Histo 21: Histology of the Endocrine System I

The hormones oxytocin and vasopressin are synthesized in the pars nervosa. Hypothalamic releasing or inhibitory hormones are synthesized in the hypothalamus. A. Both statements are TRUE B. Both statements are FALSE C. The first statement is TRUE, the second is FALSE D. The first statement is FALSE, the second is TRUE

A. Both statements are TRUE B. Both statements are FALSE C. The first statement is TRUE, the second is FALSE D. The first statement is FALSE, the second is TRUE Yes a) Synthesized in the hypothalamus

Oxytocin stimulates smooth muscle contraction. Vasopressin stimulates a decrease in water retention. A. Both statements are TRUE B. Both statements are FALSE C. The first statement is TRUE, the second is FALSE D. The first statement is FALSE, the second is TRUE

A. Both statements are TRUE B. Both statements are FALSE C. The first statement is TRUE, the second is FALSE yes D. The first statement is FALSE, the second is TRUE vasopressin = increases Na retention > which causes water retention

Which of the following statements is true? A. The acidophils consist of two cell groups: the somatotropes and mammotropes. B. The acidophils consist of three cell groups: the somatotropes, mammotropes and gonadotropes. C. The basophil cells are located in the pars nervosa. D. Somatotropes secrete prolactin. E. None of the above is true

A. The acidophils consist of two cell groups: the somatotropes and mammotropes. Yes B. The acidophils consist of three cell groups: the somatotropes, mammotropes and gonadotropes. C. The basophil cells are located in the pars nervosa > only located in pars intermedias & tuberalis D. Somatotropes secrete prolactin. > No. secretes GH E. None of the above is true

Neurohypophyseal Hormones Oxytocin •Synthesized in Paraventricular nucleus •Stimulates smooth muscle contraction: uterus during childbirth & milk expression Antidiuretic hormone (ADH/vasopressin) •Synthesized in Supraoptic nucleus •Regulates water homeostasis •Increases water retention: acts on kidney Hormone release : •Results from action potential in hypothalamic neuron •Causes "neurotransmitter" release

ADH is the main hormone involved in regulation of water homeostasis and osmolarity of body fluids. ADH facilitates resorption of water from the distal tubules and collecting ducts of the kidney by altering the permeability of the cells to water. Plasma osmolarity and blood volume are monitored by special receptors of the cardiovascular system (eg the carotid bodies). An increase in concentration of the blood, or a decrease in blood volume stimulates ADH release. Pain, trauma, emotional stress, and drugs such as nicotine also stimulate release of ADH.

Gonadotropes - basophils Secrete Luteinizing Hormone (LH)/ Interstitial-cell stimulating Hormone -Females: triggers ovulation & corpus luteum development -Males: stimulates Leydig cell's testosterone production Secrete Follicle Stimulating Hormone (FSH): -Females: stimulates growth of ovarian follicles -Males: stimulates spermatogenesis •Same cell secretes both hormones having similar structure

Gonadotropes (FSH and LH cells) : many gonadotropes are capable of secreting both FSH and LH. In females, an acute rise of LH called the LH surge triggers ovulation and development of the corpus luteum. In males, it stimulates Leydig cell production of testosterone. FSH stimulates the growth and recruitment of immature ovarian follicles in the ovary. FSH stimulates primary spermatocytes to undergo the first division of meiosis, to form secondary spermatocytes.

A. Herring body yes B. Pituicyte (dark purple) C. Acidophil D. Capillary E. Gonadotrope

In this section of the pituitary gland, identify the structure indicated by the arrow: A. Herring body B. Pituicyte C. Acidophil D. Capillary E. Gonadotrope

Somatotropes: acidophils Growth Hormone (somatotropin) •Stimulates epiphyseal plate •Abnormal secretion, -Gigantism -Dwarfism (may be congenital) -Acromegaly

Somatotropin or growth hormone indirectly stimulates the epiphyseal plate. Hormonally active tumors that originate from somatotropes are associated with hypersecretion of GH and cause gigantism in children and acromegaly in adults. Dwarfism occurs if not enough GH is produced in children, can be congenital.

