Download Homeostasis-is the process of organisms maintaining a

Homeostasis-is the process of organisms maintaining a stable environment while existing in an
environment that is constantly fluctuating.
Regulation includes.
-Temperature is regulated.
-Internal environment is regulated for nitrogenous wastes, salt, glucose, gasses like oxygen and
carbon dioxide. This is involves with the kidney and liver. Also hormones and the nervous
system aid in homeostasis.
-Glucose and other nutrients are
regulated by the vertebrate liver.
Most nutrients (except lipids) are
transported from the small intestines
to the liver via the hepatic portal vein.
The liver has the ability to convert
nutrients from one form to another. It
distributes the nutrients so that the
blood leaving the liver consistently
has the same concentration of
nutrients. For example the blood
leaving the liver usually has glucose
concentration of 90 mg/100 mL,
regardless of the amount of sugar in
the meal.
Glucose regulation is under the
influence of hormones such as
insulin which lowers glucose levels in
the blood and glucagon increases
glucose level in the blood.
If there is too much glucose in the
blood from a meal, the liver will
convert to glycogen to be stored until
needed. Once the glycogen reaches
the maximum, then it is converted to
lipids which are then stored in
adipose tissue. There 24 hrs. of
glycogen reserves for the body.
-The liver also detoxifies alcohol and other poisons. Fat-soluble poison is made water soluble by
the liver. It then travels to the gall bladder. From there it is dumped into the small intestines and
then absorbed by fiber, finally it will be excreted.
-If there is an excess of amino acids, the liver will deaminate the amine group from the amino
acid. This ammonia is converted to urea put into the blood stream and then filtered by the
kidneys
Functions of the liver in homeostasis
1. Regulates blood levels of glucose (glucose<==>glycogen)
2. Has the ability to make glycogen from excess lactic acid produced in exercising
3. Interconvert incoming organic nutrients
4. Deaminates amino acids to form NH3. May convert NH3->urea or uric acid depending on the
organism
5. Ability to detoxify some poisonous chemicals
6. Manufactures plasma proteins like globulin, fibrinogen, prothrombin, albumin
7. Manufactures plasma lipids and cholesterol
8. Stores vitamins & iron
9. Forms RBC in embryos
10. Destroys RBC
11. Excrete bile pigments
12. Synthesizes bile salts
*The liver is one organ that has the ability to regenerate itself.
Osmoregulation is the uptake and loss of water and solutes. Units milliosmoles per liter
(mOsm/L). Osmolarity of human blood is 300 mOsm/L while seawater is 1,000 mOsm/L.
TermsHyperosmotic-is when one solution has a greater concentration of solutes than a second solution.
Hypoosmotic-when one solution is more dilute than a second solution.
Isosmotic- two solutions that have the same concentration of solutes.
Osmoconformer is one that cannot regulate its uptake of fluids and therefore is isosmotic with
environment. Mostly marine organisms are isosmotic because the marine environment is pretty
stable and does not fluctuate.
Excretion- process of an organism ridding their bodies of metabolic wastes. This process also
helps regulate ions such as sodium chloride.
Osmoregulator is one that controls its internal
osmolarity independent of the environment.
Stenohaline organisms are those that cannot
tolerate great changes in the molarity of their
surrounding environment.
Euryhaline organisms are those than can
tolerate change in the molarity of their
surrounding environment. (Pacific salmon)
Most marine invertebrates are osmoconformers
•Most marine vertebrates and some
invertebrates are osmoregulators
•Marine bony fishes are hypoosmotic to sea
water
•They lose water by osmosis and gain salt by
diffusion and from food.
•They balance water loss by drinking seawater and excreting salts
Marine fish-did not evolve from marine invertebrates but from fresh water fish, therefore their
body fluids are diluted (or hypertonic) in comparison to sea water
Freshwater animals
•Freshwater animals constantly take in water by osmosis from their hypoosmotic environment
•They lose salts by diffusion and maintain
water balance by excreting large amounts of
dilute urine
•Salts lost by diffusion are replaced in foods
and by uptake across the gills
As marine animals migrated to fresh water,
natural selection preferred animals that could
tolerate more dilute body fluids. Surely you
must realize that the first marine animals in
fresh water had a tendency to lose salts and
H2O, and compensated by constantly
replacing them.
•Land animals manage water budgets by drinking and
eating moist foods and using metabolic water
•Desert animals get major water savings from simple
anatomical features and behaviors such as a nocturnal
life style
Terrestrial animals must fight desiccation.
