Excretion
• The urea is now transported through the bloodstream until it
reaches the kidneys.
• The kidneys are important filtration organ: helps in regulating
water and salts in the body. It also used to remove urea from
the blood
• The kidney consists of several nephrons,
o Structure: close to blood capillaries and are made of
tubules. The small tubes loops are around the kidney
structure layers and have capillaries around them
o Tubules merge into one giant tube known as ureter
•
•
•
•
•
Blood flows into the kidneys through the renal artery.
The start of every nephron is a bundle of blood capillaries
coiled together called a glomerulus. This bundle of
capillaries are squeezed together and the pressure forces
out small molecules our of the capillaries into the nephron
o Small molecules are allowed to pass through (water,
glucose, urea, ions)
o Larger structure such as proteins, blood cells are
kept flowing in the capillaries
The filtrate flows through the tubules and its contents is
adjusted depending of the hydration of the individual
Reabsorption happens. Water, glucose and ions are
reabsorbed by the kidney tissues surrounding the tubules.
The reabsorption depends on the concentration of the
tissues surrounding the kidney. Almost all glucose is
reabsorbed but some water and ions remain along with
urea. The resulting filtrate continues to flow and will
eventually become urine
Reabsorption by the kidney tissues will return these
substances back into the blood through the capillaries and
eventually the renal vein
Health tip
• Urine consists of salts and urea. These are water soluble
substances that can potentially crystallize given the right
conditions. When urine is too concentrated, the salt
minerals and urea can form crystal formations and these
solids will block the urinary tract
• Kidney stones 肾结石: can block urinary tract and damage
the tissues resulting to bleeding
Homeostasis
• Maintenance of a constant internal environment
• Control of internal conditions within set limits by negative
feedback
The control of the glucose concentration of the blood by the liver
and the roles of insulin and glucagon from the pancreas
•
•
Both hormones are secreted by the pancreas and are
transported to the liver in the bloodstream
Insulin control blood glucose level by increasing the uptake
of glucose by cells and stimulate cells to convert glucose to
glycogen
Type 1 diabetes
Symptoms
• Increased glucose in urine
• Blurred vision
• Slow wound healing
•
Treatment
• Insulin by injection
Regular blood glucose test
• Controlled diet
The maintenance of a constant internal body temperature in
humans in terms of vasodilation and vasoconstriction of arterioles
supplying skin surface capillaries
When you are cold, body
produces and save heat
• Shivering: muscles
contract and relax ->
produce heat
• Vasoconstriction:
arterioles near skin
become narrower ->
conserve heat
When you are hot, the body
loses more heat
• Sweating: droplets of
sweat evaporate, cooling
the body
• Vasodilation: arterioles
near skin become wider,
more blood flows near
skin surface -> lose heat
Human skin
Vasoconstriction 血管收缩
• When we are cold blood flow in capillaries slows down
because arterioles leading to the skin capillaries get
narrower
• Reduces the amount of heat lost from the blood by radiation
Vasodilation 血管扩张
• When we are hot blood flow in capillaries increases
because blood vessels to the skin capillaries get wider
• Cools the body as blood (which carries heat around the
body) is flowing at a faster rate through the skin’s surface
and so more heat is lost by radiation