Renal Physiology

Question 1

Two primary functions of the kidneys include:

Answer 1

● To rid the body of waste
● To control the volume and composition of body fluids

Question 2

Kidneys are primarily responsible for eliminating these waste products of metabolism:

Answer 2

○ Urea (from the metabolism of amino acids)
○ Creatinine (from muscle creatine)
○ Uric acid (from nucleic acids, purines)
○ End products of hemoglobin breakdown (e.g., bilirubin)
○ Metabolites of various hormones
○ Most toxins and other foreign substances (pesticides,
drugs, food additives, etc.) are also eliminated

Question 3

Electrolytes:

Answer 3

sodium, chloride,
potassium, calcium, hydrogen,
magnesium, and phosphate

Question 4

By regulating ______, the kidneys work with
the lungs to regulate the pH of
blood

Answer 4

the concentration of bicarbonate and hydrogen ions in the blood

Question 5

Kidneys are responsible for up to _____% of gluconeogenesis during fasting

Answer 5

40

Question 6

_____ – deep to the cortex,
houses the loop of Henle and
collecting ducts

Answer 6

Medulla

Question 7

_____ - sit at the end of
renal pyramids and collect formed urine

Answer 7

Calyces (minor/major)

Question 8

T/F the kidney Cannot regenerate new nephrons

Answer 8

T

Question 9

The renal corpuscle is composed of two parts:

Answer 9

● Glomerulus - ball of capillaries
○ Afferent arterioles - bring blood into
glomerulus for filtration
○ Efferent arterioles - the remaining blood
exits via these arterioles
○ The arterioles are lined with smooth
muscle - controlled by the sympathetic
nervous system
● Bowman’s capsule

Question 10

The ____ is where water and
solutes are exchanged (formation of urine)

Answer 10

renal tubule

Question 11

Glomerular filtrate route (follow the urine):

Answer 11

● Bowman’s capsule
● Renal tubules
○ Proximal convoluted tubule
○ Loop of Henle
■ Descending limb
■ Ascending limb
○ Distal convoluted tubule
○ Collecting duct

Question 12

The juxtaglomerular complex/apparatus helps regulate:

Answer 12

● Blood pressure
● Glomerular Filtration Rate (GFR)
● Located between Distal Convoluted Tubule (DCT) and afferent arteriole

Question 13

Three kinds of cells of the juxtaglomerular complex:

Answer 13

○ Macula Densa Cells (DCT): Sense decrease Na+ and Cl-
○ Mesangial Cells: Help with signaling between densa/juxta cells
○ Juxtaglomerular Cells (AKA “Granular Cells”)
■ Sense decrease in BP
■ Secrete Renin

Question 14

Renal circulation has two capillary beds:

Answer 14

1. Glomerular capillaries
   ● High hydrostatic pressure → causes rapid
   fluid filtration
2. Peritubular capillaries
   ● Lower hydrostatic pressure → permits rapid
   fluid reabsorption

Question 15

Surround renal tubules and allow
reabsorption and secretion
between blood and tubules

Answer 15

Peritubular capillaries

Question 16

Specialized peritubular capillaries
that surround the Loop of Henle

Answer 16

Vasa Recta

Question 17

Renal blood flow in the small vessels:

Answer 17

Efferent arterioles → Peritubular capillaries + Vasa Recta → Veins

Question 18

The glomerular capillary membrane is a
_____ charged membrane that has three layers that allows for filtration (due to fenestrations)

Answer 18

negatively

Question 19

GFR = ______

Answer 19

the volume (mL) of fluid that filters into the Bowman’s capsules per unit of
time (min)

Question 20

In an average, healthy adult, GFR =

Answer 20

125 mL/min (180 L/day)

Question 21

Kidney disease = _____ GFR

Answer 21

decreased

Question 22

Items freely filtered by kidneys: ____

Answer 22

Na, K, Cl, bicarb, glucose, urea, amino acids (not large proteins like albumin), insulin, and ADH

Question 23

GFR can be increased or decreased depending on various factors:

Answer 23

● Glomerular hydrostatic pressure (GHP)
● Glomerular oncotic pressure (GOP)
● Bowman’s capsule hydrostatic pressure (BHP)
● Capillary permeability
● Resistance of Afferent or Efferent arterioles

Question 24

Three things that can↑↓ Glomerular hydrostatic
pressure:

Answer 24

○ ↑or ↓ blood pressure
○ Afferent arteriole resistance
○ Efferent arteriole resistance

Question 25

Primary method of physiologic GFR regulation

Answer 25

Glomerular Hydrostatic Pressure (GHP)

Question 26

Increasing GHP increases ____

Answer 26

GFR

Question 27

Oncotic pressure =

Answer 27

osmotic pressure exerted by proteins (AKA – Colloid osmotic pressure)

Question 28

What are starling forces?

Answer 28

Hydrostatic and oncotic pressure gradients that govern passive exchange of water between interstitium and capillary walls

Question 29

Net Filtration Pressure (NFP) = ____

Answer 29

sum of hydrostatic and osmotic forces across the glomerular capillaries

Question 30

Bowman’s Capsule Hydrostatic Pressure (BHP)

Answer 30

The pressure inside Bowman’s capsule is approximately 18 mmHg

Question 31

Capillary Permeability

Answer 31

● ↑ capillary membrane permeability = ↑ GFR ● ↓ capillary membrane permeability = ↓ GFR

Question 32

Vasoconstriction that ↑ afferent resistance will ↓ Glomerular Hydrostatic Pressure = ____

Answer 32

↓ GFR

Question 33

Vasoconstriction that ↑ efferent resistance will ↑ Glomerular Hydrostatic Pressure = ____

