Summary
Summary - CCEA Unit A2 1 - Physiology and Ecosystems - Homeostasis
- Institution
- CCEA
Summary notes covering the entire CCEA A21 Biology specification in regard to the Homeostasis section.
[Show more]
Seller
Follow
Content preview
HOMEOSTATIS AND THE KIDNEYULTRAFILTRATION
-Ultrafiltration is a non-selective process
- Blood enters the glomerulus through the afferent arteriole at high hydrostatic pressure caused by
the afferent arteriole being wider than the efferent arteriole and being so close to the heart.
- All small molecules such as glucose, water, ions, and amino acids from the blood plasma are forced
out of the capillary and into the cavity of the bowman’s capsule.
- Red blood cells and large proteins do not leave the capillary due to them being too large to pass
through the basement membrane – which acts as the effective filter.
- Ultrafiltration is a process aided by pores in the walls of the capillary and gaps between the
podocytes in the walls of the bowman’s capsule.
- The liquid in the cavity of the bowman’s capsule is now called the filtrate.
SELECTIVE REABSOPRPTION
- At the proximal convoluted tubule amino acids and glucose are selectively reabsorbed by
active transport and facilitated diffusion.
- At the end of the proximal convoluted tubule all amino acids and glucose will have been
selectively reabsorbed.
- Small molecules are reabsorbed by pinocytosis
- The active reabsorption of the substances lowers the solute potential of the blood, causing
most of the water to re-enter the blood capillaries by osmosis.
- Urea is not selectively reabsorbed at the PCT, however the loss of water from the filtrate
causes the concentration of urea to increase throughout the nephron.
ADH/OSMOREGULATON
(qu.) Explain the link between a more negative blood solute and osmoregulation in the kidney.
ANS – Osmoreceptors in the hypothalamus detect the low solute potential. ADH is released from the
pituitary gland. This increases the permeability of the collecting duct and distal convoluted tubule by
opening its aquaporins. More water leaves the filtrate to be reabsorbed by the blood in the medulla.
This results in a low volume of concentrated urine.
(qu.) Explain the link between a more positive solute potential and osmoregulation in the kidney.
ANS – Less ADH is released from the pituitary gland. Therefore, permeability decreases in the
collecting duct and distal convoluted tubule due to more aquaporins closing. Less water leaves the
filtrate to be reabsorbed by the blood in the medulla. This results in a large volume of dilute urine.
ADAPTIONS OF DESERT ANIMALS
Mammals which live in particularly dry areas have a longer loop of Henle and a thicker medulla.
The longer the loop of Henle the more ions can be pumped from the filtrate to create a very low
water potential in the medulla (salt bath). More water will leave the filtrate and enter the medulla,
therefore a reduced water loss by only producing a small volume of concentrated urine.
PARTS OF THE KIDNEY
Cortex – Filtration carried out by nephrons, dense capillary network which receives blood from the
renal artery.
Medulla – Divided into pyramids, nephron extends across the cortex into the medulla
Pelvis – Urine passes into pelvis before passing into ureter
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller sophie1204. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £4.49. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
53340 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now