Hypothalamus Anatomy

Hypothalamus

• Comes from the latin words meaning below the thalamus (room or chamber)
• It's a diffuse nuclear mass below the thalamus
• Small cone-shaped structure, projecting downward, ending in the pituitary stalk
• Lies directly above the pituitary gland

Gross Anatomy

• Occupies approximately 2% of the brain volume
• Sits below the hypothalamic sulcus within the medial wall of the third ventricle, separating it from the thalamus above
• Composed of several groups of nuclei that contain neurons that respond to neural input from widespread regions of the nervous system or non-neural stimuli such as changes in temperature and blood hormone levels
• Extends from the Lamina terminalis anteriorly to the tegmentum of the midbrain posteriorly
• Superior border marked by the hypothalamic sulcus, a shallow groove separating it from the thalamus
• Inferior surface bears the optic chiasm anteriorly, the tuber cinereum centrally, and the mammillary bodies posteriorly
• Medial border formed by the inferior aspect of the third ventricle
• Lateral border formed by the substantia innominata rostrally and the posterior limb of the internal capsule caudally

Divisions & Nuclei

• Divided in the coronal plane from medial to lateral into the periventricular, intermediate (medial), and lateral zones
• The periventricular zone is thin and lies next to the midline, containing mainly the periventricular nucleus
• Some classify the suprachiasmatic and arcuate nuclei as part of this zone, but they are part of the medial zone
• Majority of neurons in this area synthesize releasing hormones that modulate the release of several anterior pituitary hormones

Intermediate (Medial) Zone

• Contains several individual nuclei and is subdivided into four regions from anterior to posterior: preoptic, supraoptic (chiasmatic), tuberal, and mammillary

Supraoptic (Chiasmatic) Region

• Lies internal to the region of the optic chiasm
• It contains four nuclei: the supraoptic, paraventricular, suprachiasmatic, and anterior hypothalamic nuclei
• Supraoptic and paraventricular nuclei contain neurons that synthesize oxytocin and antidiuretic hormone (ADH, vasopressin)
• Hormones transmitted via the supraopticohypophysial tract to the posterior pituitary and released into circulation to control water balance
• Involved in regulation of circadian rhythms through its connections with the retina, pineal gland, and other hypothalamic nuclei
• Anterior hypothalamic nucleus primary role is in the maintenance of body temperature

Tuberal Region

• Lies internal to the tuber cinereum and has the ventromedial, dorsomedial, and arcuate nuclei
• Ventromedial nucleus is one of the largest nuclei of the hypothalamus and is mainly involved in feeding behavior, said to be a "satiety center"
• Dorsomedial nucleus integrates feeding behavior with circadian activity has been implicated in aggressive emotional behavior
• Arcuate nucleus contains neurons that produce releasing hormones, transmitted to the anterior pituitary via the tuberoinfundibular tract and hypophyseal portal system
• Role in the regulation of appetite, cardiovascular system, sexual behavior, prolactin release, and the monitoring of adipose tissue fat

Mammillary Region

• Most posterior of the four medial zone regions
• Lies internal to the mammillary bodies and contains the medial, intermediate, and lateral mammillary nuclei, which collectively form the mammillary complex, the tuberomammillary nucleus, and the posterior hypothalamic nucleus
• Large medial mammillary nucleus is the main point of termination for axons of the post-commissural fornix, which arise from the hippocampal complex and relay input related to emotions
• The Tuberomammillary nucleus is involved in the promotion of wakefulness
• Posterior hypothalamic nucleus plays a similar role to the midbrain periaqueductal gray in the modulation of emotion, cardiovascular function and pain modulation/regulating body temperature

Lateral Zone

• Contains the lateral preoptic nucleus and lateral hypothalamic area.
• Lateral preoptic nucleus said to play a role in promoting sleep via connections with the reticular activating system and the orexin neuronal system
• Diffuse group of neurons forming the lateral hypothalamic area
• Smaller condensations of neuronal cells within the anterior aspect which form the lateral hypothalamic nucleus and the lateral tuberal nuclei
• Neurons of the tuberal nuclei project to the tuberoinfundibular tract, and are thus involved in the transmission of releasing hormones to the hypophyseal portal system
• Plays a role in the regulation of motor activity through connections with the cerebellum

Connections

• Extensive afferent and efferent connections to areas of the nervous system and the rest of the body through neural connections, direct neuron connections, and via the bloodstream, hormones
• Receives neural input from several structures including the limbic system, sensory and motor nuclei of the brainstem, and spinal cord
• Contains neurons with specific receptors that sense and receive non-neural input like changes in temperature, osmotic pressure, and hormone levels of circulating blood
• Sends neural and non-neural outputs through its influence on other endocrine glands and the autonomic nervous system

