ZM

Life and Living: Circulatory and Reproductive Systems

THE CIRCULATORY SYSTEM

  • A common symptom of a heart attack: sharp pain in the centre of the chest that spreads to the jaw, back and left arm.
  • Inherited tendency: many people who suffer a heart attack inherited the tendency from their ancestors.
  • Risk factors for heart attacks: fatty diet, lack of exercise, obesity, smoking and alcohol abuse.
  • Stroke: occurs when the brain is deprived of oxygen. This often happens because of a blockage in the blood vessels that lead to the brain, or when one of these vessels ruptures (tears open). The person may feel weak and confused and can become paralysed in parts of the body.

BLOOD VESSELS

  • Blood vessels are a network through which the heart pumps blood to all parts of the body.
  • There are three typical blood vessels: arteries, capillaries and veins.

Arteries

  • Transport blood at high pressure away from the heart to all body parts.
  • Walls are thick, muscular and elastic to withstand high blood pressure.

Capillary blood vessels (capillaries)

  • Arteries branch into many small, narrow ducts called capillaries within organs.
  • Capillary walls are very thin, so cells are in close contact with the blood.
  • Capillaries supply cells with oxygen and nutrients and remove waste products and carbon dioxide.
  • Capillaries unite again to form veins.

Veins

  • Transport blood at much lower pressure back to the heart.

  • Walls are thinner and less muscular than those of arteries.

  • Veins have valves that allow blood to flow in one direction and prevent backflow.

  • Blood travels through a network of ducts called blood vessels. The fluid moving in the vessels is blood.

  • Blood consists of blood plasma, red blood cells, white blood cells and platelets.

BLOOD PLASMA

  • The liquid part of blood.
  • Mainly consists of water and transports nutrients, waste products and dissolved gases in solution.

CONSTITUENTS OF BLOOD

  • There are three types of blood cells found in blood: Red blood corpuscles, white blood corpuscles and platelets.

Red blood corpuscles (RBCs)

  • They are disc-shaped cells without nuclei.
  • A hollow in the centre gives them a biconcave shape.
  • Formed in bone marrow.
  • Main function: carry oxygen to all parts of the body.

White blood corpuscles (WBCs)

  • White blood corpuscles destroy germs and defend the body against disease (the "soldiers of the body").

Platelets

  • Small fragments of cells that play a key role in blood clotting.
  • Produced in the bone marrow.

HEALTH ISSUES INVOLVING THE CIRCULATORY SYSTEM

High blood pressure (hypertension)

  • Hypertension is a constant high arterial pressure that forces the heart to work harder.
  • Effects: increased workload of the heart, heart enlarges, the heart may not pump blood efficiently, and it can cause a heart attack, kidney failure or a stroke.
  • The high pressure against artery walls can damage them.
  • Normal blood pressure varies throughout the day and rises when we are excited or nervous, or during activity.
  • Risk factors include stress, cigarette smoking, being overweight, lack of exercise and an unhealthy diet.

Heart attack

  • Occurs when a narrowing (stricture) or blood clot develops in one of the vessels supplying the heart muscle with blood.
  • If the stricture or clot is large enough, it can block blood flow to the heart muscle and cause the heart to stop pumping, possibly leading to death.

FUNCTION OF THE CIRCULATORY SYSTEM

  • The circulatory system brings nutrients and oxygen (O₂) to the cells and removes waste products.
  • Main processes:
    • Circulates blood between the heart and the lungs (pulmonary circulation) and between the heart and the rest of the body (systemic circulation).
  • Main components: heart, blood vessels (veins, arteries, capillaries) and blood.

The heart

  • Right atrium → right ventricle → lungs (via pulmonary artery) → left atrium → left ventricle → rest of the body (via aorta).

  • Pulmonary arteries carry deoxygenated blood to the lungs; pulmonary veins return oxygenated blood to the heart.

  • The main veins carry blood back to the heart; the aorta carries blood from the heart to the body.

  • The heart is a hollow muscular pumping organ located in the thoracic cavity, just above the diaphragm, between the two lungs and behind the sternum; its tip is slightly to the left.

  • Internally it has four chambers: two atria (upper chambers) and two ventricles (lower chambers).

  • The two sides are separated by a muscular wall; one-way valves between the chambers keep blood flowing in the correct direction.

  • The left ventricle has a thick muscular wall because it pumps blood at high pressure to the entire body (except the lungs).

  • The right ventricle has a thinner wall because it pumps blood at lower pressure to the lungs.

  • Blood exchanges oxygen and nutrients and removes waste products in capillaries in the body.

  • Blood flows twice through the heart during a full circulation:

    • Deoxygenated blood is pumped from the right side of the heart to the lungs to pick up oxygen.
    • Oxygenated blood returns to the left side of the heart and is pumped to the rest of the body.

  • A simplified flow sequence (pulmonary and systemic circuits):

    • Deoxygenated blood returns from the body to the right atrium via main veins.
    • Right atrium contracts and moves blood to the right ventricle.
    • Right ventricle contracts and sends blood via the heart’s pulmonary artery to the lungs.
    • In the lungs, blood becomes oxygenated and returns to the left atrium via pulmonary veins.
    • Left atrium contracts and sends blood to the left ventricle.
    • Left ventricle contracts and pumps oxygenated blood out through the aorta to the rest of the body.

  • The circulation process provides the exchange of oxygen, nutrients, and waste products between blood and body tissues through capillaries.

THE REPRODUCTIVE SYSTEM

Function

  • The main function of the reproductive system is to produce sex cells (gametes) to ensure the survival of the species.

Main processes

  • Growth: Cells divide and the baby grows and matures.
  • Cell division: Cells divide and reproduce copies of themselves as the organism grows.
  • Sexual maturation: People are sexually mature when sex organs produce sex cells (gametes).
  • Copulation: Also called sexual intercourse; the penis is inserted into the vagina.
  • Ejaculation: The release of sperm from the penis when the muscles lining, the sperm duct and urethra contract.
  • Ovulation: An egg cell (ovum) is released from the ovary.
  • Menstruation: The blood lining of the uterus detaches if fertilisation has not occurred.
  • Fertilisation: The egg and sperm unite; this occurs in the oviduct (fallopian tube) in the female.
  • Implantation: The fertilised egg attaches to the blood lining of the uterus.

Main components

  • The most important main components include the uterus and ovaries in the woman and the testes and penis in the man.
  • Uterus (womb): Found in female individuals; has a thick lining and muscular wall; embryo develops here during pregnancy.
  • Ovaries: Located inside the woman's body in the lower abdomen; produce sex cells called egg cells or ova.
  • Testes: The male sex organs; located in the scrotum; during puberty the testes produce sperm cells.
  • Penis: The external male organ used to transfer sperm to the female.

Health issues involving the reproductive system

  • Infertility: Almost 10% of heterosexual couples struggle to conceive and may not be able to reproduce sexually at all.
  • Foetal alcohol syndrome: When a pregnant mother drinks alcohol during pregnancy, it can cause severe birth defects in the unborn baby; damage is irreversible and affects the child for life.
  • Sexually transmitted diseases: HIV/AIDS, syphilis and gonorrhoea are transmitted through intercourse.

TYPES OF REPRODUCTION

  • Reproduction is the biological process whereby offspring are created from the parent(s).

Sexual Reproduction

  • This process is complex and involves the formation and transfer of gametes, followed by fertilization, formation of the zygote, and embryogenesis (e.g., mammals).

Asexual Reproduction

  • Involves only one parent and the new offspring produced is genetically similar to the parent (e.g., amoeba).