Answer 33

↑ GFR

Question 34

Mean Arterial Pressure (MAP) –____

Answer 34

Average blood pressure (not glomerular hydrostatic pressure) between systole and diastole

Question 35

When MAP falls below 80 mmHg it _____

Answer 35

triggers baroreceptor reflexes that increase sympathetic activity ● This response causes contraction of smooth muscle and affects both the afferent and efferent arterioles ● This will increase MAP and decrease GFR which will decrease urine output and conserve fluid

Question 36

______ – movement of filtered solutes/H2O from tubules back into capillaries

Answer 36

Tubular Reabsorption

Question 37

_____ “second pass” – molecules move from plasma of the peritubular capillary bed back into the renal tubule filtrate

Answer 37

Tubular Secretion

Question 38

Reabsorption is a two-step process occurring via ____ transport

Answer 38

passive or active

Question 39

Reabsorption is a two-step process:

Answer 39

1. H2O and dissolved substances from tubule → cell/interstitium 2. From the cells/interstitium, H2O and solutes → capillary walls → blood stream

Question 40

_____ – Transports through the interstitium via concentration gradients

Answer 40

Passive Transport

Question 41

Reabsorption – Na+

Answer 41

Reabsorption of Na+ (PCT) ● Active transport – Na+ /K+ Pump ● Co-transport with a.a, glucose, Cl– ● Countertransport with H+

Question 42

Reabsorption of K+ (PCT)

Answer 42

● Active transport – Na+ /K+ Pump ● Potassium channels

Question 43

Reabsorption of H2O

Answer 43

● 70% in the PCT ● 20% DCT ● 10% CD

Question 44

Reabsorption of Ca++

Answer 44

● 99% of filtered Calcium is reabsorbed ○ 70% in the PCT ○ 25% loop of Henle ○ 5% DCT

Question 45

Water can cross the plasma membranes via _____

Answer 45

aquaporins (water channels)

Question 46

Tubular Secretion

Answer 46

Occurs in the same way reabsorption does, but in REVERSE ● Passive secretion ● Active transport

Question 47

Secretion of K+

Answer 47

● Na+ /K+ Pump ○ DCT and CD

Question 48

Secretion of Ca++

Answer 48

● DCT (very limited, <1%)

Question 49

Anatomy of Excretion

Answer 49

● Calyx ○ Minor ○ Major ● Renal pelvis ● Ureter – autonomic nervous system, peristaltic action ● Bladder – Detrusor muscle, surrounded by fibrous connective tissue ● Urethra

Question 50

Control of urination is achieved via

Answer 50

● Autonomic control (involuntary) ○ Internal urethral sphincter ● Somatic control (voluntary) ○ External urethral sphincter

Question 51

ADH – Antidiuretic Hormone/“Vasopressin”

Answer 51

● Secreted from posterior pituitary ○ Stimulates aquaporin placement ■ Aquaporin ↑↑ H2O permeability ■ Conserves H2O by reducing its loss through excretion

Question 52

Conserves H2O by reducing its loss through excretion

Answer 52

ADH

Question 53

Hypothalamus measures osmolality and release of ADH:

Answer 53

● If osmolality ↑↑→ ADH released → ↑ H2O reabsorption = ↓ H2O excretion (less urine) ● If osmolality ↓↓ → no ADH → ↓↓ H2O reabsorption = ↑ H2O excretion (more urine)

Question 54

Aldosterone

Answer 54

● Steroid hormone ○ Released from adrenal cortex ○ Works in the distal tubule Principle regulator ● Reabsorption of Na+ (increase serum Na+) ● Secretion of potassium (decrease serum K+)

Question 55

Principle regulator for reabsorption of Na+ and Secretion of potassium

Answer 55

Aldosterone

Question 56

Renin

Answer 56

● Enzyme ○ Released from juxtaglomerular cells ○ Converts Angiotensinogen to Angiotensin I ○ Stimulates release of aldosterone and cortisol ● Eventually increases Angiotensin II ○ Increases thirst ○ Increase Na+ in body and release K+

Question 57

Stimulates release of aldosterone and cortisol

Answer 57

Renin

Question 58

Angiotensin Converting Enzyme (ACE)

Answer 58

● Enzyme ○ Secreted by the lungs and kidneys ○ Converts Angiotensin I into Angiotensin II ● Indirectly causes increased blood pressure via ○ Vasoconstriction of systemic arterioles ○ Adrenal cortex to release aldosterone ○ Posterior pituitary to release ADH ○ Hypothalamus induces thirst = ↑ fluid intake

Question 59

Atrial Natriuretic Peptide

Answer 59

● Peptide Hormone ● Primary roles ○ Decreases blood pressure ○ Electrolyte homeostasis

Question 60

Parathyroid Hormone (PTH)

Answer 60

● Hormone ○ Produced from the parathyroid glands ○ Triggered by ↓ plasma Ca++ ● Primary role to increase serum Ca++ levels ○ Increase absorption of Ca++ in the GI tract ■ Via calcitriol ○ Increase reabsorption of Ca++ in the kidneys ■ Loop of Henle and DCT ○ Increase resorption of Ca++ in the bone

Question 61

Primary role to increase serum Ca++ levels

Answer 61

PTH

Question 62

Calcitriol

Answer 62

○ Active form of Vitamin D3 (1,25-dihydroxycholecalciferol) ○ Produced in the proximal tubule ○ Increases GI absorption of Ca++

Question 63

Increases GI absorption of Ca++

Answer 63

Calcitriol

Question 64

Calcitonin

Answer 64

○ Released from the thyroid gland in response to elevated Ca++ levels ○ Role to decrease serum Ca++ ■ Decrease calcium reabsorption in the kidney ■ Inhibits osteoclast activity in the bones

Question 65

Role to decrease serum Ca++

Answer 65

Calcitonin