Environmental Impacts on Human Hormones

Volume 29, Number 1, September 2016

Activity

Environmental impacts on human hormones

Martin Rowland

This exercise relates to Michelle Bellingham’s article on pp. 2–6 of the September issue. Read her article first and then attempt the following questions. You may work individually or in a group.

Questions 1 to 6 relate to the content of page 4 of the article.

Question 1

The endocrine system is a collection of glands which synthesise and secrete hormones.

Construct a table like to the one below and complete it to show the endocrine glands and hormones that are named in your biology specification.

Name of endocrine gland / Hormones secreted by gland / Effect of hormone

Question 2

You secrete many more different hormones than you do different neurotransmitters. Suggest an advantage of secreting so many different hormones.

Question 3

When a hormone binds to a protein receptor on the surface membrane of its target cell, it initiates biological processes within the target cell.

Contrast the ways in which the hormones adrenaline and oestrogen initiate biological processes in their target cells.

Question 4

Negative feedback is involved in regulating hormone secretion.

(a) Complete the gaps in the following chart representing the control of ADH secretion.

(b) Use information from the chart to explain the term negative feedback.

Question 5

Diabetes mellitus results from an endocrine disorder. In this case, the hormone involved is insulin.

(a) When stimulated by insulin, liver cells increase the rate at which they take up glucose from the blood. Describe what happens to the stimulated liver cell to allow this increased uptake of glucose.

(b) Contrast the causes of Type 1 diabetes and Type 2 diabetes.

(c) After a period of fasting, two volunteers drank a glucose solution. At 30-minute intervals, a scientist took blood samples from each person. After 150 minutes, she measured the glucose concentration of each blood sample. Her results are summarised in the table below.

Time after drinking glucose
solution/minutes / Concentration of glucose in blood/mgdm−3
Person A / Person B
0 / 85 / 127
30 / 118 / 210
60 / 95 / 240
90 / 90 / 250
120 / 85 / 235
150 / 85 / 225

(i) Explain why the blood glucose concentration rose in both volunteers during the first 30minutes.

(ii) Person A was not a diabetic. Explain why her blood glucose concentration fell after 30minutes.

(iii) Person B was a diabetic. Give two pieces of evidence from the table that support this statement.

(iv) Suggest why the blood glucose concentration of person B fell after 90minutes.

Question 6

Explain the meaning of the term endogenous.

Questions 7 to 11 relate to the content of page 5 of the article.

Question 7

Explain the emboldened words in the expression persistent organic pollutants.

Question 8

Significant concentrations of polychlorinated biphenyls (PCBs) have been found in polar bears.

(a) What is the importance of this finding?

(b) Suggest why polar bears are susceptible to bioaccumulation.

Question 9

Government scientists investigated bioaccumulation in fish. They fed groups of fish (Oncorhynchusmykiss) with food containing a test substance at a concentration of 50mgkg−1. In their report, they published the following data:

Mean lipid content of fish 5.2% by body mass.
At the start of experiment, the mean concentration of pollutant in fish was 0μgkg−1 and on day 10 it was 16720μgkg−1.
On day 10 of the experiment, the mean mass of the fish was 1.218kg and on day 10 it was 1.254kg.

(a) The scientists used rainbow trout as their experimental animal. To which genus do these fish belong?

(b) Suggest why the scientists reported the mean fat content of the fish.

(d) Use the data to give a quantitative estimate of the bioaccumulation in the fish used in this study.

Question 10

Studies have been useful in highlighting the link between EDCs and an apparent reduction in human fertility but they do not prove that EDCs cause reduced human fertility.

Give two reasons why.

Question 11

Pre-natal programming involves epigenetic modification.

(a) Define the term epigenetics.

(b) Give two ways in which epigenetic modification is brought about.

Question 12 relates to the content of pages 4 and 6 of the article.

Question 12

Researchers have learnt about how EDCs affect endocrine systems using non-human animal studies.

(a) Outline the advantage(s) and disadvantage(s) of such studies.

(b) Researchers at the University of Glasgow used sheep as their animal model. Why is it important that sheep are:

(i) long-lived

(ii) outbred?

