Download Fetal Pig Information

Fetal Pig Information
Background
The majority of mammals are placental mammals in which the developing young, or fetus, grows inside the female's uterus while attached to a
membrane called the placenta. The placenta is the source of food and oxygen for the fetus, and it also serves to get rid of fetal wastes. The
dissection of the fetal pig in the laboratory is important because pigs and humans have the same level of metabolism and have similar organs and
systems. The age of the fetal pig can be estimated by measuring the body length from the tip of the snout to the attachment of the tail. The
gestation period for the pig is 112-115 days. The following numbers can be used to determine the age of a fetus. 11 mm = 21 days; 17 mm = 35
days; 2.8 cm = 49 days; 4.0 cm = 56 days; 22 cm = 100 days; 30 cm = 114 days
External Anatomy
The lips around the mouth are well developed and the upper lip has a groove called the philtrum. The philtrum in most mammals is a narrow
groove, and may carry moisture from the mouth to the nose pad to keep it wet. A wet nose pad is able to trap odor particles better than a dry one.
For humans and most primates, the philtrum serves only as a vestigial depression because higher primates rely more on vision than on smell.
Mammals have a flexible outer flap on their ears called pinnae. The pinnae help focus sound waves into the inner ear.
The nostrils or external nares can be found on the nose and are used for smell and respiration.
Many mammals have sensory facial hairs called vibrissae, more commonly called whiskers. These structures are sensitive to touch.
The eye of a fetal pig has an upper and lower lid, along with a third eyelid known as the nictitating membrane. This membrane is used to moisten
the eye as it moves across the eye. This membrane is a greatly reduced vestigial structure in humans.
Pigs, horses and deer are called unguligrade because they walk on their hooves (modified toenails). Pigs are placed in the order artiodactyla
because they have an even number of toes. Humans are plantigrade because we walk on the entire soles of the foot. Dogs and cats are digitigrade
because they walk on their digits (toes).
The umbilical cord is the pathway through which the fetal pig receives all necessary gases
and nutrients and is able to get rid of all metabolic waste. It is made up of various veins and
arteries. The largest vein is the umbilical vein, which carries blood from the placenta to the
fetus. There are two small umbilical arteries which carry blood from the fetus to the
placenta.
Anterior from the anus along the ventral surface of the pig are tiny bumps called mammary
papillary or nipples. These are present in both sexes but only in females are they associated
with functional mammary glands, which produce milk for offspring. The actual number of
papillary varies from mammal to mammal and animals having litters tend to have more.
The urogenital opening (different locations for male and female) is the opening for all
excretory and reproductive systems. The genital papilla is a fleshy flap of skin protecting the urogenital opening a female fetal pig.
Oral Cavity
The ridged roof of the mouth is the hard palate. The soft palate is the fleshy portion of the roof of the mouth and lies caudal to the hard plate.
These palates work together to create a vacuum which forces liquid into the mouth during feeding. The tongue is used for manipulating food and
the sensory papillae, also known as taste buds are located on the base and front sides of the tongue. Pigs have three general types of teeth.
Incisors located at front of the oral cavity are used for cutting or cropping. Canines are longer and are used to stab. Cheek teeth or molars are
located toward the back of the oral cavity and are used to grind food. Molars may not be present in your pig as mammals have two generations of
teeth that develop; a milk set and a permanent set.
Far back in the oral cavity is the region known as the pharynx, a common passage for food going to the esophagus and air going to the lungs. The
nasopharynx is the specific name of the cavity leading to the respiratory system. This opening carries air from the nostrils to the trachea. The
esophageal opening is the part of the pharynx which leads to the esophagus. The cone-shaped epiglottis is a flap of skin which prevents food and
liquid from entering the trachea when swallowing.
Digestive System
Most of the digestive organs are surrounded and held in place by a thin layer of tissue called the peritoneum. You will have peeled this away when
you dissected the pig.
The large, reddish-brown organ that occupies much of the abdominal cavity is the liver. A human liver has four lobes, whereas a fetal pig liver has
five lobes. Gently lift up the right lateral lobe of the liver and locate the gall bladder, which is used to store the bile made in the liver. The bile duct
carries bile from the liver to the duodenum.
The esophagus is the tube which joins the mouth to the stomach. Food moves down the esophagus by muscular contractions after being softened
by saliva in the mouth.
The stomach is where mechanical digestion occurs. The stomach is connected to the esophagus at its anterior end, known as the cardiac region.
