Module 4 Section 2

Question 1

kidneys

Answer 1

• controlled by both neural and endocrine inputs
• primary function is to maintain the ECF volume, electrolyte composition, and osmolarity
• in the presence of excess water or of a particular electrolyte (solute), the kidneys will increase their elimination
• when there is a deficit of water or of a solute, the kidneys cannot actively correct this
• they can further reduce their elimination

Question 2

major functions of kidneys

Answer 2

1. maintain water balance in the body
2. maintain body fluid osmolarity
3. maintain proper plasma volume
4. help maintain acid-base balance
5. regulate ECF solutes (such as sodium, potassium, chloride, calcium, phosphate etc)
6. excrete wastes of metabolism
7. excrete foreign compounds ingested
8. produce erythropoietin
9. produce renin
10. activate vitamin D

Question 3

kidney structure

Answer 3

• bean-shaped organs, each 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 is the renal cortex and the inner part of the renal medulla
• at the inner core of each kidney is the renal pelvis, through which the urine empties and is channeled to the ureter

Question 4

functional unit of the kidney

Answer 4

• nephron
• more than one 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

neprhon components

Answer 5

• can be divided into two components
  1. vascular component - supplies blood to the nephron
  2. tubular component - carries the filtrate throughout the nephron

Question 6

vascular component

Answer 6

• major part of the vascular component is the glomerulus, which is a ball-like capillary through which water and solutes are filtered from the plasma
• when blood enters the kidney via the renal artery, the renal artery subdivides into many small afferent arterioles, each of which supplies a nephron
• leaving the nephron are the efferent arterioles, which transport unfiltered blood from the glomerulus
• the capillaries of the nephron are different in that the arterial blood enters and then leaves, with no oxygen extracted
• the efferent arteries subdivide into capillaries, the peritubular capillaries, that deliver oxygen to the renal tissues

Question 7

tubular component

Answer 7

• filtered blood enters a hollow tube, formed by a single layer of epithelial cells, that transports urine to the renal pelvis
• even though it is technically one long continuous tube, it is divided along its length based on differences in structure and function

Question 8

tubular component - step by step

Answer 8

• begins with Bowmans capsule, which encircles the glomerulus to collect the fluid filtered from the glomerular capillaries
• fluid then passes into the proximal tubule within the renal cortex, which is highly coiled along its length
• next the loop of henle forms a hairpin loops that dips down into the renal medulla
• the descending limb of the loop of Henle travels from the cortex to the medulla while the ascending limb travels from the cortex to the medulla while the ascending limb travels from the medulla back to the cortex
• the ascending limb passes through the fork of the afferent and efferent arteries in a region called the juxtaglomerular apparatus
• the tubule now coils again and is called the distil tubule, also entirely within the cortex
• the distal tubule empties into a collecting duct, which travels deep into the medulla and ultimately drains into the renal pelvis

Question 9

cortical nephrons

Answer 9

• the glomeruli of this type of nephron lie in the outer layer of the cortex
• about 80% of all nephrons are cortical nephrons that primarily serve secretory and regulatory functions
• their loop of Henle only slightly dips into the renal medulla
• the peritubular capillaries from this type of nephron wrap around the short loops of Henle

Question 10

juxtamedullary nephrons

Answer 10

• this type of nephron is found on the inner layer of the cortex and are responsible for the concentration 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 11

3 basic renal processes

Answer 11

1. glomerular filtration (GF)
2. tubular reabsorption (TR)
3. Tubular Secretion (TS)

Question 12

glomerular filtration (GF)

Answer 12

• about 20% of the blood that flows through the glomerular capillaries is filtered into Bowmans 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 minute

Question 13

tubular reabsorption (TR)

Answer 13

• as the filtrate flows through the tubules, important substances are returned to the peritubular capillaries by the process of tubular reabsorption
• of the 180 litres of plasma filtered each day, about 178.5 is reabsorbed

Question 14

tubular secretion (TS)

Answer 14

• this is the second route for substances in the blood to enter the renal tubules
• tubular secretion is the selective transfer of substances from the peritubular capillaries into the tubules
• only 20% of the plasma is filtered in the glomeruli so this route allows excretion of selected substances from the remaining 80% of the plasma

Question 15

5 main functions of the kidney

Answer 15

1. maintain water balance in the body
2. maintain body fluid osmolarity
3. regulate ECF solutes (such as sodium, potassium, chloride, calcium, phosphate, and others)
4. maintain proper plasma volume
5. excrete wastes of metabolism