Examville.com - Physiology - Regional Circulation

Examville is a global education community where users like you can connect and interact with other students and teachers from around the world. Share, seek, download and discuss everything inside and outside the classroom. All you need is an email address and a password to get started.

JOIN US FOR FREE: http://www.examville.com

© Examville.com, LLC June 2009

REGIONAL CIRCULATION CORONARY CIRCULATION

ARTERIAL SUPPLY RIGHT CORONARY ARTERY SUPPLIES z z z z

Right atrium Major portion of right ventricle Interventricular septum (posterior part) Most of the conducting system of the heart

LEFT CORONARY ARTERY TWO BRANCHES • ANTERIOR DESCENDING ARTERY Runs in interventricular groove • LEFT CIRCUMFLEX ARTERY Runs in A-V groove SUPPLY z Whole left atrium z Most of left ventricle. z Interventricular septum, (anterior part). z Small part of right ventricle near anterior interventricular septum. z Part of left branch of bundle of his NOTE- In 50% individuals predominant supply is by right coronary artery. 30% individuals balanced 20% individuals, supply is by left coronary artery. VENOUS DRAINAGE OF THE HEART • Coronary sinus • Great cardiac veins • Anterior cardiac veins

MEASUREMENT OF CORONARY BLOOD FLOW z Nitrous oxide technique z Radionuclide technique z Coronary angiography POINTS TO REMEMBER z Normal coronary blood flow is 250 ml /min. z O2 consumption of myocardium at rest is 25ml/min. z 80% coronary blood flow occurs during diastole whereas only 20% CBF occurs during systole. PRESSURE (mm Hg)

Pressure difference

SYSTOLE

AORTA 120

LV 122

RV 25

LV -1

RV 95

DIASTOLE

80

0

0

80

80

NOTE 1. Pressure difference between aorta and left ventricle is very small during systole, therefore there is no blood flow in subendocardial portion of LV during systole. 2. 80% blood flow occurs during diastole 3. Subendocardial portion of LV is prone to MI. 4. All conditions that leads to high LV pressure leads to more chances of MI, as coronary perfusion is severely compressed during systole. 5. CCF, increase in venous pressure? Decrease aortic diastolic pressure, effective coronary perfusion pressure decreases.

REGULATION OF CORONARY BLOOD FLOW Myocardium has high O2 consumption during rest. Coronary blood flow is increased during exercise. Coronary blood flow is maintained by autoregulation.

Factors affecting autoregulation CHEMICAL FACTORS • Hypoxia leads to formation of adenosine, a potent vasodilator. It increase coronary blood flow and myocardial hypoxia is relieved. • Other vasodilator metabolites are CO2 , H ,K LACTIC ACID ,PG,ATP, ADP. NEURAL FACTORS • Alpha- adrenergic receptors----vasoconstriction • Beta- adrenergic receptors----vasodilatation FACTORS AFFECTING CORONARY BLOOD FLOW z Exercise – CBF increase during exercise by sympathetic activity. z Hypotension Reflex increase in non adrenergic discharge causing increased CBF z Stress, emotional excitement increase sympathetic activity. z Hormones – a. Thyroid – hyperthyroidism increases metabolism and increase CBF b. Epinephrine and nor-epinephrine acts through beta receptors and increase CBF. z Temperature – Increased body temperature increases CBF.

CEREBRAL CIRCULATION BLOOD SUPPLY Arterial supply Two main arteries z Two internal carotid artery z Two vertebral arteries Vertebral arteries join to form basilar artery

Venous drainage z Jugular veins z Vertebral venous plexus Cerebral blood flow is 750ml min Cerebral O 2 consumption 45ml min Brain is very sensitive to hypoxia; therefore if blood supply is stopped for 10 secs, person may get unconsciousness. METHOD FOR MEASUREMNT CEREBRAL BLOOD FLOW 1. Nitrous oxide technique 2. Xe Clearance curve technique

REGULATION OF CEREBRAL BLOOD FLOW FACTORS AFFECTING CEREBRAL BLOOD FLOW z z z z

Fall in pO2 causes vasodilatation increasing cerebral blood flow. If hypoxia is severe then vasoconstriction occurs. Rise in PCO2 causes vasodilatation, increase in cerebral blood flow. Anesthetic drugs decrease CBF. Rise in Intra cranial pressure decrease effective perfusion pressure further decreasing CBF.

MECHANISM OF CEREBRAL AUTOREGULATION z z

Mild decrease in perfusion pressure leads to vasodilation. Marked decrease in perfusion pressure leads to hypoxia.

