Kidneys and Homeostasis Flashcards
What is excretion?
It is the removal of metabolic waste made by the body. The main body excrete compounds using for excretory organs; the kidneys, the lungs, the skin and the liver.
What is egestion?
It is the removal of undigested food material in the form of faeces.
What is secretion?
It is the release of useful substances from cells.
What are the kidneys functions?
Excretion – filter the blood to remove nitrogenous from metabolic waste from the body to produce urine.
Osmoregulation – the control/regulation of the water content and solute composition of body fluids e.g blood, tissue fluid and lymph.
What is the nitrogenous waste found in plants?
They only synthesise Amino acid is in proteins which they need they don’t need to excrete nitrogen containing molecules. They uptake nitrates and ammonium from the soil by facilitated diffusion and active transport.
What adaptations do plants have which enabled them not to excrete nitrogenous waste?
Fabaceae family plants, have nitrogen fixing bacteria.
α -keto glutarate is combined with ammonia ions into glutamate (an amino acid). Glutamate is then covered into another amino acid by transamination.
What do you most aquatic organisms excrete their nitrogenous base in the form of?
Ammonia
Why do you aquatic organisms excrete ammonia?
Even though ammonia is highly toxic it is extremely soluble in water. The large surface area of fish gills and amoeba allows ammonia to diffuse out rapidly and it is immediately diluted below toxic concentrations. In softbodied invertebrates the ammonia diffuses across the whole surface into the surrounding water. In freshwater fish, ammonia is lost by ammonium ions across the epithelium of the gills with the kidneys playing a minor role in excretion.
How to birds, reptiles and insects excrete their nitrogenous waste?
They excrete their nitrogenous waste in the form of uric acid. Uric acid is almost insoluble in water and is non-toxic. It is excreted as a precipitate after nearly all water has been removed from the urine. In birds and reptiles the pace that urine is eliminated along with faeces from the intestine via the cloaca.
Why do they excrete uric acid?
As little water is required for excretion it allows them to conserve water and live in a water shortage environment or light enough for flight.
What do you most terrestrial organisms convert their nitrogenous waste into?
Urea which is then excreted as urine.
Why is urea excreted instead of ammonia.
As ammonia is extremely toxic in order for a terrestrial organism to excrete ammonia, it would have to urinate loads as it can only be transported at small and dilute concentrations. However urea can be transported in more concentrated forms as it is 100,000 times less toxic than ammonia. It enables animals who excrete urea in losing less water during excretion.
How is urea produced?
Dietary protein is digested into amino acids which are transported to the liver and then around the body where they are a simulated into proteins. Any excess amino acid is a deaminated, where the amino group is then converted into urea.
What is deamination?
It is when the amine group is removed from a molecule with the amine group being converted into urea. The removal of the group leaves ammonia and pyruvic acid.
What happens to the urea?
The ammonia is converted into urea and is released into the blood plasma and remains there until the kidneys remove it and excreted by urine.
What can pyruvic acid be used for?
Respiration as a source of energy converted into fat and stored.
What is the structure of the kidney?
Each kidney is covered by a tough renal capsule with both receiving blood from the renal artery and returning blood back into circulation by the renal vein. The blood from the renal artery is filtered in the outer layer, the cortex at the Bowman’s capsule. The medulla contains the loop of Henle and the collecting duct which carries urine to the pelvis. The pelvis emptied the urine into the ureter and carries the urine to the bladder.
What is a nephron?
It has an individual blood filtering unit with a kidney nephron being functional unit of the kidney. They are 30 mm long so provide a large surface area. Once the blood has been filtered it is carried through the nephron and the collecting ducts of many nephrons join to carry urine to the the pelvis and ureter.
What are the kidney blood vessels?
Blood is applied to each nephron in the afferent arterial where it splits into a capillary network called a glomerulus enclosed by the Bowmans capsule. From the glomerulus, blood is filtered and carried by the efferent arteriole to:
A peritubular capillary network surrounding the proximal and distal convoluted tubule
The vasa recta which is a capillary network which is surrounding the loop of Henley
What does the blood in the vasa recta do?
It delivers nutrients and oxygen to the nephron cells as well as carry water and mineral ions absorbed again from the kidneys
Where does ultrafiltration occur?
Bowmans capsule
What is ultrafiltration?
It is the filtration of small molecules (water, glucose, urea, amino acids and mineral ions) from the blood plasma to the lumen of the bowman capsule under high pressure.
What is the process of ultrafiltration?
The afferent arteriole (from the renal artery) branches into many capillaries inside the cup of the Bowman’s capsule. These capillaries reach on to form the efferent arteriole. These capillaries from a dense network called the glomerulus.
Why is there a high-pressure produced inside the glomerulus?
As the contraction of the heart creates a high-pressure in the renal artery. The difference in diameter of the afferent and the efferent arterial (the efferent arteriole is narrower than the afferent arteriole).
What are the pores called on the bowman capillary
They are called fenetrae. The small fenestrations force small molecules through into the lumen of the Bowman’s capsule.
What is the first layer of the Bowmans capsule?
It is a wall of capillaries which contains a single layer of epithelium cells with pores called fenestrae which are about 18 nm in diameter.