The area where the stomach narrows to join to the small intestine is known as the pyloric region. There are two sphincters which are muscles used
to regulate the movement of food in adult mammals. The cardiac sphincter is a muscle found where the esophagus and stomach meet and
ensures food does not go back up the esophagus. The pyloric sphincter is a muscle which regulates food leaving the stomach and entering the
small intestine.
Inside the stomach are longitudinal ridges that line the stomach called rugae. These folds allow the stomach to expand and contract as needed. A
fetal pig receives absorbed nutrients from its mother through the umbilical cord so there will be no food in the stomach. Sometimes placental
mammals will swallow amniotic fluid, which may gel up in the preservation process.
The constricted caudal portion of the stomach leads to the small intestine, where absorption of nutrients occurs. The first 3-4 cms of the small
intestine is the duodenum. Bile from the liver and digestive enzymes made by the pancreas enters the small intestine here. The mid-section of the
small intestine is called the jejunum, while the last section is called the ileum. This is where the absorption of nutrients takes place. The small
intestine is not loose in the abdominal cavity but is held in place by mesentery. There are veins and arteries in the clear mesentery that carry
absorbed nutrients and nerve signals away from the small intestine to other structures in the pig.
Inside the small intestine are microscopic, finger-like projections called villi. The villi increase the surface area of the small intestine for absorption.
Below the junction of the large and small intestine is a small pouch-like, structure called the cecum. In most animals, the cecum has little function.
However, in animals such as the pig, horse and rabbit, the cecum is very important in the digestion of fibrous feeds. The large intestine is
composed of two parts. The last part is called the colon and functions in the reabsorption of water. The terminal portion of the large intestine is
the rectum. Digestive waste material stored in the rectum leaves the body through the anus.
The pancreas makes a variety of digestive enzymes that travel to the small intestine through the pancreatic duct.
The spleen is in the area of digestive organs but is primarily used to filter out dead red blood cells.
Circulatory System
The circulatory system of the pig consists of the heart, arteries, veins, and capillaries. There are two major parts to this system. Pulmonary
circulation moves oxygen-poor blood to the lungs and returns oxygen-rich blood to the heart. The systemic circulatory system supplies all parts of
the body with oxygen-rich blood via arteries & arterioles and returns oxygen-poor blood to the heart via venuoles & veins.
Covering the heart is a thin, tough membrane called the pericardium. Partially covering the heart and towards the posterior of the trachea is the
thymus gland. The thymus is part of the immune system and makes T-cells.
The heart is composed of 4 chambers. Two upper receiving chambers called atria (sing: atrium) and 2 lower pumping chambers called ventricles.
The superior vena cava returns deoxygenated blood from the head and upper neck back to the right atrium. The inferior vena cava returns
deoxygenated blood from parts of the lower body below the diaphragm back to the right atrium. There are four pulmonary veins, two on each
side of the heart, carrying oxygenated blood from the lungs back to the left atrium of the heart. The most noticeable artery rising from the left
ventricle is the aorta. It curves to the left and supplies all oxygenated blood to the entire body of the pig. The carotid artery branches off the
aortic arch and delivers blood to the head region. The pulmonary artery arises from the anterior portion of the right ventricle and will divide into
the right and left pulmonary arteries. Its function is to carry deoxygenated blood from the heart to the lungs. Other arteries are named for the
body part they serve. The gastric artery leads to the stomach, the hepatic artery leads to the liver, the renal artery leads to the kidney.
There are two types of valves which prevent the backflow of blood. Two atrioventricular valves called the mitral (bicuspid) valve and tricuspid
valve separate the atria from the ventricles. The two semilunar valves are called the aortic valve and pulmonary valve. The aortic valve prevents
the backflow of blood entering the aorta and the pulmonary valve prevents the backflow of blood entering the pulmonary artery. The opening and
closing of the atrioventricular and semilunar valves are what make the “lub/dub” sound of a heartbeat. The structure between the two ventricles is
the septum.
A characteristic feature of the fetal mammalian heart is the ductus arteriosus. This short vessel connecting the pulmonary artery to the descending
aorta allows blood to bypass the non-functional lungs.
Respiratory System
Air enters through the external nares, is drawn into the nasopharynx and enters the trachea through an opening in the epiglottis known as the
glottis. The trachea supplies air to the lungs. The trachea is ringed with cartilage so it does not collapse. The enlargement about midway on the
trachea is the larynx (voice box) which contains the vocal cords.
