Human Behaviour week 9 #1 Physical Development: From conception to end of life (Duration: 28:00)

Developmental Psychology Defined

• Developmental psychology studies how humans develop and change over time.
• A lifespan developmental perspective examines changes from conception to death.
• It explores how individuals feel, think, and act at different ages.
• Considers the influence of both nature (genetics) and nurture (environment) on development.

Prenatal Development

• Development begins in the prenatal period.

Conception

• Fertilization of the egg by sperm.
• Typically, one sperm from approximately 300 million in the semen swims through the cervix and binds to an egg.
• The sperm cell and egg nucleus disintegrate and release chromosomes, forming a zygote.
• Zygote: A single cell containing the necessary genetic information to develop into a human being.
• Conception can also occur through intrauterine insemination and IVF, which may assist same-sex, non-binary, and trans couples or those experiencing fertility issues.

Germinal Stage (First Two Weeks)

• The zygote divides and forms a blastocyst.
• Blastocyst differentiates into three layers:
  • Ectoderm: The upper layer that develops into skin, sensory organs, and the nervous system.
  • Endoderm: The lower layer that forms organs like the digestive system, liver, and respiratory system.
  • Mesoderm: The middle layer that becomes the dermis, muscles, skeleton, and excretory systems.
• The placenta, umbilical cord, and amniotic sac form from blastocyst cells.
• Implantation: About a week after conception, the blastocyst embeds into the uterine wall, becoming an embryo, marking the beginning of prenatal development.

Embryonic Stage (Weeks 3-8)

• Growth occurs in two patterns:
  • Cephalocaudal Pattern: Head to tail development.
  • Proximodistal Pattern: From the center out.
• Vital organs develop earlier than extremities.
• Week 3: Head, brain, and circulatory system start forming.
• Week 4: The embryo is about 2 cm long; initial signs of the spinal cord, limb formation, digestive system, and brain differentiation.
• Week 5: Hands and lungs begin to form.
• Week 6: The head grows larger, further brain maturation, and limb development.
• Week 7: Muscles form and the cerebral cortex begins to develop.
• Placenta: Facilitates the exchange of oxygen, nutrients, and waste between the mother and the embryo.
• Umbilical Cord: Connects the embryo to the placenta, providing nutrients and removing waste.
• Amniotic Sac: Envelops the embryo, shielding it from shocks and maintaining a stable environment.

Fetal Stage (Week 9 to Birth)

• The longest period of prenatal development.
• The embryo becomes a fetus with major structural differentiation completed.
• Development of finer features like fingers, eyelids, and eyebrows.
• Eyes undergo significant growth, with eyelids fusing shut around ten weeks until the eyes mature at about 16 to 20 weeks.
• Rapid increase in size, physical features becoming more proportionately human by 16 weeks.
• The fetus exhibits reflexive responses to touch.
• Prenatal development is divided into trimesters.
• Second Trimester: The hands and feet are fully formed, the eyes can open and close, and the fetus can hear. The lungs begin practicing breathing movements, and features like nails, hair, and sweat glands are emerging around 16 to 18 weeks. The pregnant women often start to feel the movement of the fetus in the womb, and that frequency will increase until about 32 weeks, when it will stabilize until birth.
• Vernix: A protective substance that coats the skin, along with fine hair.
• Brain neurons continue to grow, as do glial cells, which support and feed these neurons.
• Seventh Month (Third Trimester): The fetus measures around 30 to 35 cm and weighs around 2 to 3 kg; it can perform essential functions like crying, breathing, swallowing, digesting, and sucking its thumb.
• Viability: Typically achieved by 32 to 34 weeks, meaning the fetus could survive outside the womb if born prematurely. Modern health care and neonatal intensive care units may allow survival as early as 22 weeks, though this may lead to neurological impairment and developmental delay.
• Eighth Month: The fetus weighs between 3 and 4 kilos and develops a layer of body fat for temperature regulation post-birth.
• Ninth Month: Around 50 cm long and 3.4 kg in weight, growth in size ceases, but fat continues to be stored, internal organs become more efficient, and the heart rate increases in readiness for birth and life outside the womb.

Physical Development in Infancy (Post-Birth)

Sleep Patterns

• Newborns sleep an average of 15 hours daily (range: 9-20 hours).
• At six months, sleep reduces to around 13 hours on average.
• At 24 months, it decreases to approximately 12 hours.
• Newborns divide sleep time equally between active REM sleep and non-REM sleep (crucial for brain growth).
• Non-REM sleep is characterized by rhythmic breathing and minimal muscle movement.
• Infants wake frequently (every 2-3 hours), affecting parents' sleep.
• Perinatal research explores sleep programs to help families manage infant sleep patterns.