Animals obtain water by
1. Drinking H2O
2. Food with H2O
3. Byproduct of cellular respiration
Getting rid of nitrogenous wastes. When the
liver processes amino acids, it produces
ammonia which is extremely toxic. Fresh
water fish just flushes the ammonia out of
their bodies. Mammals and amphibians
form urea and finally urine. Birds and
reptiles form uric acid which is insoluble and
less H2O is needed
for excretion. Also
uric acid will not
poison embryos in
eggs. The kidneys
are responsible for
filtering the blood and important in homeostasis.
Survey of controlling body fluids
Protonephridia-flame cell system
-Found in planaria, other invertebrates and lancets. Planaria do not have
circulatory system, or coelom. They have a simple tubular excretory
system call protonephridia. This network of closed tubules lacks internal
openings that branch throughout the body. At the end of the smallest
branch are found cellular flame cells.
-Interstitial fluid passes through a flame cell that is propelled by a current
created by the cilia moving inside the flame cell.
-The fluid is filtered and moved into excretory ducts. These ducts empty
out the body through numerous nephridiopores.
-The epithelium lining reabsorbs any salts before the fluid leaves the body.
-The epithelium lining reabsorbs any salts before the fluid leaves the body.
-Other parasitic species are isotonic to their surroundings, and this flame
cell system is used to excrete nitrogenous wastes.
Annelids-(segmented worms with a true coelom) include earthworm.
-Each segment contains a pair of metanephridia excretory tubules that have internal openings to
collect body fluids. The opening collects
the fluid from the segment that is anterior
to it.
-Coelomic fluid enters the ciliated funnel
(nephrostome)
-The fluid passes through the
metanephridium and empties into a
storage bladder that empties to the
environment via the nephridiopore
-As the fluid passes through the
metanephridium, a capillary bed which
surrounds it reabsorbs essential salts by pumping out of
the collecting tubules.
- The fluid excreted is hypotonic and dilute to offset the
continual uptake of water via osmosis.
Arthropods and malpighian tubules
-Arthropods (insects) have an open circulatory system.
The excretory organs are out pocketing between the
midgut and hindgut. These out pocketings are called malpighian tubules.
-The malpighian tubules are bathed in hemolymph.
-The transport epithelium lining moves solutes (salts and nitrogenous wastes from hemolymph
into the tubule's lumen.
-The fluid in tubule then passes through the hindgut to the rectum.
-Salts and water are reabsorbed across the epithelium of the rectum and dry nitrogenous waste is
excreted with feces.
The organ that filters the blood in vertebrates is the kidney. When the blood is filtered, it forms a
waste liquid called
urine. The kidney
functions in
excretion and
osmoregulation.
The kidneys in
humans are found
on the imbedded on
the dorsal side of
the abdominal
cavity. In humans, there is a pair of kidneys, one on each side. They are about the size of a fist.
The renal artery brings blood to the kidney and a renal vein returns the blood to the vena cava.
The ureter carries the urine to the urinary bladder to be stored. When the bladder empties, the
urine is moved from the bladder to the urethra to the outside of the body.
The kidney has three distinct layers. The outer most layer is the cortex of the kidney. Below the
cortex is the medulla. In the center is the renal pelvis which collects the urine to be sent to the
bladder.
The filtering unit of kidney is the nephron. There are over 1,000,000 such filtering units in each
kidney.
-The blood is delivered via an efferent arteriole to a capillary bed called the glomerulus.
-The blood leaves the glomerulus via the afferent arteriole forming a second capillary bed called
the peritubular capillaries that surrounds the nephron. --The blood then leaves the nephron via a
venule.
-1,100-1,200 L of blood flows through the kidneys each day.
At the beginning of the nephron is Bowman's capsule. This surrounds the glomerulus. Leading
from Bowman's capsule is the
proximal convoluted tubule
(PCT).
-From the PCT is the loop of
Henle. The filtrate moves down
the descending side and then
up the ascending side.
-The ascending side leads to
the distal convoluted tubule
(DCT).
At the beginning of the nephron
is Bowman's capsule. This
surrounds the glomerulus. Leading from Bowman's capsule is the proximal convoluted tubule
(PCT).
-From the PCT is the loop of Henle. The filtrate moves down the descending side and then up
the ascending side.
-The ascending side leads to the distal convoluted tubule (DCT).
The DCT finally empties its fluids into collecting ducts.
-The nephron is oriented so that the loop of Henle is pointed toward the pelvis of the kidney.
-Cortical nephrons have reduced loops of Henle and are confined to the renal cortex (80%)
-Juxtamedullary nephrons have long loops of Henle that extend down through the renal medulla
(20%).
