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Circulation & Gas Exchange and Osmoregulation & Excretion…
Circulation & Gas Exchange and Osmoregulation & Excretion
Circulation & Gas Exchange
Circulatory systems link exchange surfaces with cells throughout the body
Gastrovascular cavity: functions in the distribution of substances throughout the body
ex: hydras, jellies, & other cnidarians
an opening at 1 end connects the cavity to the surrounding water
fluid bathes both the inner and outer tissue layers
facilitates exchange of gases & cellular waste
body wall is a mere 2 cells thick, nutrients only need to diffuse a short distance to reach the cells of the outer tissue layer
diffusion: the random thermal motion; results in the net movement of substances from a high concentrated region to a low concentration region
Circulatory system 3 main components: a circulatory fluid, a set of interconnecting vessels, & the heart
heart: powers circulation by using metabolic energy to elevate the circulatory fluid's hydrostatic pressure
then the fluid flows through the vessels and back to the heart
open circulatory system
hemolymph: the circulatory and also interstitial fluid that bathes body cells
ex: grasshoppers
contraction of the heart pumps the hemolymph through the vessels into interconnected sinuses
w/in the sinuses, the hemolymph and body cells exchange gases and other chemicals
relaxation of the heart draws hemolymph back in through pores, which have valves that close when the heart contracts
body movements periodically squeeze the sinuses
helps circulate the hemolymph
closed circulatory system
blood is confined to vessels & is distinct from the interstitial fluid
1 or more hearts pump blood into large vessels that branch into smaller ones that infiltrate the tissues and organs
chemical exchange occurs between the blood and the interstitial fluid & between interstitial fluid and body cells
ex: annelids (earthworms), cephalopods (squids), all vertebrates
Arteries, veins, and capillaries are the 3 main types of blood vessels
arteries: carry blood from the heart to organs throughout the body
within organs, arteries branch into arterioles
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capillaries: arterioles convey blood into capillaries, microscopic vessels w/ very thin pours wall
capillary bed: a network of capillaries that infiltrate tissues, passing w/in a few cell diameters of every cell in the body
across the thin walls, dissolved gases and other chemicals are exchanged by diffusion between the blood and interstitial fluid
veins: the vessels that carry blood back to the heart from capillaries
Single circulation: blood travels through the body and returns to its starting point in a single loop
consist of 2 chambers: atrium and a ventricle
atrium: the chamber that receives blood entering the heart
chamber responsible for pumping blood out of the heart
ex: sharks, rays, and boney fish
blood pressure drops when blood flows through a capillary bed
limits the rate of blood flow in the rest of the animal's body
but as the animal swims, the contractions and relaxation of its muscles help accelerate the relatively sluggish pace of circulation
Double circulation: 2 circuits of blood flow composed into a single organ, the heart
ex: amphibians, reptiles, and mammals
in 1 circuit, the right side of the heart pumps oxygen poor blood to the capillary beds
there is a net movement of oxygen into the blood and of carbon dioxide out of the blood
Systemic circuit: the other circuit beings w/ the left side of the heart pumping oxygen-enriched blood from the gas exchange tissues to capillary beds
then, the now oxygen-poor blood returns to the heart
provides a vigorous flow of blood to the brain, muscles, and other organs
the heart repressurizes the blood after it passes through the capillary beds of the lungs or skin
Coordinated cycles of heart contraction drive double circulation in mammals
Mammal heart:
cardiac cycle: 1 complete sequence of pumping and filling blood
Systole: the contraction phase
diastole: the relaxation phase
Cardiac output: the volume of blood each ventricle pumps per minute
2 factors determine cardiac output
heart rate: the rate of concentration; number of beats per minute
stroke volume: the amount of blood pumped by a ventricle in a single contraction
4 valves in the heart prevent back flow and keep blood moving in the correct direction
Atrioventricular valve: anchored by strong fibers that prevent them from turning inside out during ventricular systole
Semilunar valves: pushed open by the pressure built up in the pulmonary artery and aorta closes the semilunar valves and prevents back flow
if blood squirts backwards through a defective valve, it may produce an abnormal sound (heart murmur)
Maintaining the heart's rhythmic beat:
Sinoaotrial node: sets the rate and timing at which all cardiac muscle cells contract
produces electrical impulses which spread rapidly w/in heart tissue
