Urinary System Study Guide PDF

Urinary System- Study Guide Structures of Urinary System: ● Kidneys: filter blood and convert the filtrate into urine ● Ureters: urine is transported by the ureters from the kidneys to the urinary bladder ● Urinary bladder: an expandable, muscular sac that stores as much as 1 liter of urine ● Ureth...

Urinary System- Study Guide Structures of Urinary System: ● Kidneys: filter blood and convert the filtrate into urine ● Ureters: urine is transported by the ureters from the kidneys to the urinary bladder ● Urinary bladder: an expandable, muscular sac that stores as much as 1 liter of urine ● Urethra: urine eliminated through urethra Functions: ● Elimination of metabolic wastes ● Regulation of ion levels ION= Elecrolytes * E.g., Na+, K+, Ca2+ ● Regulation of acid-base balance (Blood PH) * Alters levels of H+ and HCO3 ● Regulation of blood pressure ● Elimination of biologically active molecules * hormones, drugs Location of Kidneys the left kidney: in between the level of the T12 and L3 vertebrae the right kidney: about 2 centimeters inferior to the left kidney to accommodate the large size of the liver Concave medial border, hilum ● Where vessels, nerves, ureter connect to kidney Anterior Posterior 4 tissue layers that surround and support the kidneys ● Fibrous capsule: GIVES IT ITS SHAPE ○ Directly adhered to external surface of kidney ○ Dense irregular CT ○ Maintains kidney’s shape ○ Protects it from trauma ○ Prevents pathogen penetration ● Perinephric fat: CUSHION & SUPPORT ○ Adipose Connective Tissue external to fibrous capsule ○ Cushions and supports kidney ● Renal fascia: HELPS CONNECT KIDNEY TO WALL ○ External to perinephric fat ○ Dense irregular CT ○ Anchors kidney to ○ surrounding structures ● Paranephric fat: CUSHION ○ Outermost layer surrounding kidney ○ Adipose CT ○ Anchors kidney to surrounding structures Regions and components of kidney: Renal Cortex: outermost region of the kidney. Renal Columns: project into the medulla and subdivide it into renal pyramids.- Renal Pyramids: striped structures within the medulla. Medulla: inner portion of the kidney.Corticomedullary Junction: where the outer edge of the medulla meets the cortex. Renal Papilla: located at the narrow/inner part of the renal pyramids. Each funnel-shaped minor calyx is associated with a pyramid and merge into larger major calyx which then merges to form the renal pelvis which then drains into the collecting duct. The Autonomic innervation of the kidney ● ● Sympathetic nerves ○ extend from the T10-T12 segments of the spinal cord to the blood vessels of the kidney. ○ These nerves innervate the afferent and efferent arterioles, which are responsible for regulating blood flow in and out of the glomerulus ○ Decreases urine production Parasympathe4c nerves from CN X (Vagus) ○ Specific effects not known ○ extends to the juxtaglomerular apparatus, which is involved in regulating renal blood pressure and fluid balance ○ This sympathetic input plays a role in modulating renal vascular resistance and adjusting glomerular filtration rate based on physiological needs. "Sympathetic nerves originating from the T10-T12 segments of the spinal cord provide innervation to the blood vessels of the kidney, including the afferent and efferent arterioles, as well as the juxtaglomerular apparatus" Renal Corpuscle and its components ● ● The renal corpuscle is located in the renal cortex and consists of the glomerulus and the glomerular capsule. The glomerulus is a network of capillary loops where blood enters through the afferent arteriole and exits through the efferent arteriole. The glomerular capsule has two layers: ● ● a visceral layer that covers the glomerular capillaries directly, and an external parietal layer. Between the two layers of the glomerular capsule is a capsular space that receives filtrate. Components of a Renal Tubule Proximal convoluted tubule (PCT): ● First region of the renal tubule ● Composed of simple cuboidal epithelium with tall microvilli ● Microvilli increase reabsorption capacity Nephron loop: ● Begins at the sharp end of the PCT ● Includes a descending limb and ascending limb ● Portions classified as thick or thin based on epithelium lining (thick, thin, thin, thick) Distal convoluted tubule (DCT): ● Starts at the end of the nephron loop and extends to the collecting duct ● Made up of simple cuboidal epithelium ● Contains much shorter microvilli Types of nephrons and the functional difference between them The cortical nephrons are located with their corpuscles near the top edge of the cortex and have a short loop that barely touches the medulla. 