The Endocrine System Outline Part 1

communication system for nervous and endocrine systems

neurotransmitters and hormones

4 principal mechanisms of cellular communication

Gap junctions: tiny channels

Neurotransmitters: across synaptic cleft

Paracrine (local) hormones: secreted into tissue fluids, affect NEARBY cells

Hormones (far away): chemical messengers travel via blood to other tissues and organs

hormones

chemical messengers transported via blood; stimulate physiological responses in another organ, often considerable distance away

exocrine vs endocrine glands

DUCTS carry secretions to epithelial surface (ex: sweat glands)

EXTRACELLULAR effects (food digestion)

vs

NO ducts

dense, hole-y, capillary networks allow easy uptake of hormones into blood

INTRACELLULAR effects (altering target cell metabolism)

Both are involved in communication but contrast nervous and endocrine system based on internal communication, speed and persistence of response, adaptation, area of effect

chemicals that function as both hormones and neurotransmitters

norepinephrine, dopamine (also some chemicals share same target cells and regulate each other)

How is hypothalamus related to the pituitary gland?

hypothalamus acts as the master controller, sending hormonal signals to the pituitary (the “master gland”) to regulate other glands like the thyroid, adrenals, and reproductive organs, controlling functions from growth and metabolism to stress response and fluid balance

infundibulum

suspended from hypothalamus by stalk

pituitary gland is housed in …. of sphenoid bone

sella turcica (very well protected)

pituitary gland has the size and shape of a

kidney bean

adenohypophysis

(anterior pituitary)

- from hypophyseal pouch - outgrowth of pharynx

neurohypophysis

(posterior pituitary)

downgrowth from brain

adenohypophysis linked to hypothalamus by…

hypophyseal portal system (vascular connection)

• primary capillaries in hypothalamus connected to secondary capillaries in adenohypophysis by portal venules

• hypothalamic releasing-hormones (RH) regulate adenohypophysis

neurohypophysis connected to hypothalamus by…

hypothalamo-hypophyseal tract (neural connection/ nervous tissue! not a true gland)

• hypothalamic neurons secrete hormones; stored in neurohypophysis until released into blood (oxytocin and ADH)

4 releasing hormones only…

ONLY goes from hypothalamus to anterior pituitary (RH) (hypothalamic hormones)

TRH (PRL and TSH), CRH (ACTH), GnRH (LH, FSH), GHRH (GH and IGF)

these affect anterior pituitary secretion of TSH, PRL, ACTH, FSH, LH, and GH

Follicle-stimulating hormone (FSH) (targets and effects)

ant. pit

target: ovaries/testes

effects: ovarian s3x hormones, development of ovarian follicles, sperm production

Luteinizing hormone (LH) (targets and effects)

ant. pit

target: ovaries/testes

effects: stimulates ovulation, secrete progesterone and testosterone

Thyroid-stimulating hormone (TSH) (target and effects)

ant. pit

target: thyroid

effects: stimulates secretion of thyroid hormone (metabolism, T3, T4, temperature)

Adrenocorticotropic hormone (ACTH) (target and effects)

ant. pit

target: adrenal cortex

effect: secrete glucocorticoids (immune system)

Prolactin (PRL) (target and effects)

ant. pit

target: mammary glands/testes

effect: synthesize milk/secretion of testosterone

Growth hormone (GH) (target and effects)

ant. pit

target: bones, muscles, liver

effect: stimulates mitosis and cellular differentiation

ADH (antidiuretic hormone) (location and effect)

posterior pituitary hormone

increases water retention; reduces urine volume and prevents dehydration

Oxytocin (OT) (location and effect)

posterior pituitary hormones

released during sexual arousal and orgasm, stimulates labor contractions during childbirth, emotional bonding, stimulates flow of milk during lactation

