Neuroscience 1A LC12 Hypothalamus PDF - University of Northern Philippines

UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC12 HYPOTHALAMUS COLL...

UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC12 HYPOTHALAMUS COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Sudayon, Sulit, Viloria Dr. Vida Margaret Andal | November 2022 Editors: Sto. Domingo, Tan OUTLINE I. HYPOTHALAMUS A. Borders of the Hypothalamus B. Hypothalamic Nuclei 1. Medial Zone 2. Lateral Zone C. Hypothalamic Lines of Communication 1. Afferent Nervous Connection 2. Efferent Nervous Connection D. Clinical Applications II. PITUITARY GLAND A. Parts of the Pituitary Gland 1. Borders of the Pituitary Gland 2. Lobes a) Hormone Producing Cells of the Anterior Pituitary Gland (Pars Distalis) B. Hypothalamus and Pituitary Gland (Illustration 2. Location of hypothalamus) 1. Pathway Connections C. Hormones Involved D. Clinical Application A. BORDERS OF THE HYPOTHALAMUS Found below the thalamus I. HYPOTHALAMUS Forms the floor and inferior part of the lateral walls of the third ventricle - Collection of nuclei that controls the autonomic nervous system and endocrine Lateral boundary of the hypothalamus is formed by the internal capsule system Caudally, it merges with the tegmentum of the midbrain - The control of hypothalamus is done consciously, it’s automatic. - Essential for life and controls body homeostasis - Found at the center of the limbic system - Only -0.3% of the total brain. It is very small but it is essential for life and for the maintenance of life - Part of DIENCEPHALON (Illustration 1. Fetal Development of hypothalamus) (Illustration 3. Different brain parts bordering hypothalamus) - Not a distinct structure but just a collection of nuclei, many of which are not segregated from one another - It is just like a blank space, not really an empty space. It is a flat surface composed B. HYPOTHALAMIC NUCLEI of a lot of nuclei that are not really grossly differentiated from another. 1. Medial zone - Extends from the optic chiasm anteriorly to the caudal border of the mammillary Part of preoptic nucleus bodies posteriorly Anterior nucleus - Maintains homeostasis by producing hormones that are transmitted to the Part of suprachiasmatic nucleus pituitary gland or directly into the body Paraventricular nucleus o Thyrotropin-releasing hormone (TRH) Dorsomedial nucleus o Gonadotropin-releasing hormone (GnRH) Ventromedial nucleus o Growth hormone-releasing hormone (GHRH) Infundibular (arcuate) nucleus o Corticotropin-releasing hormone (CRH) Posterior nucleus o Somatostatin o Dopamine ○ Antidiuretic hormone (ADH) / Vasopressin ○ Oxytocin ***This is why your hypothalamus is located just above the pituitary gland*** Page 1 of 11 [NEUROSCIENCE 1A] 1.12 HYPOTHALAMUS – Dr. Vida Margaret Andal Conservation of body heat. Destruction causes hypothermia Lateral nucleus Stimulation induces eating. Destruction results in anorexia Stimulates sympathetic NS (Table 1. Hypothalamic nuclei, hormones secreted by the nuclei and functions to the body) C. HYPOTHALAMIC LINES OF COMMUNICATION - Nervous connections - Bloodstream - Cerebrospinal fluid 1. Afferent Nervous Connections Illustration 4. Medial Zone of the hypothalamus 2. Lateral zone Part of preoptic nucleus Part of suprachiasmatic nucleus Supraoptic nucleus Lateral nucleus Tuberomammillary nucleus Lateral tuberal nuclei (Table 2. Afferent Nervous Connections Pathway, Origin and Destination) 2. Efferent Nervous Connections (Table 3. Efferent Nervous Connections Pathway, Origin and Destination) D. CLINICAL APPLICATIONS (Illustration 5. Lateral Zone of the hypothalamus) Hormone Function Secreted Preoptic GnRH Regulation of sex hormones Stimulates parasympathetic NS Anterior Stimulates parasympathetic NS Dissipates body heat; destruction causes hyperthermia Suprachiasmatic Somatopressin Receives input from retina; control circadian rhythm (sleep- wake cycle) Supraoptic Vasopressin, Regulates water balance. oxytocin Destruction causes diabetes insipidus Paraventricular