Lecture 11: renal histology, renal func & renal circulation

Question 1

What are the 6 functions of the kidneys?

Answer 1

1. Regulation of H20 and electrolyte balance (varying output of H20 with intake and independently vary input and output of minerals eg sodium Na+)
2. Excretion of metabolic waste and bioactive substances ( eg urea from protein, creatinine from muscle creatine)
3. Regulation of arterial blood pressure ( they regulate the blood volume using the renin RAAS system)
4. Regulation of rbc’s production ( major site of rbc stimulating hormone EPO production)
5. Regulation of vitamin D production ( Calcitriol (active form of vit D ) made in kidney)
6. Gluconeogenesis ( formation of glucose from non carb substances eg protein and lipids

Question 2

How do the kidneys regulate rbc production?

Answer 2

• kidneys produce a hormone called erythropoietin - this hormones role is to stimulate bone marrow to make rbc’s
• released when oxygen levels are low

Question 3

what is the RAAS system?

Answer 3

• Renin - Angiotensin- Aldosterone System

hormone system that regulates blood pressure in arterials

Question 4

What components is the urinary system composed of?

Answer 4

• kidneys (left and right) - right is lower due to large liver on right side
• ureters’ - tubes that carry urine from kidney to bladder
• Bladder - stores urine, composed of smooth muscle
• urethra - tube that allows urine to exit from bladder

Question 5

What is the peritoneum? what does retroperitoneal mean?

Answer 5

• tissue that lines the abdominal wall and covers most of the organs in the abdomen
• retroperitoneal means the area outside/ behind the peritoneum

Question 6

What is the external structure of a kidney?

Answer 6

• Hilum - penetrated by the renal artery, renal vein, & renal pelvis

Question 7

what is the predominant type of tissue in the renal capsule (layer around kidney)? what is it surrounded by?

Answer 7

• type of tissue found in capsule = fibrous connective tissue
• surrounded by perinephric fat and perinephric fascia (adipose capsule of kidney)

Question 8

What are the 3 distinct regions in the internal structure of a kidney ?

Answer 8

• Cortex (location of the glomerulus of nephrons)
• the medulla ( consists of nephrons tubules)
• the renal pelvis

Question 9

What is the medulla further divided into? And what consists between the cortex and medulla?

Answer 9

• further divided into the outer medulla ( next to cortex) and the inner medulla
• a boundary lies between the cortex and medulla ( see image)

Question 10

What arteries are present in the kidney - list them in order of branching out?

Answer 10

1. renal artery ( where blood enters kidney)
2. segmental artery
3. interlobar artery
4. arcuate artery
5. interlobular artery

then afferent arteriole into the glomerular capsule …

Question 11

Where are arcuate arteries and veins located in the kidney?

Answer 11

• corticomedullary boundary

Question 12

where are the interlobular veins and arteries located in the kidney?

Answer 12

the cortex

Question 13

what is a nephron? what does it consist of ?

Answer 13

• the functional unit in a kidney
• consists of :

1. renal corpuscle (site of filtration of blood) containing bowman’s capsule (space around glomerulus) and glomerulus ( capillaries)
2. Renal tubule

Question 14

What is the structure of a nephron?

Answer 14

• glomerulus & bowmans capsule
• proximal tubule
• loop of henle- descending limb and ascending limb
• distal convoluted tubule
• collecting duct - cortical & medullary collecting duct

Question 15

How does the filtrate from the glomerulus enter the bowmans capsule?

Answer 15

• the bowman’s capsule is interlinked with the proximal tubule etc
• filtrate flows through the glomerular barrier to the bowman’s capsule

Question 16

What regions of the tubule does the cortex contain?

Answer 16

• distal convoluted (complex) tubule
• proximal convoluted tubule
• cortical collecting duct

Question 17

What regions of the tubule does the outer medulla contain?

Answer 17

• proximal straight tubule (pars Recta)

Question 18

What regions of the tubule does the inner medulla contain?

Answer 18

• descending loop of henle
• ascending loop of henle
• papillary collecting duct
• medullary collecting duct

Question 19

What is the function of the renal corpuscle ? what is the function of the renal tubules?

Answer 19

1. filtration of blood
2. reabsorption and secretion - helping to form urine

Question 20

What is the difference in function between the proximal and distal convoluted tubules

Answer 20

• proximal - func - reabsorption of filtrate
• distal - func - regulation of water, electrolyte and H+ balance

Question 21

What are 2 distinct types of nephron in the kidney?

