Kidneys. Urinary System. Overview of the Urinary System. Principal organs = Kidneys. Accessory organs = Ureters, Bladder, and Urethra

Transcription

1 Urinary System Overview of the Urinary System Principal organs = Kidneys Accessory organs = Ureters, Bladder, and Urethra The Urinary System regulates the content of blood plasma to maintain homeostasis of the internal fluid environment within normal limits. Bean-shaped. Kidneys Left kidney is often larger than the right. Right kidney is a little lower than the left. Located against the posterior wall of the abdomen. Refer to page 830 1

2 Kidney Kidney - Anatomy Kidney Blood Flow Kidneys are highly vascular! About 1/5 of all the blood pumped by the heart per minute goes to the kidneys. Refer to page 831 Renal artery large branch of abdominal aorta; brings blood into each kidney brings blood into the kidney. 5. Refer to page 831 Kidney Blood Flow Branching off the interlobular arteries are the afferent arterioles supplying the glomerular capillaries, which drain into efferent arterioles. Efferent arterioles divide into peritubular capillaries that provide an extensive blood supply to the cortex. Blood from these capillaries collects in renal venules and leaves the kidney via the renal vein. 2

3 Continued 8. ball of Ball capillaries of capillaries Do you see an exception to the rule here? 10. Peritubular capillaries Kidney Blood Flow Let s recap! Abdominal aorta Renal artery Segmental arteries Lobar arteries Interlobar arteries Arcuate arteries Interlobular arteries Afferent arteriole Glomerulus Efferent arteriole Peritubular capillaries (vasa recta) Interlobular veins Interlobar veins Segmental veins Arcuate veins Lobar veins Renal vein Inferior vena cava ephron! Microscopic functional unit of the kidney! Cortical nephrons - located in the renal cortex; constitute about 85% of total nephron numbers. Juxtamedullary nephrons lie near the junction of the cortical and medullary layers and have loops of Henle that dip deep into the medulla. They play an important role in concentrating urine. 3

4 ephron Parts of the nephron in the direction of blood flow 1. Renal corpuscle = Glomerulus + Bowman s capsule 2. Proximal convoluted tubule 3. Loop of Henle 4. Distal convoluted tubule 5. Collecting duct Renal corpuscle? D Now you try! Renal Corpuscle Proximal convoluted tubule? Loop of Henle? A Distal convoluted tubule? C Collecting duct? E B 4

5 Bowman s capsule Bowman s Space (contains glomerular filtrate!) Contains the primary filtering device of the nephron, the glomerulus, a network of fine capillaries. Afferent arteriole Podocytes - cells of the inner wall of Bowman s capsule. They are a crucial part of glomerular filtration. Adjacent podocytes interlock to cover the glomerular capillaries; but the podocytes leave gaps or thin filtration slits. Podocytes Efferent arteriole 2 layers of epithelium Podocytes form the final filtration barrier that restricts the passage of albumin, while allowing water and small solutes to enter the nephron. Over the past few years, the renal research community has come to realize that these podocytes are primary targets of the majority of glomerular diseases! Glomerulus Main filter of the nephron Located within Bowman's capsule. Resembles a twisted mass of tiny tubes through which the blood passes. Semipermeable, allowing water and soluble wastes to pass through and be excreted out of the Bowman's capsule as filtrate. The filtered blood passes out of the glomerulus into the efferent arteriole. 5

6 Blast from the Past! Proximal Convoluted Tubule Initial segment of the nephron s tubule Wall made up of one layer of epithelial cells with a brush border of microvilli facing the lumen of the tubule. Restores much of the filtrate to the blood in the peritubular capillaries. The length of a proximal convoluted tubule tends to be several times greater than that of a distal convoluted tubule. ephron Tubule Can you find the proximal convoluted tubule? 6

7 Loop of Henle Leads from the proximal convoluted tubule to the distal convoluted tubule in the kidney. Its primary function is to reabsorb water and ions from the filtrate. Can you find the Loop of Henle? Descending Limb: Much thinner wall than the thick part of the ascending limb. Allows water and urea to diffuse freely into or out of the tubule, depending on their concentration gradients. Ascending Limb: Much thicker wall than the descending limb. LIMITS the diffusion of most molecules including water and urea! Distal Convoluted Tubule Portion of the nephron between the loop of Henle and the collecting duct system. It is partly responsible for the regulation of potassium, sodium, calcium, and ph. 7

