Module 4 Section 2 (Overview of the Kidneys)

Question 1

Describe the roles of the kidneys. (10)

Answer 1

The kidneys, controlled by both neural and endocrine inputs, have several major functions:
1) Maintain water balance in the body
- In the presence of excess water of a particular electrolyte (solute), the kidneys will incr their elimination.
However, if there is a deficit of water or solute, the kidneys can reduce their elimination
2) Maintain body fluid osmolarity
3) Maintain proper plasma volume
4) Help maintain acid-base balance
5) Regulate ECF solutes (such as Na, K, Cl, Ca, P, and others)
6) Excrete wastes of metabolism
7) Excrete foreign compounds ingested
8) Produce erythropoietin
9) Produce renin
10)Activate vitamin D

Question 2

Describe the major structural components of a nephron.

Answer 2

Vascular component:
- Supplies blood to the nephron
- Major part of the vascular component of the nephron = glomerulus (ball-like capillary through which water and solutes are filtered from the plasma)
- When blood —(renal artery)—> kidney, the renal artery subdivides into many small afferent arterioles, each of which supplies a nephron
- The efferent arterioles leave the nephron and transport unfiltered blood from the glomerulus
- The capillaries of the nephron are different (arterial blood enters and then leaves w/ no oxygen extracted)
• Instead, the efferent arteries subdivide -> capillaries (the peritubular capillaries) that deliver O2 into the renal tissues

Tubular component:

• Carries the filtrate throughout the nephron
• Filtered blood enters a hollow tube, formed by a single layer of epithelial cells, that transports urine -> renal pelvis
• The tube is divided along its length based on differences in structure and function
  1) Bowmen’s capsule = encircles the glomerulus to collect the fluid filtered from the glomerular capillaries
  2) Fluid then passes -> proximal tubule within the renal cortex, which is highly coiled along its length
  3) Loop of Henle = forms a hairpin loop that dips down -> renal medulla
  4) the descending limb of the loop of Henle travels from cortex -> medulla, while the ascending limb travels from the medulla -> cortex
  5) The ascending limb passes through the fork of the afferent and efferent arteries into -> juxtaglomerular apparatus
  6) The tubule now coils again and is called the distal tubule, also entirely within the cortex.
  7) The distal tubule empties into a collection duct, which travels deep into the medulla and ultimately drains -> renal pelvis

Question 3

** Describe the basic renal processes involved in urine excretion.

Answer 3

Glomerular filtration (GF)

• About 20% of the blood that flows through the glomerular capillaries is filtered into Bowman’s capsule.
• This plasma filtrate is normally protein free, but does contain the same solutes as the plasma
• Collectively, about 125mL of glomerular filtrate is formed each min

Tubular Reabsorption (TR)

• As the filtrate flows through the tubules, important substances are returned to the peritubular capillaries through tubular reabsorption
• Of the 180L of plasma filtered daily, only about 178.5 is reabsorbed

Tubular Secretion (TS)

• This is the 2nd route for substances in the blood to enter the renal tubules
• It transfers substances from the peritubular capillaries -> the tubules
• Since only 20% of the plasma is filtered in the glomeruli, this route allows excretion of secreted substances from the remaining 80% of the plasma

Question 4

Discuss the structure of the kidney.

Answer 4

• Bean-shaped orgam
• About 10cm in length
• Associated with each kidney is an adrenal gland, which is situated on top of the kidney.
• The outside of the kidney = renal cortex
• The inner part of the kidney = medulla
• At the inner core of each kidney = the renal pelvis (through which the urine empties and is channeled to the ureter
• The functional unit of the kidney = the nephron, of which there are more than 1 million in a healthy adult kidney.
  • It is within the nephrons that blood is filtered to produce urine and the reabsorption of necessary fluids and molecules occurs.

Question 5

What are the 2 types of nephrons?

Answer 5

Cortical Nephrons:

• The glomeruli of this type of nephron are in the outer layer of the cortex
• 80% of all nephrons are this kind, that primarily serve secretory and regulatory functions
• Their loop of Henle only slightly dips -> renal medulla
• The peritubular capillaries from this type wrap around the short loops of Henle

Juxtamedullary Nephrons:

• This type is found on the inner layer of the cortex and are responsible for the conc and dilution of urine
• The peritubular capillaries from these nephrons form hairpin loops of vasculature, called the vasa recta, that are in close proximity to the long loops of Henle.

Question 6

Using what you have learned thus far about the nephron, match the correct terms from the list in order by which blood flows from the renal artery to the renal vein in the nephron:

• Glomerulus
• Afferent arteriole
• Efferent arteriole
• Renal artery
• Renal vein
• Peritubular capillaries

1)
2) 
3) 
4) 
5) 
6)

Answer 6

1) Renal artery
2) Afferent arteriole
3) Glomerulus
4) Efferent arteriole
5) Peritubular capillaries
6) Renal vein

Question 7

Using what you have learned thus far about the nephron, match the correct terms from the list in order by which solutes flow from the Bowmen’s capsule to the renal pelvis in the nephron:

• Collecting Duct
• Renal Pelvis
• Loop of Henle
• Bowmen’s Capsule
• Proximal Tubule
• Distal Tubule

1)
2) 
3) 
4) 
5) 
6)

Answer 7

1) Bowmen’s Capsule
2) Proximal Tubule
3) Loop of Henle
4) Distal Tubule
5) Collecting Duct
6) Renal Pelvis

Question 8

List the 5 main functions of the kidney.

Answer 8

1) Maintain water balance in the body
2) Maintain body fluid osmolarity
3) Regulate ECF solutes (such as Na, K, Cl, Ca, P, and others)
4) Maintain proper plasma volume
5) Excrete wastes of metabolism

The kidney has 5 other main functions. These are to

1) Excreting foreign compounds ingested
2) Producing erythropoietin
3) Producing renin
4) The activation of vitamin D
5) Helping to maintain the body’s acid-base balance

Question 9

Select whether the listed statement is a characteristic of the cortical nephron or juxtamedullary nephron.

1) Lies in outer layer of cortex
2) Mainly responsible for urine concentration/dilution
3) Vasa recta are in proximity to the long loops of Henle
4) Primarily serve secretory and regulatory functions
5) About 80% of all nephrons
6) Lie within inner layer of cortex
7) Peritubular capillaries form hairpin loops of vasculature, called the vasa recta
8) Loop of Henle only slightly dips into renal medulla

Answer 9

1) Lies in outer layer of cortex = cortical
2) Mainly responsible for urine concentration/dilution = juxtamedullary
3) Vasa recta are in proximity to the long loops of Henle = juxtamedullary
4) Primarily serve secretory and regulatory functions = cortical
5) About 80% of all nephrons = cortical
6) Lie within inner layer of cortex = juxtamedullary
7) Peritubular capillaries form hairpin loops of vasculature, called the vasa recta = juxtamedullary
8) Loop of Henle only slightly dips into renal medulla = cortical