36 terms

Anatomy & Physiology- CH 16- The Urinary System


Terms in this set (...)

The Urinary System
Single most important route of waste-product removal and excess water removal in the body. Parts of the system: Two kidneys, Two ureters, Urinary bladder, and urethra.
Kidney Functions
Maintain homeostasis trough blood filtration, reabsorption, secretion, fluid balance regulation, acid-base balance regulation, and production of hormones.
Kidney Functions: Blood Filtration, Reabsorption, Secretion
Useful substances that are filtered are recycled and returned to the body in a process called reabsorption. Unwanted substances that are filtered are secreted from the blood into fluid and urinated out.
Kidney Functions: Fluid Balance Regulation
Helps ensure the body contains the right amount of fluid. Too much fluid=eliminated via diuresis. Not enough fluid=fluid conserved resulting in oliguria/anuria. Controlled by antidiuretic hormone (ADH) and aldosterone.
Kidney Functions: Acid-base balance regulation
Removes bicarbonate and hydrogen ions from the blood.
Located in dorsal abdominal area ventral to and on either side of the first few lumbar vertebrae. Retroperitoneal to abdominal cavity; outside the parietal peritoneum between peritoneum and dorsal abdominal muscles. In most domestic species, right kidney is more cranial then that left. Thick layer of perirenal fat usually surrounds kidneys to help protect them from pressure exerted by surrounding organs.
Gross Anatomy of Kidneys
Fibrous connective tissue capsule, bean-shaped
Gross Anatomy of Kidneys: Hilus
Indented area on medial side of the kidney. Ureters, nerves, blood and lymph vessels enter and leave the kidney.
Gross Anatomy of Kidneys: Renal Pelvis
Funnel-shaped area inside hilus. Forms beginning of the ureter. Lined with transitional epithelium.
Gross Anatomy of Kidneys: Renal Cortex
Outer portion of the kidney
Gross Anatomy of Kidneys: Renal Medulla
Inner portion around the renal pelvis.
Gross Anatomy of Kidneys: Calyx
Cuplike extension of the renal pelvis into which the medullary pyramids fit. Calyces act as funnels to direct fluid into renal pelvis and into the ureter.
Microscopic Anatomy of Kidneys: Nephron
Basic functional unit of kidneys-microscopic filtering, reabsorbing and secreting system. Number varies per kidney- 200,00/kidney in the cat, 4,000,000/kidney in the cow. Consists of Renal Corpuscle, Proximal Convoluted Tubule, Loop of Henle, Distal Convoluted Tubule.
Renal Corpuscle
Located in renal cortex. Function: Filters blood in first stage of urine production. Composed of Glomerulus surrounded by Bowman's Capsule. Glomerulus- "tuft" of capillaries. Fluid filtered out of blood is called Glomerular Filtrate.
Proximal Convoluted Tubule (PCT)
Continuation of capsular space of Bowman's Capsule. Lined with cuboidal epithelial cells with a brush border on lumen side, increases reabsorption and secretion capabilities. Has a twisting path trough the renal cortex. Glomerular Filtrate now called the Tubular Filtrate.
Loop of Henle
Descends of PCT into medulla, turns, heads upward into cortex. Descending loop has epithelial cells similar to those of PCT. At bottom of loop, epithelial cells flatten to simple squamous epithelial cells and loose their brush border. Ascending loop wall becomes thicker again.
Distal Convoluted Tubule (DCT)
Continuation of ascending loop of henle. DCT from all nephrons in the kidney empty into collecting ducts, Carry tubular filtrate through medulla, empty into renal pelvis, primary site of action for ADH and regulation of potassium and acid-base balance.
Blood Supply
Up to 25% of the blood pumped by the heart goes to the kidney. Renal Artery enters the kidney at the hilus. Branches off of the abdominal aorta. Divides into smaller arterioles and eventually glomerular arterioles. Afferent glomerular arterioles carry blood into the glomerular capillaries of renal corpuscle. Glomerular capillaries filter some of the plasma out of blood and put it in the capsular space of Bowman's capsule(glomerular filtrate). Efferent glomerular arterioles receive blood form glomerular capillaries, still oxygenated. Efferent glomerular arterioles divide to form the peritubular capillaries- Surrounds the rest of the nephron, Oxygen transfer to the cells of the nephron takes place here, Tubular reabsorption and secretion also occurs here. Peritublar capillaries converge to form venules then larger veins and finally the renal vein. The renal vein leaves the kidney at the hilus and joins the abdominal portion of the caudal vena cava.
Filtration of Blood
Glomerular capillaries contain many large fenestrations (pores) in capillary endothelium. Fenestrations not large enough to allow blood cells or large proteins to pass through. High blood pressure in the glomerular capillaries forces some plasma out of the capillaries and into the capsular space of the Bowman's capsule, this plasma becomes the Glomerular Filtrate contains NO proteins or blood cells.
Filtration of Blood: Glomerular Filtration Rate (GFR)
How fast plasma is filtered through glomerulus. Depends on rate of blood flow to the kidneys.