Anterior pituitary Pars Intermedia (smallest part) •<2% of adenohypophysis •Composed of corticotropes (basophils) only •Cells surrounding cystic remnants of Rathke's pouch •Some cells migrate into pars nervosa

The pars intermedia surrounds a series of small cystic cavities that represent the residual lumen of Rathke's pouch. Frequently see colloid inside these cystic cavities that has not as yet been classified. Contains mainly corticotropes. Frequently the basophils and cystic cavities extend into the pars nervosa.

Pituitary Pars tuberalis •Contains gonadotropes only (basophils) •Consists of a collar of cells surrounding infundibulum

The pars tuberalis is an extension of the anterior lobe along the stalk-like infundibulum. It is a highly vascular region. Cells are arranged as in pars distalis ie. in small clusters or cords in association with the blood vessels. Consist of mainly gonadotropes (ie FSH and LH secreting cells)

The Pituitary Gland : the body's "master gland"

The pituitary gland is a small pea-sized gland that plays a major role in regulating vital body functions and general wellbeing. It is referred to as the body's 'master gland' because it controls the activity of most other hormone-secreting glands.

Posterior pituitary (neurohypophysis) Infundibulum •Connects hypophysis w/ hypothalamus •Composed of axons from Supraoptic & Paraventricular nuclei forming hypothalamic-hypophyseal tract -where hormone is synthesized & released -no synthesis in pars nervosa compared to anterior pit: -there's hormone synthesis in pars tuberalis, intermedia & distalis

The posterior lobe or neurohypophysis of the pituitary gland is an extension of the central nervous system that stores and releases secretory products synthesized in the hypothalamus. Specifically neurons in the supraoptic and paraventricular nuclei.

Feedback system for Anterior pituitary The circulating level of a specific secretory product of a target organ may act directly on cells of the anterior lobe and/or the hypothalamus to regulate the secretion of hypothalamic releasing/inhibitory factors In addition, information from most physiologic and psychologic stimuli that reach the brain also reaches the hypothalamus

acidophil releases GH, prolactin, basophil releases TSH, ACTH, FSH/LH

Subdivisions of Pituitary ANTERIOR LOBE of the pituitary gland consists of three derivatives of Rathke's pouch: -Pars distalis: comprises the bulk of the anterior lobe of the pituitary gland. -Pars intermedia: a thin remnant of the posterior wall of the pouch within which can be seen small cysts that are the remnant of the lumen of Rathke's pouch. -Pars tuberalis: which forms a collar or sheath around infundibulum (posterior lobe/neurohypophysis) POSTERIOR LOBE of pituitary gland consists of: -Pars nervosa: contains neurosecretory axons and their endings -Infundibulum: continuous w/ hypothalamus & contains neurosecretory axons

anterior lobe = right side of the left pic

Pituitary Organization •Extensive capillary beds associated w/ gland infundibulum location (center of the veins in pic)

dont have to know artery/vein names

This lecture will describe the discrete endocrine glands that release their hormones for delivery to the bloodstream for transport to target cells and organs Other lectures cover the endocrine function of individual cells within the gonads, liver, pancreas, kidney and GI tract. These are the cells of the diffuse neuroendocrine system (DNES). We are going to cover the pituitary gland, thyroid gland, parathyroid gland and the adrenal gland.

pituitary = hypophysis

Control of Anterior Pituitary secretion •Hypothalamic releasing/inhibiting factors move down axons of hypothalamic neurons •Hypothalamic factors are secreted in capillary beds of infundibulum at median eminence > synapse on capillary network & secreting releasing/inhibting factors > to network of vessels to pars distalis •Capillary beds drain into hypophyseal portal vessels, ending in pars distalis capillaries •Hypothalamic releasing factors exit capillaries to either stimulate or inhibit release of hormones in pars distalis by acidophils or basophils •Negative feedback occurs at multiple levels.

