L2 Endocrine III PDF

Endocrine III Sharon Adekanbi, MS January 22nd, 2025 Netter’s Essential Histology, 3rd Edition Ch. 10 pp. 232-244, 260 2 2  Learning objectives 1. Describe...

Endocrine III Sharon Adekanbi, MS January 22nd, 2025 Netter’s Essential Histology, 3rd Edition Ch. 10 pp. 232-244, 260 2 2  Learning objectives 1. Describe the histological regions and hormones produced by the anterior pituitary. 2. Identify the cell types and regions of the pituitary gland in a micrograph. 3. Describe the histologic features of the posterior pituitary and their functions. 4. Trace the hypothalamic-hypophyseal portal system and its function. 5. Describe the major functions, histology, and hormone produced by the pineal gland. 3 3 Overview of the Endocrine System 4 4  Endocrine Glands § Ductless structures made of secretory cells arranged in cords, clumps, or follicles. § Located near a rich vascular network (capillaries or sinusoids) for efficient hormone release into the bloodstream. § Hormones are chemical messengers that regulate physiological processes by binding to specific receptors on target cells or tissues. 5  Hypothalamus § The hypothalamus, located beneath the thalamus on either side of the third ventricle. § Maintains homeostasis via: § Produces releasing and inhibiting hormones § Autonomics: parasympathetic and sympathetic nervous system. 6  Relationship of Hypothalamus to the Pituitary Gland 7 Hypothalamus: Acts as the control center, producing hormones that regulate the pituitary. Pituitary Gland: Known as the "master gland," it releases hormones that regulate other glands and body functions. 7 Neuroendocrine Control of Organs and Systems Hypothalamic-Pituitary Axis § Hypothalamus controls the pituitary’s secretory activities § Pituitary (hypophysis) is considered the “master gland” due to its control and regulation of other endocrine glands. § It connects the endocrine and nervous systems. 8 Hypothalamic-Pituitary-X Axis Negative feedback inhibition Target gland (x) = adrenal, thyroid, ovary/testes, etc. 9 9 Pituitary Gland= Hypophysis § Bi-lobed gland suspended from the base of the hypothalamus by the infundibulum (stalk). § Rests within the sella turcica of the sphenoid bone Has two lobes § Anterior lobe = adenohypophysis Pars tuberalis Pars intermedia Pars distalis § Posterior lobe = neurohypophysis Infundibular stalk Pars nervosa 10  Divisions of the Pituitary Gland (Hypophysis) Anterior Pituitary=Adenohypophysis Posterior Pituitary= Neurohypophysis Pars tuberalis (wraps around the Infundibular stalk (stem that connects pars infundibulum) nervosa to the diencephalon) Pars intermedia (thin section between pars Pars nervosa (largest section) distalis and the neurohypophysis) Pars distalis (largest section) 11  Hypothalamic-hypophyseal Tract The hypothalamic-hypophyseal tract consists of: Axon bundles from the hypothalamic supraoptic and paraventricular nuclei extending into the neurohypophysis (posterior pituitary). These nuclei produce ADH & oxytocin. Function: Transport the oxytocin and ADH to the neurohypophysis, where they are stored and released into the capillaries. Image source: https://radiopaedia.org/cases/54348/studies/60567?lang=us 12  Hypothalamic-hypophyseal Portal System The hypothalamic-hypophyseal portal system consists of: The primary capillary plexus, which comes from the superior hypophyseal artery (a branch of the internal carotid artery). Blood from the primary plexus flows to form a secondary capillary plexus which connects to the hypophyseal portal veins. Function: Transport regulatory hormones from the hypothalamus to control hormone release from the anterior pituitary. *Superior hypophyseal arteries supply the anterior pituitary. *Inferior hypophyseal arteries supply posterior pituitary. Image source: https://radiopaedia.org/cases/54348/studies/60567?lang=us 13  Anterior and Posterior Pituitary posterior lobe anterior lobe 14 14 Anterior Pituitary: Pars Distalis § Main components are cords of secretory epithelial cells interspersed with fenestrated capillaries and fibroblasts. § Secretory cells are categorized as § Chromophobes: Poorly staining clear or white cells § Chromophils (acidophils/basophils): stain intensely due to abundant cytoplasmic storage granules. 15  Anterior Pituitary Pars Distalis Chromophils: Acidophils and Basophils Cords of secretory cells and capillaries 16  Anterior Pituitary Pars Distalis Chromophils: Acidophils and Basophils Acidophils Basophils § Stain positively with eosin § Main Stain with hematoxylin or other basic dyes § Smaller cells with larger and numerous granules § Larger cells with few granules § More abundant in the periphery of the gland § More abundant in the core of the gland § Secrete protein hormones: § Secrete glycoprotein hormones: § Somatotrophs à growth hormone (GH) § Gonadotrophs à FSH + LH § Lactotrophs à prolactin § Corticotrophs à ACTH § Thyrotrophs à TSH Mnemonic: Mnemonic: § GPA = growth hormone, prolactin, acidophils § B-FLAT = basophils, FSH, LH, ACTH, TSH 17  Anterior Pituitary Pars Distalis Chromophobes Basophils Acidophils Chromophobes § Stain positively with eosin § Stain weakly with few or no secretory granules Chromophobes 18 Immunostaining of Cell Types in Pars Distalis Immunostaining is the only way to tell the secretory cells apart. 19 19 Hormones of Anterior Pituitary: Pars Distalis 20 Anterior Pituitary: Pars Tubularis § Continuous with the pars distalis but contains mostly basophilic gonadotrophs (secrete FSH and LH) § Contains many of the capillaries of the primary capillary plexus. 