CEREBROSPINAL FLUID z z

(CSF)

Clear, colorless Specific gravity 1005- 1008

z z z z z

Protein – 20-30 mg% Lymphocytes – 0-4 Glucose less than plasma Volume 150 ml Normal CSF pressure 130 mm Hg H2O

Na K Ca HCO3 PROTEIN GLUCOSE pH OSMOLALITY

CSF 146 3.0 2.2 25

PLASMA 150 4.6 4.7 24.8

20-32 50-80 7.33 290

6000 100 7.4 290

Formation and absorption of CSF CSF is formed by choroid plexus in ventricles and blood vessels of meningeal and ependymeal lining of ventricles. Absorbed by arachnoid villi into dural sinuses and spinal veins. CSF TRAVELS VIA LATERAL VENTRCILES ↓ FORAMEN OF MONRO THIRD VENTRICLE ↓ AQUDUCT OF SYLVIUS CISTERNA MAGNA ↓ SUBARACHNOID SPACE

FUNCTIONS OF CSF • Supports the delicate brain. • Acts as buffer. • Removal of waste product from brain. BLOOD BRAIN BARRIER It is defined as barrier between blood and brain tissue. Formed between 1. Choroids plexus and CSF fluid interface 2. CSF and brain capillaries FUNCTION OF BBB z z

Protects brain from toxins in the blood. Prevents electro chemical fluctuations in the CNS.

NOTE z Highly permeable to water, O2,CO2 SULPHA DRUGS z Slightly permeable to H, Na, K HCO3 Mg z Impermeable to gold, urea, bile salts NOTE Four areas where substances in the blood can act and cause changes in brain functions without entering BBB are : 1. The posterior pituitary 2. The area postrema 3. The organosum vasculosum 4. Subfornical organs

PULMONARY CIRCULATION FEATURES It consists of 1. Pulmonary trunk 2. Pulmonary arterioles 3. Pulmonary capillaries

4. Pulmonary venules and veins Pulmonary trunk Divided into Right pulmonary artery Left pulmonary artery Pulmonary arterioles Divided into capillaries Pulmonary capillaries surround the alveoli Pulmonary venules and veins a) Receives oxygenated blood from the capillaries b) Join to form four main veins c) Finally open into the right atrium. Mean Pulmonary Artery Pressure

10 – 15 mm Hg

Systolic Blood Pressure

20 – 25 mm Hg

Diastolic Blood Pressure

8 – 12 mm Hg

Pulmonary capillary pressure

8 – 10 mm Hg

NOTE - Pulmonary blood volume is more in recumbent position and it decreases on standing. Pulmonary artery is 1. Very distensible 2. Low pressure system 3. Resistance to blood flow is low. Therefore work done by right ventricle to pump blood is less than that of left ventricle. Nerve supply Sympathetic nerve supply to lung vessels.

On stimulation, increases the pulmonary vascular resistance. Vascular Reflexes Baroreceptor reflex - Stimulation cause reflex dilation of pulmonary vessels. Chemoreceptor reflex – Stimulation cause pulmonary vasoconstriction via sympathetic nerves. Vagal mechanoreceptor present in a) Pulmonary trunk – Rise in pressure in pulmonary artery causes reflex bradycardia and hypotension. b) Junction of pulmonary vein and left atrium – Stimulation causes reflex tachycardia and diuresis. c) Effect of chemical changes on the lung vessels

HYPOXIA Acute Hypoxia – Stimulates chemoreceptor causing reflex sympathetic stimulation leading to pulmonary vasoconstriction. Chronic Hypoxia – Causes Pulmonary Hypertension, marked increase in pulmonary arterial pressure that results in right ventricular failure and pulmonary oedema. HYPERCAPNIA – No effect on pulmonary flow and resistance

SPLANCHNIC CIRCULATION Drainage of blood from liver, GIT, spleen and pancreas. The blood from GIT, spleen and pancreas drains via portal veins to the liver (Portal circulation) and from the liver via hepatic veins to the inferior vena cava. INTESTINAL CIRCULATION Intestine receives blood from Superior mesenteric artery Inferior mesenteric artery Blood flow to intestine increases during metabolic activity.

There exists a counter current system of villous blood vessels in the small intestine ROLE – Slows down the entrance of rapidly absorbed solutes into the blood. Splanchic nerve stimulation causes rise in arterial blood pressure due to a) Vasoconstriction caused by stimulation of splanchnic nerves. b) Release of adrenaline from the adrenal medulla. There exists an Autoregulation mechanism in intestine

HEPATIC CIRCULATION 80% of blood supply to the liver is through the portal vein. 20% of blood supply to the liver is through the hepatic artery.

NERVE SUPPLY Innervated by vasoconstrictor sympathetic nerves. Fall in Arterial BP ↓ Stimulation of sympathetic nerves ↓ Constriction of hepatic, mesenteric arterioles and venules ↓ Capacitance vessels constricts ↓ Blood flow is directed towards the heart

NOTE – Splanchnic constriction can pump approximately 1Litre of blood into arterial circulation in less than 1 minute. Therefore it is called Reservoir Function of the Splanchnic circulation.

Hepatic Artery Blood Flow 1. Contributes 20% of the hepatic blood flow. 2. Pressure is 100 mm Hg 3. Autoregulation of blood flow due to a) Myogenic arterial tone b) Local vasodilator metabolites 4. When portal blood flow decreases, then hepatic artery blood flow increases. Thus keeps the total hepatic blood flow constant.

Hepatic Portal Vein Blood Flow 1. Contributes 20% of hepatic blood flow. 2. Portal venous pressure is 7-12 mm Hg 3. No mechanism of autoregulation exists. 4. Increases after meals.