Chapter 18, part 2
The Endocrine System
Hypophyseal portal system
All blood entering the portal system will reach the intended target cells before returning to the general circulation
Figure 18.7 The Hypophyseal Portal System
Figure 18.8 Feedback control of Endocrine Secretion
Figure 18.8 Feedback control of Endocrine Secretion
Hormones of the adenohypophysis
Thyroid stimulating hormone (TSH)
Triggers the release of thyroid hormones
Thyrotropin releasing hormone promotes the release of TSH
Adrenocorticotropic hormone (ACTH)
Stimulates the release of glucocorticoids by the adrenal gland
Corticotrophin releasing hormone causes the secretion of ACTH
Hormones of the adenohypophysis
Follicle stimulating hormone (FSH)
Stimulates follicle development and estrogen secretion in females and sperm production in males
Leutinizing hormone (LH)
Causes ovulation and progestin production in females and androgen production in males
Gonadotropin releasing hormone (GNRH) promotes the secretion of FSH and LH
Hormones of the adenohypophysis
Prolactin (PH)
Stimulates the development of mammary glands and milk production
Growth hormone (GH or somatotropin)
Stimulates cell growth and replication through release of somatomedins or IGF
Growth-hormone releasing hormone (GH-RH)
Growth-hormone inhibiting hormone (GH-IH)
Melanocyte stimulating hormone (MSH)
May be secreted by the pars intermedia during fetal development, early childhood, pregnancy or certain diseases
Stimulates melanocytes to produce melanin
The posterior lobe of the pituitary gland (neurohypophysis)
Contains axons of hypothalamic nerves
neurons of the supraoptic nucleus manufacture antidiuretic hormone (ADH)
Decreases the amount of water lost at the kidneys
Elevates blood pressure
The posterior lobe of the pituitary gland (neurohypophysis)
Neurons of the paraventricular nucleus manufacture oxytocin
Stimulates contractile cells in mammary glands
Stimulates smooth muscle cells in uterus
Figure 18.9 Pituitary Hormones and Their Targets
SECTION 18-4 The Thyroid Gland
The thyroid
Lies near the thyroid cartilage of the larynx
Two lobes connected by an isthmus
Figure 18.11 The Thyroid Gland
Figure 18.11 The Thyroid Gland
Thyroid follicles and thyroid hormones
Thyroid gland contains numerous follicles
Release several hormones such as thyroxine (T4) and triiodothyronine (T3)
Thyroid hormones end up attached to thyroid binding globulins (TBG)
Some are attached to transthyretin or albumin
Figure 18.12 The Thyroid Follicles
Figure 18.12 The Thyroid Follicles
Thyroid hormones
Held in storage
Bound to mitochondria, thereby increasing ATP production
Bound to receptors activating genes that control energy utilization
Exert a calorigenic effect
Cells of the thyroid gland
C cells produce calcitonin
Helps regulate calcium concentration in body fluids
Figure 18.13 Thyroid Disorders
SECTION 18-5 The Parathyroid Glands
Four parathyroid glands
Embedded in the posterior surface of the thyroid gland
Chief cells produce parathyroid hormone (PTH) in response to lower than normal calcium concentrations
Parathyroid hormones plus calcitriol are primary regulators of calcium levels in healthy adults
Figure 18.14 The Parathyroid Glands
Figure 18.15 The Homeostatic Regulation of Calcium Ion Concentrations
