Page 94 - Biology_Form_3

Excretion

3. Draw the structure of the urinary urea and mineral salts are filtered out in
system of the displayed mammal Bowman’s capsule due to high hydrostatic
Question pressure. Glomerular filtration is called
1. What components make up the utrafiltration because blood is finely filtered
urinary system of the animal? through all membranes such that all plasma
tubule FOR ONLINE READING ONLY
2. How do the structures of the kidneys substances are passed except the proteins.
Bowman’s capsule joins the first convoluted
facilitate their function? region of the kidney tubule called the
The Nephrone proximal convoluted tubule. This tubule is

This is the structural and functional unit of coiled and surrounded by blood capillaries.
a kidney which is concerned with excretion The tubule has a long U-shaped structure
and homeostasis. It is the basic functional called the loop of Henle. As the filtrate
unit of the kidney involved in the production passes through the tubule, its composition
of urine. It is also known as a kidney is altered because of the secretion of some
tubule. Each kidney consists of a mass substances into it and by the selective
of nephrones, capillaries and connective reabsorption of water and mineral salts
tissue. In the cortex, the nephrone starts at from it. Selective reabsorption is the
an invaginated cup shaped capsule called process in which certain essential filtrate
the Bowman’s capsule. Within the capsule substances are taken back or reabsorbed
there is a loop of blood capillaries twisted to the blood. This process occurs in the
into a ball-shaped structure called the convoluted tubules. The loop of Henle
glomerulus (see Figure 4.3). Blood flows joins the proximal convoluted tubule at one
into and out of the glomerulus through tiny end and the distal convoluted tubule at its
arteries called arterioles. Bowman’s capsule ascending end. The distal convoluted tubule
facilitate ultrafiltration of the substances is also surrounded by blood capillaries and
carried by blood. Ultrafiltration is the joins the collecting ducts. The collecting
process whereby small molecules carried by ducts drain the urine formed into the pelvic
blood such as water, glucose, amino acids, region of the kidney.
Efferent arterioles Distal convoluted tubule
Afferent arterioles

Glomerulus
Bowman’s capsule Collecting duct
Proximal convoluted

Branch of renal artery
Branch of renal vein

Descending limb
Loop of Henle
Ascending limb

Figure 4.3: Structure of a mammalian nephrone

87

23/10/2025 11:52:44
BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 87 KAMISHNA 23/10/2025 11:52:44
BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 87

KAMISHNA