3.7 - Homeostasis and the kidney Flashcards
(36 cards)
What is meant by the term homeostasis?
The maintenance of a constant internal environment to avoid wild fluctuations beyond the optimal range.
Wet is meant by our body being within a ‘dynamic equilibrium’
The idea that factors such as body temperature and pH may constantly fluctuate around a set point due to external factors but corrective mechanisms bring the internal conditions back to the set point.
What is meant by negative feedback?
When a second change occurs to reverse the effects of a first change.
Briefly outline the process of negative feedback?
- A receptor detects the fluctuation in the internal environment.
- The receptor then sends a message to the co-ordinator or controller.
- The co-ordinator communicates with the effectors to produce a corrective response
- Internal environment returns to normal. This is detached by the receptor and the effector stops corrective response.
How does the blood glucose negative feedback system work?
When the blood glucose increases to a dangerous point the body releases insulin so that glucose can be converted to glycogen. If the levels fall below a suitable level that the body releases glucagon which converts glycogen into glucose.
How does the body temperature negative feedback system work?
When the body gets too hot our sweat glands sweat more to increase heat lost through that, our blood vessels near the surface of our skin vasodilate to lose heat easily. If we are too cold respiration is increased and the blood vessels near our skin vasoconstrict to retain heat.
What is meant by excretion?
The body removes waste produced by the body through 4 excretory organs.
What are the 4 excretory organs? And what are their waste products?
- Lungs, carbon dioxide and water in expired air
- Kidneys, urea and uric acid in urine
- Skin, urea in sweat
- Liver, bile pigments in faces.
What are the kidneys two main functions?
- Excretion, the removal of nitrogenous waste from the body
- Osmoregulation, the control of water potential of the body’s fluids.
Outline how our body produces urea.
When we have excess amino acids in our body they are deaminated in the liver (the amino group is romped and converted into ammonia) this is highly toxic so its converted into less toxic urea and removed by the kidneys.
Outline the structure of the kidney
We each have 2 kidneys which can be located on either side of the ventrebal column. Each kidney is enclosed in a tough renal capsule. Blood enters the kidney through the renal artery and leaves via the renal vein.
What is a nephron and what are the key features of one?
A nephron is a functional unit of a kidney, there are millions of them in each kidney. Key components include Bowmans capsule, PCT, DCT and loop of henle.
What is meant by the term ultrafiltration?
When products of blood are forced out of the glomerus into the Bowmans capsule.
What creates a high hydrostatic pressure within the glomerus?
The afferent arteriole is wider so more blood enters than it can leave the thinner efferent arteriole.
What are the three layers between the glomerus and the Bowmans capsule? How do they work?
- Walls of capillary, single cell layered that contains pores called fenestrations that only allow small molecules to pass through.
- Basement membrane, layer of proteins that have a selective barrier disallowing blood cells and large proteins to pass through.
- Walls of the Bowmans capsule contain padocytes which have extensions called pedicels which wrap around the capillaries. They contain slits called filtration slits which allow molecules to pass through.
How to calculate filtration rate?
Volume of filtrate produced per minute divided by volume of blood entering kidneys per minute x 100.
What is the vasa recta ?
They closely knit capillaries associated with the nephron. They follow the pathway of the loop of henle.
What processes facilitate selective reabsorption in the PCT?
- Facilitated diffusion
- Active transport.
How is the PCT specialised?
It contains highly specialised cuboidal epithelial cells. They contain microvilli which protrude into the lumen of the PCT to increase surface area for absorption. Lots of mitochondria to produce ATP for active transport. Tight junctions between cells to avoid diffusion between adjacent cells.
How are glucose and amino acids be reabsorbed into the bloodstream?
By active transport and co transport with sodium ions. Special proteins transport both glucose and sodium back into the blood stream, though co transporters.
What is meant by the glucose threshold?
Glucose is essential for respiration, it is usually all reabsorbed in the PCT. However, if the concentration of the glucose in the filtrate is too high then some will remain in the filtrate as the transport proteins are all occupied. This occurs if someone has diabetes.
Outline how water is reabsorbed in the loop of henle.
When descending down the limb, due to this area being permeable to water and the outer medulla being highly salty the water diffuses out of the loop, it does not let salt out. This is maintained as the ascending loop of henle is impermeable to water and pumps out salts into the medulla.
What is meant by the counter current multiplier?
The limbs work in opposite directions to concentrate the filtrate
How does length of loop of henle affect water absorption?
If the loop is longer than more ions can be pumped into the medulla and more water leaves and is reabsorbed by osmosis. Therefore animas living within desert conditions have longer loops of henle.
