function of the endocrine system
Regulating metabolism, water and electrolyte balance, allow body to cope with stress, regulate growth, control reproduction, regulate circulation and RBC production, control digestion and absorption of food
regulation of hormone activity
- secretion
- transport
- metabolism
- excretion
- target cell responsiveness
central regulation vs. direct regulation
central - controlled by the brain - affected by neg feedback loops - can be fast, slow or long term direct - endocrine cells respond directly to changes in extra-cellular fluid levels of substances (eg. glucose, Ca) - very rapid response to critical needs
hormones of the hypothalamus and anterior pituitary
- CRH - ACTH (trophic)
- TRH - TSH (trophic)
- GnRH - FSH & LH (trophic)
- Dopamine - Prolactin (inhibits) (non-trophic_
- GHRH - GH (both)
- Somatostatin - GH (inhibits) (both)
hormones of the posterior pituitary
- ADH
- Oxytocin
what is involved in growth?
structural growth of tissues
- synthesis of proteins
- lengthening of bones
- soft tissue cell size & number increase
non-linear
- highest in utero
- then two major growth spurts during life (postnatal and pubertal growth spurts)
factors that effect growth
- GH levels
- genetic determination of height & shape
- dietary impact (amino acids)
- chronic disease or stressful environment
- other hormones (Th, insulin, sex steroids)
effects of growth hormone (primarily metabolic)
Muscle - stimulates amino acid uptake - increase muscle mass Adipose tissue - decrease glucose uptake - increase fat breakdown Liver - increase protein synthesis - increase gluconeogenesis - stimulates IGF production
actions of IGF-I (primarily growth)
- increase bone length
- stimulates osteoblast to increase bone thickness
- soft tissue growth (hypertrophy, hyperplasia)
actions of IGF-II
promotes soft tissue and organ growth by increasing protein, RNA and DNA synthesis
excess GH secretion
Excess GH in child - giantism Excess GH in adult - widening bones in hand, feet and face - thickening of soft tissue - usually due to pituitary tumor
GH deficiency
Hyposecretion Adult - not detected Hyposecretion Child - normal body proportions - poor muscle development - if diagnosed before puberty can have near normal growth
Thyroid function
- release T3 & T4
- T4 converted to T3 in blood due to high potency
- increase metabolic rate and heat production in cells
- increase response to catecholamines
- promotes effects of GH and IGF
TH synthesis and release
- TH is attached to a backbone in colloid so it doesn’t cross the cell membrane
- released from backbone to go through follicular cell and into blood
hypothyroidism
- primary - thyroid gland failure
- secondary - deficiency TRH or TSH - decreased iodine
Symptoms - decreased metabolism
- poor cold tollerance
- weight gain
- fatigue
- slow reflexes
hyperthyroidism
Grave's Disease - TSI activates TSH inducing TH release Symptoms - increased metabolism - sweating - increased appetite but weight gain - anxiety
what is Ca used for?
- bone and teeth structure
- resting membrane potential
- nerve cell excitability
- neurotransmitter and hormone release
- muscle contraction
regulation of calcium
Acute control
- maintain constant free Ca in plasma
- through rapid exchange between ECF and bone
Chronic control
- maintain constant Ca in body long term
- adjust GI absorption and urine excretion
3 main hormones that regulate Ca
1) PTH
2) Vitamin D3
3) Calcitonin
PTH functions
Bone - increase membrane osteocyte pumps - increase reabsorption of Ca from bone fluid into plasma - increase osteocytes - decrease osteoblasts - increase reabsorption of ca & PO4 Kidney - increase Ca absorption - decrease Ca excretion - increase PO4 excretion - decrease PO4 absorption GIT - increase activation of vitamin D to vitamin D3 - IN INTESTINES - increase absorption of Ca - increase number of Ca transporters - increase bone resorption of Ca
PTH hypersecretion (hyperparathyroidism)
BONES, STONES, GROANS
- increase Ca resorption for bone causes softening and fractures
- increase Ca excretion through kidneys leads to stones
- decreased excitability of nerves and muscles
- hypercalcemia leads to nausea and constipation
PTH hyposecretion (hypoparathyroidism)
- caused by gland destruction
- parathyroid glands are essential for life
- increased nerve and muscle excitability
- cramps, twitches, tingles
action of insulin
- vesicles bring GLUT-4 to the surface of the cell, therefore glucose transports across membrane
- stimulates glycogenesis (glucose to glycogen)
- stops gylogenolysis & gluconeogenesis
- not in live, brain and exercising muscle as they don’t need insulin to uptake glucose
action of glucagon
- starts glycogneolysis and gluconeogenesis
- stops glycogenesis
- promotes ketone production
- stops protein synthesis
