Lecture 21- salt and water balance and nitrogen excretion Flashcards
What controls the volume, concentration and composition of extracellular fluids?
Excretory organs
What is osmolarity?
The number of moles of active solutes per liter of solvent
How do excretory organs control osmolarity and volume of extracellular fluids?
- Excretion of solutes in excess, NaCl, etc.
- Conserving valuable or short supply solutes- amino acids, glucose
What are osmoconformers?
Equilibirate their osmolarity with sea water
What is the osmolarity of the sea?
Very high, 300mosm/l
What are osmoregulators?
Maintain osmolarities lower than sea water
What animals are osmoconformers?
All vertebrate marine animals except sharks and rays
Where are osmoregulators found?
Extreme conditions- freshwater (too few proteins etc in interstital fluid), evaporating tide pools
What type of animal can be found in varied environments, including Utah’s great salt lake?
Brine shrimp - Artemia
2500 mosm/Liter
How do brine shrimp live in such varied environments?
In high osmolarity- Cl- is actively transported out through gills (Na+ ions follow)
In low osmolarity, chloride ion transport is reversed
What are ionic conformers?
Animals which allow their ionic composition to match their environment
What are ionic regulators?
animals which conserve some ions and excrete others to maintain ionic composition
Give an example of ionic regulators.
Some sea birds nasal glands excrete NaCl
Carbohydrates and fat end as…
Water and CO2
Proteins and nucleic acids end as…
nitrogenous waste
What is the most common nitrogenous waste?
Ammonia (NH3)
What is the name given to animals who secrete ammonia through their gills?
Ammonotelic
What do terrestrial animals do with ammonia?
Convert it to urea or uric acid
What name is given to animals which secrete urea?
Ureotelic animals
What name is given to animals which secrete insoluble uric acid?
Uricotelic animals
Most animals secrete more than one nitrogenous waste. Humans are ureotelic but also secrete:
- Uric acid from metabolism of nucleic acids and coffee
- Ammonia- regulates pH of extracellular fluid by buffering urine
What is the main excretory organ in vertebrates?
The kidney
What is the main functional unit of the kidney?
The nephron
What do nephrons do?
Filter large volumes of blood and achieve bulk reabsoption
What adaptations have bony fish made to their excretory systems in response to their environment?
Produce very little urine to conserve water
Do not absorb some ions in their gut
How have cartilaginous fish adapted to conserve water?
Convert nitrogenous waste to compounds and retain large amounts of extracellular fluid with similar osmolarity to sea water
How do amphibians maintain salt and water balance?
-Reduced permeability of their skin to water
-Estivation: a state of low metabolic activity and low water demand
Some frogs fill a large bladder with water before estivation
What three adaptation enables reptiles to live outside of water?
- Amniotic reproduction: shelled eggs
- Scaled epidermis that retards water loss
- Excretion of uric acid with little water loss
How have birds and mammals adapted to conserve water?
- Surface coverings
- Amniotic reproduction
- Birds produce uric acid
- Both can produce concentrated urine
What is the first step in urine formation in vertebrate nephrons?
-Filtration: blood is filtered in a glomerulus (a ball of capillaries)
What happens after filtration in the glomerulus?
Tubular reabsorption: Glomerular filtrate flows into renal tubule where it is modified by reabsorption of specific nutrients, ions and water
What happens after tubular reabsoption in the renal tubule?
Tubular secretion: glomerular filtrate is further modified when tubule cells transport subtances to be excreted into the tubular contents
What transports substances to and from the renal tubules?
Peritubular capillaries
Where does the glomerular filtrate go?
The Bowman’s capsule
How does blood enter the Nephron?
Through the afferent arteriole
How does blood leave the glomerulus?
Through the efferent arteriole
What does the efferent arteriole become?
The peritubular capillaries
What are podocytes?
Capsule cells that contact the glomerular capillaries- fine processes wrap around the capillaries
Why is the rate of filtration high in the glomerulus?
- High capillary blood pressure
- High permeability of glomerular capillaries and their podocytes
What is the name of the duct that leads from the kidney to the urinary bladder?
The uretar
What is the name given to the tube for urine excretion?
Urethra
On what side does the uretar, renal artery and renal vein enter the kidney?
On the concave side
What does the uretar branch and envelop?
Kidney tissues called Renal pyramids
What do renal pyramids make up?
The medulla (inner core)
What is the outer layer of the medulla?
The cortex
What surrounds the base of the urethra?
Two sphincter muscles- one controlled by the autonomic nervous system, the other voluntary.
What is in the region between the medulla and cortex?
The renal artery divides into the many arterioles that serve the nephrons
Where are all the glomeruli located?
In the cortex
What is the initial segment of a renal tube called?
The proximal convoluted tube (‘first’,’twisted’)
Where are all of the proximal convoluted tubes located?
In the cortex
What happens to the renal tube as it descends into the medulla?
The convoluted tube becomes less convoluted,
Tubule makes a hairpin turn and ascends back out
What is the hairpin turn of the renal tubule called?
The loop of Henle
What does the ascending loop of Henle become when it reaches the cortex?
The distal convoluted tube (distal-further from glomerulus)
What do the distal convoluted tubes join to become?
A collecting duct in the cortex
Where do collecting ducts go?
They descend through renal pyramids and empty into the pelvis- pelvic divisions join and leave the kidney as the ureter
How are blood vessels organised in the kidneys?
Regular arrangement, parallels that of nephrons
What is the name given to the peritubular capillaries that are parallel to the loop of Henle and collecting duct?
The vasa recta
How are all of the peritubular capillaries from all of the Nephrons arranged?
They all join into venules which lead to the renal vein
What structure is responsible for most reabsoption of water and solutes?
The proximal convoluted tubule.
How does the proximal convoluted tube maximize reabsoption?
- Microvilli increases surface area
- Many mitochondria
- Actively transport Na+, glucose and amino acids
- Water follows transport of solutes
How does urine become very concentrated?
Countercurrent multiplier mechanisms in the loops of Henle
What is countercurrent multiplier mechanisms in the loops of Henle?
Tubule fluid flows in opposite directions in the ascending and descending limbs- loop increases osmolarity of interstital fluid in a gradual way
What are the three loop of Henle segments?
- Thick ascending limb
- Thin ascending limb
- Thin descending limb
What does the thick ascending limb do?
Active transport of sodium ions (chloride follows) and raises their concentration in interstital fluid
What does the thin descending limb do?
Loses water to the neighboring interstital fluid with high sodium and chloride ions
What does the thin ascending limb do?
Receives concentrated fluid from descending limb and allows sodium and chloride diffusion into interstital fluid
What are aquaporins?
Membrane proteins abundant in highly water permable areas such as the PCT and decending loops of Henle
What are the similarities between fluid in the collecting duct and the blood fluid?
Same concentrations
Different composition
What is the major solute in the conducting duct?
Urea
How do kidneys regulate blood pH?
Kidneys remove H+ and add HCO3- to the blood buffer system
How is the blood buffer system formed?
hydration of CO2 followed by dissociation of carbonic acid
What controls the acid levels in blood?
Lungs- add more CO2
Kidneys add base portion
What is the result of renal failure?
- High blood pressure because of salt and water
- Uremic poisoning (too much urea)
- Acidosis (metabolic acids)
What does dialysis do?
Passes blood through membrane channels bathed in a plasma-like solution to remove wastes
