Topic 6.6: Hormones, Homeostasis and Reproduction Flashcards Preview

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Flashcards in Topic 6.6: Hormones, Homeostasis and Reproduction Deck (47)
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Homeostasis is the maintenance of a constant internal environment within physiological tolerance limits
1) A disease ensues if a factor deviates from its normal range


Regulation of physiological processes

Physiological processes are regulated by negative feedback
• An effect is antagonistic (opposite) to the stimulus
• This means the detected change is reversed


Endocrine System

1) It releases chemical messengers (hormones) into the blood to act on distant target cells.
2) The endocrine system works in tandem with the nervous system to maintain physiological balance (homeostasis)


Control of blood glucose concentration

Blood sugar levels are regulated by insulin and glucagon
• These hormones are secreted by cells in the pancreas



1) Secreted by β-cells to lower blood sugar levels
2) Stimulates glucose uptake by the liver and adipose cells
3) Increases the rate of glucose metabolism



1) Secreted by α-cells to raise blood sugar levels
2) Stimulates glycogen breakdown within the liver
3) Decreases the rate of glucose metabolism


Diabetes mellitus

Metabolic disorder that results from a high blood glucose concentration over a prolonged period


Diabetes mellitus Type I

1) Usually occurs during childhood
2) Body does not produce sufficient insulin
3) Caused by the destruction of B-cells
4) Requires insulin injections to regulate blood glucose


Diabetes mellitus Type II

1) Usually occurs during adulthood
2) Body does not respond to insulin production
3) Caused by the down-regulation of insulin receptors
4) Controlled by managing diet and lifestyle


Control of body temperature

Body temperature is regulated by the hormone thyroxin



1) Thermoreceptors (skin) send signals to the hypothalamus
2) Thyroxin is released from the thyroid gland when body temperature is low and increases metabolism
3) Thyroxin production requires iodine and a deficiency will result in goitre


Control of appetite

Appetite suppression is regulated by the hormone leptin



1) Adipose cells secrete leptin to suppress appetite (
2) Leptin binds to receptors located in the hypothalamus


Leptin and Obesity

1) Over-eating causes more fat cells to be produced
2) Over time, obese people become desensitized to leptin and are more likely to continue to over-eat
3) Hence, leptin treatments for obese people are ineffective (obesity linked to leptin unresponsiveness - not leptin deficiency)


Control of circadian rhythms

1) Circadian rhythms are regulated by the hormone melatonin
2) The body’s physiological responses to the 24 hour day-night cycle



1) Photoreceptors (eyes) send signals to the hypothalamus
2) Melatonin is secreted by the pineal gland (in the brain)
3) Melatonin release is inhibited by light (levels high at night)
4) High levels of melatonin promote sleep in diurnal animals


Jet lag and melatonin

1) Changing time zones can disrupt melatonin release
2) It causes headaches, lethargy, and fatigue
3) Melatonin supplements can recalibrate sleep patterns


Reproductive theories

Soil and seed theory
Modern theory


Soil and seed theory (Aristotle)

Males provide all the information for life in a ‘seed’, which forms an egg when mixed with menstrual blood (the ‘soil’)


Modern theory (William Harvey)

1) He dissected deer after the mating season and was unable to identify embryos until several months after mating
2) The ‘soil and seed’ theory was incorrect and that menstrual blood did not contribute to fetal growth


Male sex development

1) Male sex is determined by a gene on the Y chromosome which causes gonads to develop as testes and secrete testosterone
2) Testosterone produces sperm and male sex characteristics


Female sex development

1) Female reproductive organs develop in the absence of this gene
2) Estrogen and progesterone develop female sex characteristics



1) Secreted by the testes
2) Responsible for the prenatal development of male genitalia
3) Involved in sperm production
4) Involved in the development of secondary sex characteristics
5) Maintain the male sex drive (libido)


Estrogen | Progesterone

1) Promote the prenatal development of the female reproductive organs
2) Responsible for the development of secondary sex characteristics
3) Involved in monthly preparation of egg release following puberty (via the menstrual cycle)


Male reproductive system

1) Testis
2) Epididymis
3) Vas deferens
4) Seminal vesicle
5) Prostate gland
6) Erectile tissue
7) Penis
8) Urethra
9) Scrotum



Responsible for the production of sperm and testosterone



1) Site where sperm matures and develops the ability to be motile
2) Mature sperm is stored here until ejaculation


Vas Deferens

Long tube which conducts sperm from the testes to the prostate gland


Seminal Vesicle

Secretes fluid containing:
1) Fructose (to nourish sperm)
2) Mucus (to protect sperm)
3) Prostaglandin (triggers uterine contractions)


Prostate gland

Secretes an alkaline fluid to neutralise vaginal acids