EXTERNAL AND INTERNAL STRUCTURE OF THE BRAIN STEM DR A. A. NWAKANMA THE BRAINSTEM •The brainstem is made up of the medulla oblongata, pons and midbrain •It is stalklike in shape and connects the narrow spinal cord with the expanded forebrain •Occupies the posterior cranial fossa of the skull Loading… FUNCTIONS OF BRAINSTEM •It serves as a conduit for the ascending and descending tracts connecting the spinal cord to the different parts of the higher centers in the forebrain •It contains important reflex centers associated with the control of respiration and CVS. •It is also associated with the control of consciousness •It contains important nuclei of cranial nerves II through XII EXTERNAL FEATURES OF MEDULLA OBLONGATA • The medulla oblongata connects the pons superiorly with the SC inferiorly •The junction of the medulla and SC is at the origin of the anterior and posterior roots of the first cervical nerve which corresponds approximately to the level of the foramen magnum Loading… EXTERNAL FEATURES OF MEDULLA •The medulla oblongata is piriform in shape •It has a broad superior part – open part •And a lower closed part •The central canal of the SC continues upward into the lower half of the medulla •In the upper half of the medulla it expands as the cavity of the fourth ventricle EXTERNAL FEATURES OF MEDULLA •On the ant. Surface of the medulla is the anterior median fissure which is continous inferiorly with the ant. Median fissure of the SC •On each side of the median fissure is a swelling called the pyramid EXTERNAL FEATURES OF MEDULLA •The pyramids are composed of bundles of nerve fibers, corticospinal fibers which originate in large nerve cells in the precentral gyrus of the cerebral cortex •The pyramids tapers inferiorly and majority of the descending fibers cross over to the opposite side forming the decussation of the pyramids here •The ant. External arcuate fibers are a few nerve fibers that emerge from the ant. Median fissure above the decussation and pass laterally over the medulla oblongata to enter the cerebellum EXTERNAL FEATURES OF MEDULLA •Posterolateral to the pyramids are the OLIVES which are oval elevations produced by the underlying inf. Olivary nuclei •In the groove b/w the pyramid and olive emerges the rootlets of the hypoglossal nerve •Post. To the olives are the inf. Cerebellar peduncles which connect the medulla to the cerebellum EXTERNAL FEATURES OF MEDULLA •In the groove b/w the olive and the inf. Cerebellar peduncle emerges the roots of the glossopharyngeal and vagus nerves and the cranial roots of accessory nerve •The post. Surface of the sup. Half of the medulla forms the lower part of the floor of the 4th ventricle External features of medulla •The post surface of the inf. Half continues with the post. Aspect of the SC and possesses a post. Median sulcus •On each side of the median sulcus is an elongated swelling , the Gracile tubercle produced by the underlying gracile nu. •Lat. To the gracile tubercle is the cuneate tubercle produced by the underlying cuneate nu. Loading… INTERNAL STRUCTURE OF MEDULLA •The internal structure of the medulla oblongata is usually considered at 3 levels •Level of pyramidal decussation •Level of olive •Level of sensory or lemniscal decussation T/S OF MEDULLA AT THE LEVEL OF OLIVE •This level corresponds to the floor of the 4th ventricle and the cranial n. Nuclei seen include •Hypoglossal n. • Vestibular nuclei •Dorsal nu. Of vagus •Solitary tract and its nu. •Nu. Ambigus • dorsal and ventral cochlear nu. T/S OF MEDULLA AT THE LEVEL OF OLIVE •The other masses of gray matter seen at this level include •The medial and dorsal accessory olivary nu. •Lat. Reticular nu. •Arcuate nu. •The descending tracts seen include •Pyramid •Rubrospinal tract •Spinal nu. And •Tract of trigeminal n. T/S OF MEDULLA AT THE LEVEL OF OLIVE •The ascending tracts include •Medial lemniscus lying in the middle and is L shaped •Spinothalamic T •Spinocerbellar T. •Spinotectal T. •The reticular formation and the inf. Olivary nu. Are also