Hormones & Behaviour

Question 1

How can information be transmitted between animal cells?

Answer 1

Hormone signalling
Neurotransmitters
- substances released by neurons & are received by adjacent neurons & alter their membrane potential
Pheromones
- substances released by an individual as scent signals for others

Question 2

What is the Anterior pituitary’s role in hormone production?

Answer 2

Hormones from the hypothalamus reach the anterior pituitary gland via a network of blood vessels that run down through pituitary stalk.
Hormones produced here are referred to as ‘tropic’, they stimulate processes such as: control the gonads, production & regulation of growth hormone, control of milk production, etc.

Question 3

What kind of processes do hormones produced by the anterior pituitary stimulate?

Answer 3

• control gonads,
• production & regulation of growth hormones
• control of milk production

Question 4

How does the hypothalamus manage to maintain fairly constant levels of hormones?

Answer 4

Through operating a negative feedback system

Question 5

What is meant by a negative feedback system (in terms of the hypothalamus)?

Answer 5

• The Hypothalamus excites the Anterior Pituitary with thyroid stimulating hormone-releasing hormone (TRH)
• The Anterior Pituitary then excites the Thyroid gland with thyroid stimulating hormone (TSH)
• The Thyroid gland then produces thyroid hormones
• The thyroid hormones then inhibit the hypothalamus from producing TRH

Question 6

What are dimorphic organisms?

Answer 6

Dimorphic organisms exist in two biological forms (male and female)

Question 7

How is the gender of a foetus determined?

Answer 7

• Genetic information on sex chromosomes
• Females have two X chromosomes (XX)
• Males have one X and one Y chromosome (XY)

Question 8

How many chromosomes are found in the nucleus of a human cell?

Answer 8

23 pairs

- total of 46 chromosomes

Question 9

What are the first 22 pairs of chromosomes in the nucleus of a human cell called?

Answer 9

Autosomes

- they contain the same genes in the same order along their chromosomal arms

Question 10

What is the 23rd pair of chromosomes in the nucleus of a human call called?

Answer 10

Allosomes (or sex chromosomes)

- they contain the XX / XY information, so determine the sex of an individual

Question 11

Which chromosome, X or Y, is larger?

By how much?

Answer 11

X chromosome is larger

• X contains 1500 genes
• Y contains 50 genes

Question 12

What gene does the Y chromosome contain in mammals? What does this gene do?

Answer 12

Gene SRY (sex-determining region Y) 
- Triggers testis development

Question 13

How are ovaries developed?

Answer 13

Initially there are primitive gonads, if these are made of cortex tissue they have the potential to form into an ovary. If the SRY protein is not present, the cortex will develop into an ovary

Question 14

How are testis developed?

Answer 14

If primitive gonads are made up of medulla tissue, they have the potential to be a testis. If allosome is XY, the SRY gene on the Y chromosome triggers the synthesis of the SRY gene, causing the medulla to form into a testis

Question 15

What are the two sets of reproductive ducts that every foetus has before their third prenatal month?

Answer 15

Wolffian system (male)
Mullerian system (female)

Question 16

What happens to a foetus if the testes begin producing testosterone and Mullerian-inhibiting substances in the third prenatal month?

Answer 16

The wolffian system develops into male reproductive ducts (seminal vesicles, vas deferens), the mullerian system degenerates and the testes descend
(male baby)

Question 17

What happens to a foetus if there is no production of testosterone in the third prenatal month?

Answer 17

The mullerian system develops into female reproductive ducts (vagina, uterus, fallopian tubes) and the wolffian system fails to develop
(female baby)

Question 18

How do hormones effect brain development in early life?

Answer 18

Sex hormones bind to receptors in specific areas in the hypothalamus, amygdala & other areas

• anterior hypothalamus is larger in males than females & affects male sexual behaviour
• some areas of the cerebral cortex are larger in males & some are larger in females

Question 19

What makes up the HPG axis?

Answer 19

Hypothalamus
Pituitary gland
Gonads

Question 20

What happens in the Follicular phase of the ovarian cycle?

Answer 20

1. Formation of primary oocytes within follicles
2. Follicle growth
3. Maturation of follicle
4. Ovulation

Question 21

What happens in the Luteal phase of the ovarian cycle?

Answer 21

1. Degeneration of the corpus luteum

Question 22

At what day does ovulation typically begin in the menstrual cycle?

Answer 22

Day 14

Question 23

What are the three phases of the ovarian cycle?

Answer 23

Follicular phase (follicle growth) 
Ovulation 
Luteal phase (corpus luteum degeneration)

Question 24

What two hormones control the phases of the ovarian cycle?

Answer 24

Follicle Stimulating Hormone (FSH)
Luteinising Hormone (LH)

Question 25

What happens in the ovulation stage of the ovarian cycle?

Answer 25

Mature eggs are released from the ovarian follicles into the ovaduct
- one egg from each ovary is released

Question 26

Give some examples of the effects of activating sex hormones

Answer 26

1. Hormones released around the time of giving birth facilitate maternal behaviour in females
   - large amounts of estradiol, prolactin (milk production) & oxytocin (social attachment&maternal behaviour) are secreted
2. Females change patterns of hormone receptors
   - late in pregnancy, brain increases its sensitivity to estradiol in areas responsible for maternal behaviour, but not for sexual behaviour
   - these changes increase attention from mother to young
3. Activate sexual behaviour
   - partly by facilitating activity in medial preoptic area & anterior hypothalamus
   - hormones prime cells to release dopamine in response to sexual arousal
   - dopamine release evokes similar effects to addictive drugs