Glomerular filtrate contains waste products that need to be eliminated AND substances that need to be recycled/reused. Reabsorption is the process by which these useful substances are passed through the kidney tubules and put back into the blood and recirculated. When the glomerular filtrate enters the PCT, it becomes Tubular Filtrate. Substances to be reabsorbed pass out of the tubular lumen through or between tubular epithelial cells. Substances to be reabsorbed then enter interstitial fluid and pass through endothelium into peritublar capillaries.
Sodium Reabsorption
Sodium in tubular filtrate attaches to a carrier protein that moves it into the cytoplasm of the PCT epithelial cell (requires energy). Glucose and amino acids attach to the same carrier protein and follow sodium into the cell by passive transport(sodium cotransport). Sodium is activity pumped out of cell into interstitial fluid, where it moves into peritubular capillaries. Glucose and amino acids move from the peritubular capillaries by passive diffusion. Sodium ions are also reabsorbed in ascending loop of henle and DCT. Usually exchanged for hydrogen, ammonium, or potassium ions.
Reabsorption: Potassium and Calicum
Take place in the PCT ascending loop of henle and DCT. Calcium moves under the influence of Vitamin D, parathyroid hormone (PTH), and calcitonin.
Reabsorption: Magnesium
Is reabsorbed from the PCT, ascending loop henle and the collecting duct. PTH release increases the reabsorption of magnesium.
Reabsorption: Chloride (Cl-)
Diffuses from tubular filtrate into epithelial cells and interstitial space in response to electrical imbalance created by (Na+) removal. When sodium left the tubule the tubular lumen became negative and the interstitial fluid became positive. Some of the water in the filtrate moves into the interstitial space and peritublar capillaries by osmosis once sodium, glucose, amino acids and chloride have left the tubular filtrate. The remaining substances like urea are now "dehydrated" and they begin to move across into the tubular capillaries. Urea is a waste product of protein metabolism some is secreted/eliminated in the urine and some is reabsorbed back into the capillaries (blood urea nitrogen, BUN).
Primarily occurs in the DCT. When waste products are not filtered in the glomerulus they get secreted from the peritublar capillaries and into the DCT lumen/tubular filtrate. Efferent glomerular arterioles divide to form the peritublar capillaries, surrounds the rest of the nephron, oxygen transfer to the cells of the nephron takes place here, tubular reabsorption and secretion also occurs here. Hydrogen,potassium, and ammonia are eliminated by secretion. Some medications are also eliminated from the body secretion.
Urine Volume Regulation
Determined by amount of water contained in the tubular filtrate when it reaches renal pelvis, and the pressure between the nephron and the renal pelvis. Controlled of actions of ADH and aldosterone. ADH acts on the DCT and collecting ducts to promote water reabsorption, water is retained by the body less urine. Aldosterone increases resorption of sodium. Causes osmotic imbalance that encourages water to follow sodium out of the tubular filtrate and into blood.
Leaves the kidney at the hilus and connects the kidney to the bladder. Outer fibrous layer, middle smooth muscle layer, and inner layer lined with transitional epithelium. Transitional epithelium allows ureters to stretch as urine passes through them on its way to urinary bladder. Smooth muscle layer propels urine through ureter by peristaltic contractions. Enter the urinary bladder at an oblique angle. When the bladder is full it collapses the opening of the ureter preventing urine from backing up into ureter.
Urinary Bladder
Stores urine. Lined with transitional epithelium that stretches as the bladder becomes filled with urine. Wall of the urinary bladder contains smooth muscle bundles, when contracted the bladder is squeezed and urine is expelled. Neck of the bladder extends caudally from the sac into the pelvic canal and joins the urethra. Around the neck of the urinary bladder are circular muscles composed of skeletal muscle fibers. Under voluntary control allows urine to enter the urethra.
Control of Urination: Micturition or Uresis
Expulsion of urine from the urinary bladder into the urethra. 3 Steps
Control of Urination: Micturition or Uresis- Step 1
Urine accumulates until pressure of the filling bladder activates stretch receptors in bladder wall
Control of Urination: Micturition or Uresis- Step 2
A spinal reflex returns a motor impulse to bladder muscles causing them to contract. Contraction gives the sensation of having to urinate.
Control of Urination: Micturition or Uresis- Step 3
Voluntary control of the muscular sphincter around the neck of the bladder results in temporary control of urination.
Continuation of the neck of the urinary bladder. Carries urine from the urinary bladder to the external environment. Lined with transitional epithelium which allows it to expand.
Urethra: Female
Shorter and straighter then the long, curved male urethra. Opens on the ventral portion of the vestibule of the vulva.
Urethra: Male
Runs down the center of the penis and also functions in to the reproductive system. In the pelvic portion of the urethra spermatozoa are discharged into the urethra during ejaculation. The sphincter at the neck of the bladder closes to prevent semen from entering the bladder