Afferent Hypothalamic Pathways

• Neural inputs mainly from various structures of the limbic system, as well as the brainstem and spinal cord
• Information relating to the function of the hypothalamus in modulating autonomic and somatic aspects of emotional states, as well as conveying ascending visceral, gustatory, and somatic sensory information, mostly reciprocal connections
• Arise from various sites including the orbitofrontal cortex, infralimbic and cingulate cortex, septal nuclei, thalamus, hippocampus, amygdala, brainstem tegmentum, and spinal cord

Principal Afferent Tracts

• Tracts include the fornix, medial forebrain bundle, stria terminalis, ventral amygdalofugal tracts, ventral amygdalofungal tracts
• Mammillary peduncle relays sensory input from sensory pathways
• Corticohypothalamic fiber, the only direct neocortical connection to the hypothalamus, terminates in the lateral hypothalamic area, from the prefrontal cortex
• Retinohypothalamic fibers end in the suprachiasmatic nucleus and plays a role in the control of circadian rhythms
• Spinohypothalamic fibers relay nociceptive information to the autonomic control centers of the hypothalamus and involved in neuroendocrine and cardiovascular responses to painful stimuli

Efferent Hypothalamic Pathways

• Efferent fibers from its subdivisions to various areas throughout the entire nervous system
• Majority are reciprocal inputs to structures that project afferent fibers
• Sends outputs to the limbic system, autonomic and somatic motor neurons, and the pituitary gland via neural and neurovascular connections
• Outputs are largely transmitted by way of the same fiber bundles that convey inputs
• Hypothalamic efferent fibers grouped into ascending and descending projections that terminate in forebrain structures

Ascending Projections

• Consists of the mammillary fasciculus (mammillothalamic tract), hypothalamothalamic fibers, hypothalamoamygdaloid fibers, and cerebellohypothalamic fibers
• Descending projections project to brainstem and spinal cord targets
• Consists of the hypothalamospinal tract, hypothalamomedullary fibers, posterior (dorsal) longitudinal fasciculus, mammillotegmental tract, and hypothalamocerebellar fibers

Connections to the Pituitary Gland

• Controls both lobes of the pituitary gland via a vascular link with the anterior pituitary and a neural projection to the posterior pituitary Two main efferent tracts:
• Hypothalamohypophyseal tract
• Tuberohypophyseal (tuberoinfundibular) tract

Hypothalamohypophyseal Tract

• Short tract composed of axons from magnocellular (large) neurons in the supraoptic and paraventricular nuclei of the hypothalamus
• Carries antidiuretic hormone (ADH) and oxytocin hormones to the posterior pituitary

Tuberohypophyseal Tract

• Collection of axons from parvocellular (small) neurons in the arcuate and periventricular nuclei
• Projects to the infundibular capillary bed, conveying hypothalamic releasing and inhibiting hormones via the hypophyseal portal vessels:

Releasing & Inhibiting Hormones

• Thyrotropin-releasing hormone (TSH) controls the growth and function of the thyroid gland, stimulates the pituitary gland to release thyroid-stimulating hormone (TSH)
• Corticotropin-releasing hormone (CRH) stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH), stimulating synthesis and secretion of adrenocortical hormones (cortisol, androgens, and aldosterone)
• Gonadotropin-releasing hormone (GnRH) controls reproduction, stimulates the pituitary gland to release gonadotropic hormones: Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)
• Prolactin-releasing hormone (PRH) stimulates the pituitary gland to release prolactin, promoting development of the female breasts and secretion of milk (inhibited by dopamine/prolactin-inhibiting factor)
• Growth hormone-releasing hormone (GHRH) stimulates the pituitary gland to release growth hormone (GH, activating protein synthesis & overall growth of most cells and tissues
• Growth hormone-inhibiting hormone (GHIH, also known as Growth hormone-inhibiting factor, or somatostatin) inhibits the release of growth hormone

Blood Supply

• Hypothalamus receives blood supply from small perforating arteries from the circle of Willis
• Anteromedial group of perforating arteries formed from small branches of the anterior cerebral arteries/anterior communicating arteries, supplying nuclei of the preoptic/supraoptic regions and rostral portions of the lateral hypothalamic area
• Posteromedial group of perforating arteries formed from small perforating arteries from the posterior communicating arteries/proximal segment of the posterior cerebral arteries, supplying nuclei of the tuberal/mammillary regions, giving off branches to the middle and caudal parts of the lateral hypothalamic area

