Endocrinology part 2

thyroid gland

• stimulated by TSH

• 3 main hormones: T3 (metabolically active form), T4 (more of this present and increases during exercise) and calcitonin

• T3 and T4 are permissive: permits full effect of other hormones

• help regulate growth and development

calcitonin

• independent of TRH and TSH

• opposes the parathyroid (parathyroid is more active)

• blocks Ca2+ release from the bones, stimulates excretion by the kidneys, and stimulates osteoblast function

Parathyroid hormone

• primary hormone in plasma calcium regulation

• stimulates calcium release from the bones and stimulates osteoclasts and stimulates reabsorption of calcium by the kidneys

• converts Vit. D3 into another hormone that stimulates calcium absorption by GI tract

adrenal medulla

• secretes the catecholamines (epi and nor-epi)

• relation to SNS: fight or flight response

• hormones are increased during exercise in response to increasing intensity

• maintains BP and glucose levels

epinephrine

increases glycogenolysis and lipolysis

norepinephrine

• increases lipolysis

• acts as a neurotransmitter when released by sympathetic nerve fibers

• precursor to epi

beta-receptors

receptors that are positively associated with exercise

alpha-receptors

receptors that deal with organs that aren’t necessary for exercise

Beta-1

• equal amounts of E and NE

• increases HR, glycogenolysis and lipolysis

• beta-blockers

Beta-2

• E is significantly greater than NE

• increases bronchodilation and vasodilation

• inhalers

Beta-3

• NE is greater than E

• increased lipolysis

Alpha-1

• E is greater than or equal to NE

• increases vasoconstriction

• seen in digestive system

Alpha-2

• E is greater than or equal to NE

• opposes actions of B1 and B2 receptors and decreases insulin secretion

adrenal cortex

• secretes steroid hormones that are derived from cholesterol

• 3 components: mineralcorticoids, glucocorticoids, gender steroids

mineralcorticoids

• aldosterone

• maintains the sodium-potassium pump (more so sodium)

glucocorticoids

• cortisol

• regulates plasma glucose

gender steroids

• androgens and estrogens

• supports pre-pubescent growth

aldosterone

• controls water and salt balance in the kidney

• regulates blood volume and BP in conjunction with ADH

• part of the RAAS system: these levels increase during exercise

• stimulated by an independent potassium increase and decreased plasma volume

RAAS system

1. angiotensinogen is inactive from the liver

2. converted to angiotensin I by renin from the kidneys

3. converted to angiotensin II by ACE from the lungs

4. Angiotensin II acts on smooth muscle hypertension, the kidneys, the adrenal cortex, the PP for ADH secretion, and the hypothalamus

what happens to RAAS hormones during exercise

they increase around 50% of VO2max

cortisol

• stimulated by stress (ACTH) and exercise

• maintains plasma glucose by gluconeogenesis, FFA mobilization, glucose synthesis, promotes FFA for fuel, blunts insulin

• holistically catabolic

• increased levels suppress the immune system

• diurnal: highest levels are right upon waking sine there’s no fuel to mobilize

• only seen at higher intensities (GH and epi are seen at lower intensities)

pancreas

• exocrine (digestive system) and endocrine functions

• secretes insulin, glucagon, and somatostatin, and digestive enzymes/bicarbonate

insulin

• anabolic

• stores glucose, AA, and fats; LOWERS blood glucose

• decreased levels lead to diabetes (exercise can increase GLUT-4 translocation)

• from beta cells

• levels in the blood decrease with exercise (no storage with fuel mobilization)

• suppressed by catecholamines

glucagon

• catabolic

• from alpha cells

• promotes mobilization of fatty acids and glucose

• levels increase with exercise only in untrained individuals

• increases blood glucose

testosterone

• secreted from interstitial cells of the testes

• anabolic and androgenic steroid: muscle building and masculinizing effects (degrade quickly)

• levels increase during submaximal exercise

• constant levels at all times

estrogen and progesterone

• secreted from ovaries

• regulate ovulation and menstruation (can lose menstrual cycle with overtraining)

• levels vary throughout menstrual cycle

• estrogen peaks in follicular, progesterone peaks during luteal

• best performance right before ovulation

• ovulation has peak FSH and LH

• luteal decreases VO2 max and increases body temp