Urinary System PDF

Urinary System Urinary system Urinary system Urinary system The urinary system consists of : The paired kidneys Ureters Bladder The urethra. This system’s primary role is to ensure optimal properties of the blood, which the kidneys continuously monitor. This general role of the kidneys involves a co...

Urinary System Urinary system Urinary system Urinary system The urinary system consists of : The paired kidneys Ureters Bladder The urethra. This system’s primary role is to ensure optimal properties of the blood, which the kidneys continuously monitor. This general role of the kidneys involves a complex combination of renal functions: Regulation of the balance between water and electrolytes (inorganic ions) and the acid-base balance; Excretion of metabolic wastes along with excess water and electrolytes in urine, the kidneys’ excretory product which passes through the ureters for temporary storage in the bladder before its release to the exterior by the urethra; Urinary system Excretion of many bioactive substances, including many drugs; Secretion of renin, a protease important for regulation of blood pressure by cleaving circulating angiotensinogen to angiotensin I Secretion of erythropoietin, a glycoprotein growth factor that stimulates erythrocyte production in red marrow when the blood O2 level is low; Conversion of the steroid prohormone vitamin D, initially produced in the skin, to the active form (1,25-dihydroxyvitamin D3 or calcitriol); and Gluconeogenesis during starvation or periods of prolonged fasting, making glucose from amino acids to supplement this process in the liver. Urinary system The Urinary System Kidneys Ureters Urinary bladder & urethra Urine flows from each kidney, down its ureter to the bladder and to the outside via the urethra Filter the blood and return most of water and solutes to the bloodstream Urinary system Overview of kidney functions Regulation of blood ionic composition 𝑁𝑎+ , 𝑘 + , 𝐶𝑎+2 , 𝐶𝑙 − and phosphate ions Regulation of blood pH, osmolarity & glucose Regulation of blood volume conserving or eliminating water Regulation of blood pressure Secreting the enzyme renin Adjusting renal resistance Release of erythropoietin & calcitriol Excretion of wastes & foreign substances Urinary system External Anatomy of Kidney Paired kidney-bean-shaped organ 4-5 in long, 2-3 in wide,1 in thick Found just above the waist between the peritoneum & posterior wall of abdomen , retroperitoneal along with adrenal glands & ureters Protected by 11𝑡ℎ & 12𝑡ℎ ribs with right kidney lower Urinary system Kidney Main organ of the excretory system Kidney is built of billions of little tubes called the nephrons. At the beginning of each nephron, a web of capillaries releases much water and other molecules into the nephron. The urine is collected in the urinary bladder and, when it fills up, it is excreted via urethra into the outside environment. Urinary system Kidney's Internal Structure Cortex -- the outer part of the kidney; Medulla -- the inner portion of the kidney; Pyramids -- the triangular-shaped divisions of the medulla of the kidney; Papilla -- narrow, innermost tip of the pyramid; Pelvis -- the kidney or renal pelvis is an extension of the upper end of the ureter (the tube that drains urine into the bladder); Calyx -- each calyx is a division of the renal pelvis; opening into each calyx is the papilla of a pyramid. Urinary system Nephron Tubules in which urine is formed (functional unit of the kidney) Form the most abundant tissue of renal parenchyma Consist of 5 parts : Renal corpuscle Proximal convoluted tubule Medullary loop (loop of Henle) Distal convoluted tubule Collecting duct Urinary system Nephron Basic structural and functional unit of the kidney. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. Urinary system Nephron Urinary system Nephron A nephron eliminates wastes from the body, regulates blood volume and blood pressure, controls levels of electrolytes and metabolites, and regulates blood pH. Its functions are vital to life and are regulated by the endocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone. Microscopic units of a kidney, have 2 main parts : Renal corpuscle (Bowman's capsule with glomerulus) Renal tubule. Urinary system Nephron Efferent arterioles enter while the afferent arterioles leave the glomerulus at vascular pole while ultrafiltrate leave corpuscle at renal pole Capillaries forming glomerulus are fenestrated and their endothelium rests on a thick basal lamina Bowman’s capsule comprise of inner visceral and outer parietal layers and Bowmans space in btw the layers Parietal layer is formed by simple squamous cells while visceral is formed by podocytes, whose foot processes (pedicels) contact glomerular blood capillaries The connective tissue stroma of the glomerulus is constituted by mesangial cells, which support the glomerular capillaries Urinary system Renal corpuscle Glomeruli surrounded by Bowman's capsules. Bowman's capsule -- the cup-shaped top of a nephron. It is the sack-like Bowmans's capsule that surrounds the glomerulus. Glomerulus -- a network of blood capillaries tucked into Bowman's capsule. Urinary system Juxtaglomerular apparatus Formed where the DCT contacts the afferent arteriole of parent r. corpuscle Constituted by 3 cell types : Macular densa cells of DCT (t. cells that become columnar & closely packed) Juxtaglomerular cells of afferent arteriole (smooth