Topic 11.3: The Kidney Flashcards Preview

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Flashcards in Topic 11.3: The Kidney Deck (34)

Define excretion

Excretion is the removal from the body of the waste products of metabolic activities


What is label A?



What is label B?

Renal pelvis


What is label C?



What is label D?

Renal artery


What is label E?

Renal vein


What is label F?



What is label A?

Efferent arteriole


WHat is label B?

Affernet arteriole


WHat is label C?



What is label D?

Bowman's capsule


WHat is label E?

Proximal convoluted tubule


WHat is label F?

Distal convoluted tubule


WHat is label G?

Collecting duct


WHat is label H?

Vasa recta


What is label I?

Loop of Henle


What is function of the afferent arteriole?

Brings blood to the nephron to be filtered


What is the function of the efferent arteriole?

Removes blood from nephron (minus filtered components)


What is the function of the glomerulus?

Capillary tuft where filtration occurs


What is the function of the Bowman's Capsule?

First part of nephron where filtrate is collected


What is the function of the proximal convoluted tubule?

Where selective reabsorption occurs


What is the function of the loop of henle?

Important for establishing a salt gradient in the medulla


What is the function of the distal convoluted tubule?

Final site of selective reabsorption


What is the function of the collecting duct?

Feeds into ureter and is where osmoregulation occurs


What is the function of the vasa recta?

Blood network that reabsorbs components from the filtrate


When does ultrafiltration occur?

Ultrafiltration occurs when hydrostatic pressure forces blood through a semi-permeable membrane, separating blood cells and large proteins from the remainder of the serum


Where does ultrafiltration occur?

Ultrafiltration occurs between the glomerulus and the Bowman's capsule


How does hydrostatic pressur relate to ultrafiltration?

Hydrostatic Pressure

The glomerulus increases blood pressure by forming narrow branches (which also increases surface area for filtration)

This pressure is maintained by a narrow efferent arteriole (relative to the afferent arteriole), which restricts the outflow of blood, keeping pressure high

The net pressure gradient in the glomerulus forces blood into the capsule space


How does the basement membrane relate to ultrafiltration?

Basement Membrane

The basement membrane is a fine mesh that restricts the passage of blood cells and proteins - it is the sole filtration barrier

Blood can exit the glomerulus directly through pores as the capillaries are fenestrated

The filtrate can enter the Bowman's capsule directly because the podocytes that surround the glomerulus contain filtration slits between their pedicels

The basement membrane lies between the glomerulus and Bowman's capsule


Define osmoregulation

Osmoregulation is the control of the water balance of the blood, tissue or cytoplasm of a living organism


Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis and active transport (8)

The proximal convoluted tubule extends from the Bowman's capsule and is where most selective reabsorption in the nephron occurs

All glucose, amino acids, vitamins and hormones are reabsorbed here, along with most (~80%) of the mineral ions and water

The proximal convoluted tubule has a microvilli cell lining to increase the surface area for the absorption of materials from the filtrate

There are also a large number of mitochondria in these cells, as reabsorption from the filtrate involves active transport

Once materials have been activly reabsorbed into the tubule cells, they can passively diffuse into the bloodstream (along the concentration gradient)

Mineral ions and vitamins are actively transported via protein pumps or carrier proteins

Glucose is actively transported across the membrane in symport with sodium

Water follows the movement of the ions passively (via osmosis)


Explain the roles of the loop of Henle, medulla, collecting duct and ADH (vasopressin) in maintaining the water balance of the blood (10)

Creating a Salt Gradient in the Medulla

The function of the loop of Henle is to create a salt bath concentration in the fluid surrounding the tubule

The descending limb of the loop of Henle is permeable to water, but impermeable to salts

The ascending limb of the loop of Henle is permeable to salts, but impermeable to water

This means that as the loop descends into the medulla, the interstitial fluid becomes more salty (and less salty as it ascends into the cortex)

As the vasa recta blood network that surrounds the loop flows in the opposite direction (counter-current exchange), this further multiplies the effect



As the collecting duct passes through the medulla as it drains into the ureter, the hypertonic solution of the deep medulla will draw water by osmosis

Antidiuretic hormone (ADH or vasopressin) is a hormone released from the posterior pituitary in response to dehydration (detected by hypothalamus)

ADH increases the permeability of the collecting duct to water, allowing more water to be reabsorbed by osmosis (via the production of aquaporins)

This means less water remains in the filtrate and the urine becomes more concentrated

When the individual is suitably rehydrated, ADH levels will decrease and less water will be reabsorbed from the collecting ducts


Explain the difference in the concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine (9)


Proteins will be present in blood plasma, but not present in glomerular filtrate or urine

This is because proteins cannot pass across the basement membrane during ultrafiltration and thus cannot form part of the filtrate



Glucose will be present in blood plasma and glomerular filtrate, but not present in urine (normally)

This is because the glucose is selectively reabsorbed in the proximal convoluted tubule

It is reabsorbed from the filtrate into the blood by active transport (symport with Na+ ions)



Urea will be present in blood plasma, glomerular filtrate and urine

Only about 50% of urea is reabsorbed (some urea is reabsorbed to help regulate the medullary osmolarity gradient)

Because water is reabsorbed from the filtrate (by osmosis, due to the hypertonicity of the medulla), urea becomes more concentrated in urine

The concentration of urea in the urine will depend on the amount of water in the urine


Explain the presence of glucose in the urine of untreated diabetic patients (4)

The urine of non-diabetic patients should contain no glucose as it is selectively reabsorbed from the filtrate in the proximal convoluted tubule

Diabetics have higher levels of blood glucose due to either a lack of insulin secretion (type I) or insensitivity to insulin secretions (type II)

Because of this, not all of the glucose in diabetics is reabsorbed into the blood (protein pumps in tubule wall become saturated)

This results in the presence of glucose in the urine of untreated diabetics, which can be detected using test strips

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