Histology Lec-11 Endocrine

Histology (Module 3 and Lecture 1)

DATE

Endocrine System

Dr. Nicetas B. Lucero

2019A ALL GROUP MEMBER SURNAMES, ALPHABETICALLY ARRANGED 1OF10

OBJECTIVES 1. Describe the organization of the endocrine system 2. Name the components of the endocrine system 3. Describe the feedback mechanism in the control of feedback

mechanism 4. Describe the physiology of the hypophysis 5. Describe the cells found in the pituitary gland 6. Describe the histologic organization of the thyroid,

parathyroid, and adrenal gland 7. Demonstrate knowledge and understanding of the histology

of the pineal gland 8. Know the other organs with endocrine functions 9. Know common clinical conditions associated with the

endocrine system 10. Identify the different organs and specific structures in each

endocrine organ under the light microscope

INTRODUCTION The endocrine system is responsible for the synthesis and secretion of chemical messengers known as hormones. Hormones may be disseminated throughout the body by the bloodstream, where they may act on specific target organs or

affect a wide range of organs and tissues. Other hormones act locally, often arriving at their site of action by way of a specialised microcirculation. In conjunction with the nervous system, hormones coordinate and integrate the functions of all the physiological systems.

LOCATION OF MAJOR ENDOCRINE ORGANS

Major Endocrine Organs - Sole or major function of the organ

is the synthesis, storage and secretion of hormones

Pituitary

Pineal

Thyroid

Adrenal Organs Containing Endocrine Cells: hypothalamus, skin, Thymus, Heart, liver, stomach, Small intestines, pancreas, kidney, ovary, testes, adipocytes. Endocrine System

Endocrine glands are scattered throughout the body

Their secretions are call hormones which influences the metabolic processes of the body

Hormones are hydrophilic such as: Proteins, glycoproteins, peptides, or modified amino acids with receptors on the surface of target cells

Second messenger system of the body

Uses chemical messages (hormones) that are released

into the blood

Hormones control several major processes o Reproduction o Growth and development o Mobilization of body defenses o Maintenance of much of homeostasis o Regulation of metabolism

HORMONE OVERVIEW

Hormones are produced by specialized cells

Cells secrete hormones into extracellular fluids

Blood transfers hormones to target sites

These hormones regulate the activity of other cells

CONTROL OF HORMONE RELEASE

Hormone levels in the blood are maintained by negative feedback

A Stimulus or low hormone levels in the blood triggers the release of more hormone

Hormone release stops once an appropriate level in the blood is reached

Hormonal Stimuli of Endocrine Glands endocrine glands are activated by other hormones Humoral Stimuli of Endocrine Glands changing blood levels of certain ions stimulate hormone release Neural Stimuli of Endocrine Glands

Nerve impulses stimulate hormone release

Most are under control of the sympathetic nervous system

Subject Name + Lecture # (Ex. Histology 1.1)

2019A ALFELOR, BALLESTEROS, GUILLERMO 2OF10

CHARACTERISTICS OF ENDOCRINE GLANDS

1. The glands are ductless; thus hormonal secretions are poured directly to the blood through the capillaries.

2. The internal support framework is reticular tissue. 3. Highly vascular, thus provided with rich capillary

networks among and between groups of secretory cells. 4. The capillaries are fenestrated type in which endothelial

wall contains numerous pores or openings which are covered by very thin diaphragms.

CHARACTERISTICS OF ENDOCRINE GLANDS

On the basis of their germ layer of origin, the endocrine glands may either be ectodermal, mesodermal or endodermal.

