Download the exterior, nervous, urinary, and endocrine systems of domestic

ANIMAL SCIENCE
8646-F
THE EXTERIOR, NERVOUS, URINARY,
AND ENDOCRINE SYSTEMS OF DOMESTIC ANIMALS
INTRODUCTION
An agricultural producer should be knowledgeable of the anatomy and physiology of livestock. A background of
anatomical and physiological features of animals assists the producer in evaluating, selecting, breeding, and managing the herd. This topic includes a discussion of the nervous, urinary, and endocrine systems, as well as the external
anatomy of animals.
NERVOUS SYSTEM
An animal’s nervous system consists of two major parts - the central nervous system and peripheral nervous system. The brain
and spinal cord make up the central nervous system. The somatic
nerves* and autonomic nerves
make up the peripheral nervous
system. One function of the nervous system is to organize the
physical movement of the body.
Another function is to respond to
the actions of all the senses. The
nervous system allows the animal
to react to internal or external
stimuli in the environment.
Each nerve cell (neuron) consists
of an individual, long fiber (axon)
and several branched threads (dendrites). Other nerves and receptor organs (such as a sense organ) stimulate the
dendrites. An impulse then passes through the dendrites to the axon. The point at which a dendrite connects to an
axon is a synapse. The impulse may be sent to another dendrite or to an effector organ (for example, a muscle cell).
Before an impulse can reach the brain or go from the brain to an effector organ, it must pass through a number of
neurons and synapses. Not all impulses go to the brain. Some are sent directly to the effector organ.
Nerves occur as single neurons or in bundles (nerve trunks). Fat-containing sheaths cover some nerve fibers.
Ganglions consist of nerve trunks. They are outside of the brain and spinal cord. Sensory neurons are nerve cells
that get stimuli and carry them to the central nervous system. Motor neurons are nerve cells that carry messages
from the brain to muscles or glands.
* Underlined words are defined in the Glossary of Terms.
-1-
The cerebrum, cerebellum, pons, and medulla oblongata are the major parts of the brain.
The largest part is the cerebrum. It is large relative to
body size in the more intelligent animals. The cerebrum
consists of many folds and appears wrinkled. It is in
charge of the thinking process that makes the decisions for voluntary muscle activities. The cerebrum
is also responsible for reacting to sense stimuli. If
the cerebrum should become damaged, not all body
functions cease.
The cerebellum coordinates messages from other parts
of the brain for transmission to the body. It controls
muscles performing normal activities (walking, running,
eating, etc.). If the cerebellum should become damaged,
incoordination may result, but not paralysis. The pons
and medulla oblongata control reflex actions such as
eye blinking, vomiting, breathing, and swallowing. The
pons and medulla usually act independently of the cerebrum and cerebellum.
The spinal cord is the main avenue for message transferals between the brain and other parts of the body. Located
in the center of the vertebral column, the spinal cord is divided into parts or segments. A pair of spinal nerves
extends to the body from each part of the spinal cord. The spinal cord receives messages from the nerve fibers
from various body parts and transmits those messages to the brain. Motor nerve fibers in the spinal cord then
transmit the responses from the brain back to the body parts.
Somatic nerves control the functions of the body tissues other than the main body organs. All nerve structures
located outside of the brain and spinal cord make up the peripheral nervous system. Somatic nerves are a part of
that system and transmit messages between the outer parts of the body and the brain.
Autonomic nerves, also a part of the peripheral nervous system, control the functions of involuntary muscles in the
internal organs (such as the heart and stomach). Autonomic nerves provide almost automatic regulation of involuntary functions. These nerves transmit messages between the brain and the involuntary muscles.
-2-
EXTERNAL ANATOMY
(Note: The selection and evaluation series of topics provide more in-depth explanations of the external body parts
of animals.)
Skin is the external covering of the animal’s body. It is continuous with the outer layers of the respiratory, reproductive, and digestive tracts. Hair, wool, horns, feathers, toenails, and hooves are modified extensions of the skin.
Cattle, goats, sheep, and hogs have cloven or split hooves, while horses do not.
The functions of skin are to protect against disease and infection and to regulate body temperature. Skin contains
glands for secretion and excretion and sensory nerves to help the animal react to its environment.
The skin of animals consists of two layers - epidermis and dermis. The epidermis is the outer layer of the skin and
contains no blood cells. The dermis is the inner layer of the skin. It contains blood vessels, lymph vessels, nerves,
glands, hair follicles, and muscle fibers.
The primary glands of the skin are sweat glands and sebaceous glands. Sebaceous glands secrete oily substances
to lubricate the skin and hair. The dermis may also contain special types of glands, such as the sweat glands found
in the snout of a hog and mammary glands found in all mammals. Thickness of skin varies with animal species,
breed, sex, and body location.
The coat covering of cattle, goats, horses, and hogs is hair; for sheep, it is wool. In temperate, or cold climates, the
hair coat of animals grows long for protection and is shed when the climate becomes warmer. The wool of sheep
is shorn in the spring and provides a product of economic value. The mohair of goats is shorn in the early spring and
late summer, also providing a valuable economic product.
