Theme 13: Osmoregulation Overview

Biology 224

Osmoregulation Overview• Summary

– Basics• Osmoregulators • Osmosis• Trends and Concentrations• Problems • Different Environments

– Osmoregulatory Organs • Gills and Lungs

– Teleosts – CFTR

• Kidneys– Malpighian tubules– Malpighian tubules process

• Salt glands – Regulation

– Osmoregulatory Hormones– Osmoregulatory Metabolism

• Nitrogenous Waste

Basics of Osmoregulation

• Osmoregulation: regulation of osmosis through water-salt concentrations in body with semi-permeable membranes

• Conformers– Osmoregulation fluctuates with environment

• Regulators– Osmoregulation is kept different from the environment

• Sodium outside, Potassium inside • Excretion to remove certain solutes

Osmoregulation Basics: Trends

4

Solute [Plasma]g per 100 ml

[Urine]g per 100 ml

Na+ 0.30 0.3*

Cl- 0.40 0.6*

K+ 0.016 0.2*

NH3 0.001 0.04*

urea 0.08 2.0*

glucose 0.09 0

protein 7.0 0

* varies

Example - in humans:

Osmoregulators

• Maintain extracellular osmolarity and ion composition constant – Strict extracellular homeostasis

Osmosis

Problems of Osmoregulation

• Respiration – Direct contact with environment– Water loss of terrestrial animals is a problem– Aquatic environments: water and salt are

problematic

Different Environments

• Freshwater Environments– Environment is hypotonic to organism – Salt moves out of body by diffusion– Water moves into the body by osmosis

• Marine Environments– Environment is hypertonic to organism– Salt moves into the body by diffusion– Water moves out of the body by osmosis

Osmoregulatory Organs

• Bilateral Animals• System of tubules with with epithelia cells

– Regulates blood salt composition– Eliminates waste– Produces a urine

• Salts and waste moved by active transport or membrane channels

• Water moves by osmosis

Osmoregulatory Organs: Gills and Lungs

• Gills involved in ion transport and excretion of nitrogenous waste – Teleost fish – Marine fish: chloride cells, water loss

• Adaptation from freshwater to seawater by stimulating chloride secretion

– Initiated by membrane potential of Na+

– Cl- negative charge, Na+ positive, therefore will balance each other out

– Move 1 Na+ and 1 K+ out of cell, Move 2 Cl- in» Increase of NaK ATPase activity

– Freshwater fish: water gain

Water Regulation on Teleosts

• Marine teleosts absorb NaCl in order to absorb water to create an excess of salt in the blood – Use epithelial Cl- cells

to actively transport Na+ and Cl- outward

– Adaption to salinity triggers release of chloride ions to balance out sodium’s positive charge

Water Regulation on Salinity via CFTR Expression

• CFTR (Cystic Fibrosis) anion channel – In gills and intestine of epithelial cells of teleost

fish– Marine: ion secretion in apical membrane– Freshwater: ion absorption in basolateral

membrane

Osmoregulatory Organs: Salt Glands

• Excrete excess salt to maintain salt balance and allow marine animal to drink seawater

• Salt Glands Na+ K+ Pump – Basolateral membrane – Moves salt from blood to gland

• Blood through secretory cell to secretory tubule

– Na+ secreted as a concentrated solution

Osmoregulatory Organs: Salt Glands

• Process in Birds• Salt gland excited by

– Parasympathetic Nervous System– Corticosterone– ANP, atrial natriuretic peptide

• Salt gland secretes high concentration of NaCl solution

• Kidney is shut down to prevent water loss

Pathway of Salt Gland Regulation

Dehydration or HypersalinitySeawater 0.45 M

High blood osmolarity

Parasympathetic nervous system

Adrenal gland

corticosterone

Atrial natriu

retic peptide

Salt gland

High NaCl Solution0.9 M

Shut down kidney

Water conservation

Hypothalamic osmoreceptor

Pituitary gland

Heart

Osmoregulatory Organs: Kidneys

• Pronephros: immature kidney • Metanephros: developed adult kidney • Malpighian tubules: excretory and

osmoregulatory system of some insects and arachnids

• If kidney is different from the environment, then it needs mechanisms to save water– Kidney’s main function is a filtration system

• Fluid blood (plasma) is filtrated by kidneys

Osmoregulatory Organs: The Kidney

• Vertebrate Kidney– 4 key processes

• Filtration• Reabsorption• Secretion• Excretion = Filtration –

Reabsorption + Secretion

– Kidney physiology depends on:

• High blood pressure• Active transport• Passive diffusion• Regulation• Adaptation to environment

The Kidney

• Functional unit of kidney: nephron – Nephron consists of:

Bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct

– Important for fine-tuning the blood

Proximal Convoluted Tubule

Distal Convoluted Tubule

The Nephron’s Pathway; Reabsorption

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• The tubule is regionally specialized for reabsorption,

Interstitial fluid within kidney cortex & medulla is different.

cortex

medulla

low[solute]

high[solute]

Interstitial Fluid Concentration

Allows more water to be absorbed since there are 2 descending

pathways

ATP required for ascending segment

ATP

Osmoregulatory Organs: Malpighian Tubules in Insects

• Carry out osmoregulation and excretion

• 4 step process 1. Filtration2. Reabsorption3. Secretion4. Excretion

• Initial Fluid from Blood Plasma to start process (insects)

Osmoregulatory Organs: Malpighian Tubules

• 4 step process:1. Filtration: non-selective movement of water and solutes

into the proximal end of tube• Pressure driven by blood pressure • Open circulatory: bodily fluids• Closed circulatory: blood

– Hydrostatic pressure

2. Resabsorption: Specialized epithelium cells transport back nutrients into ECF of blood

3. Secretion: SELECTIVE, eliminates substances for transport 4. Excretion: waste products (urine) transported out of body

Osmoregulatory Hormones

• Atrial Natriuretic Peptide ANP– Secreted by heart – Controls high blood volume – Reduces overall blood pressure via decrease in

water, sodium, and adipose loads

Osmoregulatory Hormones

• Aldosterone– Secreted by adrenal cortex– Steroid hormone – Regulates body’s Na+ levels– Increase aldosterone: increase Na+ absorption

Osmoregulatory Hormones

• ADH, Antidiuretic Hormone– Antidiuretic: anti urine, suppression of urine– Vasopressin – Regulates water– Posterior pituitary gland– Inhibit ACH: increase water output– Alcohol and Caffeine inhibit ADH, which increases

urine secretion!

Osmoregulation: Metabolism

• Excretion of Nitrogenous Waste Products– Ammonia– Urea– Uric Acid

• Human urine is composed mainly of urea, with some traces of uric acid

Osmoregulation: Waste Products

• Determinants of Waste Products– Energy requirement

• Ammonia no energy• Uric acid needs energy

– Amount of water in environment

• Ammonia high water• Uric acid low water

– Toxicity of waste • Ammonia highly toxic• Uric acid not toxic

Fig. 42.4, p. 1054

Osmoregulation: Nitrogenous Waste Products

• Ammonia (NH3)– From metabolism of amino acids and proteins– Toxic – Strong base, alters acid-base balance – Lots of water, organisms excrete ammonia as

primary nitrogenous waste and surrounding water dilutes it