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Animal Systems (Circulation & Gas Exchange (Respiratory Organ (Gas…
Animal Systems
Circulation & Gas Exchange
Types of Circulatory Systems
Open Circulatory System
The circulatory fluid called hemolymph, heart contraction pumps the hemolymph thru the circulatory vessels into interconnected sinuses, spaces surrounding the organs
Within the sinuses, chemical exchange occurs b/w the hemolymph & body cells.
Animals such as arthopods, clams, grasshoppers have this
Closed Circulatory System
A circulatory fluid called blood is confined to vessels and is distinct from the interstitial fluid
1 or more hearts pump blood into large vessels that branch into smaller ones that infiltrate the organs
Annelids (earthworms), cephalopods (squids & octopus), & all vertebrates have this
Types of Hearts
Single Circulation
The blood passes thru the heart once in each complete circuit thru the body
Bony fishes, rays & sharks have this
Double Circulation
The pumps for 2 circuits are combined into a single organ, the heart
One pump, the right side of the heart delivers oxygen-poor blood to the capillary beds of the gas exchange tissues, where there is a net movement of O2 into the blood & of CO2 out of the blood
Amphibians, reptiles and mammals have this
Arteries, veins, capillaries
Arteries
Arteries carry blood from the heart to organs throughout the body
Within organs, arteries branch into arterioles
Veins
At their "down stream" end, capillaries converge into venules, and venules converge into veins
The vessels that carry blood back to the heart
Capillaries
Microscopic vessels w/ very thin, porous wall
Networks of capillaries called capillary beds, infiltrate tissues, passing within a few cells diameters of every cell in the body
Chemicals including dissolved gases are exchanged by diffusion b/w the blood & interstitial fluid around the tissue cells
Blood Pressure
Contraction of heart ventricle generates blood pressure, which exerts a force in all directions
Systolic Pressure
Arterial blood pressure is highest when the heart contracts during ventricular systole
For ex, animals like giraffe requires a systolic pressure of more than 250 mm Hg near the heart to get blood to its head
Diastolic Pressure
During diastole, the elastic walls of the arteries snap back. As a consequence, there is lower but still substantial blood pressure when the ventricles are relaxed
Regulation of blood pressure
Homeostatic mechanisms regulate arterial blood pressure by altering the diameter of arterioles.
Vasoconstriction
As the smooth muscles in the arteriole walls contract, the arterioles narrow
Narrowing of the arterioles increases blood pressure upstream in the arteries
Vasolidation
When the smooth muscles relax, an increase diameter
This causes blood pressure to decrease
Atria and Ventricles
Atria
The chambers that receive blood entering the heart
Ventricle
The chambers responsible for pumping blood out of the heart
Lymph Circulation
The lost fluid and proteins return to the blood via the lymphatic system, which includes a network of tiny vessels intermingled among capillaries of the cardiovascular system
The lymphatic system drains into large veins of the cardiovascular system at the base of the neck.
The joining of the lymphatic & cardiovascular system enables lipids to be transferred from the small intestine to the blood
The fluid lost by capillaries is called lymph; it's composition is about the same as that of interstitial fluid
The movement of lymph from peripheral tissues to the heart relies on much the same mechanisms that assist blood flow in veins
Disruptions in lymph flow often result in fluid accumulation, or edema, in affected tissues
For ex, certain species of parasitic worms that lodge in lymph vessels & thereby block lymph movement cause elephantiasis, a condition causing extreme swelling in limbs & other body parts
Along a lymph vessel are small, lymph filtering organs called lymph nodes, which play an important role in the body's defense
Blood
Function
Vertebrae blood is a connective tissue consisting of cells suspended in a liquid matrix called plasma
Cellular elements (cells & cell fragments) occupy about 45% of the volume of blood, the remainder is plasma
Dissolved in the plasma are ions & proteins that together w/ the blood cells function in osmotic regulation, transport, & defense
Blood contains 2 classes of cells
Red blood cells which transport O2
White blood cells which function in defense
Suspended in blood plasma are platelets, cells fragments that are involved in the clotting process
Humans normally have a pH of 7.4 ions are important in maintaining the osmotic balance of the blood
Respiratory Organ
Gas exchange or respiratory exchange is the uptake of molecular O2 from the environment & the discharge of CO2 to the environment
Partial pressure is the pressure exerted by a particular gas in a mixture of gases
A gas always undergoes net diffusion from a region of higher partial pressure to a region of lower partial pressure
The movement of O2 and CO2 across respiratory surfaces takes place by diffusion
In some animals like earthworms & amphibians the skin serves as a respiratory organ
Movement of the respir. medium over the respiratory surface, a process called ventilation, maintains the partial pressure gradients of O2 & CO2 across the gill that are necessary for gas exchage
To promote ventilation, most gill bearing animals either move their gills thru the water or move water over their gills
For ex, crayfish & lobsters have paddle like appendages that drive a current of water over the gills
In fishes, the efficiency of gas exchange is maximized by countercurrent exchange, the exchange of a substance or the heat b/w two fluids flowing in opposite directions, in a fish gill the 2 fluids are blood & water
Insect tracheal system is a network of air tubes that branch thruout the body
The large tube called the tracheae open to the outside, the finest branches extend close to the surface of nearly every cell, where gas is exchanged by diffusion across the moist epithelium that lines the tips of the tracheal branches
Bc the tracheal system brings air within a very short distance of virtually every body cell in an insect, it can transport O2 & CO2 w/o the participation of the animal circulatory system
Lungs are localized respiratory organs, most reptiles (including birds) & all mammals depend entirely on lungs for gas exchange
