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
