Human Anatomy: Skeleton, Muscles, and Reproductive Systems
The Human Body: A Concise Overview
The Skeletal System
Axial Skeleton
- Skull
- Thorax
- Spinal Column
Appendicular Skeleton
- Upper Limbs
- Lower Limbs
Cartilage
Softer than bone, composed of cartilaginous tissue. Found in the nose, ears, intervertebral discs, joints, and embryonic skeleton.
Joints
Structures that connect two bones.
Parts of a Joint:
- Ligaments: Connect bones.
- Cartilage: Covers and prevents friction.
- Synovial Cavity: Space filled with a viscous lubricant fluid.
Muscle Structure
- Muscle Fascicle: Structure formed of several muscle fibres.
- Perimysium: Layer of connective tissue that covers each muscle fascicle.
- Endomysium: Layer of connective tissue that surrounds each muscle fibre.
- Epimysium: Layer of connective tissue that surrounds the muscle.
- Muscle: Structure formed of several muscle fascicles.
- Tendon: Strong structure of connective tissue that connects the muscle to bone and transmits the muscle contraction to bone, generating movement.
Types of Muscles
- Fusiform
- Flat
- Circular
Stages of Life
- Childhood
- Adolescence: Begins with puberty.
- Adulthood
Physical Changes During Adolescence
Secondary sex characteristics are influenced by hormones (pituitary + gonads).
Reproductive Systems
Male Reproductive System
- Penis: Responsible for depositing sperm in the vagina.
- Testicles: Essential for sperm maturation, located outside the body.
- Genital Tract: Formed of the ducts that take sperm to the outside of the body: Epididymis, Urethra, Vas deferens.
- Accessory Glands: Secrete substances that mix with sperm to form semen, thanks to Seminal vesicles, Prostate gland, and Cowper’s gland.
Female Reproductive System
External Genitalia
Organs combine to form the vulva: The outside part is formed of two folds of skin (labia majora) that cover two thinner folds called labia minora. The clitoris is an organ near the top junction of labia minora, equivalent to the male glans.
Ovaries
Suspended in the abdominal cavity by small ligaments. They produce eggs and female hormones (oestrogens and progesterone).
Parts of the Ovaries:
- Medulla
- Cortex: Contains spherical cavities (follicles) that contain immature eggs called oocytes. During the menstrual cycle, mature follicles release their eggs and break down to form the corpus luteum.
Genital Tract
Formed of the ducts that take the eggs to the outside of the body:
- Fallopian Tubes: Connected to the ovaries by a section called the infundibulum, which collects the eggs.
- Uterus: Hollow muscular organ. The narrow section at the bottom is the cervix, connected to the vagina. The wall is formed of a thick layer of smooth muscle tissue (myometrium). Inside, it is covered with a layer of epithelial cells (endometrium) that contains many blood vessels.
- Vagina: Elastic duct formed of walls of muscle. Connects the cervix to the outside of the body. Glands on the vaginal walls secrete lubricants to help the penis enter the vagina. The external vaginal opening is partially covered by a membrane called the hymen.
Formation of Gametes
Formation process: Gametogenesis (Spermatogenesis / oogenesis). Gametes contain half the number of chromosomes (23) of normal body cells (46) through a special process of cell division called Meiosis.
Ovarian Cycle
- Follicular Phase (Days 1-14): FSH (pituitary gland) stimulates ovaries and the maturation of a follicle (and its oocyte). The mature follicle produces oestrogens.
- Ovulation (Day 14): High level of FSH + oestrogens. The pituitary releases LH, the follicle breaks, and releases an egg into the Fallopian tubes. This is the fertile period.
- Luteal Phase (Days 15-28): If no fertilisation occurs, the period starts (approximately day 28). The broken follicle becomes the corpus luteum, which secretes progesterone.