21 Anterior Pituitary: Pars Intermedia § Between pars distalis (PD) of anterior pituitary and pars nervosa (PN) of posterior pituitary. § Contains § basophilic cells, which secrete melanocyte- stimulating hormone (MSH) § colloid-filled cysts (C) of various sizes called Rathke’s cysts (colloid-containing cavities lined with cuboidal epithelium- remnant of Rathke’s pouch). 22  Anterior Pituitary: Pars Intermedia *Rathke’s cyst Basophilic melanotrophs *Rathke’s cyst Basophilic melanotrophs 23 23  Neurohypophysis (Posterior Pituitary) § Pars nervosa + infundibular stalk § It stains poorly and consists of nervous tissue § It does not contain the secretory cells that synthesize its two hormones § Main components: § Many unmyelinated axons with cell bodies in the hypothalamus. § Herring bodies: bulges in the terminal end of the axons from the hypothalamus (cell bodies of the neurons are in the hypothalamus) § Fenestrated capillary plexus § Pituicytes: glial cells that surround and support the unmyelinated axons What are we looking for histologically? § Dark nuclei of pituicytes § Many capillaries § Unmyelinated axons § Herring bodies 24 Pars Nervosa: Herring bodies § Herring or neurosecretory bodies: dilated areas or bulges in the axon terminals of supraoptic and paraventricular hypothalamic neurons. § They temporarily store the neurohypophseal hormones- oxytocin and antidiuretic hormone. § Always in close proximity to capillaries 25 Posterior Pituitary: Pars Nervosa Pituicytes HB=Herring body, arrowhead = capillary wall arrow = pituicytes 26 26  Posterior Pituitary: Pars Nervosa HB (NB) =Herring body Cap (C) = capillary Arrow (P) = pituicytes HT = hypothalamic-hypophyseal tract (unmyelinated axons) 27 27 Hormones of Posterior Pituitary: Pars Nervosa 28  Match A. Rathke’s cysts B. Herring bodies C. Pars intermedia D. Pars nervosa E. ADH F. ACTH G. Oxytocin H. Melanin 29  Match- Answers Pars intermedia, MSH Pars nervosa, oxytocin & ADH 30  Pineal Gland § Also called the pineal body or epiphysis cerebri § It is attached by a stalk to the posterior wall of the third ventricle. § Controlled by cervical sympathetic nerves from the hypothalamus diencephalon § There are two types of cells present within the gland: § Pinealocytes – hormone (melatonin) secreting cells. § Glial cells – supporting cells. Function § The gland receives light-generated information from the eyes and integrates this information to regulate circadian rhythms of bodily activities. 31  Pineal Gland § Pineal gland tissue has variously sized concretions called brain sand (corpora arenacea) § increase in size, abundance, and calcification with age. § Radiopacity of the pineal body, along with its central location, provides a useful landmark for radiologists Calcified pineal gland produces a radiopaque area Image Source: https://radiopaedia.org/cases/pineal-gland-calcification 32  Pineal Gland § Pinealocytes § Large irregular euchromatic nuclei with S prominent nucleoli and pale basophilic Pinealocytes (P) cytoplasm. § pale cytoplasm § irregular nuclei § Their long cytoplasmic processes terminate in swellings near blood vessels in the septa. Pia mater forms septa (S). § Secrete melatonin (regulate circadian rhythms and antigonadotropic effects). § Astroglial cells (astrocytes) Astroglial cells (A) § Heterochromatic & § Glia-like interstitial cells elongated nuclei § Elongated nuclei § Corpora arenacea (brain sand) Corpus arenaceum (CA) Brain sand 33 33 Pineal Gland capillary Pineal body covered by pia mater, which sends septa (S) of connective tissue into the gland Corpus arenaceum (brain sand) 34 34 Pineal Gland Stimulation and Melatonin Release 35 35  A 32-year-old male presents with fatigue, cold intolerance, and decreased libido. Laboratory tests show low serum cortisol, thyroid hormone, and testosterone. MRI of the brain reveals a mass compressing the pituitary stalk. Disruption of which of the following structures is most likely responsible for this patient’s hormonal abnormalities? A. Superior hypophyseal artery B. Inferior hypophyseal artery C. Hypothalamic-hypophyseal system D. Hypothalamic-hypophyseal tract E. Neurohypophysis F. Thalamus C. The hypophyseal portal system carries releasing and inhibiting hormones (e.g., thyrotropin-releasing hormone (TRH) and gonadotropin-releasing hormone (GnRH)) from the hypothalamus to the anterior pituitary (adenohypophysis). TRH stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH), which promotes thyroid hormone production. GnRH stimulates the release of luteinizing hormone (LH) and follicle- stimulating hormone (FSH), which regulate testosterone production in the testes. Disruption of this system prevents proper stimulation of the anterior pituitary, leading to decreased secretion of hormones such as ACTH, TSH, LH, and FSH. 36  This micrograph is likely from what structure? A. Pars distalis B. Pars tubularis C. Pars intermedia D. Pars nervosa E. Pineal gland E. §This is from the pineal gland. It has the following features §Pinealocytes §Large irregular euchromatic nuclei with prominent nucleoli and pale basophilic cytoplasm §Their long cytoplasmic processes terminate in swellings near blood vessels in the septa 37 §Septa formed form pia mater coverings §Astrocytes with elongated nuclei 37  Questions? Email me: [email protected] 38