Human Bio Chapter 13 - Blood Vessels and Circulation

blood vessels have three layers

Tunica intima (interna), Tunica media, Tunica externa (adventitia)

Tunica intima (interna)

Simple squamous epithelium (endothelium), thin connective tissue layer

Tunica media

Smooth muscle, may contain elastic fibers

Tunica externa (adventitia)

Connective tissue

Arteries

elastic, muscular, arterioles

elastic artery

largest arteries

muscular arteries

regulate blood flow to organs

arterioles

inside organs, no t. externa

capillaries

No t. media

Veins

Venules - no t. media

Medium, large veins

Arteries vs. veins

arteries have thicker muscle, veins have larger lumens

precapillary sphincters

regulates access to capillaries, open intermittently, are regulated by O2, CO2, temp

arteriovenous anastomoses

white blood cells are too large and so they pass through this

Blood pressure highest where?

large arteries, stretch in diastole

Where does blood pressure drop?

arterioles, many target organs

Blood pressure

drops further in capillaries, lowest in veins, gets back to the heart through muscular compression and respiratory pump

Systolic BP

peak blood pressure during ventricular systole

Diastolic BP

minimum blood pressure at the end of ventricular diastole

Systolic/Diastolic

120/80

Valves and the Muscular Pump

Valves prevent backflow, veins are deep and enclosed in muscle, muscular contraction squeezes veins, moves blood up, muscle relaxation allows veins to fill from underneath

Circulation at capillaries

Fluid leaving capillaries contains O2, nutrients, fluid entering capillaries contains CO2, wastes

Hydrostatic (blood) pressure

drives fluid out; decreases along the capillary; osmotic pressure draws fluid back in; remains constant, fluid flows out at beginning, in at the end, excess fluid drains in lymphatic system

Local autoregulation in tissues

Tissues modulate blood supply based on need, precapillary sphincters respond to O2, CO2, te

Cardiovascular homeostasis - global

Blood pressure must be maintained, if blood pressure drops, there are 2 mechanisms to increase it

Short term

neural response

long term

endocrine response

cardiovascular regulation - neural

baroreceptors

baroreceptors

in aorta and carotid arteries monitor blood pressure, regulate cardiac output and vasoconstriction, low BP increases cardiac output and vasoconstriction, high BP decreases them

chemoreceptor reflexes

chemoreceptors in aorta and carotid arteries detect blood chemistry

Double response to chemoreceptor reflexes

respiration rate increase, pick up more O2, exhale CO2, cardiac output increases, deliver fresh blood to tissues

endocrine regulation of blood pressure

short term and long term

short term

sympathetic activation - adrenal medulla releases epinephrine, cardiac output increases, vasoconstriction

long term

EPO production by kidneys increases RBC production, renin production by kidneys causes ADH production by pituitary (retain water), aldosterone production by adrenal cortex (retain Na and water by osmosis), thirst

pattern of circulation

pulmonary vs systemic circuit and digestive system

Pulmonary vs systemic circuit

mostly a parallel system, blood pressure maintained on the arterial side, blood flow to organs depends on local autoregulation

digestive system

direct blood flow to digestive organs and spleen, blood flows through liver first, store nutrients from digestive system, metabolize toxins from diet, metabolize RBC breakdown products from spleen

Fetal blood circulation

The fetus obtains its oxygen and nutrients from the placenta, not the lungs, this blood comes from the umbilical veins, which are at low pressure

Umbilical vein (oxygenated)

brings blood to liver first (for nutrients)

ductus venosus

brings it to the vena cava to the right side of the heart

the foramen ovale (a flap)

allows some of the blood to enter the left atrium

the ductus arteriosus

allows some blood to pass from pulmonary trunk to aorta

Changes at birth

umbilical cord is clamped, no more blood to liver, ductus venosus closes, baby breathes and expands lungs, opens pulmonary blood vessels, blood returns to left atrium, closes flap on foramen ovale, increased oxygen causes ductus arteriosus to spasm (close), pulmonary and systemic circulations are now separate