Physiology Flashcards
Hormone definition
chemical substance secreted by cells into extracellular fluid
4 forms of chemical signalling
Autocrine, paracrine, endocrine and neuroendocrine
Autocrine signalling is…
cells signalling to itself by releasing a ligand to bind to its own receptors
Paracrine signalling is…
cell signalling to neighbouring cells
Endocrine signalling is…
specialised cells that release hormones into the bloodstream
Neuroendocrine signalling is…
nerve cell transmits signals from synapse of one nerve to another eg acetylcholine
2 classes of hormones..
lipid-soluble - use transport proteins eg steroids.
water-soluble - circulate in free form eg amine
Glands release amino acid or lipid soluble hormones but specific hormones which are steroid based are from…
specific areas eg testosterone (testes and ovaries)
Steroid hormones have a longer or shorter effect?
Longer
Target cell activation depends on…
- Concentration of hormone
- Number of receptors on target cell
- Affinity of receptors
- Influence exerted by other hormones
3 types of hormone interaction…
Permissiveness, synergism and antagonism
Permissiveness is…
one hormone cannot exert its effects without another hormone
Synergism is…
more than one hormone produces the same effects on the target cell, these are effective individually however more affected when joint together
Antagonism is…
one or more hormones oppose the action of another hormone
Humoral stimuli is…
secretion of hormones in direct response to changing ions and nutrients blood levels
Hormonal stimuli is…
release of hormones in response to hormones produced by endocrine glands
Neural stimuli is…
nerve fibres stimulate hormone release (autonomic NS)
Pituitary gland secretes how many hormones…
9
Anterior lobe does…
synthesis and secrets a number of hormones
Posterior lobe does…
receives, stores and releases hormones from the hypothalamus
Which two hormones are sent from the hypothalamus to the posterior lobe of pituitary gland?
Oxytocin and antidiuretic
What are tropic hormones?
Made in the anterior pituitary but act on other endocrine systems
Anterior pituitary hormone examples…
hGH, FSH, LH, TSH
What does Human Growth hormone do?
- Stimulates most cells but targets bone and muscle
- promotes protein synthesis using fats for fuel (decreasing fat stores), conserving carbs
- stimulates liver, skeletal muscle, bone to produce insulin-like growth factor
- Increase muscle hypertrophy
- Increases nuclear transcription of DNA to RNA
- Increases amino acid uptake and decreases breakdown
Drawbacks of Human growth hormone…
Acetoacetic acid is byproduct of using fatty stores and then causes fatty liver disease. Also stimulates free fatty acids
hGH effects on CHO…
- decreases glucose uptake in tissues
- increases insulin secretion
- induces insulin resistance
- leads to diabetes
- increases skeletal growth
Somatomedins are…
insulin-like growth factors released by the liver once triggered by hGH
Why are somatomedins important..
Need these as well as hGH to get full hGH effects as Somatomedin C (IGF 1) also prolongs the effects
Secretion of hGH
- gradual decrease till 25% at v old age
- increased by exercise
- highest during first 2 hrs of sleep
Control of hGH is done by…
antagonistic hypothalamus hormone
Which hormone releases hGH…
Growth hormone-releasing hormone
Which hormone inhibits hGH…
Growth hormone-inhibiting hormone
hGH secretion increases during…
starvation for protein synthesis and tissue growth
4 Abnormalities of hGH sectrition…
Panhypopituitarism, panhypopituitarism dwarfism, gigantism and acromegaly
Characteristics of panhypopituitarism…
- decrease AP hormones
- congenital or acquired
- under active thyroid
Characteristics of panhypopituitarism dwarfism…
- childhood deficiency of AP
- all body parts develop at different rates
- do not pass through puberty
Characteristics of gigantism…
- hyper hGH production until adolescence
Characteristic of acromegaly…
- thicker bones as cant grow taller
- everything else grows larger eg liver, nose, jaw
4 anterior pituitary ‘tropic hormones’
- thyroid stimulating hormone
- adrenocorticotropic H.
- gonadotropins (FSH + LH)
- prolactin
all released by hypothalmic (their name) releasing-hormone
Adrenocorticotropic do….
- stimulates adrenal cortex to release cortisol
- internal and external factors can release cortisol RH which then leads adrenocorticotropic released causing cortisol being released.
Gonadotropins do…
- Follicle stimulating hormone (FSH) and luteinizing hormones (LH)
- regulate function of ovaries and testes
Prolactins do…
- Produce milk in breast tissue
- Suckling stimulates PRH and encourages milk production
Role of posterior pituitary…
stores and releases hormones synthesised by hypothalamus
Examples of posterior pituitary hormones…
- Oxytocin
- Antidiuretic
- Both of these use PIP-calcium secondary messenger
Role of oxytocin…
Triggers milk ejection, induce or hasten labour
Role of antidiuretic hormone (ADH)…
- Helps to avoid dehydration or water overload through inserting aquaporins in DCT or collecting duct.
- Inhibited by caffeine and water but nicotine increases it
Diabetes insipidus is…
3rd type of diabetes where someone cannot retain fluids caused by neurogenic (ADH not being released)
Thyroid facts…
- Largest endocrine gland
- v.rich blood supply
- Filled with follicle cells made of calloid
- Needs iodine to function
Thyroid produces which hormones?
93% Thyroxine (T4) and 7% Triodotyroxine (T3)
T3 = 4x T4
Synthesis of thyroid hormones…
- Basolateral membrane pumps iodide into thyroid cell
- thyroglobulin is synthesised and discharged into lumen of follicle cell
- iodides (i-) are actively taken up and oxidised to produce iodine (i2)
- iodine and tyrosine are released into the lumen together
- they form T1 and T2
- then form T3 and T4 which through a lysosome leave into the blood
Transport of thyroid hormones…
- T4 and T3 bind to thyroxine-binding globulins (TBG) produced by the liver
- Both then bind to target receptors with T3 being 10x more powerful
- taken up by peripheral tissues
Effects of thyroid hormones…
- Glucose oxidation
- increase metabolic rate
- heat production
contribute to : maintaining blood pressure, regulating tissue growth and developing skeletal and nervous system
Thyroid effects on growth…
Hypothyroidism - retarded growth and brain development
Hyperthyroidism - excessive skeletal growth early - gigantism avoided
Effects of thyroid-hormone - specific functions…
CHO metabolism - glucose uptake, gluconeogenesis, insulin secretion
Lipid metabolism - adipose tissue lipolysis, FFA oxidation
Hyperthyroid - Q increases, HR increases respiratory rate increases
CNS excitation - hyper = extremely nervous, vigor muscle contractions, muscle tremor, trouble sleeping
CNS excitation - hypo = sluggish contraction/relaxation, somnolence
