Biology VIII: Locomotion, Reproduction, and Development

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Support and Movement

Skeletons: hydrostatic skeleton, exoskeleton, endoskeleton. The human skeleton has an axial part (skull, vertebral column, ribs, sternum) and an appendicular part (limbs and girdles). Bone structure (compact and spongy bone; marrow), cartilage, ligaments, and tendons.
Joints: fixed, slightly movable, and synovial (hinge at the elbow and knee, ball-and-socket at the shoulder and hip, pivot, gliding).
Muscle types: skeletal (striated, voluntary), smooth (involuntary), and cardiac. Muscles work in antagonistic pairs.
Sliding filament theory: a nerve impulse releases Ca²⁺ in the muscle fibre; Ca²⁺ binds troponin, moving tropomyosin and exposing binding sites on actin; myosin heads form cross-bridges and pull the actin filaments using ATP, shortening the sarcomere. Energy for contraction comes from ATP, creatine phosphate, and respiration.
Disorders: osteoporosis, arthritis, muscular dystrophy, fractures.

Human Reproduction

Male system: testes (seminiferous tubules produce sperm with the help of Sertoli cells; Leydig cells produce testosterone), epididymis, vas deferens, seminal vesicles, prostate gland, urethra. Spermatogenesis under FSH, LH, and testosterone.
Female system: ovaries, oviducts (fertilization), uterus, cervix, vagina. Oogenesis begins before birth; one egg is usually released per cycle.
Menstrual cycle (about 28 days): FSH stimulates follicle growth; oestrogen rises; an LH surge triggers ovulation (about day 14); the corpus luteum produces progesterone; if there is no pregnancy, hormone levels fall and menstruation occurs.
Fertilization in the oviduct; the zygote divides and the blastocyst implants in the uterine lining. The placenta exchanges nutrients, gases, and wastes, and produces hormones (hCG maintains early pregnancy). Pregnancy lasts about 40 weeks. Birth involves positive feedback with oxytocin; lactation is controlled by prolactin and oxytocin.
Contraception: barrier, hormonal, intrauterine devices, surgical, and natural methods; each has advantages and risks. Infertility and assisted reproduction (IVF).
Sexually transmitted infections (such as HIV, syphilis, gonorrhoea, chlamydia, hepatitis B) and prevention. Approach this subject with maturity, accuracy, and respect.

Development

Cleavage, blastula, gastrula (three germ layers: ectoderm, mesoderm, endoderm), organ formation, growth. Stages of human development: embryo and fetus. Factors affecting development: nutrition, drugs, infections (rubella), alcohol, and smoking. Growth is regulated by hormones.

Common Mistakes

Reversing the roles of FSH and LH.
Saying that fertilization occurs in the uterus.
Forgetting that the corpus luteum secretes progesterone.

CHAPTER 11