L1: Renal Histology, Function and Circulation

Question 1

Functions of the Kidneys?

Answer 1

Regulation of water and electrolyte balance

Excretion of metabolic waste and bioactive substances

Regulation of arterial blood pressure

Regulation of erythrocyte production

Regulation of Vitamin D production

Gluconeogenesis (glucose synthesis)

Question 2

What metabolic waste and bioactive substances do the kidneys excrete?

Answer 2

Urea (from protein)

Uric acid (from nucleic acids)

Creatinine (from muscle creatine)

Drugs/Hormones

Question 3

How do the kidneys regulate arterial pressure?

Answer 3

Regulation of blood volume

Renin production (Renin-Angiotensin-Aldosterone System (RAAS))

Question 4

Role of Kidneys in regulating erythrocyte production?

Answer 4

Kidney is major site of Erythropoietin (EPO) production (Fibroblasts)

Released fro fibroblast cells when local tissue oxygen levels are reduced

EPO stimulates the bone marrow to increase production of erythrocytes and therefore haemoglobin

Question 5

How do the kidneys regulate Vitamin D Production?

Answer 5

Active form of Vitamin D (Calcitriol) is made in the kidneys => Promotes calcium and phosphate absorption from the gut

Question 6

Role of Kidneys in Maintaining blood glucose?

Answer 6

Gluconeogenesis: Synthesis of glucose from non carbohydrate sources during periods of fasting

Question 7

Predominant type of tissue type in renal capsule is ____________ connective tissue

Surrounded by perinephric fat and then by the ______________, which also encloses the ____________________________

Answer 7

Predominant type of tissue type in renal capsule is fibrous connective tissue

Surrounded by perinephric fat and then by the perinephric (perirenal) fascia, which also enclose the adrenal gland (produces aldosterone)

Question 8

What penetrates the renal Hilum?

Answer 8

Renal artery
Renal vein
Lymphatics
Renal nerve
Renal pelvis

Question 9

Three distinct regions of the kidney and their constituents?

Answer 9

Cortex (Location of glomeruli of nephrons)

Medulla (Nephrons’ tubules)

Renal pelvis (major and minor calyces collect urine and empty it into the renal pelvis)

Question 10

Answer 10

Question 11

Arteries/Veins located at the boundary of cortex and medulla of kidneys?

Answer 11

Arcuate Arteries/Veins

Question 12

Arteries/Veins located in the cortex of kidneys?

Answer 12

Interlobular Arteries/ Veins

Question 13

Path of blood flow in kidneys?

Answer 13

Question 14

Vascular supply to the two types of Nephrons in Kidneys?

Answer 14

Peritubular Capillaries (Cortical Nephrons)

Vasa Recta Capillaries (Juxtamedullary Nephrons)

Question 15

Cortical vs. Juxtamedullary Nephrons?

Cortical Nephrons:

• Glomeruli located in the ___________
• Responsible for _______________________
• Supplied by ____________________

Juxtamedullary Nephrons:

• Glomeruli are in the ___________________
• Produce __________________________
• Supplied by ________________________

Answer 15

Cortical Nephrons:

• Glomeruli located in the outer cortex
• Responsible for majority of reabsorption within the kidney (80-85% of nephrons)
• Supplied by Peritubular Capillaries

Juxtamedullary Nephrons:

• Glomeruli are in the inner cortex (near the medulla)- NO Glomeruli in Medulla!!
• Produce concentrated/diluted urine
• Supplied by Vasa Recta Capillaries (Straight Vessels)

Question 16

Collections of straight tubules form the ________, which run up the centre axis of a renal lobule

Region of cortex between the rays is called ___________

Answer 16

Collections of straight tubules form the medullary rays, which run up the centre axis of a renal lobule

Region of cortex between the rays called the cortical labyrinth

Question 17

Structures of the Juxtaglomerular Apparatus?

Answer 17

Macula Densa of the Thick Ascending Limb: columnar epithelial cells that act as salt sensors

Extraglomerular Mesangial Cells: specialized smooth muscle cells that regulate blood flow

Granular Cells (Afferent Arteriole): specialized smooth muscle cells that manufacture, store and release RENIN

Question 18

Columnar epithelial cells of the Juxtaglomerular Apparatus that act as salt sensors?

Answer 18

Macula Densa (Thick Ascending Limb)

Question 19

Specialized smooth muscle cells of the Juxtaglomerular Apparatus that regulate blood flow?

Answer 19

Extraglomerular Mesangial Cells

Question 20

Specialized smooth muscle cells of the Juxtaglomerular Apparatus that manufacture, store and release RENIN

Answer 20

Granular cells (Afferent Arteriole)

Question 21

Thickness of Renal Tubule?

Answer 21

All tubules are a single layer of epithelial cells: permits exchange of fluid/solutes between the tubule and the surrounding interstitial/vasculature

Question 22

Section of renal tubule composed of simple cuboidal epithelial cells with extended brush borders?

Answer 22

Proximal tubule

Question 23

Section of renal tubule composed of Squamous (flattened) epithelium

Answer 23

Thin Descending and Ascending Limbs

Question 24

Section of renal tubule composed of Cuboidal epithelium with invaginated basolateral membranes?

Answer 24

Thick Ascending Limb and the Distal Tubule

Question 25

Section of Renal Tubule composed of columnar epithelium?

Answer 25

Collecting Duct Cells: * principal cells (NaCl reabsorption and K+secretion) * intercalated cells (acid-base balance)

Question 26

Cell Type of the Renal Collecting duct responsible for NaCl reabsorption and K+ secretion?

Answer 26

Principal Cells

Question 27

Cell Type of the Renal Collecting duct responsible for Acid-Base balance?

Answer 27

Intercalated Cells

Question 28

Blood Flow to Kidneys?

Answer 28

Renal blood flow **~950 –1100 ml/min** (_20% of the cardiac output_) Far in excess of kidneys’ metabolic needs providing kidneys the flexibility to alter blood flow in response to physiological demand

Question 29

Capillary Beds in the Kidney

Answer 29

Question 30

Why is hydrostatic pressure at afferent renal arterioles high relative to non-renal vascular beds?

Answer 30

Presence of second set of arterioles after glomerular capillaries -Efferent arterioles offer resistance to the blood flow Branching of glomerular capillaries leads to increased cross-sectional area and results in only minor drop in pressure

Question 31

Glomerular capillary hydrostatic pressure (PCAP)?

Answer 31

45mmHg –60mmHg

Question 32

Why does Π CAP increase along the length of the glomerular capillaries?

Answer 32

1. fluid leaving glomerular capillaries 2. large proteins not filtered

Question 33

Purpose of variable pressures along the renal circulation?

Answer 33

Influences filtration and reabsorption Net Filtration: occurs along the length of *glomerular capillaries* -afferent end (18mmHg) and efferent end (5mmHg) Reabsorption: along the length of *peritubular capillaries* due to further reduction in Capillary hydrostatic pressure in efferent arterioles, whereas oncotic pressure is high (35mmHg)

Question 34

What is the normal value for net filtration pressure (NFP) at the afferent vs. efferent end of glomerular capillaries?

Answer 34

5 mm HG NET Outward pressure from afferent to efferent

Question 35

Where in the Renal Vascular bed does net filtration occur?

Answer 35

Glomerular Capillaries

Question 36

Where in the Renal Vascular Bed does net Reabsorption occur?

Answer 36

Peritubular Capillaries