Ectodermal in origin o Pituitary gland o Pineal gland o Adrenal Medulla

Mesodermal in origin o Adrenal Cortex o Leydig Cells of the testes o Theca interna cells of the ovary

Endodermal in origin o Thyroid gland o Parathyroid gland o Islets of Langerhans o Parafollicular cells or C-cells

THE PITUITARY GLAND

The pituitary gland (hypophysis) is a small bean-shaped gland,

about 1 cm diameter, at the base of the brain beneath the third ventricle, sitting in a bony cavity in the base of the skull (the sella turcica). The gland is divided into anterior and posterior parts which have different embryological origins, functions and control mechanisms. Development of the Pituitary Gland

Develops from two sources

Rathkes pouch o Ectodermal outpocketing of the stomodeum (future

mouth) o Gives rise to the Adenohypophysis (anterior pituitary)

Anterior wall = Pars Distalis, Pars Tuberalis Posterior wall = Pars Intermedia

Infundibulum o Downward extension of the diencephalon o Gives rise to the neruohypophysis (posterior pituitary)

Pars nervosa (infundibular process) Infundibular stem (stalk) Median Eminence of tuber cinerum

Pars Distalis

largest subdivision of the adenohypophysis

2 categories of cells o Acidophils secrete prolactin and growth hormone o Basophils - secrete FSH, LH, TSH, ACTH

Chromophobes o Smallest and least numerous among the cells in the pars

distalis o Since they are small, their nuclei lie close to each other;

and their cytoplasm is scanty, thus hardly seen. o These cells are referred to as reserve cells since some of

them may differentiate into acidophils or basophils as the need arises.

Hypothalamic Hormones Regulating Cells of the Anterior Pituitary



Pars Intermedia

It is found between the pars distalis and the infundibular process

It is characterized by the presence of follicles or cysts filled with colloid and lined by columnar epithelium, which are called Rathkes cyst.

Also found are polygonal basophilic cells.

The hormone of the pars intermedia is the melanocyte stimulating hormone (MSH), which causes the dispersion

of melanin pigments in the melanoblast and increase the pigmentation of the skin.

Pars Tuberalis

It is the most highly vascular portion of the hypophysis.

It is formed of longitudinal columns or cords of cells that descend towards the pars distalis.

The cell types are: 1. Undifferentiated cells 2. Small basophils and acidophils

There is no hormone isolated in the pars tuberalis. Hypophyseal System

It is formed of venules that connect the capillaries in the median eminence with the capillary sinusoids in the pars distalis. It is thru the hypophyseal portal circulation that the releasing hormones from the hypothalamus reach the secretory cells of the pars distalis.

The neurohormones from the hypothalamus reach the pars distalis through nerve fibers.

The blood supply of the hypophysis is derived from the superior hypohyseal arteries, branches of the internal carotid and branches of the posterior communicating arteries

NEUROHYPOPHYSIS

The neurohypophysis is formed of unmyelinated nerve fibers of the hypothalamo-hypophyseal tract, which are formed of axons of the neurons in the hypothalamic nuclei.

The axons descend through the median eminence to the infundibular stalk and infundibular process.

Also found in the neurohypophysis, part of the pars nervosa, are the pituicytes cells with numerous processes and are considered as modified neuroglial cells.

Herring bodies are small, spherical structures containing neurohormones ( ADH and Oxytocin) stored in the pars nervosa or in the infundibular process. These are neuro-secretory materials secreted by the neurons in the hypothalamic nuclei and travel along the axons of these

neurons to be stored and released from the axolemma of the nerve fibers.

HORMONES IN THE PARS NERVOSA

Found in the infundibular process or pars nervosa (Posterior pituitary DOES NOT contain the cells that synthesize its 2 hormones)

1. Pitocin (Oxytocin)

Synthesized by the paraventricular nuclei of the hypothalamus

Stimulates uterine contraction & mammary glands 2. Pitressin or ADH (Anti-Diuretic Hormone)

Synthesized by the supraoptic nuclei of the hypothalamus

Increase water retention



THE THYROID GLAND

DEVELOPMENT OF THE THYROID GLAND

Develops from epithelial proliferation in the floor of the pharynx between the tuberculum impar and copula, at a point later indicated by the foramen cecum.

It descends in front of the pharyngeal gut as a bilobed diverticulum. This is connected to the tongue by a narrow canal, the thyroglossal duct, which later disappears. The

cystic remnants of the thyroglossal duct is called the thyroglossal cyst.