CRH, TRH, Projects to autonomic nuclei of oxytocin brainstem and spinal cord (Table 4. Hypothalamic Damage Classification and Lesions) Dorsomedial TRH Stimulation results in obesity and savage behavior Ventromedial TRH Satiety center; destruction results 1. Germinoma t obesity (hyperphagia)and savage Arise from germ cells behavior. Frequently occur during childhood and young adulthood Infundibular/arcuate Dopamine, Inhibits prolactin release Most commonly in pineal region and hypothalamic regions GHRH, GnRH Homogenous, well-marginated round sloid masses Posterior Stimulates sympathetic NS T1 hypointense, iso- to slightly hyperintense T2 Page 2 of 11 [NEUROSCIENCE 1A] 1.12 HYPOTHALAMUS – Dr. Vida Margaret Andal (Illustration 6. Simultaneous hypothalamic and pineal gland germinoma in an MRI scan) 2. Hypothalamic-Chiasmatic Glioma 10-15% of supratentorial tumors in children 20-50% of patients have a family history of von Recklinghausen disease (neurofibromatosis type 1) T1 hypointense, T2/FLAIR hyperintense (Illustration 9. Hemorrhagic pituitary adenoma in an MRI scan) Large tumors are typically heterogenous with cystic and solid components You can’t see the sella turcica anymore. It’s affecting not only the hypothalamus, even the thalamus and third ventricle is affected. Because it is very big, you could have a necrotic hemorrhagic center. II. PITUITARY GLAND - Also called hypophysis cerebri - Weighs only 500mg, measures 8mm in AP, 12mm in transverse. It is wider than it is longer. - Found below the optic chiasm and the hypothalamus - Receives hormones from the hypothalamus - Releases a different set of hormones to the rest of the body - Located within the sella turcica of the sphenoid (Illustration 7. Location of Hypothalamic-Chiasmatic Glioma in an MRI scan) 3. Encephalitis Inflammation of the brain parenchyma May be due to infectious or noninfectious causes Most common infectious cause is viral (Illustration 10. Location of Pituitary Gland in the Brain) Most common noninfectious cause is Langerhans cell histiocytosis and sarcoidosis Edema in the hypothalamus is hyperintense on T2/FLAIR, iso or hypo- intense on T1 (Illustration 11. Location of Sella Turcica in the Sphenoid Bone of the Cranium on (a.) superior view and (b.) coronal section) (Illustration 8. MRI View of Hypothalamic Encephalitis) 4. Lesions arising from surrounding structures 4a. Large pituitary adenomas Variable signal intensity depending on the necrotic, cystic or hemorrhagic components Page 3 of 11 [NEUROSCIENCE 1A] 1.12 HYPOTHALAMUS – Dr. Vida Margaret Andal 3. Hormone Producing Cells of the Anterior Pituitary Gland (Pars Distalis) Acidophils o Composed of polypeptide hormones o Cytoplasm stains red to orange in color o Somatotrophs, Lactotrophs Basophils ○ Composed of glycoprotein hormones ○ Cytoplasm stains blue to purple in color ○ Ex: Thyrotrophs, Gonadotrophs, Corticotrophs Chromophobes ○ Do not stain well ○ Represent stem cells that are yet to differentiate into mature (Illustration 12. Location of Sella Turcica in the Sphenoid Bone on the lateral view of the Cranium) hormone-producing cells A. Parts of the Pituitary Gland 1. Borders of the Pituitary Gland Acidophils Bounded laterally by the cavernous sinus (contains the internal carotid artery, sympathetic fibers, CN III-VI) Bounded superiorly by the optic chiasm, part of the third ventricle, Basophils hypothalamus Basically, a part of venous system. Within cavernous sinus, you have nerves and blood vessels. Internal carotid artery has a cavernous segment Chromophobe s (Illustration 15. Stained Slide of Hormone-Producing Cells in a Microscope) (Illustration 13. Bordering Organs of the Pituitary Gland on a Coronal View) 2. LOBES Anterior lobe (Adenohypophysis) o Pars tuberalis - The “Stalk”. Proximal part - Tubular stalk composed of unmyelinated axons. - Really just a pathway o Pars intermedia - Seen between pars distalis and the posterior lobe. - Made up of follicles containing a colloidal matrix - Includes remainder of Rathke’s pouch cleft - Mostly