Day 3 Osmoregulation in Terrestrial Organisms

Mammals have keratin in skin to

to reduce evaporative water loss

Mammals experience more water loss because

they use sweating or panting for cooling

Mammals have kidneys to

to produce hyperosmotic urine

Main waste product in mammals

urea

Excretory systems

1. secretion system

2. filtration-reabsorption system

Secretion system

actively secrete excess ions and water and wasters from ECF

Filtration-reabsorption system

water and all solutes leave ECF by bulk flow then useful substances are reabsorbed back into the ECF

Filtration-reabsorption system takes place in

the kidneys

Flow of urine through the Renel system

kidney, ureter, urinary bladder, urethra

Nephron structures

make urine

Cortex concentration

normal ECF concentration

Medulla concentration

concentration of ECF increases as you go down

Order/Path of nephron structure

Bowman’s capsule, Proximal tubule, Loop of Henle, Distal tubule, Collecting Duct

Structures in the cortex

Proximal tubule, Distal tubule

Structures in the medulla

Loop of Henle, Collecting duct

Makes up the renal corpuscle

glomerulus and Bowman’s capsule

What the Renal Corpuscle forms

primary urine via filtration

Path of filtrate in renal Corpuscle

filtrate leaves the glomerulus and enters Bowman’s capsule

What’s filtrated in the Bowman’s capsule/Renal Corpuscle

small solutes and fluid enter the nephron

larger molecules and proteins are held back because pores are small enough

Stage of filtration

Renal Corpuscle/Bowman’s capsule

Main stage of reabsorption

Proximal tubule

What’s reabsorbed into the ECF in the proximal tubule

NaCl, Glucose, Water

How NaCl and Glucose is reabsorbed by ECF

active transporter (carrier protein)

How water is reabsorbed by ECF

osmosis via aquaporins

Volume of urine before proximal tubule vs. volume after 

drops about 2/3 (100 —> 30)

Concentration of the Loop of Henle down left side

concentration increases

Concentration of the Loop of Henle up the right side

concentration decreases

What happens on the left side of the Loop of Henle

water leaves via osmosis

What happens on the right side of the Loop of Henle

NaCl moves out 

How does NaCl move out of the Loop of Henle

channel proteins for thin wall

carrier proteins for thick wall

urine volume and concentration before vs. after the Loop of Henle

volume decreases (30 —> 10)

concentration decreases (300 —>100)

Loop of Henle effect on medulla

creates a concentration gradient in the medulla

Collecting duct

alters the final concentration of urine

Collecting duct response to dehydration

water leaves — lower urine volume

• concentration increases in nephron as you go down

Collecting duct response to over-hydration

water moves in — higher urine volume

• concentration in nephron stays the same as you go down

Controls final urine volume

hormone ADH

Effector of ADH

collecting duct

Regulated variable of ADH

amount of body water

ADH and low body water

ADH levels increase, increase in density of aquaporins in collecting duct, increase water reabsorption, increase urine concentration, decrease urine volume

ADH and high body water

ADH levels decrease, decrease in density of aquaporins in collecting duct, decrease water reabsorption, decrease urine concentration, increase urine volume

Distal Tubule

regulates sodium levels

Urine sodium concentration is controlled by

aldosterone

Aldosterone response to low Na levels

increase aldosterone levels, increase density of Na transporters in distil tubule, increase Na reabsorption

Aldosterone response to high Na levels

decrease aldosterone levels, decrease Na transporters (no transport), decrease Na reabsorption

How does Na leave nephron in distil tubule

active transporters

Step of filtration

Bowman’s capsule

Primary step of reabsorption

Proximal tubule

Step of Counter-current multiplication

Loop of Henle

Step of secretion and reabsorption

Distil Tubule

Step of final urine concentration

Collecting duct

Xero tolerant mammals

have a relatively deep renal medulla to increase concentrating ability

• good at conserving water

Thicker medulla

higher concentration

Thinner medulla

lower concentration

Roles of mammalian kidneys

1. Regulate total ECF volume by adjusting urine volume (controlled by ADH)

2. regulate specific ions (Na by aldosterone)

3. regulate overall osmolarity

4. eliminate wastes - urea

Vertebrate kidney

1. filtration-reabsorption system

2. urine non-selective for solutes

3. energetically expensive to reabsorb good stuff but good at eliminating many toxins

Mammals gain water by

drinking, food, and metabolism

Mammals gain ions by

food, some water sources

Mammals lose water by

respiration, panting, sweating, defecation

Mammals lose ions by

sweat, defecation

Categories of osmoregulation in vertebrates

1. Chondrichthyes

2. Actinopterygii

3. Reptilia (including birds)

4. Mammalia

Chondrichthyes

rectal gland is major excretory organ

produce urea for osmoregulation

Osmo conforms but regulate ions

Actinopterygii

Osmo regulates in both hypo and hyperosmotic waters

Gills are main excretory organ

Produce ammonia

Reptilia (including birds)

Most are terrestrial osmoregulators

Kidneys are main excretory organ: some have salt glands

Produce uric acid

Mammalia

Most are terrestrial osmoregulators

Kidneys are main excretory organ — make hypoosmotic urine

Produce urea

Makes hyperosmotic urine

mammalia

Osmoregulation challenges for insects

1. terrestrial environment — many live in xeric environments

2. small size and thin appendages — high SA:V ratio

Adaptions for osmoregulation in insects

1. highly permeable integument, due to chitin and waxes

2. respiratory system efficient for water loss

3. produce uric acid

4. excretory system concentrates the waste solutes

Reduction of evaporative loss in insects

1. tracheal system limits respiratory loss

2. wax and chitin in cuticle limits cutaneous loss

Excretory system in insects

secretion-driven excretory system by Malpighian tubules

Process of excretory system in insects

1. primary urine is high in secreted K+ which draws in water and other solutes

2. Urine then enters the gut, where final concentration takes place