85% of nephrons are cortical. The juxtamedullary nephrons corpuscle lies near where the renal medulla and renal cortex meet. Its loop extends deep into the renal medulla. These nephrons are important in establishing salt concentration gradient in ISF, which allows regulation of urine concentration by ADH. Collecting tubules & Collecting ducts ● ● ● ● Each kidney contains numerous collecting tubules and larger collecting ducts. Tubules and ducts project towards the renal papilla. Collecting ducts empty into papillary ducts within the renal papilla. Epithelial cells in tubules start as cuboidal-shaped and then transition to columnar shape in the collecting ducts. Functions of the two types of specialized epithelial cells found within collecting tubules and ducts principal cells: have cellular receptors to bind both aldosterone (released from the adrenal cortex) and antidiuretic hormone (released from the posterior pituitary) intercalated cells (types A and B): specialized epithelial cells that help regulate urine pH and blood pH Location & structure of the Juxtaglomerular Apparatus ● The juxtaglomerular apparatus is where the DCT (Distal convoluted tubule) of a nephron makes contact with afferent arteriole of the same nephron, this is important in regulating filtration formation and systemic BP. ● Contract when stimulated by stretch or sympathetic stimulation Synthesize, store and release Renin The granular cells are modified smooth muscle cells of the afferent arteriole located near the entrance to renal corpuscle. One function is to contract when stimulated by stretch or sympathetic division. They also synthesize, stores and releases renin enzyme which is required to make angiotensin I. The macula densa cells are modified cells in the DCT where they make contact with the granular cells only on the tubular side next to the afferent arteriole, and they are narrow and tall. These cells detect changes in NaCl concentration of fluid in the lumen of DCT. They also signal granular cells to release the renin. Blood Supply to the Kidneys (Arteries that supply the kidney, in sequence from largest to smallest) Renal artery segmental arteries interlobar arteries arcuate arteries interlobular arteries afferent arterioles glomerulus efferent arterioles peritubular capillaries/vasa recta interlobular veins arcuate veins interlobar veins renal vein. Veins through which blood leaves the kidney in sequence from smallest to largest. cortical radiate veins arcuate veins interlobar veins renal vein There are three types of capillaries in the kidneys, namely afferent arterioles, efferent arterioles, and vasa recta. The afferent arteriole delivers blood to the glomerulus, and that blood is then filtered into the glomerular capsule. Through the efferent arteriole the blood leaves the glomerulus, and flowing through the efferent arteriole it is no longer filtered. From the efferent arterioles, vasa recta are separate, and these are the capillaries through which blood flows. As blood flows through the vasa recta, there is an exchange of nutrients and gases. Capillary beds through which blood must pass in the kidney. Blood passes through afferent arteriole to glomerulus. After filtration, blood enters the second capillary bed of peritubular capillaries or vasa recta via the efferent arteriole. Peritubular capillaries are intertwined around proximal and distal convoluted tubules, primarily reside in cortex. Vasa recta capillaries are straight vessels associated with nephron loop, primarily reside in medulla Filtrate, Tubular fluid, and Urine Filtrate ● A filtrate is a fluid formed by filtering blood into the glomerulus ● Through the glomerular membrane, the blood filtrate enters the capsular space. ● Large molecules remain in the blood, which does not pass through the glomerular membrane. Tubular fluid ● formed in the tubules of the nephron ● is formed due to the exchange of gases and Nutrients from the filtrate that enters the tubules. Urine ● ● by collecting ducts, the kidneys leave the urine Urine is final when it leaves the collecting duct until it excretes from the body. Structures That Transport Fluids Through the Urinary System ( In order) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. Capsular Space Proximal convoluted tubule Descending Limb of nephron loop Ascending limb of nephron loop Distal convoluted tubule Collecting tubules Collecting duct Papillary duct Minor Calyx Major Calyx Renal