Principles of Anatomy and Physiology Thirteenth Edition Gerard J. Tortora • Bryan H. Derrickson Chapter 21 The Cardiovascular System: Blood Vessels and Hemodynamics Copyright © 2012 by John Wiley & Sons, Inc.

TUNICA INTERNA: Endothelium Basement membrane Valve Internal elastic lamina TUNICA MEDIA: Smooth muscle External elastic lamina TUNICA EXTERNA Lumen Lumen (a) Artery (b) Vein

Lumen Basement membrane Endothelium (c) Capillary

(d) Transverse section through an artery Internal elastic lamina External elastic lamina Tunica externa Lumen with blood cells Tunica interna Tunica media Connective tissue LM 200x (d) Transverse section through an artery

(e) Red blood cells passing through a capillary Connective tissue Red blood cell Capillary endothelial cells LM 600x (e) Red blood cells passing through a capillary

Aorta and elastic arteries Blood continues to flow toward capillaries Blood flows toward capillaries Left ventricle relaxes (diastole) and fills with blood Left atrium Left ventricle contracts (systole) and ejects blood (a) Elastic aorta and arteries stretch during ventricular contraction (b) Elastic aorta and arteries recoil during ventricular relaxation

(a) Sphincters relaxed: blood flowing through capillaries Smooth muscle fiber From heart Endothelium ARTERIOLE METARTERIOLE Precapillary sphincters (relaxed) CAPILLARY CAPILLARY BED Thoroughfare channel POSTCAPILLARY VENULE MUSCULAR VENULE Endothelium Smooth muscle fiber To heart (a) Sphincters relaxed: blood flowing through capillaries

(b) Sphincters contracted: blood flowing through thoroughfare channel From heart ARTERIOLE METARTERIOLE Precapillary sphincters (contracted) MUSCULAR VENULE Thoroughfare channel To heart (b) Sphincters contracted: blood flowing through thoroughfare channel

(a) Continuous capillary formed by endothelial cells Pinocytic vesicle Basement membrane Nucleus of endothelial cell Lumen Intercellular cleft (a) Continuous capillary formed by endothelial cells

(b) Fenestrated capillary Fenestration (pore) Intercellular cleft Basement membrane Lumen Nucleus of endothelial cell Pinocytic vesicle (b) Fenestrated capillary

Incomplete basement membrane Lumen Nucleus of endothelial cell Intercellular cleft (c) Sinusoid

Transverse section, superior view Vein Cusps of valve Transverse plane Transverse section, superior view Vein Frontal plane Cusps of valve Longitudinally cut Photographs of valve in vein

Systemic veins and venules Heart 7% Pulmonary vessels 9% Systemic arteries and arterioles 13% Systemic capillaries 7% Systemic veins and venules (blood reservoirs) 64%

Lymphatic fluid (lymph) returns to capillary Blood plasma Tissue cell Key: BHP = Blood hydrostatic pressure IFHP = Interstitial fluid hydrostatic pressure BCOP = Blood colloid osmotic pressure IFOP = Interstitial fluid osmotic pressure NFP = Net filtration pressure Interstitial fluid Blood flow from arteriole into capillary IFOP = 1 mmHg Blood flow from capillary into venule IFHP = 0 mmHg BHP = 35 mmHg BCOP = 26 mmHg BHP = 16 mmHg BCOP = 26 mmHg N F P N F P Net filtration at arterial end of capillaries (20 liters per day) (BHP + IFOP) Pressures promoting filtration Net reabsorption at venous end of capillaries (17 liters per day) (BCOP + IFHP) Pressures promoting reabsorption Net filtration pressure (NFP) = – Arterial end Venous end NFP = (35 + 1) – (26 + 0) = 10 mmHg NFP = (16 + 1) – (26 + 0) = –9 mmHg Result Net filtration Net reabsorption

140 Systolic blood pressure 120 100 80 Pressure (mmHg) 60 Diastolic blood pressure 40 20 Vena cavae Aorta Arteries Arterioles Capillaries Venules Veins

Proximal valve Distal valve 1 2 3

Increased blood volume Skeletal muscle pump Respiratory pump Venoconstriction Decreased parasympathetic impulses Increased sympathetic impulses and hormones from adrenal medulla Increased venous return Increased number of red blood cells, as in polycythemia Increased body size, as in obesity Increased heart rate (HR) Increased stroke volume (SV) Increased blood viscosity Increased total blood vessel length Decreased blood vessel radius (vasoconstriction) Increased cardiac output (CO) Increased systemic vascular resistance (SVR) Increased mean arterial pressure (MAP)

