Biology: 3.7 Homeostasis and the kidney Flashcards
Define Homeostasis
It is a stable equilibrium between interdependent elements, especially as maintained by physiological processes in the body.
What are the two functions of the kindey?
1: Removal of nitrogenous metabolic waste (urea) from the body - excretion.
2: Osmoregulation, the mechanism by which the balance of water and dissolved solutes is regulated.
How is urea produced?
It is a poisonous chemical made by the liver. Produced when amino acids, which make up protein, are deaminated - NH2 groups are removed.
What is the Bowman’s capsule responsible for?
It is the site of ultrafiltration. Its blood supply enters as an afferent arteriole which enters the glomerulus and leaves as the efferent arteriole. This is narrower than the afferent arteriole.
Where does the efferent arteriole carry blood to?
1: A capillary network serving the proximal and distal convoluted tubules.
2: A capillary network running beside the loop of Henle known as the vasa recta.
How does the glomerulus speed up the rate of filtration?
Endothelium of the capillaries has pores between the cells to speed up the process of filtration.
What are podocytes?
Podocytes are the cells of the inner wall of the Bowman’s capsule. They have many processes which are wrapped around the capillaries of the glomerulus.
Large gaps between these processes allow free passage of the filtrate from the blood into the lumen of the renal capsule.
What is the basement membrane?
It acts as a selective barrier allowing water and small molecules to pass from the blood of the nephron.
Where does ultrafiltration occur?
In the glomerulus.
How does ultrafiltration work?
Filtration under pressure that forces small soluble molecules from the plasma. Basement membrane of the capillary forms the selective barrier between the blood and the nephron and acts as a molecular sieve. Small molecules can pass through, but the plasma proteins and erythrocytes remain in the blood due to their larger size.
What causes the high pressure causing filtration?
Hydrostatic pressure of the blood in the glomerular capillaries which is increased due to efferent arterioles being smaller than afferent arterioles and also by water potential of blood.
What is selective reabsorption?
Selective as only certain molecules are removed from the glomerular filtrate. Re-absorption as all the molecules have already been absorbed once from the intestines.
What does the proximal convoluted tubule reabsorb?
All the glucose and most of the water and salt.
What does the distal convoluted tubule reabsorb?
Small amounts of water and salt for fine regulation of blood ion concentration.
Where is most of the water reabsorbed from?
The collecting duct.