Physiology II: Urinary system III - Countercurrent secretions

In the proximal tubule and loop of Henle a … is reabsorbed

constant percentage of flited Na+

In the distal tubule and collecting tubules reabsorption of Na+ (8%) is under … → can be varied according to body needs

hormonal control

increased Na+ load → … → … → … → … → …

increased water retention, increased ECF volume, increased bp, reduced RAAS, reduced Na+ reabsorption

Decreased Na+ load → … → … → … → … → …

decreases ECF volume, decreased blood pressure, activation of RAAS, increased aldosterone, increased Na+ reabsorption

The renin-angiotensin mechanism is triggered when the … release renin into the circulation

granular cells of the JGA

angiotensinogen is a …

plasma globulin

Renin-angiotensin mechanism: … → … → … → … → … → …

Angiotensinogen, renin, angiotensin I, ACE (lungs), angiotensin II, aldosterone (adrenal cortex)

Granular cells act as … → secrete renin

baroreceptors

The macula densa cells respond to … (3) by triggering an increase in renin secretion by granular cells

drop in NaCl of DALH, drop in ECF volume, bp fall

As bp falls baroreceptors activate the … → direct stimulation of granular cells via … to release renin

sympathetic system, B1-adrenergic receptors

Aldosterone acts on three areas in the kidneys: … (3)

thick segment of ALH, distal convoluted tubule, cortical portion of collecting duct

Aldosterone physiological effect: … (2)

retains NaCl and water, maintains blood volume

Two types of cells at DCT and Collecting tubules: …

intercalated cells, principal cells

…: site of action of aldosterone and vasopressin

principal cells

…: concerned with acid-base balance

intercalated cells

Increased aldosterone increases Na+ reabsorption by; … in luminal membranes of principal cells

increases Na+ leak channels

Increased aldosterone increases Na+ reabsorption by; … in basolateral membrane of distal convoluted tubule and collecting duct cells

increases Na/K pumps

Increased plasma volume (ECF): decreased RAAS → decreased Na+ reabsorption → increased urine Na+, due to reduction in ….

leak channels and Na/K pumps

Natriuretic peptides: … (2)

atrial natriuretic peptides, brain natriuretic peptides

…: secreted by cardiac atria in response to distension

atrial natriuretic peptides

…: secreted by cardiac ventricles in response to distension

Brain natriuretic peptide

Atrial and brain natriuretic peptide are secretes in cases of expanded … and …

plasma volume, cardiac chamber

Natriuretic peptides act on … of nephron

distal parts

Natriuretic peptides inhibit: … (4)

Na reabsorption, RAAS, vasopressin, sympathetic nervous system

Natiuretic peptides increase GFR by … and …

dilating afferent arteriole, constricting efferent arteriole

…: increased urine volume output

diuresis

…: Increased sodium content in the urine

natriuresis

… are used i cardiology as an indirect measure of … (severity of left ventricle failure)

Brain natriuretic peptide, left ventricle

… occurs in the final tubular segments (distal convoluted tubule and collecting duct)

Vasopressin-controlled variable water reabsorption

Vasopressin …., an osmotic gradient exists outside the tubules → transport of water by osmosis

increases tubule cell permeability to water

Vasopressin works on tubule cells through …

cyclic AMP mechanism

Water reabsorption occurs throughout the renal tubule except …

thick segment of ascending limb

2/3 of water reabsorption occurs in the proximal convoluted tubule by three mechanisms: … (3)

aquaporins, between cells, into blood plasma

…: the maximum amount of solute the renal tubule can reabsorb due to the limited number of transport proteins

Transport maximum

The threshold of glucose in the plasma is …, above this you have glycosuria

300mg/100mL

…: to generate a salinity gradient that enables the collecting duct to concentrate the urine and conserve water

Loop of Henle

Thick segment of the loop is …, tubular fluid becomes very dilute by the time i reaches the distal convoluted tubule

impermeable to water

…: Selective movement of nonfiltered substances from the peritubular capillaries into the tubular lumen

Tubular secretion

By the process of tubular secretion kidney tubules can … substances to the substances already filtered

selectively add

Most important secretory systems are for … (3)

H+, K+, organic ions

…: important in regulating acid-base balance, secreted in proximal, distal, and collecting tubules

H+

…: keeps plasma bleep concentration at appropriate level to maintain normal membrane excitability in muscles and nerves, secreted only in the distal and collecting tubules under control of aldosterone (K+ exchange for Na+)

K+

…: accomplish more efficient elimination of foreign organic compounds from the body, secreted only in the proximal tubule

organic ions

…: it reabsorbs water and concentrates the urine, begins in the cortex and passes through the medulla

collecting duct

The osmolarity of the filtrate is four times as high in the … as it i in the cortex

lower medulla

The medullary portion of the collecting duct is more permeable to … than to …

H2O, NaCl

In … - urine volume reduced and more concentrated

dehydration

Dehydration and High blood osmolarity → release ADH → renal tubules synthesize … → install them in the plasma membrane → collecting duct reabsorbs more water

aquaporins

…: the ability of the collecting duct to concentrate urine depends on the osmotic gradient of the renal medulla

Countercurrent multiplier

Salt is continuously deposited into the deep medulla, creating a … that allows the collecting duct to reabsorb water and produce concentrated urine, especially under the influence of ADH.

hyperosmotic interstitium

In the lower end of the collecting duct, … helps to maintain (40%) the osmotic gradient in the medulla

urea

A large, … is established in the interstitial fluid of the medulla (from 300 to 1200 mosm/liter) This increase follows the hairpin loop of Henle deeper and deeper into the medulla

vertical osmotic gradient

… of the collecting duct is permeable to urea; urea diffuses into the ECF

lower end

Urea … the lower end of the descending thin segment of the loop of Henle; but the thick segment of the loop and DCT is NOT permeable to urea. Therefore, continual recycling of urea from the CD to the medulla and back

enters

In the proximal tubule ..., but only after water, Na+, amino acids, and glucose are actively reabsorbed, this creates a concentration gradient that causes urea to diffuse out of the tubule

urea is passively reabsorbed

Glucose and amino acids are reabsorbed by … - symport carrier

sodium-dependent secondary active transport

Electrolytes other then Na+ that are reabsorbed by the tubules have their own … within the proximal tubule

independently functioning carrier systems

… that supply the medulla recycle the salt and urea

vasa recta

…: blood of the vasa recta flows in opposite directions in adjacent parallel capillaries called countercurrent exchange systems

countercurrent exchange system

As blood of the vasa recta flows downward it exchanges …

water for salt

As blood flows back up towards the cortex it exchanges …

salt for water

…: Creates and maintains the vertical osmotic gradient in the renal medulla

Countercurrent multiplier by the loops of henle

…: Preserves the vertical osmotic gradient in the renal medulla. Ensures isotonic blood enters and leaves the kidneys

Countercurrent exchange by the vasa recta