Lecture 11 Anatomy of Urinary System PDF

Alayen University Anesthesia Department Lecture 11 Anatomy of Urinary System By Dr. Ahmed Adil FUNCTIONS OF THE URINARY SYSTEM The urinary system is the major excretory system of the body. The ur...

Alayen University Anesthesia Department Lecture 11 Anatomy of Urinary System By Dr. Ahmed Adil FUNCTIONS OF THE URINARY SYSTEM The urinary system is the major excretory system of the body. The urinary system consists of two kidneys, the primary excretory organs. Each kidney’s waste products are carried by a ureter to a single urinary bladder. The waste is emptied from the urinary bladder by the urethra. The kidneys each filter a large volume of blood. Wastes from the blood are collected and form urine. Urine consists of (1) excess water, (2) excess ions, (3) metabolic wastes, including the protein by-product urea, and (4) toxic substances. The kidneys can suffer extensive damage and still maintain homeostasis. As long as about one-third of one kidney remains functional, survival is possible. The kidney functions include: 1. Excretion. The kidneys remove waste products from the blood. Most of the waste products are metabolic by-products of cell metabolism. 2. Regulation of blood volume and pressure. The kidneys play a major role in controlling the extracellular fluid volume in the body. The kidneys can produce either a large volume of dilute urine or a small volume of concentrated urine, depending on the hydration level of the body. 3. Regulation of blood solute concentrations. The kidneys help regulate the concentration of the major molecules and ions, such as glucose, Na+, Cl−, K+, Ca2+, HCO3−, and HPO42−.  4. Regulation of extracellular fluid pH. The kidneys excrete variable amounts of H+ to help regulate extracellular fluid pH. 5. Regulation of red blood cell synthesis. The kidneys secrete a hormone, erythropoietin, which regulates the synthesis of red blood cells in bone marrow. 6. Regulation of vitamin D synthesis. The kidneys play an important role in controlling blood levels of Ca2+ by regulating the synthesis of vitamin D. ANATOMY OF THE KIDNEYS Location and External Anatomy of the Kidneys The kidneys are behind the peritoneum and located on each side of the vertebral column. They are bean-shaped organs, each about the size of a tightly clenched fist. A layer of connective tissue called the renal capsule surrounds each kidney. Around the renal capsule is a thick layer of adipose tissue, which protects the kidney from mechanical shock. On the medial side of each kidney is the hilum, where the renal artery and nerves enter and where the renal vein, ureter, and lymphatic vessels exit the kidney. The hilum opens into a cavity called the renal sinus, which contains blood vessels, part of the system for collecting urine. Internal Anatomy of the Kidneys The kidneys are organized into two major regions: (1) an outer cortex and (2) an inner medulla that surrounds the renal sinus. The cortex is the location for the blood-filtering structures of the kidney. The medulla is composed of many cone-shaped structures called renal pyramids, whose bases project into the cortex. The renal pyramids are a collection of tubes and ducts that transport fluid throughout the kidney and modify it into urine. Once urine is formed, ducts in the renal pyramids transport it toward the renal sinus. The tips of the pyramids, the renal papillae, point toward the renal sinus. In the renal sinus, another set of tubes collects the urine for movement to the urinary bladder. When urine leaves a renal papilla, it empties into a small, funnel- shaped chamber surrounding the tip of the papilla called a calyx. Urine from several calyces is emptied into a single, enlarged, funnel-shaped chamber called the renal pelvis. At the hilum, it narrows significantly, forming the small-diameter tube called the ureter. Urine moves from the renal pelvis into the ureter for transport to the urinary bladder. Structure of a Nephron The nephron (Greek for kidney) is the histological and functional unit of the kidney. It consists of specialized structures including small tubes that are called tubules. There are approximately 1.3 million nephrons distributed throughout the cortex and medulla of each kidney. The four regions of a nephron are: (1) a renal corpuscle, (2) a proximal convoluted tubule, (3) a loop of Henle, and (4) a distal convoluted tubule. Each portion of a nephron plays a different role in urine production. The renal corpuscle filters the blood, the proximal convoluted tubule returns filtered substances to the blood, the loop of Henle helps conserve water and solutes, and the distal convoluted tubule rids the blood of additional wastes.