-The longer the loop of Henle, the more water that is conserved or retained by the body.
Kangaroo rats have very long loops of Henle.
-The collecting ducts extend down through the cortex, through the medulla, to the pelvis.
-There is a salt gradient that becomes more saline as one goes from the renal cortex to the
pelvis.
-The nephrons process 180 L of filtrate each day.
Mechanism of urine formation by the kidney
3 processes
1. Ultrafiltration-Filtered by the glomerulus
2. Reabsorption-Material moving from
nephron back into the capillary bed
surrounding the nephron.
3. Tubular excretion-Material is transported
into the nephron at the convoluted tubules.
1844 Carl Ludwig-Suggested that the
glomerulus act as a mechanical filter. The
hydrostatic pressure of the glomerulus would
push or filter molecules small enough to pass
through the pores into Bowman's capsule. If
that is correct, then the filtrate should have the
same composition of plasma (minus plasma
proteins).
A.N. Richards was able to insert a microscopic
pipette into the capsule to verify this and prove
that the filtrate had the concentration of ions and other solutes as in the plasma.
Problem-urine the final produce does not have the same concentration of solutes as the filtrate,
and also it was determined that 180 liters of filtrate was produced but yet only produced 1-2 liters
of urine was excreted a day.
Therefore, conclude that H2O, glucose, amino acids were reabsorbed. Water, NaCl, K+ and
nutrients were reabsorbed in the PCT. NaCl was reabsorbed in the ascending loop of Henle, and
the collecting duct. Some urea is actually reabsorbed by the collecting duct with water. Some
solutes are transported into the nephron like NH3, K+, and H+. This is called tubular excretion. It
was found that the concentration of Na+ was
just slightly lower in the DCT than the PCT.
Yet it was found that Na+ was actively
pumped out of the ascending loop of Henle.
Therefore it was concluded that the salt
diffused back around to the descending loop
and passively flowed into descending loop
because the concentration of Na+ was
higher in the surrounding tissue than the
loop.
Water is permeable in the descending loop
of Henle. As the water moves through the
descending loop, the surrounding tissue
becomes more saline. More water is lost via
osmosis and the filtrate becomes very
concentrated (from 300 mosmoles/L to 1200
mosmoles/L).
In the ascending loop, the loop is
impermeable to water BUT the loop actively
transports salt out of the filtrate. Because of the removal of salt, the filtrate in the ascending loop
has become much more dilute (from 1200 to 100 mosmoles/L). The filtrate is going to go through
the salt gradient one more time. but can be reabsorbed in the collecting tubule to concentrate the
urine even more.
in the collecting tubule to
concentrate the urine even
more. The permeability of the
collection tubule varies and is
under the control of hormones.
The net effect of this system is
to reabsorb water. Over 1,200
L of material (mostly water) is
filtered every day but yet on 1-2
L of urine is excreted.Control of
Excretion
There are three different
hormonal systems that help
regulate excretion, the ADH,
RAAS, and ANP.
ADH- This system involves
antidiuretic hormone (ADH)
produced by the hypothalamus
and stored in the pituitary
gland. Let’s suppose that your
blood becomes more concentrated due to eating some salty food or not drinking fluids. The
hypothalamus (found in the brain) releases ADH. This is secreted into the blood stream and
makes its way to the kidneys. At the kidneys, ADH will attach to receptor sites on the cells of the
collecting tubules. This will cause a reaction involving aquaporins, which will become part of the
plasma membrane allowing water to be reabsorbed by the kidneys. This causes urine to become
or concentrated. It also causes the sensation of thirst. Drinking will cause the blood to become
more dilute.
RAAS-Rennin, angiotensin, aldosterone, Another way to
regulate electrolytes also involve regulating the blood
pressure. There is some sensitive tissue on the artery
delivering blood to the glomerulus. This is called the
juxtaglomerular apparatus (JGA). When blood pressure
drops, the JGA secretes an enzyme, rennin into the blood
stream. Rennin causes a plasma protein called
angiotensin I to be converted into angiotensin II.
Angiotensin II will cause arterioles to constrict and all
cause the adrenal gland to release a hormone called
aldosterone. Aldosterone causes more Na+ to be
reabsorbed which causes water to be reabsorbed by the
tissue surrounding from the nephron. This also increases
blood volume and ultimately blood pressure. Another
hormone, atrial natriuretic peptide (ANP), opposes the
RAAS. ANP is released in response to an increase in blood
volume and pressure and inhibits the release of renin. This
decreases blood pressure.