Hormones and Homeostasis

Question 1

Van’t Hoff equation

Answer 1

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

Question 2

Water potential

Answer 2

ψ=ψs+ψp
Where ψs is solute potential (=-π)
And ψp is pressure potential

Question 3

Einstein diffusion equation

Answer 3

t=x^2/2D
Where t=time
x= distance
D= diffusion coefficient, which depends on the substance, size and medium it’s diffusing through

Question 4

Methods to speed up transport within cells (4)

Answer 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

Question 5

Darcy’s law of flow

Answer 5

Q=ΔP/R
Q= flow rate ml/min
ΔP= difference in pressure
R= resistance in tube
Adapted from V=IR

Question 6

How do plant and animal cells not burst

Answer 6

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

Question 7

Homeostasis

Answer 7

The maintenance of relatively constant conditions in the body for physiological processes that act to counter any departure from the normal

Question 8

Comformers

Answer 8

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

Question 9

Feedback loops

Answer 9

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

Question 10

Neurocrines

Answer 10

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

Question 11

Endocrine

Answer 11

Hormones; Chemical messengers secreted by a specific tissue into the blood stream
E.g. adrenaline, testosterone, ADH

Question 12

Paracrine

Answer 12

Chemical messengers like hormones but act locally rather than travelling in the blood
E.g. nitric oxide, histamine

Question 13

Autocrine

Answer 13

Chemical messengers similar to paracrines but only act in the same type of cell
E.g noradrenaline, histamine

Question 14

Cytokines

Answer 14

Chemical transmitter secreted by white blood cells

Question 15

Pheromones

Answer 15

Chemical messengers like hormones but released into the external environment that only affects members of the same species

Question 16

Water-soluble hormones

Answer 16

Packaged into vesicles
Released by exocytosis
Usually travel ‘loose’ in the plasma
Bind to receptors on plasma membrane
Most have short-term effects

Question 17

Types of water-soluble hormones

Answer 17

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

Question 18

Lipid-soluble hormones

Answer 18

Diffuse out of cells
Travel in blood bound to carrier proteins
Bind to receptors inside cells
Often have long-lasting effects

Question 19

Types of lipid-soluble hormones (4)

Answer 19

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

Question 20

Receptors

Answer 20

A receptor for a hormone is often found on multiple tissues. Hormonal activity can be regulated by controlling receptor expression.

Question 21

G-protein couples receptors (GPCRs)

Answer 21

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.

Question 22

Receptors for lipid-soluble hormones

Answer 22

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.

Question 23

Destruction of chemical messengers

Answer 23

Most hormones metablosied by liver or kidneys, some are excreted in urine.

Question 24

Half-life of hormones

Answer 24

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

Question 25

Pituitary gland

Answer 25

Endocrine gland that lies beneath the hypothalamus. It is called the hypophysis

Question 26

Posterior pituitary gland control

Answer 26

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

Question 27

Main hormones released by posterior pituitary gland

Answer 27

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

Question 28

Anterior pituitary gland

Answer 28

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.

Question 29

Anterior PG control

Answer 29

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

Question 30

Anterior pituitary hormones

Answer 30

Involved in control of endocrine glands elsewhere in the body, e.g. thyroid gland, adrenal cortex, gonads

Question 31

Long-loop feedback

Answer 31

Feedback on the hypothalamus or pituitary from a hormone produced elsewhere in the body

Question 32

Short-loop feedback

Answer 32

Pituitary hormone feeds back on synthesis or release of a hypothalamic hormone

Question 33

Ultra-short-loop feedback

Answer 33

Hypothalamic hormones inhibiting their own production

Question 34

Steroid hormones

Answer 34

Steroids: made from cholesterol, e.g. testosterone and oestrogen

Question 35

Thyroid hormones

Answer 35

Made from tyrosine, e.g. thyroxine/T4 which contains Iodine

Question 36

Fatty acid derivatives

Answer 36

Require enzyme cyclooxygenase. E.g prostaglandins which mediate inflammation

Question 37

Indolamines

Answer 37

e.g. melatonin, synthesised in pineal gland, coordinates circadian activities and seasonal based reproduction. Has characteristics of both water and lipid soluble hormones