muscle cells of tunica media that become spherical and contain renin granules) Extraglomerular mesangial cells (similar to those within glomerulus and surrounded by thick BL) Produce renin which converts angiotensinogen to angiotensin, (a vasoconstrictor which raises blood pressure thus flow of ultrafiltrate) Urinary system Juxtaglomerular apparatus The juxtaglomerular apparatus is a microscopic structure in the kidney, which regulates the function of each nephron. There are three cellular components of the apparatus which are the : Macula densa, Extraglomerular mesangial cells, Juxtaglomerular cells (also known as granular cells). Urinary system Juxtaglomerular apparatus As mentioned above, the distal tubule contacts the glomerulus forming a specialized section of tubular epithelium, the macula densa. At the point of contact with the glomerulus, the distal tubule is always in close contact with the endothelial cells of the efferent and afferent arterioles of the glomerulus. Other parts of the juxtaglomerular apparatus are extraglomerular mesangial cells (or lacis cell) and the juxtaglomerular cells surrounding the afferent arteriole (modified smooth muscle cells), which produce and secrete renin. Urinary system Juxtaglomerular apparatus Renin activates angiotensinogen, a precursor found in the bloodstream, leading to the formation of angiotensin I, which is converted to angiotensin II. Angiotensin II is the most potent vasoconstrictor known. It also stimulates the secretion of aldosterone. Different theories exist that try to explain the interactions between the cells that eventually lead to the release of renin. One of them, the baroreceptor theory, assumes that the juxtaglomerular cells function as stretch receptors (high blood pressure would inhibit the release of renin). Another theory, the macula densa theory, claims that the secretion of renin is regulated by the composition of the fluid in the distal tubule and/or the afferent arteriole (low sodium would increase in the release of renin). Urinary system Urinary system Renal tubule Proximal convoluted tubule -- the first segment of a renal tubule, called proximal because it lies nearest the tubule's origin from Bowman's capsule, and convoluted because it has several bends in it. Loop of Henle -- the extension of the proximal tubule; observe that the loop of Henle consists of a straight descending (directed downward) limb, a loop, and a straight ascending limb (directed upwards). Urinary system Proximal convoluted tubule Reabsorption of water, nutrients and solids (obligatory) Lined by simple cuboidal epithithelium resting on a thin b. lamina Tubule cells have microvilli on their luminal surfaces (typical brush border) Tubule cells appear striated due to numerous basal infoldings & plenty of mitochondria Urinary system Distal convoluted tubule The part of the tubule distal to the ascending limb of Henle. It is the extension of the ascending limb of Henle. Collecting tubule A straight (not convoluted) part of a renal tubule; distal tubules of several nephrons join to form a single collecting tubule Urinary system Histology : Bowman's capsule Cells of the outer or parietal layer of Bowman's capsule form a simple squamous epithelium. Cells of the inner layer, podocytes in the visceral layer, are extremely complex in shape. Small foot-like processes, pedicles, of their cytoplasm form a fenestrated epithelium around the fenestrated capillaries of the glomerulus. The openings between the pedicles are called filtration slits. They are spanned by a thin membrane, the filtration slit membrane. Between the podocytes and the endothelial cells of the capillaries a comparatively thick basal lamina, which can be subdivided into an outer lamina externa, a middle lamina densa and an inner lamina interna. Urinary system Histology : Bowman's capsule The basal lamina and the slit membranes form the glomerular filtration barrier, which prevents some large molecules from entering the capsular space between the outer and inner epithelial layers of Bowman's capsule. Mesangial cells in the glomerulus form the connective tissue that gives structural support to podocytes and vessels. Urinary system Histology : proximal tubule Walls - low columnar epithelium. The eosinophilic cells of the epithelium have a wide brush border and are active in endocytosis. Histology : Loop of Henle It is 'U' shaped and has descending and ascending segments. Thin descending segment has flattened epithelium( squamous). It is permeable to water but not solutes. Urinary system Histology : Distal convoluted tubule Straight part of the DCT is formed by the low cuboidal cells without a brush border. The diameter of the tubule gradually expands to about 35 microns. Convoluted part and comes in contact with the Glomerulus forming the Macula Densa. Urinary system Histology : Renal Tubule & Collecting Duct Proximal convoluted tubule Simple cuboidal with brush border of microvilli that increase surface area Descending limb of loop of Henle Simple squamous Ascending limb of loop of Henle Simple cuboidal to low columnar Forms juxtaglomerular apparatus where makes contact with afferent arteriole Macula densa is special part of ascending limb Distal convoluted & collecting ducts Simple cuboidal composed of principal & intercalated cells which have microvilli Urinary system Collecting tubule Drain urine from nephron to renal pelvis Lie on medullary ray within cortex