Download 4. Collecting duct

Cells are organized in the following ways:
• Tissues (groups of similar cells performing a
common function. Animal tissues are organized
into four general categories…
• Epithelial (tissue such as outer skin layers and internal protective
coverings)
• Connective (tissue such as bone, cartilage, and blood)
• Nervous (tissue of the nervous system)
• Muscle (tissue of the muscular system)
• Organs (groups of tissues functioning together)
• Organ Systems (groups of organs functioning
together
• Organism (the whole banana!)
The function of many animal systems is to contribute
toward homeostasis, or maintenance of stable,
internal conditions within narrow limits.
In many cases,
homeostasis is
maintained by negative
feedback. A sensing
mechanism (a receptor)
detects a change in
conditions beyond
specific range.
A control center, or integrator (often the brain),
evaluates the change and activates a second
mechanism (an effector) to correct the condition.
In “negative” feedback, the original condition is
negated, so that the conditions are returned to
normal. (see below)
Compare this with
positive feedback, in
which an action
intensifies a
condition so that it is
driven further
beyond normal limits.
(Lactation is
stimulated in
response to
increased nursing of
an infant.
Animal cells require O2 for aerobic respiration. Cells must
have some mechanism for providing gas exchange , delivering
O2 and removing waste CO2.
The process, on a cellular level, produces ATP within the
mitochondria of cells (review respiration PPT). The following
gas exchange mechanisms are found in animals:
• direct with the
environment: such as
platyhelminthes, where every cell is
exposed to the outside environment,
and gases may diffuse readily.
• gills which are evaginated (outgrowths) from the body,
that create a large surface area over which gas exchange
occurs. Circulatory system delivers O2 and carries away
CO2 from gills.
Gills can be internal, covered
by operculum (fish), and
external and unprotected)
•tracheae found in insects which have chitin-lined tubes that permeate
their bodies. (insects) O2 enters, and CO2 exits through openings
called spiracles
• lungs which are
invaginated (cavities
within the body). Book
lungs are found within
many spiders, are
stacks of flattened
membranes enclosed
•Nose, pharynx, larynx: air enters the nose and passes through the nasal
cavity, pharynx, and larynx. The larynx (voice box) contains the vocal cords.
• Trachea: air enters a cartilage-lined tube called the trachea.
A flap called the
epiglottis covers the trachea when food is being swallowed. It prevents the
entrance of solid and liquid materials from getting into the lungs.
• Bronchi, bronchioles: the trachea branches into two bronchi, which enter
the lungs and then branch repeatedly, forming narrower tubes called bronchioles.
• Alveolus: each bronchiole branch ends in a small sac called an alveolus (plural,
alveoli). Each alveolus is densely surrounded by blood-carrying capillaries.
• Diffusion between alveolar chambers and blood: gas exchange
occurs by diffusion across the moist, sac membranes of the alveoli. Oxygen
diffuses into the red blood cells in the capillary beds surrounding the alveoli, and
CO2 diffuses out in the opposite direction.
• Bulk flow of O2: The circulatory system transports O2 throughout the body
within red blood cells, which contain hemoglobin, iron-containing proteins to which
O2 bonds.
• Diffusion between blood and cells: blood capillaries permeate the
body. Oxygen diffuses out of the red blood cells, across blood capillary walls, into
interstitial fluids (the fluids surrounding the cells), and across cell membranes.
Carbon dioxide diffuses in the opposite direction.
• Bulk flow of CO2: Most CO2 is transported as dissolved bicarbonate ions
(HCO3-) in the plasma, the liquid portion of the blood. The formation of HCO3-,
however, occurs in the red blood cells, where the formation of carbonic acid
(H2CO3) is catalyzed by the enzyme carbonic anhydrase, as follows:
CO2 + H2O
H2CO3
H+ + HCO3-
Following their formation in the red blood cells, HCO3- ions
diffuse back into the plasma. Some CO2, however, does not
become HCO3-; instead, it mixes directly with the plasma (as
CO2 gas) or binds with the amino groups of the hemoglobin
molecules inside red blood cells.
