Topic 9.1 Chemical Control

Question 1

MR H GREN

Answer 1

M etabolism
R esponse
H omeostasis
G rowth
R eproduction
E xcretion
N utrition

Question 2

Homeostasis

Answer 2

The maintenance of a constant internal environment.
—> Involves constant changes around an optimum point
This involves constant fluctuations in:
-temperature
-pH
-water potential

Question 3

Internal coordination

Answer 3

All organisms have optimal conditions under which they work optimally.
-Temperature
-Water potential
-pH
-Metabolic substrate/waste concentration

Question 4

External coordination

Answer 4

All organisms have optimal conditions under which they work optimally.
-Temperature
-Toxins or inhibitors
-Humidity
-Light intensity

Question 5

Importance of homeostasis

Answer 5

-Changes in pH and temperature affect proteins
–> Changes can cause a reduction in the rate of reaction or denaturation
-Changes in water potential of tissue fluid or blood can cause a change in volumes of cells due to osmosis.

Question 6

Control mechanism

Answer 6

1) Optimum- the point at which the reaction works best
2) Receptors- detects change from the optimum
3) Coordinator- links the receptor and the effector
4) Effector- muscle or gland which brings changes to return system to optimum.

Question 7

Positive feedback

Answer 7

A fluctuation triggers changes that result in an even greater deviation from the normal level.
-Positive feedback causes the amplification of a response
-System deviates from the optimum
-Change is detected by the receptor
-A change is then produced which causes an even greater deviation from the optimum
(Eg. Sodium channels open in a membrane)

Question 8

Positive Feedback example: Oxytocin and childbirth

Answer 8

Question 9

Negative feedback

Answer 9

Self-regulatory mechanisms return the internal environment to optimum when there is a fluctuation.
-System deviates from the optimum
-Change is detected by the receptor
-A change is then produced which returns the system back closer to the optimum

Question 10

Hormones

Answer 10

-Hormones are organic chemicals produces in an endocrine glands
-They travel in the blood and can be widespread or targeted
-Protein or peptide hormones examples are insulin, ADH
-Steroid hormone examples oestrogen and progesterone

Question 11

Endocrine glands

Answer 11

Endocrine glands can be stimulated to release hormones by both nerves or other hormones
-In particular, the pituitary gland is one which often secretes hormones which affect other glands

Question 12

The pituitary and the hypothalamus

Answer 12

-The pituitary and hypothalamus are located in the brain
-The hypothalamus often controls the pituitary gland

Question 13

Neurosecretory cells 1

Answer 13

-The hypothalamus contain neurosecretory cells which produce secretions from the axons
-Neorsecretory cells 1, produce substances that stimulate or inhibit the release of hormone from the anterior pitiutry
-They are known as releasing factors (if they stimulate) or release-inhibiting factors (if they inhibit).

Question 14

Neurosecretory cells 2

Answer 14

Neurosecretory cells 2 produce secretions that are stored in the posterior pituitary and released later as hormones.

Question 15

Pituitary gland

Answer 15

Produces growth hormone, which controls growth of bones and muscles; anti diuretic hormone, which increases reabsorption of water in kidneys; and gonadotrophin which control development of ovaries and testes.

Question 16

Thyroid gland

Answer 16

Produces thyroxine which controls rate of metabolism and rate that glucose is used up in respiration, and promotes growth.

Question 17

Adrenal gland

Answer 17

Produces adrenaline which increases heart and breathing rate and raises blood sugar level.

Question 18

Testis

Answer 18

Produces testosterone which controls sperm production and secondary sexual characteristics.

Question 19

Pineal gland

Answer 19

Produces melatonin which affects reproductive development and daily cycles.

Question 20

Thymus

Answer 20

Produces thymosin and promotes production and maturation of white blood cells

Question 21

Pancreas

Answer 21

Produces insulin which converts excess glucose into glycogen in the liver; and glycogen, which converts glycogen back to glucose in the liver.

Question 22

Ovary

Answer 22

Produces oestrogen, which controls ovulation and secondary sexual characteristics; and progesterone, oestrogen, which controls ovulation and secondary sexual characteristics; and progesterone, which prepares the uterus lining for receiving an embryo.

Question 23

Oxytocin

Answer 23

-Posterior
Stimulates the muscles of the uterus to contract during labour and also stimulates the contraction of cells in the mammary tissue so that milk is squeezed out when an infant suckles.

Question 24

ADH (antidiuretic hormone)

Answer 24

-Posterior
Decreases the urine volume by affecting the tubules of the kidney ad also causes the arteries to constrict after haemorrhage, preventing excess blood loss and raising blood pressure.

Question 25

Prolactin

Answer 25

-Anterior
Stimulates and maintains the production of milk by the mammory glands.

Question 26

Luteinising hormone (LH)

Answer 26

-Anterior
Stimulates ovulation and the formation of the corpus luted in females. It prepares the uterus for implantation. In males it stimulates the testes to produce testosterone.

Question 27

Follicle stimulating hormone (FSH)

Answer 27

-Anterior
Has different effects in males and females. In females it stimulates the ovaries to produce oestrogen and also stimulates the development of ova in the menstrual cycle. In males it stimulates the testes to produce sperm.

Question 28

Adrenocorticotrophic hormone (ACTH)

Answer 28

-Anterior
Controls secretion of some of the hormones of the adrenal cortex of the adrenal glands.

Question 29

Growth hormone (GH)

Answer 29

-Anterior
Stimulates the growth of body cells and increases the build-up of proteins.

Question 30

Hormone action

Answer 30

There are 2 modes of action:
1) Release of a second messenger
2) The hormone enters the cells

Question 31

General stages in negative feedback

Answer 31

Receptors detect deviation –> coordinator –> corrective mechanism by effector –> receptors detect that conditions have returned to normal

Question 32

Why is it important that blood pH remains stable?

Answer 32

Maintain stable rate of enzyme-controlled reactions (& optimum conditions for other proteins).
Acidic pH = H+ ions interact with H-bonds & ionic bonds in tertiary structure of enzymes –> shape of active site changes so no ES complex form.

Question 33

Explain the mode of action of adrenaline

Answer 33

Secondary messenger model:
1) Hormone-receptor complex forms.
2) Conformational change to receptor activates G-protein.
3) Activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP).
4) cAMP activates protein kinase A pathway.
5) Results in glycogenolysis.

Question 34

Explain the mode of action of oestrogen

Answer 34

1) Steroid hormone diffuses through cell membrane
2) Forms hormone-receptor complex with ER α receptor in the cytoplasm.
3) Complex enters the nucleus & acts as transcription factor.