Homeostasis - Darin Ali G

Big Questions

Why do organisms need to regulate their internal conditions?
How is regulation accomplished?


Animals Only

Animals are really the only organisms who are able to regulate their temperature. Even among animals there is a wide diverstiy of abilities to regulate temperature. Many animals are ectothermic, which essentially makes them thermoconformers.


- able to maintain internal temperature at a different level than ambient temperature
- birds and mammals


- internal temperature conforms to ambient temperature'
- all other animals

Metabolic activity is the major source of heat production in organisms. Endothermic organisms have a higher metabolic rate than ectothermic organisms

Controlling Heat Exchange

The skin is the major mechanism of heat exchange between animals and the environment.
Organisms that live in pronounced heat sink environments (oceans) utilize countercurrent exchange to decrease heat loss in extremities.
Mammals utilize circulatory, integumentary (skin) and muscular processes to maintain temperature within a homeostatic range.
    - Too cold: shivering and constriction of sin capillaries
    - Too hot: sweating and dilation of skin blood vessels

Endothermic ex: Hippopatamus
Ectothermic ex: Lizard
Endothermic ex: Harbor seal
Ectothermic ex: Dragonfly

Measuring Metabolism

Metabolism can be measured in organisms by measuring heat exchange and metabolic indicators (respiratory rate, heart rate, etc.)

In Ectotherms: 

Metabolic rate is a function of temperature. The higher the ambient temperature, the greater an animal's metabolic rate. 
Standard metabolic rate: The metabolic rate of an ectotherm at rest at a particular temperature.

In Endotherms:

Basal Metabolic Rate: The minimum metabolic rate of an endotherm at rest (not correlated to temperature)
Basal Metabolic Rate(BMR) is a function of body size, with larger organisms consuming more oxygen more oxygen per hour than smaller organisms

Energy Budgets

Comparison of energy requirements for three different endotherms and an ectotherm. The ectotherm has to spend no energy on thermoregulation. Also compared to the comparatively sized endotherm, the ectotherm has a greatly reduced energy requirement. 


Refers to a state of decreased activity and metabolism, which enables organisms to expend less energy during times when food acquisition is unfavorable or dangerous.
Common in small endotherms (usually during the night)
Hibernation: long term winter torpor
Estivation: long term summer torpor



Due to their inability to move, plants are essentially osmoconformers.
However, internal osmolarity has serious consequences for plant physiology. 

Osmoconformers vs. Osmoregulators

Animals that remain isosmotic with their surroundings are osmoconformers
Osmoconformers must be surrounded by saltwater

Animals that regulate their internal osmolarity are osmoregulators.
Osmoregulators can live in many different environments.
Osmoregulation, Osmolarity, and Excretion
Animals regulate their osmolarity by controling the amount of solute that they retain in their bodily fluids. Intake of water, excretion of fluid and dissolved solute is the major way that animals control internal osmolarity. Excretory systems depend on specialized transport epithelia to move specific solutes either in or out of bodily fluids. 

Nitrogenous Waste

Waste molecules produced by cells from the breakdown of proteins and nucleic acids.
Three Major Kinds
    - Ammonia: most toxic. only produced by aquatic animals
    - Urea: formed by combining ammonia with carbon dioxide. Not as toxic, so it can be tolerated at higher concentrations than ammonia and released with less water
    - Uric Acid: least soluble. can be excreted with the least amount of water. more energetically expensive to produce than urea

Excretory Systems

All excretory systems involve four major processes. 
    - Filtration: initial movement of fluid and solutes from the body to the system
    - Reabsorption: water and desirable solutes are reclaimed by transport epithelium
    - Secretion: excess waste solute is sent to the filtrate
    - Excretion: the modified filtrate is expelled from the body
All excretory systems utilize tubules for collection of filtrate

The Vertebrate Excretory System

Kidneys: filtrate collection and urine production
Ureters: transport urine to the bladder
Bladder: urine storage
Urethra: urine excretion

The Kidney

The organ is responsible for filtration and urine production


For indivisuals with kidney failure. Do the same thing that your kidneys do but
    - more expensive
    - time consuming
    - not a long term solution for kidney failure


The interface between the circulatory system and the excretory system 
Responsible for filtration reabsorption and secretion

A tube surrounded by capillaries
    - Glomerulus: ball of capillaries that passes filtrate into the nephron at the "Bowman's capsule"
    - Proximal tubule: reabsorption of water, salt, and bicarbonate ions. Active transport
    - Loop of Henle: reabsorption of water and salt (osmosis)


ADH: When blood osmolarity increases, the pituary gland releases andidiuretic hormone which increases water absorption in the collecting duct of the nephron.