prominent features found at this level T/S OF THE MEDULLA AT THE LEVEL OF LEMNISCAL DECUSSATION •The level represented by this section lies a little above the level of the pyramidal decussation •The structures found at this level include •Central canal surrounded by gray matter •Medial lemniscus •The pyramids the nu. And fasciculus cuneatus •Spinal nu. Of trigeminal n. •The reticular formation T/S OF THE MEDULLA AT THE LEVEL OF LEMNISCAL DECUSSATION •Internal arcuate fibers which arise from the nu. Gracilis and cuneatus and arch forward on the medial side of the gray matter crossing in the midline to form the lemniscal or sensory decussation •Accessory cuneate nu. Lying dorsolateral to the cuneate nu. T/S OF THE MEDULLA AT THE LEVEL OF LEMNISCAL DECUSSATION •The cranial nerve nuclei seen at this level include •Hypoglossal nu. •Dorsal motor nu. Of vagus •Arcuate nu. •Nu. Of solitary tract •Nu. Ambigus •Other structures include •Lower part of inf. Olivary nu. •Lat. Reticular nu. •Arcuate nu. •Lat. & ventral spinothalamic tr. •Doral and ventral spinocerebella tr. •Spino-olivary tr. •Pyramids •Vestibulospinal tr. •Corticospinal tr. •Medial longitudinal fasciculus Connections of the Inferior Olivary Complex • The main afferents of the inferior olivary nucleus are from the cerebral cortex and from the spinal cord • The main efferents are to the cerebellar cortex. • An olivospinal tract is traditionally described, but some authorities hold that the inferior olivary nuclei do not send any fibres to the spinal cord. •The nucleus may be regarded as a relay station on the cortico-olivo-cerebellar and spino-olivo-cerebellar pathways. • The accessory olivary nuclei are connected to the cerebellum by parolivo-cerebellar fibres. THE PONS •The pons is the middle part of the brainstem •Its continuous below with the medulla oblongata and above with the midbrain •It is seperated from the cerbellum by the 4th ventricle •Pons has two surfaces: •Ventral and dorsal External Features Of Ventral Surface Of Pons •The ventral surface of pons shows the following features •The ventral surface is convex and has a shallow groove in the midline called the basilar groove which lodges basillar artery •Transvesely running fibers connecting the pons to the cerebellum thru the middle cerebellar peduncle •The two roots of trigeminal nerve (sensory and motor) emerge at the jxn b/w the ventral surface of pons and middle cerebellar peduncle EXTERNAL FEATURES OF DORSAL PONS •The dorsal surface of pons shows the following features •Median sulcus in the median plane •Medial eminence – shows rounded elevation in the lower part called facial colliculus which overlies the nu. Of abducent n. •Sulcus limitans – is lat. To the medial eminence and seperates medial eminence from vestibular area T/S THROUGH CAUDAL PART OF PONS •The features seen at this level include •Medial lemniscus in the most ant. Part of the tegmentum •The facial nu. Lies post to the lat. Part of the medial lemniscus •The fibers of the facial nerve wind around the nu. Of the abducent nerve producing the facial colliculus T/S THROUGH CAUDAL PART OF PONS •The medial longitudinal fasciculus is situated beneath the floor of the 4th ventricle on either side of the midline •The medial longitudinal fasciculus is the main pathway that connects the vestibular and cochlear nuclei with the nuclei controlling the extraocular muscles (oculomotor, trochlear and abducent) •The medial vestibular nu. Is situated lat. To the abducent nu. And in close relationship to the inf. Cerebellar peduncle T/S THROUGH CAUDAL PART OF PONS •The sup. Part of the lat. And inf. Part of sup. Vestibular nu. Are found at this level •Post. And ant. Cochlear nu. Are also found at this level •The spinal nu.of trigeminal nerve and tract lie on the anteromedial aspect of the inf. Cerebellar peduncle T/S THROUGH CAUDAL PART OF PONS •The trapezoid body is made up of fibers derived from the cochlear nuclei and the nuclei of trapezoid body •They run transversely in the ant. Part of the tegmentum •The