Excretory System Flashcards
What are the main functions of the excretory systems?
- Maintenance of the right concentrations of inorganic solutes in the internal fluids
- maintenance of an appropriate plasma volume
- removal of toxic substances
- removal of hormones
- maintenance of osmotic and ionic balance
Which organ systems are involved in excretory function and retention?
- Respiratory systems (gills, lungs)
- digestive systems (liver, intestine)
- integument (skin) and glands (sweat gland, salt gland)
- renal organs (protonephridia, antennal glands, kidneys)
What are the fundamental phases of renal excretory processes?
- Filtration
- secretion
- reabsorption
- osmoconcentration
What are protonephridia and where are they found?
Protonephridia are excretory structures found in simple animals like
- rotifers
- flatworms
- larvae of annelids
- molluscs
- fish
- amphibians
What is the function of protonephridia?
- They use ultrafiltration driven by cilia
- along with secretion and reabsorption, to filter body fluids.
What are metanephridia and where are they found?
Metanephridia are excretory structures found in
- adult molluscs
- annelids
- crustaceans
- vertebrates
What is the function of metanephridia?
They perform
- ultrafiltration
- secretion
- reabsorption
- sometimes osmoconcentration
How do metanephridia function in annelids?
They consist of tubules communicating with the coelomic cavity
- secreting KCl and other substances
- (no ultrafiltration)
- with reabsorption and secretion processes
occurring as the fluid moves through the tubules.
How do metanephridia function in crustaceans?
They consist of an
- end-sac for ultrafiltration
- a labyrinth for reabsorption and secretion
- a bladder for urine accumulation and excretion
How do metanephridia function in molluscs?
They are
- tubular or saccular structures
- filter blood ultrafiltrate through the pericardial cavity
- reabsorbing glucose and amino acids
- discharging the final urine into the mantle cavity
What is the functional unit of the vertebrate kidney?
The nephron
What are the components of the nephron?
Tubules associated with a vascular component for
- filtration
- reabsorption
- secretion processes
What regulates the glomerular filtration rate (GFR) in the kidneys?
The juxtaglomerular apparatus, which
- detects changes in tubular saline concentration (macula densa, distal tube)
- releases vasoactive factors (ATP and adenosine) by granular cells
- to modulate arteriole contraction.
How do tubules reabsorb substances from the tubular lumen to the blood?
Through transepithelial transport mechanisms, preventing the passage of molecules between cells due to tight junctions.
How is glucose reabsorbed in the proximal tubule?
- secondary active transport with Na+ at the luminal membrane
- facilitated diffusion through the basolateral membrane
same transport mechanisms for amino acids
What happens when the tubular maximum (Tm) for glucose is exceeded?
Excess glucose is not reabsorbed and is excreted in the urine
What percentage of Na+ is reabsorbed in different parts of the nephron?
- 67% in the proximal tubule
- 25% in the loop of Henle
- 8% in the distal tubule and collecting ducts
What is the importance of Na+ reabsorption in the proximal tubule?
It is essential for the reabsorption of
- glucose
- amino acids
- water
- chloride
- urea
and for regulating the volume of extracellular fluid
Which system stimulates Na+ reabsorption in the distal tubule?
The renin-angiotensin-aldosterone system (RAAS)
How does atrial natriuretic peptide (ANP) affect Na+ reabsorption?
ANP antagonizes the RAAS, reducing Na+ reabsorption and promoting Na+ excretion
How does vasopressin (ADH) regulate urine osmoconcentration?
Vasopressin increases the permeability of the distal and collecting tubules to water by promoting the insertion of aquaporins in the cell membranes
What triggers the release of vasopressin?
Changes in osmotic pressure detected by hypothalamic osmoreceptors
What happens after the release of vasopressin? (steps)
What does NKCC stand for and what is its function?
NKCC stands for
Na+-K+-2Cl- cotransporter
which moves
- sodium
- potassium
- and chloride ions
into tubular cells
How does the NKCC transporter contribute to ion balance?
It helps create an electrochemical gradient that facilitates the diffusion of chloride and sodium ions.
Where is the NKCC transporter especially important?
- In the rectal gland of cartilaginous fish
- the gills of bony fish for salt regulation
How do marine mammals’ kidneys differ from those of other mammals?
Marine mammals’ kidneys are made up of numerous reniculi, which are small independent lobes with discrete cortical tissue
- they are shorter
- reduced NaCl reabsorption
How do cartilaginous fish regulate their plasma concentration?
- maintaining a lower plasma concentration of NaCl than seawater
- eliminating excess NaCl through the rectal gland
- their osmolarity is equal to/ slightly higher than external environment due to the presence of osmolytes (urea or TMAO)
How do bony fish eliminate excess NaCl?
Through chloride cells in the gills using a mechanism similar to the NKCC cotransporter
What are the three methods reptiles use to conserve water?
- they eliminate uric acid
- reabsorb water in the cloaca
- eliminate high salt concentration liquid through the salt gland
How do seabirds manage to drink seawater?
They possess a salt gland that removes NaCl from the blood without losing water, becoming active when the bird is dehydrated or overloaded with salt
How do body systems work together in response to homeostatic challenges
All body systems integrate to maintain homeostasis, responding to physiological changes such as injury from a predator attack
