D.5 Hormones and metabolism Flashcards
What are hormones involved in regulating?
- Metabolism
- Development
- Homeostasis
- Digestion
- Excretion
- Sleep
- Reproductive cycles
- Growth
- Secondary sexual characteristics
- Sensory perception
- Mood
- Hunger
- Birth
- Lactation
Hormones are produced by the ___ system
Endocrine
How are hormones distributed throughout the body?
They are often released directly into the bloodstream by endocrine glands.
Why is the endocrine system considered to be one system?
Even though the glands of the endocrine system are scattered throughout the body, they are still considered to be one system because they have similar functions and mechanisms of influence.
What are endocrine glands?
Special groups of cells that secrete hormones into the blood.
What are the major endocrine glands?
- The pituitary, pineal, thymus, thyroid, and adrenal glands, and the pancreas.
- In addition, men produce hormones in their testes and women produce them in their ovaries.
Diagram showing the development of endocrine glands
Which organs play a part in the endocrine system?
- In addition to the major endocrine glands, other organs have some hormonal activity as part of their function.
- These include the stomach, small intestines, heart, thymus and placenta.
What is the target tissue of a hormone?
- The target tissue of a hormone consists of cells that have receptor sites for a given hormone.
- In some cases, the target tissue is found in a single gland or organ.
- In other cases, the target tissue is scattered throughout the body so that many areas are affected.
Where are hormones produced?
Endocrine glands
Define hormones
Chemical messengers secreted by cells or glands of the endocrine system that control and regulate the activity of other cells or glands in other parts of the body.
How are hormones classified?
Acording to their chemical composition, mainly either proteins or steroids.
What kinds of hormones are most of the hormones in the human body?
Proteins or protein derivatives.
What are the steroid hormones in the human body?
Sex hormones (oestrogen, progesterone, testosterone) and those from the adrenal cortex (aldosterone, cortisol and estradiol).
Examples of protein or peptide derivative hormones in the human body
- Epinephrine (adrenaline)
- Thyroxin
- Insulin
- Glucagon
- Oxytocin
- Prolactin
- Growth hormone (somatotropin)
- ADH (vasopressin)
- Thyroid stimulating hormone (TSH)
- Follicle stimulating hormone (FSH)
Site of production for insulin
Pancreas (beta cells)
Site of production for glucagon
Pancreas (alpha cells)
Site of production for oxytocin
Hypothalamus
Site of production for prolactin
Pituitary
Site of production for growth hormone (somatotropin)
Anterior pituitary gland
Site of production for ADH (vasopressin)
Hypothalamus
Site of production for follicle-stimulating hormone (FSH)
pituitary gland
Target organs for insulin
Muscle cells and fat cells
Target organs for glucagon
Liver
Target organs for oxytocin
Uterus, mammary glands
Target organs for prolactin
Mammary glands
Target organs for growth hormone (somatotropin)
Muscle, liver, bones
Target organs for ADH (vasopressin)
Kidney
Target organs for follicle-stimulating hormone (FSH)
Ovary/testes
Main functions of insulin
Promote absorption of glucose.
Main functions of glucagon
Convert stored glycogen to glucose.
Main functions of oxytocin
Birth and lactation
Main functions of prolactin
Milk production, metabolism
Main functions of growth hormone (somatotropin)
Growth
Main functions of ADH (vasopressin)
Water reabsorption, homeostasis.
Main functions of follicle-stimulating hormone (FSH)
Maturation of follicle/sperm production.
Examples of steroids
- Cortisol
- Oestrogen
- Progesterone
- Testosterone
Site of production of oestrogen
Ovary, placenta, liver, muscle and brain, as well as the fat cells
Site of production of progesterone
Ovary
Site of production of testosterone
Testes, ovary and adrenal cortex
Target organs of oestrogen
Many organs
Target organs of progesterone
Uterus
Target organs of testosterone
Many organs
Main functions of oestrogen
Secondary sexual characteristics, accelerate metabolism, and increase uterine growth and endometrium.
Main functions of progesterone
Maintain endometrium
Main functions of testosterone
Secondary sexual characteristics, anabolic effect.
What is the lifespan of hormones and how are they secreted?
Hormones have a limited lifespan and are secreted in pulses.
Feedback mechanisms for hormones
- Hormones have a limited lifespan and are secreted in pulses.
- This determines the need to control their production though feedback mechanisms.
- These can be positive or negative feedback mechanisms, although the latter is more common.
Define negative feedback
When the output of a pathway inhibits inputs to the pathway.
When do diseases occur?
When there is a problem in positive and negative feedback control mechanisms, as the concentration could be too high or too low.
What are the stages in which the concentration of hormones can be controlled?
- Synthesis
- Delivery
- Elimination
Synthesis as a way of controlling the concentration of hormones
The rate of production can be regulated by positive or negative feedback.
Delivery as a way of controlling the concentration of hormones
In endocrine glands, this is regulated by blood flow.
Elimination as a way of controlling the concentration of hormones
Hormones are metabolised and excreted once their half-life is over.
Flow diagram showing an example of how the hypothalamus and pituitary glands are involved in the negative feedback of a hypothetical endocrine gland
Steroid hormones
- Steroid hormones are lipophilic (fat-loving) – meaning they can freely diffuse across the plasma membrane of a cell
- They bind to receptors in either the cytoplasm or nucleus of the target cell, to form an active receptor-hormone complex
- This activated complex will move into the nucleus and bind directly to DNA, acting as a transcription factor for gene expression
- Examples of steroid hormones include those produced by the gonads (i.e. estrogen, progesterone, and testosterone)
Diagram of how steroid hormones work
Peptide hormones
- Peptide hormones are hydrophilic and lipophobic (fat-hating) – meaning they cannot freely cross the plasma membrane
-They bind to a specific receptor at the cell surface of a target cell
- Binding to the receptor triggers a secondary messenger inside the cell (examples include cyclic AMP, or cAMP)
- The secondary messenger activates a signaling cascade, which leads to the phosphorylation of specific enzymes, activating or inactivating them
- Changing the activity of enzymes changes the activity of the cell
- Peptide hormones include insulin, glucagon, leptin, ADH, and oxytocin
Diagram showing how peptide hormones work
Diagram showing action of steroid and peptide hormones
What is epinephrine?
