25. Urinary System

Mechanisms for the medullary osmotic gradient

Urine Formation

Medullary osmotic gradient: countercurrent multiplier, urea recycling & vasa recta exchange

Countercurrent Multiplication in the Loop of Henle

Forming urine (influencing factors), Forming dilute urine & Forming concentrated urine

Regulation of Glomerular Filtration Rate (GFR) - Extrinsic and Intrinsic Mechanisms

 Normally, proteins are too large to be filtered. 

 Which substance would NOT normally be expected in urine? 

The Collecting Duct

 Filtrate is converted to urine in the renal tubules. 

 Reabsorption is carried out in the renal tubules. 

 Secretion is carried out in the renal tubules. 

 All of the following functions are carried out in the renal tubules EXCEPT __________. 

Nephrology - Physiology Reabsorption and Secretion

The Urinary System

Glomerular Filtration: Net Ultrafiltration Pressure

The net filtration pressure (NFP), responsible for filtrate formation, involves forces acting at the glomerular bed. Glomerular hydrostatic pressure (HPg), which is essentially glomerular blood pressure, is the chief force pushing water and solutes out of the blood and across the filtration membrane.

 The hydrostatic pressure in glomerular capillaries is the chief force pushing water and solutes out of the blood and across the filtration membrane. 

 Every day the kidneys filter nearly 200 liters of fluid from the bloodstream. 

 Every day the kidneys filter nearly __________ of fluid from the bloodstream. 

Forces of Filtration

 The renal corpuscle is composed of the glomerulus and glomerular (Bowman's) capsule. This portion of the nephron serves as a filtering unit. 

 In what part of the nephron is plasma filtered? 

Countercurrent Multiplier System and Loop of Henle

Distal Convoluted Tubule

Urine Formation : Tubular Secretion

 The proximal convoluted tubule is not the countercurrent multiplier in the kidney. 

 the glomerular (Bowman’s) capsule around the glomerulus 

 The glomerular capsule is not the countercurrent multiplier in the kidney. 

 the loop of Henle of a juxtamedullary nephron 

 The vasa recta constitute the countercurrent exchanger. 

 Which of the following is the countercurrent multiplier in the kidney? 

Reabsorption 6 - Distal Convoluted Tubule & Collecting Duct

Urinary System: Tubular Reabsorption 

Regulation of Glomerular Filtration Rate

Regulation of GFR: autoregulation via myogenic mechanism Myogenic mechanism

 Water can leave the descending limb of the nephron loop but not the ascending limb. 

 Water can leave the ascending limb of the nephron loop. 

Formation of Urine - Nephron Function, Animation

 eliminating undesirable substances or end products that have been reabsorbed by passive processes 

Tubular secretion is important for (1) disposing of substances, such as certain drugs and metabolites that are tightly bound to plasma proteins; (2) eliminating undesirable substances or end products that have been reabsorbed by passive processes; (3) ridding the body of excess K+; and (4) controlling blood pH.

 disposing of substances, such as certain drugs 

 Tubular secretion is important for all EXCEPT which of the following? 

Sodium Regulation: Distal Convoluted Tubule and Collecting Duct

 glucose is secreted in the collecting ducts of diabetics 

There is a transport maximum (Tm) for nearly every substance that is reabsorbed using a transport protein in the membrane. When transporters are saturated&mdash;that is, all bound to the substance they transport&mdash;the excess is excreted in urine. This occurs in individuals who become hyperglycemic because of uncontrolled diabetes mellitus. As plasma levels of glucose approach and exceed 180 mg/dl, the glucose Tm is exceeded and large amounts of glucose may be lost in the urine, even though the renal tubules are still functioning normally.

 glucose is too large to be filtered by the nephron 

 glucose cannot be reabsorbed by the kidney 

 the transport maximum for glucose reabsorption has been exceeded 

 The reason glucose is detected in the urine of individuals with uncontrolled diabetes mellitus is that __________. 

 ADH enhances urea transport out of the medullary collecting duct. 

 Urea transport out of the medullary collecting duct is enhanced by __________. 

Reaborption and Secretion in the Proximal Tubule

 The vasa recta serve juxtamedullary nephrons, extending deep into the medulla, and play an important role in forming concentrated urine. 

 Which nephron capillary bed specializes in forming concentrated urine? 

 The renin-angiotensin-aldosterone mechanism results in increased blood pressure in response to hormone release. 

 renin-angiotensin-aldosterone mechanism 

 Which process results in increased blood pressure in response to hormone release? 

Renal | Loop of Henle

 An important factor directly affecting the glomerular filtration rate is __________. 

How does Antidiuretic Hormone (ADH) work?

 The countercurrent multiplier functions because of two factors: (1) the descending limb of the nephron loop is relatively impermeable to solutes and freely permeable to water; and (2) the ascending limb is permeable to solutes but not to water. 

 The descending limb of the nephron loop is relatively impermeable to solutes and freely permeable to water. 

 As enlarged smooth muscle cells in the arteriolar walls, granular cells release renin in response to a drop in mean arterial blood pressure. 

 What structure(s) is/are part of the juxtaglomerular complex and act(s) as a mechanoreceptor, sensing blood pressure in the afferent arteriole? 

 If the efferent arteriole constricts while the afferent arteriole remains unchanged, the glomerular filtration rate increases. This will increase glomerular hydrostatic pressure. 

 If the efferent arteriole constricts while the afferent arteriole remains unchanged, the glomerular filtration rate __________. 

Tubular Reabsorption | Reabsorption or Tubular Reabsorption

Na+ is reabsorbed by active transport using ATP. Most of the energy used for reabsorption is for Na+.

Tubular Reabsorption & Secretion 

Processing of Salt and Water in the Nephron

 less water is reabsorbed by the nephron and collecting duct 

 Less urine is produced when the concentration of ADH increases. 

 the specific gravity of the urine decreases 

 When the concentration of ADH increases, __________. 

Proximal Convoluted Tubule

Analyzing Urine Samples

Reabsorption 7- Medullary concentration gradient

Regulation of GFR: autoregulation via tubuloglomerular feedback, neural & hormonal regulation

Glomerular Filtration

 The basement membrane is composed of the fused basal laminae of the fenestrated endothelium and the visceral membrane, and it is considered part of the filtration membrane in the glomerulus. 

 The visceral layer is considered part of the filtration membrane in the glomerulus. 

 The fenestrated endothelium is considered part of the filtration membrane in the glomerulus. 

 All of the following are layers of the filtration membrane in the glomerular membrane EXCEPT the __________. 

A Summary of Kidney Function

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