..

ALI RAZA

BS ZOLOGY 6th

SEMESTER

ROLL #4029

ROLE OF KIDNEY IN

OSOMOREGULATION

..

OSMOREGULATION

“To maintain the water and salt balance in the body or control of osmosis is called osmoregulation”.

KIDNEY

The kidney has 6 roles in the maintenance of homeostasis

6 MAIN FUNCTIONS 1. Ion Balance - Especially Na+ and K+ 2. Osmotic Balance - Determine volume of

urine produced 3. Blood Pressure - Controls blood volume

and ECF volume 4. pH Balance - Retains or excretes H+ or

HCO3 - 5. Excretion - of nitrogenous wastes & other hydrophillic toxins 6. Hormone Production

STRUCTURE OF KIDNEY

NEPHRON The functional unit of the kidney is

called the nephron. Nephrons are composed of 3

elements: ◦ Glomerulus Twisted ball of capillaries Delivers fluid to the tubule ◦ Renal tubule Composed of a single layer of cells Collecting duct

Fig. 44-14cCorticalnephro

n

Juxtamedullary

nephron

Collecting

duct

Nephron types

Torenalpelvi

s

Renalmedulla

Renalcorte

x

Bowman's capsule

The tubule is composed of epithelial cells

with characteristic transport properties that allow them to reclaim specific

solutes and expel others. Bowman’s capsule: ◦ mouth of the tubule ◦ Cuplike expansion surrounds the

glomerulus

Fluid in lumen moves through successive

specialized regions of the tubule: 1. Proximal Convoluted Tubule 2. Loop of Henle 3. Distal Convoluted Tubule Fluid from multiple tubules, drain into collecting ducts, several of which

fuse to form papillary ducts, which empty into the minor calyx.

PROCESS OF URINE FORMATION1) Filtration 2) Reabsorption3) Secretion4) Excretion

CONCENTRATION OF EXCRETORY PRODUCTS:

Kidney has two adaptations: limited supply of water -reabsorption takes place in tubules Excessive supply of water Reabsorption of water reduce from the

filtrate resulted dilute urine is produce. The mammlian kidney is adapted to

conserv 99.5% of water by reabsoption of glomerular filterate.there are two methods for making the urine concentrate.these are hormonal and counter current method

COUNTER CURRENT MULTIPLIER:

The opposite flow of adjacent fluid that maximize transfer rate is called counter current multiplier.

Decending loop of henle: Thin and permeable to water Ascending loop of henle: Thick and permeable to Na

HORMONES There are two hormones involve in the

reabsorption of water and salt in the kidney. Antidiuretic hormone Aldosteron hormone

HORMONES CONTROL OSMOREGULATION

Antidiuretic hormone (ADH)Produced by the hypothalamus and secreted

by the posterior pituitary glandStimulated by an increase in the osmolarity of

blood Causes walls of distal tubule and collecting

ducts to become more permeable to water Aquaporins

More ADH increases reabsorption of water Makes a more concentrated urine

19

.

Fig. 44-19

Thirst

Drinking reduces

blood osmolarit

yto set point.

Osmoreceptors in hypothalamus

triggerrelease of ADH.

Increasedpermeabili

ty

Pituitary

gland

ADH

Hypothalamus

Distal

tubule

H2O reab-sorption

helpsprevent

furtherosmolarityincrease.

STIMULUS:Increase in

bloodosmolarity

Collecting duct

Homeostasis:Blood osmolarit

y(300 mOsm/L)(a

)

Exocytosis

(b)

Aquaporin

waterchannels

H2O

H2O

Storage

vesicle

Second messenger

signaling molecule

cAMP

INTERSTITIALFLUID

ADHrecepto

r

ADH

COLLECTINGDUCTLUMEN

COLLECTING

DUCT CELL

EXCESS WATER IN BODY FLUIDS

When this condition arises, the urine passed out of the body is more dilute or hypotonic than the body fluids to expel the excess of water. This is because excess of water in the body fluids lowers the osmotic pressure of the blood and increases the blood volume. These changes disturbs the exchange of materials between the blood pressure and causes cardiovascular dysfunctioning respectively.

It involves 2 processes. They are: a) Ultra filtration b) Decreased reabsorption. Ultra filtration is increased due to the

increase in hydrostatic pressure due to the excess of water. So more nephric filtrate is filtered out from the glomerular capillaries into Bowman's capsule.

SHORTAGE OF WATER IN BODY FLUIDS

When the volume of body fluids decreases due sweating during heavy exercise or high temperature or excessive bleeding or a prolonged delay in fluid intake, the rate of ultra filtration is decreased due to decreased blood volume and low hydrostatic pressure of blood in the glomerular capillaries and rate of reabsorption of water is increased by increasing the permeability of the wall of DCT and collecting tubules due to increased release of ADH from the posterior pituitary. Less ultrafiltration and more reabsorption produce small amount of hypertonic urine which increases body fluid volume to normal.

HORMONES CONTROL OSMOREGULATION

Aldosterone Secreted by the adrenal cortexStimulated by low levels of Na+ in the blood Causes distal convoluted tubule and collecting

ducts to reabsorb Na+

Reabsorption of Cl– and water followsLow levels of Na+ in the blood are accompanied

by a decrease in blood volume Renin-angiotensin-aldosterone system is activated

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HORMONES CONTROL OSMOREGULATION

Atrial natriuretic hormone (ANH)Opposes the action of aldosterone in promoting

salt and water retentionSecreted by the right atrium of the heart in

response to an increased blood volumePromotes the excretion of salt and water in the

urine and lowering blood volume

27

I am happy that now you

know more about me!!!

REFERENCES Wikipedia Guyton and hall physiology book. tata Mcgraw hill medical physiology

book. Physiology FIFTH EDITION Linda S. Costanzo, PhD. PHYSIOLOGY, SECOND EDITION Thomas A. Brown, MD.