Homeostasis And The Endocrine System Flashcards
Give 3 examples of receptors that can detect stimuli and help maintain homeostasis
- Chemoreceptors - hormones and neurotransmitters
- Thermoreceptors - heat
- Nocireceptors - pain
Define NEGATIVE FEEDBACK and give 2 examples
- Response that opposes the effect of the stimulus to maintain homeostasis
- e.g. Control of blood glucose, control of body temperature
Define POSITIVE FEEDBACK and give 2 examples
- Response that acts to increase the effect of the stimulus and causes further change
- e.g. Blood clotting cascade, ovulation (FSH)
Explain why someone may experience jet lag after a long haul flight
- Cues from environment (ZEITGEBERS) keep body on a 24 hour cycle e.g. light, temperature, eating/drinking, social interaction and exercise
- Mismatch between environmental cues and body clock during a long haul flight
How is the osmotic pressure of the blood plasma measured?
OSMORECEPTORS in the hypothalamus
Why is the total body water (as % lean body mass) less for women than men?
Women have a higher fat content than men
Describe the compartmentalism of the total body water in a 70kg man (~42 L)
- INTERCELLULAR FLUID -> ~67% at 28 L
- EXTRACELLULAR FLUID -> ~22% at 9.4 L
- BLOOD PLASMA -> ~11% at 4.6 L
Briefly explain how a stimulus can bring about a response in the body
- Receptor detects stimuli and sends signal down AFFERENT pathway leading to the control centre
- Control centre interprets change to environment and determines a response
- Response sent down EFFERENT pathway to effectors which cause change and initiate response
What is the difference between OSMOLARITY and OSMOLALITY?
- OSMOLARITY is the number of osmoles per Litre of solution - VOLUME
- OSMOLALITY is the number of osmoles per Kg of solution - MASS
Explain how the body responds to an INCREASE in blood osmolality
- Hypotonic -> BODY NEEDS TO CONSERVE WATER
- Osmoreceptors in hypothalamus detect TONICITY of blood plasma
- Stimulate thirst receptors so you drink more to reduce osmolality
- Stimulates release of ADH from posterior pituitary so more water absorbed in kidneys and less urine produced
Explain how the body responds to a DECREASE in blood osmolality
- Hypertonic - BODY NEEDS TO GET RID OF WATER
- Osmoreceptors in hypothalamus detect change in TONICITY of blood plasma
- Decreased ADH secretion from posterior pituitary so less water absorbed in kidneys and larger volume of urine produced
Name 5 glands that are associated with the endocrine system
- Pituitary gland
- Thyroid/Parathyroid glands
- Adrenal glands
- Hypothalamus
- Testes/Ovaries
What is a ‘hormone’?
CHEMICAL SIGNALS produced and secreted by endocrine glands that travel in bloodstream to target tissues and stimulate an effect
List 3 organs/tissues in the body (apart from endocrine glands) that also secrete important hormones
- STOMACH (gastrin, ghrelin)
- ADIPOSE TISSUE (leptin)
- LIVER (IGF1)
Name 4 mechanisms by which hormones can communicate with target cells
- AUTOCRINE (signal acts back on original cell)
- PARACRINE (signal acts on adjacent cells a short distance away)
- ENDOCRINE (signal enters bloodstream and is transported to target tissue)
- NEUROCRINE (signal originates in neurone and is passed down axon and released into bloodstream)
How are neurones and endocrine cells similar?
- Both capable of SECRETION (hormones, neurotransmitters)
- Both can be DEPOLARISED
- Mechanism of action requires interaction with specific RECEPTORS on target cells
- Both work in parallel to maintain HOMEOSTASIS
Explain the classification of hormones
- PEPTIDE -> water soluble, chains of AA, e.g. Insulin
- AA DERIVATIVES -> water soluble (Thyroid Hs are lipid soluble), synthesised from AA, e.g. Neurotransmitters, thyroid hormones
- STEROID -> lipid soluble, synthesised from cholesterol, e.g. Cortisol
- GLYCOPROTEINS -> water soluble, protein molecules with carb side chain, e.g. FSH, LH
Name 4 steroid hormones that are synthesised by cholesterol
PACT:
- Progesterone
- Aldosterone
- Cortisol
- Testosterone
What are the roles of carrier proteins in transportation of some hormones?
- Increase solubility of hormone in plasma
- Increase half life of hormone
- Readily accessible reserve
Explain why some hormones must be bound to carriers for transportation
- Hormones transported in bloodstream
- Some hormones are water soluble (peptide, glycoprotein, adrenal medulla hormones)
- Most hormones are lipid soluble so must bind to proteins (some have specific proteins e.g. Thyroxine-binding globulin TBG)
What factors determine the level of hormones in blood plasma?