basilar part of the pons at this level contain masses of nervr cells called pontine nuclei T/S THROUGH CAUDAL PART OF PONS •The axons of these cells give origin to the transverse fibers of the pons which cross the midline and intersect the corticospinal and corticonuclear tracts breaking them up into small bundles Loading… INTERNAL STRUCTURE OF CRANIAL PART OF PONS •The internal structure of the cranial part of pons is similar to that seen at the caudal level but contains the motor and principal sensory nuclei of the trigeminal nerve •The motor nu. Of the trigeminal nerve is situated beneath the lat. Part of the 4th ventricle within the reticular formation INTERNAL STRUCTURE OF CRANIAL PART OF PONS •The principal sensory nu. Of the trigeminal nerve is situated lateral to the motor nu. •The sup. Cerebellar peduncle is situated posterolat. To the motor nu. Of trigeminal nerve EXTERNAL FEATURES OF MIDBRAIN •Midbrain measures about 2cm in length and connects the pons and cerebellum with the forebrain •The midbrain is traversed by a narrow channel – the cerebral aqueduct ( which is filled with CSF) •On the posterior surface are four rounded eminences that are divided into superior and inferior pairs •The sup. Colliculi are centers for visual reflexes while the inf. Are lower auditory centers •In the midline below the inf. Colliculi emerges the trochlear nerves EXTERNAL FEATURES OF MIDBRAIN •Each colliculi is related to a ridge called brachium •The sup. Brachium passes from the sup. Colliculus to the lat. Geniculate body and the optic tract •The inf. brachium connects the inf colliculus to the medial geniculate body EXTERNAL FEATURES OF MIDBRAIN •On the anterior aspect of the midbrain is a deep depression in the midline called the interpeduncular fossa which is bounded on either side by the crus cerebri •Many blood vessels perforate the floor of the interpeduncular fossa and this region is termed the post. Perforated substance INTERNAL STRUCTURE OF MIDBRAIN •The midbrain is divided into two parts – •An upper tectum and •A lower part called cerebral peduncles •The upper part (tectum) contains mainly the colliculi of the two sides and represents the dorsal part of the midbrain •The cerebral peduncles are subdivided by the substantia nigra into •The tegmentum and •Crus cerebri STRUCTURE OF MIDBRAIN AT OF INF. COLLICULUS •The structures seen at this level include •Crus cerebri- this contain descending fibers from different parts of the cerebral cortex •The medial 1/6 contain frontopontine fibers •The intemediate 2/3 contain corticospinal and corticonuclear fibers •The lat. 1/6 contain temporopontine fibers •Other structures include •Substantia nigra •Cerebral aqueduct : this is surrounded by the central gray matter. •Ventral to this aqueduct is the oculomotor and trochlear nerves STRUCTURE OF MIDBRAIN AT OF INF. COLLICULUS •Reticular formation b/w the substantia nigra and gray matter •Inferior colliculus •Mesocephalic nu. Of trigeminal nerve •Compact bundle of fibers lies in the tegmentum dorsomedial to the substantia nigra •This bundle consistsof the medial lemniscus, trigeminal lemniscus and spinal lemniscus •Medial longitudinal fasciculus •Superior cerebellar peduncle •Rubrospinal tract Structure of midbrain at the level of sup. colliculus •The following structures are seen at this level •Sup. Colliculus in the tectum •Red nu. In the tegmentum dorsomedial to the substantia nigra •Oculomotor nuclei near the central gray matter •Bundles of ascending fibers consisting of medial lemniscus, spinal lemniscus and trigeminal lemniscus Structure of midbrain at the level of sup. colliculus •Dorsal tegmental decussation : this consists of fibers originating in the sup. Colliculus, it crosses to the opp. Side and descend as the tectospinal tract •Ventral tegmental decussation : this originates in the red nu