Answers

Question 1

Your answer will depend on which specification you are studying. The table shows examples common to all specifications.

Name of endocrine gland / Hormones secreted by gland / Effect of hormone
β cells in pancreas / Insulin / Stimulates uptake of glucose by liver cells
Stimulates polymerisation of glucose to glycogen
Osmoreceptors in hypothalamus / Antidiuretic hormone (ADH) / Increases permeability to water of walls of collecting ducts (and of distal convoluted tubules) in kidneys
etc.

Question 2

Neurotransmitters are secreted directly onto their target cell, so have little effect on other tissues.

Hormones travel through the blood, reaching every cell in the body. They only affect those with a specific type of protein receptor molecule on their surface membranes. A large variety of hormones ensures only specific tissues are targeted.

Question 3

Adrenaline molecules cannot pass through the cell surface membranes of their target cells but oestrogen molecules can and pass into the nuclei of their target cells.

Adrenaline molecules have an indirect effect on the activity of their target cells, via the second messenger model of hormone action whereas oestrogen molecules bind to an intracellular oestrogen receptor that then initiates gene transcription.

Question 4

(a) Note: an increase in the water potential results in the water potential becoming less negative; a decrease results in the water potential becoming more negative.

(b) A change in the water potential of the blood results in a mechanism that returns it to its baseline value. For example, when the blood becomes more dilute (water potential increases), less water is reabsorbed, so more is lost in the urine and the water potential of the blood falls back to its baseline value.

Question 5

(a) The liver cell recruits into its surface membrane more channel proteins that allow faster facilitated diffusion of glucose molecules into the cell. Insulin also stimulates the liver cell to increase its rate of conversion of glucose to glycogen, thus increasing the glucose concentration gradient into the cell.

(b) Type 1 results in no/low rates of secretion of insulin by β cells of the pancreas, whereas Type 2 results when insulin receptor molecules on the surface membranes of liver cells no longer respond to insulin.

(c)(i) They both absorbed glucose from their small intestines (by co-transport with sodium ions) into their blood.

(ii) The increase in glucose concentration caused her to secrete (more) insulin, which resulted in the uptake of glucose from her blood into her liver cells.

(iii) Compared with person A, the concentration of glucose in her blood was much higher and did not begin fall after 30 minutes.

(iv) Probably because her tissues used the glucose in aerobic respiration.

Question 6

Naturally occurring in the body

Question 7

Persistent means that these pollutants are not quickly broken down and so remain active for a long time.

Organic means the molecules of these pollutants are complex and based on carbon.

Question 8

(a) Polar bears inhabit remote, unpolluted areas in the Arctic Circle. If they have accumulated PCBs, it means that pollution by PCBs is worldwide.

(b) They are top carnivores so the PCBs have already been accumulated by their prey; the PCBs in the animals they eat remain in their own bodies for a long time.

Question 9

(a) Oncorhynchus(don’t forget, answers are often given in the information you should read before attempting to answer a question.)

(b) Pollutants are stored mainly in fatty tissue.

(d) Your answer could be, e.g., a mean of 1672 μg kg−1 day−1.

Question 10

Experiments are conducted to test a null hypothesis, which is either disproved or supported by the data collected. They cannot prove a hypothesis to be true.

The observed relationship between EDCs and an apparent reduction in human fertility might be due to some other, unidentified, factor.

Question 11

(a) Epigenetics is a heritable change in gene function without any change to the base sequence of the gene involved.

(b) Increased methylation of DNA; decreased acetylation of histones around which the DNA is wound.

Question 12

(a) First, it would not be ethical to test the effects of toxic EDCs on humans. Second, as the non-human animals are thought to have similar control mechanisms to those of humans, the results of these studies can be extended to humans. In contrast, there might be differences in the physiology of these non-human animals and the physiology of humans.

(b)(i) This allows time for the sheep to accumulate the EDCs so that any long-term effects become apparent. If the results of these trials are to be extended to humans, it is important that long-term effects are studied.

(ii) A gene pool of a population that is outbred will have greater genetic variation than one that is inbred. This enables scientists to model human populations better.