Hypothalamic releasing or inhibiting factors move down axons from neuronal cell bodies located in the hypothalamus. The releasing factors are secreted into capillary beds in the region of the median eminence. These capillary beds drain into hypophyseal portal vessels, ending in capillary network in the pars distalis. Here the releasing factors exit the capillaries and either stimulate or inhibit release of hormones in the pars distalis. Negative feedback occurs either by levels of circulating hormones affecting the cells in the pituitary or cells in the hypothalamus. The hypothalamus also receives information from most physiologic and psychologic stimuli that reach the brain. Therefore, the secretion of these releasing factors by the hypothalamus is the primary mechanism by which changes in emotional state are translated into changes in the physiologic homeostatic state.

A. Basophil (teal highlight circle) B. Chromophobe (no stain: on the edge of the violet circle next to the green/blue stain) echo 32:56 C. Pituicyte D. Acidophil yes E. None of the above teal circle highlight = basophil

Identify the cell at the tip of the blue arrow. A. Basophil B. Chromophobe C. Pituicyte D. Acidophil E. None of the above

Mnemonic A: Acidophils •Smart: Somatotrope (GH) •Move: Mammotropes (prolactin) By: Basophils •The: Thyrotropes (TSH) •Clever: Corticotropes (ACTH) •Girls: Gonadotropes (FSH/LH)

MEMORIZE

Anterior Pituitary (adenohypophysis) Pars distalis Structure: •Forms majority of pituitary gland •Glandular, with cells in cords, protein secreting •Reticular fiber framework •Fenestrated capillaries

Makes up the bulk of the pituitary gland. Has a glandular appearance, cells arranged in cords separated by fenestrated capillaries. These cells respond to signals from the hypothalamus and synthesize and secrete a number of pituitary hormones

Mammotropes - acidophils •Secrete Prolactin: -during pregnancy, cells undergo hypertrophy causing pituitary gland to increase in size •Stimulates milk secretion •Galactorrhea: continuous milk production (pituitary tumor) -men

Mammotropes produce prolactin. During pregnancy and lactation, these cells undergo hypertrophy causing the pituitary gland to increase in size. Galactorrhea may be caused by a tumor in the pituitary. Galactorrhea in men In males, galactorrhea may be associated with testosterone deficiency (male hypogonadism) and usually occurs with breast enlargement or tenderness. Galactorrhea in newborns Galactorrhea sometimes occurs in newborns. High maternal estrogen levels cross the placenta into the baby's blood. This can cause enlargement of the baby's breast tissue, which may be associated with a milky nipple discharge.

Cell Types : based on staining properties Chromophobes: smallest cells: pale staining •No secretory granules •Reserve/Degranulated chromophil cells Chromophils •Secretory granules with protein hormone •Acidophils (eosin affinity granules: pink or orange) [red circle] •Basophils (hematoxylin affinity granules: blue or green/purple) [blue circle]

The cells within the pars distalis vary in size, shape and staining properties. Early descriptions of the cells within the pars distalis were based solely on the staining properties of secretory vesicles within the cells. Using mixtures of acidic and basic dyes, histologists identified three types of cells according to their staining reaction, namely, basophils (10%), acidophils (40%) and chromophobes (50%) However, this classification contains no information regarding the hormonal secretory activity or functional role of these cells The section on the left is stained with H & E. (acidophils have pink-staining granules in the cytoplasm; basophils have magenta-staining granules) The section on the right is stained with the Masson stain (acidophils stain orange while basophils stain greenish/purple). The connective tissue of the gland is also stained green.