20% of the mass of adrenal gland. It is made up of interlacing cords of cells known as chromaffin cells. Chromaffin cells are also called pheochrome cells or chromophil cells. These cells contain fine granules which are stained brown by potassium dichromate. Types of chromaffin cells Adrenal medulla is formed by two types of chromaffin cells: 1. Adrenaline-secreting cells (90%) 2. Noradrenaline-secreting cells (10%). „ HORMONES OF ADRENAL MEDULLA Adrenal medullary hormones are the amines derived from catechol and so these hormones are called catecholamines. Catecholamines secreted by adrenal medulla 1. Adrenaline or epinephrine 2. Noradrenaline or norepinephrine 3. Dopamine. „ PLASMA LEVEL OF CATECHOLAMINES 1. Adrenaline : 3 μg/dL 2. Noradrenaline : 30 μg/dL 3. Dopamine : 3.5 μg/dL „ HALF-LIFE OF CATECHOLAMINES Half-life of catecholamines is about 2 minutes. „ SYNTHESIS OF CATECHOLAMINES Catecholamines are synthesized from the amino acid tyrosine in the chromaffin cells of adrenal medulla (Fig. 71.1). These hormones are formed from phenylalanine also. But phenylalanine has to be converted into tyrosine. Stages of Synthesis of Catecholamines 1. Formation of tyrosine from phenylalanine in the presence of enzyme phenylalanine hydroxylase 2. Uptake of tyrosine from blood into the chromaffin cells of adrenal medulla by active transport 3. Conversion of tyrosine into dihydroxyphenylalanine (DOPA) by hydroxylation in the presence of tyrosine hydroxylase 440 Section 6tEndocrinology FIGURE 71.1: Synthesis of catecholamines. DOPA = Di- hydroxyphenylalanine, PNMT = Phenylethanolamine-N- methyltransferase. 4. Decarboxylation of DOPA into dopamine by DOPA decarboxylase 5. Entry of dopamine into granules of chromaffin cells 6. Hydroxylation of dopamine into noradrenaline by the enzyme dopamine beta-hydroxylase 7. Release of noradrenaline from granules into the cytoplasm 8. Methylation of noradrenaline into adrenaline by the most important enzyme called phenylethanolamine- N-methyltransferase (PNMT). PNMT is present in chromaffin cells. „ METABOLISM OF CATECHOLAMINES Eighty five percent of noradrenaline is taken up by the sympathetic adrenergic neurons. Remaining 15% of noradrenaline and adrenaline are degraded (Fig. 71.2). FIGURE 71.2: Metabolism of catecholamines. COMT = Catechol-O-methyltransferase, MAO = Monoamine oxidase. Stages of Metabolism of Catecholamines 1. Methoxylation of adrenaline into meta-adrenaline and noradrenaline into metanoradrenaline in the presence of ‘catechol-O-methyltransferase’ (COMT). Meta-adrenaline and meta-noradrenaline are together called metanephrines 2. Oxidation of metanephrines into vanillylmandelic acid (VMA) by monoamine oxidase (MAO) Removal of Catecholamines Catecholamines are removed from body through urine in three forms: i. 15% as free adrenaline and free noradrenaline ii. 50% as free or conjugated meta-adrenaline and meta-noradrenaline iii. 35% as vanillylmandelic acid (VMA). „ ACTIONS OF ADRENALINE AND NORADRENALINE Adrenaline and noradrenaline stimulate the nervous system. Adrenaline has significant effects on metabolic functions and both adrenaline and noradrenaline have significant effects on cardiovascular system. „ MODE OF ACTION OF ADRENALINE AND NORADRENALINE – ADRENERGIC RECEPTORS Actions of adrenaline and noradrenaline are executed by binding with receptors called adrenergic receptors, which are present in the target organs. Chapter 71tAdrenal Medulla 441 Adrenergic receptors are of two types: 1. Alpha-adrenergic receptors, which are subdivided into alpha-1 and alpha-2 receptors 2. Beta-adrenergic receptors, which are subdivided into beta-1 and beta-2 receptors. Refer Table 71.1 for the mode of action of these receptors. „ ACTIONS Circulating adrenaline and noradrenaline have similar effect of sympathetic stimulation. But, the effect of adrenal hormones is prolonged 10 times more than that of sympathetic stimulation. It is because of the slow inactivation, slow degradation and slow removal of these hormones. Effects of adrenaline and noradrenaline on various target organs depend upon the type of receptors present in the cells of the organs. Adrenaline acts through both alpha and beta receptors equally. Noradrenaline acts mainly through alpha receptors and occasionally through beta receptors. 