When food is swallowed, the larynx (the upperpart of the respiratory tract) moves upward & tips the epiglottis over the glottis which is the opening of the trachea
From the larynx, air passes into the trachea, the trachea branches into 2 bronchi
Within the lung, the bronchi branch repeatedly into finer & finer tubes called bronchioles
Gas exchange in mammals occur in alveoli which are air sacs clustered at the tips of the tiniest bronchioles. Humans lungs contain millions of alveoli which together have surface area of about 100m-50 times that of the skin
Breathing
The process that ventilates the lungs is breathing, the inhalation & exhalation of air
Amphibian
Amphibian such as frogs ventilates its lungs by positive pressure breathing, inflating the lungs w/ forced airflow
During the first stage of inhalation, muscles lower the floor of an amphibian's oral cavity, drawing in air thru its nostrils
Next, w/ the nostrils & mouth closed, the floor of the oral cavity rises, forcing air down the trachea
During exhalation, air is forces back out by the elastic recoil of the lungs & by compression of the muscular body wall
Bird
Birds use 8 or 9 air sacs situated on either side of the lungs. The air sacs don't function directly in gas exchange but act as bellows that keep air flowing thru the lungs
Bird lungs are tiny channels called parabronchi, passage of air thru the entire system lungs & air sacs requires 2 cycles of inhalation & exhalation
First, when birds breathe, they pass air over the gas exchange surface in only one direction. Second, incoming fresh air doesn't mix w/ air that has already carried out gas exchange
Mammals
Mammals breathe by negative pressure breathing pulling, rather than pushing air into their lungs
Using muscle contraction to actively expand the thoracic cavity, mammals lower air pressure in their lungs below that of the air outside their body
Air rushes thru the nostrils & mouth & down the breathing tubes to the alveoli.
During exhalation, the muscles controlling the thoracic cavity relax & the volume of the cavity is reduced. The increased air pressure in the alveoli forces air up the breathing tubes & out the body
Inhalation is always active & requires work, whereas exhalation is usually passive
Osmoregulation & Excretion
Osmosis
The movement of water thru a semipermeable membrane from hypotonic (less salt) site to hypertonic (more salt) side
For ex, if you sprinkle salt on a slug, the slug will become dehydrated
Osmoregulation- the process by which animals control solute concentration & balance water gain & loss
Osmolarity- the unit of measurement for solute concentration
An animal can maintain water balance in two ways
Osmoregulator
to control internal osmolarity independent of that of the external environment
Osmoconformer
to be isoosmotic w/ its surroundings
Freshwater Animals
The osmoregulatory problems of freshwater animals are the opposite of those of marine animals
The body fluids of freshwater animals must be hyperosmotic b/c animal cells can't tolerate salt concentration as low as that of lake or river water
Having internal fluids w/ an osmolarity higher than that of their surroundings, freshwater animals face the problem of gaining water by osmosis & losing salts by diffusion
Many freshwater animals including bony fishes such as the perch maintain water balance by drinking almost no water & excreting large amount of very dilute urine
Marine Animals
Most marine invertebrates are osmoconformers, their osmolarity is the same as that of seawater
They face no substantial challenges in water balance. However, b/c these animals differ considerably from seawater in the concentrations of specific solutes, they must actively transport these solutes to maintain homeostasis
Many marine vertebrates & some marine invertebrates are osmoregulators. (For ex, marine fishes such as cod constantly lose water by osmosis such fishes the water loss drinking large amount of seawater & they eliminate the ingested salts thru their gills & kidneys
Ammonia, urea & uric acid
Ammonia excretion is most common in aquatic species. Ammonia is when proteins & nucleic acids are broken apart for energy or converted to carbs or fats, enzymes remove nitrogen
Animals excrete nitrogenous wastes as ammonia need access to lots of water b/c ammonia can be tolerated only at very low concentrations
Fishes use ammonia excretion
Uric Acid
Uric Acid is relatively nontoxic & doesn't readily dissolve in water. It therefore can be excreted as a semisolid paste w/very little water loss
However, uric acid is even more energetically expensive than urea, requiring considerable ATP for synthesis from ammonia
Urea
Ammonia excretion doesn't work well for land animals. Instead they mainly excrete a different nitrogenous waste called urea
Urea is the product of metabolic cycle that combines ammonia w/ carbon dioxide in the liver. (Humans excrete urea)
The main advantage of urea is its very low toxicity
The main disadvantage is its energy cost. Animals must expend energy to produce urea from ammonia
Major excretory organs
Excretory Process
Reabsorption
Secretion
Filtration
Excretion
Kidneys, a pair of organs each about 10 cm in length as well as organs for transporting & storing urine
During urination, urine is expelled from the bladder thru a tube called the urethra
The two ureters drain into a common sac called urinary bladder
Urine produced by each kidney exits thru a duct called the ureter
Insects & other terrestrial arthropods have organs called malpighian tubules that remove nitrogenous wastes & that also function in osmoregulation
Most annelids or earthworms have metanephridia, excretory organs that collect fluid directly from the coelom
Protonrphridia which form a network of dead end tubules the tubules are connected to external openings branch throughout the flatworm body which lacks a coelom
Nephrons
Waving back & forth across the renal cortex & medulla are the nephrons, the functional units of the vertebrae kidney
Of the 1 million nephrons in the human kidney, 85% are cortical nephrons, which reach only a short distance into the medulla
The remainder, the juxtamedullary nephrons extend deeply into the medulla. Juxtamedullary nephrons are essential for production of urine that is hyperosmotic to body fluids, a key adaptation for water conservation in mammals
