7- Urinary System Microanatomy- Pt 2.docx

- **Distal Convoluted Tubules (DCT)** - The DCT continues from the thick ascending segment of the loop of Henle. - The DCT is composed of a single layer of [cuboidal epithelial cells] with basal striations, and it lacks microvilli (brush border). - The...

- **Distal Convoluted Tubules (DCT)** - The DCT continues from the thick ascending segment of the loop of Henle. - The DCT is composed of a single layer of [cuboidal epithelial cells] with basal striations, and it lacks microvilli (brush border). - The DCT are only found in the cortex of the kidneys, and is the site of action for aldosterone. - The DCT contains specialized chemoreceptor cells of the macula densa (which only some cells have) - The DCT is intimately associated with the renal vasculature: juxtaglomerular apparatus. - **Collecting Ducts** - Collecting ducts connect the DCT to the renal papillae/crest, and they are not considered to be a part of the nephron. - The collecting ducts have lumen which contain primitive urine. - The collecting ducts are lined by [simple cuboidal to low columnar epithelium] which are composed of principal and intercalated cells. - **Principal cells** function to reabsorb sodium and water. - **Intercalated cells** participate in acid-base balance. - The collecting ducts are the site of action for ADH (anti-diuretic hormone) via aquaporin receptors. - **ADH (vasopressin)** is secreted by neurons in the hypothalamus, and works to reabsorb solute-free water and return it to circulation. - **Renal Papilla (Papillary Ducts)** - Papillary ducts are the terminal portion of the collecting ducts, which empty at the **area cribrosa** of the renal crest (or renal papilla). - The renal crest may be referred to as the renal papilla, based on the species of animal that is being referenced. - The **vasa recta** functions to take away water passing through collecting and papillary ducts. - **Vasculature** - There is a high blood supply (25% cardiac output) at the terminal (end) artery system. - The artery vasculature includes: renal artery, interlobular artery, arcuate artery, interlobular artery, and intralobular (arcuate) artery. - The arcuate artery is located directly between the cortex and medulla of the kidneys. - The vein vasculature include: intralobular vein, interlobular vein, and arcuate vein. - Afferent arterioles include the glomerulus (capillaries). - Efferent arterioles include the peritubular capillaries (surround tubules), and vasa recta (surround loops of Henle). - **Urinary System: General Info** - The **interstitium** is very sparse, especially in the cortex, and it works by supporting the functionality of kidney cells. - There is more interstitium in the (inner) medulla. - Interstitial cells include: fibroblasts, bone marrow-derived cells, and a unique **lipid-laden interstitial cell** (stellate-shaped) that is especially prominent in the inner medulla (which produces prostaglandin E2). - The medulla is the site of prostaglandin (E2) production. - - **Lymphatics** are found in the interstitium surrounding the intraarterial arteries. - The kidneys have efferent innervation to the smooth muscle arteries, afferent and efferent arterioles, and descending vasa recta. - Tubular organs have **4 layers (tunics/tela),** which are in the following order from deep to superficial: Tunica mucosa, tunica submucosa, tunica muscularis, tunica serosa/adventitia - Tunica mucosa, which has 3 layers: - Lamina mucosa/epithelium - Lamina propria - Lamina muscularis - Tunica submucosa - Tunica muscularis - Tunica serosa/Adventitia) - **Juxtaglomerular Apparatus** - The juxtaglomerular apparatus has 2 components: - Macula densa cells (part of DCT wall) are (sodium) chemoreceptors that sense sodium concentrations in filtrate. - **Juxtaglomerular cells** are modified smooth muscle cells, which are of (mainly) afferent and slightly efferent arteriole. - Juxtaglomerular cells (of afferent and efferent arterioles) detect variations in blood pressure ([baroreceptors]) and [secrete renin] into vessel lumen - Renin is secreted in response to low sodium concentrations in filtrate, and in response to low blood pressure. - **Cause and Effect** - If there is a decreased blood pressure at the afferent arterioles, the juxtaglomerular cells will release Renin. - If there is decreased sodium levels in the distal convoluted tubules, the Macula Densa will become stimulated. - Once the **Macula Densa** is stimulated, the juxtaglomerular cells will release Renin, which will increase the blood pressure. - **Renin** increase blood pressure by converting angiotensinogen into angiotensin 1 (in the liver). Then Angiotensin 1 is converted to Angiotensin 2 (in the lungs and kidneys). Then Angiotensin 2 is converted to Aldosterone (in the zona glomerulus of the adrenal gland). **Aldosterone** works to increase sodium and water retention at the DCT, resulting in increased blood pressure. - If there is increased sympathetic tone, the juxtaglomerular cells will release Renin. - **Ureters** - Ureters function to convey urine form the renal pelvis to the bladder. - The **tunica mucosa** is composed of urothelium (transitional epithelium) which are epithelial cells that flatten when stretched. - The **tunica submucosa** is composed of lamina propria which lacks a lamina muscularis in the Ureters. - The **tunica muscularis** is composed of 3 layers of smooth muscle, an outer and inner longitudinal, middle circular layer, and autonomic innervation for peristalsis. - The ureters also contain the tunica adventitia (outer most) layer. - **Urinary Bladder** - The urinary bladder is essentially an expended ureter that functions to store urine. - The urinary bladder is composed of the all 4 tunics. - The **tunica mucosa** is composed of urothelium, and it has the lamina present with lamina muscularis (as thin incomplete bands of smooth muscle, except in cats). - The urinary bladder has the tunica submucosa layer directly above the tunica mucosa layer. - The **tunica muscularis** is above the tunica submucosa layer, and it has 3 layers of an inner and outer longitudinal layers, and middle circular layer. - The smooth muscle makes up the detrusor muscle. - The skeletal muscle makes up the sphincter near the urethra. - The urinary bladder has the tunica serosa/adventitia layer directly above the tunica muscularis. - Horses have a urinary bladder with **glands**, which causes them to secrete cloudy, white urine. - **Urethra** - The urethra is similar to the ureters and urinary bladder, in structure. - The urethra has urothelium proximally, and stratified squamous epithelium distally. - The urethra has accessory sex glands, and mucous glands. - The mucous glands are diffuse in ruminant, boar, and cats. - In males, they have the following urethral features: - Vascular stratum (corpus spongiosum) - Tunica muscularis/urethral sphincter which has smooth muscle proximally to the bladder, and skeletal muscle distal to the bladder. - In females, the urethra is shorter than it is in males. - The urethra is lined initially with transitional epithelium (urothelial), and then it is lined with stratified squamous epithelium (near the external urethral orifice). - **Renal Development (Embryology)** - In embryology, the [kidneys] develop from the intermediate **mesoderm**. - The **pronephros** [regresses] within mammals. - The **mesonephros** will: - Form the [nephrons] that secrete fluid into amnion early in development, and regresses later. - Form the [mesonephric duct (wolffian duct),] which is retained in males, and form the epididymis, vas deferens, and seminal vesicles. - The **metanephros** plays the following roles in renal development: - [Ureteric bud] formation, which is the outgrowth of the mesonephric duct - [Collecting tubule] formation, bifurcation (leading to lobular architecture), and the beginning of nephron development - The metanephros duct becomes the [ureter] - In embryology, the [urinary bladder and urethra] are derived from the **endoderm**.