Intro to Kidney

Question 1

What are the functions of the kidney?

Answer 1

1) Regulate body fluid volume
2) Regulate body fluid composition
3) Excrete metabolic waste and toxins
4) Endocrine functions

Key processes are filtration, reabsorption and secretion to eventually form urine which is excreted.

Question 2

What is a uriniferous tubule?

Answer 2

Uriniferous tubule = nephron + collecting duct

Many nephrons drain into the same collecting duct

Question 3

What is a nephron?

Answer 3

Nephron is a functional unit of kidney

Nephron = renal corpuscle + proximal convoluted tubule (PT) + Loop of Henle + distal convoluted tubule (DT)

~1 million per kidney

Many nephrons drain into the same collecting duct

Question 4

What is the cortex made up of?

Answer 4

Mostly renal corpuscles, PT and DT

Question 5

What is the medulla made up of?

Answer 5

Mostly loops of Henle and collecting ducts

Question 6

What are the 2 different types of nephrons?

Answer 6

Cortical (~80%) or juxtamedullary (~20%) depending on position of renal corpuscle

Question 7

What is the renal corpuscle made up of?

Answer 7

Glomerulus + Bowman’s capsule

Question 8

Describe the blood supply to the kidneys

Answer 8

Renal artery –> Segmental arteries –> Interlobar arteries –> Arcuate arteries (run along corticomedullary junction) –> Interlobular arteries (give off afferent arterioles to the renal corpuscles)

Question 9

Describe the two capillary beds that blood to the kidney passes through

Answer 9

1) High pressure glomerular capillaries (filtration)

2) Low pressure peritubular capillaries (reabsorption/secretion)

Question 10

Describe the two layers of the Bowman’s capsule

Answer 10

Outer layer = parietal layer
Containment -> Simple squamous

Inner layer = visceral layer
Filtration -> Modified simple squamous (podocytes)

Question 11

What are mesangial cells?

Answer 11

Mesangial cells provide support between the glomerular capillary loops

Question 12

Why is there an arteriole at either end of glomerular capillary bed?

Answer 12

Allows high pressure for filtration

Question 13

What is the filtration barrier formed by?

Answer 13

1) Glomerular capillary endothelium (fenestrated)
2) Basement membrane (negative charge)
3) Epithelial cells (podocytes) (interdigitating foot processes and filtration slits)

Limits passage of substances from blood based on their size, charge and shape

Question 14

What type of filtrate is found in the proximal convoluted tubule?

Answer 14

• Unmodified filtrate
• Majority of water, sodium, chloride, amino acids, glucose reabsorption takes place here
• Secretion of some drugs and waste molecules

Question 15

What type of cells are found in the proximal convoluted tubule?

Answer 15

Simple cuboidal cells with microvilli forming a ‘brush border’ to increase surface area

Question 16

Describe the thin descending limb of loop of Henle

Answer 16

Permeable to water - no active reabsorption or secretion of solutes

Simple squamous epithelium

Question 17

Describe the thin ascending limb of loop of Henle

Answer 17

Impermeable to water.

Essentially no active reabsorption or secretion of solutes

Simple squamous epithelium

Question 18

Describe the thick ascending limb of loop of Henle

Answer 18

Impermeable to water.

Active reabsorption of sodium and other solutes.

Simple cuboidal cells

Question 19

Describe the distal convoluted tubule

Answer 19

Divided into early and late parts

Active reabsorption of sodium and other solutes; secretion of potassium and hydrogen ions

Simple cuboidal cells

Variable water permeability depending on precise part of distal tubule and presence of antidiuretic hormone (ADH)

Early distal tubule passes back to the vascular pole of its own renal corpuscle to form part of juxtaglomerular apparatus

Question 20

What is the purpose of the juxtaglomerular apparatus (JGA)?

Answer 20

Involved in tubuloglomerular feedback and control of blood pressure

Question 21

What are the three components to the juxtaglomerular apparatus (JGA)?

Answer 21

1) Macula densa - specialised cells within part of early distal tubule that passes next to the vascular pole of its own renal corpuscle
2) Extraglomerular mesangial cells (Lacis cells)
3) Granular or juxtaglomerular cells in afferent artieriole

Question 22

Describe the medullary collecting duct

Answer 22

Final site for urine processing

Water permeability of this part of nephron under hormonal control by antidiuretic hormone (ADH)

Surrounded by a medullary interstitium with a high concentration of solutes

Key role in regulating degree of urine concentration

Simple columnar cells

Question 23

How much of the body weight is water?

Answer 23

~60% of body weight

Varies with age, gender and body fat

Question 24

What are the main cations and anions in Extra Cellular Fluid?

Answer 24

Na+ is main cation

Cl- is main anion

Question 25

What are the main cations and anions in IntraCellular Fluid?

Answer 25

K+ is main cation

PO4 is main anion

Question 26

Define osmosis

Answer 26

Osmosis is movement of water across a semi-permeable membrane from an area of low solute concentration to a region of high solute concentration

Question 27

Define osmoles

Answer 27

Osmoles refers to the number of osmotically active particles in a solution