N-Trivia
| Fertilization Posted: 24 Dec 2010 06:18 PM PST 
Definition Fertilization is the union of an ovum and a spermatozoon. It is also called conception, impregnation or fecundation and usually occurs in the outer third of the fallopian tube, the ampullar portion. Important facts about fertilization - An ovum is capable of fertilization for 24 to 48 hours. After this time, the ovum atrophies and becomes nonfunctional.
- The functional life of a spermatozoon is about 48-72 hours.
- The normal amount of semen in an ejaculation is about 3-5 cc (average: 2.5 ml).
- The number of sperms in an ejaculate is 50-200 million per milliliter or an average of 400 million sperm per ejaculation.
- Spermatozoon reaches the cervix within 80 seconds and the outer end of the fallopian tube within 5 minutes.
Sequential Events of Fertilization - An ovum is surrounded by a ring of polysaccharide called the zona pellucida and a circle of cells called corona radiate as it is forced out of the graafian follicle of the ovary during ovulation. These surrounding cells serve as a protective buffer of the ovum against injury.
- The fimbrae, fine, hair-like structures that line the openings of the fallopian tubes initiate currents that propel the ovum and surrounding cells into the nearby fallopian tube.
- The ovum is propelled along the length of the tube through the peristaltic action of the fallopian tube and the movements of cilia.
- It is easier for spermatozoon to penetrate the vagina as the viscosity of cervical mucus is decreased.
- Spermatozoon moves through the cervix and the body of the uterus and into the fallopian tubes to the ovum by means of their tails (flagella) and uterine contractions.
- Capacitation, a process where sperm-binding receptor sites are revealed, takes place right before fertilization.
- As the sperms move toward the ovum and cluster around the ovum's protective layer of cells HYALURONIDASE is released and dissolves the layer of cells that protects the ovum.
- Right after penetration, the chromosomal material of the ovum and sperm combine. The resulting structure is termed zygote (fertilized ovum).
- The ovum always contains the X-chromosome. A sperm contains either an x or Y chromosome. If an X-carrying sperm fertilizes an ovum the resulting structure will have two X chromosomes and the child will be female (XX). If a Y-carrying chromosome fuses with an ovum, the resulting structure will have an X and Y chromosome and the child will be male (XY).
image from chariho.k12.ri.us Related posts: - Stages of Fetal Development
- Intrauterine Reproductive Development
- Ambiguous Genetalia
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| Bilirubin Conjugation Posted: 24 Dec 2010 06:11 PM PST 
Definition of terms Bilirubin – a product of hemoglobin degradation and is toxic once it accumulates in the body. Unconjugated bilirubin – also termed as indirect bilirubin. This type of bilirubin is soluble in fat but not in water. Because it is fat soluble it may be absorbed by the subcutaneous fat, causing the yellowish discoloration of skin or jaundice. Conjugated bilirubin – also termed as direct bilirubin. This type of bilirubin is water soluble. It is in this form that bilirubin is excreted out of the body. Conjugated bilirubin is less toxic that the other type. Factors Contributing to Bilirubin Production Approximately 6-8 mg/kg of bilirubin is produced in infants each day during the first 2 weeks of life and adults have a rate of 2.5 times than that of neonates. In adults RBC's life span is 120 days. In preterm infants the RBCs last only for 60-70 days and 80-100 days in term infants. Neonates' erythrocytes are more fragile and susceptible to damage and injury than those of adults. Red blood cells break down faster in neonates and thereby producing more amount of bilirubin than adults. The liver normally produces adequate amounts of the enzyme glucoronyl transferase to conjugate bilirubin and be excreted out of the body. The newborn's immature liver may not be able to produce adequate amounts of this enzyme resulting to the limited amount of bilirubin that can be conjugated. Two factors may result to high levels of unconjugated bilirubin: - Sterile intestines of newborns at birth – conjugated bilirubin cannot be reduced to urobilirubin or stercobilin to be excreted out of the body without the intervention of intestinal flora.
- Large amount of beta-glucuronidase enzyme in the newborn's intestines – beta-gucuronidase changes bilirubin back to the unconjugated state.
