Excretory Flashcards
What are two of the major waste products and how are they removed from the body
Carbon dioxide and water; through the respiratory system
Animal cells produce waste while doing what
Carrying out the physiological processes that are necessary for life
What is the third type of waste produced by metabolic processes
The nitrogenous wastes urea and uric acid
When are urea and uric acid created
Amino and nucleic acids are broken down
What have animals done in response to nitrogenous waste
Developed a variety of systems that also play important roles in regulating water and salt balance
How do cnidarians solve the problem of nitrogenous waste
Simple diffusion - most cells of a cnidarian are in contact with the external environment, meaning that nitrogenous wastes can diffuse across the cell membranes and into the surrounding water
Describe the annelid system for excretion
Two small tubes called nephridia exist in each of the annelid’s body segments. The tubes are surrounded by capillaries. Nitrogenous waste in the form of urea is passed from the blood into the nephridia. The waste collected in the nephridia eventually exits the worm through pores in the skin.
What are the Malpighian tubules
A system of structures that are bathed in the fluid of the arthropod’s open circulatory system. It is the annelid’s ways of excreting waste. Nitrogenous waste in the form of uric acid collects in tubules, the waste empties into the digestive tract where water is reabsorbed. Without water, urea converts to solid crystals of uric acid, which are excreted along with the solid waste produced by digestion
What is the answer of the vertebrates to the problem of water balance and nitrogenous waste excretion
The kidneys
What do the kidneys do and how many are there
There are two, and they filter blood, removing urea in the form of urine while also regulating the levels of water and salt present in the blood plasma.
From each kidney, where does urine travel
Through the ureter and then into the urinary bladder
Describe the ureter
A large duct
Describe the bladder
A muscular organ that expands to store urine
What happens when the bladder contracts
Urine is pushed through another duct known as the urethra and out of the body
What is the basic functional unit of the kidney
The nephron (the kidney has millions of nephrons)
What is a nephron
A tiny tubule whose special structure makes it ideal for its blood filtering task
What do nephrons consist of
A cluster of capillaries called the glomerulus
What is the glomerulus surrounded by
A hollow bulb known as Bowman’s capsule
What does the Bowman’s capsule lead into
A long, convoluted tubule with four sections: the proximal tubule, the loop of Henle, the distal tubule, and the collecting duct
Where do the collecting ducts empty into
The central cavity of the kidney, the renal pelvis, which connects to the ureter (that carries urine to the bladder)
How does blood enter the kidney and what happens there
Through renal arteries, which quickly split into smaller vessels and then branch further into the very narrow clusters of capillaries that make up the glomerulus of the nephron
Why is the blood pressure high in the glomerulus’s capillaries
Because the capillaries are very narrow
What does the high pressure do
It squeezes the liquid portion of blood (filtrate) through a sieve structure and into the Bowman’s capsule but leaves the blood cells, platelets, and large protein molecules behind (filtration)
What does the filtrate contain
Large amounts of water, glucose, salts, and amino acids as well as urea
Where does the filtrate go from Bowman’s capsule
The proximal tubule of the nephron
What happens in the proximal tubule
Important molecules for life (sodium, water, amino acids, and glucose) are pumped out of the proximal tubule to be reabsorbed by the blood (a process called reabsorption)
When is the filtrate called urine
After reabsorption
From the proximal tubule where does the urine go
The next part of the nephron, the loop of Henle
What percent of the initial water content and volume has the urine lost by the time it reaches the loop of Henle
75
Where is the loop of Henle
It descends from the outer region of the kidney, the cortex, into the medulla
What are the walls of the descending loop permeable to
Water but not salt
The medulla of the kidney has a high concentration of what and what does that create
Salt, creating a concentration gradient: water is drawn out of the descending loop and into the medulla, leaving the salts behind
When the urine reaches the ascending part of the loop of Henle, what percent of the original water content remains
6
What is the ascending loop of Henle permeable to
Permeable to salt but not water
What happens because the urine lost so much water content in the descending loop?
The salt content at the beginning of the ascending loop is very high
In the ascending loop, what happens with the salt and what does that help to do
Salt diffuses from the ascending loop into the medulla of the kidney which helps to maintain the high salt content of medulla
Once urine finishes traveling through the ascending loop, what percent of the original salt content of the filtrate remains and what does the urine mainly consist of
4; urea and other waste products
After the ascending loop, where does the urine go
Into the distal tubule
How does the distal tubule operate
Similarly to the proximal tubule - salt is pumped out of the urine, and the water follows osmotically
At the end of the distal tubule, what percent of the original water content remains in the urine
3
At the end of the distal tubule, what is the salt content
Negligible
What takes place in the distal tubules? (3)
Filtration
Reabsorption
Secretion (when salt and water are leaving the tubules, hydrogen and potassium ions are actively transported from the blood into the urine of the tubule so they can be excreted)
Where does the urine go after the distal tubule
The collecting duct
Where is the collecting duct
The medulla portion of the kidney
Does the medulla have a high or low salt content
High
Because of the medulla salt content, what?
As much as 75% of the remaining water can be re absorbed as the urine travels through the collecting duct
What does the amount of water reabsorbed in the collecting duct depend on
The permeability of the walls of the duct
What is the permeability of the walls of the duct regulated by
The antidiuretic hormone ADH secreted by the posterior pituitary gland
What does ADH do to the walls of the collecting ducts
It acts on them to make them more permeable to water but, if ADH levels are low, less water will be reabsorbed
If a person is dehydrated and needs to conserve water, what happens to the levels of ADH
They rise
If a person has sufficient levels of water in the blood then what happens to the ADH levels
They are low -> less re absorbed water + more dilute urine
The lower portions of the collecting duct are permeable to what, allowing what to happen
Water and urea, allowing some of the urea to enter the medulla of the kidney.
What does the release of urea allow the medulla to do
Maintain its high ion concentration, which is important in the functioning of the nephron
What is another hormone that has an effect on the nephron (in addition of ADH)
Aldosterone
Where is aldosterone produced
The adrenal cortex
What does aldosterone do
Increases the sodium and water re absorption in the distal tubule
What do kidneys do
Control the amount of water that is reabsorbed from the filtrate, which has an effect on blood volume and blood pressure, and release an enzyme into the blood
What enzyme do kidneys release into the blood
Renin
What does renin do
It sets off a series of reactions in the blood that results in the production of another enzyme
What enzyme does renin cause to be made
Angiotensin II
What does angiotensin II do
Constricts blood vessels, causing a rise in blood pressure.
Causes the adrenal cortex to release more aldosterone
What does aldosterone do
Raises blood volume and blood pressure
