Session 7 Flashcards
What types of feedback are there?
- Negative
- Positive
What are the components of control systems?
- Communication
- Control centre
- Receptor
- Effector
What is a biological rhythm?
- Set point can vary over time instead of being a fixed value
- Cortisol levels, menstrual cycle
What does the body water consist of?
- Intracellular fluid
- Extracellular fluid
- Blood plasma
What is osmalality and Na+ concentration monitored by?
- Osmoreceptors in hypothalamus
What happens if osmolality of blood plasma increases?
- Antidiuretic hormone is released from the posterior pituitary gland
- Increased reabsorption of water from urine in collecting ducts of kidney
- Osmolality of blood plasma decreases
What are endocrine hormones?
- Chemical signals produced in endocrine glands or tissues that travel in the bloodstream to cause an effect on other tissues
What is the hierarchy of control of glands?
- Hypothalamus
- Anterior pituitary gland
- Endocrine glands
What are the classes of hormone?
- Peptide/polypeptide hormones
- Glycoprotein hormones
- Amino Acid derivatives
- Steroids
What are peptide/polypeptide hormones?
- Short or long chains of amino acids
- Eg insulin, glucagon, growth hormone, placental lactogen
What are glycoprotein hormones?
- Large protein molecules with carbohydrate side chains
- Eg anterior pituitary hormones: luteinizing hormone, follicle stimulating hormone, thyroid stimulating hormone
What are amino acid derivative hormones?
- Small molecules synthesised from amino acids
- eg adrenaline, thyroid hormones (thyroxine)
What are steroids?
- Derived from cholesterol
- Eg cortisol, aldosterone, testosterone, oestrogen
How are hormones transported?
- Hydrophilic hormones (peptide; glycoprotein and adrenaline): in bloodstream dissolved in blood plasma
- Hydrophobic (steroid; thyroid): need specialised transported proteins
What form of the hormone is biologically active?
- Free form (unbound to protein)
What is the role of carrier proteins?
- Increase solubility of hormone in plasma
- Increase half-life
- Readily accessible reserve
How do hormones produce a response?
- Bind to receptors in or on target cells
What does the magnitude of response to a hormone depend on?
- Concentration of active hormone at target tissue
- Receptor number
- Affinity of hormone for receptor
- Degree of signal amplification (enzymes involved - cascade)
What are the steps involved in hormone action?
- If a hormone cannot cross membrane it binds to a receptor on the cell surface
- Activates a Second messenger
- Second internal messenger exerts metabolic effects eg modifying enzyme action
Which hormones can cross cell surface membrane?
- Steroid hormones
- Instead bind to receptors inside cell (cytoplasmic/nuclear)
What hormones are produced by the anterior pituitary gland and what do they do?
- Thyroid stimulating hormone (affects thyroid gland)
- Adrenocorticotrophic hormone (affects adrenal gland)
- Leuteinizing hormone (affects ovary and testes function)
- Follicle stimulating hormone (affects ovary and testes function)
- Growth hormone (affects metabolism)
- Prolactin (affects breast development and milk production)
What are tropic hormones?
- Hormones that control the secretion of others
Which hormones released by the anterior pituitary gland are tropic hormones?
- Thyroid stimulating hormone
- Adrenocorticotrophic hormone
- Leuteinizing hormone
- Follicle stimulating hormone
How is the secretion of tropic hormones controlled?
- Negative feedback: when the hormone that they control increases in concentration, the tropic hormone secretion reduces and when the hormone they control decreases in concentration the tropic hormone secretion increases
- Eg when thyroid hormone is high, this negatively feedsback and thyroid stimulating hormone secretion decreases
- Also releasing and inhibiting hormones
What are releasing and inhibiting hormones?
- From nerve cells in hypothalamus to anterior pituitary gland via hypophyseal portal vessels (specialised blood vessels)
- How the brain controls hormone secretion
Give examples of releasing and inhibiting hormones
- Thyrotrophin releasing hormone: stimulates thyroid stimulating hormone release
- Corticotrophin releasing hormone: stimulates Adrenocorticotrophic hormone release
- Somatotrophin releasing hormone: stimulates growth hormone release
- Somatostatin: inhibits growth hormone release
How are hormones inactivated?
