Urinary System Lecture Notes PDF

ANATOMY & PHYSIOLOGY II Eng Razaz Salih URINARY SYSTEM Lecture (6)  URINARY SYSTEM The urinary system is also known as the renal system or urinary tract, The urinary system consists of organs, muscles, tubes, and...

ANATOMY & PHYSIOLOGY II Eng Razaz Salih URINARY SYSTEM Lecture (6)  URINARY SYSTEM The urinary system is also known as the renal system or urinary tract, The urinary system consists of organs, muscles, tubes, and nerves that are responsible for producing, transporting, and storing urine.  Functions Of The Urinary System 1. Eliminate waste from the body, 2. Regulates blood volume 3. Regulates blood pressure, 4. Control levels of electrolytes and metabolites, 5. Regulates blood pH.  Anatomy Of Urinary Tract The urinary tract is made up of the following organs: A pair of Kidneys – forms the urine A pair of Ureters – Transports the urine A urinary Bladder – stores urine A Urethra – carries urine outside the body They filter blood and remove waste from the body in the form of urine.  THE KIDNEYS It is the major organ of urinary system It is a bean shaped organ situated in the retro peritoneal position in the superior lumbar region The right kidney present slightly lower than the left Mass of an adult kidney is 150gms It is about 12cm long and 6cm wide & 3cm thick.  Functions of Kidneys 1. Regulate the concentration of Na+, K+, Ca2+, Cl- in the blood 2. Regulation of blood pH 3. Regulation of blood volume 4. Regulation blood pressure 5. Regulation blood osmolarity 6. Production of hormones 7. Regulation blood glucose level 8. Excretion of waste and foreign substances  Structure Of The Kidney The kidney is divided into three different zones: 1. Renal Cortex: This is the outer most zone, It is light in colour and has granular appearance 2. Renal Medulla: This zone lies beneath the cortex , It is darker in colour and consist of medullary and renal pyramids 3. Renal Pelvis: It is the funnel shaped tube, Which joins the ureter at the hilum  Nephrons Nephrons is the basic structural and functional unit of the kidney It filters the waste products from the blood Reabsorbs the required nutrients into the body Excrete the remaining things in the urine Thereby it regulates the water and sodium salt concentration in the blood Types of Nephron: 1. Cortical Nephrons: renal corpuscles present near the renal cortex 2. Juxtamedullary Nephrons: Renal corpuscles present near the renal medulla  Structure of Nephrons Nephrons. Each kidney contains over a million tiny structures called nephrons, and they are responsible for forming urine, it is composed of: 1. Glomerulus: One of the main structures of a nephron, a glomerulus is a knot of capillaries. 2. Renal tubule: Another one of the main structures in a nephron is the renal tubule. 3. Bowman’s capsule: The closed end of the renal tubule is enlarged and cup-shaped and completely surrounds the glomerulus, and it is called the glomerular or Bowman’s capsule  Structure of Nephrons 4. Collecting duct: As the tubule extends from the glomerular capsule, it coils and twists before forming a hairpin loop and then again becomes coiled and twisted before entering a collecting tubule called the collecting duct, which receives urine from many nephrons. 5. Proximal convoluted tubule: This is the part of the tubule that is near to the glomerular capsule.  Glomerulus Each nephron includes a filter, called the glomerulus glomerulus is a mass of capillaries which is supplied with blood by an afferent arteries of the renal circulation. Blood pressure within the glomerulus provides the driving force for water and solutes to be filtered out of the blood and reach the Bowman’s capsule.  Glomerulus The remaining blood passes into the efferent arteriole(narrower than the afferent arteriole ) blood along with reabsorbed substances reaches the vasa recta (collecting capillaries attached tothe convoluted tubules). The vasa recta and the efferent venules coming from other nephrons combine to join the renal vein and the main blood circulation.  Bowman’s or Glomerular Capsule It is the capsule surrounds the glomerulus It is made up of: visceral inner layer : contains specialized cells called podocytes parietal outer layer: contain single layer of flat cells called simple squamous epithelium.  