Urinary system and water/ electrolyte balance Flashcards
What are the major sites of ion and water exchange in the body?
Skin
Respiratory system
Digestive system
Excretory system
Give a basic overview of osmoregulation in freshwater fish.
Uptake of water and some ions in food
Uptake of salt ions by gills
Osmotic water gain through gills and other parts of body surface
Excretion of large amounts of water in dilute urine from kidneys
What is metabolic water?
Water produced by the catabolism of food stuffs
Why is there obligatory respiratory water loss?
Aerobic catabolism requires oxygen
When animals breath to obtain oxygen they lose water by evaporation
Why is there obligatory urinary water loss?
Loss of urine water is mandated by ingestion of food molecules
Protein catabolism is usual cause of loss as it produces nitrogenous wastes (urea in mammals) that must be excreted
What is obligatory faecal water loss?
Loss of water that must occur in faeces for food catabolism to take place
How do Desert Kangaroo Rats avoid dehydration without access to water to drink? When fed only air-dried barley grain
Able to gain metabolic water in a net fashion by metabolising barley
What are the 3 types of regulation relating to the composition of blood plasma?
Osmotic regulation
Ionic regulation
Volume regulation
What does it mean if an exchange of ions and water between an animal and its environment is obligatory?
Responding to factors beyond the animal’s physiological control
What does it mean if an exchange of ions and water between an animal and its environment is regulated?
Physiologically controlled and required for maintaining homeostasis
What is osmoregulation?
Maintenance of a constant or nearly constant osmotic pressure in the blood plasma
What is an osmoregulator?
An aquatic animal that actively regulates the osmolarity of its extracellular fluid
What is an osmoconformer?
An aquatic animal that equilibrates the osmolarity of its extracellular fluid to be the same as that of the external environment
Why do freshwater organisms face challenges with volume, osmotic and ionic regulation?
Because water constantly enters the body from the dilute environment due to osmotic gradient
Entering water decreases osmotic pressure of ECF
Ions constantly moving from ECF to surrounding water and entering water dilutes
How do marine animals prevent water loss?
Integuments and epithelia of marine fishes are poorly penetrable to water
Marine fishes drink water and absorb it via gut epithelia
Kidneys produce small amounts of isosmotic urine
Define stenohaline animal.
Animal with tolerance to only a narrow range of salt concentrations
Define euryhaline animal.
Animal with tolerance to wide variance of salt concentration
What are the functions of the urinary system?
Removal of organic waste products
Regulation of volume and solute concentration of blood plasma
Elimination of waste products into the environment
Where are the kidneys?
Either side of the midline on the posterior wall of the abdomen
Behind parietal peritoneum, surrounded by adipose tissue
Where are the adrenal glands?
On the top of each kidney
What are the 2 parts of the adrenal glands?
Cortex and medulla
Which kidney is located slightly inferior to the other?
The right kidney is located slightly inferior to the left
What is the purpose of adipose tissue around the kidneys?
Protection
Support and cushioning
Describe the shape of the kidneys.
Indented ovoid, bean shaped
Around 10cm long, 5cm wide and 2.5 cm thick
What is the functional unit in the renal lobe?
Nephron
What are the ureters?
Hollow muscular tubes 25-30cm in length which propel urine from the kidney to the bladder
Located in both the abdomen and pelvis
How is back flow from into the ureters from the bladder prevented?
When the bladder is full, compression closes off the ureters (valves)
Describe the length and position of the female urethra.
4-5cm long
Passes through the pelvic floor and opens anterior to vagina
What is the length of the male urethra? What shape is it and what are the 4 regions?
20cm long
S shaped
Pre-prostatic, prostatic, membranous, penile
What are the main functions of the mammalian kidney?
Water balance Osmotic balance Ion balance pH balance Excretion of waste Hormone production Regulation of blood pressure
What are the 4 principle processes in urine formation by the mammalian kidneys?
Filtration
Reabsorption
Secretion
Excretion
What is the Starling principle of fluid exchange?
The direction of fluid flow across a capillary wall is the result of Net Filtration Pressure
What is reabsorbed in the Proximal Convoluted Tubule?
Around 75% of water, sodium and chloride ions from the primary urine
Osmotic pressure ….. with depth in the medulla of the mammalian kidney. [increases or decreases]
Osmotic pressure increases with depth in the medulla of the mammalian kidney.
Why is there a steep osmotic gradient in the inner medulla?
To facilitate constant reabsorption of water from the descending limb of the loop of Henle
Important for keeping equally high concentration in most distal segment of collecting duct and thus in final product: urine
What do the urea transport proteins do?
UT-A1 and UT-A3
Uniporters
Facilitate passive diffusion of urea from intertubular to interstitial fluid
Increases osmotic pressure, leading to reabsorption of water
How are the urea transporters UT-A1 and UT-A3 controlled?
Hormonal control
Vasopressin (ADH) upregulates expression
What do the Juxtaglomerular cells produce?
Renin
What is renin?
Enzyme released from kidneys in response to a drop in the glomerular filtration rate
Together with angiotensin converting enzyme, it converts an inactive protein in the blood into angiotensin
What is an aquaporin?
Transport protein in plant and cell membranes through which water passes in osmosis
What is angiotensin?
Peptide hormone that raises blood pressure by causing peripheral tissues to constrict
Maintains glomerular filtration by constricting efferent vessels and stimulates thirst and the release of aldosterone
