Lecture 1 - Structure and Function of the Kidney

Question 1

Describe the excretory functions of the kidney.

Answer 1

1. Metabolites: urea (from proteins) and uric acid (from nucleic acids)
2. Foreign products

Question 2

What are the 6 functions of the kidney? Which 2 are related to urine formation?

Answer 2

1. Homeostasis***
2. Excretory***
3. Endocrine
4. Paracrine
5. Autocrine
6. Metabolic

Question 3

In how much time does the kidney filter the entire plasma volume?

Answer 3

30 min

Question 4

Describe the 3 endocrine functions of the kidney.

Answer 4

1. Erythropoietin: precursor for RBC generation in the red bone marrow
2. Renin: protease that converts angiotensinogen to angiotensin I
3. 1-α-hydroxylase: enzyme that converts 25-hydroxy vitamin D to 1,25-dihydroxy vitamin D (active form of vitamin D)

Question 5

Describe the metabolic functions of the kidney.

Answer 5

1. Gluconeogenesis

2. Ammoniagenesis

Question 6

Is urine formation continuous in the kidneys?

Answer 6

YUP

Question 7

What are the 3 parts of the functional anatomy of the kidney?

Answer 7

1. Renal parenchyma
2. Nephron
3. Blood supply

Question 8

What is the functional and structural unit of the kidney?

Answer 8

The nephron

Question 9

What is the kidney nephron?

Answer 9

Single cell thick tube

Question 10

What is fluid called while it is inside the nephron? What about before it gets there? What about when it leaves?

Answer 10

Blood/plasma => tubular fluid => urine

Question 11

How many nephrons in the kidneys? How does this number vary?

Answer 11

1 M/kidney

Born with 1 M and then starting at age 20 we lose 1% of them a year

Question 12

Describe the structure of a kidney nephron.

Answer 12

RENAL CORPUSCLE:

1. Glomerulus = glomerular capillary tufts
2. Bowman’s capsule = tubular structure that surrounds the capillaries as a sphere

URINIFEROUS TUBULE:

3. Proximal tubule with convoluted and straight segments
4. Loop of Henle with descending and then ascending limb
5. Distal tubule with convoluted and straight segments

COLLECTING DUCTS:
6. Collecting duct

Question 13

In what part of the kidney are the nephrons located?

Answer 13

• Glomerulus, Bowman’s capsule, and proximal convoluted tubule in the cortex
• Part of the proximal straight tubule and Loop of Henle in the medullary pyramids
• Part of the thick ascending limb of the loop of Henle and distal convoluted tubule in cortex
• Collecting tubule both in cortex in medullary pyramid

Question 14

What are the 3 parts of the proximal tubule?

Answer 14

1. Early proximal convoluted tubule (S1)
2. Mid-proximal convoluted tubule (S2)
3. Proximal straight tubule (S3)

Question 15

What are the 3 parts of the loop of Henle?

Answer 15

1. Thin descending limb
2. Thin ascending limb
3. Thick ascending limb

Question 16

What are the 4 parts of the distal convoluted tubule?

Answer 16

TBD

Question 17

Describe the pathway of the blood supply to the kidneys along with pressure drops.

Answer 17

Renal artery => interlobar artery between kidney lobes (minimal pressure drop) => arcuate artery at the cortico-medullary junction (sharp turn and still minimal pressure drop) => interlobular artery into medullary rays substance (minimal pressure drop) => afferent arteriole (pressure drop from 100 to 50 mmHg) => capillary bundle of the glomerulus => efferent arteriole => peritubular capillaries (pressure drop from 50 to 20 mmHg) => venule => interlobular vein => arcuate vein => interlobar vein => renal vein => IVC

Question 18

Other name for the renal arcuate artery?

Answer 18

Angled artery

Question 19

Other name for interlobular artery?

Answer 19

Cortico-radial artery

Question 20

Is the pressure in the glomerulus similar to that of other capillaries in the body? Why?

