Chapter 02: Chemical Messengers

Question 1

• Coordination of the body is achieved through what 2 systems?
• What is homeostasis?
• Explain the difference between endocrine and exocrine glands and give an examples of each.
• What are the 10 main endocrine glands?
• Describe what a hormone is.
• Describe what a paracrine is.
• Describe how hormones are specific.

Answer 1

• Nervous and endocrine system.
• Homeostasis: maintenance of a stable internal environment, irrespective to the changes of the external environment.
• Endocrine glands are ductless glands secreting hormones into the extracellular fluid which diffuse through capillary walls into the blood to be transported throughout the body. Whereas exocrine glands secrete substances into a duct which carries the secretion to body surface or cavities.
  1. Hypothalamus 2.pituitary gland 3.pineal gland 4.thymus 5.thyroid gland 6.parathyroid glands 7.adrenal glands 8.pancreas 9.ovaries 10.testes
• A regulatory substance secreted by endocrine glands in the form of proteins, steroids or amines. They are transported by blood and may affect all or particular groups of cells.
• Chemicals secreted by cells into the extra cellular fluid diffusing into adjacent cells.
• Hormones are only able to influence cells that have the correct receptor for the hormone.

Question 2

• How do protein and amine hormones work?
• Explain why the addition of more hormones does not continue to increase the rate of the response.
• Why is there variation in the sensitivities of cells to hormones and other substances.
• How do steroid hormones work?
• How do hormones change the functioning of cells?
• What are the 3 functions of hormones?
• What can just 1 hormone molecule do in terms of activation of enzyme molecules? Explain this process.

Answer 2

• They bind to receptor proteins on surface of membrane of cell causing a secondary messenger substance inside to be released and activate particular enzymes.
• Once all the receptor proteins on cell membrane are occupied, there can be no greater effect. This is called saturation.
• Different cells have different types and number of receptor proteins.
• By entering (lipid-soluble) and combining with receptor proteins inside the cell, on the mitochondria, other organelles or nucleus. The hormone-receptor complex activates genes controlling the formation of particular proteins.
• Changing type, activities or quantities of proteins produced.
• Activates certain genes in nucleus so particular proteins are produced, change structure of enzymes turning it on/off and change rate of protein production by changing rate of transcription/translation.
• This process is called enzyme amplification where the 1 hormone molecule triggers a cascading effect causing the number of reacting molecules involved is increased thousands of times for each step along the metabolic pathway. L

Question 3

• What happens when a hormone has produced the required effect?
• Compare positive and negative feedback?
• What does the hypothalamus secrete
• What is the hypothalamus.
• What is the pituitary gland
• How is the anterior and posterior lobe connected to the hypothalamus?
• Why is the posterior lobe not a true gland?
• Describe the origin of the hormones of the posterior lobe.

Answer 3

• It is turned off by being broken down in the target cell, liver or kidneys, then excreted either in bile or urine.
• Negative feedback is a regulatory mechanism in which a stimulus causes an opposite output. Whereas positive feedback is a regulatory mechanism in which a stimulusis’ effect is enhanced.
• Releasing and inhibiting factors into the pituitary gland, stimulating or slowing the release of hormones.
• Located at the brain’s base, it receives sensory info from the body to regulate many bodily functions carried out through the pituitary gland, eg body temp, water balance and HR.
• Lies under the hypothalamus joined by a stalk- infundibulum. It is vital for normal functioning of the body.
• AL is connected by networks of complex blood vessels and the PL is connected by nerve fibres from nerve cell bodies of hypothalamus.
• It does not secrete its own substances.
• OT and ADH are produced in special nerve cells bodies in the hypothalamus. These cells have long extensions that carries the hormones to the PL when nerve impulses are initiated.

Question 4

• Why is the pituitary sometimes known as the ‘master gland?’
• How are releasing and inhibiting factors hormones aswell?
• What initiates the hormones manufactured in the nerve cells of hypothalamus to transport down into the posterior lobe?
• Describe the 2 hormones that the posterior lobe secretes.
• Describe the 5 hormones secreted by the anterior lobe of the pituitary gland.

Answer 4

• Many pituitary hormones regulate activity of other endocrine glands, eg TSH stimulates release of thyroxine.
• They’re secreted into the extracellular fluid of the hypothalamus and are carried by blood to the anterior lobe.
• The release of the hormones is triggered by nerve impulses initiated in the hypothalamus and conducted along the cell extensions.
  1. Oxytocin: Targets the uterus to stimulate contractions during child birth. Also targets the mammary glands to release milk.
  2. Antidiuretic hormone: Targets the kidneys to Reabsorb water from forming urine back into the bloodstream.
  1. FSH: Targets the ovaries stimulating growth of the follicles and targets testes stimulating production of sperm.
  2. LH: Targets ovaries stimulating ovulation and maintenance of corpus luteum and testes stimulating secretion of testosterone.
  3. GH: Targets all cells stimulating growth and protein synthesis.
  4. TSH: Targets the thyroid gland stimulating secretion of its hormones.
  5. Adrenocorticotropic hormone: Targets the adrenal cortex stimulating secretion of its hormones.
  6. Prolactin hormone: Targets the mammary glands stimulating milk secretion.