The 5th pharyngeal pouch gives rise to the ultimobranchial body, which later is incorporated in the thyroid gland. The cells of the ultimobranchial body give rise to parafollicular or C-cells of the thyroid gland secreting calcitonin.

THYROID GLAND

The thyroid gland is a butterfly-shaped endocrine gland lying in the neck in front of the upper part of the trachea. The thyroid gland produces hormones of two types: o Iodine containing Hormones (tri-iodothyronine or T3 and

thyroxine (tetra-iodothyronine or T4) o Calcitonin

The gland is found in the anterior part of the neck, consisting of two lobes connected by a narrow isthmus, which crosses the trachea just below the cricoid cartilage.

It has a connective tissue capsule that is continuous with the surrounding cervical fascia. The outer capsule is loosely on its deep surface of another layer of moderately dense connective tissue that is intimately adherent to the gland.

The structural unit is the spherical cystlike follicles, which are lined by simple cuboidal epithelium and containing a gelatinous colloid.

Aside from the follicular cells, there are cells which are

found singly or in groups wedged between the follicular cells and the basal lamina or between the thyroid follicles.

These were originally called parafollicular cells based on their position, but with the discovery that they produce calcitonin, they are now called C-cells. Other names are light cells, mitochondria-rich cells and ultimobranchial cells.

FUNCTION OF THE THYROID GLAND

Synthesize, store and release hormones concerned with the regulation of metabolic rate (tri-iodothyroxine or T3 and tetra-iodotyroxine or T4) by the follicular epithelial cells. (TH



increase metabolic rate)

Decrease blood calcium level by the C-cells or parafollicular cells through the secretion of calcitonin. (inhibits osteoclast activity)

DEVELOPMENT OF THE PARATHYROID GLAND It develops from:

Superior parathyroid o Dorsal wing of the 4th pharyngeal pouches

Inferior parathyroid o Dorsal wing of the 3rd pharyngeal pouches

THE PARATHYROID GLAND

These are two pairs of glands which are small, yellow-brown oval bodies adhering to the posterior surface of the thyroid gland.

A connective tissue capsule separates them from the thyroid gland.

Delicate connective tissue septa partially divide the gland into poorly defined lobules and still finer ones separate the epithelial cells into anastomosing cords and groups.

The parenchyma is composed of two types of cells:

Principal or Chief cells Constant occurrence Polyhedral cells with round nuclei, with loosely

arranged chromatin giving a vesicular appearance, and basophilic cytoplasm

Oxyphil cells Appears only at the end of the first decade of

life until puberty Larger cells with smaller and darker nuclei and

acidophilic cytoplasm The parathyroid glands regulate calcium concentration by

stimulating resorption of bone and reabsorption of calcium ions from ultrafiltration of the kidneys and with the aid of the vitamin D absorption of calcium from the gut.

Through the principal cell secretion of parathyroid hormone (PTH), blood calcium level increases.( by

stimulatng osteoclast activity)

THE THYROID GLAND

THE DEVELOPMENT OF THE ADRENAL GLAND Adrenal cortex

About the 5th week of development, mesothelial cells proliferate and later differentiate into large acidophilic structures forming the primitive or fetal cortex of the adrenal gland

Shortly later, a second wave of cells from the mesothelium penetrate and surround the original acidophilic mass. These cells will form the definitive cortex of the adrenal gland.

Adrenal medulla Arises from neural crest cells. These cells invade the

medial aspect and become cords and clusters forming the medulla of the adrenal gland.

The cells of the adrenal medulla are stained yellowish brown with chrome salts. Hence, they are called chromaffin cells.

THE ADRENAL GLAND The paired adrenal or suprarenal glands are roughly

triangular, flattened organs embedded in the retroperitoneal fat tissue at the cranial pole of each kidney.

It has a thick capsule of connective tissue that extends into the cortex as trabeculae.

