriction or vasodilation. The external tunic is the tunica externa; protects and reinforces the vessels.

Blood viscosity

The internal resistance to flow that exits in all fluids is viscosity and is related to thickness or stickness of a fluid

The kidneys play an important role in maintaining MAP by influencing which variable? Explain how renal artery obstruction could cause secondary hypertension.

The kidneys help maintain MAP by influencing blood volume. In renal artery obstruction, the blood pressure in the kidney is lower than in the rest of the body (because it is downstream of the obstruction). Low renal blood pressure triggers both direct and indirect renal mechanisms to increase blood pressure by increasing blood volume. This can cause hypertension (called "secondary hypertension" because it is secondary to a defined cause—in this case the renal artery obstruction).

Continuous Capillaries

The least permeable and most common and uses pericytes for pinocytosis.

Sinusoid Capillaries

The most permeable and have limited distribution occurring in the liver, bone, marrow, spleen, adrenal medulla; have large intercellular clefts and fenestrations but with few tight junctions. Blood flows slowly through their tortuous channels.

Resistance

The opposition to flow and is a measure of the amount of friction blood encounters as it passes through vessels

Venous Blood Pressure

The pressure of blood in the thoracic vena cava, near the right atrium of the heart, reflecting the amount of blood returning to the heart and the ability of the heart to pump the blood into the arterial system.

Arterioles

The smallest Arteries but the larger ones have 3 tunics; when they constrict the tissues served are largely bypassed. When these dilate, blood flow into the local capillaries increase dramatically.

Capillaries

The smallest blood vessels with only a endothelial cell for the wall

Which branch of the autonomic nervous system innervates blood vessels? Which layer of the blood vessel wall do these nerves innervate? What are the effectors (cells that carry out the response)?

The sympathetic nervous system innervates blood vessels. The sympathetic nerves innervate the tunica media. The effector cells in the tunica media are smooth muscle cells.

List three factors that determine resistance in a vessel. Which of these factors is physiologically most important?

The three factors that determine resistance are blood viscosity, vessel length, and vessel diameter. Vessel diameter is physiologically most important.

Blood flow

The volume of blood flowing through a vessel, in organ, or that entire circulation in a given.

True capillaries have an occasional alternative passage, what is it?

They occasionally spring from the terminal arterioles and empty directly into the venue.

Elastic Arteries

Thick-walled Arteries heart the heart. Present in all 3 tunics. Are pressure reservoirs, expanding and recoiling as the heart ejects blood also called conducting arteries

What is the function of venous valves? What forms the valves?

Valves prevent blood from flowing backwards in veins. They are formed from folds of the tunica intima.

What are the 2 types of vessels in a capillary bed and how do they differ?

Vascular Shunt: A short vessel that directly connects the arterioles and venue at opposite ends of the bed; consists of metarteriole and thoroughfare channels. True Capillaries: Branch from metarteriole and return to thoroughfare channel; the actual exchange vessels.

Which have more anastomoses, arteries or veins?

Veins have more anastomoses than arteries.

If the precapillary sphincter is constricted where does the blood flow move to in order to drain out? What about when they are relaxed?

When constricted: Thoroughfare channel and Metarteriole When relaxed: stays in true capillaries and moves directly

When vascular smooth muscle contracts, what happens to the diameter of the blood vessel? What is this called?

When vascular smooth muscle contracts, the diameter of the blood vessel becomes smaller. This is called vasoconstriction.

Describe the baroreceptor reflex changes that occur to maintain blood pressure when you rise from a lying-down to a standing position.

When you first stand up, mean arterial pressure (MAP) temporarily decreases and this is sensed by aortic and carotid baroreceptors. Medullary cardiac and vasomotor center reflexes increase sympathetic and decrease parasympathetic outflow to the heart. Heart rate and contractility increase, increasing cardiac output, and therefore MAP. Further, sympathetic constriction of arterioles increases peripheral resistance, also increasing MAP. (In addition, increased constriction of veins increases venous return, which increases end diastolic volume, increasing stroke volume, and therefore cardiac output and MAP.)

Vascular Shock

blood volume is normal, but circulation is poor as a result of extreme vasodilation

Postcapillary venules function

carry the blood from capillary bed to larger venules then to veins to the heart through superior and inferior vena cava

Hypovolemic Shock

results from large-scale blood or fluid loss, as might follow acute hemorrhage, severe vomiting or diarrhea, or extensive burns.