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Hormones, homeostasis and reproduction

Topic 6
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6

Biology SL

➢ Its target cells are in the hypothalamus of the brainstem
➢ People who are obese are known to have a greater level of leptin circulating in their
bloodstream
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Their hypothalamus has become “desensitized”

Melatonin
➢ It’s produced by a very small gland in the brain called pineal gland
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It helps regulate our 24-hour cycle of activity (circadian rhythm)

➢ We have very little melatonin during the day
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From there it goes to veins and then to
hepatic portal vein which leads to the liver
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The concentration of glucose in the hepatic portal vein varies

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Blood levels fluctuate to a large extent too

➢ Hepatocytes are liver cells that process blood
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Triggered into action by insulin and glucagon
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The 2 hormones are antagonistic

Glucose rises
➢ In the pancreas there are cells known as β cells that produce the hormone insulin
➢ All cells are exposed to insulin, as it opens protein channels in their plasma
membrane so glucose can diffuse into them
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Hormones, homeostasis and reproduction
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Topic 6
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6

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Poor wound healing and possibly gangrene

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Kidney failure

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Nerve damage

Biology SL

Human reproduction
➢ Fertilization occurs when a haploid male gamete (sperm) meets a haploid female
gamete (egg)
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Promotes variation

➢ Hormones play a key role in both the development of sexual dimorphism and the
regulation of sexual physiology

Male structure

Function

Testis

Sperm are produced here in small tubes

Epididymis

Where sperm become mature

Scrotum

Sacs that hold the testis

Vas deferens

A muscular tube that carries mature sperm

called seminiferous tubules

from the epididymis to the urethra during
an ejaculation

Seminal vesicles

Glands that produce seminal fluid

Prostate gland

Produces much of the seminal fluid

Penis

Organ that becomes erect due to blood

including carbohydrates for the sperm

engorgement to facilitate ejaculation
Urethra

The tube via which the semen leaves the
penis

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Hormones, homeostasis and reproduction

Topic 6
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6

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Enlargement of larynx/deepening of voice

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Increased muscle mass

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Enlargement of penis

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Growth of facial, underarm, chest and pubic hair

Biology SL

Menstrual cycle

➢ Menstrual cycle is a hormonal cycle that lasts on average 28 days, which times the
release of an ovum for possible fertilization and later implantation into the
endometrium
➢ The implantation will occur when the endometrium is rich with blood vessels
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If there i

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