Blood Vessels

Chapter 19

Types of Blood Vessels

Arteries - vessels that transport blood away from the heart

Veins - return blood back to the heart Capillaries - microscopic blood

vessels that allow exchanges between blood and tissues

Structure of a blood vessel Tunica externa (adventitia) - outermost layer

made of loose connective tissue. Serves to anchor, protect and prevent overstretching

Tunica media - middle layer composed of smooth muscle; functions in dilation and constriction of blood vessels

Tunica interna(intima) - innermost layer made of endothelium (s.squamous epithelium)

Blood flow through tissues From the heart blood flows into

Aorta Arteries Arterioles Capillaries Venules Veins Superior/ Inferior Vena Cava

Back to the heart

Arteries Elastic (conducting) arteries

Larger arteries Muscular (distributing) arteries

Medium arterties Arterioles

Tiny, tiny arteries Metarteriole

Capillaries Microscopic vessels that connect

arterioles and venules Walls consist of a single layer of simple

squamous epithelial cells that allow the exchange of gases

Precapillary sphincters regulate blood flow

Continuous/Fenestrated capillaries

Veins Venules merge to form veins Have 3 distinct layers; thinner walled

than arteries due to thin tunica interna and media

Large lumens and posses valves Varicose veins Blood reservoir

Systemic Circulation The aorta and its major branches Arterial supply to neck and head Arterial supply to upper extremities Arterial supply to thorax Arterial supply to abdomen Arterial supply to pelvic region and

lower extremities

Systemic Veins Venous drainage of the head and neck Major tributaries of the inferior vena

cava Venous drainage of the upper

extremities Venous drainage of the lower

extremities

Hepatic Portal System Routes blood from the stomach, spleen,

pancreas, small and large intestines to the liver

Blood from these structures all drain into the hepatic portal vein, then into the liver

Blood is returned to the inferior vena cava via the hepatic vein

Fetal Circulation Placenta - site where exchange of

materials between fetus and mother occur Umbilical arteries (2) - carry fetal blood

high in CO2 / low in O2 to the placenta Umbilical vein - returns oxygenated blood

from the placenta to the fetus

Fetal Circulation Ductus venosus - allows blood to bypass

the liver Foramen ovale - opening in interatrial

septum allowing blood to bypass the lungs Blood flows from r.atrium ->l.atrium

Ductus arteriosus - vessel connecting pulmonary artery to the aorta

1. superior vena cava 2. inferior vena cava 3. pulmonary veins 4. pulmonary trunk (p. artery, p. aorta) 5. systemic aorta

A. Great Vessels

Branches of systemic aorta 1. from ascending aorta, right and left

coronary artery 2. from aortic arch, brachiocephalic artery a. right subclavian artery (1) r. axillary artery (a) r. brachial artery 1. r. ulnar artery 2. r. radial artery

3. superficial and deep palmar arches

(anastomoses) (b) deep brachial artery (c) posterior circumflex (2) r. vertebral artery

Branches of systemic aorta

b. right common carotid artery (a) r. external carotid artery (b) r. internal carotid artery c. (cat, not human) left common

carotid artery (a) l. external carotid artery (b) l. internal carotid artery

Branches of systemic aorta

3. from aortic arch (human, not cat), left common carotid artery

a. l. external carotid artery b. l. internal carotid artery

Branches of systemic aorta

4. from aortic arch, left subclavian artery (cat and human) a. l. axillary artery

(1) l. brachial artery (a) l. ulnar artery (b) l. radial artery (c) superficial and deep palmar arches (anastomoses)

Branches of systemic aorta

(2) deep brachial artery (3) posterior circumflex

b. l. vertebral artery 5. from descending thoracic aorta

a. paired bronchial arteries b. paired intercostal arteries

Branches of systemic aorta

6. from abdominal aorta a. celiac trunk (1) splenic artery (2) l. gastric artery (3) hepatic artery

