Anatomy of Pancreas , Gonads Thymus & Others
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ANATOMY OF PANCREAS , GONADS THYMUS & OTHERS Dr. Sangeeta Kotrannavar Dept. of Anatomy USM-KLE IMP Belagavi Objectives • Recall the features of pancreas, thymus gland and testis • Describe the islets of langerhans of pancreas • Describe the thymus gland • Describe the interstitial cells of leydig of the testis • Describe corpus luteum of the ovary • Describe the pineal gland Testis Introduction The male reproductive system consists of • Male gonads • Two testes • A system of genital ducts • Epididymis • Vas Deferens • Accessory glands • Seminal vesicles • Prostate • Bulbourethral glands • Penis Coverings of testes 1. Tunica Vaginalis 2. Tunica Albuginea 3. Tunica Vasculosa Sagittal section of Testis Thick connective tissue tunica albuginea surrounds testes and forms mediastinum testis Thin connective tissue septa from mediastinum testis separate testis into testicular lobules Each lobule contains 1 to 4 tightly coiled tubules, the seminiferous tubules The tubules open into rete testis (a network of channels) Small efferent ductules connect the rete testis to the upper end of the epididymis Testis Microanatomy Seminiferous tubules Lined by specialised stratified germinal epithelium (Seminiferous) • Spermatogenic cells – involved in spermatogenesis (in different stages -from spermatogonia - spermatocytes - spermatids – mature sperm) • Supporting cells (sertoli cells) Interstitial Tissue & Cells • Interstitial tissue is a delicate vascular connective tissue that surrounds and supports the seminiferous tubule and is continuous with tunica vasculosa of testes at the periphery. • It contains specialised endocrine cells called Leydig cells, occurs singly or in clumps which secrete testosterone. Leydig cells (interstitial cells) • Are mesenchymal in origin • Round nucleus at periphery • Are large, polygonal, cells that typically contain lipid droplets. • Eosinophilic cytoplasm contains smooth endoplasmic reticulum (SER), several mitochondria and crystals. • Crystals • Rod-shaped known as crystals of Reinke, appears as retractile structures in H&E • Exact nature and function of crystals are remain unknown Functions of Leydig cells • Leydig cells differentiate and secrete testosterone during early fetal life. • Secretion of testosterone is required during embryonic development, sexual maturation, and reproductive function: • In the embryo, secretion of testosterone & other androgens is essential for the normal development of the gonads in the male fetus. • At puberty, secretion of testosterone is responsible for the initiation of sperm production, accessory sex gland secretion, and development of secondary sex characteristics. • In the adult, secretion of testosterone is essential for maintenance of spermatogenesis & of secondary sex characteristics, genital excurrent ducts, & accessory sex glands. Hormonal regulation of Leydig cell Ref Ross Hormonal regulation • Spermatogenesis dependent on luteinizing and follicle stimulating hormones produced by the pituitary gland • Luteinizing hormone (LH or ICSH) binds to receptors on interstitial cells and stimulates testosterone secretion • Follicle-stimulating hormone (FSH) stimulates Sertoli cells to produce androgen-binding protein(ABP) into seminiferous tubules to bind testosterone • Testosterone is vital for spermatogenesis and accessory gland function • Sertoli cells produce inhibin, which inhibits FSH production from pituitary gland via negative feedback Applied –Leydig cells • Leydig cell tumors represents predominately benign tumors, which occur during two distinct periods (in childhood and in adults between 20 and 60 years old). • Features • They are hormonally active and secrete androgens or combination of androgens and estrogens. • Testicular enlargement, usually is related to abnormal level of hormone production. • In prepubertal boys, this leads to sexual precocity (unexpected pubertal changes in early age), • Whereas in adults it may be observed as feminization (development of female sexual characteristics) and gynecomastia (development of breast in males). Ovary Female Reproductive System Ovary • Female gonad • Location: in ovarian fossa, in post part of broad ligament, & lateral wall of pelvis • Has tubular pole – connected to suspensory ligament • Has uterine pole – connect to uterus via proper ligament of ovary • 2 major functions - production of gamete (oocytes) - production of hormones 1. Estrogen – promotes maturation of internal and external genitalia, and development of mammary gland 2. Progesterone – prepare uterus for pregnancy, and mammary gland for lactation. • Both hormones play key role in menstrual cycle Structure of ovary 1- Germinal Epithelium- Single layer of low cuboidal cells 2- Tunica Albuginea - Dense connective tissue layer beneath epithelium 3- Cortex (Peripheral)- Contains Follicles, collagen and reticular fibers 4- Medulla (Central)- Dense irregular connective tissue. It Contains blood vessels, nerves & lymphatics Stages of Follicular Maturation 1. Primoridal follicle 2. Primary follicle - Unilaminar - Multilaminar 3. Secondary / antral follicle 4. Tertiary follicle / Graafian follicle 5. Atretic follicle Ovary Maturation of Ovarian follicle • Primordial follicle - Earliest follicle , contains primary oocyte & is surrounded by a single layer of flat cells • Primary follicle • Unilaminar - covered by a single layer of cuboidal cells. • Multilaminar - on further growth, single layer proliferate & becomes multilayered. Now cells are called granulosa cells. Maturation of Ovarian follicle • Secondary / antral follicle • Cavities appear between granulosa cells forming an antrum & filled with antral fluid • Mature /Graafian Follicle • A large Antrum - filled with follicular fluid • Primary oocyte is supported by a group of granulosa cells called cumulus oophorus. • The granulosa cells surrounding antrum are named as membrana granulosa • Inner theca interna – Vasular layer • Outer theca externa Ovulation • Ovulation – mature follicle ruptures and release secondary oocyte along with corona radiata cells into the peritoneal cavity capture by the fimbria of fallopian tube • Just before ovulation it completes meiosis 1st division to form secondary oocyte Ovulation Corpus Luteum • The dominant follicle after releasing the ovum formed as Corpus luteum. • Cells undergo hypertrophy & cytoplasm filled with the yellow pigment called lutein hence corpus luteum. • Theca granulosa granulosa lutein cells derived from granulosa cells secrets the hormone progesterone acts on endometrium & prepares it to receive & implant the zygote. • Theca interna theca lutein cells derived from theca interna cells - secrets the hormone oestrogen cause proliferation of endometrium Corpus luteum TLC cavity GLC Granulosa lutein cells (GLC) - have a large polygonal cells with large amount of eosinophilic cytoplasm & round nucleus. Contains lipid droplets giving yellow colour Theca lutein cells (TLC) have a spherical nucleus, but the cells are considerably smaller than granulosa lutein cells with pale cytoplasm Corpus Luteum corpus haemorrhagicum - Bleedingin the cavity Functions • Corpus luteum primarily secrets the hormone progesterone • Responsible for ovulation • secretory phase of endometrium • maintenance of pregnancy Changes in corpus luteum • Fertilization occurs corpus luteum of pregnancy (survive for 3 months) • No fertilization corpus luteum of menstruation (survive for 10-12 days ) • At the end - regress corpus albicans, white fibrous scar • Atretic follicles - Most ovarian follicles do not attain maturity and undergo degeneration (atresia) and become atretic follicles (finally replaced by connective tissue) Hormonal regulation of ovarian cycle This diagram illustrates the relation of the morphologic changes in the endometrium and ovary to the pituitary and ovarian blood hormone levels that occur during the menstrual cycle. The pituitary and ovarian hormones and their plasma concentrations are indicated in arbitrary units. LH, luteinizing hormone; FSH, folliclestimulating hormone. Hormonal regulation of ovarian cycle FOLLICULAR PHASE OVULATION LUTEAL PHASE 10-20 primordial follicles begin to develop in Theca and granulosa cells transform into the corpus response to FSH and LH levels. luteum and secrete large amounts of progesterone. FSH and LH stimulate theca and granulosa cells. No fertilization, corpus luteum degenerates. Production of estrogen and progesterone. If fertilization does occur, HCG released from the embryo Surge of LH induces ovulation. maintains corpus luteum Polycystic TA ovarian disease • Characterized by bilaterally enlarged ovaries with numerous follicular cysts • Have a smooth, pearl-white surface because of no ovulations hence no scarring • An unusually thick tunica albuginea • Anovulatory cycle characterized by only estrogenic stimulation of the endometrium because of the inhibition of progesterone production. • Progesterone inhibition is caused by failure of the Graafian follicle to transform into a progesterone-producing corpus luteum. MTF •Regarding testis and ovary F A Leydigs cells located inside lumen of seminiferous tubules F B FSH stimulates Leydigs cells F E Sertoli cells secrete testesterone F C Corpus luteum develops under the influence of FSH F D Corpus luteum is formed before ovulation SEQ • Describe the interstitial cells of leydig of the testis • Describe corpus luteum of the ovary Thymus Thymus- Gross features • Thymus is both immune & endocrine organ • Double embryonic origin: epithelial reticular cells from endoderm & lymphocytes