Progressively increase in diameter towards medullar In inner medullar, CD from different renal lobes unite to form large papillary ducts, which open into renal pelvis Urinary system Collecting tubule Drain urine from nephron to r. pelvis Progressively increase in diameter towards medullar In inner medullar, unite with other CDs to form large papillary ducts, which open into renal pelvis CD are lined by epithelium that has 2 cell types : Collecting duct cells Cuboidal in cortical part, Columnar in medullary Intercalated /dark cells Resemble those of DCT but Bulge into lumen of the CD Both cell types rest on a thin BM and lack basal infoldings Permeability of CD to water and ions is regulated by ADH Urinary system Filtration Membrane Stops all cells and platelets Stops large plasma proteins Stops medium-sized proteins, not small ones Urinary system Anatomy of Ureters 10 to 12 in long Varies in diameter from 1-10 mm Extends from renal pelvis to bladder Retroperitoneal Enters posterior wall of bladder Physiological valve only Bladder wall compresses arterial opening as it expands during filling Flow results from peristalsis, gravity & hydrostatic pressure Urinary system Histology of Ureters 3 layers in wall : Mucosa Is transitional epithelium & lamina propria Since organ must inflate & deflate Mucus prevents the cells from being contacted by urine Muscularis Inner longitudinal & outer circular smooth muscle layer Distal 1/3 has additional longitudinal layer Peristalsis contributes to urine flow Adventitia Layer of loose connective tissue anchors in place contains lymphatics and blood vessels to supply ureter Urinary system Histology of Ureters The wall of the ureter is made 3 layers. From inside outwards they are : Mucosa- which is made up of epithelium & lamina propria Muscular coat – made of smooth muscles Fibrosa – made of fibrous connective tissue Mucosa- is thrown into folds and thus gives the appearance of star shaped lumen. Urinary system Histology of Ureters Transitional epithelium. 3-5 layers thickness. Lamina propria- dense, irregular layer of fibroelastic connective tissue The epithelium is separated from the lamina propria by a basal lamina. Urinary system Histology of Ureters Conducts urine from kidney to bladder Has 3 tissue layers Tunica mucosa; lined by 5-6 cell layer of transitional epith that rests on lamina propria of loose c. tissue having bld vessels, lymphatics and with tubular mucus glands in the equidae T. muscularis; has inner and outer longitudinal and middle layer of smooth muscles T. serosa/ adventitia Urinary system Histology of Ureters Muscular layer – Upper 2/3 of the ureter is made of two layers of smooth muscle cells. Inner longitudinal and outer circular layer( in contrast to the wall of GIT which has inner circular & outer longitudinal !). Lower 1/3 of the ureter has a third outer layer of longitudinal muscles( inner longitudinal, middle circular, outer loingitudinal ). Fibrous coat – is made up of fibrous connective tissue Urinary system Urethra Female: relatively short, exits just anterior to the vagina Male: longer, divided into three sections the prostatic, membranous and spongy urethra. The prostatic urethra is enclosed in the prostate gland. The membranous urethra is a short section that penetrates the urogenital diaphragm. The spongy urethra or penile urethra extends from the membranous urethra to the external urethral orifice (meatus). Urinary system Urethra Histology: In both male and females the urethra starts out as transitional cell but quickly becomes stratified squamous in the female. The male urethra is more variable but ends up stratified squamous as well. Urinary system Urethra Its wall has 4 tissue layers Tunica mucosa; epith. transitional but changes to stratified squamous at external urethral orifice T. submucosa; has cavernous tissue spaces that are typical of erectile tissue T. muscularis; has inner and outer longi and middle layer of smooth muscles as in bladder but towards external urethral orifice, it acquires an external layer of skeletal muscle called striated urethralis muscle T. serosa/ adventitia Urinary system Histology of Urinary Bladder 3 layers in wall Mucosa : is transitional epithelium & lamina propria Since organ must inflate & deflate , mucus prevents the cells from being contacted by urine Muscularis : (known as detrusor muscle) , its 3 layers of smooth muscle Inner longitudinal, middle circular & outer longitudinal Circular smooth muscle fibers form internal urethral sphincter Circular skeletal muscle forms external urethral sphincter Adventitia : Layer of loose connective tissue anchors in place Superior surface has serosal layer (visceral peritoneum) Mucosa of transitional epithelium, Submucosa, and thick muscular layer know as the detrusor muscle Urinary system Histology of Urinary Bladder Its wall has 4 tissue layers :Tunica mucosa; lined by up to 14 cell layers of transitional epith that rests on lamina propria of loose c. tissue T. submucosa; highly vascular and rich in elastic fibers T. muscularis; has inner and outer longitudinal and middle layer of smooth muscles (dextruser muscles) T. serosa/ adventitia The longi muscles form sphincters at ureterovesicular junction to prevent backflow of urine and at neck of bladder to regulate urine emptying Urinary system Disorders of Urinary System Renal calculi Urinary tract infections Glomerular disease Renal failure Polycystic kidney disease