Zoology: Body Systems

The Functions of the Muscular and Skeletal Systems:

Skeletal muscle is responsible for all voluntary movements. It is also involved in some involuntary actions such as breathing, shivering, and maintaining posture. Cardiac muscle is responsible for the beating action of the heart. Smooth muscle creates the movement in many hollow internal organs, such as the gut, bladder, and blood vessels, and is under the control of the autonomic nervous system.

Vertebrate Muscle Types:

Vertebrate Muscle Types

The Relationship among Sarcomeres, Myofibrils, Muscle Fibers, and a Muscle:

Muscle contraction is due to the interaction between actin and myosin. Each muscle is composed of muscle fibers and each muscle fiber is packed with myofibrils – bundles of thin actin and thick myosin filaments arranged in orderly fashion. The contractile unit of the myofibril is called a sarcomere.


Z lines – anchor thin filaments

actin – thin filaments

myosin – thick filaments

titin – protein that holds myosin filaments in centered position

A band – contains all myosin filaments

M band – contains proteins that help hold myosin filaments in their regular arrangement

I band and H zone – regions where actin and myosin do not overlap in the relaxed muscle

Twitch in relation to muscle function:

The spread of an action potential through a muscle fiber’s T tubule system causes a minimum unit contraction called a twitch. A twitch can be measured by the force it generates (tension).

Twitch in relation to the total tension produced by a muscle:

A twitch is only a fraction of the total tension produced by a muscle. The force generated by an action potential can vary enormously depending on how many muscle fibers are in the motor unit it innervates.


Two Types of Skeletal Muscle Fibers:

  • Fast Twitch
    • Color – Red
    • Myoglobin – No
    • ATPase activity – High
    • Muscles with these type of fibers are built for…? – Power
    • Types of high-level athletes who have a lot of this type of muscle – Weight Lifters, Sprinters
  • Slow Twitch
    • Color – White
    • Myoglobin – Yes
    • ATPase activity – Low
    • Muscles with these type of fibers are built for…? – Endurance
    • Types of high-level athletes who have a lot of this type of muscle – Long Distance Runners, Cyclists, Swimmers


Three types of skeletons found in the animal kingdom:

Skeleton Type:  Hydrostatic

Basic Description:  Volume of fluid enclosed in cavity surrounded by muscle

Organisms in which this is found:  Cnidarians, Annelids, other soft-bodied invertebrates


Skeleton Type:  Exoskeleton

Basic Description:  Hardened, rigid outer surface where muscles can be attached

Organisms in which this is found:  Arthropod, Nematode


Skeleton Type:  Endoskeleton

Basic Description:  Internal scaffolding; muscles are attached to it and pull against it

Organisms in which this is found:  Humans and other vertebrates


Different types of connective tissue in the skeleton:


Cartilage Compact Bone Spongy Bone
Components Collagen fibers; gel-like matrix


Haversian systems Numerous cavities
Basic structure Tough, rubbery mixture of polysaccharides and proteins Thin, concentric bony cylinders, between which are the osteocytes in their lacunae Internal meshwork constitutes support system
Primary Function Supportive tissue in stiff but flexible structures Supportive; resistant to fractures Contains bone marrow where red blood cells are produced
Where found in the body Joints, larynx, nose ,ears


Most bones Most bones; Ends of long bones


Circulatory System

The circulatory system is responsible for the transport of oxygen and carbon dioxide, nutrients, wastes, and certain nonspecific immune defenses to the desired location in the body.

The evolution and diversity of circulatory systems in animals and within vertebrates:

Circulatory System Absent Open Circulatory System Closed Circulatory System
Components Special skin that allows for the diffusion of gases, nutrients, and wastes Heart, vessels, hemolymph, ostia Heart, vascular system


Found in which animal groups? Single-celled organisms in aquatic or very moist terrestrial environments Arthropods, mollusks, and some other invertebrate groups Vertebrates and annelids
Why this system “works” for these animals (i.e. advantages,  or how it effectively meets needs) All needs are met through passive diffusion of materials into the organism Heart pumps hemolymph to different parts of the body; ostia prevent flow in reverse direction System of vessels keeps blood separate from interstitial fluid; blood reaches even the smallest tissues effectively and efficiently
Vertebrate Group Fish Lungfish Amphibians Reptiles Crocodiles Birds and Mammals
Single or double circulation Single Double Double Double Double Double
Heart structure


Two chamber Two chamber Three chamber Three chamber Four chamber Four chamber
Can blood bypass lungs or gills? How? No Systemic circuit; gill bypasses Partial separation of pulmonary and systemic circulation Ventricle partially divided by a septum Two separate ventricles; connection between two aortas Separate pulmonary and systemic circuits
Why this system “works” for these animals (see above) Efficient blood flow to all tissues Blood vessels pick up oxygen from air gulped in lungs Blood can avoid large pressure drop that occurs in gas exchange Intermittent breathing Intermittent breathing Operate at different pressures, gas exchange maximized

The path of a single red blood cell through the mammalian circulatory system:

The blood proceeds from the left ventricle to the aorta to the arteries to the arterioles to the tissue capillaries where oxygen is dropped off. The deoxygenated blood proceeds to the venules to the veins to the superior and inferior vena cava to the right atrium. The blood moves to the right ventricle to the pulmonary arteries to the lungs where the blood is oxygenated. The oxygenated blood returns to the left atrium of the heart via the pulmonary veins. Systemic circulation involves the path from the heart to the body while pulmonary circulation involves the path from the heart to the lungs.

