Circulation and gas exchange. Osmoregulation and excretion
Circulation and gas exchange. Osmoregulation and excretion
CHAPTER 42: CIRCULATION AND GAS EXCHANGE
Function and types of circulatory systems
A circulatory system has three basic components
muscular pump (heart)
The circulatory system, powered by
the heart, then carries the oxygen-rich blood to all parts of the body
Arthropods and most molluscs
circulatory fluid bathes the organs directly
the circulatory fluid,
called hemolymph, is also the interstitial fluid that bathes body cells
Contraction of one or more hearts pumps the
hemolymph through the circulatory vessels into interconnected
sinuses, spaces surrounding the organs.
Closed circulatory system
a circulatory fluid
called blood is confined to vessels and is distinct from the
One or more hearts pump
blood into large vessels that branch into smaller ones that infiltrate
the organs. Chemical exchange occurs between the
blood and the interstitial fluid, as well as between the interstitial
fluid and body cells.
Annelids (including earthworms),
cephalopods (including squids and octopuses), and all vertebrates
have closed circulatory systems.
Bony fishes, rays, and sharks have a single circuit of blood flow and
a single circulatory pump—a heart with two chambers.
Amphibians, reptiles, and mammals have two circuits of blood
flow and two pumps fused into a multi-chambered heart.
CHAPTER 44: OSMOREGULATION AND EXCRETION
Osmosis and how it works
thus requires osmoregulation
the general term for the
processes by which animals control solute concentrations and
balance water gain and loss.
regulating the chemical composition
of body fluids depends on balancing the uptake and loss of
water and solutes.
All animals—regardless of habitat or type of waste produced—
face the same need to balance water uptake and loss.
If water uptake is excessive, animal cells swell and burst; if water loss
is substantial, they shrivel and die
Water enters and leaves cells by osmosis.
osmosis, a special case of diffusion, is the
movement of water across a selectively permeable membrane
It occurs whenever two solutions separated by the membrane
differ in osmotic pressure, or osmolarity (total solute concentration
expressed as molarity, that is, moles of solute per
liter of solution).
of human blood is about 300 mOsm/L.
If two solutions separated by a selectively permeable membrane
have the same osmolarity, they are said to be isoosmotic.
. When two solutions differ in osmolarity,
the one with the greater concentration of solutes is said
to be hyperosmotic,
the more dilute solution is said to be
Water flows by osmosis from a
hypoosmotic solution to a hyperosmotic one.
Difference between freshwater and marine animals
osmoconformer: to be isoosmotic with its surroundings. (marine animals)
osmoregulator: to control internal
osmolarity independent of that of its environment (freshwater)
Osmoregulation enables animals to live in environments
that are uninhabitable for osmoconformers, such as freshwater
and terrestrial habitats. To survive in a hypoosmotic
environment, an osmoregulator must discharge excess water.
In a hyperosmotic environment, an osmoregulator must instead
take in water to offset osmotic loss.
They therefore face no substantial
challenges in water balance. However, because these
animals differ considerably from seawater in the concentrations
of specific solutes, they must actively transport these
solutes to maintain homeostasis.
The osmoregulatory problems of freshwater animals are the opposite
of those of marine animals. The body fluids of freshwater
animals must be hyperosmotic because animal cells cannot tolerate
salt concentrations as low as that of lake or river water.
Having internal fluids with an osmolarity higher than that of
their surroundings, freshwater animals face the problem of
gaining water by osmosis and losing salts by diffusion. Many
freshwater animals, including bony fishes, solve the problem of
water balance by drinking almost no water and excreting large
amounts of very dilute urine. At the same time, salts lost by diffusion
and in the urine are replenished by eating. F
Forms of Nitrogenous Waste
Animals excrete nitrogenous wastes as ammonia, urea, or
uric acid. These different forms vary significantly in their toxicity
and the energy costs of producing them.
ammonia excretion is
most common in aquatic species.
mammals, most adult amphibians, sharks, and some
marine bony fishes and turtles mainly excrete a different nitrogenous
Insects, land snails, and many reptiles, including birds, excrete
uric acid as their primary nitrogenous waste. (Bird droppings,
or guano, are a mixture of white uric acid and brown feces.) Uric
acid is relatively nontoxic and does not readily dissolve in water
Major excretory organs and their functions
about 10 cm in length, as well as organs for
transporting and storing urine. Urine produced
by each kidney exits through a duct called the ureter
:the two ureters drain into
a common sac called the urinary bladder
:During urination, urine is expelled from the
bladder through a tube called the urethra
which empties to the outside near the vagina
in females and through the penis in males.
Sphincter muscles near the junction of the
urethra and bladder regulate urination.
