Chapter 18 Endocrine Glands

Hormones of the Adrenal medulla

-80% epinephrine (adrenaline) -20% norepinephrine

Posterior Pituitary Hormones

-ADH -Oxytocin

Anterior pituitary

-Adenohypophysis -Develops from the roof of the embryonic oral cavity -Secretes 9 major hormones

PTH promotes?

-Ca2+ reabsorption by the kindeys and the formation of active vitamin D by the kidney -Decreased blood Ca2+ levels stimulate PTH secretion

Melatonin

-Can inhibit reproductive maturation -May regulate sleep-wake cycles

Indirect effect of GHRH

-Causes liver and skeletal muscle to produce somatomedins -Insulin-like growth factors bind to receptors on membranes of target cells

Hypothalamohypophysial portal system

-Connects the hypothalamus and the anterior pituitary -Hormones are produced in hypothalamic neurons -Through the portal system, the hormones inhibit or stimulate hormone production in the anterior pituitary

Hypothalamohypophysial tract

-Connects the hypothalamus and the posterior pituitary -Neurohormones are produced in hypothalamic neurons -The hormones move down the axons of the tract and are secreted from the posterior pituitary

When are peak GH levels?

-During deep sleep -Levels lower at other times of day

What is insulin secretion stimulated by?

-Elevated blood glucose levels -increase in some amino acids -parasympathetic stimulation -gastrointestinal hormones

Anterior Pituitary Hormones

-GH -TSH -ACTH -Lipotropins -Beta endorphins -MSH -LH -FSH -Prolactin

Zona fasciculata

-Glucocorticoids- help the body resist stress (keeping blood sugar levels relatively constant, maintaining blood volume and preventing water shift into tissue) Cortisol

Zona reticularis

-Gonadocorticoids (Sex Hormones) Androgens : onset of puperty, appearance of secondary sex characteristics, and sex drive in females

Why is GHRH secreted?

-In response to low blood glucose, stress, increase in certain amino acids

What are the target tissues of insulin?

-Liver -Adipose tissue -Muscle -Satiety center in the hypothalamus

What is glucagon secretion stimulated by?

-Low blood glucose levels -Certain amino acids -Sympathetic stimulation

Thymus

-Major hormonal products are thymopoietins and thymosins -These hormones are essential for the development of the T cells of the immune system

Zona glomerulosa

-Mineralocorticoids- regulate electrolytes in extracellular fluid Aldosterone

Posterior pituitary

-Neurohypophysis -Develops from the floor of the brain and connects to the hypothalamus by the infundibulum

Thyroid gland

-One of the largest endocrine glands*****

Adrenal glands

-Paired, pyramid-shaped organs that sit on top of the kidneys -4 glands in one -Adrenal medulla (inner area) -Adrenal cortex (outer area)

Endocrine glands include

-Pituitary -Thyroid -Parathyroid -Adrenal -Pineal -Thymus

Kidneys

-Produce erythropoietin -Stimulates red blood cell production

Glucagon

-Produced by Alpha cells -Causes the breakdown of glycogen to glucose -Stimulates the synthesis of glucose from amino acids -Liver releases glucose into the blood

Insulin

-Produced by Beta cells -Nervous system relies on blood glucose levels maintained by insulin -Increases the uptake of glucose and amino acids by cells

GI tract

-Produces gastrin, secretin, and cholecystokinin -Regulates digestive functions

GHRH

-Released from the hypothalamus: causes release of GH from the anterior pituitary gland

GHIH (somatostatin)

-Released from the hypothalamus: inhibits production of GH by anterior pituitary -Secreted in response to high blood glucose levels

Parathyroid glands

-Secrete a polypeptide hormone called parathyroid hormone (PTH)

Ovaries

-Secrete estrogens and progesterone -Maturation of the reproductive organs -Appearance of secondary sexual characteristics -Breast development and cyclical changes in the uterine mucosa

Testes

-Secrete testosterone -Initiates maturation of male reproductive organs -Causes appearance of secondary sexual characteristics and sex drive -Maintains sex organs in their functional state

Placenta

-Secretes human chorionic gonadotropin (hCG) -Essential for the maintenance of pregnancy

Pineal gland

-Small, pinecone-shaped structure -Located superior and posterior to the thalamus -Secretory product is melatonin