• Mechanics of respiration: air is moved into and out of the lungs by
changing their volume. The volume of the lungs is increased by the contraction of
the diaphragm and the intercostal muscles between the ribs. When the lung volume
increases, the air pressure within the lungs decreases. This causes a pressure
difference between the air in the lungs and the air outside the body. As a result,
air rushes into the lungs by bulk flow. When the diaphragm and intercostal muscles
relax, the volume of the lungs decreases, raising the pressure on the air, causing
the air to rush out.
• Control of respiration:
chemoreceptors in the carotid
arteries (supply blood to the brain)
monitor the pH of the blood. When
a body is active, CO2 production
increases. When CO2 enters the
plasma and is converted to HCO3-,
and H+, the blood pH drops. In
response, the chemoreceptors send
nerve impulses to the diaphragm and
intercostal muscles to increase
respiratory rate. This results in a
faster turnover in gas exchange,
which returns blood pH to normal.
This is a homeostatic negative
feedback loop.
Large organisms require a transport system to distribute
nutrients and oxygen and to remove wastes from cells. Two
kinds of circulatory systems accomplish this:
• Open Circulatory System:
pump blood into an internal cavity called a
hemocoel, or sinuses, which bathe tissues
with an oxygen-and nutrient-carrying
fluid called hemolymph. The hemolymph
returns to the pumping mechanism of the
system, a heart, through holes called
ostia. Open circulatory systems occur in
insects and most mollusks.
• Closed Circulatory Systems: the nutrient, oxygen, and waste-carrying
fluid, known as blood, is confined to vessels. Closed circulatory systems are found
among members of the phylum annelida, certain mollusks, (octopuses and squids)
and vertebrates.
In the closed circulatory system of vertebrates, vessels moving away from the
heart are called arteries. Arteries branch into smaller arterioles, and then branch
further into the smallest vessels, capillaries. Gas and nutrient exchange occurs by
diffusion across capillary walls into interstitial fluids and into surrounding cells.
Wastes and excess interstitial fluids move in
the opposite direction as they diffuse into
capillaries. The blood, now deoxygenated,
remains in the capillaries and returns to the
heart through venules, which merge to form
veins. The heart then pumps the
deoxygenated blood to the respiratory organ
(gills or lungs), where arteries again branch
into a capillary bed for gas exchange. The
oxygenated blood then returns to the heart
through veins. From here, the oxygenated
blood is pumped once again, through the body.
• KNOW the
path of blood
through the
body, heart,
and lungs!!!
• KNOW in
which vessels
it is
deoxygenated
and in which
vessels it is
oxygenated.
The pathway of blood between the right side of the heart, to
the lungs, and back to the left side of the heart is called the
pulmonary circuit. The circulation pathway throughout the
body is the systemic circuit.
• The cardiac or heart cycle:
refers to the rhythmic contraction and
relaxation of heart muscles. It is regulated by specialized tissues in the heart
called autorhythmic cells, which are self-excitable and able to initiate contractions
without external stimulation by nerve cells. The cycle occurs as follows:
The SA (sinoatrial) node, or pacemaker: found in upper
wall of right atrium, spontaneously initiates the cycle by
simultaneously contracting both atria and also sending a
delayed impulse that stimulates the AV
(atrioventricular) node.
The AV node found in the lower wall of the right atrium
sends an impulse through the bundle of His, nodal tissue
that passes down between both ventricles and then
branches into the ventricles through the Purkinje fibers.
This impulse results in the contraction of the ventricles.
When the ventricles contract (the systole phase), blood
is forced through the pulmonary arteries and aorta. Also
the AV valves are closed. When the ventricles relax (the
diastole phase), backflow into the ventricles causes the
semilunar valves to close. The closing of the AV valves,
followed by the closing of the semilunar valves, produces
the characteristic “lub-dub” sound of the heart.
Wastes and excess interstitial fluids enter the circulatory system when they
diffuse into capillaries. However, not all of the interstitial fluids enter the
capillaries. Instead, some are returned to the circulatory system by way of the
lymphatic system, which is a second network of capillaries and veins.