Feathers, the body covering of poultry, are molted in the late summer. New feathers grow before winter to protect
the fowl. Hair, wool, and feathers are all composed of protein and produced by gene action.
-3-
URINARY SYSTEM
The parts of the urinary system include the kidneys,
ureters, bladder, and urethra. The kidneys, located in
the abdominal cavity just under the lumbar vertebrae,
are closely attached to the abdominal wall. In cattle
and poultry, the kidneys consist of various lobes or
parts. In horses, the right kidney is heart-shaped while
the left kidney is bean-shaped. In sheep and hogs, the
kidneys are both bean-shaped.
Each kidney consists of an outer tissue layer (renal cortex) and an inner portion (renal medulla). The medulla
contains many blood vessels and urinary tubules. The
renal artery conveys blood to the kidneys. Blood filters
from the capillaries into the blind sac of the urinary tubules. The urinary tubules network together and form
larger tubules toward the center of the kidney where
urine-containing body wastes are collected.
One of the main functions of the kidneys is to filter waste
products from the blood. Some of the waste products
include mineral salts and various wastes from protein
metabolism, such as urea, uric acid, and creatinine.
The kidneys also regulate blood composition and maintain normal internal life support conditions. An animal
cannot survive if both kidneys fail to function.
The ureters are tubules that connect the kidneys with the bladder. They transport urine from the kidneys to the
bladder. The bladder, an expandable sac, stores the urine until it is expelled from the animal’s body. Urine passes
from the bladder through an elastic tubule (urethra) to be voided from the body. The urethra is in the penis in males
and is connected to the vagina in females.
In poultry, there is no bladder and the urine is transported by the ureters to the cloaca, where it is excreted with
feces. No liquid urine is excreted by poultry. The white material in the droppings of poultry is uric acid, the urinary
excretion of poultry. In other domestic animals, urinary waste is excreted in the form of urinary nitrogen.
ENDOCRINE SYSTEM
The proper functioning of the many cells and organs that comprise an animal’s body is largely dependent upon the
action and interaction of chemical substances secreted by endocrine glands. Endocrine glands are usually small and
located in various body parts. They secrete hormones. Because endocrine glands are ductless, they secrete the
hormones directly into the bloodstream. Conversely, exocrine glands release their secretions into ducts that lead to
the body surface or into cavities within the body.
The pancreas is both an exocrine gland (secretes pancreatic juices into the small intestine) and an endocrine gland
(secretes insulin into the bloodstream). Small amounts of hormones are excreted into the bloodstream but have
powerful effects on the body. For example, 1/1,000,000 (one millionth) gram of oxytocin will cause immediate
letdown of milk in lactating females.
-4-
After being secreted into the bloodstream, hormones travel to different body parts where they stimulate certain
organs to perform specific functions. Some body functions in which hormones play an important role include
growth and fattening, reproduction, lactation, and egg laying. The efficiency and performance of animals depend on
the proper level and chemical balance of the hormones in performing specific functions.
The pituitary gland, also known as the “master gland” of the body, is composed of two parts - anterior pituitary
gland and posterior pituitary gland. The pituitary gland is located in a bony depression at the base of the brain. The
anterior pituitary gland is cherry-shaped with its stem attached to the brain. It directly and indirectly controls the
hormonal secretions of various endocrine glands.
If the pituitary is removed or becomes dysfunctional, the adrenal cortex, gonads (ovaries or testicles), and the
thyroid gland do not secrete the hormones for which they are responsible. This results in arrested growth, inactivity
of the gonads and accessory sex organs, suppression of lactation, and atrophy of the thyroid, adrenal cortex, and
parathyroids. Other hormonal malfunctions include increased sensitivity to insulin, a lowered metabolic rate, and
less resistance to infection and shock.
The hypothalamus is located directly above the pituitary gland. It is a small area of the brain that coordinates
hormonal activity by regulating the release of hormones from the anterior pituitary gland and producing hormones
that are stored and released from the posterior pituitary gland.
Stimulating or inhibiting hormones produced by the hypothalamus are transported to the anterior pituitary by means
of portal blood vessels. The hormones oxytocin and vasopressin produced in the hypothalamus travel to the
posterior pituitary by means of nerve cells.
-5-
The thyroid gland consists of two connected lobes located on either side of the trachea or windpipe. The production of the hormone thyroxine by the thyroid gland is stimulated by thyrotropic hormones produced by the anterior
pituitary gland. Thyroxine controls body metabolism and growth by increasing energy production and oxygen
consumption by most body tissues. Calcitonin, a hormone also produced by the thyroid, controls the calcium level
in the blood and promotes incorporation of calcium into bone.
The parathyroid glands include four small glands adjacent to or embedded in the thyroid gland. They produce
parathyroid hormones that maintain or increase the level of calcium and phosphorus in the blood.
The adrenal glands, consisting of a medulla and cortex, are located in front of the center of the kidneys. The
medulla produces the hormone adrenaline (epinephrine) that stimulates the heart and controls its rate and strength
of contraction. The medulla also produces nonepinephrine, which helps maintain blood pressure and stimulates
smooth muscles. The cortex produces steroids, some of which are involved in protein, carbohydrate, and fat
metabolism. Androgens and estrogens produced by the gonads (ovaries and testicles) and the anatomy and physiology of the reproductive system are discussed in detail in a separate topic on animal reproduction.
