Transport Mechanisms + Intro to Glomerulus

Question 1

Define reabsorption

Answer 1

Movement of substance from tubular fluid back into circulation

Question 2

Define secretion

Answer 2

Movement of substances from blood into tubular fluid via;

• Tubular cells (active transport)
• Intracellular spaces (passive)

Question 3

Define excretion

Answer 3

Removal of waste products from blood, and net result of filtration, secretion and reabsorption of a substance

Question 4

Describe 2 way solutes can be transported

Answer 4

Paracellular movement- Across tight junctions, down Conc. gradient

Transcellular movement- Through cell, down or against Conc. gradient (water follows by osmosis)

Question 5

What is the main contributor to maintaining a stable internal environment?

Answer 5

Urinary system (controls concentration of a wide range of ions and small organic molecules)

Question 6

Name 6 substances/ ions that are recovered by 99-100% by the kidney

Name 1 ion that is actively secreted

Answer 6

• H2O
• Glucose
• Amino acids
• Na+
• Cl-
• Bicarbonate (HCO3)

H+

Question 7

What is the Ultra-filtrate

Answer 7

Fluid that has been filtered through glomerulus

Question 8

Compare Osmolarity and Osmolality

Answer 8

Osmolarity: Number of osmoles of solute per litre of solvent (measured in milli-osmoles)

Osmolality: Solute per kg of solvent

Question 9

The Glomeruli are only found in the cortex.

What is the Filtration Fraction? What value is it normally? (Same in both types of nephrons)

Answer 9

Proportion of fluid reaching kidneys that passes into renal tubules (GFR/ RPF, Renal Plasma Flow)

20% (therefore 80% of blood exits via efferent arteriole and is unfiltered)

Question 10

Proteins do not normally enter the renal tubules.

What about RBCs and platelets

Answer 10

No

Question 11

Through what gaps do solutes in blood pass through into the Bowman’s Space

How are proteins prevented from entering?

Answer 11

Through Filtration Slits (spaces between Podocyte processes/ Pedicels)

Negatively charged pedicels repel negatively charged proteins

Question 12

What forces affect the filtration into the glomerulus

Explain the net effect

Answer 12

1. Hydrostatic capillary pressure: Pushes fluid into glomerulus
2. Hydrostatic pressure in Bowman’s Capsule: Pushes fluid back into capillaries
3. Oncotic pressure of blood: Draws fluid back into capillaries

1 Is larger than 2 and 3 combined

Question 13

The Renal Blood Flow and Glomerular Filtration Rate are kept fairly constant by 2 mechanisms of Auto-regulation

Name the 2 mechanisms

(RBF- 800ml/Min, GFR- 120ml/Min/1.73 metres squared)

Answer 13

• Myogenic (Mainly preglomerular vessels such as Arcuate/ Interlobar/ Afferent arterioles)
• Tubuloglomerular feedback

Question 14

Briefly, how does the Myogenic mechanism work to control GFR

Answer 14

Arterial smooth muscle responds to changes in vascular wall tension, causing Afferent/ Efferent arterioles to constrict/ expand

Question 15

Via Myogenic mechanism, what are 2 ways to increase GFR

Answer 15

• Constrict Efferent Arteriole

- Dilate Afferent Arteriole

Question 16

Via Myogenic mechanism, what are 2 ways to decrease GFR

Answer 16

• Constrict Afferent Arteriole

- Dilate Efferent Arteriole

Question 17

The Tubuloglomerular feedback mechanism links the concentration of which 2 ions at the Macula Densa of the JGA (DCT Cells)?

What are its 2 components

Answer 17

Na+ and Cl-

• Afferent Arteriole resistance
• Efferent arteriolar feedback (via hormones)
• (controls distal solute delivery and tubular reabsorption)

Question 18

Outline how the Tubuloglomerular Feedback mechanism opposes a High GFR

Answer 18

• Macula Densa of DCT detect high Na+ and Cl- concentration in fluid
• Send signal to Juxtaglomerular/ Granular cells
• Vasoconstriction of Smooth Muscle of Afferent Arterioles-> Reduced GFR

Question 19

Outline how the Tubuloglomerular Feedback mechanism opposes a Low GFR

Answer 19

• Macula Densa of DCT detect low Na+ and Cl-
• Release prostaglandins to attenuate constriction of afferent arteriole
• Renin released by Juxtaglomerular/ Granular cells
• Renin allows Angiotensinogen to change to Angiotensin 1->II
• Angiotensin II constricts Efferent Arterioles, increasing GFR

Question 20

What 3 stimuli are responsible for the release of Renin from the Juxtaglomerular/ Granular cells

Answer 20

• Signals generated by Macula Densa in response to Low Na+ and Cl- delivery
• Sympathetic nerve stimulation
• Reduced stretch of Efferent Arterioles