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Learn about the main components and functions of the urinary system, including waste excretion, water regulation, and hormone production. Explore the structure of the kidney and the process of urine formation through the nephron.
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Final lecture Dr. Tarek Atia
The main components of the urinary system are the kidneys, ureters, urinary bladder and urethra. • Functions of the urinary system (kidney): • Excretion of the waste products from the body. • Elimination of foreign substances. • Regulation of the amount of water in the body. • Control of the concentration of most compounds in the extracellular fluid .
Functionally the processes can be divided into two steps, each of which have their anatomical correlate: • Filtration: glomeruli of the kidney. • Selective resorption and excretion:tubular system of the kidney.
In addition, the kidney also functions as an endocrine organ: • Fibrocytes in the cortex release the hormone erythropoietin, which stimulates the formation of red blood cells. • Modified Fibrocytes of the medulla secrete prostaglandins which are able to decrease blood pressure.
Structure of the Kidney • Kidney is formed of multiple lobes, each lobe made up of a renal pyramid (base in cortex, apex in medulla). • Capsule: fibrous CT. • Renal Cortex: contains renal corpuscles • Renal medulla: multiple medullary pyramids separated by regions of cortex.
Cortex and Medulla • Millions of nephrons are packed into each kidney. • The cortex consists of convoluted tubules together with the renal corpuscles. • The medulla consists of loops of Henleand collecting ducts.
The Nephron • The nephronis the functional unit of the kidney, each one consists of one renal corpuscle and its associated tubule. • The renal corpusclesare the sites where the process of urine formation begins with a filtrate of blood plasma. • Renaltubulesare differentiated into several segments. • A proximal convoluted tubule drains filtrate away from a renal corpuscle. • A loop of Henledescends into the medulla, makes a hairpin turn, and returns to the cortex. • The distal convoluted tubule passes near to the original corpuscle then leads to a collecting duct. • A collecting duct receives fluid from several distal tubules, then passes through the medulla and drains into the pelvis.
The Glomerulus (renal corpuscle) is the round (~200μm in diameter) blind beginning of the nephron. • It is invaginated by a tuft of capillaries at the vascular pole of the glomerulus. • Substances which leave the capillaries enter the renal tubule at the urinary pole of the glomerulus.
The glomerulus is enclosed by two layers of epithelium (Bowman's capsule). • Cells of the outer layer of the capsule are simple squamous epithelium. • Cells of the inner layer (podocytes), are extremely complex in shape. • They have small foot-like processes (pedicles) of their cytoplasm form a fenestrated epithelium around the fenestrated capillaries of the glomerulus.
Tubules of the Nephron • The tubular system can be divided into proximaland distaltubules, which in turn have convoluted and straight portions. • The loop of Henle, intermediate tubules connect the proximal and distal tubules. Running from the cortex of the kidney towards the medulla (descending), then turning and running back towards the cortex (ascending).
The male reproductive system consists of the external genitalia and a series of glands and ducts that produce and transport the male gametes (sperms) and the semen. A. Glands: include the testes and other accessory glands. • Testes: are the primary gonadal glands, with both exocrine and endocrine functions. • Accessory glands: include the seminal vesicles, prostate glands, bulbourethral glands, and glands of Littre. B. Ducts: The ducts of the male reproductive system include epididymis, and vas deferens.
Testes • The testes are bilateral gonads lying within the scrotum. • The parenchyma composed of seminiferous tubules (~ 250 lobules). • Each lobule contains 1-4 seminiferous tubules that are separated from one another by a CT stroma within which are found the hormone producing interstitial (Leydig) cells.
The seminiferous tubules are formed by the seminiferous epithelium, a complexly stratified epithelium resting upon a basal lamina and containing two types of cell: Sertoli cells and germ (spermatogenic) cells.
Sertoli cells • Sertoli cellsare columnar, non-replicating support cells that extend from the basal lamina to the lumen; they have extensive apical and lateral projections that envelop the adjacent germ cells and make contact with adjacent Sertoli cells.
The germ cells are arranged in four to eight layers; their function is to produce spermatozoa. • They are composed of spermatagonia, spermatocytes, spermatids and spermatozoa.
The spermatogonia divide by mitosis to create stem cells and primary spermatocytes, which undergo further differentiation to form secondary spermatocytes, then spermatids and finally spermatozoa. • The production of spermatozoa is called spermatogenesis, a process that includes cell division through mitosis and meiosis. • Spermiogenesis; is a maturation of spermatids into mature and motile spermatozoa. It is the final stage of spermatogenesis.
The female genetal tract begins with the paired of ovaries, leads through the opening of the fallopian tubes (oviducts) to the uterus, and then opens through the cervix into the vagina. • Special structures, the placenta and the umbilical cord, develop during pregnancy.
Ovary • The surface of the ovary is covered by germinal epithelium. • The outer portion of the ovary is called the cortex, and the inner portion is called the medulla. • Ovarian stroma consists of spindle-shaped stromal cells similar to fibroblasts. • Several ovarian follicles are embedded in the stroma of the ovarian cortex. • Each follicle contains a single oocyte surrounded by granulosa cells, which are separated from the surrounding stroma by a basement membrane.
Ovarian Follicles • All of follicles that a woman have are present in the ovary at birth. • The primordial follicles are present in resting condition. • During each monthly cycle, a few follicles are activated by follicle stimulating hormone (FSH) from the pituitary gland and begin maturate from: • Primary follicles, • Secondary follicles, • And tertiary or Graafian follicles.
Following ovulation and under the influence of luteinizing hormone (LH), the ruptured follicle reorganizes into a specialized endocrine structure called the corpus luteum ("yellow body").
Ovarian Follicles Secondary follicle Primary follicle
Fallopian tube Vagina Uterus
Thyroid follicles and thyroid hormones • Thyroid gland contains numerous follicles • Release several hormones such as thyroxine (T4) and triiodothyronine (T3) • Thyroid hormones end up attached to thyroid binding globulins (TBG) • Some are attached to transthyretin or albumin
Follicular cells: Secrete Thyroid hormone • Parafollicular Cells: Secrete Calcitonin hormone that regulate calcium concentration in body fluids The parafollicular or c-cells (arrows) Principal cells/ Follicular cells Parafollicular cell
Small dark staining Chief cells and larger, pall Oxyphil cells The parathyroid gland contains two cell types. Chief cells : Secrete Parathyroid Hormone. Oxyphil Cells: are of Uncertain Function.