In addition to the nutrients and hormones transported in the liquid portion of the blood, the plasma contains water, salts, and proteins. There are four functions of these components of the plasma, as well as cellular components of mammalian blood.

The higher concentration of salts and protein in the blood prevent water from escaping the blood into the interstitial fluid. Other proteins in the blood, such as immunoglobulins function in the specific humoral immune system. Other proteins are also involved in chemical digestion and reach their destinations via the blood. Calcium functions in muscle contraction, while sodium, chloride, and potassium function in nerve impulse transmission.

The cellular components of blood include erythrocytes, leukocytes, and platelets. Erythrocytes function in oxygen and carbon dioxide transport, leukocytes are the active components of the immune system that fight off foreign substances, and platelets are responsible for blood clotting.

The process of blood clotting has two major parts:

1) formation of a platelet plug

2) production of fibrin.

What triggers formation of a platelet plug? What are the steps to fibrin production and where do the precursors to fibrin come from?

Blood clotting is triggered by tissue damage that exposes the blood to certain proteins that it is normally separated from. This exposure activates platelets and the clotting factor cascade. The end result of the cascade is to convert an inactive circulating enzyme, prothrombin, to its active form, thrombin. Once activated, thrombin cleaves fibrinogen to form fibrin, which provides a scaffold for the formation of scar tissue.

Structure and function of arteries, veins, and capillaries in mammals:

Arteries Capillaries Veins
Structure of vessel wall



Extracellular collagen and elastic fibers, smooth muscle Single layer of thin endothelial cells Collagen, elastic fibers, smooth muscle
Valves present or absent Absent Absent Present
List the function(s) of the vessels and describe how the structure of each vessel relates to these functions.




Carry blood away from the heart; thick to withstand high pressures generated from the heart Thin layer for gas, ion and small molecule exchange Carry blood to the heart; thinner, valves to prevent backflow
Blood pressure within vessel (high or low) High Low Low
Primary mechanism that causes blood flow through the vessels Smooth muscle cell contraction Blood pressure from arterial end Contractions of surrounding skeletal muscle


How the lymph system and the circulatory system interact to maintain homeostasis of fluid levels in the tissues:

The lymphatic vessels prevent fluid build-up in the tissues by returning interstitial fluid to the blood. Fine lymphatic capillaries merge into progressively larger vessels into the left and  right thoracic ducts, which empty into large veins at the base of the neck.

Excretory System

The two main roles of the excretory system are to maintain the volume, concentration, and composition of extracellular fluids as well as excrete waste products.

  • Filtration – the separation of solids from fluids by interposing a medium through which only fluid can pass
  • Secretion – the process of releasing a chemical substance from a cell or gland
  • Reabsorption – the act or process of absorbing again, as the absorption by the kidneys of substances that were already secreted into the tubules, such as glucose, proteins, or sodium
  • What kind of troubles do saltwater organisms face in terms of salt and water balance? Freshwater organisms?  Terrestrial organisms?

Animals that live in marine, freshwater, or terrestrial environments face different salt and water balance problems. In the terrestrial environment, salts and water can be scarce and usually must be conserved by excretory systems. In the freshwater environment, water is plentiful but salts are scarce. Controlling the volume, solute concentration, and composition of extracellular fluids is not a huge problem for marine life however, because their extracellular fluids are very similar to the seawater and their nitrogenous wastes can simply diffuse into the aqueous environment.

Osmoconformers and Osmoregulators.

Most marine invertebrates equilibrate their extracellular fluid osmolarity with the ocean water and are therefore, called osmoconformers.  Osmoconformers decrease the net flux of water into their bodies from diffusion to maintain internal solute concentrations at a level equal to the osmolarity of the surrounding medium. However, there are limits to osmoconformity. No animal could survive with the osmolarity of fresh water or extremely high solute concentrations (denature proteins). Osmoregulators, on the other hand, maintain extracellular fluid osmolarities much lower than seawater. They tightly regulate the osmolarity of their fluids to keep them from becoming too dilute or too concentrated.

What kinds of animals (and why) excrete ammonia? Urea?  Uric acid?

If ammonia builds up in the extracellular fluids, it becomes toxic at rather low levels and is a dangerous metabolite for terrestrial animals. Ammonia is highly soluble in water and diffuses rapidly, so its continuous excretion is relatively simple for many aquatic invertebrates (and bony fishes) that continuously lose ammonia from their blood to the environment.

Ureotelic animals, such as mammals, most amphibians, and cartilaginous fishes (sharks and rays), excrete urea as their principal nitrogenous waste product. Urea is quite soluble in water, but its excretion can result in a large loss of water that many animals cannot afford. By producing concentrated urea solutions, these animals can conserve water.

Animals that conserve water by excreting nitrogenous wastes mostly as uric acid are uricotelic. Insects, reptiles (+birds), and some amphibians are uricotelic. Uric acid is not very soluble in water, so it forms a colloidal suspension in the urine and is secreted as a semisolid. A uricotelic animal loses very little water as it disposes of its nitrogenous wastes.


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