Chapter 19: Blood Vessels

Comprehensive flashcards covering Chapter 19 of Human Anatomy and Physiology 11th Edition, focusing on blood vessel structure, types, hemodynamics, and regulation.

What is the general function of blood vessels in the human body?

They serve as a delivery system of dynamic structures that begin and end at the heart and work with the lymphatic system to circulate fluids.

Which type of blood vessels carry blood away from the heart?

Arteries

Are arteries always oxygenated?

No, they are oxygenated except for pulmonary circulation and the umbilical vessels of a fetus.

What is the function of capillaries?

To maintain direct contact with tissue cells and directly serve cellular needs.

Which blood vessels carry blood toward the heart?

Veins

Except for capillaries, what are the three layers or tunics that make up the walls of blood vessels?

Tunica intima, tunica media, and tunica externa.

What specific tissue type makes up the endothelium of the tunica intima?

Simple squamous epithelium

Which layer of the blood vessel wall is responsible for maintaining blood flow and pressure through vasoconstriction and vasodilation?

Tunica media

What are the two primary components of the tunica media?

Smooth muscle and sheets of elastin.

What is the function of the tunica externa (tunica adventitia)?

It is composed of loose collagen fibers that protect and reinforce the wall and anchor it to surrounding structures.

What is the term for the system of tiny blood vessels found in larger vessels that nourish the outermost external layer?

Vasa vasorum

Into which three groups are arteries divided based on size and function?

Elastic arteries, muscular arteries, and arterioles.

Why are elastic arteries also referred to as conducting arteries?

Because they conduct blood from the heart to medium sized vessels.

Which group of arteries acts as pressure reservoirs that expand and recoil as blood is ejected from the heart?

Elastic arteries

Why are muscular arteries also called distributing arteries?

Because they deliver blood to body organs.

Which arterial layer is the thickest in muscular arteries?

Tunica media

Why are arterioles called resistance arteries?

Because changing their diameters changes the resistance to blood flow.

What is the function of capillaries regarding substance transfer?

Exchange of gases, nutrients, wastes, and hormones between blood and interstitial fluid.

What are the three types of capillaries?

Continuous capillaries, fenestrated capillaries, and sinusoidal capillaries.

Which type of capillary forms the blood brain barrier?

Continuous capillaries of the brain

Where are fenestrated capillaries typically found?

In areas involved in active filtration (kidneys), absorption (intestines), or endocrine hormone secretion.

What characterizes the endothelial cells of fenestrated capillaries?

They contain Swiss cheese–like pores called fenestrations.

In what locations are sinusoidal capillaries found?

Only in the liver, bone marrow, spleen, and adrenal medulla.

What is the purpose of the sluggish blood flow in sinusoidal capillaries?

It allows time for the modification of large molecules and blood cells passing between blood and tissue.

What constitutes a capillary bed?

An interwoven network of capillaries between arterioles and venules.

What term describes the flow of blood through a capillary bed from an arteriole to a venule?

Microcirculation

What is a vascular shunt?

A channel that directly connects an arteriole with a venule, bypassing true capillaries.

Which structure acts as a valve regulating blood flow into the capillary bed and is controlled by local chemical conditions?

Precapillary sphincter

Why are veins called capacitance vessels or blood reservoirs?

Because they contain up to $65\%$ of the blood supply.

What are two adaptations that ensure the return of blood to the heart given the lower blood pressure in veins?

Large-diameter lumens (offering little resistance) and venous valves (preventing backflow).

What are venous sinuses?

Flattened veins with extremely thin walls composed only of endothelium, such as the coronary sinus or dural sinuses.

What are varicose veins?

Dilated and painful veins due to incompetent (leaky) valves.

What are arterial anastomoses?

Interconnections of blood vessels that provide alternate pathways (collateral channels) to ensure continuous flow if an artery is blocked.

Define blood flow as it relates to the entire vascular system.

The volume of blood flowing through a vessel, organ, or entire circulation in a given period, measured in $ml/min$ and equivalent to cardiac output ($CO$).

What are the three important sources of peripheral resistance?

Blood viscosity, total blood vessel length, and blood vessel diameter.

How is resistance related to blood vessel diameter?

Resistance varies inversely with the fourth power of the vessel radius.

If the radius of a blood vessel is doubled, by how much does the resistance drop?

It drops to $\frac{1}{16}$ of its original value.

Where does the steepest drop in systemic blood pressure occur?

In the arterioles

What is systolic pressure?

The pressure exerted in the aorta during ventricular contraction, averaging $120\,mm\,Hg$ in a normal adult.

What is pulse pressure?

The difference between systolic and diastolic pressure.

How is Mean Arterial Pressure (MAP) calculated?

$$\text{Diastolic pressure} + (\frac{1}{3} \times \text{Pulse pressure})$$

Which factors aid in venous return?

The muscular pump, the respiratory pump, and sympathetic venoconstriction.

What are the three main factors regulating blood pressure?

Cardiac output ($CO$), peripheral resistance ($PR$), and blood volume.

The cardiovascular center, which controls blood pressure, is located in which part of the brain?

The medulla (specifically the clusters of sympathetic neurons in the medulla).

How do baroreceptors respond to high MAP?

They stimulate the cardioinhibitory center and inhibit the vasomotor and cardioacceleratory centers to decrease blood pressure.

What are the effects of Angiotensin II on blood pressure stabilization?

It stimulates aldosterone secretion, causes $ADH$ release, triggers the hypothalamic thirst center, and acts as a potent vasoconstrictor.

What is the definition of hypertension?

Sustained elevated arterial pressure of $140/90\,mm\,Hg$ or higher.

What is the difference between primary and secondary hypertension?

Primary hypertension has no identified underlying cause ($90\%$ of cases), while secondary hypertension is due to identifiable disorders like kidney disease.

What is orthostatic hypotension?

Temporary low blood pressure and dizziness when suddenly rising from a sitting or reclining position.

Name and define the three types of circulatory shock.

Hypovolemic shock (large-scale blood loss), vascular shock (extreme vasodilation), and cardiogenic shock (inefficient heart cannot sustain circulation).