Hormones and Homeostasis Flashcards
Van’t Hoff equation
π=RTC
π is osmotic pressure
R is the gas constant, 0.0083 MPa litre /mol/K
T is the temp in K
C is concentration in osmoles per litre
Water potential
ψ=ψs+ψp
Where ψs is solute potential (=-π)
And ψp is pressure potential
Einstein diffusion equation
t=x^2/2D
Where t=time
x= distance
D= diffusion coefficient, which depends on the substance, size and medium it’s diffusing through
Methods to speed up transport within cells (4)
1) Cytoplasmic streaming
2) Axonal transport, transport via axon
3) Bulk flow- fluid movement driven by mechanical energy gradient, usually pressure
4) Polar auxin transport
Darcy’s law of flow
Q=ΔP/R
Q= flow rate ml/min
ΔP= difference in pressure
R= resistance in tube
Adapted from V=IR
How do plant and animal cells not burst
Plant- have cell wall so at water enters cell, ψp increases until isotonic
Animal- no cell wall so pump solutes out to decrease ψs of extracellular solution until isotonic
Homeostasis
The maintenance of relatively constant conditions in the body for physiological processes that act to counter any departure from the normal
Comformers
Animals that do not regulate some aspect of their internal environment so it varies with the external
E.g. osmoconformers- don’t regulate int. conc
Poikilotherm- organism whose body temp varies considerably w the environment
Feedback loops
Negative loops are often used in homeostasis. A sensor detects deviance from set value, sends a signal to the brain which corrects it
Positive feedback loops are rarely used, but good at rapid change but need to be self limiting.
Some e.gs are rise phase of APs, parturition (giving birth), urination, metamorphosis
Neurocrines
Chemical messengers secreted by nerve cells. If being secreted to a receptor on another nerve cell it is called a neurotransmitter
E.g. ACh, ADH
Endocrine
Hormones; Chemical messengers secreted by a specific tissue into the blood stream
E.g. adrenaline, testosterone, ADH
Paracrine
Chemical messengers like hormones but act locally rather than travelling in the blood
E.g. nitric oxide, histamine
Autocrine
Chemical messengers similar to paracrines but only act in the same type of cell
E.g noradrenaline, histamine
Cytokines
Chemical transmitter secreted by white blood cells
Pheromones
Chemical messengers like hormones but released into the external environment that only affects members of the same species
Water-soluble hormones
Packaged into vesicles
Released by exocytosis
Usually travel ‘loose’ in the plasma
Bind to receptors on plasma membrane
Most have short-term effects
Types of water-soluble hormones
Peptide/polypeptide hormones: 3-200 amino acids long. E.g. insulin, TRH
Glycoprotein: oligosaccharide covalently bonded to a protein. E.g. LH, hCG
Catecholamines: made from tyrosine, e.g. adrenaline
Lipid-soluble hormones
Diffuse out of cells
Travel in blood bound to carrier proteins
Bind to receptors inside cells
Often have long-lasting effects
Types of lipid-soluble hormones (4)
Steroids: made from cholesterol, e.g. testosterone and oestrogen
Thyroid hormones: made from tyrosine, e.g. thyroxine/T4 which contains Iodine
Fatty acid derivatives: require enzyme cyclooxygenase. E.g prostaglandins which mediate inflammation
Indolamines: e.g. melatonin, synthesised in pineal gland, coordinates circadian activities and seasonal based reproduction. Has characteristics of both water and lipid soluble hormones
Receptors
A receptor for a hormone is often found on multiple tissues. Hormonal activity can be regulated by controlling receptor expression.
G-protein couples receptors (GPCRs)
Membrane bound for water-soluble hormones. G-protein have an α- and βγ-subunit. When hormone binds to receptor, α-subunit release GDP and bind to GTP. Subunits then dissociate from receptor and each other. α- binds to Adenylate cyclase, ATP->cAMP, activated protein kinase A, phosphorylation cascade, which has many steps so fine control. Phosphodiesterase hydrolyses cAMP to terminate response.
Receptors for lipid-soluble hormones
Some dissociate from carrier proteins, then diffuse across CSM
Thyroid hormones require membrane/based transports
Some others are taken up w their carrier proteins via receptor-mediated endocytosis
Some steroid hormones bind to receptors in cytoplasm which then move into nucleus, others and thyroid hormones bind to receptors in the nucleus. These receptors are ligand-modulated transcription factors.
Destruction of chemical messengers
Most hormones metablosied by liver or kidneys, some are excreted in urine.
Half-life of hormones
The half-lives of hormones in plasma varies from 1-3 mins for adrenaline to 7 days for thyroxine, which is protected by its carrier protein. The long half life helps keep levels constant as thyroxine affects metabolic rate so levels shouldn’t change suddenly
Pituitary gland
Endocrine gland that lies beneath the hypothalamus. It is called the hypophysis
Posterior pituitary gland control
Also called neurohypophysis, it is a downgrowth of the brain. To control, hormones are made in cell bodies of nerves in the paraventricular and supraoptic nuclei in the hypothalamus. They travel down axons down the hypothalamic-hypophyseal tract to the PPG and await release. An AP down these axons to cause release by exocytosis into the blood
Main hormones released by posterior pituitary gland
Antidiuretic hormone- released under conditions of high osmotic pressure and low blood volume. It increases water permeability of kidney collecting ducts. At high conc is causes vasoconstriction to compensate for loss of blood volume
Oxytocin- causes contraction of uterus during parturition (labour) in response to cervix contraction- forms a positive-feedback loop
Also causes ejection of milk in response to suckling
Anterior pituitary gland
And upgrowth of the mouth in an embryo that develops into hormone-producing glandular cells and is therefore outside of the blood-brain barrier. It is also called the adenohypophysis.
Anterior PG control
No direct neural connections. Instead neuroma from various hypothalamic nuclei have axons terminating in the median eminence. When stimulated they release neuroendocrine transmitters into capillary beds. The capillaries drain into the hypothalamic-hypophyseal portal vessels which carry the hormones to more capillaries in the APG. The hormones are either Releasing hormones (RH) or inhibitory hormones to promote or suppress hormone secretion from the APG
Anterior pituitary hormones
Involved in control of endocrine glands elsewhere in the body, e.g. thyroid gland, adrenal cortex, gonads
Long-loop feedback
Feedback on the hypothalamus or pituitary from a hormone produced elsewhere in the body
Short-loop feedback
Pituitary hormone feeds back on synthesis or release of a hypothalamic hormone
Ultra-short-loop feedback
Hypothalamic hormones inhibiting their own production
Steroid hormones
Steroids: made from cholesterol, e.g. testosterone and oestrogen
Thyroid hormones
Made from tyrosine, e.g. thyroxine/T4 which contains Iodine
Fatty acid derivatives
Require enzyme cyclooxygenase. E.g prostaglandins which mediate inflammation
Indolamines
e.g. melatonin, synthesised in pineal gland, coordinates circadian activities and seasonal based reproduction. Has characteristics of both water and lipid soluble hormones