The fluid in these lymphatic veins, called
lymph, moves slowly through lymphatic
vessels by the contractions of adjacent
muscles. Valves in the lymphatic veins
prevent backflow. Lymph returns to the
blood circulatory system through two
ducts located in the shoulder region. In
addition to returning fluids to the
circulatory system, the lymphatic
system functions as a filter. Lymph
nodes, enlarged bodies throughout the
lymphatic system, act as cleaning filters
and as immune response centers that
defend against infection. This is why
they tend to get “swollen” when you are
ill.
Blood contains each of the following:
• Red blood cells (erythrocytes) transport oxygen and catalyze the
conversion of CO2 and H2O to H2CO3. Mature red blood cells lack a nucleus,
thereby maximizing hemoglobin content and thus their ability to transport O2.
• White blood cells (leukocytes) consist of five major groups of
disease-fighting cells that defend the body against infection.
• Platelets are cell fragments
that are involved in blood clotting.
Platelets release factors that are
involved in the conversion of the
major clotting agent, fibrinogen,
into its active form, fibrin.
Threads of fibrin protein form a
network that stops blood flow.
• Plasma is the liquid portion of WBCs: Monocytes; Neutrophiles,
the blood that contains various
dissolved substances.
Eosinophiles, Basophiles, and
Macrophages. (each has its own
function within the blood)
In general, the excretory system helps maintain homeostasis
in organisms by regulating water balance and by removing
harmful substances.
Osmoregulation: is the absorption and excretion of water and dissolved substances
(solutes) so that proper water balance is maintained between the organism and its
surroundings. Two examples:
•Marine Fish: are hypoosmotic with their
environment. (less salty than the
surrounding water). Water is constantly lost
through osmosis. To maintain proper internal
environment, marine fish constantly drink,
rarely urinate, and secrete accumulated salts
through their gills.
• Fresh Water Fish: are hyperosmotic, or
saltier than the surrounding water. Thus,
water constantly diffuses into the fish. In
response, fresh water fish rarely drink,
constantly urinate, and absorb salts through
their gills.
Many mechanisms have evolved for osmoregulation in animals,
and for the regulation of toxic substances, such as the byproducts of cellular metabolism (nitrogen products of protein
breakdown). Examples:
Contractile Vacuole: found in the
cytoplasm of Protists like paramecia and
amoeba. They accumulate water within
the organism, merge with the plasma
membrane, and release water.
Flame Cells: found within
Platyhelminthes, such as planaria.
Ciliated cells filter body fluids moving
through a tube system. Water is
excreted from pores that exit the body.
Nephridia (or metanephridia) occur in
pairs within each segment of most
annelids. Fluids pass through a series of
collecting tubules, where needed
substances are reabsorbed. Wastes are
excreted through excretory pores.
• Malpighian tubules: occur in many arthropods, such as insects. Tubes attached
to the midsection of the digestive tract collect body fluids from the hemolymph
that bathes the cells. Waste materials, and needed materials are deposited into
the midgut. Needed materials continue through the digestive system, while wastes
continue and are excreted through the anus.
Kidneys: occur in
vertebrates, and
consist of about a
million individual
filtering tubes called
nephrons. Two kidneys
produce waste fluids,
or urine, which pass
through ureters to the
bladder for temporary
storage. From the
bladder, the urine is
excreted through the
urethra.
Let’s get a
closer look…
The Nephron
2
1
4
2
1. Bowman’s capsule: the
nephron tube begins with
a bulb-shaped body at
one end. A branch of the
renal artery (afferent
arteriole) enters into the
Bowman’s capsule,
branches to form a
dense ball of capillaries
called the glomerulus,
and then exits the
capsule (efferent
arteriole)
2. Convoluted tubule: long
twisting tub beginning
with the proximal
convoluted tubule
3
(proximal to the
Bowman’s capsule) and
3. Loop of Henle: occurs in between the proximal and
ends with the distal
distal convoluted tubule.
convoluted tubule
(distant to Bowman’s
4. Collecting duct: The distal convoluted tubule empties
capsule), where it joins
into the collection duct, which empties into the renal
the collecting duct.
pelvis, draining into the ureter.