Cross-sectional area Velocity Venae cavae Aorta Arteries Arterioles Capillaries Venules Veins

Cardiovascular (CV) center Vagus nerves (parasympathetic) INPUT TO CARDIOVASCULAR CENTER (nerve impulses) From higher brain centers: cerebral cortex, limbic system, and hypothalamus From proprioceptors: monitor joint movements From baroreceptors: monitor blood pressure From chemoreceptors: monitor blood acidity (H+), CO2, and O2 OUTPUT TO EFFECTORS (increased frequency of nerve impulses) Heart: decreased rate Heart: increased rate and contractility Blood vessels: vasoconstriction Vagus nerves (parasympathetic) Cardiac accelerator nerves (sympathetic) Vasomotor nerves (sympathetic) Cardiovascular (CV) center

Baroreceptors in carotid sinus Glossopharyngeal nerves (cranial nerve IX) Cardiovascular (CV) center Baroreceptors in arch of aorta Vagus nerves (cranial nerve X, parasympathetic) Medulla oblongata SA node AV node Ventricular myocardium Spinal cord Cardiac accelerator nerve (sympathetic) Key: Sensory (afferent) neurons Motor (efferent) neurons Sympathetic trunk ganglion

Receptors Control centers Effectors Some stimulus disrupts homeostasis by Decreasing Blood pressure Receptors Baroreceptors in arch of aorta and carotid sinus are stretched less Decreased rate of nerve impulses Input Control centers Return to homeostasis when increased cardiac output and increased vascular resistance bring blood pressure back to normal CV center in medulla oblongata and adrenal medulla Increased sympathetic, decreased parasympathetic stimulation Output Increased secretion of epinephrine and norepinephrine from adrenal medulla Effectors Constriction of blood vessels increases systemic vascular resistance (SVR) Increased stroke volume and heart rate lead to increased cardiac output (CO) Increased blood pressure

Superficial temporal artery Facial artery Femoral artery Common carotid artery Brachial artery Popliteal artery Radial artery Dorsal artery of the foot (dorsalis pedis artery)

Pressure in cuff 140 120 100 Pressure (mmHg) 80 60 Systolic blood pressure (first sound heard) Diastolic blood pressure (last sound heard) Time

Receptors Control center Control center Control center Effectors Hypovolemic shock disrupts homeostasis by Moderately decreasing Blood volume and blood pressure Receptors Baroreceptors in kidneys (juxtaglomerular cells) Baroreceptors in arch of aorta and carotid sinus Inputs Increased secretion of renin Decreased rate of nerve impulses Control center Control center Control center Return to homeostasis when responses bring blood volume and blood pressure back to normal Angiotensinogen in blood Hypothalamus and posterior pituitary Cardiovascular center in medulla oblongata ADH Increased sympathetic stimulation and hormones from adrenal medulla Angiotensin II in blood ADH in blood Outputs Effectors Adrenal cortex liberates aldosterone Kidneys conserve salt and water Blood vessels constrict Heart rate and contractility increase Increased blood volume Increased systemic vascular resistance Increased blood pressure

Systemic capillaries of head, neck, and upper limbs = Oxygenated blood = Deoxygenated blood Systemic capillaries of head, neck, and upper limbs Internal jugular vein Common carotid artery Aorta Left pulmonary artery Pulmonary trunk Pulmonary capillaries of left lung Left pulmonary veins Superior vena cava Left atrium Right atrium Left ventricle Right ventricle Celiac trunk Common hepatic artery Inferior vena cava Splenic artery Hepatic vein Left gastric artery Sinusoids of liver Capillaries of spleen Hepatic portal vein Capillaries of stomach Superior mesenteric artery Systemic capillaries of gastrointestinal tract Inferior mesenteric artery Common iliac vein Common iliac artery Internal iliac vein Internal iliac artery External iliac vein External iliac artery Systemic capillaries of pelvis Arterioles Systemic capillaries of lower limbs Venules

