Chapter 8 Osmoregulation

Osmolarity

solute concentration of a solution and Determines movement of water across membrane

Isoosmotic

Equal solute concentration of two solutions (No net water movement)

Hypoosmotic

Lower solute concentration

Hyperosmotic

Higher solute concentration

Osmoconformer

Isoosmotic with their surroundings; don’t regulate osmolarity. This happens in Marine organisms

Osmoregulator

Not isoosmotic with surroundings; spend energy to control water gain/loss

Challenges in osmoregularity

Land animals have mechanisms to prevent dehydration
Most have body coverings that help reduce water loss, but lose water through many routes
They maintain water balance by drinking water and eating moist foods

Ammonia

(NH3 ) convert to less toxic compounds before excretion

Urea

Less toxic and Conversion product of ammonia

Uric Acid

Semisolid paste. less toxic, water retention, energetically expensive to produce

Excretion

Process that rids body of nitrogenous metabolites & other metabolic waste products

Steps to excretion steps

1. Filtration- Water & solutes cross membrane due to blood pressure; forms filtrate. Cells & large molecules don’t cross.

2. Reabsorption- Returns substances from filtrate to body

3. Secretion- Nonessential solutes & waste move into filtrate

4. Excretion- Processed filtrate released as urine

Protonephridia

Flatworms use this
Tubule networks connected to external openings
Dilute urine emptied into external environment

Malpighian Tubules

Insectes use this to secrate waste into lumen
Filtrate goes to digestive tract where water is reabsorbed
Produce dry waste

Kidney

Functions in osmoregulation and excretion
Has tubules closely associated with network of capillaries Excretory system includes ducts that carry urine from tubules out of the body

Nephron

Basic unit of mammalian kidney

Basic unit of mammalian kidney

capillary bed that retains blood cells and large molecules

filtrate

Allows water and small solutes to pass

Bowman capsule

Filtrates pass through this before continuing to tubules

How much liters of blood through kidney/ day

1600 liters

How many liters does it flow through the inital filtrate

180 liters

What happens after reabsorption, how much liters go to urine.

1.5 liters

Proximal tubule

Reabsorption of ions, water, & nutrients
Arrows from filtrate to interstitial fluid
Solutes move and water follows
Some toxic molecules actively secreted into filtrate

Descending limb loop of henle

Reabsorption of water via aquaporins

Protein transport channels for water Water reabsorption driven by high osmolarity of interstitial fluid

Hyperosmotic to filtrate- “water follows salt” Concentrates filtrate

Ascending limb loop of henle

Salt is reabsorbed Does not have aquaporins

No water movement Filtrate becomes dilute

This contributes to the high osmolarity of the interstitial fluid of kidney (last slide)

Distal tubule

Regulates potassium & sodium concentrations of body fluids

Secretes K+ & Na+ into filtrate Aquaporins for some water reabsorption

Slight concentration of filtrate (due to ions)

Collecting duct

Reabsorption of water (lots) and ions (little)

Produces concentrated filtrate ◦ In humans- osmolarity of blood = ~300 mOsm/L ◦ Kidney concentrates up to 4x ◦ Water conservation

Carries filtrate to renal pelvis

What happens after the tubules

Filtrate goes from renal pelvis to ureter before entering urinary bladder

Bladder with tissue that stretches ◦ Bladder has two sphincters

Urine leaves body via urethra

Urine

95% water, 5% solutes under normal conditions Usually sterile, unless you have a urinary tract infection pH around 6 normally, but it can vary due to metabolism or diet If you’re dying of thirst, you can drink it (but not repeatedly) ◦ Without water, the more you urinate, the more concentrated it becomes

Desert mammals

excrete the most hyperosmotic urine, have long loops of Henle and have lots of water absorption

Birds

have shorter loops of Henle but conserve water by excreting uric acid instead of urea

South American bats

can produce either very dilute or very concentrated urine ◦ This allows the bats to reduce their body weight rapidly or digest large amounts of protein while conserving water

What is the key effector in negative feedback loops regulating blood pressure.

Kidney

Renin-Angiotensin-Aldosterone System (RAAS)

Decreased blood volume & pressure cause RAAS to increase water & Na+ reabsorption

Angiotensin II raises BP

regulated by hormones

Hypertension drugs block angiotensin II production

Antiduretic hormone

Makes collecting duct more permeable to water

Decreased blood osmolarity reduces ADH secretion- less water reabsorption

Alcohol inhibits ADH secretion

Dehydration

loss of water by extracellular fluid leads to loss by intracellular fluid

Hypotonic hydration

due to renal insufficiency or overconsumption of water

Too much water in extracellular fluid leads to too much in intracellular fluid and swollen cells

Can lead to nausea, cramping, cerebral edema (bad), possible death