- Rate of production
- Rate of delivery
- Rate of degradation
Explain how endocrine hormones travelling in blood have specificity to target tissues
Target tissues express SPECIFIC COMPLEMENTARY RECEPTORS on their plasma membranes which are recognised by the hormones and can initiate a response (those cells without specific receptors are unaffected by hormone)
Explain why only some hormones must bind to receptors in order to initiate a response within the cell
- Some hormones e.g. Steroid are LIPID SOLUBLE so can diffuse straight across phospholipid bilayer and initiate a response within the cell
- WATER SOLUBLE hormones e.g. Insulin cannot diffuse through the the lipid bilayer so rely on receptors to initiate response via a cascade mechanism
Explain how a G PROTEIN COUPLED RECEPTOR allows a hormone to initiate a response within the cell
- Hormone (e.g. Adrenaline) binds to receptor causing a dissociation of the G protein α subunit
- Activation of effector protein ADENYL CYCLASE stimulates formation of secondary messenger cAMP from AMP
- Protein KINASE enzymes activated and PHOSPHORYLATION of target proteins occurs, causing a cellular response
Explain how hormones produced in the hypothalamus act in 2 distinct NEUROCRINE pathways
- Hormones produced in hypothalamus are transported to posterior pituitary and secreted to have direct effects on distant target tissues
- Hormones secreted into HYPOPHYSEAL PORTAL SYSTEM affect endocrine anterior pituitary to initiate release of other hormones which affect distant target tissues
Name 2 hormones that are produced by the hypothalamus and secreted by the posterior pituitary and state their effects
- OXYTOCIN affects milk let down and uterine contractions during birth
- ANTI-DIURETIC HORMONE acts on walls of collecting duct in kidneys for regulation of body water volume
What is meant by a TROPIC HORMONE?
- Hormone that stimulates the secretion of another hormone
- Hypothalamus contains 7 tropic hormones that stimulate the secretion of other hormones from the anterior pituitary
Name 3 tropic releasing hormones produced by the hypothalamus and state their affect on the anterior pituitary
- Thyrotropin releasing hormone TRH -> stimulates anterior pituitary to release TSH
- Corticotropin releasing hormone CRH -> stimulates anterior pituitary to release ACTH
- Gonadotropin releasing hormone GnRH -> stimulates anterior pituitary to release FSH and LH
What is the difference between TROPHIC and TROPIC hormones?
- TROPHIC hormones affect growth
- TROPIC hormones affect the release of another hormone
Describe the position of the pituitary gland in relation to the hypothalamus and explain why this is advantageous
- Pituitary gland located beneath hypothalamus on a socket of bone called the SELLA TURCICA
- Allows the neurocrine transition of hormones produced in the hypothalamus to the pituitary for secretion and activation of other hormones
Explain how the hypothalamus is physically linked to the posterior pituitary gland
Linked via the INFUNDIBULUM (pituitary stalk)
Describe the neurocrine function of the posterior pituitary gland
- Hormones e.g. OXYTOCIN and ADH produced in hypothalamus are transported down NERVE AXONS to posterior pituitary
- Hormones are then STORED
or SECRETED from posterior pituitary to distant target tissues
Explain how the hypothalamus controls the secretion of hormones homeostatically
- TROPIC hormones produced by hypothalamus are stored at axon endings (MEDIAN EMINENCE) and are not released into HYPOPHYSEAL PORTAL SYSTEM unless stimulated by changes in the body’s internal environment
- Once released they enter the anterior pituitary and can stimulate or inhibit the production of other hormones
What is the role of the HYPOPHYSEAL PORTAL SYSTEM?
- System of blood capillaries that connects hypothalamus to anterior pituitary gland
- Allows rapid transportation of tropic hormones produced in hypothalamus to anterior pituitary which stimulate the production and secretion of other hormones (which can affect distant target tissues)
Name 6 hormones produced by the anterior pituitary gland
- TSH (thyroid stimulating hormone)
- LH (luteinising hormone)
- FSH (follicle-stimulating hormone)
- ACTH (adrenocorticotropic hormone)
- GH (growth hormone)
- PRL (prolactin)
Explain how the hypothalamus-pituitary adrenal axis is an example of negative feedback
- Stress stimulus causes hypothalamus to release CRH into hypophyseal portal system which travels to anterior pituitary
- CRH stimulates production and secretion of ACTH which stimulates adrenal gland to secrete CORTISOL
- Cortisol can then inhibit hypothalamus from producing further CRH to inhibit further release of cortisol, maintaining cortisol concentrations in blood
Which 2 nuclei in the hypothalamus are involved in the production of oxytocin and ADH?
- PARAVENTRICULAR NUCLEUS controls ADH production
- SUPRAOPTIC NUCLEUS controls oxytocin production
- Both hormones are stored and secreted in the posterior pituitary gland (pass down from hypothalamus via infundibulum)