There are two functionally and structurally distinct parts: o Cortex o Medulla

The principal secretory cells of the medulla are derived from the neural crest cells.

The secretory cells of the cortex are derived from the mesodermal cells in the nephrogenic ridge.

ADRENAL CORTEX

The cortex forms the bulk of the gland. It has three distinguishable concentric zones:

o Zona glomerulosa o Zona fasciculata o Zona reticularis

ZONA GLUMERULOSA

Adjacent to the capsule is a narrow zone in which the cords of columnar cells are in ovoid groups.

There is no central cavity within a cell group as in exocrine glands, but there is a rich network of blood vessels externally.

It produces Aldosterone, a potent mineralocorticoid causing water and sodium retention in exchange for potassium in the kidney.

ZONA FASICULATA The middle and broadest zone is composed of cell cords

coursing parallel to one another in radial direction toward the medulla.

The secretory cells are cuboidal or polyhedral, and sometimes binucleated, which are vesicular.

These cells secrete Glucocorticoids , especially Cortisol ZONA RETICULARIS

Network of cell cords, which are smaller than those of the fasciculata, darker nuclei, fewer lipid droplets and numerous lipofucshin granules.

Also produce Cortisol but primarily secrete Weak



Androgens including Dehydroepiandrosterone (DHEA) precursors for testosterone & Estrogen

Cortisol, the most important glucocorticoid, has a protein wasting effect and promotes gluconeogenesis; suppress immune cell activities

It is probable that the outer part of the fasciculata produces much of the cortisol in unstressed individuals.

ADRENAL MEDULLA

The secretory cells ( Chromaffin cells) here are in anastomosing groups associated with blood vessels.

The parenchymal to columnar, and contain cytoplasmic granules, which become brown when oxidized by potassium bichromate.

The chromaffin reaction of the granules is due to their content of catecholamines epinephrine and norepinephrine.

EPINEPHRINE AND NOR-EPINEPHRINE Epinephrine increases the heart rate and cardiac output

without signifying increasing the blood pressure and other metabolic effects; constricts vessels

Norepinephrine is in the brain and peripheral tissues, the principal transmitter substance of adrenergic neurons; dilates vessels and increases glucose release

THE PINEAL GLAND

THE DEVELOPMENT OF THE PINEAL GLAND The pineal gland develops from the caudal part of the roof

of the diencephalon. It appears as an epithelial

thickening on the midline by the 7th week of development. Then, it invaginates to become a solid organ located at the roof of the mesothelium.

PINEAL GLAND Also known as epiphysis cerebri. The pineal gland is a slightly flattened cone shape

appendage of the brain, attached to the roof of the 3rd ventricle by the peduncle.

It is made up of pale staining epitheloid cells, with round or oval granular nuclei and prominent nucleoli, the pinealocytes.

The second cell type is the interstitial cells, which occur in the perivascular areas.

They are less numerous and the nuclei are darker and smaller.

These neuroglial cells provide supporting network to the cells.

Brain sand (corpora arenacea or Psammomas bodies) are mulberry shaped concretions largely of hydroxyapatite, which makes the radiological landmark.

The gland reaches its maximal development by the middle of the first decade and regresses later in life.

It has a high level of serotonin and melatonin secreted by the pinealocytes.

The pineal gland controls the onset of puberty; regulates circadian rhythms

PANCREAS

The pancreas has an exocrine portion, which secretes digestive juice essential for the digestion of carbohydrates, fats and proteins, and an endocrine portion secreting hormones.

The endocrine function is performed by a highly vascularized aggregation of secreting cells, the islets of Langerhans, which are scattered all throughout.

They are over a million, but comprised only one to two per cent of the gland.

DEVELOPMENT OF THE ISLET OF LANGERHANS

The islets of Langerhans develops from the parenchymatous pancreatic tissue during the 3rd month of development and scattered throughout the gland.

Insulin secretion begins on the 5th month of development ISLET OF LANGERHANS

The islets are spheroidal masses of pale staining cells arranged in a form of irregular anastomosing cords, with a few fine connective tissue fibers.

