IB Biology HL Section 11.3: The Kidney and Osmoregulation

What is the sixth step in the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis, and active transport?

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

What are the 9 major parts of the annotated diagram of a glomerulus and associated nephron? In other words, what all does the nephron include?

1.) Afferent arteriole 2.) Efferent arteriole 3.) Glomerulus 4.) Bowman's Capsule 5.) Proximal Convoluted Tubule (PCT) 6.) Loop of Henle 7.) Distal Convoluted Tubule (DCT) 8.) Collecting Duct 9.) Vasa Recta

What are the 6 major parts of the human kidney, which is also in the diagram?

1.) Cortex 2.) Renal Pelvis 3.) Medulla 4.) Renal Artery 5.) Renal Vein 6.) Ureter

What two things does ultrafiltration require in order to form the filtrate?

1.) Hydrostatic pressure 2.) Basement Membrane

What is the third major step in osmoregulation? In other words, what does ADH increase, in return allowing what?

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

What is the second step in the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis, and active transport?

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

What is the first major step in osmoregulation?

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.

What further multiplies the effect of the more salty and less salty characteristics of the descending vs. ascending characteristic?

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

Explain the presence of glucose in the urine of untreated diabetic patients. Furthermore, since the reason why diabetics have higher levels of blood glucose is due to either a lack insulin secretion (type I) or insensitivity to insulin secretions (type II), what happens to the glucose because of this?

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

What is the seventh step in the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis, and active transport?

Glucose is actively transported across the membrane in symport with sodium.

What is excretion?

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

Where is there concentration of glucose?

In blood plasma and glomerular filtrate.

Where is there concentration of urea?

In blood plasma, glomerular filtrate, and urine.

Where is there concentration of proteins?

In blood plasma.

What will the concentration of urea in the urine depend on?

It will depend on the amount of water in the urine.

What is the function of the afferent arteriole?

It brings blood to the nephron to be filtered.

How can the filtrate enter the Bowman's capsule directly (Third Step of Basement Membrane)?

It can enter it directly because the podocytes that surround the glomerulus contain filtration slits between their pedicels.

How can the blood exit the glomerulus directly (Second Step of Basement Membrane)?

It can exit directly through pores as the capillaries are fenestrated.

What is the overall role of the Loop of Henle?

It creates a salt gradient in the medulla.

What is the function of the collecting duct?

It feeds into ureter and is where osmoregulation occurs.

How does the glomerulus increase blood pressure (First Step of Hydrostatic Pressure)?

It increases blood pressure by forming narrow branches.

What is the basement membrane (First Step of Basement Membrane)?

It is a fine mesh that restricts the passage of blood cells and proteins - it is the sole filtration barrier.

What is the second major step in osmoregulation? In other words, what is the antidiuretic hormone (ADH or vasopressin)?

It is a hormone released from the posterior pituitary in response to dehydration (detected by hypothalamus).

Explain the presence of glucose in the urine of untreated diabetic patients. Furthermore, why do diabetics have higher levels of blood glucose.

It is because they either lack insulin secretion (type I) or insensitivity to insulin secretions (type II).

What is the descending limb of the Loop of Henle impermeable to?

It is impermeable to salts.

What is the ascending limb of the Loop of Henle impermeable to?

It is impermeable to water.

What is the function of the Loop of Henle?

It is important for establishing a salt gradient in the medulla.

How is the increased blood pressure by glomerulus maintained (Second Step of Hydrostatic Pressure) ?

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

Why is glucose not normally present in urine?

It is not present because the glucose is selectively reabsorbed in the proximal convoluted tubule (PCT).

What is the ascending limb of the Loop of Henle permeable to?

It is permeable to salts.

What is the descending limb of the Loop of Henle permeable to?

It is permeable to water.

How is water reabsorbed from the filtrate?

It is reabsorbed by osmosis, due to the hypertonicity of the medulla).

What is the function of the vasa recta?

It is the blood network that reabsorbs components from the filtrate.

What is the function of the Glomerulus?

It is the capillary tuft where filtration occurs.

What is osmoregulation?

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

What is the function of the Distal Convoluted Tubule (DCT)?

It is the final site of selective reabsorption.

What is the function of the Bowman's Capsule?

It is the first part of nephron where filtrate is collected.

What is the function of the Loop of Henle (longer version of its overall role)?

It is to create a salt bath concentration in the fluid surrounding the tubule.

What is the function of the Proximal Convoluted Tubule (PCT)?

It is where selective reabsorption occurs.

Where does the basement trade lie (Fourth Step of Basement Membrane)?

It lies between the glomerulus and Bowman's capsule.

What is the fourth major step in osmoregulation? In other words, what does it mean when more water is allowed to be reabsorbed by osmosis?

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

What does the descending vs. ascending characteristic mean?

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

Where does ultrafiltration occur?

It occurs between the glomerulus and the Bowman's capsule.

What is the function of the efferent arteriole?

It removes blood from the nephron (minus filtered components).

Explain the presence of glucose in the urine of untreated diabetic patients. Furthermore, what shouldn't the urine of non-diabetic patients contain?

It should not contain any glucose as it is selectively reabsorbed from the filtrate in the proximal convoluted tubule (PCT).

What is the fifth step in the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis, and active transport?

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

How much of urea is reabsorbed?

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

What is the nephron consider as?

The nephron is the functional unit of the kidney.

What forces the blood from the glomerulus into the capsule space (Third Step of Hydrostatic Pressure)?

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

Explain the process of ultrafiltration, what are its 4 general parts?

The process of ultrafiltration includes blood pressure, pressure, fenestrated blood capillaries, and basement membrane.

What is the first step in the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis, and active transport?

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

What is the third step in the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis, and active transport?

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

When glomerulus increases blood pressure by forming branches, what happens as a result (First Step of Hydrostatic Pressure)?

The result is it also increases surface area for filtration.

What is the width of the cortex?

The width of the cortex is thin.

What is the width of the medulla?

The width of the medulla is thick.

What is the fourth step in the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis, and active transport?

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

How many steps are there to the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis, and active transport?

There are eight steps.

How many major steps does the process of osmoregulation have?

There are five major steps.

How many major parts are there to the process of ultrafiltration?

There are two major parts.

Why are proteins not present in glomerular filtrate or urine?

They are not present because they cannot pass across the basement membrane during ultrafiltration and thus cannot form part of the filtrate.

When does ultrafiltration occur (also known as the first part of ultrafiltration?

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

What is the eighth step in the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis, and active transport?

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

What happens because water is reabsorbed from the filtrate?

What happens is that urea becomes more concentrated in urine.

What happens when not all of the glucose in diabetics is reabsorbed into the blood?

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

What is the five major step in osmoregulation? In other words, what happens to the ADH levels when the individual is suitably rehydrated?

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