Histology of Kidney Tissue

Question 1

What does the urinary system consist of?

Answer 1

• two kidneys
• two ureters
• one bladder
• one urethra

Question 2

Explain what happens to urine after it is produced in the kidney

Answer 2

It is conducted by the ureters to the bladder where it is stored and leaves the body via the urethra.

Question 3

Explain the blood supply and drainage to and from the kidney

Answer 3

Renal arteries arise from the abdominal aorta. One of more renal veins drain each kidney to the inferior vena cava.

Question 4

Give and explain the 4 functions of the kidney

Answer 4

• Homeostasis (of water, electrolytes, acid/base)
• Excretion (of soluble toxic metabolic waste products, particularly nitrogenous urea and creatinine
• Hormonal (synthesis of renin, synthesis of erythropoietin)
• Metabolic (vitamin D is converted to active form in kidney)

Question 5

What are the 3 parts to kidney function?

Answer 5

1. Filtration (of most small molecules from blood plasma to form ultra filtrate of plasma - most negative molecules repelled and do not enter filtrate)
2. Selective reabsorption (of most water and some molecules from ultra filtrate, leaving behind excess and waste to be excreted)
3. Secretion (of soluble waste products from blood, and of H+ ions for acid/base balance

Question 6

Is the filtrate further processed after the kidney?

Answer 6

No

Question 7

Give details on kidney structure

Answer 7

• consists of outer cortex and inner medulla
• medullary pyramids project into subdivisions of the renal pelvis
• the renal pelvis narrows as it leaves the kidney to give the ureter
• the hilum: site of entry and exit of renal blood vessels and ureter
• the whole kidney is surrounded by a fibrous capsule, which also surrounds the attached adrenal gland (sits ontop of the kidney), also surrounded by a thick layer of fat

Question 8

How is the kidney organised?

Answer 8

A medullary pyramid and its associated cortex forms a lobe.
A human kidney has 10-18 lobes.
The functional unit of a kidney is the nephron.
Kidney donation reflects the way the 10^6 nephrons are arranged.
Accurate and interlobular vessels. The renal artery brings the blood in and then then divides to form the individual filtration units.

Question 9

What does a nephron consist of?

Answer 9

A renal corpuscle and a renal tubule.

Question 10

What happens in a nephron when the cortex is met again?

Answer 10

blood flows into the distal convoluted tubule

Question 11

What is most of the cortex formed of?

Answer 11

The proximal convoluted tubule

Question 12

Give details on each of these 
Renal corpuscle 
Bowmans capsule
Glomerulus 
Renal tubule

Answer 12

rc - plasma filtration, consists of 2 structures
bc - distended, blind end of the renal tubule
g - packed capillaries that invaginate Bowmans capsule derive from the afferent arteriole
rt - reabsorption, extends from Bowmans capsule to the collecting duct, convoluted in shape and has 4 zones (proximal convolutes tubule, loop of henle, distal convoluted tubule, collecting tubule

Question 13

What does the renal cortex contain?
Tubules make up the vast bulk of the —– between the ——.
What is parenchyma?

Answer 13

Renal corpuscles

parenchyma, corpuscles

Surrounding tissue of the tubules

Question 14

Explain the movement of the afferent and efferent arterioles

Answer 14

Wide afferent arteriole enters the Bowmans Capsule at the vascular pole, branches to form a network of capillaries.
Efferent arterioles is smaller in diameter, so to maintain a pressure gradient that drives filtration of plasma into Bowmans space

Question 15

What do parietal cells do?

Where do podocytes sit?

Answer 15

Surround the Bowmans capsule

On the outside of the Bowmans capsule

Question 16

What is the purpose of a mesangial cell?

Answer 16

They are phagocytic. They pick up dead matter such as if you had kidney damage or an infection.

Question 17

What are the 3 layers which the filtrate must pass through before entering the renal tubule? Give some details

Answer 17

1. Capillary endothelium (fenestrated)
2. Glomerular basement membrane (thick as formed by 2 basal laminae of podocytes and endothelia. contains type 4 collagen
3. Between the podocytes lining the capsule (indigitating pedicels). Gaps between pedicles are filtration slits

Question 18

Give information about what would be seen under EM microscope of the podocyte filter

Answer 18

Primary and secondary pedicels resemble octopus tentacles that completely cover the endothelia. These create very small spaces.

Cells are flat with large bulging nuclei. Each podocyte has several long primary processes that can cover more than one capillary.
At greater magnification, the secondary pedicles can be seen as lateral extensions of the primary processes.

Question 19

What gives rise to regularly spaced filtration slits of uniform width?

Answer 19

Interdigitation of processes

Question 20

Why is there a darkening seen under the microscope where the pedicles come together?

Answer 20

A collection of proteins with a negative charge.

Question 21

Give details on the proximal convolted tubule

Answer 21

Longest part of the renal tubule. Approximately 75% of filtrate is reabsorbed at the PCT. Simple tall columnar epithelium with large brush border (BB) of tall microvilli. Many capillaries (C) arise from efferent arteriole - receive molecules reabsorbed by PCT.

