Chapter 25 - Kidneys

Question 1

Functions of Kidneys

Answer 1

Regulating total water volume and solute concentration in water
Regulating ECF ion concentrations
Long-term acid-base balance
Removal of metabolic wastes, toxins, drugs
Endocrine functions
Renin - regulation of blood pressure
Erythropoietin - regulation of RBC production
Activation of vitamin D
Gluconeogenesis during prolonged fasting

Question 2

3 layers of Kidneys

Answer 2

Renal cortex
Renal medulla
Renal Pelvis

Question 3

Nephrons

Answer 3

Structural and functional units that form unrine

Question 4

Renal Corpuscle

Answer 4

Glomerulus: Tuft of capillaries; fenestrated endothelium, porous, filtrate formation. Specialized for filtration, Different from other capillary beds – fed and drained by arteriole. Blood pressure in glomerulus high:
-Afferent arterioles larger in diameter than efferent arterioles and arterioles are high-resistance vessels

Glomerular capsule (Bowman’s capsule): Hollow structure surrounding glomerulus

Question 5

Proximal convoluted tubule (PCT)

Answer 5

Proximal convoluted tubule (PCT): Cuboidal cells with dense microvilli (surface area); large mitochondria
Functions in reabsorption and secretion
Confined to cortex

Question 6

Distal convoluted tubule (DCT)

Answer 6

Distal convoluted tubule (DCT): Cuboidal cells with very few microvilli, Function more in secretion than reabsorption, Confined to cortex

Question 7

Collecting Duct

Answer 7

Principal cells: Sparse, short microvilli, Maintain water and Na+ balance

Intercalated cells: Cuboidal cells; lots of microvilli; maintain acid-base balance

Question 8

Peritubular capillaries:

Answer 8

Peritubular capillaries: Low-pressure, porous capillaries adapted for absorption Arise from efferent arterioles
Cling to adjacent renal tubules in cortex

Question 9

3 Main parts of Renal tubule

Answer 9

Proximal Convoluted Tubule
Nephron Loop
Distal Convoluted Tubule

Question 10

3 Steps of Urine formation

Answer 10

1. Glomerular filtration: produces cell and protein-free filtrate
2. Tubular reabsorption: Selectively returns 99% of substances from filtrate to blood in renal tubules and collecting ducts
3. Tubular secretion: Selectively moves substances from blood to filtrate in renal tubules and collecting ducts

Question 11

What types of molecules can pass through filteration membrane

Answer 11

Molecules smaller than 3 nm to pass
Water, glucose, amino acids, nitrogenous wastes
Plasma proteins remain in blood maintains colloid osmotic pressure prevents loss of all water

Question 12

Chief force pushing water, solutes out?

Answer 12

Hydrostatic pressure in glomerular capillaries

Question 13

Net Filtration Pressure

Answer 13

Pressure responsible for filtrate formation

Main controllable factor determining glomerular filtration rate (GFR)

Question 14

Glomerular Filtration Rate (GFR)

Answer 14

Volume of filtrate formed per minute by both kidneys (120–125 ml/min)
GFR directly proportional to
NFP: primary pressure is hydrostatic pressure in glomerulus
Total surface area for filtration: mesangial cells control by contracting
Filtration membrane permeability – much more permeable than other capillaries

Question 15

Regulation of Glomerular Filtration

Answer 15

Constant GFR allows kidneys to make filtrate and maintain homeostasis
Goal of intrinsic controls - maintain GFR in kidney

GFR affects systemic blood pressure
GFR urine output blood pressure, and vice versa
Goal of extrinsic controls - maintain systemic blood pressure

Question 16

Intrinsic Control

Answer 16

Myogenic Mechanism
Smooth muscle contracts when stretched
Raised BP - muscle stretch - constriction of afferent arterioles - restricts blood flow into glomerulus
Decreased BP - dilation of afferent arterioles

