chapter 14 Flashcards
Define homeostasis.
Homeostasis is the maintenance of a
constant internal environment by the
biological systems of the body.
Why is homeostasis necessary?
Homeostasis ensures that the cells and tissues
of the body have the correct environment to
function e.g. optimum temperature and pH,
enough glucose for energy.
Define negative feedback.
Negative feedback is a response of a biological
system. When a change from the optimum is
detected, the system that produced the change
is turned off to return the variable to its optimum
level.
Which component of a biological system detects a stimulus?
A receptor.
Describe the role of a coordination system in homeostasis.
A coordination system (e.g. nervous system,
endocrine system) receives information about
stimuli from receptors and determines what the
response should be by sending instructions to
effectors.
In homeostasis, what are effectors?
Effectors are components of a homeostatic
mechanism that produce a response to a
stimulus. Muscles and glands are effectors.
Describe the ways in which the body can
conserve heat in a cold environment.
● Shivering
● Vasoconstriction of blood vessels to prevent
heat loss from the blood
● Raising hairs to trap a layer of insulating air next
to the skin
Describe the ways in which the body can
rapidly lose heat in a warm environment.
● Vasodilation of blood vessels to increase heat
loss from the blood
● Increase in sweating - as the sweat
evaporates, it cools the skin.
Define osmoregulation. Why is it
important?
The regulation of the water potential of the
blood. It is important because cells may shrink
or burst if the water potential of the blood is
too high or low, due to movement of water by
osmosis.
Where and how is urea formed?
Urea is produced in the liver from the deamination (removal of the amine group) of excess amino acids.
Outline the gross structure of the kidney
https://ibb.co/FsHPnw9
What is a nephron?
A nephron is one functional unit of the
kidney.
Name the structures of the nephron. https://ibb.co/qFw0r0c
https://ibb.co/K9j1Pnb
Outline the blood vessels associated
with a nephron.
An afferent arteriole from the renal artery forms the
glomerulus. The efferent arteriole takes blood away from the glomerulus.
The efferent arteriole branches to form the capillaries that surround the nephron tubules. These combine to form the renal vein which drains the kidney.
Describe the process of ultrafiltration.
Within the glomerular capillaries, there is hydrostatic
pressure. This filters the blood, forcing water, glucose,
urea and ions into Bowman’s capsule to form the
glomerular filtrate.
Proteins and cells are too big and are not filtered into
Bowman’s capsule; they stay in the blood.
Describe how the structure of Bowman’s
capsule and the glomerular capillaries is
suited to its function.
● The capillary endothelial wall is one cell thick, and there are gaps between cells to allow substances to pass through
● The renal capsule has podocytes, which have spaces in between them to allow the filtrate to pass into the renal capsule
● The connective tissue between the capillaries and renal capsule prevents larger molecules, like proteins and red blood cells, leaving the blood
In which part of the nephron does
selective reabsorption occur?
In the proximal convoluted tubule.
Water, glucose and ions are reabsorbed
back into the blood.
Describe the process of selective
reabsorption of glucose.
Co-transport of glucose with Na+ ions into the cells of the proximal convoluted tubule. Glucose diffuses out of the cell and into the blood.
Active transport of Na+ ions out of the cells is required to ensure there is a low concentration. This maintains the Na+ diffusion gradient.
The presence of glucose and Na+ ions in the cells reduces the water potential, which draws water out of the tubule by osmosis.
What happens in the loop of Henle in the
nephron?
In the ascending limb, Na+ and Cl- are actively transported into the medulla. The water potential of the medulla is very low, which draws water out of the
descending limb by osmosis. The water potential of the
surrounding tissue is much lower at the bottom of the
loop than at the top.
Describe what happens in the distal
convoluted tubule and collecting duct.
In the collecting duct, Na+ ions are actively transported out of the tubule, resulting in water reabsorption.
The collecting duct moves through the medulla tissue
which has a lower water potential from the loop of Henle. This results in further water reabsorption.
What is the role of the hypothalamus in
osmoregulation?
It contains osmoreceptors which detect
the water potential of the blood. If the
water potential is low, the hypothalamus
releases antidiuretic hormone (ADH).
Where is ADH released into the blood?
ADH from the hypothalamus is transferred to the
posterior pituitary gland where it is secreted into the
blood.
Explain how ADH increases the water
potential of the blood.
ADH binds to receptors on the cells of the distal convoluted tubule and collecting duct. It increases the number of aquaporins in the membrane of the cells in this part of the nephron. This increases permeability to water, which increases absorption and therefore the water potential of the blood.
What happens to the secretion of ADH
once the water potential of the blood has
been restored?
Secretion is reduced to prevent too much
water reabsorption, which would make the
water potential of the blood too high. This is
an example of negative feedback.