Pelvis Ureter Urinary Bladder Urethra Steps of Urine Formation 1. Glomerular Filtration- turning blood plasma into filtrate ● The movement of substances from the blood within the glomerulus into the capsular space ● separates some water and dissolved solutes from the blood plasma within glomerulus. ● H2O and solutes enter capsular space due to a pressure difference across the membrane. (this fluid is called filtrate) 2. Tubular Reabsorption ● The movement of substances from the tubular fluid back into the blood ● Tubular fluid moves by transport process (e.g. diffusion, active transport etc.) from the lumen of collecting tubules and ducts across their walls and return to blood through capillaries. ● Generally, all solutes and most waters are reabsorbed, excess solutes and H2O remain in the fluid. 3. Tubular secretion: ● The movement of substances from the blood into the tubular fluid ● movement of solutes by active transport out of the blood and into the tubular fluid. ● Materials are selectively moved into tubules to be eliminated. Glomerular Filtration Membrane Layers Endothelium of glomerulus allows plasma and its dissolved substances to be filtered while restricting passage of large structures, like formed elements Basement membrane of glomerulus restricts passage of large plasma proteins while allowing smaller substances to pass Visceral layer of glomerulus ● composed cells called podocytes, octopus-like cells, long "feet" that wrap around glomerular capillaries to support capillary wall. ● The "feet" are separated by thin filtration silts that are covered with membrane. One podocytes "feet" interlock with another to restrict the passage of most small proteins. Examples of substances that are freely filtered, that are not filtered, and that are filtered in a limited way. Freely filtered- Water, glucose, amino acids, ions, urea, some hormones etc can pass easily through a filtered membrane and become part of filtrate and have the same concentration as plasma. Not filtered- Formed elements (RBCs, WBCs etc) and large proteins cannot normally pass-through filtration membranes. Cannot become part of filtrate. Limited filtration- Intermediate sized proteins are generally not filtered. They are blocked either because of size or - charge since the membrane had a negative charge. Glomerular Hydrostatic Pressure (HPg) Pressures that oppose HPg (pushing back against) Blood colloid osmotic pressure (OPg) - Osmotic pressure exerted by dissolved solutes E.g., plasma proteins Capsular hydrosta@c pressure (HPc) (pushing back into capsule) - Pressure in glomerular capsule due to filtrate - Impedes movement of additional fluid Glomerular Filtration Rate and the factors that influence it Glomerular Filtration Rate (GFR) ● Rate at which the volume of Filtrate is formed ● Volume per unit of time (usually 1 min) ● Helps kidney control urine production based on physiologic conditions Influenced by: ● Increased blood volume and increased blood pressure will increase GFR. ● Constriction in the afferent arterioles going into the glomerulus and dilation of the efferent arterioles coming out of the glomerulus will decrease GFR Intrinsic and Extrinsic controls Intrinsic controls ● Intrinsic ability of kidney to maintain constant blood pressure and GFR ● Maintains in spite of changes in systemic arterial pressure ● Functions by two mechanisms: ○ Myogenic response ( Myo= Muscle)- within kidney ■ Contraction or relaxation of smooth muscle of afferent arteriole in response to stretch ■ Allows more blood into glomerulus ■ ■ ■ ■ ■ ■ ■ ■ ■ ○ E.g., Decreased blood pressure = less stretch of smooth muscle in arteriole Compensates for lower system pressure GFR remains normal With increased blood pressure, more stretch of smooth muscle in arteriole Vessels constrict Allows less blood into glomerulus Compensates for greater systemic pressure GFR remaining normal Example:Renal autoregulation, decrease in systemic blood pressure (when taking a nap), causes vasodilation of afferent arteriole, allowing more blood into glomerulus, which compensates for lower systemic blood pressure. Tubuloglomerular feedback mechanism- outside of kidney ■ “Backup” to myogenic mechanism response to increased blood pressure ■ If glomerular blood pressure increased: ● Amount of NaCl in tubular fluid also increased ● Detected by macula densa cells in juxtaglomerular apparatus ● Results in further vasoconstriction of afferent arteriole ● Example:Exercise, Activating sympathetic division for fight-or-flight response results in