Urinary 1

Tubular reabsorption

renal tubule to peritubular capillaries (filterate to blood)

Tubular secretion

Peritubular capillaries to renal tubule (blood to filerate)

Urinary excretion

elimination from body

excreted= filtered + secreted - reabsorbed

Glomerular filteration

glomerulus to capsular space (blood to filterate)

How does glomerular filteration work?

Uses pressure to move substances through the membrane

• Filtration creates a filtrate, substances leave blood-→ capsular space—> renal tubule

What is unique about glomerual capillaries?

more efficient filter than other capillary beds

How does the glomerulus accomplish it’s unique feature?

1. larger surface area

2. More permeability=leakier

3. Higher blood pressure

High glomerular filteration rate

increased urinary excretion(poor absorption)

valuable substances are eliminated in urine

Low glomerular filteration rate

Decreased urinary excretion(high absorption)

linked to kidney problems as it cannot eliminate things

What establishes a filterate

When substance arrives at the capsular space

4 starling forces

1. Blood hydrostatic pressure(P_GC)

2. Filterate somatic pressure(π_CS)

3. Filtrate hydrostatic pressure(P_CS)

4. Blood osmotic pressure(π_GC)

Filtrate somatic pressure P_CS

Filtration favoured: Filtration is Glomerulus to the capsular space

• occurs at the start of the capillary bed

Blood osmotic pressure π_GC

oppose filtration: Filtration is the capsular space of the glomerulus

• occurs at end of capillaru bed

Net filtration pressure (see formula)

always favours filtration, positive value

Renal autroregulation

homeostasis of glomerular filtration rate

• occurs in the kidneys to keep GFR at a given tolerance while BP fluctuates

2 types of renal autoregulation

1. Myogenic mechanism

2. Tubuloglomerular feedback

Myogenic mechanism

fast

stimulus= BP change affecting PGC and strech of arteriole

Response= changes contraction of smooth muscle around arteriole, affects arteriole radius and atlers PGC, NFP and GFR

vasoconstrict afferent arteriole= decrease everything

vasodilate efferent arteriole=increase everything

Tubuloglomerular feedback

slower

stimulus= BP change affecting PGC and salt concentration at macula densa cells of juxtaglomerular apparatus(JGA)

Reponse: JGA release NO, changes arteriole radius(more or less vasodialation), alters PGC, NFP and GFR

How does NFP affect GFR

positive correlation

High BP= High PGC= High NFP= High GFR

Extrinstic mechanisms to regulate GFR(See diagram)

neural and hormonal changes that are drastic enough that renal autoregulation cannot correct them