selective reabsorption Flashcards
What is selective reabsorption, and where does it take place? (3)
The process where useful substances (e.g., glucose)
Are reabsorbed back into the blood from the filtrate
As it flows through the PCT, loop of Henle, and DCT in the medulla and cortex of the kidney
What are the adaptations of the epithelial cells lining the PCT for selective reabsorption? (4)
Microvilli
Provide a large surface area for reabsorption
Many mitochondria
Provide ATP for active transport
How are useful solutes reabsorbed during selective reabsorption? (3)
Glucose, amino acids, vitamins, and some salts are reabsorbed along the PCT
By active transport and facilitated diffusion
Some urea is reabsorbed by diffusion
How is water reabsorbed during selective reabsorption? (2)
Water enters the blood by osmosis because the water potential of the blood is lower than the filtrate
Water is reabsorbed from the loop of Henle, DCT, and collecting duct
What does the filtrate that remains in the nephron become, and what does it consist of? (5)
Becomes urine that consists of:
Water
Dissolved salts
Urea
Hormones and excess vitamins
What substances are not found in urine in a healthy person, and why? (4)
Proteins and blood cells
Too large to pass through the basement membrane
Glucose, amino acids, and vitamins
Selectively reabsorbed back into the blood
What happens to the unwanted substances that remain in the filtrate? (3)
- They pass through the tubules
- Along the ureter to the bladder
- Are expelled as urine
How does the filtered blood leave the kidneys? (1)
The filtered blood passes out of the kidneys through the renal vein
What covers the outside of the kidney? (2)
Thin, strong membrane
Renal capsule
What lies beneath the renal capsule in the kidney? (1)
Cortex
What is the indented part of the kidney called? (1)
Renal hilum
What structures come out of the renal hilum? (3)
Renal vein
Renal artery
Ureter
How can you differentiate the renal artery, renal vein, and ureter during external examination? (2)
The renal artery has a thicker wall than the vein
The ureter is likely to have the most adipose (fatty) tissue around it
What does the cortex of the kidney look like during an internal examination? (1)
Appears dense, grainy, and darker than the medulla
What structures are found in the medulla of the kidney, and what do they look like? (3)
Renal pyramids
Cone-shaped structures that appear stripy
Because they contain straight sections of the nephron (loop of Henle and collecting ducts).
What structures lead from the base of the renal pyramids? (3)
Renal calyces
Hollow cavities that lead to the larger renal pelvis
Which connects to the ureter
What can you see when examining a stained section of the cortex of the kidney? (3)
Glomerulus: Bundles of capillaries
Bowman’s capsule: A white area around the glomerulus
PCTs and DCTs: Circular areas surrounded by squamous epithelial cells
What can you see when examining a stained section of the medulla of the kidney? (2)
Loops of Henle: White areas surrounded by capillaries
Red dots in the capillaries represent red blood cells
What can you observe when examining the cortex of a stained section of the kidney? (3)
Glomerulus
Bowman’s capsule
PCTs and DCTs:
Circular areas surrounded by squamous epithelial cells
What is the countercurrent multiplier mechanism, and how does it help reabsorb water? (4) - part 1
- Loop of Henle acts as a countercurrent multiplier
- Na⁺ and Cl⁻ ions are actively transported out of the ascending limb into the medulla (the ascending limb is impermeable to water)
- This creates a low water potential in the medulla
- Water moves out of the descending limb (which is permeable to water) by osmosis into the medulla
What is the countercurrent multiplier mechanism, and how does it help reabsorb water? (3) - part 2
- The filtrate becomes more concentrated as ions cannot leave the descending limb
- Water in the medulla is reabsorbed into the blood through the capillary network
- Na⁺ and Cl⁻ ions diffuse out near the bottom of the ascending limb, further lowering the medulla’s water potential
How does the collecting duct contribute to water reabsorption? (2)
The water potential gradient created in the medulla causes water to move out of the collecting duct by osmosis
This water is reabsorbed into the blood via the capillary network
How is the volume of water reabsorbed into the capillaries controlled? (1)
By changing the permeability of the DCT and the collecting duct
How does the length of the loop of Henle affect water reabsorption? (3)
A longer loop of Henle allows more sodium and chloride ions to be actively pumped out
Creating a greater water potential gradient in the medulla
This allows more water to be reabsorbed by osmosis, resulting in more concentrated urine