decrease in GFR due to vasoconstriction of afferent arteriole. Nerve signals sent to kidneys during exercise cause vasoconstriction in afferent and efferent arterioles, greatly reduces blood flow into glomerulus. Characteristics and conditions that affect tubular reabsorption and secretion Tubular reabsorption – Substances move from tubule into blood Peritubular capillary – Low hydrostatic pressure, high colloid osmotic pressure Transcellular transport – Movement of substances across and epithelial cell Paracellular transport – Movement of substances between epithelial cells Tubular secretion – Substances move from blood into tubule Substances for which reabsorption is regulated Na+, water, K+, HCO3- and Ca2+. Sodium, water, Potassium, Bicarbonate, and Calcium Reabsorption of sodium, potassium, calcium, and Phosphate Sodium Amount reabsorbed from tubular fluid can vary from 98-100%. ● It is reabsorbed along the entire length of the nephron tubule, collecting tubules and collecting ducts, majority (65%) reabsorbed in proximal convoluted tubule, 25% in nephron loop, 5% in DCT. ● Na+ moves down its concentration gradient across luminal membrane into tubular cell of PCT. ● Na+/K+ pumps move Na+ within tubular cell into interstitial fluid, Na+ concentration low in tubule cells. Na+ enter peritubular and vasa recta capillaries through intercellular clefts. Potassium Reabsorption depends upon movement of Na+. 1.Sodium is reabsorbed across luminal membrane. 2. Water follows Na+. 3. Concentration of the remaining solutes in the tubular fluid increases as water follows movement of Na+. 4. Potassium moves down it concentration gradient from tubular fluid into blood by paracellular route. 5. These conditions also allow passive reabsorption of other solutes, including other cations (Mg2+, Ca2+), phosphate ion, fatty acids, and urea. 10-20% of K+ in tubular fluid is reabsorbed in thick segment of nephron looop ascending limb by transcellular and paracellular transport. Calcium & Phosphate Amount excreted in urine is regulated by parathyroid hormone (PTH) influences blood levels of Ca2+ and PO4 1. PTH is released from the parathyroid gland in response to decreased blood calcium. 2. PTH inhibits phosphate reabsorption in proximal convoluted tubule, stimulates calcium reabsorption in distal convoluted tubule. Reabsorption of water, and compare how it is regulated by the actions of aldosterone and antidiuretic hormone ● ● ● ● ● Reabsorbed by paracellular transport between cells, by transcellular transport through specific water transport proteins - aquaporins. Movement of water out of proximal convoluted tubule follows Na+ by osmosis, referred to as obligatory water reabsorption. Water moves from descending limb of nephron loop into vasa recta. Aldosterone increases number of Na+/K+ pumps and Na+ channels in principal cells, increase Na+ and water reabsorption. Antidiuretic hormone (ADH) released from posterior pituitary gland when we are dehydrated. ADH binds to receptors of principal cells of collecting tubules and collecting ducts to increase migration of vesicles containing aquaporins to the luminal membrane.This provides additional channels for water reabsorption. Nitrogenous waste products, and their fate Urea, Uric Acid, and Creatinine. Urea and uric acid are reabsorbed and secreted. Creatinine is only secreted. Substances eliminated as waste products: Most secretion occurring in PCT ● ● ● Certain drugs E.g., penicillin, sulfonamides, aspirin Other metabolic wastes E.g., urobilin(causes yellow color in pee), hormone metabolites (estrogens, progestogens, androgens, cortisol and melatonin) Some hormones – Human chorionic gonadotropin (hCG), epinephrine Explain what is meant by the countercurrent multiplier that occurs within the nephron loop. ● ● ● ● involves nephron loop and helps establish gradient. Juxtamedullary nephrons are primarily involved Kidney countercurrent multiplication refers to the process in which energy is used to create an osmotic gradient that enables the reabsorption of water from the tubular fluid, so that urine can be concentrated. Countercurrent multiplication creates this gradient by actively moving sodium chloride from the tubular fluid into the interstitial space deep within the kidneys. Partially responsible for establishing salt concentration gradient within interstitial fluid. Countercurrent refers to tubular fluid's "reversing" its relative direction as ot moves first through descending limb then through ascending limb. Multiplier is positive feedback loop