8 Collecting Duct Can you find the distal convoluted tubule? Connects nephrons to ureter. Like the distal convoluted tubule, it participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and antidiuretic hormone. Let s Review! Can you find the collecting duct? 8

9 Let s Review! (again) Tube which carries the urine from the kidneys to the bladder. Ureters Composed of 3 layers: a mucous lining, a muscular middle layer, and a fibrous outer layer. Urinary Bladder Muscular bag which stores and expels urine. Located behind the pubic symphysis and in front of the rectum. In woman, it rests on the anterior vagina and in front of the uterus. In men, it sits on the prostate. 9

10 Urinary Bladder Wall is mostly smooth muscle tissue = detrusor muscle with criss-crossing bundles of oblique, circular, and longitudinal. Lined with mucous transitional epithelium which forms folds called rugae can distend considerably! Involuntary Voluntary Urethra canal through which urine is discharged from the bladder In females, the urethra lies posterior to the symphysis pubis and anterior to the vagina. It is about 3 cm long. In males, the urethra is part of the urinary system, as well as part of the reproductive system Urethra In the male, after leaving the bladder, the urethra passes through the prostate gland where it is joined by 2 ejaculatory ducts. From the prostate, it extends through the penis, and ends as a urinary meatus. A male s urethra is about 20 cm long. 10

11 Chief functions of the kidney are to: Process blood plasma Excrete urine Basic functional unit of the kidney is the nephron which forms urine via 3 processes: 1. Filtration 2. Reabsorption 3. Secretion Refer to page 839 What Do Our Kidney s Keep In Check? Sodium Potassium 189 L Chloride 190 L itrogenous wastes (especially urea) OTE: Our kidneys do not only filter out harmful or excess material. At first, they filter out most of the blood plasma; then they reabsorb what should be kept before the filtrate becomes urine! g Refer to page

12 Filtration Passive process based on hydrostatic pressure of the blood in the glomerulus. Movement of water and protein - free solutes from the plasma in the glomerulus into Bowman s capsule. Filtration occurs faster out of glomerular capillaries than all other capillaries because of the many pores (fenestrations) and the higher hydrostatic pressure! Regulation of Glomerular Filtration Intrinsic - Renin Renin is an enzyme released by the Juxtaglomerular Apparatus to help control the body's sodium-potassium balance, fluid volume, and blood pressure. Plasma renin activity (PRA), also called plasma renin assay, may be used to screen for high blood pressure (hypertension) of kidney origin. Extrinsic - Sympathetic Nervous System 12

13 Juxtaglomerular Apparatus Located where the afferent arteriole brushes past the distal tubule Important to maintenance of blood flow homeostasis by secreting renin when blood pressure in the afferent arteriole drops. Reabsorption 2 nd step in urine formation. Passive & Active transport mechanisms from all parts of the renal tubules. MOST reabsorption into the peritubular blood is from the Proximal Tubule! Reabsorption in the Proximal Tubule 1. Sodium is actively transported out of the tubule fluid and into the blood. 2. Glucose and amino acids hitch a ride with sodium and passively move out of the tubule fluid (Sodium cotransport). 3. Chloride ions passively move into blood plasma b/c of imbalance of electrical charge. 4. Blood is now hypertonic to filtrate, so water passively moves into the blood (Osmosis!) Refer to page About ½ of the urea moves out of the tubule. 13

14 Reabsorption in the Loop of Henle is due to : COU TERCURRE T FLOW! Countercurrent flow refers to flow in opposite directions. Tubule filtrate in the loop of Henle flows in a countercurrent manner, as does blood flowing within the vasa recta of the peritubular capillary network. Refer to page 842 a + and Cl - are actively pumped from the ascending limb into the interstitial fluid. Water is OT allowed to follow! Interstitial fluid develops a high solute concentration. H 2 O leaves the descending limb and enters the interstitial fluid. Urea diffuses into the descending limb Refer to page 843 Reabsorption in the Loop of Henle The filtrate entering is ISOtonic to interstitial fluid. Both are 300 mosm. This makes the tubule fluid dilute (HYPOTO IC) and creates a high osmotic pressure, or high solute concentration, of the medulla s interstitial fluid. The filtrate leaving is now HYPOtonic! 14