Renal tubule This 3cm long tubule exits the glomerular capsule A renal tubule is made up of : 1. Proximal convoluted tubule (pct) 2. Loop of Henle 3. Distal convoluted tubule 4. Collecting duct  Urine Formation Processes The kidneys filter unwanted substances from the blood and produce urine to excrete them. There are three main steps of urine formation: 1. Glomerular filtration 2. Reabsorption 3. Secretion. These processes ensure that only waste and excess water are removed from the body.  Glomerular Filtration The Glomerulus Filters Water and Other Substances from the Bloodstream As blood flows through the glomerulus, blood pressure pushes water and solutes from the capillaries into the capsule through a filtration membrane. This glomerular filtration begins the urine formation process.  Glomerular Filtration The Filtration Membrane Keeps Blood Cells and Large Proteins in the Bloodstream Inside the glomerulus, blood pressure pushes fluid from capillaries into the glomerular capsule through a specialized layer of cells. This layer, the filtration membrane, allows water and small solutes to pass but blocks blood cells and large proteins. Those components remain in the bloodstream. The filtrate (the fluid that has passed through the membrane) flows from the glomerular capsule further into the nephron.  Reabsorption Reabsorption Moves Nutrients and Water Back into the Bloodstream The glomerulus filters water and small solutes out of the bloodstream. The resulting filtrate contains waste, but also other substances the body needs: essential ions, glucose, amino acids, and smaller proteins. When the filtrate exits the glomerulus, it flows into a duct in the nephron called the renal tubule. As it moves, the needed substances and some water are reabsorbed through the tube wall into adjacent capillaries. This reabsorption of vital nutrients from the filtrate is the second step in urine creation.  Secretion The filtrate absorbed in the glomerulus flows through the renal tubule, where nutrients and water are reabsorbed into capillaries. At the same time, waste ions and hydrogen ions pass from the capillaries into the renal tubule. This process is called secretion. The secreted ions combine with the remaining filtrate and become urine. The urine flows out of the nephron tubule into a collecting duct. It passes out of the kidney through the renal pelvis, into the ureter, and down to the bladder.  URETERS Urine drains from the renal pelvis of each kidney into the ureters. The ureters are long, thin tubes made of smooth muscle. Contractions of the smooth muscle push urine down through the ureters and into the bladder. In adults, the ureters are 25–30 cm long, about the length of a 12-inch ruler.  URINARY BLADDER Urine flows through the ureters into the urinary bladder. In women, the bladder located in front of the vagina and below the uterus. In men, the bladder sits in front of the rectum and above the prostate gland. The wall of the bladder contains folds called rugae, and a layer of smooth muscle called the detrusor muscle.  URINARY BLADDER As urine fills the bladder, the rugae smooth out to accommodate the volume. The detrusor relaxes to hold the urine, then contracts for urination. An adult bladder is full at about half a liter, or about two cups.  URETHRA The urethra is a thin-walled tube that carries urine by peristalsis from the bladder to the outside of the body. Internal urethral sphincter: At the bladder-urethral junction, a thickening of the smooth muscle forms the internal urethral sphincter, an involuntary sphincter that keeps the urethra closed when the urine is not being passed. External urethral sphincter: A second sphincter, the external urethral sphincter, is fashioned by skeletal muscle as the urethra passes through the pelvic floor and is voluntarily controlled.  Female Urethra The female urethra is about 3 to 4 cm (1.5 inches) long, and its external orifice, or opening, lies anteriorly to the vaginal opening. It extends from the bladder neck to the external urethral orifice in the vestibule of the vagina.  Male Urethra Male urethra. In me, the urethra is approximately 20 cm (8 inches) long and has three named regions: a. the prostatic, b. Membranous c. spongy (penile) urethrae it opens at the tip of the penis after traveling down its length.