• Filtration:
when blood enters the glomerulus, pressure forces water and
solutes through the capillary walls into the Bowman’s capsule. Solutes include
glucose, salts, vitamins, nitrogen wastes, and any other substances small enough to
pass through the capillary walls. Red blood cells, and proteins remain in the
capillaries. The other materials diffuse into the Bowman’s capsule, and then flow
into the convoluted tubule.
• Secretion:
As a filtrete passes through the proximal tubule and, later,
through the distal tubule, additional material from the interstitial fluids joins the
filtrete. This material is selectively secreted into the convoluted tubule by both
passive and active transport.
• Reabsorption:
when filtrete moves down the loop of Henle, it becomes more
concentrated due to passive flow of H2O out of the tube. As the filtrete moves up
the loop of Henle, it becomes more dilute due to passive and active transport of
salts out of the tubule. These salts move into the interstitial fluids, and as the
tubule passes towards the renal pelvis, water passively moves out of the collecting
duct and into the interstitial fluids. (osmosis, homeostasis). When the filtrete
drains into the renal pelvis, it is concentrated urine.
1. Antidiuretic hormone (ADH) increases the reabsorption of water by the
body and increases the concentration of salts in the urine. It does this by increasing the
permeability of the collecting duct to water. As a result, more water diffuses out of the
collecting duct as the filtrete descends into the renal pelvis.
2. Aldosterone increases both the reabsorption of water and the reabsorption of
Na+. It does this by increasing the permeability of the distal convoluted tubule and
collecting duct to Na+. As a result, more Na+ diffuses out of this tubule and duct. Since
the Na+ increases the salt concentration outside the tubule, water passively follows.
Nitrogen forms a major waste product in animals. When amino acids and
nucleic acids are broken down, they release toxic ammonia (NH3). To rid
the body of this toxin, several mechanisms have evolved, each appropriate
to the habitat or survival of the animal.
• Aquatic animals excrete NH3 directly into the surrounding water
• Mammals convert NH3 to urea in their livers. Urea is significantly less toxic
than NH3, and thus requires less water to excrete in the urine
• Birds, insects, and many reptiles convert urea to uric acid, which is a solid.
This allows considerable water conservation by permitting the excretion of
nitrogen waste as a solid.
Simply put, is the breakdown of food into smaller molecules. It can occur
in cells (lysosomes containing digestive enzymes merge with food vacuoles,
and it can be extracellular as well. Food ingested is too large to be
engulfed by individual cells, thus it is first digested in the gastrovascular
cavity, and then absorbed by individual cells.
During digestion there are four molecules are
commonly encountered:
• Starches: broken down into glucose
molecules
• Proteins: broken down into amino acids
• Fats (lipids): broken down into fatty
acids, and glycerol
• Nucleic acids: broken down into
nucleotides
In humans and other mammals, digestion follows a particular
series of events. Molecules are digested by specific enzymes.
It begins in the MOUTH…
• Mouth (Salivary Amylase): secreted into the mouth by the salivary
glands, begins the breakdown of starches into maltose (a disaccharide).
Chewing reduces the size of food
(mechanical digestion), thereby
increasing the surface area upon which
amylase and subsequent enzymes can
operate. Food is shaped into a ball
(bolus) and then swallowed.
• Pharynx: when food is swallowed
and passed into the throat, or pharynx,
a flap of tissue, called the epiglottis,
blocks the trachea so that solid and
liquid material enter only the
esophagus (tube to stomach).
• Esophagus:
food moves through
the esophagus by muscular
contractions called peristalsis.
• Stomach: secretes gastric juice, a
mixture of digestive enzymes (pepsin)
and hydrochloric acid.
The stomach serves a variety of functions:
•Storage: because of its
accordion-like folds, the wall of
the stomach can expand to store
two to four liters of material.
• Mixing:
mixes the food with
water and gastric juice to
produce a creamy medium called
chyme (KIME)
• Physical Breakdown:
muscles churn the contents
breaking the food into smaller
particles (mechanical digestion).
• Chemical Breakdown:
Proteins are chemically broken
down with pepsin, and HCL. The
stomach is protected by a layer
of mucous. Failure of this lining
can lead to peptic ulcers.
