Page 349 - Biology_F5

Biology for Advanced Level Secondary Schools

Parts of the kidney Description

Kidney nephrons The functional units where the kidney’s main functions are performed:
There are about a million nephrons in each kidney
Collecting duct This part of the kidney nephron collects urine and drains into papillary
ducts, minor calyx, and major calyx, and finally into the ureter and
urinary bladder
FOR ONLINE READING ONLY
Ureter The tubular structure that conveys urine from the pelvis of the kidney
to the urinary bladder

(e) Regulation of pH of the blood water and other materials. Each kidney
Kidneys excrete hydrogen ions into has more than a million nephrons in the
urine. At the same time, they conserve renal cortex, which gives it a granular
bicarbonate ions which are an important appearance on sagittal section (Figure
buffer of hydrogen ions. 7.7). Nephrons are used to separate water,

(f) Regulation of the ionic composition ions and small molecules from the blood
of blood molecule, and filter out wastes and toxic
Kidneys regulate the quantities of ions materials, then it selectively returns the
in the blood. Important examples of needed molecules to the blood. The most
ions whose quantities are regulated by primitive nephrons (pronephros) are found
the kidneys include sodium, potassium, in the kidneys of primitive fish, amphibian
calcium, chloride and phosphate ions. larvae, and embryos of more advanced
vertebrates. The nephrons found in the
(g) Synthesis of vitamin D
Kidneys are involved in the synthesis kidneys of amphibians and most fish,
of calciferol, which is an active form of and in the late embryonic development
vitamin D. of more advanced vertebrates, are only
slightly more advanced in structure
The nephron (mesonephros). The most advanced

Task 7.5 nephrons occur in the adult kidneys, or
Search from the library and internet metanephros of land vertebrates, such as
sources the structure of nephron and reptiles, birds, and mammals.
its physiological activities. Write short
notes on the searched information. There are two types of nephrons, namely
cortical nephrons, (which are found deep
The nephron is the kidney’s functional unit in the renal cortex) and the juxtamedullary
that is involved in production of urine in nephrons, which make up about 15
the process of removing waste and excess percent of total nephrons and lie close to
substances from the blood. Generally, the medulla. The nephrons consist of a
nephron is responsible for the filtration, renal corpuscle, a tubule, and a capillary
excretion and re-absorption of most of the network. These originate from the small

Form Five Student’s Book
342