1. On Metabolism (via Alpha and Beta Receptors) Adrenaline influences the metabolic functions more than noradrenaline. i. General metabolism: Adrenaline increases oxygen consumption and carbon dioxide removal. It increases basal metabolic rate. So, it is said to be a calorigenic hormone ii. Carbohydrate metabolism: Adrenaline increases the blood glucose level by increasing the glycogenolysis in liver and muscle. So, a large quantity of glucose enters the circulation iii. Fat metabolism: Adrenaline causes mobilization of free fatty acids from adipose tissues. Catecholamines need the presence of glucocorticoids for this action. 2. On Blood (via Beta Receptors) Adrenaline decreases blood coagulation time. It increases RBC count in blood by contracting smooth muscless

„ INTRODUCTION Medulla is the inner part of adrenal gland and it forms 20% of the mass of adrenal gland. It is made up of interlacing cords of cells known as chromaffin cells. Chromaffin cells are also called pheochrome cells or chromophil cells. These cells contain fine granules which are stained brown by potassium dichromate. Types of chromaffin cells Adrenal medulla is formed by two types of chromaffin cells: 1. Adrenaline-secreting cells (90%) 2. Noradrenaline-secreting cells (10%). „ HORMONES OF ADRENAL MEDULLA Adrenal medullary hormones are the amines derived from catechol and so these hormones are called catecholamines. Catecholamines secreted by adrenal medulla 1. Adrenaline or epinephrine 2. Noradrenaline or norepinephrine 3. Dopamine. „ PLASMA LEVEL OF CATECHOLAMINES 1. Adrenaline : 3 μg/dL 2. Noradrenaline : 30 μg/dL 3. Dopamine : 3.5 μg/dL „ HALF-LIFE OF CATECHOLAMINES Half-life of catecholamines is about 2 minutes. „ SYNTHESIS OF CATECHOLAMINES Catecholamines are synthesized from the amino acid tyrosine in the chromaffin cells of adrenal medulla (Fig. 71.1). These hormones are formed from phenylalanine also. But phenylalanine has to be converted into tyrosine. Stages of Synthesis of Catecholamines 1. Formation of tyrosine from phenylalanine in the presence of enzyme phenylalanine hydroxylase 2. Uptake of tyrosine from blood into the chromaffin cells of adrenal medulla by active transport 3. Conversion of tyrosine into dihydroxyphenylalanine (DOPA) by hydroxylation in the presence of tyrosine hydroxylase 440 Section 6tEndocrinology FIGURE 71.1: Synthesis of catecholamines. DOPA = Di- hydroxyphenylalanine, PNMT = Phenylethanolamine-N- methyltransferase. 4. Decarboxylation of DOPA into dopamine by DOPA decarboxylase 5. Entry of dopamine into granules of chromaffin cells 6. Hydroxylation of dopamine into noradrenaline by the enzyme dopamine beta-hydroxylase 7. Release of noradrenaline from granules into the cytoplasm 8. Methylation of noradrenaline into adrenaline by the most important enzyme called phenylethanolamine- N-methyltransferase (PNMT). PNMT is present in chromaffin cells. „ METABOLISM OF CATECHOLAMINES Eighty five percent of noradrenaline is taken up by the sympathetic adrenergic neurons. Remaining 15% of noradrenaline and adrenaline are degraded (Fig. 71.2). FIGURE 71.2: Metabolism of catecholamines. COMT = Catechol-O-methyltransferase, MAO = Monoamine oxidase. Stages of Metabolism of Catecholamines 1. Methoxylation of adrenaline into meta-adrenaline and noradrenaline into metanoradrenaline in the presence of ‘catechol-O-methyltransferase’ (COMT). Meta-adrenaline and meta-noradrenaline are together called metanephrines 2. Oxidation of metanephrines into vanillylmandelic acid (VMA) by monoamine oxidase (MAO) Removal of Catecholamines Catecholamines are removed from body through urine in three forms: i. 15% as free adrenaline and free noradrenaline ii. 50% as free or conjugated meta-adrenaline and meta-noradrenaline iii. 35% as vanillylmandelic acid (VMA). „ ACTIONS OF ADRENALINE AND NORADRENALINE Adrenaline and noradrenaline stimulate the nervous system. Adrenaline has significant effects on metabolic