(a) Overall anterior view of the principal branches of aorta Right internal carotid Right external carotid Right vertebral Left common carotid Right common carotid Left subclavian Right subclavian ARCH OF AORTA Brachiocephalic trunk Left axillary ASCENDING AORTA THORACIC AORTA Right brachial Diaphragm ABDOMINAL AORTA Left gastric Celiac trunk Splenic Common hepatic Left renal Superior mesenteric Right radial Left external iliac Left gonadal (testicular or ovarian) Right renal Inferior mesenteric Right ulnar Left internal iliac Left common iliac Right deep palmar arch Left common palmar digital Right deep femoral Left femoral Right superficial palmar arch Left proper palmar digital Left deep femoral Left popliteal Left anterior tibial Left posterior tibial Left fibular (peroneal) Left dorsal artery of foot (dorsalis pedis) Left arcuate Left dorsal metatarsal Left dorsal digital (a) Overall anterior view of the principal branches of aorta

(b) Detailed anterior view of the principal branches of the aorta Left common carotid Right common carotid Left vertebral Left subclavian Right vertebral ARCH OF AORTA Right subclavian Axillary Brachiocephalic trunk THORACIC AORTA ASCENDING AORTA Mediastinals Bronchials Left brachial Esophageals Pericardials Left superior phrenic Right posterior intercostal Left inferior phrenic Diaphragm Left gastric Right inferior phrenic Splenic Common hepatic Left middle suprarenal (adrenal) Celiac trunk Left renal Superior mesenteric Right middle suprarenal (adrenal) Left gonadal (testicular or ovarian) Right renal ABDOMINAL AORTA Right gonadal (testicular or ovarian) Inferior mesenteric Right lumbars Left common iliac Inguinal ligament Left internal iliac Left external iliac Median sacral Left deep artery of the thigh (deep femoral) Left femoral (b) Detailed anterior view of the principal branches of the aorta

SCHEME OF DISTRIBUTION Ascending aorta Right coronary artery Left coronary artery Posterior interventricular branch Marginal branch Anterior interventricular branch Circumflex branch

ANTERIOR INTERVENTRICULAR BRANCH Arch of aorta ASCENDING AORTA Arch of aorta LEFT CORONARY Left pulmonary artery RIGHT CORONARY ASCENDING AORTA Pulmonary trunk Left auricle Left auricle Pulmonary trunk Right auricle GREAT CARDIAC VEIN CIRCUMFLEX BRANCH Right atrium ANTERIOR INTERVENTRICULAR BRANCH LEFT MARGINAL BRANCH POSTERIOR INTER- VENTRICULAR BRANCH ANTERIOR CARDIAC VEIN TRIBUTARY TO GREAT CARDIAC VEIN MARGINAL BRANCH Left ventricle Left ventricle Right ventricle Right ventricle Anterior view of coronary arteries and their major branches

SCHEME OF DISTRIBUTION Basilar Right posterior cerebral Left posterior cerebral Right anterior cerebral Right middle cerebral Left anterior cerebral Left middle cerebral Right external carotid Right internal carotid Left internal carotid Left external carotid Right vertebral Left vertebral Right subclavian Right common carotid Brachiocephalic trunk Right axillary Left subclavian Left common carotid Right brachial Arch of aorta Left axillary (gives rise to same branches as right axillary, except that arteries are labeled left instead of right) Right radial Right ulnar Right superficial palmar arch Right deep palmar arch Right common palmar digital Right palmar metacarpal Right proper palmar digital

Brachiocephalic trunk Right common carotid Left common carotid Right vertebral Left subclavian Right subclavian Arch of aorta Right axillary Right brachial Right internal thoracic (mammary) Right radial Right ulnar Right deep palmar arch Right palmar metacarpal Right superficial palmar arch Right common palmar digital (a) Anterior view of branches of brachiocephalic trunk in upper limb Right proper palmar digital

Right superficial temporal Right maxillary Right internal carotid Right facial Right external carotid Right common carotid Right subclavian Right vertebral Right axillary Clavicle First rib Brachiocephalic trunk (b) Right lateral view of branches of brachiocephalic trunk in neck and head

(c) Inferior view of base of brain showing cerebral arterial circle ANTERIOR Cerebral arterial circle (circle of Willis): Frontal lobe of cerebrum Anterior cerebral Middle cerebral Anterior communicating Temporal lobe of cerebrum Internal carotid Posterior communicating Pons Posterior cerebral Basilar Medulla oblongata Vertebral Cerebellum POSTERIOR (c) Inferior view of base of brain showing cerebral arterial circle

(d) Anterior view of branches of arch of aorta Left subclavian Clavicle (cut) Right common carotid First rib (cut) Right subclavian Left axillary Trachea Left common carotid Brachiocephalic Vagus nerve (recurrent laryngeal branch) Right internal thoracic (mammary) Phrenic nerve Arch of aorta Left lung Pulmonary trunk Heart (d) Anterior view of branches of arch of aorta

