Homeostasis is the maintenance of a steady internal environment and this concept covers a range of topics in the functioning of all living things. The following topics lead on to a number of sub-topics all of which you need to think about in terms of how the body manages to keep a healthy chemical balance of the blood and cells.
Topic 1: The Kidney - This is to do with Osmoregulation because the kidney is the osmoregulatory organ for many animals including humans. It controls blood pH, volume and chemistry of body fluids.
The functional structure of the kidney is the Nephron of which there are millions in each kidney.
It is the nephron that carries out all the work of osmoregulation.
You need to learn the following:
Ultrafiltration which is all about the filtering of water and solutes from the blood; blood pressure controls how effective ultrafiltration is. Low blood pressure means inefficient ultrafiltration and a consequent imbalance in body water and, blood chemistry.
Ultrafiltration takes place in the Bowman's capsule.
Image
This image shows the glomerulus (the bundle of capillaries in a Bowman's Capsule) as well as some cross sections of kidney tubules. The red blood cells can be seen within the wall of each tubule.
Selective reabsorption is all about the reabsorption of water and salts once unltrafiltration has occurred. Selective reabsorption takes place in the Proximal Convoluted Tubule PCT)
Tubular Secretion is the last function of the nephron and this refers to the secretion of certain soluble substances, by Active Transport, into the Distal convoluted Tubule (DCT).
These soluble substances are Uric acid, H+ ions, creatinine al of which provide an osmotic balance to urine output. At work here, in the location of the DCT, are the Hormones ADH and Aldosterone.
ADH = Anti-diuretic Hormone (diuretic means something that gets rid of excess water) increases water reabsorption and it is released under conditions such as dehydration. ADH controls the permeability of the DCT and, collecting ducts. More ADH = greater permeability = greater water reabsorption.
Aldosterone causes uptake of sodium ions from the tubular filtrate (this is the fluid that's left after all the reabsorption). When the sodium ions taken up, hydrogen ions take their place in the filtrate. H+ ions cause acidity therefore their movement into the filtrate prevents a condition of the blood called 'acidosis' - acid blood.
Aldosterone also causes potassium ions to be secreted into the filtrate when there is a build up of K+ ions in extracellular fluid surrounding the kidney (or elsewhere).
So, Ultrafiltration, Selective Reabsorption and Tubular Secretion sum up the work of a nephron. It's quite complicated in places but like all things, keep reading and re-reading and get information from different courses - don't just rely on one book to learn all this.
