Transport Mechanisms + Intro to Glomerulus Flashcards
Define reabsorption
Movement of substance from tubular fluid back into circulation
Define secretion
Movement of substances from blood into tubular fluid via;
- Tubular cells (active transport)
- Intracellular spaces (passive)
Define excretion
Removal of waste products from blood, and net result of filtration, secretion and reabsorption of a substance
Describe 2 way solutes can be transported
Paracellular movement- Across tight junctions, down Conc. gradient
Transcellular movement- Through cell, down or against Conc. gradient (water follows by osmosis)
What is the main contributor to maintaining a stable internal environment?
Urinary system (controls concentration of a wide range of ions and small organic molecules)
Name 6 substances/ ions that are recovered by 99-100% by the kidney
Name 1 ion that is actively secreted
- H2O
- Glucose
- Amino acids
- Na+
- Cl-
- Bicarbonate (HCO3)
H+
What is the Ultra-filtrate
Fluid that has been filtered through glomerulus
Compare Osmolarity and Osmolality
Osmolarity: Number of osmoles of solute per litre of solvent (measured in milli-osmoles)
Osmolality: Solute per kg of solvent
The Glomeruli are only found in the cortex.
What is the Filtration Fraction? What value is it normally? (Same in both types of nephrons)
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)
Proteins do not normally enter the renal tubules.
What about RBCs and platelets
No
Through what gaps do solutes in blood pass through into the Bowman’s Space
How are proteins prevented from entering?
Through Filtration Slits (spaces between Podocyte processes/ Pedicels)
Negatively charged pedicels repel negatively charged proteins
What forces affect the filtration into the glomerulus
Explain the net effect
- Hydrostatic capillary pressure: Pushes fluid into glomerulus
- Hydrostatic pressure in Bowman’s Capsule: Pushes fluid back into capillaries
- Oncotic pressure of blood: Draws fluid back into capillaries
1 Is larger than 2 and 3 combined
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)
- Myogenic (Mainly preglomerular vessels such as Arcuate/ Interlobar/ Afferent arterioles)
- Tubuloglomerular feedback
Briefly, how does the Myogenic mechanism work to control GFR
Arterial smooth muscle responds to changes in vascular wall tension, causing Afferent/ Efferent arterioles to constrict/ expand
Via Myogenic mechanism, what are 2 ways to increase GFR
- Constrict Efferent Arteriole
- Dilate Afferent Arteriole
Via Myogenic mechanism, what are 2 ways to decrease GFR
- Constrict Afferent Arteriole
- Dilate Efferent Arteriole
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
Na+ and Cl-
- Afferent Arteriole resistance
- Efferent arteriolar feedback (via hormones)
- (controls distal solute delivery and tubular reabsorption)
Outline how the Tubuloglomerular Feedback mechanism opposes a High GFR
- 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
Outline how the Tubuloglomerular Feedback mechanism opposes a Low GFR
- 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
What 3 stimuli are responsible for the release of Renin from the Juxtaglomerular/ Granular cells
- Signals generated by Macula Densa in response to Low Na+ and Cl- delivery
- Sympathetic nerve stimulation
- Reduced stretch of Efferent Arterioles