nonfunctioning but also produces melanocyte- stimulating hormones, endorphins and some pituitary stem cells o Pars distalis - Makes the bulk of anterior pituitary - Forms bulk of the anterior pituitary (Illustration 16. Production of Different Hormones in the Anterior Lobe of Pituitary Gland) - Where most pituitary hormones are secreted from - Composed of follicles of varying sizes that contain the hormone-producing cells. Posterior lobe (Neurohypophysis) (Illustration 14. Lobes of the Pituitary Gland and its Parts) Page 4 of 11 [NEUROSCIENCE 1A] 1.12 HYPOTHALAMUS – Dr. Vida Margaret Andal 2. Hypophyseal Portal System Long and short portal blood vessels that connect sinusoids in the median eminence and infundibulum with capillary plexuses in the anterior lobe of the hypophysis. From hypothalamus to the anterior lobe via blood vessels. (Illustration 16. Storage of Different Hormones in the Posterior Lobe of Pituitary Gland) (Flowchart 2. Process of Hypophyseal Tract) Only stores oxytocin and vasopressin Oxytocin and Vasopressin are actually hormones released by your hypothalamus. They will get stored in posterior lobe, then eventually released to reach different parts of the body where they will exert its effect. Vasopressin will travel to reach your kidneys and actually to your blood vessels Oxytocin will travel to reach your mammary glands and uterus. Oxytocin and vasopressin are not produced by pituitary gland but just stored in the posterior lobe. B. HYPOTHALAMUS AND PITUITARY GLAND A. PATHWAY CONNECTIONS 1. Hypothalamohypophyseal Tract Hypophysis = pituitary gland Nerve fibers that travel from the supraoptic and paraventricular nuclei to the posterior pituitary. Because they will store the (Illustration 18. Location of Hypophyseal Tract Between the Hypothalamus and Pituitary Gland) oxytocin and vasopressin here. Direct travel from hypothalamus to the posterior lobe. HYPOPHYSEAL PORTAL SYSTEM –BLOOD o This is another diagram showing you the direct connections of the hypothalamus to your posterior lobe and the vessels that will be used in the portal system to reach the anterior lobe. o Seen here are the acidophils, basophils, and chromophobes which produces hormones (Flowchart 1. Process of Hypothalamo-hypophyseal Tract) (Illustration 19. Blood Supply of the Pituitary Gland provided by the hypophyseal portal system) o This is the internal carotid artery showing you that this is where the (Illustration 17. Location of Hypothalamo-hypophyseal Tract Between the Hypothalamus and superior hypophyseal artery branches out, as well for inferior Pituitary Gland) hypophyseal artery. Page 5 of 11 [NEUROSCIENCE 1A] 1.12 HYPOTHALAMUS – Dr. Vida Margaret Andal C. HORMONES INVOLVED 1. Hormones produced by the anterior lobe of pituitary gland (Illustration 20. Internal Carotid Artery and Its Parts) A3. Hypothalamic-Pituitary Feedback (Illustration 21. Production of Different Hormones in the Anterior Lobe of Pituitary Gland) a. Adrenocorticotropic Hormone (ACTH) Released in response to corticotropin releasing hormone (CRH) produced by the hypothalamus during stress The CRH will then signal the pituitary to produce ACTH. ACTH will travel to the bloodstream to reach its target organ which is the ADRENAL GLANDS. Target organ: adrenal glands (part of endocrine system) Final product: glucocorticoids (or steroid hormones which will travel to different areas of the body in order to perform different functions) (Flowchart 3. Hypothalamic-Pituitary Feedback) The hypothalamic-pituitary feedback is a mechanism that your body uses to signal one or the other, either the hypothalamus or the pituitary gland, to GO or to STOP producing different hormones. Blue pathway indicates GO; Red pathway indicates STOP. For example, you need something to be done in your body (e.g., lactating mother). Your supraoptic nucleus will want to release oxytocin in order for you to express breastmilk. It will be released to the pituitary gland, it will get stored, it will travel to the bloodstream to reach your target