Parts of a nephron and its functions
proximal tubule, the loop of Henle
distal tubule. A collecting duct
Proximal tubule. Reabsorption in the proximal tubule
is critical for the recapture of ions, water, and valuable nutrients
from the huge volume of initial filtrate. NaCl (salt) in the filtrate
diffuses into the cells of the transport epithelium, where Na
actively transported into the interstitial fluid.
Descending limb of the loop of Henle. Reabsorption
of water continues as the filtrate moves into the descending
limb of the loop of Henle. Here numerous water channels
formed by aquaporin
Distal tubule. The distal tubule plays a key role in regulating NaCi concentrain of body fludis
Collecting duct. The collecting duct carries the filtrate
through the medulla to the renal pelvis. The transport
epithelium of the nephron and collecting duct processes
the filtrate, forming the urine.
Respiratory organ function and specialized structures
the uptake of molecular O2 from the environment
and the discharge of CO2 to the environment.
Specialization for gas exchange is apparent in the structure of
the respiratory surface, the part of an animal’s body where
gas exchange occurs.
The skin serves as a respiratory organ in some animals, including
earthworms and some amphibians.
To promote ventilation,
most gill-bearing animals either move their gills through
the water or move water over their gills
The arrangement of capillaries in a fish gill allows for
countercurrent exchange, the exchange of a substance
or heat between two fluids flowing in opposite directions.
lungs are localized respiratory organs.
all mammals depend
entirely on lungs for gas exchange.
From the nasal cavity and
pharynx, inhaled air passes through the larynx, trachea, and bronchi to the bronchioles,
which end in microscopic alveoli lined by a thin, moist epithelium. Branches of the pulmonary
arteries convey oxygen-poor blood to the alveoli; branches of the pulmonary veins transport
oxygen-rich blood from the alveoli back to the hea
includes a network of tiny vessels intermingled
among capillaries of the cardiovascular system.
After entering the lymphatic system by diffusion, the fluid
lost by capillaries is called lymph;
lost fluid and proteins return to the blood via the lymphatic system
its composition is about
the same as that of interstitial fluid.
Along a lymph vessel are organs called lymph nodes
The lymphatic system drains into large veins of the circulatory system at the base of the neck
By filtering the lymph and by housing cells
that attack viruses and bacteria, lymph nodes play an important
role in the body’s defense.
Blood pressure is generally measured for
an artery in the arm at the same height
as the heart
A sphygmomanometer, an inflatable cuff attached to a pressure
gauge, measures blood pressure in an artery. The cuff is inflated until the
pressure closes the artery, so that no blood flows past the cuff. When this
occurs, the pressure exerted by the cuff exceeds the pressure in the artery
The cuff is allowed to deflate gradually. When
the pressure exerted by the cuff falls just below
that in the artery, blood pulses into the forearm,
generating sounds that can be heard with the
stethoscope. The pressure measured at this point
is the systolic pressure
The cuff is allowed to deflate
further, just until the blood flows
freely through the artery and the
sounds below the cuff disappear.
The pressure at this point is the
Vertebrate blood is a connective tissue consisting of cells suspended
in a liquid matrix
liquid matrix called plasma.
Dissolved in the
plasma are ions and proteins that, together with the blood
cells, function in osmotic regulation, transport, and defense.
Separating the components of blood using a centrifuge reveals
that cellular elements (cells and cell fragments) occupy
about 45% of the volume of blood, the rest is the plasma
Fish heart/Frog heart/mammal heart
In the three-chambered heart of turtles,
snakes, and lizards, an incomplete septum
partially divides the single ventricle into
separate right and left chambers. Two
major arteries, called aortas, lead to the
Frogs and other amphibians have a heart
with three chambers: two atria and one
In mammals and birds, there are two atria
and two completely divided ventricles. The
left side of the heart receives and pumps
only oxygen-rich blood, while the right
side receives and pumps only oxygen-poor
Difference between arteries, veins, and capillaries
are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart;
are the blood vessels that deliver oxygen-rich blood from the heart to the tissues of the body. Each artery is a muscular tube lined by smooth tissue
is a small blood vessel from 5 to 10 micrometres in diameter, and having a wall one endothelial cell thick. They are the smallest blood vessels in the body: they convey blood between the arterioles and venules. These microvessels are the site of exchange of many substances with the interstitial fluid surrounding them.
An amphibian such as a frog ventilates its lungs by positive
pressure breathing, inflating the lungs with forced airflow.
During the first stage of inhalation, muscles lower the
floor of an amphibian’s oral cavity, drawing in air through its
nostrils. Next, with the nostrils and mouth closed, the floor
of the oral cavity rises, forcing air down the trachea. During
exhalation, air is forced back out by the elastic recoil of the
lungs and by compression of the muscular body wall.
mammals employ negative
pressure breathing—pulling, rather than pushing, air into
their lungs (Figure 42.28). Using muscle contraction to actively
expand the thoracic cavity, mammals lower air pressure
in their lungs below that of the air outside their body