functions and both adrenaline and noradrenaline have significant effects on cardiovascular system. „ MODE OF ACTION OF ADRENALINE AND NORADRENALINE – ADRENERGIC RECEPTORS Actions of adrenaline and noradrenaline are executed by binding with receptors called adrenergic receptors, which are present in the target organs. Chapter 71tAdrenal Medulla 441 Adrenergic receptors are of two types: 1. Alpha-adrenergic receptors, which are subdivided into alpha-1 and alpha-2 receptors 2. Beta-adrenergic receptors, which are subdivided into beta-1 and beta-2 receptors. Refer Table 71.1 for the mode of action of these receptors. „ ACTIONS Circulating adrenaline and noradrenaline have similar effect of sympathetic stimulation. But, the effect of adrenal hormones is prolonged 10 times more than that of sympathetic stimulation. It is because of the slow inactivation, slow degradation and slow removal of these hormones. Effects of adrenaline and noradrenaline on various target organs depend upon the type of receptors present in the cells of the organs. Adrenaline acts through both alpha and beta receptors equally. Noradrenaline acts mainly through alpha receptors and occasionally through beta receptors. 1. On Metabolism (via Alpha and Beta Receptors) Adrenaline influences the metabolic functions more than noradrenaline. i. General metabolism: Adrenaline increases oxygen consumption and carbon dioxide removal. It increases basal metabolic rate. So, it is said to be a calorigenic hormone ii. Carbohydrate metabolism: Adrenaline increases the blood glucose level by increasing the glycogenolysis in liver and muscle. So, a large quantity of glucose enters the circulation iii. Fat metabolism: Adrenaline causes mobilization of free fatty acids from adipose tissues. Catecholamines need the presence of glucocorticoids for this action. 2. On Blood (via Beta Receptors) Adrenaline decreases blood coagulation time. It increases RBC count in blood by contracting smooth muscles of splenic capsule and releasing RBCs from spleen into circulation. 3. On Heart (via Beta Receptors) Adrenaline has stronger effects on heart than nor- adrenaline. It increases overall activity of the heart, i.e. i. Heart rate (chronotropic effect) ii. Force of contraction (inotropic effect) iii. Excitability of heart muscle (bathmotropic effect) iv. Conductivity in heart muscle (dromotropic effect). 4. On Blood Vessels (via Alpha and Beta-2 Receptors) Noradrenaline has strong effects on blood vessels. It causes constriction of blood vessels throughout the body via alpha receptors. So it is called ‘general vasoconstrictor’. Vasoconstrictor effect of noradrena- line increases total peripheral resistance. Adrenaline also causes constriction of blood vessels. However, it causes dilatation of blood vessels in skeletal muscle, liver and heart through beta-2 receptors. So, the total peripheral resistance is decreased by adrenaline. Catecholamines need the presence of glucocor- ticoids, for these vascular effects. 5. On Blood Pressure (via Alpha and Beta Receptors) Adrenaline increases systolic blood pressure by increasing the force of contraction of the heart and cardiac output. But, it decreases diastolic blood pressure by reducing the total peripheral resistance. Noradrenaline increases diastolic pressure due to general vasoconstrictor effect by increasing the total peripheral resistance. It also increases the systolic blood pressure to a slight extent by its actions on heart. The action of catecholamines on blood pressure needs the presence of glucocorticoids. TABLE 71.1: Adrenergic receptors Receptor Mode of action Response Alpha-1 receptor Activates IP3 through phospholipase C Mediates more of noradrenaline actions than adrenaline actions Alpha-2 receptor Inhibits adenyl cyclase and cAMP Beta-1 receptor Activates adenyl cyclase and cAMP Mediates actions of adrenaline and noradrenaline equally Beta-2 receptor Activates adenyl cyclase and cAMP Mediates more of adrenaline actions than noradrenaline actions IP3 = Inositol triphosphate 442 Section 6tEndocrinology Thus, hypersecretion of catecholamines leads to hypertension. 