Question 22

Where does material which is reabsorbed go?

Answer 22

Taken into capillaries which filter into the renal vein

Question 23

What does the EM of PCT show?

Answer 23

EM reveals microvilli (Mv), many vesicles (M) and lysosomes (L). Capillaries (Cap) under the basal lamella (BM) take the reabsorbed solutes after transport accords the epithelial cells.

Many lysosomes because the cell is also phagocytic taking up particulate matter that gets though the kidney filter.

Question 24

Which loop of henle is the thin loop?

What happens here?

Answer 24

The descending limb and a small amount of the ascending limb.
This is so water can leave the filtrate passively.

Question 25

What makes the ascending loop thicker?

Which limb is shorter?

Answer 25

It has more columnar cells

Thin ascending limb

Question 26

Give details on where the loop of Henle is

Answer 26

Arises in cortex, dips into medulla (descending limb), returns to cortex as ascending limb

Question 27

Where is the distal convoluted tubule found?
What occurs here?
Explain the cell histology

Answer 27

Found in the cortex
Reabsoprtion of sodium ions from tubule lumen (aldosterone control)
Simple cuboidal epithelium, no brush border, many mitochondria

Question 28

Explain the juxtaglomerular apparatus

Answer 28

It is a specialisation of the afferent arteriole and the DCT of the same nephron. Regulates blood pressure via renin-angiotensin-aldosterone system.

Question 29

What is the macula densa?

Answer 29

An area of large closely packed tall epithelial cells - DCT adjacent to the juxtaglomerular apparatus. These cells are sensitive to the ionic composition and the blood pressure.

Question 30

What are Lacis cells derived from and what do they secrete?

Answer 30

Derived from mesangial cells and secrete erythopoietin

Question 31

What are proximal collecting tubules and distal collecting tubules lined by?

Answer 31

Proximal - mixture of DCT cells and collecting tubule cells

Distal - principal cells with interspersed intercalated cells

Question 32

Give histology and role of principal cells and intercalated cells

Answer 32

Principal - pale cytoplasm, scanty organelles, short microvilli. Actively reabsorbs Na+ and secretes K+.

Intercalated - darker cytoplasm, mitochondria, polyribosomes and vesivles. Important for acid-bases homeostasis as secretes H+ and reabsorbs K+ and HCO3-

Question 33

Where do collecting tubules extend from?

What do several collecting tubules converge to form?

Answer 33

The DCT.

Collecting ducts

Question 34

Urine is concentrated by passive —– of water into medullary —– following the —– gradient created by the counter current —– systems of loops of Henle. This is controlled by —–

Answer 34

Reabsorption
Interstitium
Osmotic
Multiplier

ADH

Question 35

What are the ducts called which are formed from collecting ducts and drain urine from tip of renal papilla into renal pelvis?

Answer 35

Ducts of Bellini

Question 36

Give details on the renal papilla

Answer 36

Forms the apex of the medullary pyramid; projects into the proximal renal pelvis or pelivicalceal space.
Ducts of Bellini converge to drain urine at the tip of the papilla.

Question 37

What is the pelvicalceal space lined with?

Answer 37

Transitional epithelium

Question 38

What is the ureter?

Answer 38

A muscular tube that connects urine from the kidney to the bladder. This is a passive process.
Urine moved by peristaltic action of ureteric wall.

Question 39

Explain the smooth msucle in the ureter?

What is the lumen of the ureter lined with?

Answer 39

Two layers of smooth muscle.
Longitudinal inner layer and circular outer layer.

Lumen of ureter is lined with transitional epithelium, with deeps lamina propriety rich in collagen (LP).

Question 40

Urinary (transitional) epithelium

Where is it found?
What type of epithelium is it?
Give any more details

Answer 40

Found within the conducting passages of the urinary system.

It is stratified epithelium. It is only squamous when it is distended (swollen).

Cytoplasm consists of thick iflexible plaques with narrow zones of normal membrane.
It leads to much folding and formation of deep clefts of fusiform vesicle - renders epithelium impermeable to urine.

Question 41

How many smooth muscle layers does the bladder have?

What are each of these?

Answer 41

3 layers.

Inner longitudinal layer, outer circular and outermost longitudinal.

Question 42

Explain the countercurrent multiplier mechanism

Answer 42

Loop of Henle - produces an increasing osmotic gradient from the cortex to the tip of the renal papilla.
Active transport of sodium and chloride ions into the medullary interstitium by the ascending thin limb, which is impermeable to water.

Think descending limb contains water and ions from PCT at low osmotic concentration. Epithelial lining is freely permeable.

Question 43

The juxtaglomerular cells monitor blood pressure. Explain it does so.

Answer 43

Reduced blood pressure means reduced filtration and a lower concentration of sodium ions in DCT. Cells of mucula densa sense this and promote renin secretion.

Renin in bloodstream catalyses conversion of plasma angiotensinogen to angiotension 1. This constrict blood vessels and promotes release of aldosterone from adrenal cortex.