CHP 19 - KIDNEYS

most important functions of kidneys

• homeostatic regulation of the water and ion content of the blood

• balancing intake of ions and water with their excretion in the urine

how much plasma do the kidneys filter out each day

180 L of plasma a day

how much cardiac output goes into kidneys

20%

what do afferent arterioles control

inflow

function of glomerulus

filtration

function of efferent arterioles

controls flow

function of peritubular capillaries

reabsorption

function of vasa recta

reabsorbtion

2 layers of the kidneys

• outer cortex

• inner medulla

the outer cortex of the kidney contains

• 80% of nephrons

• short cortical nephrons

• all bowmans capsules

• proximal and distal tubules

the inner medulla contains

• 20% of nephrons

• long justamedullary nephrons

• loops of henle

• collecting ducts

function of bowmans capsule

site of plasma filtration with the glomerulus

what is glomerulus and plasma filtration referred to as together

renal corpuscle

loop of henle contains

• descending limb

• ascending limb

function of collecting ducts

converge and drain into renal pelvis

distal nephrons contain

distal tubule and collecting ducts

filtration of kidneys

• fluid from blood into lumen of the nephron

• occurs at renal corpuscle

• filtered plasma is called filtrate - excreted unless reabsorbed

reabsorption at the kidneys

• most reabsorbtion occurs in the proximal tubules

• only 1.5 are excreted

• active or passive transport

• materials in the filtrate are passed back into the blood

• occurs with peritubular cappilaries

secretion at the kidneys

• transfer of molecules from the extracellular fluid into lumen of the nephron

• enables the nephron to enhance excretion of a substance

• depends mostly on membrane proteins for transport

• active process moving against concentration gradients

• materials from blood into lumen of tubule

• occurs with peritubular capillaries

4 steps of the kidneys

1. filtration

2. reabsorption

3. secretion

4. excretion

how much plasma is filtered in the nephron

about 20%

how much plasma flows into peritubular capillaries

80%

what is filtration fraction

percentage of total plasma that enters the renal corpuscle and filters into the tubule

where does filtration is kidneys occur

renal corpuscle (glomerulus and bowmans capsule)

what are the 3 filtration barriers of renal corpuscle

1. pores in endothelium

2. basal lamina

3. foot processes of podocyte (epithelia of bowmans capsule)

what is the hydrostatic pressure in the glomerulus

pressure exerted by the blood within the glomerular capillaries. This pressure drives the filtration of plasma from the blood into the Bowman's capsule, forming the initial filtrate that will become urine

what two forces oppose glomerulus hydrostatic pressure

1. colloid osmotic pressure

2. bowman’s hydrostatic pressure

what is capsular hydrostatic pressure

The pressure exerted by the fluid already present in Bowman's capsule (about 10–15 mmHg).

what is colloid osmotic pressure

The osmotic pull of proteins (mainly albumin) in the blood plasma that resists the filtration of water (about 25–30 mmHg)

what regulates glomerulus filtration rate

1. renal blood flow

2. blood pressure

3. permeability of bowmans capsule

what is the hormone that influences glomerulus filtration rate

angiotensin 2 - powerful vascontrictor

regulation of GFR inflow: if the afferent arteriole constricts what is the effect on

• renal blood flow

• hydrostatic pressure in bowmans

• glomerulus filtration rate

• RBF - decreases

• hydrostatic pressure in bowmans - decrease

• GFR - decreases

regulation of GFR inflow: if the afferent arteriole dilates what is the effect on

• renal blood flow

• hydrostatic pressure in bowmans

• glomerulus filtration rate

• renal blood flow - increases

• hydrostatic pressure in bowmans - increases

• glomerulus filtration rate - increases

regulation of GFR outflow: if the efferent arteriole constricts what is the effect on

• renal blood flow

• hydrostatic pressure in Bowmans

• glomerulus filtration rate

• renal blood flow - stays the same

• hydrostatic pressure in Bowmans - increases

• glomerulus filtration rate - increases

what is myogenic response for glomerulus filtration regulation

• intrinsic ability of vascular smooth muscle to respond tp pressure changes

• constricts or dilates

what is tubuloglomerular feed for glomerulus filtration regulation

• local control pathway where fluid flow through tubule influences GFR

• paracrine control

what is the juxtaglomerular apparatus

• specialized structure in the nephron of the kidney that plays a critical role in regulating blood pressure, blood volume, and the filtration rate of the glomerulus

• located at the point where the distal convoluted tubule (DCT) comes into close proximity to the afferent and efferent arterioles of the glomerulus.

granular cells secrete??

renin

what are macula densa cells

cells that create a barrier between the tubular system and arteriole system

explain the steps

1. GFR increases

2. flow through tubule increases

3. flow past macula densa increses

4. paracrine the macula densa to afferent arteriole

5. afferent arteriole constricts

6. GFR decreases

4 steps of tubular reabsorption in the kidneys

1. Na+ is reabsorbed via active transport

2. electrochemical gradient drive anion reabsorption (gets more negative)

3. water moves by osmosis following solute reabsorption

4. the concentration of other solutes increases as fluid volume in lumen decreases

4b. Permeable solutes are reabsorbed by diffusion or by the paracellular pathway