Visual Development

• Infants have limited vision at birth (lack visual acuity).
• They improve visual abilities quickly, focusing best at 20-25 cm.
• Visual acuity reaches adult-like levels by age two.
• Infants prefer scanning and tracking moving objects, especially human faces.
• They prefer upright face-like patterns and recognize a mother's face early as two months old.
• Face perception continues to develop, with infants as young as three months making fine distinctions between facial features and recognizing emotional expressions by about five months old.

Auditory Development

• Fetuses can hear low-frequency sounds in utero.
• Babies have binaural input at birth, enabling sound localization (vital for survival).
• Sensitivity to higher frequency sounds develops until about six months.
• The ability to detect loudness differences improves and is fully developed at about six months.

Motor Development

Reflexes

• Innate, automatic responses to stimuli, crucial for survival and adaptation.
• Categorized into primitive, postural, and locomotor reflexes.
• Examples:
  • Sucking (aids in feeding).
  • Moro reflex (embracing reflex).
• Some reflexes persist throughout life (blinking, breathing, yawning, swallowing), while others disappear in the first six months.
• Reflexes facilitate the acquisition of food and aid in the infant's survival and development.

Motor Skills

• Voluntary movements of the body.
• Categorized into gross motor skills (large muscles) and fine motor skills (smaller muscles).
• Examples:
  • Gross motor skills: crawling, walking, jumping.
  • Fine motor skills: reaching and grasping.
• Development follows cephalocaudal and proximodistal principles.
• Milestones may deviate from these trends.
• Individual variations exist; some babies may skip crawling.
• Cultural and gender variations are observed.
• African cultures promote early gross motor skill development.
• Child-rearing practices can influence motor skill development, such as propping infants in sitting positions.

Physical Development in Childhood and Adolescence

Early to Middle Childhood

• Refinement of gross and fine motor skills.
• Improved balance and coordination (ages 2-6).
• Children can run, jump, hop, skip, and climb.
• They can ride bicycles and throw and catch balls.

Middle Childhood

• Refinement of early skills with increased speed, accuracy, and endurance.
• Mastery of skills like running, jumping, throwing, and catching.
• Introduction to organized sports.

Adolescence

• Further refinement of motor skills.
• Driven by participation in sports or physical activities.
• Increased strength, speed, and agility.
• Specialization in specific sports.
• Development of more complex movements and strategies in sports.

Nutrition and Physical Activity

• Children need a balanced diet with sufficient kilojoules, protein, vitamins, and minerals.
• Malnutrition hinders physical and cognitive development, with long-term effects across developmental domains.
• Linked to diminished exploratory behavior, social interaction, memory impairments, and academic performance.
• Stunted growth is associated with adverse psychosocial outcomes.
• Early childhood is a critical development window for later obesity.
• Sedentary activities increase the likelihood of being overweight or obese.

Puberty

• Physical changes that result in the completion of sexual development.
• Initiated by the release of hormones from the pituitary gland.
• Stimulates the testes (male) and ovaries (female) to produce sex hormones (androgens, testosterone, and estrogen).
• Hormone levels drive sexual development.
• Females: Estrogen promotes primary sexual characteristics (enlargement of ovaries, uterus, vagina, etc.).
• Estrogen and progesterone facilitate ovum production and regulate the menstrual cycle.
• The first menstrual period typically occurs around age 12.
• Males: Testosterone triggers primary sex characteristics (enlargement of penis and scrotum) around age 12.
• The testes have the seminal vesicles responsible for sperm production, which gradually matures along with the prostate gland to facilitate ejaculation, typically occurring during the male growth spurt around ages 13 to 14.
• Secondary sex characteristics (pubic hair, underarm hair, voice deepening) also develop.
• Puberty in males typically concludes by around age 15.

Physical Development in Adulthood

Early Adulthood (18-28)

• Completion of physical growth.
• Gradual and less pronounced changes.
• Possible increases in height and fat accumulation.

Middle Adulthood (30s)

• Subtle physical deterioration.
• Reductions in muscular strength and sensory capabilities.
• Cardiovascular health declines.
• Maximum heart rate decreases by 5-10 beats per decade.

Health-Seeking Behaviors

• Eating a diet low in cholesterol, fats, calories, and additives, and high in fiber, fruits, and vegetables.
• Physical exercise (70-85% of maximum heart rate, 20-30 minutes, three times per week).
• Regulating stress (mind and body response to challenges).

Health-Compromising Behaviors

• (Not detailed due to time constraints—the original source said).

Physical Development in Midlife and Late Adulthood

Midlife

• Women reach menopause on average in the early 50s (range: 40s to later).
• Menopause lasts for several years and can include negative symptoms like hot flushes and irritability; some women report menopause to be a positive experience.
• Men remain fertile for the rest of their life.

Late Adulthood and Aging

• Physical appearance changes: greying and loss of hair, wrinkling of skin.
• Vision and hearing changes: reduced ability to perceive contrast, difficulty adapting to dark environments, and hearing loss.
• Ageism: Discrimination against people because they are old.