Renal Function

Chapter 18

Begin reading!!!!!

Bring Your Text to Class! We will be viewing Figs. 18.1 - 3

Renal Processes

Filtration: driven by hydrostatic pressure across a selectively permeable capillary

Reabsorption: solutes moved from filtrate back into blood

Secretion

solutes moved from blood into filtrate

filtrate becomes urine

Kidney Layers

Cortex

Medulla

Renal Pelvis

NEPHRONS:

CORTICAL (80%)

JUXTAMEDULLARY (20%)

Each nephron has a

Tubular component

Vascular component

Nephron Components

Tubular:

Filtrate -----> Urine

Vascular

Blood supply

Nephron Components

Glomerulus & Bowman’s Capsule

Visceral and parietal layers of B.C.

Proximal convoluted tubule (PCT)

Loop of Henle

Distal convoluted tubule (DCT)

Collecting Duct

Afferent and efferent arterioles

Peritubular capillaries

Vasa recta

Renal Processes

Filtration

Fluid forced from plasma

Approx. 20% of plasma becomes filtrate

Filtrate becomes urine after modifications

Includes solutes small enough to pass through filter-membrane, i.e., smaller than 69,000 MW

Renal Processes: Reabsorption

Desireable substances in filtrate removed and returned to plasma

Active process

Renal Processes: Secretion

Remaining undesireable substances in plasma transported into filtrate

Active process

Tubular Component

Macula Densa

Part of DCT

Juxtaglomerular cells

Cells of Afferent Arteriole

Release renin in response to low renal BF and tubular fluid Na⁺ or Cl^- content

Cortical vs. Juxtamedullary Nephrons

Location

Peritubular vs. Vasa Recta capillaries

Function

Glomerular Filtration

Glomerular Filtration Rate (GFR): ml filtrate formed / min

Depends upon renal blood flow and renal BP

Glomerular Filtration

Capillary endothelium

lamina fenestra

Glomerular basement membrane

Podocytes

Visceral layer of Bowman’s Capsule

Glomerular Membrane Permeability

Substance MW MR F/PW

Inulin 5,000 1.4 1.0

Myoglobin 14,000 2.0 0.75

Hemoglobin 68,000 3.3 0.03

Serum

Albumin 69,000 3.6 0.001

Factors Affecting GFR

Glomerular ultrafiltration Coefficient (K_f)

Hydrostatic Pressure

Renal Blood Flow

BC pressure

Osmotic Pressures in BC & Plasma

GlomerularFiltrate

filter cutoff ~ 69,000 MW

negatively charged molecules retarded by - charged filter

Small solutes: [filtrate] = [plasma]

Glomerular Filtration

See Figure 18-6 for forces across glomerular capillaries that favor filtration

Up - Downs in your future

GFR is constant over range of BPs that kidney can autoregulate its blood flow.

90 --> 200 mm Hg

Mechanisms of Renal Autoregulation

Myogenic regulates blood flow

Tubule-glomerular feedback regulates by tubular-dependent flow

Increase/decrease GFR

Increased/decreased NaCl delivery to macula densa of DCT

macula densa signals juxtaglomerular cells to change blood flow

Regulation of Renal Blood Flow

Sympathetic nerves - NE onto a1 on afferent arteriole to decrease RBF and GFR

ANP - increase GFR by dilation of afferent arteriole

ADH - decrease by constriction

NO - dilates & increases

Endothelin, adenosine & ATP - constricts and decreases - via stretch of vessels

Angiotensin II constricts afferent and efferent* at HIGH doses - decreases

Regulation of Renal Blood Flow

Note feedback loop in Figure 18-8

(Hmmmm........)