Hypothalamic Regulation of the Anterior Pituitary Gland

-Stimuli from nervous system regulate the secretion of releasing/inhibiting hormones from hypothalamus -Releasing/inhibiting hormones pass through the hypothalamohypophysial portal system and the anterior pituitary gland -Releasing/inhibiting hormones leave capillaries and stimulate or inhibit the release of hormones from pituitary gland -In response to releasing hormones, anterior pituitary hormones travel through the blood to their target tissues

Hypothalamic Regulation of the Posterior Pituitary Gland

-Stimuli within the nervous system stimulate hypothalamic neurons to either increase or decrease their action potential frequency -Action potentials are carried by axons through the hypothalamohypophysial tract to the posterior pituitary. The axons of neurons store hormones in the posterior pituitary -In the posterior pituitary gland, action potentials cause the release of neurohormones (red spheres) from axon terminals into the circulatory system. -The neurohormones pass through the circulatory system and influence the activity of their target tissues

Growth hormone secretion

-Stress and decreased blood glucose increase of GHRH and decrease the release of GHIH from the hypothalamus -GHRH and GHIH travel through the hypothalamohypophysial portal system to the anterior pituitary gland causing GH secretion -GH have a negative feedback effect on the hypothalamus

Calcitonin

-Thyroid gland secretes this hormone -Parafollicular cells secrete calcitonin

ACTH (Adrenocorticotropic hormone) target tissue

Adrenal cortex -Increased glucocorticoid hormone secretion

Beta endophins target tissue

Brain -Analgesia in the brain, inhibition of gonadotropin-releasing hormone secretion

Infundibulum

Connects hypothalamus to anterior/posterior pituitary

Endocrine Glands

Ductless glands that secrete chemicals into the circulatory system

PTH

Essential in regulating Ca2+ balance in the blood (much more important than calcitonin

Lipotropins target tissue

Fat tissues -Increased fat breakdown

FSH (Follicle-stimulating hormone) target tissue

Follicles in ovaries in females; seminiferous tubules in males -Follicle maturation and estrogen secretion in ovaries; sperm cell production in testes

Direct effect of GHRH

GH binds to receptors on cells and causes changes within the cells

Where do the nervous and endocrine systems interact?

Hypothalamus

ADH target tissue

Kidneys -Increased water reabsorption (less water is lost in form of urine)

What is the target tissue of glucagon?

Liver

MSH (Melanocyte-stimulating hormone) target tissue

Melanocytes in the skin -Increased melanin production in melanocytes to make the skin darker in color

GH (Growth Hormone) target tissue

Most tissues -increased growth in tissues, increased amino acid uptake and protein synthesis, increased breakdown of lipids and release of fatty acids from cells

Prolactin target tissues

Ovaries and mammary glands in females -Milk production in lactating women; increased response of follicle to LH and FSH; unclear in males

LH (Luteinizing hormone) target tissue

Ovaries in females; testes in males -Ovulation and progesterone production in ovaries; testosterone synthesis and support for sperm cell production in testes

Which organs have both endocrine and exocrine glands

Pancreas and gonads

Epinephrine (adrenaline)

Prepare the body for physical activity: -Increasing blood glucose levels -Increasing the use of glycogen and glucose by skeletal muscle -Increasing heart rate and contraction

Hypothalamus

Regulates secretions of the anterior pituitary gland through hormones and action potentials

Norepinephrine

Released by the sympathetic division of the ANS in response to: -Emotions -Injury -Stress -Exercise -Low blood glucose levels

Pituitary gland

Secretes at least 9 major hormones that regulate numerous body functions and other endocrine glands

Hormones of the Adrenal cortex

Synthesizes and releases steroid hormones called corticosteroids -Zona glomerulosa -Zona fasciculata -Zona reticularis

Calcitonin targets?

The skeleton -Inhibit osteoclast activity:reduce the release of calcium from the bone matrix -Stimulate Ca2+ uptake: incorporation into the bone matrix

TSH (Thyroid-stimulating hormone) target tissue

Thyroid gland -increased thyroid hormone secretion

Pancreas

Triangular gland that has both exocrine and endocrine cells, located behind the stomach

Oxytocin target tissue

Uterus, mammary glands -Increased uterine contractions, increased milk expulsion from mammary glands, unclear function in males