The excretory system regulates chemical composition in body fluids by removing wastes and retaining proper amounts of water, salts, and nutrients. The kidneys filter blood, removing waste and producing urine, which travels through ureters to the bladder. Nephrons are the basic functional units of the kidney that filter blood, reabsorbing necessary substances and excreting the rest as urine through a multi-step process involving filtration, reabsorption, and secretion.

1. EXCRETORY
SYSTEM
- regulates the chemical composition
of body fluids by removing metabolic
wastes and retaining the proper
amounts of water, salts, and
nutrients

2. Kidneys
are located in the back of the abdominal cavity.
excrete urine into one of the ureters.
serve a variety of functions including regulating
blood pressure, maintaining the body’s acid-base
balance and regulating electrolytes.
They also naturally filter the blood, diverting the
waste towards the urinary bladder.

3. Ureters
a muscular tube that brings the urine between the
kidneys and the urinary bladder.
usually have a diameter of between 3 and 4 mm
and a length of between 25 and 30 cm.
cross over the pelvic brim close to the bifurcation
of iliac arteries, which is where kidney stones are
commonly found.

4. Bladder
is responsible for collecting any urine that
the kidneys excrete.
the urine is stored here before urination
occurs.
an elastic, hollow, and muscular organ that
rests on a person’s pelvic floor.

5. Urethra
a tube which connects a person’s urinary
bladder to their genitals so that urine can be
removed from the body.
there is also an external urethral sphincter
which allows us to voluntarily control urination.

6. Nephrons
basic structural and functional unit of the kidney.
chief function is to regulate the concentration of
water and soluble substances like sodium salts by
filtering the blood, reabsorbing what is needed and
excreting the rest as urine.
In humans, a normal kidney contains 800,000 to
1.5 million nephrons.

7. Two Regions
1. Bowman's capsule (or the Bowman capsule, capsula
glomeruli, or glomerular capsule) is a cup-like sac at the
beginning of the tubular component of a nephron in the
mammalian kidney that performs the first step in the
filtration of blood to form urine. A glomerulus is enclosed
in the sac. Fluids from blood in the glomerulus are
collected in the Bowman's capsule and further processed
along the nephron to form urine.

9. 2. The renal tubule is the portion of the nephron
containing the tubular fluid filtered through the
glomerulus.
The components of the renal tubule are:
•Proximal convoluted tubule (lies in cortex and
lined by simple cuboidal epithelium with brushed
borders which help to increase the area of
absorption greatly.)
•Loop of Henle (hair-pin like, U-shaped and lies in
medulla) adjust water concentration in the urine
•Distal convoluted tubule - helps in tubular
secretion

11. URINE FORMATION
•Filtration involves the transfer of soluble components
such as water and waste from the blood into the
glomerulus.
•Reabsorption involves the absorption of molecules, ions,
and water that are necessary for the body to maintain
homeostasis from the glomerular filtrate back into the
blood.
•Secretion involves the transfer of hydrogen ions,
creatinine, and drugs from the blood into the collecting
duct.