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Urinary System : Dr Mustafa
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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
• 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
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
• 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
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.
AortaRenal 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
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
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
Regional differences in nephron structure: Cortical and Juxtamedullary nephronsTwo 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
Capillary Beds of the Nephron
Every nephron has two capillary bedsGlomerulus Peritubular capillaries
Each glomerulus is: Fed by an afferent arteriole Drained by an efferent arteriole
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
Filtration Membrane
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
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
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
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
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
Cells of the cortical collecting ducts
Two types of cells:1. 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
2. Intercalated cells: Involve in acid base balance
Secretion of H+ for acid base balance
Cells of the medullary collecting ducts
Composed mainly of principal cells Permeability of water and urea is
hormonally regulated
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