Chapter 20: The Circulatory System: Blood Vessels and Circulationary

arteriole

small artery

what arteries do?

carry blood away from the heart

What do veins do?

carry blood toward the heart

What are capillaries?

microscopic, thin-walled vessels that connect the smallest arteries to the smallest veins

What do capillaries do?

the site of the transfer of materials into and out of tissues

venule

small vein

Exchange of materials (gases, nutrients, wastes,

hormones, etc.) with the tissues occurs only in

capillaries and in some venules

No cell in the body is more than about five cell

widths away from a _blank_ (except in ligaments, tendons, cartilage, cornea, and the lens).

capillaries

capillary exchange

passage of materials across the walls of capillaries

what are the three routes of capillary exchange?

Through the endothelial cells, spaces between the endothelial cells, and the filtration pores of fenestrated

capillaries

capillary beds

arrangement of capillaries in web-like networks

how can flow to particular capillaries be regulated?

constriction or dilation of upstream arterioles or by precapillary sphincters

what is blood flow?

the amount of blood flowing through an organ, tissue, or blood vessel in a given amount of time (mL/min)

How is pressure and resistance related to blood flow?

blood flow=

Difference in Pressure/Resistance

what is blood pressure?

the force that blood exerts against the wall of a vessel

how can blood pressure be measured directly?

by inserting a catheter or needle connected to an external manometer

How is blood pressure typically measured?

we take blood pressure from the brachial artery as an approximation using a sphygmomanometer to measure it.

systolic pressure

the peak pressure recorded during ventricular systole

diastolic pressure

the minimum arterial pressure, measured during ventricular diastole.

what is pulse pressure?

The difference between the systolic and diastolic pressure

what is mean arterial pressure?

average pressure in the arteries

how can mean arterial pressure be calculated?

MAP=1/3 systolic pressure + 2/3 diastolic

How can gravity affect mean arterial pressure?

in a standing person,MAP is about 62 mm Hg in arteries of the head and about 180 mm Hg in arteries of the ankle

What is hypotension?

chronic low blood pressure

what is hypertension?

a chronic resting blood pressure higher than 140/90.

what are the health complications of long-term hypertension?

Heart Attack - due to atherosclerosis

Stroke - due to atherosclerosis

Heart Failure

Aneurysm

Metabolic Syndrome - high "bad" cholesterol,

low "good" cholesterol, high tryglycerides,

high insulin levels, extra body weight. Can

lead to heart disease, stroke, and diabetes

mellitus.

how does arteriosclerosis affect blood pressure?

Blood pressure increases with age as the arteries become less distensible

what is atherosclerosis?

The growth of lipid deposits in the walls of the arteries that can calcify and cause rigidity. High blood pressure.

what is blood pressured determined by?

cardiac output, blood volume, and resistance to flow

what are the three factors upon which peripheral resistance depends?

Blood viscosity, vessel length, Vessel Radius (can be altered via vasoconstriction and vasodilation)

what are bareoreflexes?

Neural Control

what structures are involved in baroreflexes?

Baroreceptors can be found in the aortic arch

and in the carotid sinuses (at base of internal

carotid artery).

What happens to baroreflexes if blood pressure is high?

this causes decreases in heart

rate/cardiac output and vasodilation in general.

This is regulated through the autonomic nervous

system.

what are chemoreflexes?

Neural Control

what structures are involved with chemoreflexes?

Chemoreceptors for oxygen, carbon dioxide,

and pH are found in the aortic arch and in the

carotid bodies (at base of external carotid

artery)

what happens to chemoreflexes if oxygen levels are low or if carbon dioxide or acidity levels are high?

cause widespread vasoconstriction. This increases overall BP, increasing blood flow to the lungs to promote

gas exchange. Respiration rate is also

increased.

aldostereone

promotes sodium and water retention in the kidneys

Angiotensin II

causes vasoconstriction

Antidiuretic hormone

promotes water retention, but it will also cause vasoconstriction.

Epinephrine/Norepinephrine

cause vasoconstriction in most blood vessels to increase blood pressure in the main arteries. This allows for increased blood flow to the brain, heart, and skeletal muscles.

what is Venous Return?

The flow of blood back to the heart

what are the five mechanisms that assist with Venous Return?

1.Pressure Gradient - Pressure falls as we

move from venules to the venae cavae.

This promotes flow toward the heart.

2.Gravity - At least from the head and neck.

3. The Skeletal Muscle Pump - Contractions of

muscles and presence of valves pushes blood

in one direction.

4. The Thoracic Pump - When you inhale, the

thoracic cavity expands and thoracic pressure

drops, while at the same time the diaphragm

moves downward to increase abdominal

pressure. This moves blood toward the thoracic

cavity.

5. Cardiac Suction - Suction from the empty atria

draws blood in.