They are more abundant in the tail of the pancreas. The secretion is released into the interstitium where it has

access to the bloodstream. By special methods, there are six cell types distinguished.



PRINCIPAL CELLS OF THE ISLETS OF LANGERHANS Alpha cells

Periphery, Secrete glucagon ( increase blood glucose) Beta cells

Predominant type distributed throughout the islet comprising 60% to 90% of its mass, Secrete insulin

(decrease blood glucose levels) Delta cells

Least abundant occurring anywhere in the islet, Secrete somatostatin ( inhibit secretion of

insulin,glucagon and somatotropin) Pancreatic polypeptide rare, + gastric chief cells;

inhibit bile secretion,pancreatic enzyme & bicarbonate secretion and intestinal motility

ISLET OF LANGERHANS

The hormones secreted by the three principal types are all involved in the control of level of blood glucose.

When the sugar falls below the optimal level, the Alpha cells secrete glucagon, which raises the blood sugar.

When glucose levels rise too high, the Beta cells release insulin, which lower it.

The somatostatin produced by the Delta cells is capable of suppressing the secretion of insulin and glucagon and modulate the activity of the Alpha and Beta cells to maintain normal glucose levels.

TESTES (ANG PABORITO NI MANAY MO)

The testes is a compound tubular gland enclosed in a thick fibrous capsule, the tunica albuginea. Thin fibrous septa, the septula testis, extend radially dividing the organ into compartments, the lobuli testis.

Each lobule is composed of one to four highly convoluted seminiferous tubules, which constitute to the exocrine portion of the testis.

DEVELOPMENT OF THE LEYDIG CELLS OF TESTIS/TESTES

Develops from the mesenchyme between the seminiferous tubules, which are particularly abundant during the 4th to 6th months of development.

The endocrine component of the testis, the Leydig cells, are located in the interstices between the seminiferous tubules. The cells occur in groups of various sizes. Small blood vessels are usually present. The cells are large and ovoid or polygonal. They have a large eccentric nucleus and granular acidophilic cytoplasm, which is peripherally vacuolated. The ultrastructure typifies that of steroid secreting cells which have extensive smooth endoplasmic reticula. Peculiar to human, is a variable number of proteinaceous crystals, Reinkes crystals.

The Leydig cells synthesize testosterone.

SE-Seminiferous tubules; I-Interstitium which conatins your Leydig Cells; C-Capillaries.

OVARIES (ANG PABORITO NI MANOY MO)

The ovaries are slightly flattened, ovoid, paired organs suspended on either side of the uterus.

In sections side of the ovary has two zones; a central deeper zone, the medulla, and a broad outer zone, the cortex.

The cortex consists of a compact, cellular connective tissue in which are scattered the characteristic epithelial structures of the ovary, the ovarian follicles in different stages of growth and degeneration.

As the follicles increase in size, the theca folliculi differentiates into a highly vascular inner layer of secretory cells, the theca interna, which secretes estrogen, and an outer layer, the theca externa, composed mainly of connective tissue.



TE-Theca Externa; TI-Theca Interna; ZG-Zona Glumerolosa; FA-Follicular Antrum; O-Oocyte; CO-Cumulu Oophorus

DEVELOPMENT OF THE THECA INTERNA CELLS OF THE

OVARY

Develop from secondary cortical cords from the proliferation of cells in the stroma ovarii

OVARIES Following ovulation, the follicular wall collapses and its

granulosa cell lining is thrown into folds. There is extravasation of blood from the capillaries of the theca interna, resulting in a central clot. The theca interna and granulosa cells then enlarge and accumulate lipid and are transformed into plump, pale staining polygonal cells, the Lutein cells.

This structure is now called the Corpus luteum. Two kinds of Lutein cells are distinguishable; the peripheral,

smaller and darker stained theca lutein cells, which secrete a small amount of estrogen and the larger, granulosa lutein cells, which secrete progesterone.