15 Reabsorption in the Loop of Henle Reabsorption in the Distal Tubules and Collecting Ducts Distal tubule reabsorbs some sodium by active transport. H 2 O cannot follow! Therefore, the solute concentration of the tubule fluid continues to decrease. The collecting duct also prevents H 2 O from leaving the filtrate. Refer to page 844 Hypotonic urine is produced by the nephron. However, ADH (antidiuretic hormone) prevents excessive H 2 O loss 15

16 Hypertonic urine can be formed when ADH is present. ADH, a posterior pituitary hormone, increases the water permeability of the distal tubule and collecting duct. Effect of ADH on ephron Refer to page 845 Secretion Movement of molecules out of the blood and into the tubule for excretion Descending limb of Loop of Henle removes urea by diffusion. Distal Tubule and Collecting Tubules Secretes K +, H +, and H 4 + K + or H + ions are actively transported out of the blood into the tubule fluid in exchange for a + that diffuse back into the blood. K + secretion increases when blood aldosterone increases. Aldosterone is a hormone secreted by the adrenal cortex that targets distal and collecting tubule cells and causes them to move a + out of the tubule and K + in! 16

17 Urine Formation Urine Volume Refer to page and X rovy& R=1 REVIEW of Regulation of Urine Volume Begins with a in blood pressure Renin is secreted by Juxtaglomerular Apparatus. Renin triggers the release of Angiotensin II, which triggers the release of aldosterone from the adrenal cortex and ADH from the pituitary! ADH, secreted by the pituitary gland, increases water reabsorption by the kidneys by increasing water permeability of the distal tubules and collecting ducts. ADH reduces water loss! Aldosterone, secreted by adrenal cortex, increases distal tubule absorption of sodium, raising the sodium concentration of blood and thus promoting reabsorption of water 17

18 Urine Composition Approximately 95% water with several substances dissolved in it. The most important are itrogenous wastes result of protein metabolism; Ex: Urea (most abundant solute in urine), uric acid, ammonia, and creatinine Electrolytes mainly the following ions: sodium, potassium, ammonium, chloride, bicarbonate, phosphate, and sulfate; amounts and kinds of minerals vary with diet and other factors Urea Urine Composition Toxins during disease, bacterial poisons leave the body in the urine. Pigments especially urochromes (yellowish pigments from the break down of old rbc s. Hormones high hormone levels may spill into the filtrate. Abnormal constituents such as blood, glucose, albumin, casts (chunks of material like mucus that harden inside the urinary passages and are then washed out in the urine), or calculi (small stones). Eating asparagus can cause a strong odor caused by the body's breakdown of asparagusic acid. Very spicy foods can have a similar effect because their compounds sometimes pass through the kidneys without being fully broken down before exiting the body. Micturition (Urination) Urinary control depends upon communication between the cerebrum, pons, and peripheral nerves. We feel the need to void when the bladder is about 250 ml full. Ascending fibers send this message to the cerebrum. The cerebrum now switches the pons to emptying mode. The internal sphincter relaxes and detrusor contraction begins! 18

19 Kidney Stones Most kidney stones are carried out of the kidney and through the urinary tract when they are still small enough to pass easily out of the body. Larger stones, however, may become stuck in the tubes that carry urine from the kidney to the bladder (ureters). The Artificial Kidney: Here is a picture of the dialysis machine. It is slow dialysis used over a 24 hour period on critically ill patients who cannot tolerate the large fluid shifts of hemodialysis. This is an active filtration system Peritoneal Dialysis uses membranes in the abdomen to create dialysis. Thanks Mrs. Cusack! ot commonly used in the ICU. 19

20 Urinary Tract Infection UTI - infection anywhere in the urinary tract. Usually, a UTI is caused by bacteria that can also live in the digestive tract, in the vagina, or around the urethra. Most often these bacteria enter the urethra and travel to the bladder and kidneys. Usually, your body removes the bacteria, and you have no symptoms. However, some people seem to be prone to infection, including women and older people. Urinary Tract Infection You should see your doctor if you have any of these symptoms: Burning feeling when you urinate Frequent or intense urges to urinate, even when you have little urine to pass Pain in your back or lower abdomen Cloudy, dark, bloody, or unusualsmelling urine Fever or chills 20