Lecture 1 - Structure and Function of the Kidney Flashcards
Describe the excretory functions of the kidney.
- Metabolites: urea (from proteins) and uric acid (from nucleic acids)
- Foreign products
What are the 6 functions of the kidney? Which 2 are related to urine formation?
- Homeostasis***
- Excretory***
- Endocrine
- Paracrine
- Autocrine
- Metabolic
In how much time does the kidney filter the entire plasma volume?
30 min
Describe the 3 endocrine functions of the kidney.
- Erythropoietin: precursor for RBC generation in the red bone marrow
- Renin: protease that converts angiotensinogen to angiotensin I
- 1-α-hydroxylase: enzyme that converts 25-hydroxy vitamin D to 1,25-dihydroxy vitamin D (active form of vitamin D)
Describe the metabolic functions of the kidney.
- Gluconeogenesis
2. Ammoniagenesis
Is urine formation continuous in the kidneys?
YUP
What are the 3 parts of the functional anatomy of the kidney?
- Renal parenchyma
- Nephron
- Blood supply
What is the functional and structural unit of the kidney?
The nephron
What is the kidney nephron?
Single cell thick tube
What is fluid called while it is inside the nephron? What about before it gets there? What about when it leaves?
Blood/plasma => tubular fluid => urine
How many nephrons in the kidneys? How does this number vary?
1 M/kidney
Born with 1 M and then starting at age 20 we lose 1% of them a year
Describe the structure of a kidney nephron.
RENAL CORPUSCLE:
- Glomerulus = glomerular capillary tufts
- Bowman’s capsule = tubular structure that surrounds the capillaries as a sphere
URINIFEROUS TUBULE:
- Proximal tubule with convoluted and straight segments
- Loop of Henle with descending and then ascending limb
- Distal tubule with convoluted and straight segments
COLLECTING DUCTS:
6. Collecting duct
In what part of the kidney are the nephrons located?
- 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
What are the 3 parts of the proximal tubule?
- Early proximal convoluted tubule (S1)
- Mid-proximal convoluted tubule (S2)
- Proximal straight tubule (S3)
What are the 3 parts of the loop of Henle?
- Thin descending limb
- Thin ascending limb
- Thick ascending limb
What are the 4 parts of the distal convoluted tubule?
TBD
Describe the pathway of the blood supply to the kidneys along with pressure drops.
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
Other name for the renal arcuate artery?
Angled artery
Other name for interlobular artery?
Cortico-radial artery
Is the pressure in the glomerulus similar to that of other capillaries in the body? Why?
NOPE because it is surrounded by arterioles on both sides (~50 mmHg instead of 20 mmHg)
What do the peritubular capillaries surround?
Both the proximal and distal convoluted tubules in the cortex
What happens at the glomerular capillaries?
Initiating event for filtration and movement of plasma into the kidney tubules at high pressure
What is nephron heterogeneity?
There are different types of nephrons based on their location:
- Outer cortical nephrons: smaller, shorter loop of Henle, smaller glomerulus, smaller proximal convoluted tubule, efferent arteriole forms peritubular capillaries, which surround the entire nephron
- Mid-cortical nephrons: intermediate
- 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
Other name for outer cortical nephrons?
Superficial nephrons
Other name for juxtamedullary nephrons?
Deep nephrons
What is the significance of longer loops of Henle in deep nephrons?
Greater capacity to make concentrated urine
What is the ratio of long loop to short loop nephrons in humans? How does this vary in different species?
15:85 in humans
Depends on water availability and need to generate concentrated urine: more water means more short loops
Role of vasa recta instead of peritubular capillary bundles?
Greater capacity to make concentrated urine and supplies the medullary substance
What is a juxtaglomerular apparatus? Can it happen in both superficial and deep nephrons?
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:
- Juxtaglomerular cells
- Macula densa cells
YUP
What do we call the cells of the distal convoluted tubule that are juxtaposed to the glomerulus blood supply? Why? Role?
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
What are the juxtaglomerular cells?
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
What part of the kidney contain/produce renin?
Juxtaglomerular cells in membrane-bound granules
What cells of the kidney have a brush border?
Those in the proximal tubule ONLY
LIST and DEFINE the three processes involved in the formation of urine.
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Other name for collecting duct?
Papillary duct
What does the depth of the loops of Henle depend on?
Upon the location of their associated renal corpuscles in the cortical substance
Where are the hairpin loops of the loops of Henle of the superficial nephrons located?
Outer medulla and even cortex
Can different populations of nephrons respond differently to chronic and acute renal insults?
YUP
What are the capillaries from the efferent arteriole of the nephron called?
Vasa convulata
How do the vasa recta of the juxtamedullary glomeruli work?
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
Describe the capillaries comprising the vasa recta and the vasa convoluta.
Fenestrated with diaphragms
