9.2 - Endocrinology + Endocrine Control Of Appetite Flashcards
What is homeostasis
mechanisms that act to counteract changes in the internal environment
- Dynamic equilibrium
- Variables are regulated so that conditions remain stable and relatively constant
- Failure in homeostasis → disease
- Mechanisms exist at all levels:
☞ cell (ie Ca2+ regulation)
☞ tissue (balance between cell proliferation + apoptosis)
☞ organ (kidney regulating water)
☞ organism (constant body temperature)
Elements of a homeostatic control system
stimulus is a change in environment → receptor detects stimuli → communication via afferent pathway (via nervous system or endocrine system) → control system (ie hypothalamus) determines the set point, analyses afferent input and determines response → communication via efferent pathway → effector causes change ie sweat glands, muscle → negative (or positive) feedback
What are the 3 main roles of the control centre
Ie the hypothalamus
- determine the set point ie core body temp
- analyse the afferent input ie thermoreceptors detecting a rise in core body temp
- determine the appropriate response ie lower core body temp by sweating etc
What are the different types of receptors
- chemoreceptors detect chemical changes eg O2, CO2 and pH levels
- thermoreceptors detect changes in temp
- proprioreceptors detect changes in position and movment (postioning of limbs)
- mechanoreceptors detect mechanical stimuli, such as pressure and stretch
- nociceptors detect potentially dangerous stimuli at the skin, such as temperature and pressure extremes. Ie detects pain
Biological rhythms
- Set point of control centre can change, resulting in biological rhythms
- circadian aka diurnal rhythms
- Human biological clock found in the hypothalamus in the form of a small group of neurones called the suprachiasmatic nucleus
- The biological clock receives input from environmental cues akazeitgeibers (light, temp, physical activity)
- Keep body on 24 hour cycle
-
melatonin hormone is secreted from pineal gland + is involved in setting biological clock
☞ examples of biological rhythms include: cortisol (peaks at 9am) and the menstrual cycle (where levels of different hormones have set points that vary according to a monthly cycle)
Positive + negative feedback
negative
- Opposing direction of change
- Most common form of feedback in physiological systems
- Brings variable back to set point
positive
- Much rarer form of feedback
- Amplifies the stimulus
- This causes variable to deviate even further from set point
- Ie during labour where loop acts to increase strength of each uterine contraction
Osmolarity vs osmolality
osmolarity = the number of osmoles per litre of solution (therefore volume)
osmolality = the number of osmoles per kg of solution (therefore mass)
Osmole = the amount of substance that dissociates in solution to form one mole of osmotically active particles
ie 1mM solution of NaCl ⇢ Na+ + Cl- (therefore osmolarity of 2mOsmol/L (1 from Na+ and 1 from Cl-)
ADH + its role in body fluid homeostasis
high blood osmolality → body needs to conserve more water → detected by osmoreceptors in hypothalamus → thirst (which causes drinking, reducing osmolality) + stimulates posterior pituitary to secrete more ADH → increased reabsorption of H2O from urine into the blood in collecting ducts in the kidney → small volume of concentrated urine → normal blood osmolality
low blood osmolality → body needs to excrete water → detected by osmoreceptors in hypothalamus → posterior pituitary secretes less ADH → decreased reabsorption of H2O from urine into blood in collecting ducts of kidney → large volume of dilute urine → normal blood osmolality
Plasma glucose homeostasis (in broad terms)
in fed state → glucose concentration increases → β cells in islets of Langerhans (pancreas) secrete insulin → stimulates glucose uptake into tissues via GLUT4 + stimulates glycogenesis in liver → plasma glucose declines
in fasted state → decreased plasma glucose → α cells in islets of Langerhans (pancreas) releases glucagon → stimulates glycogenolysis in liver → glucose released into blood → plasma glucose increases
Endocrine system: what are hormones
☞ Chemical signals produced in endocrine glands or tissues that travel in the bloodstream to cause an effect on other tissues
☞ hormones often act on distant target cell
☞ present in the blood at very low concentrations
☞ Has many different methods of communication via hormones ie autocrine, paracrine, endocrine + neurocrine (more detail on separate card)
What are some of the major endocrine glands (and other important organs + tissues)
major endocrine glands
- Hypothalamus
- Pituitary
- Pineal
- Thyroid
- Parathyroid
- Thymus
- Adrenal
- Pancreas
- Ovary / testis
other important organs + tissues
- Heart (ANP + BNP to regulate blood pressure)
- Liver (IGF1 for insulin)
- Stomach (gastrin + ghrelin)
- Placenta (inhibin, placental lactogen)
- Adipose (leptin)
- Kidney (erythropoietin, renin + calcitriol)
Methods of communication via hormones
- autocrine where hormone signal acts back on the cell of origin
- paracrine where hormone signal carried to adjacent cells over a short distance via interstitial fluid
- endocrine where hormone signal is released into blood and carried to distant target cells
- neurocrine where hormone originates in neurone, passed down axon before travelling in bloodstream, and carried to distant target cells
Endocrine + nervous system (similarities + differences)
similarities
- Both neurons + endocrine cells are capable of secreting
- Both cells can be depolarised (ie they are excitable)
- Some molecules act as both neurotransmitter + hormone (ie dopamine)
- The mechanism of action requires interaction with specific receptors in target cells
- Both systems work in parallel to control homeostasis
- Both require receptors
differences
- signal E = hormones, N = neurotransmitters + action potentials
- nature E = chemical, N = chemical + electrical
- transporting E = bloodstream, N = synapses + axons
- speed E = slow, N = fast
Classification of hormones
peptide / polypeptide
- Short chains of AAs
- Ie insulin, glucagon + growth hormone
- All water soluble
glycoproteins
- Large protein molecules with carbohydrate side chain
- Often made up of subunits
- Eg LH, FSH + TSH
- All water soluble
amino acid deriratives (amines)
- Synthesised from aromatic amino acids
- Ie adrenaline, noradrenaline, thyroid hormones (from tyrosine)
- Ie melatonin (from tryptophan)
- Mixture of water (adrenal medulla hormones) and lipid soluble (thyroid hormones)
steroid
- All derived from cholesterol
- Steroidogenic tissues convert cholesterol to different hormones
- Ie cortisol, aldosterone + testosterone
- All lipid soluble
What are the steroid hormones (names)
all derived from cholesterol + are lipid soluble
- Aldosterone
- Testosterone
- Progesterone
- Cortisol
