CH 22: The Cardiovascular System: Vessels & Circulation Keyconcepts: Describe the histological similarities and differences of the blood vessels Explain the pattern and names of the major arteries and veins of the pulmonary & systemic circulations Describe the circulatory changes that occur at birth, and the ones occurring with exercise.

1 aorta & 1 pulmonary trunk ~ 2.5 cm 10 bio capillaries (~ length 5,000 miles) ?

Histology of Blood Vessels Tunica interna or intima (endothelium + c.t.) Tunica media (muscle + c.t.) Tunica externa or adventitia (thick layer of c.t.)

Distinguishing Arteries from Veins: Artery walls thicker (more muscle and elastic fibers) Additional: internal & external elastic membranes Artefacts when fixing slides: Arterial walls contract; endothelium cannot contract: pleated appearance Veins collapse Fig 22.1 Compare to Fig 22.1

Arteries – ALWAYS carry blood away from heart elastic arteries muscular arteries arterioles large vein medium-sized vein venules capillaries Arteries – ALWAYS carry blood away from heart Veins – ALWAYS return blood to heart, contain about 2/3 body's blood at any given time

Pulmonary trunk & aorta and their major branches Largest, conducting arteries – lead directly from heart, subject to high pressures Superior & inferior vena cava and their tributaries Pulmonary trunk & aorta and their major branches

 2 - 9 mm  ~ 4 mm External and internal jugular, brachial & femoral veins External and internal carotids, brachial & femoral arteries

 ~ 10-50 µm  ~ 30 µm

Capillaries Only endothelium Variably permeable Most body regions Characterized by circular fenestrae or pores that penetrate the endothelium -permit exchange of larger molecules. somewhat permeable Most body regions Intestinal mucosa Choroid plexus, endocrine glands, kidneys

Sinusoids Resemble fenestrated capillaries, yet irregular shapes have longer pores thinner (or no) basement membranes Blood movement very slow Found in the liver, heart, etc. sometimes called sinusoidal capillary. In liver and bone marrow

Capillary Bed = Capillary region supplying a body area Metarteriole – shunt - preferred channel through a capillary bed Precapillary sphincter - closes bed temporarily to redistribute blood flow Arteriovenous anastomosis: interconnections , alternative routes of supply Fig 22.4

Normal: From capillary bed into veins and back to heart 3 exceptions Hypophysis _________________ Liver _________________ In kidney nephrons Fig 19.6 Fig 22.26

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Uneven Distribution of Blood Total blood volume: ? 65 -70% in veins (= blood reservoir) lumen is larger than in corresponding arteries 30-35% in heart, arteries and capillaries Table 22.7

Why are valves found in veins but not in arteries? Do all veins have valves? Venous valve pathology ?

Blood Vessel Pathologies Aneurysms Atherosclerosis = type of Arteriosclerosis) thickening and toughening of arterial walls Pathogenesis covered in Physiology

Abdominal Aortic Aneurysm Repair Cerebral aneurysms Most common type: berry aneurysm Usually occur at the bifurcations and branches of the large arteries located at the Circle of Willis

Gross Anatomy of Circulatory System Pulmonary & Systemic Circulations

Pulmonary Circuit Right ventricle into pulmonary trunk to pulmonary arteries to lungs Return by way of 4 pulmonary veins to left atrium Fig 22.9

Systemic Circuit Aortic Arch Left common carotid Brachiocephalic trunk 2 Brachiocephalic trunk 1 Left subclavian 3

Circle of Willis = Cerebral Arterial Circle = Ring of vessels surrounding pituitary gland - supplies cerebrum and cerebellum Brain can receive blood from carotids or vertebrals (significance?) ic v Fig 22.13

Circle of Willis

Descending aorta • thoracic aorta • abdominal aorta Abdominal aorta Common iliac External iliac Femoral

Descending Aorta - Thoracic Area Bronchial arteries - supply bronchi and lungs Pericardial arteries - supply pericardium Mediastinal arteries - supply mediatinal structures Esophageal arteries - supply esophagus Paired intercostal arteries- thoracic wall Superior phrenic arteries - supply diaphragm Fig 22.17

Descending Aorta - Abdominal Area Celiac trunc - 3 branches – to liver, gallbladder, esophagus, stomach, duodenum, pancreas, and spleen Superior mesenteric– to pancreas and duodenum, small intestine and colon Paired suprarenal - to adrenal glands Paired renal – to kidneys Paired gonadal – to testes or ovaries Inferior mesenteric – to terminal colon and rectum Paired lumbar – to body wall Fig 22.17

Circulation Changes at Birth No blood coming from placenta Ductus venosus becomes ligamentum venosus (=ligamentum teres) Foramen ovale closes & becomes fossa ovale Ductus arteriosus closes and becomes ligamentum arteriosum Umbilical vein and arteries degenerate

The End Patent foramen ovale For more congenital circulatory problems see p. 606 The End