Human Reproduction, Development & Locomotor System
Human Reproduction
Sexual Maturity
- Primary (0-10): Present at birth. Boys have a penis and scrotum, while girls have a vulva.
- Puberty. Secondary Sexual Characteristics (10-14):
- Boys: First sperm production, growth of testes and penis, increased bone and muscle mass, deepened voice, appearance of beard and pubic/underarm hair.
- Girls: First menstruation, breast development, widening of hips, appearance of pubic and underarm hair.
- Adolescence. Maturity (14-20): Need for independence, exploration of feelings and body, sexual desire, seeking emotional support in friends, sometimes conflicting relationships with adults.
- Adulthood. End of Development (20-25 years): Body prepared for reproduction.
Female Gametes: Ovules
Large cells that mature in the Graafian follicle within the ovaries. When the follicle ruptures, the egg is released into the fallopian tubes. The egg is surrounded by a protective layer of cells. If not fertilized within 24 hours, the egg dies.
Male Gametes: Spermatozoa
Produced continuously in the seminiferous tubules of the testes. They mature over several days in the epididymis. Thousands mature each day. During ejaculation, semen (containing sperm, lubricant, and prostate fluid) is released into the vagina. Sperm can remain alive for 3 to 5 days.
Hormonal Cycles in Female Reproduction
Estrogen and Progesterone: Estrogen is produced in the ovaries and is responsible for the development and maintenance of female sexual characteristics. It also induces the formation of the Graafian follicle. Progesterone is produced by the Graafian follicle after ovulation and induces the growth and maturation of the endometrium (uterine lining), where the fertilized egg implants. If fertilization does not occur, the egg dies, the follicle degenerates, progesterone production stops, and the endometrium is shed, causing menstruation.
Fertilization
Ovulation occurs around 14 days after the start of menstruation. The egg can be fertilized for up to 24 hours after ovulation. During intercourse, the penis is inserted into the vagina, and sperm is ejaculated. Sperm travel through the vagina, cervix, uterus, and fallopian tubes. If sperm encounter an egg, one sperm penetrates the egg, and fertilization occurs, resulting in a zygote.
Embryonic Development
The zygote begins to divide, forming a hollow sphere of cells. When it reaches the uterus, it implants in the endometrium (nidation). From this moment, it is called an embryo.
Placenta
The placenta forms and connects the mother and embryo through the umbilical cord. The umbilical cord contains blood vessels (2 arteries and 1 vein) that transport nutrients and waste between the mother and embryo. The embryo is also enclosed in the amniotic sac, filled with amniotic fluid.
Fetal Development
- 1st Trimester: Head, trunk, and limbs develop, along with internal organs (circulatory, excretory, and reproductive). By the 3rd month, the heart beats. The embryo is now called a fetus.
- 2nd Trimester: The nervous system matures, and the fetus responds to stimuli and makes movements. The circulatory and excretory systems are completed. By the 4th month, the sex can be determined.
- 3rd Trimester: Organs mature, the fetus grows in size and weight, and fat develops under the skin. The fetus moves a lot and has periods of sleep and wakefulness.
Birth
The cervix dilates, the uterine muscles contract rhythmically, the amniotic sac ruptures, and amniotic fluid is released. The fetus is pushed out through the cervix and vagina by uterine contractions. The umbilical cord is cut, and the placenta is expelled.
Sterility
- Male: Insufficient sperm production, immature sperm, or disorders that prevent sperm from reaching the egg.
- Female: Obstruction of the fallopian tubes, absence of ovulation, or inability of the zygote to implant in the endometrium.
Assisted Reproduction Techniques
- Artificial Insemination: Used when the male is sterile. Sperm is introduced directly into the uterus.
- In Vitro Fertilization (IVF): Used when there are problems with ovulation or implantation. Eggs are extracted from the woman and fertilized with sperm in a laboratory. The resulting embryos are then implanted in the uterus.
The Locomotor System
The locomotor system allows for movement and provides support. It consists of:
Skeletal System
The passive part of the locomotor system, formed by the skeleton (bones, joints, and ligaments). Bones provide support, shape, and protection. The skeleton is divided into the head, trunk, and limbs.
Bones
Bones are living and growing tissues composed of calcium, phosphorus, and collagen. They are made of compact bone tissue (outer layer) and spongy bone tissue (inner layer). There are three types of bones:
- Short bones: Rounded shape, e.g., vertebrae.
- Flat bones: Flat shape, protective function, e.g., skull bones.
- Long bones: Cylindrical shape, support and movement function, e.g., femur.
Bone Growth (Ossification)
Before birth, bones are made of cartilage. Cartilage is gradually replaced by bone tissue until growth is complete (around age 16 in girls and 18 in boys).
Joints
Joints are where bones connect. There are three types of joints:
- Immobile joints: Do not allow movement, e.g., sutures in the skull.
- Slightly mobile joints: Allow limited movement, e.g., joints between vertebrae.
- Mobile joints (synovial joints): Allow a wide range of movement, e.g., knee joint.
Muscular System
The active part of the locomotor system, formed by muscles and tendons. Muscles produce movement. There are three types of muscles:
- Smooth muscles: Slow, involuntary contractions, found in the walls of internal organs.
- Cardiac muscle: Fast, involuntary contractions, found in the heart.
- Skeletal muscles: Fast, voluntary contractions, attached to bones.
Skeletal Muscle Classification
Skeletal muscles are classified by shape (e.g., annular, plane, orbicular, spindle) and function (e.g., flexors, extensors, abductors, adductors, pronators, supinators, elevators, depressors, sphincters).
Infectious Diseases
Infectious diseases are caused by pathogens (fungi, viruses, bacteria, protozoa) that enter the body and reproduce, causing damage. Pathogens can be transmitted through air, contaminated objects, direct physical contact, or ingestion of contaminated food or water.
Agents Causing Infectious Diseases
- Fungi: Some are parasites that feed on human tissues, causing skin infections (e.g., candidiasis).
- Protozoa: Found in contaminated water or food or transmitted by insects. They reproduce in the body, causing disorders like malaria.
- Bacteria: Can enter through wounds, contaminated food, etc., causing infections like pneumonia.
- Viruses: Protein capsules containing DNA or RNA that infect cells and replicate, causing diseases like the flu.
Body’s Defenses
- Physical barriers: Skin and mucous membranes prevent pathogens from entering the body.
- Nonspecific immune response: Phagocytes (white blood cells) engulf and destroy pathogens that have entered the body.
- Specific immune response: Lymphocytes (another type of white blood cell) recognize and attack specific pathogens. They produce antibodies that neutralize antigens (foreign substances) on the pathogens.
Treatment and Prevention of Infectious Diseases
- Treatment: Antifungal medications for fungal infections, antibiotics for bacterial infections, specific chemicals for protozoa, and antiviral medications or antibodies for viruses.
- Vaccines: Inactivated or weakened pathogens are injected to stimulate the immune system to produce antibodies and become immune to the disease.
Noninfectious Diseases, Injuries, and Damage
Noninfectious diseases are caused by factors other than pathogens, such as metabolic deficiencies, lack of oxygen, or cell proliferation. Examples include diabetes, osteoarthritis, autoimmune diseases, and cancer.