signals from SA node spread through atria
then signals are delayed at AV node
Then double branches pass signals to heart apex
Then signals spread throughout ventricles
Atrioventricular node (AV): auto rhythmic cells that are located in the wall between the left and right atria form a relay point
Electrocardiogram (ECG): electrodes place on the skin record the currents, measuring electrical activity of the heart
Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels
Blood vessel structure and function:
all blood vessels contain a central lumen lined w/ an endothelium
endothelium: a single layer of flattened epithelial cell; the smooth endothelial layer minimizes resistance to fluid flow
capillaries are the smallest blood vessels
the exchange of substances between the blood and interstitial fluid occurs in capillaries
because only there are the vessel walls thin enough to permit this exchange
arteries and veins consist of 2 layers of tissue
outer layer is formed by connective tissue that contains elastic fibers, which allow the vessel to stretch & recoil, & collagen which provides strength
the other layer contains smooth muscle and more elastic fibers
arterial walls can accommodate blood pumped in high pressure by the heart, bulging outward as blood enters and recoiling as the heart relaxes between contractions
the smooth muscles in the walls of arteries and arterioles help regulate the path of blood flow
Blood Pressure:
Systolic pressure: the pressure that is at its highest, which is when the heart contracts during ventricular systole
each ventricular contraction causes a spike in blood pressure that stretches the walls of the arteries
during diastole, the elastic walls of the arteries snap back
Diastolic pressure: there is a lower but still substantial blood pressure when the ventricles are relaxed
Vasoconstriction: increases blood pressure upstream in the arteries
Vasodilation: an increase in diameter that causes blood pressure in the arteries to fall
120/70 is a healthy blood pressure
gravity has a significant effect on blood pressure, blood flow in veins, especially in legs
ex: standing for a long period of time means the blood in your feet impedes its upward return to the heart
Fluid return by the lymphatic system:
Lymphatic system: where the lost fluid and the proteins w/in it are recovered and returned to the blood
fluid diffuses into the lymphatic system via a network of tiny vessels intermingled w/ capillaries
lymph: the recovery fluid, which circulates w/in the lymphatic system before draining into a pair of large veins of the cardiovascular system
lymph vessels have valves that prevent the back flow of fluid
lymph nodes: they are along a lymph vessel
has spaces filled by white blood cells, which function in defense
when the body is fighting an infection, the white blood cells multiply, and the lymph nodes become swollen
Blood
Blood composition and function:
plasma: a liquid matrix
functions in osmotic regulation, transport, and defense
plasma proteins act as buffers against pH changes and help maintain the osmotic balance between blood and interstitial fluid
contains many other substances in transit, including nutrients, metabolic wastes, respiratory gases, and hormones
platelets: cell fragments that are involved in the clotting process
Erythrocytes (red blood cells):O2 transport
their shape increases surface area, enhancing the rate of diffusion of O2 across the plasma membrane
hemoglobin: the iron-containing protein that transport O2
Leukocytes (white blood cells): fight infections
some are phagocytic
stem cell: can reproduce indefinitely, dividing mitotically to produce 1 daughter cell that remains a stem cell and another that adopts a specialized function
erythrocytes, leukocytes, and platelets all develop from step cells
erythropoietin: stimulates the generation of more erythrocytes
thrombus: a clot that is within a blood vessel which blocks the flow of blood
Cardiovascular disease:
atherosclerosis: the hardening of the arteries by accumulation of fatty deposits
Low density lipoprotein: delivers cholesterol to cells for membrane production
high density lipoprotein: scavenges excess cholesterols for return to the liver
heart attack: the damage or death of cardiac muscle tissue
results in blockage of 1 or more coronary arteries, which supply oxygen-rich blood to the heart muscle
stroke: the death of nervous tissue in the brain due to lack of O2
usually result from rupture or blockage of arteries in head
Gas exchange occurs across specialized respiratory surfaces
Partial pressure: the pressure exerted by a particular gas in a mixture of gasses
specialization for gas exchange is important in the structure of the respiratory surface
ex: all living cells, the cells that carry out gas exchange has a plasma membrane that must be in contact w/ an aqueous solution
gills in aquatic animals:
have a total surface area much greater than that of the rest of the body's exterior