The trachea splits in the chest cavity into two bronchi. Each of these air tubes extends into the lungs and splits into smaller tubes called
bronchioles. The lungs are where oxygen and carbon dioxide are exchanged. Inside each lung is approximately 300 million air sacs called alveoli
where this gas exchange occurs.
The thin muscular diaphragm is the muscle is responsible for drawing air into the chest cavity. Spasms of this muscle result in hiccups.
Sitting on top of the trachea is the V-shaped structure known as the thyroid gland. This gland secretes hormones which control metabolism.
Urogenital System
The two lumps low in the abdominal cavity are the bean-shaped kidneys. Each kidney is made up over 1 million individual filtering units called
nephrons.
Sitting top each kidney is a gland known as the adrenal gland. The adrenal glands release hormones which control metabolism and blood pressure.
They also produce adrenaline which helps an animal respond to stress.
The ureters are the tubes which extend from the kidneys to the bag-like urinary bladder. The urinary bladder temporarily stores liquid wastes
filtered from the blood. The urethra is the tube which carries urine out of the body through the urogenital opening.
Male Reproductive System
Each scrotal sac contains a testis, where sperm are produced. The testes of mammals descend just before birth to the outside of the body. This
procedure is very important, as the ordinary temperature of the human body (98.6°) would kill sperm. The 3-4-degree lower temperature of the
testes outside the body keeps the sperm alive. The coiled tubule surrounding each testis is the epididymis. Immature sperm cells produced in the
testis pass through the epididymis, where they will mature and travel to the ductus deferens. The ductus deferens (vas deferens) transports
mature sperm to the urethra where sperm and urine will be released. At this point, as in humans, the urethra becomes a urogenital duct. The
copulatory structure of the male pig, the penis can be found internally located in the flap with the umbilical cord.
Female Reproductive System
Two oval-shaped ovaries can be found just below the kidneys. The ovaries produce eggs and hormones. Leading from the ovaries are the twisted
oviducts (Fallopian tubes in humans). These are narrow tubes that are attached to the upper part of the uterus at each uterine horn and serve as
tunnels for the ova (egg cells) to travel from the ovaries to the uterus. Conception, the fertilization of an egg by a sperm, normally occurs in the
fallopian tubes. The fertilized egg then moves to the uterus, where it implants into the lining of the uterine wall. The uterus leads to the cervix
which leads to the vagina, which is also known as the birth canal. The urogenital opening is where the urethra joins with the vagina. This cavity
opens to the outside of the animal and is covered by the genial papilla.
Nervous System
The central nervous system consists of the brain and spinal cord. The highly folded outer most part of the brain is called the cerebrum or cerebral
cortex. It controls all the senses and motor processes, especially in things like movement, sensory processing, olfactory senses, languages and
speech, learning and memorizing. The cerebrum has multiple lobes including the temporal, occipital, parietal and frontal. The temporal lobe is
located on the bottom, middle portion of the cortex and is primarily in charge of hearing. The occipital lobe is located on the back part of the
cortex and is responsible for processing visual information. The parietal lobe is located on the mid dorsal part of the cortex and is responsible for
taste, temperature and touch. The frontal lobe is located on the frontal, upper area of the cortex and is responsible for the higher mental
processes such as thinking, and decision making.
The cerebellum works closely with the spinal cord and is the part of the brain responsible for balance and coordination of muscles. It is located
behind the top part of the brain stem (where the spinal cord meets the brain).
Deep inside the center of the brain is the thalamus and hypothalamus. The thalamus is positioned above the hypothalamus and its functions
include relaying sensory and motor signals to the proper lobes of the cerebral cortex and the regulation of consciousness, sleep and alertness. The
hypothalamus is found below the thalamus and is responsible for hunger, thirst and regulating body temperature. The pituitary gland is a pea
sized gland located underneath the hypothalamus. It is considered the master gland because it controls all the other endocrine glands in the body
(thyroid, adrenal)
The brain stem is considered the trunk of the brain and the lower portion of the brainstem where it meets the spinal cord is called the medulla
oblongata. The medulla is the most important part of our brain as it controls the involuntary functions which keep the animal alive. These
functions include breathing, heart rate, swallowing and transferring messages from the brain to the spinal cord. The spinal cord is the main
conduit between the brain and the body. It is through the spinal cord that neural message travel.
Virtual dissections
https://www.whitman.edu/academics/departments-and-programs/biology/virtual-pig
https://www.biologycorner.com/myimages/fetal-pig-dissection/
http://home.apu.edu/~jsimons/Bio101/PigDissectionGuide.htm