Hormones are produced and required in very small amounts to perform their specific functions. Hormones affect
the growth of animals, shape of the animals’ bodies, feed efficiency, and adaptation of animals to the environment.
Some specific hormones act on different tissues in different species. Hormones may be quickly deactivated and
disappear from the bloodstream within a few hours, but their effects may not become apparent until a few hours or
days after being administered.
After they are in the bloodstream, hormones do not reach target organs merely by accident. They are attracted by
receptors within the cells of tissues for which they are intended and bind with specific substances. After the hormone interacts with the receptor, the desired response or action is initiated. The production of hormones by
endocrine glands is carefully balanced, and an imbalance can result in illness or improper development of the
animal. The interaction of various hormones or the actual level of the specific hormone in the bloodstream may
control this delicate balance.
Acknowledgements
Kristy Corley, Graduate Technician, Department of Agricultural Education,
Texas A&M University, revised this topic.
Larry Ermis, Curriculum Specialist, Instructional Materials Service,
Texas A&M University, reviewed this topic.
Vickie Marriott, Office Software Associate, Instructional Materials Service,
Texas A&M University, prepared the layout and design of this topic.
Christine Stetter, Artist, Instructional Materials Service,
Texas A&M University, prepared the illustrations for this topic.
-6-
REFERENCES
Bogart, Ralph and Robert E. Taylor. Scientific Farm Animal Production. Minneapolis, MN: Burgess Publishing Company, 2000.
Campbell, John R. and John F. Lasley. The Science of Animals That Serve Humanity. St. Louis, MO:
McGraw Hill Book Company, 2001.
Endocrine System. [On-line]. Available: http://encarta.msn.com/find/search.asp?search=endocrine. [2002, March].
Frandson, R. D. Anatomy and Physiology of Animals. Philadelphia, PA: Lea & Fibiger, 1992.
Nervous System. [On-line]. Available: http://encarta.msn.com/find/search.asp?search=nervous. [2002, March].
Organization of the Nervous System. [On-line]. Available: http://www.ultranet.com/
~jkimball/BiologyPages/P/PNS.html. [2002, March].
Pathophysiology of Endocrine System. [On-line]. Available: http://arbl.cvmbs.colostate.edu/
hbooks/pathphys/endocrine/index.html. [2002, March].
Urinary System. [On-line]. Available: http://encarta.msn.com/find/search.asp?search=urinary. [2002, March].
GLOSSARY OF TERMS
Autonomic nerves – Nerves that regulate involuntary action, as of the intestines, heart, and glands.
Creatinine – A creatine anhydride, C4H7 N3 O, formed by the metabolism of creatine and found in muscle tissue
and blood and normally excreted in the urine as a metabolic waste.
Effector organ – An organ or tissue that effects or causes a reaction in animals in response to a stimuli.
Gene – The smallest unit of inheritance; genes occur in pairs on chromosomes in the nucleus of a cell.
Hormones – Chemical substances produced in the body by endocrine glands and transported by the blood to
other organs to stimulate their functions.
Somatic nerves – Nerves that control voluntary movements in the body, such as those performed by the
skeletal muscles.
SELECTED STUDENT ACTIVITIES
SHORT ANSWER/LISTING: Answer the following questions or statements in the space provided or on
additional paper.
1.
Why is basic knowledge of animal anatomy and physiology important to an agricultural producer?
____________________________________________________________________________
____________________________________________________________________________
2.
Name the two major parts of the nervous system and briefly list the components of each.
a. _________________________________________________________________________
b. _________________________________________________________________________
3.
Name the four major parts of the brain.
a.
_______________________________
b.
_______________________________
-7-
c.
d.
_______________________________
_______________________________
4.
What is the difference between somatic nerves and autonomic nerves?
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
5.
Differentiate between the epidermis and dermis of skin.
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
6.
Name and briefly list a function of each of the four parts of the urinary system.
a. _________________________________________________________________________
b. _________________________________________________________________________
c. _________________________________________________________________________
d. _________________________________________________________________________
7.
How is urine expelled from a chicken’s body?
____________________________________________________________________________
8.
What is the purpose of the endocrine glands?
____________________________________________________________________________
9.
Where is the pituitary gland located?
____________________________________________________________________________
10. How do hormones reach their intended targets?
____________________________________________________________________________
ADVANCED ACTIVITIES
1.
Research the endocrine system in other available information resources for an animal species (for example,
search the Internet for “endocrine system AND sheep”). Then, in your own words, explain the endocrine
system’s function for the animal species. Explain the relationship between the endocrine system and other
body organ systems of the animal species.
2.
Leather is made from the hides of animals. Research and report on the processes involved in making leather.
ALL RIGHTS RESERVED
Reproduction prohibited without written permission.
Instructional Materials Service
Texas A&M University
2588 TAMUS
College Station, Texas 77843-2588
http://www-ims.tamu.edu
2002
-8-