organ (mammillary tissue). If you are producing enough oxytocin already, the mammillary tissue will send signals to inhibit the pituitary gland from releasing more oxytocin. At the same time, it will also release inhibiting factors which will inhibit the supraoptic nuclei of the hypothalamus. If the purpose has already been served, there will be a NEGATIVE FEEDBACK that will go either to the pituitary gland, to the hypothalamus, or both so (Illustration 22. Disturbance of stress on ACTH production) that you don’t keep on producing hormones which are not necessary anymore. b. Thyroid Stimulating Hormone (TSH) Hypothalamus will produce TRH which will reach the anterior pituitary, which will release TSH to reach the thyroid gland, which in turn will produce T3 and T4 hormones that will travel to different organs in the body so that you can maintain homeostasis. Released in response to thyrotropin-releasing hormone (TRH) Target organ: thyroid gland Final product: T3, T4 (growth and development, increased catecholamine response Negative feedback: T3, T4, dopamine, somatostatin, glucocorticoids (too much T3 and T4 will inhibit the hypothalamus to produce TRH Page 6 of 11 [NEUROSCIENCE 1A] 1.12 HYPOTHALAMUS – Dr. Vida Margaret Andal (Flowchart 5. Negative Feedback) c. Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) (Illustration 23. Release, Inhibitions and Sites of GH) Hypothalamus will release GnRH (gonadotropin releasing hormones), it will eventually reach the pituitary which will then release two kinds e. Prolactin (PRL) of hormones, LH and FSH. Released (by the anterior pituitary) in response to prolactin-releasing Released in response to gonadotropin releasing hormone (GnRH) hormone (PRH) (once it reaches the hypothalamus) Target organ (males): PRH is released by the sucking of the breast and mother’s sight of the o LH: Leydig cells of the testes → testosterone baby o FSH: Sertoli cells of the testes → spermatogenesis Target organ: mammary ducts Target organ (females): Negative feedback from Dopamine o LH: ovaries →estrogen, progesterone Prolactin will stimulate MILK PRODUCTION while oxytocin will stimulate o FSH: granulosa cells of the ovaries → follicular development for the LET-DOWN of the milk ovulation by the mature Graafian follicle (Illustration 23. Glands produced going to the hypothalamus) d. Growth hormone (GH) (Flowchart 6. Stimulation and Production of Breastmilk) Released in response to growth hormone-releasing hormone (GHRH) (from the hypothalamus) GHRH will travel to the anterior hypothalamus inducing it to produce growth hormones (GH) that will travel through the bloodstream. Target organ: adipose cells, muscle, liver (have certain functions, all of which is to trigger mechanisms to promote cell growth in the body. Negative feedback from GH and IGF-1 (from liver) Page 7 of 11 [NEUROSCIENCE 1A] 1.12 HYPOTHALAMUS – Dr. Vida Margaret Andal D. CLINICAL APPLICATION 2. Hormones stored in the posterior lobe of the pituitary gland a. Oxytocin 1. Pituitary Adenoma Direct product of the hypothalamus that is stored in the pituitary and travels Most common mass lesion in the sella and parasellar region to the uterus to promote uterine contraction, which is why breastfeeding If >1cm, macroadenoma. If 50%) with CSF with no visualized pituitary gland. Primary ESS: idiopathic cause. Associated with obesity and hypertension. Usually asymptomatic. (Illustration 33. MRI view brain with Craniopharyngioma) (Illustration 31. Comparison of Normal, Partial Empty and Complete Empty Sella) Secondary ESS: treated pituitary tumor, head trauma, idiopathic intracranial hypertension (pseudotumor cerebri), radiation. Symptoms reflect loss of pituitary hormones. Page 10 of 11 [NEUROSCIENCE 1A] 1.12 HYPOTHALAMUS – Dr. Vida Margaret Andal Practice Questions: (e) The neuroglial cells of the hypothalamus are responsible for the production of the release inhibiting hormones. 