SCHEME OF DISTRIBUTION Thoracic aorta Visceral branches Parietal branches Pericardial Posterior intercostal Bronchial Subcostal Esophageal Superior phrenic Mediastinal

Detailed anterior view of principal branches of aorta Left common carotid Right common carotid Left vertebral Left subclavian Right vertebral ARCH OF AORTA Right subclavian Axillary Brachiocephalic trunk THORACIC AORTA ASCENDING AORTA Mediastinals Bronchials Left brachial Esophageals Pericardials Left superior phrenic Right posterior intercostal Left inferior phrenic Diaphragm Left gastric Right inferior phrenic Splenic Common hepatic Left middle suprarenal (adrenal) Celiac trunk Left renal Superior mesenteric Right middle suprarenal (adrenal) Left gonadal (testicular or ovarian) Right renal ABDOMINAL AORTA Right gonadal (testicular or ovarian) Inferior mesenteric Right lumbars Left common iliac Inguinal ligament Left internal iliac Left external iliac Median sacral Left deep artery of the thigh (deep femoral) Left femoral Detailed anterior view of principal branches of aorta

SCHEME OF DISTRIBUTION Abdominal aorta Visceral branches 1. Celiac trunk Parietal branches 1. Inferior phrenic 2. Lumbar 3. Median sacral Left gastric Splenic Common hepatic Hepatic artery proper Right gastric Gastro- duodenal Pancreatic Left gastroepiploic Short gastric 2. Superior mesenteric Inferior Pancreatico- duodenal Jejunal Ileocolic Right colic Middle colic 3. Suprarenal 4. Renal 5. Gonadal (testicular or ovarian) 6. Inferior mesenteric Left colic Sigmoid Superior rectal

(a) Anterior view of celiac trunk and its branches Stomach (turned upward) Left gastroepiploic Right gastroepiploic Short gastrics Right gastric Diaphragm Celiac trunk Left gastric Proper hepatic Spleen Splenic Common hepatic Pancreatic Gastroduodenal Pancreas Superior pancreaticoduodenal Superior mesenteric Jejunum of small intestine Duodenum of small intestine Abdominal aorta (a) Anterior view of celiac trunk and its branches

(b) Anterior view of superior mesenteric artery and its branches Transverse colon of large intestine Middle colic Superior mesenteric Inferior pancreaticoduodenal Jejunum Right colic Jejunals Ileocolic Inferior mesenteric Ileals Ascending colon of large intestine Ileum of small intestine Appendix (b) Anterior view of superior mesenteric artery and its branches

(c) Anterior view of inferior mesenteric artery and its branches Transverse colon of large intestine Superior mesenteric Inferior mesenteric Left colic Anastomosis between left colic and sigmoid Abdominal aorta Descending colon of large intestine Common iliac Sigmoids Superior rectal Sigmoid colon Rectum of large intestine (c) Anterior view of inferior mesenteric artery and its branches

(d) Anterior view of arteries of abdomen and pelvis Hepatic veins Diaphragm Esophageal hiatus Inferior vena cava Common hepatic Right adrenal (suprarenal) gland Splenic Right kidney Celiac trunk Superior mesenteric Right renal Abdominal aorta Right common iliac Inferior mesenteric Right internal iliac Ureter Right external iliac (d) Anterior view of arteries of abdomen and pelvis

SCHEME OF DISTRIBUTION Abdominal aorta Right common iliac Left common iliac (gives rise to same branches as right common iliac, except that arteries are labeled left instead of right) Right external iliac Right internal iliac Right femoral Right deep artery of the thigh (deep peroneal) Right popliteal Right anterior tibial Right posterior tibial Right dorsal artery of foot (dorsalis pedis) Right fibular (peroneal) Right arcuate Right dorsal metatarsal Right lateral plantar Right medial plantar Right plantar arch Right dorsal digital Right plantar metatarsal Right plantar digital

Abdominal aorta Right common iliac Left common iliac Right internal iliac Right external iliac Right deep artery of the thigh (deep femoral) Right femoral Right popliteal Right anterior tibial Right posterior tibial Right fibular (peroneal) Right dorsal artery of foot (dorsalis pedis) Right lateral plantar Right medial plantar Right dorsal metatarsal Right plantar arch Right arcuate Right plantar metatarsal Right dorsal digital Right plantar digital (a) Anterior view (b) Posterior view