Hypothalamic and cerebral control to respond to cold and stress

HT stimulates anterior lobe to release TSH- generate body heat

ACTH- cortisol- tissue repair

Neuroendocrine reflexes example suckling infant

stimulates nerve endings- HT- posterior lobe- oxytocin- milk ejection

(higher brain centers) Milk ejection reflex can be triggered by

a baby’s cry

Negative feedback

increased target hormone levels INHIBIT further release of hormones

Positive feedback

stretching of uterus increases oxytocin release, MORE contractions, MORE stretching, etc. until delivery

Insulin-like Growth Factors (IGF-I) does what

PROLONGS growth hormone action

LONGER hormone half life- time required for 50% of hormone to be cleared from blood

Prolactin vs oxytocin

milk synthesis vs milk ejection

Growth hormone effects

Protein synthesis increases

Lipid metabolism increases

Carbohydrate metabolism- save glucose for brain

Electrolyte balance- sodium and potassium retention by kidneys, enhances calcium absorption in intestines

pineal gland synthesizes…

MELATONIN (signals body to rest) from serotonin at night- synchronize physiology with 24-hour circadian rhythms of daylight/darkness

Seasonal affective disorder (SAD)

occurs in winter of northern climates

• depression, sleepiness, irritability, carbohydrate craving

• 2-3 hours of exposure to bright light/ day reduces melatonin levels and symptoms (phototherapy)

Thymus hormones (3) and effects

site of maturation of T cells- immune defense

hormones: thymopoietin, thymosin, thymulin- stimulates nervous system

Thyroid gland hormones (3) and effects

hormones: thyroxine (T4 more abundant), triiodothyronine (T3 more potent)

• increases metabolic rate, O2 consumption, heat production, appetite, GH secretion alertness

another hormone is calcitonin

• lowers blood calcium levels (stimulates osteoblast activity)

Parathyroid glands hormone (1) and effects

(posterior side of thyroid gland)

Parathyroid hormone (PTH)

• increases blood calcium levels

• increases bone resorption

Adrenal glands location and 2 types

on top of kidney

adrenal cortex (3 layers, yellow outside) & medulla (inner core)

Adrenal medulla dual nature and hormones (3)

dual nature: endocrine gland and sympathetic ganglion of sympathetic nervous system

• innervated by sympathetic preganglionic fibers

• consists of modified sympathetic postganglionic neurons: chromaffin cells

release catecholamines (epinephrine & norepinephrine) and trace of dopamine into blood

effect of adrenal medulla hormones

longer lasting than neurotransmitters

• increases alertness, preps body for physical activity

• mobilizes high energy fuels, lactate, fatty acids, glucose

• glycogenolysis & gluconeogenesis boost glucose levels

• glucose sparing effect b/c inhibits insulin secretion

• increases blood pressure, HR, metabolic rate, etc.

• decreases digestion and urine production

this is a lot like: FIGHT OR FLIGHT

Adrenal cortex secretes…

major steroid hormones from 3 layers of glandular tissue

Zona glomerulosa (adrenal cortex thin outer layer) secretes what class of hormones? And what does this class do?

mineralocorticoids

• regulates electrolyte balance

• Aldosterone (raises BP) stimulates sodium retention and potassium excretion

• water retained with sodium by osmosis, so blood volume and BP maintained

Zona fasciculata (adrenal cortex thick, middle layer) secretes what class of hormones? And what does this class do?

glucocorticoids

• cortisol (stress hormone)- stimulates fat and protein catabolism, gluconeogenesis, release of fatty acids and glucose into blood

• ACTH makes cortisol

• helps adapt to stress and repair tissues

• anti-inflammatory effect becomes immune suppression with long-term use

Zona reticularis (adrenal cortex narrow, inner layer) secretes what class of hormones? And what does this class do?

sex steroids (testosterone and estrogen)

• androgens: sets libido; important role in prenatal male development (includes DHEA which converts to testosterone)

• estradiol: small quantity, but important after menopause for substaining bone mass; fat converts androgens into estrogen