T-Zone of Theca Lutein Cells; S-Speta; G-Zone of granulosa lutein cells; B-Corpus Luteum with blood clot from menstruation

OTHER ORGANS WITH ENDOCRINE FUNCTIONS

Placenta Fat Kidney Heart Thymus

PLACENTA (DITO NAKA-KABIT PUSOD MO DATI!)

The syncitiotrophoblast of the chorionic villi secrete Human chorionic gonadotrophic hormone (HCG).



FAT (MERON KA NETO!)

Adipose tissue is a special type of connective tissue in which fat cells predominate. Fat cells are found isolated in all loose connective tissue, but in certain places they are present in such large numbers and have such organization as to justify the designation of adipose tissue.

Adipose cells are large, oval or spherical shaped cells, whose cytoplasm is displaced to the peripheral region of the cell by the presence of a single large fat droplet . The nucleus is flattened and surrounded by a small amount of cytoplasm in the periphery giving a characteristic signet ring appearance.

KIDNEY

Juxta-glomerular (JG) cells: On one side of the wall of the afferent arteriole at the

vascular pole becomes transformed into modified smooth muscle cells called juxta-glomerular cells or JG cells, which have a slightly basophilic cytoplasm and their specific granules are clearly demonstrated. Electron microscopy of secretory granules of JG cells shows that cells are variable in shape and membrane bounded with an internal crystalline structure. JG cells secrete Renin, which activates Angiotensinogen into

Angiotensin I. Angiotensin I is inactive but is converted in the lungs to Angiotensin II, which is a potent vasoconstrictor, increasing blood pressure.

Lacis cells or extraglomerular mesangial cells: Also known as polar cushion or polkissens cells.

These cells are formed at one angle between the afferent and efferent arteriole at the vascular pole. They may produce Erythropoietin, a hormone that stimulates

erythropoiesis in the bone marrow.

THYMUS

Located posterior to the sternum

Largest in infants and children

Produces thymosin Matures some types of white blood cells Important in developing the immune system

FUNTIONAL - CLINICAL CORRELATION

Disorders of the endocrine system involve hyposecretion or hypersecretion of hormones

Pituitary dwarfism = hyposecretion of growth hormone by the adenohypophysis

Gigantism = hypersecretion of growth hormone during childhood

Acromegaly = hypersecretion of growth hormone during adulthood

Diabetes insipidus = hyposecretion of ADH caused by damage to the neurohypophysis or the supraoptic nucleus

Diabetes mellitus = a heterogenous group of diseases, all of which lead to an elevation of blood sugar and excretion of glucose in the urine

Cretinism = hyposecretion of thyroid hormones during the growth years. Two clinical manifestations of the cretin are dwarfism and mental retardation

Myxedema = hypothyroidism during adulthood. Hallmark of this disorder is an edema that causes the facial tissues to swell and look puffy

Graves disease = hyperthyroidism during adult life. This gives rise to exophthalmic goiter.

Tetany = muscle twitches or spasm and convulsions as a result of hypoparathyroidism (deficiency in calcium)

Osteitis fibrosa cystica = hyperparathyroidism that causes demineralization of bone

Aldosteronism = hypersecretion of the mineralocorticoid, aldosterone, characterized by a decrease in the bodys potassium concentration

Addisons disease = primary adrenal insufficiency that results in hyposecretion of glucocorticoids. Clinical manifestations include lethargy, weight loss and hypoglycemia, which leads to muscular weakness

Cushingsyndrome = hypersecretion of glucocorticoids, especially cortisol and cortisone. Clinical manifestations include moon face, buffalo hump on the back and pendulous abdomen



Pheochromocytoma = tumor of the chromaffin cells of the adrenal medulla, causes hypersecretion of the medullary hormones

FREEDOM SPACE

Kung akala niyo tapos na.. HINDI pa! andito pa kami! Hahahaha.. :P

REFERENCES 1. Dr. Luceros ppt 2. Wheaters Histology book

Histology Lec-11 Endocrine

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