Overall anterior view of principal veins Superior sagittal sinus Inferior sagittal sinus Right internal jugular Right external jugular Straight sinus Right transverse sinus Right subclavian Sigmoid sinus Right brachiocephalic Pulmonary trunk Coronary sinus Superior vena cava Great cardiac Right axillary Hepatic portal Right cephalic Splenic Right hepatic Superior mesenteric Right brachials Left renal Right median cubital Inferior mesenteric Right basilic Right radial Inferior vena cava Left common iliac Right median antebrachial Left internal iliac Right ulnar Right palmar venous plexus Left external iliac Right palmar digital Left femoral Right proper palmar digital Left great saphenous Left popliteal Left small saphenous Left anterior tibial Left posterior tibial Left dorsal venous arch Left dorsal metatarsal Left dorsal digital Overall anterior view of principal veins

Inferior sagittal sinus SCHEME OF DRAINAGE Inferior sagittal sinus Superior sagittal sinus Straight sinus Cavernous sinuses Right transverse sinus Left transverse sinus Right sigmoid sinus Left sigmoid sinus Right external jugular Left external jugular Right subclavian Right internal jugular Left internal jugular Left subclavian Right vertebral Left vertebral Right brachiocephalic Left brachiocephalic Superior vena cava

Superior sagittal sinus Right cavernous sinus Inferior sagittal sinus Great cerebral Right ophthalmic Straight sinus Inferior petrosal sinus Right transverse sinus Right superficial temporal Right sigmoid sinus Inferior petrosal sinus Right maxillary Right vertebral Right facial Right internal jugular Right external jugular Right subclavian Right brachiocephalic Right axillary Right lateral view

SCHEME OF DRAINAGE Superior vena cava Right brachiocephalic Right internal jugular Right subclavian Right axillary Right brachial Right cephalic Right basilic Right median cubital Right radial Right ulnar Right accessory cephalic Right median antebrachial Right dorsal venous network of hand (dorsal venous arch) Right deep palmar venous arch Right superficial palmar venous arch Right palmar venous plexus Right palmar digital Right palmar metacarpal Right common palmar digital Right dorsal metacarpal Right proper palmar digital Right dorsal digital

(a) Posterior view of superficial veins of hand Right cephalic Right dorsal venous network of hand (dorsal venous arch) Right dorsal metacarpal Right dorsal digital (a) Posterior view of superficial veins of hand

(b) Anterior view of superficial veins Right external jugular Right subclavian Right internal jugular Right brachiocephalic Superior vena cava Right axillary Right basilic Sternum Right cephalic Right median cubital Right accessory cephalic Right basilic Right cephalic Right median antebrachial Right palmar venous plexus Right palmar digital (b) Anterior view of superficial veins

(c) Anterior view of deep veins Right external jugular Right subclavian Right internal jugular Right brachiocephalic Superior vena cava Right axillary Right brachial Right radials Right ulnars Anastomotic veins Right deep palmar venous arch Right superficial palmar venous arch Right common palmar digital Right proper palmar digital (c) Anterior view of deep veins

(d) Anteromedial view of superficial veins of arm and forearm Biceps brachii muscle Brachial Median cubital Basilic Cephalic Median antebrachial (d) Anteromedial view of superficial veins of arm and forearm

Right internal jugular Right subclavian SCHEME OF DRAINAGE Right internal jugular Right subclavian Right brachiocephalic Accessory hemiazygos Superior vena cava Azygos Hemiazygos Right subcostal Right ascending lumbar Left subcostal Left ascending lumbar

Anterior view Right internal jugular Left internal jugular Right external jugular Left external jugular Right brachiocephalic Left subclavian Left brachiocephalic Right superior intercostal Left superior intercostal Superior vena cava Left axillary Right posterior intercostal Left cephalic Left posterior intercostal Azygos Left brachial Mediastinals Accessory hemiazygos Bronchial Left basilic Pericardial Esophageals Diaphragm Hemiazygos Hepatics Left inferior phrenics Right suprarenal Left suprarenal Right subcostal Left renal Left ascending lumbar Right renal Left gonadal (testicular or ovarian) Right ascending lumbar Inferior vena cava Right gonadal (testicular or ovarian) Left lumbar Right lumbar Left common iliac Middle sacral Right common iliac Left internal iliac Right internal iliac Inguinal ligament Right external iliac Left external iliac Left femoral Anterior view