Thyrotropes - basophils -Secrete Thyroid stimulating hormone (TSH)

Thyrotropes : produce thyroid-stimulating hormone (TSH). Acts on the follicular cells of the thyroid gland to stimulate production of thyroglobulin and thyroid hormones.

exocrine vs. endocrine: -method of product distribution -site of product release -method of product release -site of product action -secretory product -cell polarity 2 major groups according to how their products are released: 1. Exocrine glands secrete their products onto a surface directly or through epithelial ducts or tubes that are connected to a surface 2. Endocrine glands lack a duct system. They secrete their products into the connective tissue, from which they enter the bloodstream to reach their target cells. The products of endocrine glands are called HORMONES Cells of exocrine glands exhibit different methods of secretion: 1. Merocrine: secretory product is delivered in membrane-bounded vesicles to the apical surface of the cell. -Here vesicles fuse with the plasma membrane and extrude their contents by exocytosis -This is the most common mechanism of secretion. 2. Apocrine: secretory product is released in the apical portion of the cell, surrounded by a thin layer of cytoplasm within an envelope of plasma membrane. -Found in the lactating mammary gland, where it is responsible for releasing large lipid droplets into the milk -not seen in histology 3. Holocrine: secretory product accumulates within the maturing cell, which simultaneously undergoes programmed cell death. -Both secretory products and cell debris are discharged into the lumen of the gland -This mechanism is found in sebaceous glands of the skin Hormones serve as effectors to regulate the activities of various cells, tissues & organs in the body. -Its functions are essential in maintaining homeostasis and coordinating body growth and development and are similar to that of the nervous system Both communicate information to peripheral cells and organs. Communication in the endocrine system is through hormones, which are carried to their destination via connective tissue spaces and the vascular system. Communication in the nervous system is through transmission of neural impulses along nerve cell processes and the discharge of neurotransmitter. The nervous system and endocrine system are functionally interrelated. The endocrine system produces a slower and more prolonged response than the nervous system. Both systems may act simultaneously on the same target cells and tissues, and some nerve cells secrete hormones.

endocrine secretion: -messenger released into vascular network -to target cell's receptor -mediate effects

Posterior pituitary Pars nervosa •Axons from hypothalamus terminate (Herring bodies) > stores 2 hormones released in posterior pit. •Pituicytes also present -Glial cells, highly polymorphic -In humans may have pigment and resemble Herring bodies

herring bodies: large light pink round (next to dark purple & white stains) Pituicytes: dark purple stains -analogous to glial cells in NS (supporting cells)

Origins of the Pituitary Gland 1. Outgrowth from roof of oral cavity projects upward: Rathke's pouch = Anterior pituitary (adenohypophysis) -glandular epithelial tissue -ectodermal origin 2. Outgrowth from hypothalamus = Posterior pituitary (neurohypophysis) -neural secretory tissue -neural origin

pituitary gland, along with the hypothalamus of the brain, is a major regulatory gland of the body. The pituitary gland is composed of both glandular epithelial tissue and neural tissue. It has two functional components: Anterior Lobe (Adenohypophysis) - glandular epithelial tissue Posterior Lobe (Neurohypophysis) - neural secretory tissue The structure of the adult pituitary gland results from two concurrent developmental processes. Beginning around the fourth week of gestation in humans, the anterior lobe of the pituitary gland, shown here in red, begins to form as an outgrowth from the roof of the developing oral cavity. This developing structure is called Rathke's pouch and projects upward towards the brain. The connection to the oral cavity is lost as development to proceeds. At the same time, the posterior lobe of the pituitary gland, shown in blue, is forming as a downgrowth from the hypothalamus and retains its connection with the brain (the infundibulum). Remnants of the original lumen of Rathke's pouch are retained in the adult as small fissures or cysts. The sphenoid bone grows around the pituitary gland by intramembranous ossification forming the sella turcica.

Control of Neurohypophyseal secretion •No synthesis of hormone in pars nervosa •Oxytocin •ADH/Vasopressin: -Stored in axon terminals (Herring bodies) after being synthesized in the paraventricular & supraoptic nuclei of hypothalamus

release via action potential