Lenticulostriate Branches

• Supply the nuclei of the tuberal and mammillary regions of the hypothalamus and giving off branches to the middle and caudal parts of the lateral hypothalamic area
• Gives off branches to the middle and caudal parts of the lateral hypothalamic area (from the proximal region of the middle cerebral arteries/anterior choroidal branches)
• Main arterial supply to the lateral hypothalamus
• Internal carotid artery gives rise to the hypophyseal arteries (inferior and superior branches) that provide blood supply to the pituitary gland, contributing to the formation of the primary and secondary capillary plexuses of the hypophyseal portal system (responsible for distributing secreted pituitary hormones into general circulation)

Functions

• Modulates the release of pituitary hormones via 2 groups of neurons: parvocellular neurons and magnocellular neurons
• Plays into the pituitary glands control of food intake/fluid intake and the autonomic nervous system
• Role in Stress and emotional expression and aggression as well as impacts to the sleep and waking and in the sexual arousal of the body
• Influence in memory via the pituitary gland and as a thermostat regulating Body temperature

Pineal Gland

• Also called the "epiphysis"
• Neuroendocrine gland that secretes the hormone melatonin and other polypeptide hormones with a regulatory function on other endocrine glands

Functions

• Maintains the body's circadian rhythm and regulates sleep-wake cycle
• Modulates the onset of puberty and the development of the reproductive system

Location & Structure

• Small cone-like structure that comprises a part of the diencephalon
• Develops as an outward projection from the posterior wall of the third ventricle, above the quadrigeminal plate, below the splenium of corpus callosum
• Attached to the rest of the brain by the pineal stalk that divides into inferior and superior laminae

Parenchyma

• Mostly cords and clusters of pinealocytes, highly modified neurons that secrete melatonin into the surrounding network of fenestrated capillaries
• Also contains supporting astrocyte-like neuroglial cells
• Deposits of calcium, phosphates, and carbonates forming multilaminar corpuscles that accumulate with age
• Note*: called brain sand that are used as landmarks during radiologic examinations/microscopic identification

Blood Supply

• Blood supply derived from the posterior cerebral artery from its choroidal branches
• Internal cerebral veins drain the blood, which join to form the great cerebral vein of Galen

Hormones & Functions

• Secretory circumventricular organ, with direct bloodstream access via fenestrated capillaries
• Function to gather day-night cycle information and regulate melatonin production

Melatonin

• Derived is secreted rhythmically by pinealocytes.
• Regulates modulates sleep-wake.

Adrenal Gland

• Also known as the suprarenal gland
• Asymmetrical located suprarenally and bilaterally in the retroabdominal cavity
• Secretion to stimulate necessary stress mitigation

Structure

• Consists of two homeostatically significant layers surrounded by added protecting fatty capsule

Adrenal Cortex Subdivisions

• Zone glomerulosa regulates water regulation
• Zone fasciculata secretion, increase blood glucose
• Zona reticularis produces androge precursors

Medulla

• Resides chromaffin cell, regulate catecholamine production

Function Regulators

• Both stimulation regulation by hormonal regulation to influence bodily aspects

Innervations

• Cortex is activated via ACTH and pituitary gland
• Postsympthatic Fibers form form T5-T8 to spinal nerves

Lymphatic Drainage

• Achieved vis Para-aortic nodes

Clinical Manifestations

• Pathology from Cushing syndrome and Pituitary Adremomas
• Pheochromoctia impacts suprarenal

Pituitary Gland

• Master gland of the endocrine system
• Ovoid structured located in brain. Linked to hypothalmmus

Connections

• Connects by tuber cinereum section. Hypothyseal portal system

Pituitary Structure

• 3 parts. Anterior Posterior and intermediate to regulate hormone activity through vasuclar

Blood Supply

• Sphenodial arter

Thymus

• Location
  • lies in the superior and anterior mediastinum, close to the pericardium and deep in the sternum
• Primary lymphoid organ located in the mediastinum consists of 2 lobes connected by an isthmus
• Histologically divided into lobules, each one consisting of a lobules, each one consisting of
• Note*: Central Medulla and Peripheral Cortex

Blood Supply

• Derives from artery and numerous vessels and vein supply

Lymphatics

• No afferent to help filter lymph
• Node to release mature t cells in peripheral

Thymus Structure

• Covers tissues connected to capsule.

Innervation and Structure

• Minimal nerve signals from nerves to regulate primarily
• • Vagul/sympathetic nerves from nervous system

Function/Histology

• Is site for stem cell maturation for T lymphocutes
• The Epithelial cells regulate blood flow and development

Thymus Origins

• Originated in the 6th week by development stemming in part from embryonic activity

Pancreas Information

• Part of digestive and endocrine system
• Has hormone production and regulation
• Part of five areas of organ with internal duct networks
• Not covered by perotineum

Parts

• Unicinate process, head, neck, body and tail