- Steroid hormones: small change in chemical structure that increases water solubility; can be exerted from the body in urine or via bile
- Protein hormones: more extensive chemical changes; are degraded to amino acids that are refused
Where does hormone inactivation take place?
- Kidneys
- Liver
What are the components of the hypothalamic-pituitary-adrenal axis?
- Hypothalamus (releases corticotrophin releasing factor)
- Anterior pituitary gland (releases adrenocorticotrophic hormone)
- Adrenal cortex/zone fasciculata (releases cortisol)
How is the hypothalamus-pituitary-adrenal axis controlled?
- Negative feedback of Adrenocorticotrophic hormone on Corticotrophin releasing hormone release
- Negative feedback of cortisol on Adrenocorticotrophic hormone release and corticotrophin releasing hormone release
Where is appetite controlled?
- Satiety centre located in arcuate nucleus in the hypothalamus
What types of neurones does the arcuate nucleus contain?
- Primary: senses metabolite levels (glucose and fatty acids) in blood; responds to hormones
- Secondary: synthesises input from primary neurones; co-ordinates a response via vagus nerve
How can primary neurones be sub-divided?
- Excitatory: stimulates appetite via release of peptides neuropeptide Y (NPY) and agouti-related peptide (AgRP)
- Inhibitory: suppress appetite by release of prohormone pro-opiomelanocortin (POMC)
What can POMC be cleaved into?
- Several peptide hormones:
~ B-endorphin (reward system - feelings of euphoria/tiredness)
~ adrenocorticotrophic hormone (ACTH)
~ a-melanocyte stimulating hormone (a-MSH) - suppresses appetite
What hormones feedback from the gut to the hypothalamus?
- Ghrelin
- PYY
- Leptin
- Insulin
- Amylin
What is the structure and function of Ghrelin?
- Peptide hormone
- Released from stomach walk when empty
- Stimulates excitatory neurones in arcuate nucleus
- Stimulates appetite
- Filing of stomach inhibits Ghrelin release
What is the function of PYY?
- Peptide hormone
- Released from wall of small intestine
- Suppresses appetite
What is the function of Leptin?
- Peptide hormone
- Released from adipocytes
- Stimulates inhibitory neurones in arcuate nucleus
- Suppresses appetite
- Induces expression of uncoupling proteins in mitochondria so energy is dissipated as heat
What is the function of insulin?
- Suppresses appetite
- Same mechanism as Leptin but less important
What is the function of Amylin?
- Peptide hormone
- Secreted from B cells in pancreas
- Suppresses appetite
What are the pattern of symptoms for metabolic syndrome?
- Insulin resistance
- Dyslipidaemia
- Glucose intolerance
- Hypertension
- Central adiposity
What is the WHO criteria for metabolic syndrome?
- Waist hip ratio: >0.9 men; >0.85 women
- BMI: >30 kg/m2
- Blood pressure: >140/90 mmHg
- Triglycerides: >1.7 mM
- HDL: 7.8 mM
- Glucose uptake in lowest quartile
What is insulin resistance associated with?
- Dyslipidaemia (high VLDL; high LDL; low HDL lol)
- is highly atherogenic
- Increased risk of hypertension
What is the Barker hypothesis?
- Studies showed that some adult diseases (coronary heart disease, hypertension, type 2 diabetes) are related to low birth weight
- Suggests that the experience of the foetus in utero during development somehow determines the future health of the individual
What is fetal programming?
- Fetus adapts to conditions in utero eg supply of nutrients
- Biochemical adaptations become programmed in, predisposing to adult disease conditions
- Programming involves switching genes on and off at critical times during fetal development
What is the definition of epigenetics?
- An epigenetic trait is a stably inherited phenotype resulting from changes in a chromosome without alterations in the DNA sequence
How is it possible for low birth weight to passed on through several generations?
- Epigenetics: adaptations in the phenotype can be passed down (without changes in DNA)
- Mechanism involves methylation of DNA at crucial positions and changes in histone structure, causes suppression of gene transcription
