Lecture 22 Osmoregulation and excretion Flashcards
osmoregulation
controls solute concentrations and balances water gain and loss.
Excretion
rids the body of nitrogenous metabolites and other waste products.
Osmolarity (sides)
Hyperosmotic side:
* Higher solute concentration
* Lower free H2O concentration
Hypoosmotic side:
* Lower solute concentration
* Higher free H2O concentration
Osmolarity
determines the movement of water
across a selectively permeable membrane
two solutions are Isosmotic
water molecules will cross the membrane at equal rates in both directions
Two solutions differ in osmolarity
hypoosmotic (less concentrated)
hyperosmotic (more concentrated)
Osmoregulation
control of movement of solutes
between internal fluids and the external environment.
Osmoconformers
are isoosmotic with their surroundings and do not regulate their osmolarity.
Osmoregulators
expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic
environment.
Water animals Marine Animals vs freshwater - Osmoregulators
slide 11
Land Animals
● Adaptations to reduce water loss
are key to survival on land.
● Body coverings help prevent
dehydration
● maintain water balance by eating
moist food and producing water
metabolically through cellular
respiration.
Summary of osmotic challenges
slide 13
Transport epithelia
are epithelial cells specialized for controlled movement of solutes in specific
directions.
They are typically arranged into complex tubular networks.
Animals regulate the solute content of body fluid that bathes their cells.
Nitrogenous wastes
Among the most significant wastes are nitrogenous breakdown products of proteins and nucleic acids.
Animals excrete nitrogenous wastes in different forms:
● ammonia
● urea
● uric acid
These differ in toxicity and the energy costs of producing them.
The kind of nitrogenous wastes excreted depends on an animal’s evolutionary history and habitat, especially water availability
Excretory systems
● Excretory systems are variations on a tubular theme.
● Excretory systems regulate solute movement between internal fluids and the external environment.
● These systems are central to homeostasis.
what does the Mammalian Excretory System consist of?
Kidney and nephron
The vertebrate excretory system also includes ducts and other structures that carry urine from the tubules out of the kidney and out of the body
kidney
the excretory organs of vertebrates, function in both excretion and osmoregulation.
The numerous tubles of kidneys are highly organized.
Nephron
the functional unit
Excretory Processes
Most excretory systems produce urine by
refining a filtrate derived from body
fluids (slide 23)
1.filtration. the excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure accross membrane
2.reabsorbtion. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids
3.secretion. toxins and excess ions are extracted from body fluids and added to the contents of the excretory tubule
4.excretion. the altered filtrate (urine) leaves the system and the body
Filtration
Most excretory systems produce urine by
refining a filtrate derived from body
fluids
Reabsorption
Reclaiming valuable solutes
Secretion
Adding nonessential solutes and
wastes to the filtrate
Excretion
Processed filtrate containing nitrogenous
wastes is released from the body
REMEMBER selectiely permeable membrane
slide 28 and 29
Bowman’s capsule: Filtration
The filtrate produced in Bowman’s
capsule contains salts, glucose,
amino acids, vitamins, nitrogenous
wastes, and other small molecules. (slide 31)
Proximal tubule: Reabsorption
Proximal tubule
Reabsorption of ions, water, and nutrients takes place in the
Molecules are transported actively and passively from the filtrate into the
interstitial fluid and then capillaries (glucose reabsorption for example).
As the filtrate passes through the proximal tubule, materials to be excreted become concentrated.
Some toxic materials are actively secreted into the filtrate.
(slide 32)
Facilitated diffusion: channel proteins
uses aquaporins
Aquaporins
Pores for water.
They are selectively permeable for water
Can be opened and closed, and allow fast passage of many molecules
are the “plumbing system for cells”
look at descending loop (slide 36 and 33)
Descending Limb of the Loop of Henle
Reabsorption of water continues through
channels formed by aquaporin proteins.
Movement is driven by the high osmolarity of
the interstitial fluid, which is hyperosmotic to the filtrate.
The filtrate becomes increasingly concentrated.
Ascending Limb of the Loop of Henle: diluting by recovering salt
In the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluid.
The filtrate becomes increasingly dilute. (slide 38)
Distal tubule
The distal tubule regulates the K+ and NaCl
concentrations of body fluids.
The controlled movement of ions (H+ and HCO3–) contributes to pH regulation.
collecting duct
slide 40
Adaptation: long nephrons
Mammals that inhabit dry environments have long loops of Henle, while those in fresh water have relatively short loops
Water Conservation
● The mammalian kidney’s ability to conserve water is a key terrestrial adaptation.
● Hyperosmotic urine can be produced only because considerable energy is expended to transport solutes against concentration gradients.
● The two primary solutes affecting osmolarity are NaCl and urea.
collecting ducts
deals with water conservation
● The collecting duct carries filtrate through the medulla to the renal pelvis.
● One of the most important tasks is reabsorption of solutes and water.
● Urine is hyperosmotic to body fluids.
Homeostasis: Variable-Blood osmolarity
A combination of nervous and hormonal controls manages the osmoregulatory functions of the mammalian kidney.
These controls contribute to homeostasis for blood pressure and blood volume.
Osmoreceptor cells in the
hypothalamus monitor blood
osmolarity and regulate
release of ADH from the
posterior pituitary.
When osmolarity rises above
its set point, ADH release into
the bloodstream increases.
When osmolarity drops below
a set point, it causes a
reduction in ADH secretion.
Control of collecting duct permeability
Antidiuretic hormone, ADH (vasopressin)
● Released from the posterior pituitary
● Bind and activate membrane receptors on
collecting duct cells.
● Signal cascade ● Insertion of aquaporin proteins into the membrane lining the
collection duct.
● Increase in water recapture
● Reduces urine volume
increases the number of aquaporin
proteins in the membrane of
collecting duct cells
Diabetes
Diabetes insipidus (DI) is an uncommon condition that occurs when the kidneys
are unable to conserve water as they perform their function of filtering blood