1. The following statements concern the hypothalamus: (a) It lies below the thalamus in the tectum of the midbrain. (b) It is not related to the limbic system. (c) The nuclei of the hypothalamus are divided by an imaginary plane formed by the columns of the fornix and the mammillothalamic tract into medial and lateral groups. (d) The suprachiasmatic nucleus does not receive nerve fibers from the retina. (e) The lateral boundary of the hypothalamus is formed by the external capsule. 2. The following statements concern the hypothalamus: (a) When seen from the inferior aspect, the hypothalamus is related to the following structures, from anterior to posterior: (i) the olfactory stria, (ii) the anterior perforated substance, and (iii) the mammillary bodies. (b) The margins of the different nuclei can be clearly seen with the naked eye. (c) The mammillary body does not overlap the medial and lateral groups of hypothalamic nuclei. (d) The preoptic area of the hypothalamus is located between the septum pellucidum and the optic chiasma. (e) The blood-brain barrier is absent in the median eminence of the hypothalamus, thus permitting the neurons to sample the chemical content of the plasma directly. 3. The following statements concern the afferent fibers passing to the hypothalamus: (a) Fibers pass from the hippocampus to the mammillary bodies, bringing information from the auditory system. (b) Olfactory impulses reach the hypothalamus through the lateral forebrain bundle. (c) The hypothalamus receives many afferent fibers from the viscera via the reticular formation. (d) The dorsomedial nucleus receives axons from the posterior lobe of the pituitary. (e) The pineal gland sends fibers via the habenular commissure to the hypothalamus. 4. The following statements concern the hypothalamus: (a) Somatic efferent fibers leave the hypothalamic nuclei via the medial and spinal lemnisci. (b) It does not integrate the autonomic and neuroendocrine systems. (c) The posterior portion of the hypothalamus controls those mechanisms that dissipate heat loss. (d) The nerve cells of the hypothalamus produce releasing and release-inhibiting hormones that control the production of various hormones in the anterior lobe of the hypophysis. (e) The hunger center is probably located in the posterior hypothalamic nuclei. 5. The following statements concern the functional activities of the hypothalamus: (a) The hypothalamus brings about the physical changes associated with emotion, such as increased heart rate and flushing or pallor of the skin. (b) The medial hypothalamic nuclei are concerned with fluid intake. (c) The corticotropin-releasing hormone (CRH) is produced in the anterior nucleus of the hypothalamus. (d) The suprachiasmatic nucleus plays no part in controlling circadian rhythms. (e) The hypothalamus controls the lower autonomic centers by means of pathways through the tectospinal tract. 6. The following statements concern the hypothalamohypophyseal tract: (a) Oxytocin inhibits the contraction of the smooth muscle of the uterus. (b) The nerve cells of the supraoptic and paraventricular nuclei produce the hormones vasopressin and oxytocin. (c) The hormones travel in lymph vessels with protein carriers called neurophysins. (d) Vasopressin stimulates the proximal convoluted tubules of the kidney, causing increased absorption of water from the urine. (e) The hormones are absorbed into the bloodstream in the capillaries of the anterior lobe of the hypophysis. 7. The following statements concern the hypophyseal portal system: (a) It carries releasing hormones and release-inhibiting hormones to the secretory cells of the anterior lobe of the hypophysis. (b) The production of the releasing hormones and the release-inhibiting hormones cannot be influenced by the level of the hormone produced by the target organ controlled by the hypophysis. (c) The blood vessels commence superiorly in the median eminence and end inferiorly in the vascular sinusoids of the posterior lobe of the hypophysis cerebri. (d) Efferent nerve fibers leaving the hypothalamus influence the production of the releasing hormones by nerve cells. Page 11 of 11