Movement of chyme into the small intestine is
• Controlled Release: regulated by a valve called the pyloric sphincter.
• Small Intestine:
the first twenty-five cm of the small intestine is called
the duodenum continues digestion of starches and proteins. Enzymes originate
from the following sources:
• small intestine: the wall of the small
intestine is the source of various
enzymes, including proteolytic
enzymes (digesting proteins), maltase
and lactase (digesting carbohydrates),
and phosphateses (digestion of
nucleotides).
• pancreas: produces trypsin and
chymotrypsin, lipase (digestion of
fats), and pancreatic amylase (starch
digestion) These and other enzymes
serve to neutralize the HCL in the
chyme entering the duodenum.
• Liver: produces bile which functions to emulsify fats. This is the physical
breaking up of fat into smaller fat droplets, increasing the surface area upon which
fat-digesting enzymes (lipase) can operate. Since bile does not chemically change
anything, it is not an enzyme. While bile is produced in the liver, in most organisms,
it is stored in the gall bladder.
• The remainder of the small intestine (jejunum, and ileum)
which is nearly six meters in length, absorbs the breakdown
products of food. Villi and microvilli, fingerlike projections of
the intestinal wall, increase the surface area greatly,
facilitating a greater reabsorptive potential. Amino acids and
sugars are absorbed into the blood capillaries, while most of
the fatty acids and glycerol are absorbed into the lymphatic
system.
•Large intestine: the main function of the large intestine (colon) is the
reabsorption of water to form solid waste, or feces. Feces are stored at the end
of the large intestine, in the rectum, and are excreted through the anus.
Various mutualistic bacteria live
within the large intestine, including
some that produce vitamin K, which is
absorbed through the intestinal wall.
At the beginning of the large
The colon has five parts you
should be aware of:
• Cecum: short dead-end pouch from
which the vestigial appendix hangs.
Endocrine and digestion:
• Gastrin: produced by stomach lining when
nervous system senses the availability of food
(sight or smell) stimulates production of
gastric juice.
• Secretin: produced by duodenum, stimulates
pancreas to produce bicarbonate, neutralizing
acid in chyme.
• Ascending colon: moves up the right
side of the body
• Transverse colon: moves across the
abdomen.
• Descending colon: moves down the
left side of the abdomen
• Sigmoid colon: last section shaped
like an “S” empties into the rectum.
There are two types of skeletal systems. An exoskeleton can be found on
many invertebrate arthropods, such as insects and crustaceans. It is a
chitinous skeleton surrounding the exterior of the organism. It serves to
anchor internal organs, and provide support and protection for body
systems.
The other type of skeleton is
the one we are most familiar
with, because we have one
ourselves! It is an
endoskeleton. This skeleton
serves to protect and support
us from within our bodies. All
vertebrates (except some very
primitive fishes) have a
complex bony skeleton.
• Provides a framework and support structure for the tissues of your body
to attach to
• Protects your internal organs, including your heart, lungs, and brain
• Produces red blood cells, and some white blood cells
• Along with muscles, acts to help the body with locomotion and other
movement
• A storehouse for minerals such as calcium and phosphorous
The adult human skeleton has 206 bones, give or take. All
bony tissue is not the same, however.
• Compact bone: the outer most dense bony material
• Spongy bone: inner porous less dense bone
• Marrow: soft material in the inner cavity of bone
Found inside compact bone…
They are long tubular systems which run
the length of compact bone tissue, and
contain nerves and tiny blood vessels
Bone marrow is a special, spongy, fatty tissue that houses
stem cells, located inside a few large bones. These stem cells
transform themselves into white and red blood cells and
platelets, essential for immunity and circulation. Anemia,
leukemia, and other lymphoma cancers can compromise the
resilience of bone marrow.
Our skull, sternum, ribs, pelvis, and femur bones all contain
bone marrow, but other smaller bones do not. Inside this
special tissue, immature stems cells reside, along with extra
iron. While they are undifferentiated, the stem cells wait until
unhealthy, weakened, or damaged cells need to be replaced. A
stem cell can turn itself into a platelet, a white blood cell like a
T-cell, or a red blood cell. This is the only way such cells get
replaced to keep our body healthy.