What is the second layer of the Bowmans capsule?
It is the capillary basement membrane which is an extracellular layer of proteins mainly collagen and glycoproteins. This layer acts as a molecular sieve as it is a filter with a selective barrier between the blood and the nephron
What is the final layers of the Bowmans capsule?
The wall/lining of the Bowmans capsule is made from squamous epithelium cells called podocytes. Extensions of the podocytes are called pedicels which wraps around the capillary pulling it closer to the basement membrane. The large gaps between the pedicels are called filtration slits.
What is the role/function of the basement membrane?
The basement membrane of the Bowmans capsule form is a selective barrier between the blood and the Bowmans capsule. It acts as a molecular sieve with only small molecules able to pass through.
Which molecules can’t pass through the basement membrane?
Blood cells, platelets and large proteins like antibodies and albumin, these then remain in the blood.
Does the blood have a high or low water potential from the glomerulus into the efferent arteriole?
It has a low water potential as a lot of water has been lost with a high concentration of proteins remaining.
What is the filtration rate?
It is the rate at which fluid passes from the blood in the glomerular capillaries into the Bowmans capsule. Filtration occurs because of the low water potential. The net effect of high hydrostatic pressure in the capillaries and low-sodium potential in the Bowmans capsule causes water to move out the blood.
Where does selective reabsorption occur?
In the proximal convoluted tubule
What is selective reabsorption?
It is when the useful products: glucose, amino acids, ions (Na+ and Cl-), water and vitamins are reabsorbed from the filtrate in the nephron back into the blood plasma. This process is indirectly active for glucose and amino acids.
What is the PCT?
It is the longest and widest part of the nephron. It carries the filtrate away from the Bowmans capsule. A blood in the capillaries surrounding the PCT absorbs all glucose and amino acids, some of the urea and most of the water and Na and Cl ions from the filtrate in the proximal convoluted tubule.
What is the PCT made out of?
Small cuboidal epithelium cells are found in its walls with invaginations called basal channels which are in the surface facing the basement membrane and capillaries.
Name the adaptations of the PCT?
It has a large surface area because of the microvilli as well as it being long with a large number of nephrons in the kidney. There are numerous carrier proteins embedded in the membrane.
Numerous mitochondria to provide ATP for active transport.
They have a close association with peritubular capillaries to have a short diffusion distance between the cells and the blood.
Tight junctions between the PCT epithelium cells. These are multi protein complexes that encircle a cell which attach tightly to neighbours. This prevents seepage of reabsorbed materials back into the filtrate.
How does sodium ions move into the PCT?
They diffuse passively by facilitated diffusion into the PCT cell, down the concentration gradient.
What is sodium and glucose transport?
Glucose and amino acids are filtered and reabsorbed into the blood by secondary active transport with sodium ions. A glucose molecule and two sodium ions bind to the transport to protein in the cuboidal epithelium cell membrane. Transporting the sodium out has provided a concentration gradient which brings glucose from the filtrate to the tissues. The sodium ions are pumped into the capillary with glucose moving in by facilitated diffusion is. Glucose is taken in by the PCT cell and then into the blood.
What is secondary active transport?
The coupling of diffusion e.g. sodium ions down and electrochemical gradient providing energy for the transport e.g. glucose up its concentration gradient.
Why is secondary active transport useful?
It enhances diffusion into the cell as it keeps the sodium concentrations low in the epithelium as it carries glucose down the concentration gradient.
How can you test if someone was to have diabetes?
You could take a urine sample as people with diabetes have a high concentration of glucose is present this means there won’t be enough available transport molecules (all are saturated with glucose molecules) in the membrane to absorb all this causes glucose to pass through the loop of Henley will be lost in the urine. Normal individuals won’t have any glucose is present in the urine indicating if a patient has diabetes.
How is glucose and amino acids transported?
Secondary active transport/co-transport via facilitated diffusion with Na+ into the cell.
Diffusion through the cell.
Glucose diffuses via facilitated diffusion through a channel protein into the capillary and Na is taken away actively.
What is the percentage of ions reabsorbed in the PCT to the blood?
About 70%. Amino acid, water soluble vitamins and Cl ions across transported with any ions. Most reabsorption uses active methods i.e. active transport however some do use passive methods.
What happens to the solute potential/water potential in the filtrate?
As ions and glucose leave the filtrate the solute potential decreases/water potential increases. Therefore water moves freely out of the filtrate into the blood by osmosis.
How much water is reabsorbed?
85%
How much urea and small proteins are reabsorbed?
About 50% of urea and small proteins are reabsorbed back into the blood of a diffusion. So alot of water has been lost from the filtrate so has a much greater concentration in the blood resulting in the steep concentration gradient.
What is the water potential like at the base of the PCT?
At the base of the PCT the filtrate is isotonic with the blood plasma at the end.
Where is the other 15% of water reabsorbed into?
The DCT in the cortex and the loop of Henle in the medulla and 5% is reabsorbed from the collecting duct.
What is the loop of Henle?
It is a hairpin counter current multiplier with the function to conserve water. It concentrates salts (Na and Cl) in the tissue fluid of the Medulla of the kidney by active transport. Water is reabsorbed from the fluid into the blood to produce a concentrated urine.