Answer 21

1. cortical nephrons - lie in the outer cortex and have short loops of henle that barely penetrate the medulla
2. Juxtamedullary ( near medulla) nephrons - lie in the innr cortex and have long loops of henle that lie in the inner cortex

Question 22

Compare the difference in blood supply to the cortical nephrons and the juxtamedullary nephrons?

Answer 22

• cortical nephrons - efferent arterioles take blood away from glomerulus enters capillary network called the peritubular capillaries
• Juxtamedullary nephrons - efferent arterioles take blood away from glomerulus follows loop of henle down to medulla in a set of long loops (vasa recta )

Question 23

Compare the difference in function in cortical nephrons vs juxtamedullary nephrons

Answer 23

• cortical - responsible for most of the re-absorption in the kidney
• juxtamedullary - involved in formation of concentrated and diluted urine

Question 24

What are the interlobular veins?

Answer 24

• any of the veins in the kidney that empty into the arcuate veins

Question 25

Where are the glomeruli of the cortical vs juxtamedullary nephrons **located**?

Answer 25

* **cortical nephrons** have **glomeruli in the outer cortex** * **juxtamedullar**y have glomeruli **near the cortical - medullary boundary**

Question 26

what are **medullary rays**?

Answer 26

* **middle part of a cortical lobule** (or renal lobule) * located in cortex but 'medullary" refers to their **destination**, not their location * consists of bundles of renal tubules

Question 27

What 3 structures make up the **juxtaglomerular apparatus**?

Answer 27

* **Macula densa** of thick ascending limb (columnar epithelial cells that act as salt sensors) * **extraglomerular mesangial cells** (specialized smooth muscle cell that regulates blood flow) * **Granular cells** of afferent arteriole ( specialized smooth muscle cells that manufacture, store & release renin)

Question 28

What epithelial cells are present in different regions of the renal tubule?

Answer 28

* **all tubules are a single layer of epithelial cells NB** 1. **Proximal tubule** - _simple cuboidal_ epithelial cells 2. **Thin ascending and descending limbs****-squamous** epithelium 3. **thick ascending limb and distal tubule** -**cuboidal** epithelium 4. **collecting duct cells** - _columnar epithelium_ (principal - NA+ reab and K+ secretion and intercalated cells -acid base balance)

Question 29

What are the major divisions of a nephron?

Answer 29

* Renal corpuscle * **proximal** convoluted tubule * thin and thick limb of **loop of henle** * **distal convoluted tubule** * **collecting tubule**

Question 30

Describe the division of vasculature in the kidney

Answer 30

* kidney receives blood from renal artery * renal artery divides into 2 or more ateries @ the hilium * in renal sinus, they branch into interlobular arteries * interlobular arteries branch further into arcuate arteries and afferent arterioles

Question 31

How does blood leave the glomerular capillaries?

Answer 31

via the efferent arteriole which branch out to form the peritubular capillaries

Question 32

The difference between cortical and juxtamedullary nephrons is that cortical nephrons have their glomeruli in the cortex whereas the glomeruli of juxtamedullary nephrons are located in the medulla. True or false?

Answer 32

* False - the glomeruli of the juxtamedullary nephrons are located near the medulla (juxta = near)

Question 33

Erythropoietin is secreted by granular cells of the juxtamedullary apparatus - true or false?

Answer 33

* False - the mesangial cells are smooth muscle cells that regulate blood flow

Question 34

What are the **3 general types of tubules** that occur in the **cortical labyrinth and medullary rays of the cortex?**

Answer 34

* Proximal convoluted tubule * Distal convoluted tubule * Collecting ducts ( in medullary ray)

Question 35

Answer 35

* What region shown - cortex * Tubules labelled A and B - * A = proximal tubule as it has an occluded ( closed ) lumen - presence of microvilli on epithelial cells of lumen * B= distal convoluted tubule - clear lumen, no microvilli present

Question 36

What are tubules in the cortex surrounded by?

Answer 36

* **peritubular capillaries** - tiny blood vessels that travel alongside the nephron to allow reabsorption & secretion between blood and inner lumen of nephron

Question 37

Why is blood flow reduced from the cortex to the inner medulla?

Answer 37

* crucial to **prevent hyperosmolar gradient** in the medullary interstitium from being washed away