ventilation: maintains the partial pressure gradients of O2 and CO2 across the gill that are necessary for gas exchange
move their gills through the water or move water over the gills
countercurrent exchange: the exchange of a substance or heat between 2 fluids flowing in opposite directions
ex: in a fish gills, the 2 fluids are blood and water
very efficient
tracheal systems in insects:
tracheal system: a network of air tubes that branch throughout the body
consist of tubes such as the trachea
Lungs: localized respiratory organs; for gas exchange
has a larynx, trachea, bronchi, bronchioles, alveoli, surfactant, and diaphragm
larynx: when food is swallowed, the larynx moves upward
trachea: windpipe
bronchi: 2 tubes leading the each lung
bronchioles: bronchi branch repeatedly into finer and finer tubes
alveoli: air sacs clustered t the tips of the tiniest bronchioles
surfactant: coats the alveoli and reduces surface tension
ex: most reptiles and all mammals
Breathing: the alternating inhalation and exhalation of air
Positive pressure: inflating the lungs w/ forced air flow
ex: amphibians
negative pressure: pulling air into their lungs
ex: mammals
diaphragm: a sheet of skeletal muscle that forms the bottom wall of the cavity
rib gage expands as rib muscles contract
rib cage gets smaller as rib muscles relax
Osmoregulation & Gas Exchange
Osmoregulation balances the uptake and loss of water and solutes
water enters and leaves cells by osmosis
Osmosis occurs when 2 solutions separated by a membrane differ in total solute concentration
osmolarity: the number of moles of solute per liter os solution
2 solutions w/ the same osmolarity are said to be isoosmotic
an animal can maintain water balance by being an osmoconformer or osmoregulator
osmconformer: to be isoosmotic w/ its surroundings
ex: marine animals
don't face substantial challenges in water balance
osmoregulator: to control internal osmolarity independent of that of the external environment
enables animals to live in environments that are uninhabitable for osmoconformers, such as freshwater and terrestrial habitats
in a hypoosmotic environment, it must discharge excess water
In a hyperosmotic environment, it must take in water to offset osmotic loss
marine animals:
balance water loss by drinking a lot of seawater
excess salts ingested w/ seawater are eliminated through the gills and kidneys
freshwater animals:
body fluids must be hyperosmotic bc animal cells can't tolerate salt concentrations
face the problem of gaining water by osmosis
water balance relies on excreting large amounts of very dilute urine and drinking almost no water
animals that live in temporary waters:
anhydrobiosis: a dormant state when animals habitats dry up; life w/out water
ex: water bears
they have a active, hydrated state where they contain around 85% water by weight
land animals:
lose water in many routes
urine and feces
across the skin
from the surfaces of gas exchange organs
An animal's nitrogenous wastes reflect its phylogeny and habitat
forms of nitrogenous waste:
Ammonina: very toxic in part because its ion, ammonium, can interfere w/ oxidative phosphorylation
ex: aquatic species
animals that excrete it, need access to lots of water bc ammonia can be tolerated only at very low concentrations
Urea: a different nitrogenous waste
in vertebrates, urea is the product of an energy-consuming metabolic cycle that combines ammonia w/ carbon dioxide in the liver
ex: mammals, most amphibians, sharks, and some boney fish
low toxicity
disadvantage: energy cost
must expend energy to produce urea from ammonia
Uric Acid: a type of nitrogenous waste
ex: insects, land snails, birds
nontoxic
doesn't readily dissolve in water
more energetically expensive, requiring considerable ATP for synthesis from ammonia
Diverse excretory systems are variations on a tubular theme
excretory organs:
Metanephridia: collects fluid directly from the coelom
ex: earthworms
balance the water influx by producing urine that is dilute
Malpighian tubules: remove nitrogenous wastes and that also function in osmoregulation
ex: insects
the transport epithelium that lines the tubules secretes certain solutes
includes nitrogenous waste
kidneys: functions in both osmoregulation and excretion
ex: humans
nephron: the functional units of the vertebrate kidney
each nephron consists of a single long tubule as well as a ball of capillaries called the glomerulus
contains bowman capsule
filtrate is formed when blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman's capsule
processing occurs as the filtrate passes through the proximal tubule, the loop of Henley. and the distal tubule
a collecting duct receives processed filtrate from many nephrons and transports it to the renal pelvis
supplied w/ blood by an afferent arteriole
Particular capplilaries: which surround the proximal and distal tubules
process:
proximal tubule
descending limbs to the loop of henle
ascending limb of the loop of hence
distal tubule
collecting duct