that increases the concentration of salts within interstitial fluid. Contribution of urea cycling to the concentration gradient. ● ● ● ● ● Recycled urea makes up one-half of the solutes in ISF (interstitial fluid) concentration gradient. Urea is removed in collecting ducts via urea uniporters. It diffuses back into tubular fluid at the ascending limb. DCT ( distal convoluted tubule)will not let urea leave, so when it reaches the collecting ducts it is removed there. Urea is cycled between collecting tubules and nephron loops. Summary of reabsorption and secretion • After filtration • Majority or most other substances reabsorbed or secreted • Nephron loop, vasa recta, and urea recycling • Responsible for establishing concentration gradient of interstitial fluid • Necessary for normal function of ADH • Regulation of specific substances • Hormonal controls • Urine • Composed of water, dissolved substances, waste products • Drained into renal sinus of kidney • Excreted by urinary tract Procedure for measuring the glomerular filtration rate to determine how well kidneys work: 1.Someone is injected with inulin which is freely filtered and is not reabsorbed nor secreted in the kidney. SO the amount of inulin in urine is equal to the amount that is filtered. Urine collected and measured for volume and concentration Plasma concentration of inulin measured at given time intervals Normal GFR 125 mL/min-Less than this indicates decrease in kidney function Renal plasma clearance Renal clearance of a substance refers to how quickly a particular substance is removed from the plasma by the kidney and excreted in urine.So something with a high renal clearance means that it will be quickly removed from the blood, and vice versa. Kidney Transplant Identify the substance that may be measured to estimate the glomerular filtration rate. If a substance (such as inulin) is NEITHER reabsorbed or secreted the RPC will be the same as GRF, but if its reabsorbed then the RPC will be lower than GFR. Due to fluid leaving. Substances that are BOTH reabsorbed and secreted will have a RPC higher than GRF because extra substances are secreted back into tubular fluid. Composition of Urine and its characteristics. • Product of Filtered and processed blood plasma • Sterile unless contaminated with microbes in kidney or urinary tract • Characteristics: composition, volume, pH, specific gravity, color and turbidity, smell • Composition • 95% water, 5% solutes • Salts, nitrogenous wastes, some hormones drugs, ketone bodies • Abnormal constituents –glucose, blood cells, proteins • Volume • Average 1 to 2 L per day • Variations due to fluid intake, blood pressure, temperature, diuretics,diabetes, other fluid Excretion • WE NEED Minimum of 0.5 L to eliminate wastes from body • Below 0.40, wastes will accumulate in blood Structure and Function of the Ureters ● ● ● ● Ureters are long fibromuscular tubes that transport urine from kidney to the urinary bladder. They originate at the renal pelvis and exit the hilum of the kidney and extend towards the base of the urinary bladder. Enter posterolateral wall of base of urinary bladder Wall contains three tunics (in to out): muscoa, muscularis, and adventita. Structure of the Urinary Bladder ● ● ● ● ● ● Urinary bladder is an expandable, muscular organ that serves as a reservoir for urine. In females the bladder is anteroinferior to the uterus and directly inferior to the vagina. Males the bladder is anterior to the rectum and superior to the prostate gland. This is a retroperitoneal organ and only the superior surface is covered with parietal peritoneum. When it is empty it resembles an inverted pyramid shape and when it is full it is oval shaped. Trigone are imaginary lines connecting ureter openings and urethra, and funnels to direct urine into urethra. Distinguishing characteristics of the female and male urethra. Female: Single function is to transport urine from the bladder to the outside. Inside lined with stratified squamous epithelium opens at external opening in female perineum. Shorter urethra Male: Passageway for urine and semen, longer than female urethra Three segments: prostatic urethra, membranous urethra, spongy urethra Conscious control over micturition: Starts from the cerebral cortex through the pudendal nerve. This causes relaxation of the external urethral sphincter which is facilitated by voluntary contraction of abdominal and expiratory muscles, and after emptying detrusor muscle relaxed,micturition reflex inhibited, and storage reflex activated.