Tubuloglomerular Feedback Mechanism
Flow-dependent mechanism directed by macula densa cells; respond to filtrate NaCl concentration
If GFR raised - filtrate flow rate increased - decreased reabsorption time high filtrate NaCl levels  constriction of afferent arteriole, decreased NFP & GFR more time for NaCl reabsorption
Opposite for decreased GFR

Question 17

Extrinsic Control

Answer 17

Sympathetic Control
If extracellular fluid volume extremely low, norepinephrine and epinephrine released

Systemic vasoconstriction increased blood pressure
Constriction of afferent arterioles GFR increased blood volume and pressure

Renin-Angiotensin- Aldosterone Mechanism
Main mechanism for increasing BP
Three pathways to renin release
Direct stimulation of granular cells by sympathetic nervous system
Stimulation by activated macula densa cells if filtrate NaCl concentration low
Reduced stretch of granular cells

Question 18

Tubular Reabsorption

Answer 18

Most of contents reabsorbed to blood
Selective transepithelial process
~ All organic nutrients reabsorbed
Water and ion reabsorption hormonally regulated and adjusted

Question 19

Transcellular Route

Answer 19

Transport across the apical membrane
Diffusion through cytosol
Transport across the basolateral membrane
Movements through interstitial fluid and into capillary

Question 20

Paracellular

Answer 20

Movement through leaky tight junctions, particularly in the PCT.
Movement through interstitial fluid and into capillary

Question 21

Steps of Reabsorption in Proximal Convoluted Tubular

Answer 21

At the basolateral membrane, Na+ is pumped into the interstitial space by the Na+-K+ ATPase. Active Na+ transport creates concentration gradients that drive

“Downhill” Na+ entry at the apical membrane.

Reabsorption of organic nutrients and certain ions by cotransport at the apical membrane.

Reabsorption of water by osmosis through aquaporins. Water reabsorption increases the concentration of the
solutes that are left behind. These solutes can then be reabsorbed as they move down their gradients:

Lipid-soluble substances diffuse by the transcellular route.

Various ions (e.g., Cl−, Ca2+, K+) and urea diffuse by the paracellular route.

Question 22

How is water reabsorbed

Answer 22

Movement of Na+ and solutes creates osmotic gradient for water.

Water reabsorbed by osmosis, aided by water-filled pores called aquaporins
-Aquaporins always present in PCT obligatory water
reabsorption

-Aquaporins inserted in collecting ducts only if ADH
present facultative water reabsorption

Question 23

Hormones that affect reabsorption

Answer 23

ADH - released by posterior pit gland
Aldosterone - Targets collecting ducts and distal PCT
Atrial Natriuretic peptide - Reduces blood Na+, decreases blood volume, and blood pressure, Released by cardiac atrial cells.
Parathyroid Hormone - Acts on DCT to increase Ca2+ Reabsorption.

Question 24

Tubular secretion

Answer 24

Reabsorption in reverse; almost all in PCT
Disposes of substances (e.g., drugs) bound to plasma proteins
Eliminates undesirable substances passively reabsorbed (urea and uric acid)
Rids body of excess K+ (aldosterone)
Controls blood pH by altering amounts of H+ or HCO3– in urine

Question 25

Diuretics

Answer 25

ADH inhibitors (alcohol)
Na+ reabsorption inhibitors (and resultant H2O reabsorption) (caffeine, hypertension or edema drugs)
Loop diuretics inhibit medullary gradient
Osmotic diuretics - substance not reabsorbed so water remains in urine, (high glucose of diabetic patient)

Question 26

Chemical Composition of Urine

Answer 26

95% water and 5% solutes
Nitrogenous wastes 
Urea (amino acid breakdown) 
Uric acid (nucleic acid metabolism)
Creatinine (metabolite of creatine phosphate)

Question 27

3 events must happen for urination or micturition

Answer 27

Contraction of detrusor muscle by ANS
Opening of internal urethral sphincter by ANS
Opening of external urethral sphincter by somatic nervous system