A peptide hormone produced by the adrenal glands in response to stress and during exercise.
What is human growth hormone (HGH) or Somatotropin?
- A protein hormone synthesised by the anterior pituitary gland.
- It is involved in the regulation of bone and muscle growth.
How can HGH be used in sports?
To induce anabolic effects
What is the effect of HGH on the body?
- It has been proven that HGH significantly reduces body fat mass and increases body cell mass and sprint capacity when administered together with testosterone.
- Anabolic steroid hormones have several adverse effects, as they can produce sexual and mental problems and it increases the risk of coronary heart disease (CHD).
What are some of the adverse effects of anabolic steroid hormones?
- Increase in size of testes and ovaries, impaired spermatogenesis, growth of breasts in males.
- Psychiatric disturbance.
- Toxic to the liver.
- Dyslipidemia (raised LDL and triglycerides and reduced HDL).
- Hypertension.
- Increased coagulation and platelet aggregation.
- Exaggerated left ventricle growth.
Hypothalamus
- The hypothalamus is the section of the brain that links the nervous and endocrine systems to maintain homeostasis
- It receives information from nerves throughout the body and other parts of the brain and initiates endocrine responses
- It secretes neurochemicals (called releasing factors) into a portal system that target the anterior lobe of the pituitary gland
- It also secretes hormones directly into the blood via neurosecretory cells that extend into the posterior pituitary lobe
Pituitary Gland
- The pituitary gland lies adjacent to the hypothalamus and is in direct contact due to a portal blood system
- The pituitary gland receives instructions from the hypothalamus and consists of two lobes (anterior and posterior lobe)
Anterior lobe of the pituitary
- The anterior lobe is also called the adenohypophysis (‘adeno’ = relating to glands)
- The hypothalamus produces releasing factors, which are released into portal vessels by neurosecretory cells
- The releasing factors cause endocrine cells in the anterior pituitary to release specific hormones into the bloodstream
- An example of a releasing factor is GnRH, which triggers the release of LH and FSH from the anterior pituitary
Posterior lobe of the pituitary
- The posterior lobe is also called the neurohypophysis (‘neuro’ = relating to nerves)
- The posterior lobe releases hormones produced by the hypothalamus itself (via neurosecretory cells)
- These neurosecretory cells extend into the posterior lobe from the hypothalamus and release hormones into the blood
Diagram of endocrine signaling via the pituitary
What is the function of the oxytocin released by the posterior pituitary gland?
It acts on the uterus, increasing contraction during childbirth, and breasts, inducing milk discharge in lactation.
What is the function of FSH and LH?
They are involved in the growth of follicles and ovulation respectively in ovaries in females, and in sperm formation in testes in males.
What is the function of TSH?
It is a hormone that induces the thyroid gland to produce thyroxin and other thyroid hormones.
What is the function of ACTH?
It acts on the adrenal glands, inducing the production of steroid hormones such as cortisol.
What is the function of somatotropin or growth hormone (GH)?
It stimulates growth, cell reproduction and regeneration in bones and soft tissues.
Diagram showing ontrol of the pituitary gland by the hypothalamus
What is the function of prolactin?
It is involved in milk production.
Why do breasts increase in size during pregnancy?
- Because of an increase in lobules and alveoli.
- The release of estrogen and progesterone from the placenta and prolactin from the anterior pituitary causes this breast development.
What kind of glands are mammary glands?
Exocrine glands
Give the name of two major endocrine hormones involved in the initiation and control of lactation
Prolactin and oxytocin
Overview of the role of hormones in breastfeeding
- The production and secretion of milk by maternal mammary glands following birth is called lactation
- It is predominantly controlled and regulated by two key hormones – oxytocin and prolactin
Explain the role of prolactin in breastfeeding
- Prolactin is responsible for the development of the mammary glands and the production of milk
- It is secreted by the anterior pituitary in response to the release of PRH (prolactin-releasing hormone) from the hypothalamus
- The effects of prolactin are inhibited by progesterone, which prevents milk production from occurring prior to birth
Explain the role of oxytocin in breastfeeding
- Oxytocin is responsible for the release of milk from the mammary glands (milk ejection reflex)
- It is produced in the hypothalamus and secreted by neurosecretory cells that extend into the posterior pituitary
- Oxytocin release is triggered by the stimulation of sensory receptors in the breast tissue by the suckling of an infant
- This creates a positive feedback loop that will result in continuous oxytocin secretion until the infant stops feeding
What is milk secretion an example of?
An exocrine gland controlled by the pituitary gland that at the same time is controlled by the hypothalamus.
Which hormone requires iodine for its synthesis?
Thyroxine
Growth hormone
Growth hormone (also known as somatotropin) is an anabolic peptide hormone that stimulates growth
- It acts directly to reduce the formation of adipose cells (i.e. fewer nutrients stored as fat)
- It acts indirectly via insulin growth factor (IGF) – produced by the liver – to increase muscle mass and bone size
Due to its role in promoting growth and regeneration, it is used by some athletes as a performance enhancer
- The use of human growth hormone is banned in sports, with proven cases of doping strictly punished
- Traditional urine testing could not detect doping, which historically made bans difficult to enforce
- Recent blood tests can now identify between natural and artificial variants of growth hormone
