Physiology

Urinary System : Dr Mustafa

1. Kidney’s Function Filter 180 liters of blood daily, allowing excretion of metabolic wastes, foreign chemicals and excess ions to leave the body in urine Regulation of water and electrolyte balances Regulation of arterial pressure Regulation of acid-base balance Secretion, metabolism, and excretion of hormones Gluconeogenesis

2. The urinary system compose of paired kidneys and ureters, the urinary bladder and the urethra Urine is produced in the kidneys Paired ureters – transport urine from the kidneys to the bladder Urinary bladder – provides a temporary storage reservoir for urine Urethra – transports urine from the bladder out of the body Physiologic anatomy of the kidneys

3. The two kidneys lie on the posterior wall of the abdomen, outside the peritoneal cavity. The medial side of each kidney contains an indented region called the hilum through which pass the renal artery and vein, lymphatics, nerve supply, and ureter, which carries the final urine from the kidney to the bladder. The kidney is surrounded by a tough, fibrous capsule that protects its delicate inner structures. Adrenal gland lying on top of each kidney Physiologic anatomy of the kidneys

4. Two regions, the outer cortex and inner medulla The medulla divided into multiple cone-shaped masses of tissue called renal pyramids The pyramid terminates in the papilla, which projects into the space of renel pelvis, a funnel shaped continuation of the upper end of the ureter Physiologic anatomy of the kidneys

5. Renal blood supply Section of the human kidney showing the major vessels that supply the blood flow to the kidney and schematic of the microcirculation of each nephron. Aorta Renal a. Segmental a. Interlobar a. Arcuate a. Interlobular a. Afferent arteriole Glomerulus Efferent arteriole Peritubular Capillaries Vasa recta Interlobular v. Arcuate v. Interlobar v. Renal v. Inferior vena cava

6. The Nephron Is the Functional Unit of the Kidney Each kidney in the human contains about 1 million nephrons, each capable of forming urine. The kidney cannot regenerate new nephrons. Each nephron contains (1) Renal corpuscle which blood plasma is filtered and (2) a long renal tubule in which the filtered fluid is converted into urine on its way to the pelvis of the kidney

7. The Nephron Is the Functional Unit of the Kidney The renal corpuscle consist of glomerulus and glomerular (Bowman’s ) capsule. Fluid filtered from the glomerular capillaries flows into Bowman's capsule Renal tubule divided into the proximal tubule, loop of Henle, distal tubule and collecting ducts Descending segment of the loop of Henle and the ascending limb The wall in the descending and lower end of the ascending limb called thin segment of loop of Henle At the end of the thick ascending limb is a short segment called macula densa Then fluid enters distal tubule, followed by cortical collecting tubule, which lead to cortical collecting duct, medullary collecting ducts The collecting ducts merge to form progressively larger ducts that empty into the renal pelvis

8. Regional differences in nephron structure: Cortical and Juxtamedullary nephrons Two types of nephrons: cortical nephrons and Juxtamedullary nephrons Cortical nephrons, glomeruli located in the outer cortex , they have short loop of Henle, penetrate only a short distance into the medulla Cortical nephrons is surrounded by peritubular capillaries Juxtamedullary nephrons, glomeruli that lie deep in the renal cortex near the medulla, these have long loops of Henle that dip deeply into the medulla Juxtamedullary nephrons is divided into specialized peritubular capillaries called vasa recta

9. Capillary Beds of the Nephron Every nephron has two capillary beds Glomerulus Peritubular capillaries Each glomerulus is: Fed by an afferent arteriole Drained by an efferent arteriole

10. Cellular features of renal corpuscle Wrapped around the capillaries of the glomerulus is cells called podocytes Capsular space: is the region within the glomerular capsule that collect the filtrate being force out of the blood The endothelial contain fenestration, which allows passage of water and ions and small molecules Basement membrane encloses the capillaries endothelium Surrounding the basement membrane is long footlike processes podocyte The foot processes are separated by gaps called slit pores through which glomerular filtrate moves

11. Filtration Membrane

12. The fenestrated capillary endothelium, basement membrane, and podocyte makes up the filtration membrane The filtration membrane permits the escape of small molecules while preventing large molecules (proteins) from leaving the bloodstream and passing through into the capsular space

13. The cuboidal epithelial cells of proximal tubule have extensive microvilli in their luminal surfaces The cells contain mitochondria that provide ATP for active transport CELLS OF THE Proximal Tubule

14. Cells in the thin segment of loop of Henle The cells in the thin descending segment of the loop of Henle are simple squamous epithelial cells Lack of brush borders Permeable to water not to solute The thin ascending limb is permeable to solute not to water

15. Cells of the thick ascending loop of Henle and distal tubule Compose of cuboidal epithelium cells Fewer and smaller microvilli compared to proximal tubule Ascending limb highly permeable to solute, highly permeable to solute not to water Distal tubule more permeable to water than ascending limb Distal tubule is the end of the nephron

16. Where the cells of afferent arterioles and the ascending thick loop of Henle are in contact with each other they form juxtaglomerular apparatus Macula densa, specialized cells. They are part of the juxtaglomerular apparatus and appear to be sensitive to the content and rate of the flow of the filtrate Juxtaglomerular cells, smooth muscle cells of the afferent arteriole. Play role in GFR and blood pressure regulation by producing renin The Juxtaglomerular Apparatus

17. Cells of the cortical collecting ducts Two types of cells: Principal cells: Fewer microvilli. They are respond to aldosterone and ADH hormone that regulate their permeability to water and solute Principal cells permeability to water and solutes is regulated by hormones Intercalated cells: Involve in acid base balance Secretion of H + for acid base balance

18. Cells of the medullary collecting ducts Composed mainly of principal cells Permeability of water and urea is hormonally regulated

19. Flow of fluid from the glomerular filtrate to the urine Glomerular capsule proximal tubule Loop of Henle distal tubule collecting duct papillary duct minor calyx major calyx renal pelvis ureter urinary bladder urethra