Urinary System PDF

# Urinary System ## Overview - Kidneys maintain purity and chemical constancy of blood. - Major excretory organs. - Primary function: to filter waste from blood and excrete it as urine. - Organs of the urinary system include: - Kidneys - Ureters - Urinary bladder - Urethra ##...

# Urinary System ## Overview - Kidneys maintain purity and chemical constancy of blood. - Major excretory organs. - Primary function: to filter waste from blood and excrete it as urine. - Organs of the urinary system include: - Kidneys - Ureters - Urinary bladder - Urethra ## Kidneys ### Location and External Anatomy - Kidneys lie behind parietal peritoneum in the superior lumbar region of the posterior abdominal wall: - Superiorly to the 11th or 12th thoracic vertebrae. - Inferiorly to the 3rd lumbar vertebrae. - Right kidney is slightly lower than the left because of its placement by the liver. - Lateral surface is convex. - Medial surface is concave. - Renal hilum: where vessels, ureters, and nerves enter and leave the kidney. - Fibrous capsule: lies directly on kidney's surface, helps maintain shape and forms a barrier to inhibit the spread of infection. ### Internal Anatomy - There are two distinct regions of the kidney: - Renal cortex: superficial region, lighter in color and granular appearance. - Renal medulla: deep to the cortex. - Renal medulla is made up of cone-shaped masses called renal pyramids. - Renal columns are inward extensions of the renal cortex that separates the pyramids. - Renal Pelvis: funnel-shaped tube that is the expanded part of the ureter. - Branching from the renal pelvis are the major calices, which divide into minor calices. - Calices collect urine draining from the papillae and empty it into the renal pelvis. - From the renal pelvis, urine travels down the ureter and into the bladder. ### Vasculature and Nerve Supply - Kidneys have a rich blood supply. - Renal arteries: blood vessels that supply oxygenated blood to kidneys - Origin: branches of abdominal aorta (near L1 & L2 vertebrae). - Renal arteries divide into smaller branches: - Segmental arteries (5) enter the hilum. - Interlobar arteries: Lie in the renal columns between the renal pyramids. - Arcuate arteries: arch over bases of renal pyramids. - Interlobular arteries (cortical radiate arteries) are located within the renal cortex - Glomerular arterioles (afferent arterioles): supply blood to the glomerulus. - Veins work in reverse and exit through the hilum. - Nerve supply is provided by the renal plexus. ### Microscopic Anatomy - The main structural and functional unit of the kidney is the nephron. ### Urine Production - There are three interacting mechanisms that produce urine: - Filtration: "cleaning the blood" - Acts as a strainer that separates smaller wastes and useful substances from the blood so it can enter the nephron. - Reabsorption: taking back what the body needs - Your body 'reclaims' useful substances (nutrients and water) from filtered fluid and sends it back to the bloodstream. - Secretion: getting rid of extra waste - Extra waste products/ unwanted substances are secreted from the blood into the tubules to be excreted as urine ## Nephron Structure - Renal Corpuscle: where filtration occurs and is strictly in the cortex. - Glomerulus: tiny ball of capillaries inside a capsule where blood filtration starts. - Bowman's capsule: surrounds the glomerulus, collects filtered blood plasma (filtrate), acts like a strainer. - Glomerulus is covered with podocytes. - Proximal convoluted tubule (PCT): "reabsorbing" - First part after Bowman's capsule. - Reabsorbs a lot of water, glucose, amino acids, and important salts that were filtered out of the blood and returned to blood stream. - Loop of Henle: "contracting" part - U-shaped tube that dips down into the medulla to maintain balance. - Key role in reabsorbing water and sodium to maintain balance. - Descending limb: allows water to be reabsorbed. - Ascending limb: actively transports sodium back into the bloodstream. - Distal convoluted tubule (DCT): "fine-tuning" part - No water is reabsorbed here. - Kidneys adjust the balance of sodium, potassium, and pH of blood. - Can reabsorb water if the body needs it. ## Collecting Duct: "final collection" part - Receives fluid from multiple nephrons and carries it towards the center of the kidneys and drains into renal pelvis. - Depending on what the body needs, water and salt reabsorption continues. - Antidiuretic hormone (ADH) helps regulate how much water is reabsorbed here. ## Classes of Nephrons - Cortical nephrons: 85% of all nephrons, located almost entirely in the cortex. - Involved in basic filtration and reabsorption. - Shorter loops of Henle. - Juxtamedullary nephrons: 15% of all nephrons, cortex-medulla junction. - Specialized for concentration of urine. - Longer loops of Henle for water conservation. ## Blood Vessels - Peritubular capillaries: rise from efferent arterioles. - Allow for reabsorption and secretion. - Vasa recta: (in juxtamedullary nephrons) help concentrate urine. - Juxtaglomerular complex: regulation of blood pressure. ## Ureters ### Gross Anatomy - Ureters: slender tubes that carry urine from the kidneys to the bladder. - Oblique entry prevents backflow. ### Microscopic Anatomy - Has three basic layers: - Mucosa: transitional epithelium that stretches when ureters fill with urine. - Muscularis: middle layer. - Adventitia: external layer of connective tissue. ## Urinary Bladder ### Gross Anatomy - Urinary bladder: collapsible, muscular sac that stores and expels urine. - Inferior to peritoneal cavity on pelvic floor. - When full, bladder appears spherical and expands into abdominal cavity. - Empty bladder looks like an upside-down pyramid. - Posterolateral angles receive ureters. ## Urethra - Urethra: thin-walled tube that drains urine from the bladder and expels it from the body. - Consists of smooth muscle and an inner mucosa. - Internal urethral sphincter: involuntary sphincter of smooth muscle that keeps urethra closed when you aren't peeing and prevents leakage. - External urethral sphincter: voluntary constrictor of urethra, skeletal muscle used to inhibit urination until the right time. ## Micturition - Micturition is the act of emptying the bladder (peeing). - Contraction of bladder's detrusor muscle. - Controlled by the brain - Involves autonomic and somatic pathways. - As bladder fills it activates stretch receptors. - Lower pons acts as an on/off switch.