Chapter 20 Blood Vessels and Circulation

arteries

carry blood away from the heart

elastic arteries

Include the aorta and its major branches, which contain large lumens for low resistance, and large thick-walled arteries with elastin; they act as pressure reservoirs to expand, recoil and smooth out pressure fluctuations as blood is ejected from the heart. Also called conducting arteries; closer to the heart; allow stretch as blood is pumped into them and recoil when ventricles relax; contain all 3 tunicas; few smooth muscle fibers, high density of elastic fibers

muscular arteries

distal to elastic arteries; deliver blood to body organs; contain tunica intima, tunica media, and tunica externa; greater percentage of smooth muscle fibers than elastic fibers

arterioles

Very small arteries, poorly defined tunica externa, contain smooth muscle that constrict/dilate to regulate BP and reroute blood - major determinant of pressure (pressure points)

venules

the smallest veins; connect the capillaries with the larger systemic veins; consist of tunica intima and tunica externa

medium veins

up to 10 mm in diameter; thin tunica media and thick tunica externa; tunica interna forms venous valves; varicose veins result in part from the failure of these valves; skeletal muscle pump propels venous blood back toward the heart

large veins

include the inferior and superior venae cavae and their tributaries. All three tunicas are present

vasodilation

increase in diameter of a blood vessel

vasoconstriction

A decrease in the diameter of blood vessels caused by contraction of smooth muscles in the vessel walls; under sympathetic control

venoconstriction

reduces volume of blood in reservoirs and allows greater blood volume to flow where needed; under sympathetic control pushes blood toward heart

endothelium

the specialized epithelial tissue that lines the blood and lymph vessels

venous valves

prevent backflow of blood; most abundant in veins of limbs

arteriosclerosis

hardening of the arteries; age is a risk factor due to loss of elastic fibers; includes 2 subcategories: atherosclerosis and focal calcification

atherosclerosis

condition in which fatty deposits called plaque build up on the inner walls of the arteries; risk factors include high blood cholesterol levels, high blood pressure, cigarette smoking, diabetes mellitus, obesity, stress, sedentary behaviour.

capillaries

Microscopic vessel through which exchanges take place between the blood and cells of the body

continuous capillaries

most common type of capillary

fenestrated capillaries

have pores in vessel wall; found in kidneys, intestines, and endocrine glands

sinusoid capillaries

These vessels are very wide and porous. They are found in bone marrow, the spleen, the liver. Have gaps between neighbouring endothelial cells and in the basement membrane.

precapillary sphincter

a band of smooth muscle fibers that encircles the capillaries at the arteriole-capillary junctions and controls blood flow to the tissues

arterial anastomosis

fusion of two collateral arteries

collateral arteries

Are connections, or anastomoses, between the branches of the coronary circulation in parts of the heart (or other areas of high O2 demand). Protects the heart from ischemia. Are formed by arteriogenesis or angiogenesis.

arteriovenous anastomosis

direct connection between arteriole and venule (bypass capillary)

angiogenesis

formation of new blood vessels

arteriogenesis

new artery branching off from preexisting artery

thoroughfare channel

metarteriole that continues through capillary bed to venule

hemorrhoids

swollen, twisted, varicose veins in the rectal region

varicose veins

abnormally swollen, twisted veins with defective valves; most often seen in the legs

capacitance vessels

the term for veins because they have the ability to stretch. they have a large diameter and are more distensible to hold more blood. this reduces stress on the heart.

pressure points

arterial pulse, they are compressed to stop blood flow into distal tissues during hemorrhage

Total Peripheral Resistance (TPR)

the resistance to the flow of blood through the entire systemic circulation

Capillary Hydrostatic Pressure (CHP)

the blood pressure within capillary beds, and it provides the driving force for filtration

Interstitial Hydrostatic Pressure (IHP)

pressure exerted by interstitial fluid on external surface of blood vessels

Blood colloid osmotic pressure (BCOP)

osmotic pressure caused by proteins in blood

Interstitial colloid osmotic pressure

Osmotic pressure in the interstitium due to the amount of solutes, especially proteins. Tends to pull fluid into interstitium.

Net Filtration Pressure (NFP)

the difference between net hydrostatic pressure and net osmotic pressure

Net Hydrostatic Pressure (NHP)

difference between CHP and IHP

Net Osmotic Pressure

The difference between BCOP and ICOP. Because ICOP is almost zero, the net osmotic pressure is considered to be the same as BCOP. Net osmotic pressure tends to drive water from the interstitial fluids into the capillary.

laminar flow

a smooth pattern of flow

hypertension

abnormally high blood pressure

hypotension

abnormally low blood pressure

muscular pump

contraction of skeletal muscles "milks" blood toward heart; valves prevent backflow

respiratory pump

pressure changes during breathing move blood toward heart by reducing pressure in the thoracic cavity during inspiration

diffusion

Passive movement of molecules from an area of higher concentration to an area of lower concentration.

osmosis

Diffusion of water through a selectively permeable membrane

osmolarity

total concentration of all solute particles in a solution

capillary filtration

movement of fluid through capillary walls through hydrostatic pressure

capillary reabsorption

the process by which water moves by osmosis from the interstitial fluid into protein-rich plasma at the venous end of a capillary bed

edema

Abnormal accumulation of fluid in interstitial spaces of tissues resulting in swelling.

recall of fluids

occurs when blood pressure drops due to volume changes(hemorrhage and dehydration). Hemorrhage decreased BP, decreases CHP, decreases NFP and increases reabsorption

vasomotion

changes in diameter of the blood vessel brought about by smooth muscle

cardiovascular center

Medulla Oblongata: cardiac center adjusts force and rate of heart contraction, vasomotor center adjusts blood vessel diameter for blood pressure regulation

baroreceptors

a sensory nerve receptor that is stimulated by a change in pressure, perhaps blood pressure

chemoreceptors

respond to chemicals (e.g., smell, taste, changes in blood chemistry)

carotid sinus

A dilation of a common carotid artery; involved in regulation of systemic blood pressure.

Cardiac Output (CO)

measurement of the amount of blood ejected per minute from either ventricle of the heart

Heart Rate (HR)

number of heart beats per minute

Stroke Volume (SV)

The volume of blood pumped forward with each ventricular contraction.

renin

enzyme that is produced by the kidney; important for blood pressure and volume regulation; catalyzes the conversion of circulating angiotensinogen to angiotensin I

angiotensin converting enzyme (ACE)

enzyme that converts angiotensin I to angiotensin II

angiotensin II

vasoconstrictor; increases blood pressure by stimulating kidneys to reabsorb more water and by releasing aldosterone and ADH; stimulates thirst

Anti-diuretic hormone (ADH)

A hormone produced by the posterior pituitary gland when the body is dehydrated. It causes the kidneys to reabsorb more water into the blood making the urine more concentrated.

Aldosterone

Hormone that stimulates the kidney to retain sodium ions and water

Natriuretic peptides

hormones that decrease blood pressure and increase Na and water excretion; natural antagonists to renin-angiotensin-aldosterone system.

Erythropoietin (EPO)

hormone secreted by the kidney to stimulate the production of red blood cells by bone marrow

tunica interna

another name for tunica intima

tunica adventitia

another name for tunica externa

vaso vasorum

small blood vessels that supply blood to the cells of the walls of the arteries and veins

Mean Arterial Pressure (MAP)

diastolic pressure + 1/3 pulse pressure

pulse pressure

difference between systolic and diastolic pressure