Stages of postnatal growth and their hormones Flashcards
Factors affecting growth
Genotype:
- breed
- species
Non-genetic:
- Sex
- Weaning age
Factors affecting post-natal growth
Genetics
Nutrition
Sex
Hormones
Environment
Stages of Post-natal growth
1) Suckling
2) Puberty
3) Adulthood
4) Senescence
Survival of calf at neonatal (Suckling stage)
- expresion of appropriate behaviour of dam
- calf components - stand and suckle within 1-2 hours of birth (delays increase mortality)
- successful suckling depends on - vigor of the calf, teat seeking behaviour and udder or teat conformation
- dystocia, maternal death, poor udder and teat conformation, neonatal infections, dehydration
Weaning (suckling stage)
A major source of stress
- strategies to reduce stress = creep feeding and gradually decrease milk, separation dam and calf with fence but allow to nose-flaps for 1-2 weeks
Puberty
The time at which animals reach a level of sexual development that makes them capable of reproduction
Physiological event at puberty:
- Female - the first estrus with ovulation
- Male - the first ejaculate with fertile sperm
Neither are sexually mature at puberty if:
- Females are to small to bear young
- Males is not capable or fertile enough to breed regularly
Endocrine events associated with onset of puberty in a heifer
1) Decreased negative feedback
2) increased LH pulse frequency
3) Increased follicle growth
4) LH surge
5) Short luteal phase
Adulthood and Senescence
- Generally, we do not understand the naturally aging process in farm animals because once the “productive” life is complete, the animal is removed from the population
- breeding animals only
- peak production at adulthood
- weight and reproductive function decline in late maturity
- senescence is a process by which a cell ages and permanently stops diving but does not die
- IGF-1 and GH decline
Senescence
- the decrease in survival with increasing age
- reduction in muscle mass
- Increased time to repair injuries
- loss of organ functional units
- loss of reproductive capacity
- death
Hormones
- Produce by endocrine (ductles) glands and secrete into the bloodstream
- Hormones may affect a wide array of target cells to produce multiple effects
- Three types:
1) Amino acids-derived hormones (Tyrosine and typtophan derivatives)
2) Peptide hormones
3) Lipid derivatives or Lipid soluble hormones
Cell Signaling types
Endocrine signaling
Paracrine signaling
Autocrine Signaling
Endocrine Signalling
endocrine signalling uses the circulatory system to transport ligands
slower response but long lasting
Paracrine Signalling
A cell target nearby cell
For quick response
Ligand molecules quickly degrade or remove
Autocrine Signalling
Cell target itself
Cell division
Tissue and liver regeneration
Lipid Derived Hormone (Steroid Hormone)
1) steroid hormones enter through the cell membrane and bind to receptors inside of the target cell
2) these hormones may directly stimulate transcription of genes to make certain proteins
3) because steroids by works by triggering gene activity, the response is slower than peptide hormones
Important Hormones that affect growth in animals
- Growth hormone
- Insulin and glucagon
- Thyroid hormones
- Glucocorticoids
- Prolactin
- Gonadal steroids (androgens and estrogens)
Growth Hormone
Growth hormone - highest at birth and declines with age
Regulates post-natal growth
maximizes lipid utilization and protein synthesis
Pulsatile
Has both direct and indirect effects on tissues
Growth Hormone: Direct effects
Muscle
- increases protein synthesis
- Glucose uptake
- production of IGF-1
- Decreases amino acid uptake
Liver
- increases glucose release
- Glycogenolysis
- Decreases AA oxidation
Adipose
- increase lipolysis and IGF-1
- Reduces lipogenesis, glucose uptake and oxidation
Growth Hormone: Indirect Effects
Muscle
- stimulates protein synthesis
- Increases AA and glucose uptake
- Reduces protein degration
Adipose
- increases lipid synthesis
- Reduces lipolysis
Insulin Like Growth Factors (IGF)
- IGF-I and IGF-II (somatomedins)
- Structure like pro-insulin
- produce by liver and skeletal muscle
- increase glucose and amino acid uptake
- Decrease proteolysis
- Increase protein synthesis
- Stimulates lipogenesis/ decreases lipolysis muscle fibers
- Increase collagen and proteoglycan synthesis
- Induce hypertrophy of fast-glycolytic (type IIB
IGF-binding protein (IGFBP)
- sequester IGFs to controll excess
- Binding in reversible (non-covalent)
- Secretes by liver
- Provides a constant source of IGFs
- Binding to an IGFBP increases the half-life of IGF in the circulation and blocks its potential binding to the insulin receptor
- Binding increases the delivery efficiency of IGFs
- IGFs released by proteolysis of IGFBP or binding of IGFBP to extracellular matrix
Thyroid Hormones
- Effects on muscle growth are potent
- Enable action of growth hormone and IGF-1
- important for CNS growthand development
- GH encourages de-iodinating to active type
- Stimulate basal metabolism through oxidative metabolism and anabolic activity in virtually all tissues
- stimulated metabolism directly increases heat production
Hypothyroidism
UNDER ACTIVE THYROID
- decrease endochondral ossification
- slow/ stunt growth
- reduce both GH and IGF-1 levels
Hyperthyroidism
OVER ACTIVE THYROID
- weight loss
- increased heart rate
- Goiter
- fatigue
Thyroid Hormones: Thyroxine (T4) and triiodothyronine (T3)
- important for the growth and development of the CNS
- Stimulate synthesis of protein and RNA in muscle
- Promote to change of muscle fiber types
- If too high - protein degradation
Insulin
- Released by the pancreas in response to high blood glucose
- Promotes storage of cellular
- Stimulates amino acid transport, protein synthesis
- Inhibits protein degradation
Glucagon
- Released by the pancreas in response to low blood glucose
- Promotes glycogenolysis in liver
Sex steroids
Testosterone and estrogen
- regulate reproduction
- formation and maintenance of secondary sex characteristics
3 major forms of physiological estrogens in females:
1) Estrone (E1): primary form of estrogen after reproductive years (menopause age)
2) Estradiol (E2): primary form of estrogen in animal body during reproductive years
3) Estroil (E3): primary form of estrogen during pregnancy
Testosterone
- Responsible for male secondary sex characteristics
- anabolic effect on muscle
- Sex drive
- Natural testosterone increases both protein synthesis and degradation
- Testosterone can activate the androgen receptor itself or after conversion to dihydroestosterone by the enzyme 5a-reductive