Question 5

• Describe the pineal gland and it’s role.
• Describe the thyroid gland, its role and how its production is controlled.
• Describe the hormones and function of the ovaries.
• Describe the hormones and function of the testes.
• Apart from the major endocrine glands, there are many tissues that aren’t called endocrine glands that secrete hormones. Discuss 4 of them and their hormones.

Answer 5

• Found inside the brain and secretes the melatonin whichever is involved in sleep patterns regulation and is stimulated by darkness and inhibited by light.
• Found below the larynx and secretes thyroxine which targets most cells to increase metabolic rate and therefore O2 consumption and heat production. Secreted in response to TSH through negative feedback. High thyroxine in the blood means low TSH and high TSH means low thyroxine.
• Secretes oestrogen targeting many tissues stimulating development of female characteristics and regulates the menstrual cycle. Also secretes progesterone targeting the uterus and mammary glands that regulates the menstrual cycle, pregnancy and prepares mammary glands for milk secretion.
• Secretes androgen targeting many tissues stimulating sperm production, growth of skeleton, muscles and male characteristics.
  1. Stomach and small intestine secrete hormones coordinating exocrine glands of the digestive system.
  2. Kidneys secreting erythropoietin (EPO) stimulating RBC production.
  3. Heart secreting a hormone reducing blood pressure.
  4. Placenta secreting hormones to help maintain pregnancy stimulating development of the foetus and stimulate the mothers mammary glands.

Question 6

• Describe the parathyroid glands and its function.
• Describe the thymus and its function.
• Describe the structure of the adrenal glands.
• Describe the function of the adrenal cortex.
• Describe the function of the adrenal medulla.
• What is the pancreas and what is special about it?
• What does the exocrine part of the pancreas do?
• What are the endocrine parts of the pancreas and describe its function.
• What is a feedback system?

Answer 6

-There are 4 parathyroid glands embedded in the rear surface of the thyroid gland. It secretes parathyroid hormone targeting bones and kidneys to increase blood calcium levels.
-Found behind the sternum and secretes targeting T-lymphocytes to stimulate development and maturation.
-There are 2 adrenal glands found above each kidney and each consists of an inner adrenal medulla and an adrenal cortex.
-Secretes corticosteroids including aldosterone targeting kidneys to increase reabsorption of sodium ions and excretion of potassium ions.
Also cortisol targeting most cells promoting normal metabolism; helps the body deal with stress and promotes repair of damaged tissues.
-Secretes adrenaline and noradrenaline targeting most tissues to prepare body for fight or flight responses.
-A organ that lies below the stomach and alongside the duodenum that is both an exocrine and endocrine gland.
-Secretes digestive enzymes into the S.I via pancreatic duct.
-The islets of Langerhans secrete insulin targeting most cells stimulating glucose uptake. Also secretes glucagon targeting liver and fat storage tissues stimulating breakdown of glycogen and fat to increase blood glucose level.
-A homeostatic mechanism that controls an aspect of the internal environment.

Question 7

• What is a target organ?
• Some athletes take illegally the hormone erythropoietin to improve their performance. How would it improve performance?
• An Egyptian pharaoh who lived 3500 years ago is portrayed in statues with feminine features. Which 3 glands could it be that was not functioning correctly?
• Explain the 3 differences between hormones and paracrines.
• What 4 pituitary hormones are involved in the control of other endocrine glands?

Answer 7

• A organ that responds to stimulation of a particular hormone.
• Erythropoietin stimulates RBC production so more RBC circulates through the body resulting in greater uptake and transport of O2 to cells. Aerobic respiration uses O2 to produce energy for muscle contraction so enhances performance.
• Testes not producing testosterone or anterior lobe not producing luteinising hormone stimulating the testes to produce testosterone or the hypothalamus not secreting gonadotropin releasing factors.
  1. Paracrines are secretions of cells where hormones are secretions of endocrine glands.
  2. Paracrines target adjacent cells through diffusion, where hormones transports by the blood and to target cells.
  3. All cells secrete paracrines where as only specialised cells secrete hormones.
• FSH, LH, TSH and Adrenocorticotropic hormone.

Question 8

• Describe a flow diagram to show how negative feedback is used to control the level of metabolism in the body.
• TSH is secreted by the anterior lobe of the pituitary gland. If a cancer patient had the thyroid gland removed, would you expect the level of TSH in the person’s blood to rise or fall? Explain.
• Identify one hormone produced by the ovaries and discuss the negative feedback it has on other hormones.
• Describe the process that causes the change in the rate of urine production.
• During the ovarian cycle, the ovum is released from a mature follicle. What is the hormone that directly stimulates the release of the ovum?

Answer 8

S-Low blood thyroxine level
R-Hypothalamus is alerted
M-Hypothalamus secreting TSH releasing factors to pituitary gland
E-Pituitary gland secretes TSH
R-TSH causes thyroid gland to secrete thyroxine.
F-Increased thyroxine blood level.
-Rise because there is no more thyroid gland to secrete thyroxine causing a negative feedback to the pituitary to secrete more TSH.
-Oestrogen or protesterone. High FSH=high oestrogen =positive feedback. High LH=high progesterone=positive feedback.
-When the blood water concentration is low, ADH is secreted and acts on nephron tubule to increase permeability to water increasing water reabsorption back into blood and decreasing urine production.
-Luteinising hormone (LH)