Page 348 - Biology_F5

Regulation (Homeostasis)

(b) Water balance by producing a blood vessel constricting
As kidneys are key in the chemical protein, angiotensin, which also signals
breakdown of urine, they react to changes the body to retain sodium and water. Both
in the body’s water level every minute. As constriction and retention help restore
water intake decreases, the kidneys adjust normal blood pressure.
FOR ONLINE READING ONLY
accordingly and leave water in the body
instead of helping to excrete it. (d) Red blood cell regulation
When the kidneys do not get enough
(c) Blood pressure regulation oxygen, they send out a distress call in
The kidneys need constant pressure to the form of erythropoietin; a hormone that
filter the blood. When it drops too low, the stimulates the bone marrow to produce
kidneys increase the pressure. One way is more red blood cells. This process is
called erythropoiesis.

Table 7.1: Summary of parts of the kidney and their functions

Parts of the kidney Description

Renal hilus An indentation near the centre of the concavity of the kidney where the
renal vein and ureter leave the kidney and the renal artery enters the
kidney

Renal capsule A tough, fibrous membrane, surrounding the kidney. It consists of
dense, irregular connective tissues which protect and help to maintain
the kidney’s shape. It is also surrounded by fatty tissue which helps to
protect the kidney from damage

Renal cortex The outer reddish part of the kidney that has a smooth texture; it is
where the Bowman’s capsule, glomeruli, proximal and distal convoluted
tubules and blood vessels are found
Renal medulla The inner striated redish-brown part of the kidney

Renal pyramids Stripped and triangular in structure within the medulla, that are made of
straight tubules and corresponding blood vessels

Renal pelvis The funnel-shaped cavity that receives urine drained from the nephrons
through the collecting ducts and papillary ducts

Renal artery The blood vessel that delivers oxygen-rich blood to the kidney; it enters
the kidney through the hilus and divides into smaller arteries, which
separate into afferent arterioles that serve each of the nephrons

Renal vein The blood vessel that receives deoxygenated blood from the kidney
and returns it to the systemic circulation

Afferent arteriole The blood vessel that delivers oxygen-rich blood to the glomerulus
under high pressure
Efferent arteriole The blood vessel that receives oxygenated blood from the glomerulus

Form Five Student’s Book
341