6. On Respiration (via Beta-2 Receptors) Adrenaline increases rate and force of respiration. Adrenaline injection produces apnea, which is known as adrenaline apnea. It also causes bronchodilation. 7. On Skin (via Alpha and Beta-2 Receptors) Adrenaline causes contraction of arrector pili. It also increases the secretion of sweat. 8. On Skeletal Muscle (via Alpha and Beta-2 Receptors) Adrenaline causes severe contraction and quick fatigue of skeletal muscle. It increases glycogenolysis and release of glucose from muscle into blood. It also causes vasodilatation in skeletal muscles. 9. On Smooth Muscle (via Alpha and Beta Receptors) Catecholamines cause contraction of smooth muscles in the following organs: i. Splenic capsule ii. Sphincters of gastrointestinal (GI) tract iii. Arrector pili of skin iv. Gallbladder v. Uterus vi. Dilator pupillae of iris vii. Nictitating membrane of cat. Catecholamines cause relaxation of smooth muscles in the following organs: i. Non-sphincteric part of GI tract (esophagus, stomach and intestine) ii. Bronchioles iii. Urinary bladder. 10. On Central Nervous System (via Beta Receptors) Adrenaline increases the activity of brain. Adrenaline secretion increases during ‘fight or flight reactions’ after exposure to stress. It enhances the cortical arousal and other facilitatory functions of central nervous system. 11. Other Effects of Catecholamines i. On salivary glands (via alpha and beta-2 receptors): Cause vasoconstriction in salivary gland, leading to mild increase in salivary secretion ii. On sweat glands (via beta-2 receptors): Increase the secretion of apocrine sweat glands iii. On lacrimal glands (via alpha receptors): Increase the secretion of tears iv. On ACTH secretion (via alpha receptors): Adrenaline increases ACTH secretion v. On nerve fibers (via alpha receptors): Adrenaline decreases the latency of action potential in the nerve fibers, i.e. electrical activity is accelerated vi. On renin secretion (via beta receptors): Increase the rennin secretion from juxtaglomerular apparatus of the kidney. „ REGULATION OF SECRETION OF ADRENALINE AND NORADRENALINE Adrenaline and noradrenaline are secreted from adrenal medulla in small quantities even during rest. During stress conditions, due to sympathoadrenal discharge, a large quantity of catecholamines is secreted. These hormones prepare the body for fight or flight reactions. Catecholamine secretion increases during exposure to cold and hypoglycemia also. „ DOPAMINE Dopamine is secreted by adrenal medulla. Type of cells secreting this hormone is not known. Dopamine is also secreted by dopaminergic neurons in some areas of brain, particularly basal ganglia. In brain, this hormone acts as a neurotransmitter. Injected dopamine produces the following effects: 1. Vasoconstriction by releasing norepinephrine 2. Vasodilatation in mesentery 3. Increase in heart rate via beta receptors 4. Increase in systolic blood pressure. Dopamine does not affect diastolic blood pressure. Deficiency of dopamine in basal ganglia produces nervous disorder called parkinsonism (Chapter 151). „ APPLIED PHYSIOLOGY – PHEOCHROMOCYTOMA Pheochromocytoma is a condition characterized by hypersecretion of catecholamines. Cause Pheochromocytoma is caused by tumor of chromophil cells in adrenal medulla. It is also caused rarely by tumor of sympathetic ganglia (extra-adrenal pheochromocytoma). Chapter 71tAdrenal Medulla 443 Signs and Symptoms Characteristic feature of pheochromocytoma is hyper- tension. This type of hypertension is known as endocrine or secondary hypertension. Other features: 1. Anxiety 2. Chest pain 3. Fever 4. Headache 5. Hyperglycemia 6. Metabolic disorders 7. Nausea and vomiting 8. Palpitation 9. Polyuria and glucosuria 10. Sweating and flushing 11. Tachycardia 12. Weight loss. Tests for Pheochromocytoma Pheochromocytoma is detected by measuring meta- nephrines and vanillylmandelic acid in urine and Cathecolamines in olasma