Chapter 24- Urinary system lecture

What are the functions of the kidneys

What are the functions of the kidneys

• Remove metabolic waste

• Regulation of ion concentration

• regulation of blood ph

• Regulation of blood volume/pressure

• elimination of hormones and drugs

• contribute to metabolic processes

What is the functional unit of the kidneys

• nephron

What are the two parts of the nephron and what do they do

• Renal corpuscles

  • glomerulus → filters plasma and creates glomerular filtrate

  • Glomerular → collects filtered plasma

• Renal tubules

  • proximal convoluted tubule

  • Nephron loop

  • Distal convoluted tubule

What are the two types of nephrons

• Cortical

  • 85% of nephrons

• Juxtamedullary

  • 15% of nephrons

In cortical nephrons, where do efferent arterioles lead to

• Pertitubular capillaries

• They will eventually become veins as oxygen is filtered out

In juxtamedullary nephrons what are the extensions called

• Vasa recta

What are the two cells found in the juxtaglomerular apparatus?

• Granular cells

• Macula densa

What do granular cells in the juxtaglomerular apparatus do

• detect stretch increase in stretch, which increase BP and causes contraction

• same for decrease, but granular cells secrete renin

What do macula densa cells in the juxtaglomerular apparatus do

• Detect changes in NaCl passing through the DCT and send signals as necessary

What are the three stages of urine formation

• Glomerular filtration

• Tubular reabsorption

• Tubular secretion

What are the layers of the filtration membrane

• Fenestrated endothelium

• basement membrane

• Filtration slits

What can be passed through the filtration membrane

• water

• ions

• glucose, fatty acids and amino acids

• nitrogenous wastes

• water soluable vitmians

What cannot be passed through the filtration membrane?

• Albumins

• blood cells

• calcium

• iron

• thyroid hormone

What can sometimes pass through the filtration membrane

• intermediate sized proteins

What are the 3 starling forces related to glomerular pressure

• HPg → out of capillary

• HPc → in capillary

• COPg → in capillary

How is glomerular filtration regulated

• Renal autoregulation

• Neural and hormonal control

What are the two ways that renal autoregulation work

• Myogenic mechanism

• Tubloglomerular feedback

Define myogenic mechanisms

• Autoregulation mechanism

• Occurs when blood pressure is out of normal range

• Smooth muscle in afferent arterioles either

  • Dialate to increase the incoming volume

  • Constrict to decrease incoming volume

Define Tubuloglomerular feedback

• Works when myogenic mechanisms fail to maintain GBP

  • Glomerulus receives the status of “downstream” tubular fluid and constricts or dilates in order to maintain normal PCT absorption

What is the normal MAP range of GFR (glomerular filtration rate)

• 80-180 mmHg

  • under 70 mmHg urine out put ceases

What is the average GFR values for males and females

• Males: 180 L/day

• Females: 150 L/day

  • (50-60 times more the amount blood filtered)

What is the average healthy adult reabsorption rate?

99%

What is normal urine output per day?

1-2 L/day

What is newly formed glomerular filtrate called once it enters the PCT?

• Tubular Fluid

Where does tubular reabsorption start

• The PCT

What are the 2 reabsorption pathways

• Paracellular

• Transcellular

What is the difference between paracellular and transcellular reaborption

• Paracellular → movement between tubular cells

• Transcellular → across the luminal membrane, tubular cell, basolateral membrane. IF, and peritubular capillary

Whats the difference between primary and secondary active transport

• Primary requires ATP

• Secondary relies on primary and usually is a symport

When fluid is being filtered out what happens to the HPb and COPb

• HPb is low

• COPb is high

How does tubular reabsorption of sodium occur

• Sodium diffuses down gradient from the tubular fluid into the tubule cell

• Sodium is moved against concentration gradient into the interstitial fluid from the tubule cell

• Then sodium is transported into the blood and is reabsorbed into the blood

How does tubular reabsorption of glucose occur

• Glucose is transported from the tubular fluid into the tubule cell by secondary active transport

• Glucose in the cell diffuses down concentration gradient and into the blood

How does tubular reabsorption of water occur with transcellular and cellular movement

• transcellular is via aquaporins

• Paracellular is via tight junctions, which are leaky

What happens in the descending loop of henle during filtration

• Impermeable to sodium

• freely permeable to water

  • Low sodium in IF, so water leaves

What happens in the ascending loop of henle during filtration

• Permeable to sodium

• Impermeable to water

  • Sodium leave tubule

What is the benefit of the countercurrent flow in the ascending and descending loop of henle

• It increases the osmotic gradient between the tubular fluid and IF

How much reabsorption happens in the PCT for sodium and water

• Both are 65%

How much reabsorption happens in the descending limb for water

• 10%

How much reabsorption happens in the ascending limb for sodium

• 25%