Hormones
- An endocrine gland secretes a hormone, which is a chemical messenger. It always travels in blood to its target organs.
- Hormones regulate the functions of many organelles and coordinate many processes in the body.
Pituitary Gland:
- The 'master gland' regulates other endocrine glands.
Thyroid Gland:
- Produces hormone Thyroxine (TSH)
→ Regulates rate of metabolism.
→ Excess → hyperactivity
→ Deficiency → Overweight and sluggishness
Adrenal Gland:
- Produces adrenaline → 'fight/flight' response, which results in:
- Increased heart and breathing rate.
- Blood diverted to the muscles.
- Increased respiration and blood glucose levels.
Pancreas:
- Insulin: Acts to decrease blood glucose.
- Glucagon: Acts to increase blood glucose.
Ovaries:
- Oestrogen: It is responsible for controlling the development of female sexual characteristics and regulating the menstrual cycle.
- Progesterone: Preserves the lining of the uterus during certain stages of menstruation.
Testes:
- Produces testosterone.
- It fosters the growth of masculine sexual traits.
- All above from the pituitary gland.
- Usually the body reacts slowly to hormones as they coordinate long-term body changes, e.g., growth hormone, but some hormones act quickly, e.g., adrenaline.
Process:
Adrenaline
Heart:
- Heart rate increases:
→ As more blood, carrying glucose and oxygen, flows around the body, cellular respiration may increase.
Lungs:
- Breathing rate increases:
→ To increase blood oxygen and eliminate CO₂ through increased respiration.
Liver:
- More glycogen converted to glucose:
→ Increase the amount of glucose in the blood to facilitate aerobic breathing.
Muscles:
- Increased blood flow supplies more glucose and oxygen.
- Muscle cells can respire more actively in response to 'fight, flight, or fright' and be prepared to move.
Pancreas:
- The release of more glucagon results in a reduction in insulin production.
- Glucagon increases the breakdown of glycogen to glucose in the liver and muscles.
Brain:
- Increased blood supply:
→ It enhances the supply of glucose and oxygen to the brain, enabling it to make survival-related decisions.
Cortisol:
- Stress hormone:
→ The adrenal gland releases another hormone in response to fear, which acts much slower than adrenaline but has much longer-lasting effects.
Negative Feedback
- The control system reverses any deviation from the optimal level. 
- Negative feedback prevents a system from becoming overactive.
- The system's own products hinder its performance.
Hormone Interactions:
- The nervous system and endocrine system can work together.
- E.g., when we get a fright, the brain sends signals to the adrenal glands to release adrenaline.
→ This causes a fight-or-flight response.
Different hormones can also work together.
→ E.g., insulin, glucagon, thyroxine, and adrenaline are all involved in glucose metabolism.
→ E.g., LH, FSH, oestrogen, and progesterone all regulate the menstrual cycle.
Human Reproduction
Male:
Female:
Fertilisation
It happens in oviducts.
The zygote moves towards the uterus, where mitosis occurs until a ball of cells forms the embryo.
- Uterus lining remains thick during the gestation period. Therefore, your hormones change, and levels of progesterone stay high.
- When the embryo is 16/32 cells, it sinks into the uterus lining and implants. Placenta forms a while later.
Menstrual Cycle
- The uterus prepares for pregnancy during the monthly cycle of egg production and release.
→ Last average: 28 days.
The cycle is controlled by four hormones:
Oestrogen: Ovary
Progesterone: Ovary
LH (Luteinising Hormone): Pituitary
FSH (Follicle Stimulating Hormone): Pituitary
Day 1: First day of period.
Day 4/5: Menstruation: The uterus lining breaks down, and a follicle begins to develop in the ovary.
Day 7-10: The follicle becomes a corpus luteum.
Day 9/10: Glands continue to develop.
Day 10/11: In the event of a fertilised egg, the lining (endometrium) begins to grow.
Day 14(ish): Ovulation:
→ The ovary releases the egg.
→ After releasing the egg, the follicle, known as the corpus luteum, begins to thicken.
Day 20/21: Uterus lining starts to thicken.
→ Corpus luteum develops.
→ The egg travels along the oviduct to the uterus.
Day 27: Without fertilisation, the corpus luteum disintegrates.
- Corpus Luteum: After ovulation, the follicle produces this gland, which secretes hormones.
- Start of the cycle: FSH released from the pituitary.
- Stimulates follicle production/egg formation.- As the egg develops, the follicle begins to secrete oestrogen.
- Oestrogen inhibits FSH production (negative feedback).
- Oestrogen prepares the uterus for a fertilised egg by building up a spongy lining.
- High estrogen levels cause a "surge" of LH from the pituitary.
- LH surge causes ovulation.
- The corpus luteum, also known as the gland, is the follicle that releases the egg.
- The corpus luteum secretes progesterone.
- Progesterone maintains the thickness of the uterus lining.
- Progesterone inhibits FSH.
- If the egg isn't fertilised, the corpus luteum degenerates and progesterone levels fall.
- This triggers menstruation.
- During pregnancy, progesterone is continually produced.