SCHEME OF DRAINAGE Heart Inferior phrenic Hepatic Hepatic portal Suprarenal Renal Gonadal Lumbar Inferior vena cava Right common iliac Left common iliac Right external iliac Right internal iliac Left internal iliac Left external iliac

Right medial and lateral plantar Right dorsal venous arch SCHEME OF DRAINAGE Inferior vena cava Right common iliac Right external iliac Right internal iliac Right femoral Right deep vein of the thigh (deep femoral) Right popliteal Right posterior tibial Right anterior tibial Right great saphenous Right small saphenous Right medial and lateral plantar Right dorsal venous arch Right deep plantar venous arch Right dorsal venous arch Right plantar metatarsal Right dorsal metatarsal Right dorsal digital Right plantar digital

(a) Anterior view (b) Posterior view Inferior vena cava Left common iliac Right common iliac Right internal iliac Right external iliac Right deep vein of the thigh (deep femoral) Right femoral Right accessory saphenous Right great saphenous Right popliteal Right anterior tibial Right anterior tibial Right small saphenous Right posterior tibial Right fibular (peroneal) Right small saphenous Right great saphenous Right dorsal venous arch Right medial plantar Right lateral plantar Right dorsal metatarsal Right deep plantar venous arch Right dorsal digital Right plantar metatarsal Right plantar digital (a) Anterior view (b) Posterior view

(a) Anterior view of veins draining into hepatic portal vein Inferior vena cava Stomach Spleen HEPATIC PORTAL Short gastric Left gastric Liver Pancreas (behind stomach) Cystic Pancreatic Gallbladder Left gastroepiploic Duodenum Right gastric Pancreaticoduodenal SPLENIC Pancreas SUPERIOR MESENTERIC Right gastroepiploic Transverse colon Left colic Middle colic Right colic Inferior mesenteric Jejunal and ileal Ascending colon Descending colon Ileocolic Cecum Sigmoidal Appendix Ileum Sigmoid colon Drain into superior mesenteric vein Superior rectal Drain into splenic vein Drain into inferior mesenteric vein Rectum (a) Anterior view of veins draining into hepatic portal vein

Abdominal aorta Inferior vena cava Heart Proper hepatic artery Hepatic veins Tributaries from portions of stomach, pancreas, and portions of large intestine Splenic vein Liver Hepatic portal vein Superior mesenteric vein Tributaries from small intestine and portions of large intestine, stomach, and pancreas (b) Scheme of principal blood vessels of hepatic portal circulation and arterial supply and venous drainage of liver

Arch of aorta Superior vena cava Ascending aorta Right pulmonary artery Left pulmonary artery Pulmonary trunk Left pulmonary veins Right pulmonary veins Left lung Right lung Diaphragm Inferior vena cava Abdominal aorta (a) Anterior view

(b) Scheme of pulmonary circulation Right pulmonary artery Left pulmonary artery Pulmonary trunk Air sacs (alveoli) of right lung Air sacs (alveoli) of left lung Right ventricle Right pulmonary veins Left pulmonary veins Left atrium (b) Scheme of pulmonary circulation

(b) Circulation at birth Arch of aorta Superior vena cava Left atrium DUCTUS ARTERIOSUS becomes Ligamentum arteriosum Right atrium Lung Pulmonary artery Pulmonary veins Heart Right ventricle FORAMEN OVALE becomes Fossa ovalis Left ventricle Inferior vena cava Liver DUCTUS VENOSUS becomes Ligamentum venosum Hepatic portal vein UMBILICAL VEIN becomes Ligamentum teres Umbilicus Inferior vena cava Abdominal aorta Common iliac artery UMBILICAL ARTERIES become Medial umbilical ligaments Urinary bladder Urethra (b) Circulation at birth UMBILICAL CORD Oxygenated blood Mixed oxygenated and deoxygenated blood Deoxygenated blood Placenta (a) Fetal circulation

(c) Scheme of fetal circulation Pulmonary trunk Lungs Ductus arteriosus Right ventricle Pulmonary veins Right atrium Foramen ovale Left atrium Left ventricle Aorta Inferior vena cava Systemic circulation Ductus venosus Liver Umbilical arteries Umbilical vein Placenta (c) Scheme of fetal circulation

Blood islands Angioblasts Wall of yolk sac: Mesoderm Endoderm Endothelial lining Blood cells Space (future lumen) Lumen of blood vessel Blood cells