Answer 20

NOPE because it is surrounded by arterioles on both sides (~50 mmHg instead of 20 mmHg)

Question 21

What do the peritubular capillaries surround?

Answer 21

Both the proximal and distal convoluted tubules in the cortex

Question 22

What happens at the glomerular capillaries?

Answer 22

Initiating event for filtration and movement of plasma into the kidney tubules at high pressure

Question 23

What is nephron heterogeneity?

Answer 23

There are different types of nephrons based on their location:

1. Outer cortical nephrons: smaller, shorter loop of Henle, smaller glomerulus, smaller proximal convoluted tubule, efferent arteriole forms peritubular capillaries, which surround the entire nephron
2. Mid-cortical nephrons: intermediate
3. Juxtamedullary nephrons: larger, longer loop of Henle, larger glomerulus, efferent arteriole is unusually large and form capillary bundles which then form descending vasa recta around the loop of Henle, longer proximal convoluted tubule

Question 24

Other name for outer cortical nephrons?

Answer 24

Superficial nephrons

Question 25

Other name for juxtamedullary nephrons?

Answer 25

Deep nephrons

Question 26

What is the significance of longer loops of Henle in deep nephrons?

Answer 26

Greater capacity to make concentrated urine

Question 27

What is the ratio of long loop to short loop nephrons in humans? How does this vary in different species?

Answer 27

15:85 in humans Depends on water availability and need to generate concentrated urine: more water means more short loops

Question 28

Role of vasa recta instead of peritubular capillary bundles?

Answer 28

Greater capacity to make concentrated urine and supplies the medullary substance

Question 29

What is a juxtaglomerular apparatus? Can it happen in both superficial and deep nephrons?

Answer 29

Early distal tubule comes back to its parent glomerulus to the point that its proximity to the vessels that feed the glomerulus is very very close: 1. Juxtaglomerular cells 2. Macula densa cells YUP

Question 30

What do we call the cells of the distal convoluted tubule that are juxtaposed to the glomerulus blood supply? Why? Role?

Answer 30

Macula densa cells because they stain dark on EM due to dark particles => sensor cells that sense the composition/flow of the tubular fluid in the distal tubule and can then signal the rest of the cells of the arterioles to change their caliber accordingly => nephron can regulate its own flow

Question 31

What are the juxtaglomerular cells?

Answer 31

Cells between the macula densa cells and the cells of the glomerulus blood supply which are modified smooth muscle cells of the afferent arteriole MAINLY

Question 32

What part of the kidney contain/produce renin?

Answer 32

Juxtaglomerular cells in membrane-bound granules

Question 33

What cells of the kidney have a brush border?

Answer 33

Those in the proximal tubule ONLY

Question 34

LIST and DEFINE the three processes involved in the formation of urine.

Answer 34

1. Glomerular filtration 2. Tubular reabsorption 3. Tubular secretion

Question 35

Other name for collecting duct?

Answer 35

Papillary duct

Question 36

What does the depth of the loops of Henle depend on?

Answer 36

Upon the location of their associated renal corpuscles in the cortical substance

Question 37

Where are the hairpin loops of the loops of Henle of the superficial nephrons located?

Answer 37

Outer medulla and even cortex

Question 38

Can different populations of nephrons respond differently to chronic and acute renal insults?

Answer 38

YUP

Question 39

What are the capillaries from the efferent arteriole of the nephron called?

Answer 39

Vasa convulata

Question 40

How do the vasa recta of the juxtamedullary glomeruli work?

Answer 40

As the vasa recta descends into the medulla it gives off capillary plexuses to the inner and outer stripes of the outer medulla and to the inner medulla => the blood from the capillary plexuses in the medulla then returns to the cortex by merging with vessels of the ascending vasa recta => this system of capillaries is responsible for supplying blood flow to the medulla and for establishing a countercurrent exchange system important for maintaining the osmotic gradient within the medullary pyramid

Question 41

Describe the capillaries comprising the vasa recta and the vasa convoluta.

Answer 41

Fenestrated with diaphragms