Branches of systemic aorta

b. superior mesenteric artery c. paired renal arteries d. paired gonadal arteries e. paired lumbar arteries f. inferior mesenteric artery

Branches of systemic aorta

g. right and left common iliac arteries (1) internal iliacs (2) external iliacs->femorals->

popliteal->tibial->dorsalis pedis-> plantar arches

Branches of systemic aorta

C. Major veins A. coronary circulation: coronary sinus

B. pulmonary circulation: pulmonary veins C. hepatic portal circulation: hepatic portal vein drains 1. inferior mesenteric which drains splenic vein 2. superior mesenteric vein

D. Cranial Circulation: cranial venous

sinuses

E. Systemic Circulation: 1. superior vena cava drains

a. azygos system b. right and left brachiocephalic veins c. internal jugular and subclavian vein d. external jugular and axillary e. cephalic vein (superficial) and brachial vein (deep) which drainsradial, ulnar, median cubital and basilic veins

2. inferior vena cava drains a. hepatic vein b. phrenic vein c. paired renal veins d. paired gonadal veins

e. paired common iliac veins which drain (1) paired internal iliac veins (2) paired external iliac veins which drain (a) femoral veins which drain 1. popliteal veins which drain a peroneal vein b anterior and posterior tibial veins (b) great saphenous veins

Capillary Exchange

Mechanisms of Exchange Diffusion - major method used to

exchange substances such as O2, CO2, glucose, and amino acids

Vesicular transport - endocytosis and exocytosis of lipid-insoluble molecules

Bulk flow - involves filtration and reabsorption

Arteries Veins Pressures

promoting filtration Blood hydrostatic

pressure*** Interstitial fluid

osmotic pressure

Pressures promoting reabsorption

Blood colloid osmotic pressure***

Interstitial fluid hydrostatic pressure

Physiology of Circulation

Important Terms Blood Flow Blood pressure Resistance

Blood Flow Blood flow - is the amount of blood flowing

through a tissue in a given period of time Velocity of blood flow is inversely related to

the diameter of the blood vessel Blood flows most slowly in areas of greatest

width

Blood Pressure Force that the blood exerts against the

walls of a blood vessels Factors affecting BP include cardiac

output, blood volume, viscosity, resistance, and the elasticity of the arteries

Cardiac Output CO=Stroke volume X Heart Rate Any factor that increases SV or HR will

increase blood pressure

Peripheral Resistance Resistance to blood flow due to the force of

friction between vessel wall and blood Resistance affected by blood viscosity,

vessel length and vessel radius

Sources affecting Resistance Blood viscosity- how thick or thin the blood

is. Measured by hematocrit. Vessel length- longer the vessel, the

greater the resistance, the greater the BP Vessel radius- smaller the vessel the

greater the resistance

Blood Volume ↓ Blood volume , ↓ Blood pressure ↑ Blood volume, ↑Blood pressure Blood volume & blood pressure monitored

by the cardiovascular center in the medulla (ANS), baroreceptors and chemoreceptors and by hormonal regulation

Hormonal Regulation of Blood Pressure

Renin- angiotensin pathway Angiotensin II - powerful vasoconstrictor

thus raising resistance Stimulates secretion of aldosterone from the

adrenal gland promoting sodium retention ADH - antidiuretic hormone from the pituitary

causing the kidneys to reabsorb more water

Hormone lowering BP ANP - atrial natriutic peptide

released by atrial cells promoting the loss of salt and water in the urine , thus ↓ blood volume and causing vasodilation which then ↓ blood pressure

PTH - parathyroid hormone causes vasodilation

Endothelin = potent vasoconstrictorresponds to low blood flow

NO (nitrous oxide) = powerful vasodilator; balances endothelin and dilates vessels in response to high blood flow.

Normal Blood Pressure Newborn = 90/55 mm Hg Adults = 120/80 mm Hg Old Age = 150/90 Systolic Pressure = peak pressure during

systole Diastolic pressure = lowest pressure during

diastole (filling of ventricles)