Feeding the newborn helps to establish a normal intestinal flora and promotes the passage of meconium. Meconium contains high amounts of bilirubin. In cases where feeding is delayed or meconium is not excreted the beta-glucuronidase exposure in the intestine is prolonged thus increasing the chance of converting the unconjugated bilirubin to the conjugated state. Trauma at birth (e.g. bruising) results to the increased hemolysis of RBC. Hemolysis of RBC results to the production of additional bilirubin. Bilirubin conjugation - Unconjugated bilirubin (UCB) is released into the bloodstream and attaches to the albumin binding sites in the plasma to be carried to the liver.
- Once unconjugated bilirubin is already at the liver, the enzyme glucuronyl transferase in the smooth endoplasmic reticulum of liver cells binds the UCB to ligandin and other proteins to become a conjugated bilirubin.
- Conjugated bilirubin (CB) is then excreted into the bile and into the duodenum.
- As CB reaches the intestines, the normal intervenes on conjugated bilirubin and converts it to urobilinogen and stercobilin.
- Urobilinogen and stercobilin are excreted in the stools and some urobilinogen are excreted by the kidneys.
image from ahdc.vet.cornell.edu Related posts: - Neonatal Gastrointestinal Adaptation Processes
- Neonatal Immune System Adaptation Processes
- Online Nursing Care Plan – Hyperbilirubinemia (Jaundice)
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| Neural Tube Defects Posted: 24 Dec 2010 05:33 PM PST 
Definition  anencephaly Neural tube defects (NTDs) are birth defects of either the brain or spinal cord. This group of disorders is characterized by an opening in the brain or spinal cord occurring at an early stage of human development. Incidence NTDs are one of the most common birth defects. - Female predominance is observed. About 60-70% of all cases are females.
- The incidence of neural tube disorders have fallen dramatically in recent years from 3 cases in every 1000 births to only 0.6 cases in every 1000 births.
Risk Factors - Cigarette smoking and maternal exposure to cigarette smoke
- Maternal diabetes
- Maternal obesity
Causes - Polygenic inheritance pattern
- Poor maternal nutrition
- Maternal diet deficient in folic acid
- Intake of folate antimetabolites (methotrexate)
- Use of teratogens
Review of the related anatomy and physiology The central nervous system is the first observable structure in a human embryo. This embryo passes through 23 stages of development after conception. Two processes work in order to form the CNS: - Primary neurolation
 - Secondary neurolation
Primary neurolation is the formation of the neural structures into a tube. This forms the brain and the spinal cord. Secondary neurolation is the formation of the lower spinal cord. This gives rise to the lumbar and sacral elements. Types of Neural Tube disorders - Anencephaly – absence of the cerebral hemispheres. Closure of the anterior neuropore occurs at stage 11 at about 23-26 days age of gestation. Failure of this point to close results to anencephaly. Children with this disorder cannot survive because of the absence of cerebral function. These children may only survive for a number days because the respiratory and cardiac centers are located in the intact medulla.
- Microcephaly – characterized by a slow brain growth. Generally, infants with this disorder are cognitively challenged because of the lack of functioning brain tissue. The head circumference of affected neonates is decreased.
- Spina Bifida Occulta – occurs when the posterior laminae of the vertebra fail to fuse at 26-28 days age of gestation. The most common site is the fifth lumbar or sacral level though it may occur at any point along the spinal canal.
- Meningocele – herniation of the meninges through the unformed vertebrae of the spinal cord. Generally, it occurs at the lumbar area but it can be present anywhere along the spinal canal. It is characterized by an appearance of an orange-shaped mass at the center of the back.
- Myelomeningocele – herniation of the spinal cord and meninges through the unformed vertebrae. The spinal cord ends at the pint of protrusion, thus, motor and sensory function beyond the point of herniation is absent.
images from neuropathologyweb.org, bio.davidson.edu, neurosurgery.ufl.edu Related posts: - Anencephaly
- Encephalocele
- Accutane (Isotretinion) on Birth Defects
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