hormones and nutrient partitioning

7/31/2019 Hormones and Nutrient Partitioning

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Hormones and nutrient

partitioning

Dr. Mark Meade


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Control of nutrient utilization

Nutrient utilization controlled by metabolicpathways and metabolites themselves but

are primarily controlled by hormones Hormonea chemical messenger produced in

the body by one tissue that effects the actions ofother tissues

Many hormones involved in partitioning theuse of energy to those areas where its neededin the body


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Insulin and Glucagon

Produced by (glucagon) and (insulin) cells of

pancreas

Insulin released in response to high blood glucose Also in response to glucagon, GH, and gastric

inhibitory peptide (glucose-dependent insulin-releasing

peptide)

Glucagon released in response to low bloodglucose


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Insulin

Overall, makes sure cells can take up nutrients

(glucose)

Increases rate of uptake of glucose by liver, muscle andfat cells

Stimulates glycogenesis (formation of new glucose)

Stimulates release of fatty acids from liver and fat

Stimulates uptake of amino acids by liver and muscle


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Abnormalities associated with

insulin Diabetes mellitus (type I)associated with

a loss of cells in pancreas (autoimmune)

Diabetes mellitus (type II)associated with

defective signal reception for insulin

Both lead to hyperglycemia, glycosuria, and

reduced stores of lipids and proteins


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Growth Hormone (GH or

somatotropin) Produced by anterior pituitary

Release controlled by two hypothalamic

neurohormones

GH releasing hormone (GRH)

GH inhibiting hormone (GIH or somatostatin)

Blood glucose can effect release of

hypothalamic hormones


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GH

Increases blood glucose by

Stimulating gluconeogenesis

Blocking glucose uptake by tissues other than

nervous system

Promotes utilization of fatty acids as an energy

source Promotes use of other substrates than glucose


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GH functions

Promotes RNA and protein synthesis

Promotes growth of bone and cartilage

Promotes growth by increasing cell

numbers


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Response to GH

Depends on age of animal

Neonatal mammal is insensitive

Stimulates liver to produce other growth-

promoting factors (insulin-like growth

factors)


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GH abnormalities

Gigantismcaused by hypersecretion of

GH before puberty

Acromegalycaused by hypersecretion of

GH after puberty

Dwarfismcaused by by hyposecretion of

GH during childhood and adolescence


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IGF

Insulin-like growth factors

Many different forms produced by many tissues

IGF-I produced by liver

IGF-I mediates the effects of GH on tissues

Helps GH cause muscle growth

Independently reduces uptake of glucose by fat cells


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Catecholamines and

Glucocorticoids Adrenal gland

hormones

Catecholamineadrenal medulla

(ectodermal origin)

Glucocorticoids

adrenal cortex(mesodermal origin)


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Chromaffin cells

(modifiedpostganglionicsympathetic neurons)


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Synthesis and release of

catecholamines Both a neurotransmitter and hormone

Involved in famed fight or flight response

As a hormone, acts to: Cause contraction/relaxation of smooth muscle

Stimulate glycolysis and lipolysis

Increase heart rate and contraction Known to increase muscle production and

decrease stored lipid


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Chromaffin cells

Found with steroidogenic tissues in

mammals

Significance is steroidogenic tissue inducesproduction of more epi than nor-epi

Found as separate tissue in other vertebrates

(e.g., fishes)


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Epi and Nor-epi release

Chromaffin cells

stimulated by action of

preganglionicsympathetic nerves


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Pos and Neg feedback

Release of epi causes more blood flow to adrenals

and thus more release of epi (pos)

Release of nor-epi inhibits further release of nor-epi (neg)

ATP (in secretory granules) reduces calcium

influx and thus inhibits release (neg)

Hypoxia can also stimulate release of

catecholamines (pos)


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Effects of catecholamines

Many effects depending on the type of adrenergic

receptors (adrenoreceptors)

-increase metabolic rate and blood flow - increase blood glucose and fatty acid conentrations

Also stimulate protein synthesis in muscle and lipolysis in

adipose (fat) tissue

Thus stimulation of receptors will enhance growth

Ractopaminea agonist used in pigs and cattle to

stimulate increased muscle


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Glucocorticoids

Released from adrenal cortex when

stimulated by the anterior pituitary hormone

ACTH 3 categories actually secreted

Glucocorticoids

Mineralcorticoids

Reproductive hormones


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Glucocorticoids

Cortisol

Cortisone

corticosterone


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CRH release

Glucocorticoid levels highest in morning

Starvation

Stress


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Glucocorticoid effects

Liver

Promotes gluconeogenesis

Fat cells Release fatty acids (direct source of energy)

Muscle cells

Lose amino acids (opposite the effects of

catecholamines) Also stimulate gastric secretion, inhibit immune

response


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Thyroid hormones

Cells (follicles) of thyroid are stimulated by

TSH from anterior pituitary

Two major thyroid hormones

3,5,3-triiodothyronine (T3)

Thyroxine (T4)

Steroid-like hormones which have longlasting effects on target cells


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Effects of thyroid hormones on

target tissues Causes organs to be more sensitive to

epinephrine, stimulating cellular respiration,

oxygen consumption, and metabolic rate

Affect development and maturation of some

mammals (protein synthesis)

Only in presence of GH


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Thyroid abnormalities

Cretinism (humans)results from

hypothyroidism (lack of dietary iodine)

Somatic, neural, and sexual development

Metabolic rate reduced

Immune responses limited

Hypothalamus continues to secrete TSH andcauses thyroid gland to hypertrophy (goiter)


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Leptin

A hormone produced by fat tissue

A satiety hormone that plays role in

regulating appetite.

Acts as a body fat sensor

Increased in body when fats high thus decreasing

appetite Decreased in body when fats low thus increasing

appetite


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Regulation of milk production

Can require huge amounts of energy and animalwill sacrifice nutrients to make sure lactationoccurs properly

Controlled by GH, IGF-I, and estrogen (an ovary

hormone) in ruminants Controlled by prolactin (another pituitary

hormone) and estrogen in non-ruminants

Insulin may have some stimulatory effect since itresults in glucose availabiltiy

Glucocorticoids may inhibit lactation

Thyroid hormones may also stimulate lactation

hormones and nutrient partitioning

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